Metal CastingMetal Casting

By  S K MondalBy  S K Mondal

Sand castingS d i di d h iSand casting uses ordinary sand as the primarymould material.The sand grains are mixed with small amounts ofother materials such as clay and water to improveother materials, such as clay and water, to improvemouldability and cohesive strength, and are thenpacked around a pattern that has the shape of thepacked around a pattern that has the shape of thedesired casting.The pattern must be removed before pouring, themold is usually made in two or more pieces.mold is usually made in two or more pieces.An opening called a sprue hole is cut from the top ofth ld th h th d d t d tthe mold through the sand and connected to asystem of channels called runners. Contd….

The molten metal is poured into the sprue hole, flowsp pthrough the runners, and enters the mold cavitythrough an opening called a gate.through an opening called a gate.Gravity flow is the most common means ofi t d i th t l i t th ldintroducing the metal into the mold.After solidification, the mold is broken and thefinished casting is removed.The casting is then “fettled” by cutting off the ingateThe casting is then fettled by cutting off the ingateand the feeder head.Because the mold is destroyed, a new mold must bemade for each casting.g

Contd…

Sequential steps in making a sand castingA pattern board is placed between the bottom (drag) and top (cope) halves of a flask, with the bottom side up.p ( p ) , p

S d i   h   k d i   h  d  h lf  f  h   ld  Sand is then packed into the drag half of the mold. 

A bottom board is positioned on top of the packed sand, and the mold is turned over  showing the top (cope) half and the mold is turned over, showing the top (cope) half of pattern with sprue and riser pins in place. 

The cope half of the mold is then packed with sand  The cope half of the mold is then packed with sand. Contd…

The mold is opened, the pattern board is drawn(removed), and the runner and gate are cut into thesurface of the sand.

Th ld i bl d ith th tt b dThe mold is reassembled with the pattern boardremoved, and molten metal is poured through thesprue.

The contents are shaken from the flask and the metali d f h d d f f hsegment is separated from the sand, ready for further

processing.

Casting TermsFlask: A moulding flask is one which holds the sand

mould intact. It is made up of wood for temporary

applications or metal for long‐term use.

Drag: Lower moulding flask.

Cope: Upper moulding flask.

h k d ld fl k d hCheek: Intermediate moulding flask used in three‐

piece mouldingpiece moulding.Contd…For-2013 (IES, GATE & PSUs) Page 1

Pattern: Pattern is a replica of the final object to bePattern: Pattern is a replica of the final object to be

made with some modifications.made with some modifications.

Parting line: This is the dividing line between the twog g

moulding flasks that makes up the sand mould.

Bottom board: This is a board normally made of wood,

which is used at the start of the mould making.

Contd…

Moulding sand: The freshly prepared refractory

material used for making the mould cavity. It is a

mixture of silica, clay and moisture in appropriate

iproportions.

B ki d Thi i d f d d b tBacking sand: This is made up of used and burnt

sandsand.

Core: Used for making hollow cavities in castingsCore: Used for making hollow cavities in castings.

Pouring basin: A small funnel shaped cavity at the topPouring basin: A small funnel‐shaped cavity at the top

of the mould into which the molten metal is poured.p

Sprue: The passage through which the molten metal

from the pouring basin reaches the mould cavity.

Runner: The passage ways in the parting plane through

hi h l l fl i l d b f h hwhich molten metal flow is regulated before they reach

the mould cavitythe mould cavity.

Gate: The actual entry point through which molteny p g

metal enters the mould cavity in a controlled rate. Contd…

Chaplet: Chaplets are used to support cores inside the

mould cavitymould cavity.

Chill: Chills are metallic objects, which are placed inChill: Chills are metallic objects, which are placed in

the mould to increase the cooling rate of castings.

Riser: It is a reservoir of molten metal provided in the

casting so that hot metal can flow back into the mould

i h h i d i i l f l dcavity when there is a reduction in volume of metal due

to solidificationto solidificationContd…

PaddingTapering of thinner section towards thicker sectionis known as 'padding'is known as padding .This will require extra material.If padding is not provided, centre line shrinkage orporosity will result in the thinner section.p y

IES‐2001

Th i f h l t iThe main purpose of chaplets is

(a) To ensure directional solidification(a) To ensure directional solidification

(b) To provide efficient venting(b) To provide efficient venting

(c) For aligning the mold boxes(c) For aligning the mold boxes

(d) To support the cores(d) To support the cores

IES‐1996Which of the following methods are used for

obtaining directional solidification for riser design

1. Suitable placement of chills

2. Suitable placement of chaplets

l dd3. Employing padding

S l t th tSelect the correct answer.

(a) 1 and 2 (b) 1 and 3 (c) 2 and 3 (d) 1 2 and 3(a) 1 and 2 (b) 1 and 3 (c) 2 and 3 (d) 1, 2 and 3

IES 2007

Which one of the following is the correctWhich one of the following is the correctstatement?G i id d i ldGate is provided in moulds to(a) Feed the casting at a constant rate( ) g(b) Give passage to gases( ) C f h i k(c) Compensate for shrinkage(d) Avoid cavities( )

GATE‐2009

Match the items in Column I and Column II.Column I                       Column IIColumn I                       Column IIP. Metallic Chills            1. Support for the coreQ  M t lli  Ch l t        R i   f th   lt   t lQ. Metallic Chaplets     2. Reservoir of the molten metalR. Riser                           3. Control cooling of critical        

isectionsS. Exothermic Padding 4. Progressive solidification(a) P‐1,Q‐3, R‐2, S‐4 (b) P‐1,Q‐4, R‐2, S‐3(c) P‐3, Q‐4, R‐2, S‐1 (d) P‐4, Q‐1, R‐2, S‐3( ) 3, Q 4, , ( ) 4, Q , , 3

For-2013 (IES, GATE & PSUs) Page 2

GATE‐1992In a green‐sand moulding process, uniform ramming leads toramming leads to(a) Less chance of gas porosity(b) Uniform flow of molten metal into the mould cavitycavity(c) Greater dimensional stability of the casting(d) Less sand expansion type of casting defect

GATE 2011Green sand mould indicates that(a) polymeric mould has been cured(a) polymeric mould has been cured(b) mould has been totally dried(c) mould is green in colour(d) mould contains moisture(d) mould contains moisture

PatternA pattern is a replica of the object to be made by thecasting process, with some modifications.

Themain modifications areThemain modifications areThe addition of pattern allowances,The provision of core prints, andElimination of fine details, which cannot be obtainedElimination of fine details, which cannot be obtainedby casting and hence are to be obtained by furtherprocessingprocessing

Pattern Allowances1. Shrinkage or contraction allowanceg

2. Draft or taper allowance

3. Machining or finish allowance

4. Distortion or camber allowance

5. Rapping allowance

Shrinkage allowanceAll metals shrink when cooling except perhaps

bismuth.

This is because of the inter‐atomic vibrations which

l f d bare amplified by an increase in temperature.

Th h i k ll i l b dd d hThe shrinkage allowance is always to be added to the

linear dimensions Even in case of internal dimensionslinear dimensions. Even in case of internal dimensions.

Contd…

Liquid shrinkage and solid shrinkageLiquid shrinkage refers to the reduction involume when the metal changes from liquid tovolume when the metal changes from liquid tosolid state at the solidus temperature. To accountf hi i id d i h ldfor this, risers are provided in the moulds.

Solid shrinkage is the reduction in volumecaused when a metal loses temperature in thecaused, when a metal loses temperature in thesolid state. The shrinkage allowance is provided tok f hi d itake care of this reduction.

Pattern AllowancesCast Iron 10 mm/mBrass, Copper, Aluminium 15 mm/mBrass, Copper, Aluminium 15 mm/mSteel 20 mm/mZinc, Lead 25 mm/m

In grey cast iron and spheroidal graphite iron, thef hi i i l h lamount of graphitization controls the actual

shrinkage. When graphitization is more, theshrinkage would be less and vice versa.

IES‐1995Which one of the following materials will require

the largest size of riser for the same size of casting?

(a) Aluminium

(b) Cast iron

(c) Steel

(d)(d) Copper.

GATE‐1999

Which of the following materials requires theWhich of the following materials requires thelargest shrinkage allowance, while making apattern for casting?pattern for casting?(a) Aluminium(b) Brass(c) Cast Iron(c) Cast Iron(d) Plain Carbon Steel

For-2013 (IES, GATE & PSUs) Page 3

IES‐1999In solidification of metal during casting,

f l dcompensation for solid contraction is

( ) P id d b h i(a) Provided by the oversize pattern

(b) A hi d b l l d i(b) Achieved by properly placed risers

(c) Obtained by promoting directional(c) Obtained by promoting directional

solidificationsolidification

(d) Made by providing chills( ) y p g

ISRO‐2007ISRO‐2007Shrinkage allowance is made byShrinkage allowance is made by(a) Adding to external and internal dimensions(b) Subtracting from external and internaldimensions(c) Subtracting from external dimensions andadding to internal dimensionsadding to internal dimensions(d) Adding to external dimensions and subtractingfrom internal dimensions

GATE‐2001Shrinkage allowance on pattern is provided tocompensate for shrinkage when(a) The temperature of liquid metal drops from(a) The temperature of liquid metal drops from

pouring to freezing temperature(b) Th t l h f li id t lid t t t(b) The metal changes from liquid to solid state at

freezing temperature(c) The temperature of solid phase drops from

freezing to room temperaturefreezing to room temperature(d) The temperature of metal drops from pouring

to room temperature

GATE‐2004

Gray cast iron blocks 200 x 100 x 10 mm are to beGray cast iron blocks 200 x 100 x 10 mm are to becast in sand moulds. Shrinkage allowance forpattern making is 1% The ratio of the volume ofpattern making is 1%. The ratio of the volume ofpattern to that of the casting will be

(a) 0 97 (b) 0 99 (c) 1 01 (d) 1 03(a) 0.97 (b) 0.99 (c) 1.01 (d) 1.03

GATE‐2008

Whil li bi l ti f idWhile cooling, a cubical casting of side 40 mm

undergoes 3% 4% and 5% volume shrinkageundergoes 3%, 4% and 5% volume shrinkage

during the liquid state, phase transition and solidg q p

state, respectively. The volume of metal

compensated from the riser is

(a) 2% (b) 7% (c) 8% (d) 9%

GATE 2011A cubic casting of 50 mm side undergoes volumetricsolidification shrinkage and volumetric solidgcontraction of 4% and 6% respectively. No riser isused Assume uniform cooling in all directions Theused. Assume uniform cooling in all directions. Theside of the cube after solidification and contraction is( ) 8(a) 48.32 mm(b) 49.90 mm( ) 49 9(c) 49.94 mm(d)(d) 49.96 mm

IAS‐1995Assertion (A): A pattern is made exactly similar tothe part to be cast.the part to be cast.Reason (R): Pattern is used to make the mouldcavity for pouring in molten for castingcavity for pouring in molten for casting.(a) Both A and R are individually true and R is the

l i f Acorrect explanation of A(b) Both A and R are individually true but R is not theycorrect explanation of A(c) A is true but R is false(c) A is true but R is false(d) A is false but R is true

IAS‐2003Match List I (Material to be cast) with List II(Shrinkage Allowance in mm/m) and select the( g / )correct answer using the codes given below the lists:List‐I List‐IIList I List II(Material to Cast)  (Shrinkage Allowance in mm/m)(A) Grey cast iron 1 7  10(A) Grey cast iron 1. 7 ‐ 10(B) Brass 2. 15( ) l(C) Steel 3. 20(D) Zinc 4. 24

Codes:A B C D A B C D(a)  1 2  3 4 (b)  3  4  1 2(a)  1 2  3 4 (b)  3  4  1 2(c)  1  4  3 2 (d)  3  2 1 4

DraftTo reduce the chances of the damage of the mould

h f l h l fcavity at the time of pattern removal, the vertical faces

of the pattern are always tapered from the parting lineof the pattern are always tapered from the parting line.

This provision is called draft allowance.This provision is called draft allowance.

Inner surfaces of the pattern require higher draft thanp q g

outer surfaces.

Draft is always provided as an extra metal.

For-2013 (IES, GATE & PSUs) Page 4

DRAFT ALLOWANCE

Shake Allowance

At the time of pattern removal, the pattern is rappedp , p pp

all around the vertical faces to enlarge the mould

cavity slightly to facilitates its removal.

It is a negative allowance and is to be applied only to

those dimensions, which are parallel to the parting

lplane.

Distortion Allowance A metal when it has just solidified is very weak andtherefore is likely to be distortion prone.

This is particularly so for weaker sections such as longfl t ti V U ti i li t d tiflat portions, V, U sections or in a complicated castingwhich may have thin and long sections which areconnected to thick sections.

The foundry practice should be to make extrai l i i f d i h di imaterial provision for reducing the distortion.

Pattern MaterialsWood patterns are relatively easy to make. Wood is notvery dimensionally stable. Commonly used teak, whitey y y ,pine and mahogany wood.Metal patterns are more expensive but are moreMetal patterns are more expensive but are moredimensionally stable and more durable. Commonly usedCI Brass aluminium and white metalCI, Brass, aluminium and white metal.Hard plastics, such as urethanes, and are often preferred

h h ll b d d dwith processes that use strong, organically bonded sandsthat tend to stick to other pattern materials.In the full‐mold process, expanded polystyrene (EPS) isused.Investment casting uses wax patterns.

The pattern material should beEasily worked, shaped and joined

Light in weight

Strong, hard and durable

R i t t t     d  b iResistant to wear and abrasion

Resistant to corrosion, and to chemical reactionsResistant to corrosion, and to chemical reactions

Dimensionally stable and unaffected by variations in     

temperature and humidity.

Available at low cost.

IES‐1994Which of the following materials can be used for

making patterns?

1. Aluminium 2. Wax 3. Mercury 4. Lead

Select the correct answer using the codes given below:

Codes:

( ) d (b) d ( ) d (d) d(a) 1,3 and 4 (b) 2,3 and 4 (c) 1, 2 and 4 (d) 1, 2 and 3

GATE‐2000

Di bl   tt     d   fDisposable patterns are made of

(a) Wood (a) Wood 

(b) Rubber (b) Rubber 

(c) Metal (c) Metal 

(d) Polystyrene(d) Polystyrene

Types of PatternSingle Piece Pattern

These are inexpensive and the simplest type ofThese are inexpensive and the simplest type ofpatterns. As the name indicates, they are made of asingle piecesingle piece.

Gated PatternGating and runner system are integral with theGating and runner system are integral with thepattern. This would eliminate the hand cutting ofthe runners and gates and help in improving thethe runners and gates and help in improving theproductivity of a moulding.

Types of PatternSplit Pattern or Two Piece PatternThis is the most widely used type of pattern for intricatey yp pcastings. When the contour of the casting makes itswithdrawal from the mould difficult, or when the depthwithdrawal from the mould difficult, or when the depthof the casting is too high, then the pattern is split into twoparts so that one part is in the drag and the other in theparts so that one part is in the drag and the other in thecope.

For-2013 (IES, GATE & PSUs) Page 5

Types of PatternCope and Drag Pattern

These are similar to split patterns. In addition tosplitting the pattern, the cope and drag halves ofp g p , p gthe pattern along with the gating and riser systemsare attached separately to the metal or woodenare attached separately to the metal or woodenplates along with the alignment pins. They arecalled the cope and drag patternscalled the cope and drag patterns.

Types of PatternMatch Plate PatternMatch Plate Pattern

The cope and drag patterns along with thei d h i i d i lgating and the risering are mounted on a single

matching metal or wooden plate on either side.g p

Types of PatternLoose Piece Pattern

This type of pattern is also used when thecontour of the part is such that withdrawing thecontour of the part is such that withdrawing thepattern from the mould is not possible.

Types of PatternF ll B d PFollow Board Pattern

This type of pattern is adopted for thoseyp p pcastings where there are some portions, whichare structurally weak and if not supportedare structurally weak and if not supportedproperly are likely to break under the force oframmingramming.

IES‐2008

The pattern adopted for those castings where thereThe pattern adopted for those castings where thereare some portions which are structurally weak andare likely to break by the force of ramming areare likely to break by the force of ramming arecalled:(a) Loose piece pattern(b) Follow board pattern(b) Follow board pattern(c) Skelton pattern(d) Single piece pattern

Types of PatternSweep Pattern

It is used to sweep the complete casting by meansIt is used to sweep the complete casting by meansof a plane sweep. These are used for generatinglarge shapes which are axi symmetrical orlarge shapes, which are axi‐symmetrical orprismatic in nature such as bell‐shaped orli d i lcylindrical.

Types of PatternSk l PSkeleton Pattern

A skeleton of the pattern made of strips of woodp pis used for building the final pattern by packingsand around the skeleton After packing thesand around the skeleton. After packing thesand, the desired form is obtained with the helpof a strickle This t pe of pattern is usefulof a strickle. This type of pattern is usefulgenerally for very large castings, required in

ll h lsmall quantities where large expense oncomplete wooden pattern is not justified.p p j

Cooling Curveg FluidityThe ability of a metal to flow and fill a mold is knownas fluidity.

Pouring TemperatureThe most important controlling factor of fluidity is theThe most important controlling factor of fluidity is thepouring temperature or the amount of superheat.Higher the pouring temperature the higher the fluidityHigher the pouring temperature, the higher the fluidity.Excessive temperatures should be avoided, however. Athigh pouring temperatures metal‐mold reactions arehigh pouring temperatures, metal‐mold reactions areaccelerated and the fluidity may be so great as to permitpenetration.penetration.Penetration is a defect where the metal not only fills themold cavity but also fills the small voids between the sandmold cavity but also fills the small voids between the sandparticles in a sand mold.

For-2013 (IES, GATE & PSUs) Page 6

GATE 2012 (PI)GATE 2012 (PI)In sand casting, fluidity of the molten metalIn sand casting, fluidity of the molten metalincreases with(A) i i d f h(A) increase in degree of superheat(B) decrease in pouring rate( ) p g(C) increase in thermal conductivity of the mould(D) i i d i i(D) increase in sand grain size

ISRO‐2011Fluidity in casting (CI) operation is greatly

influenced by

a) Melting temperature of molten metal

b) Pouring temperature of molten metal

c) Finish of the mould

d) Carbon content of molten metal

CoreUsed for making cavities and hollow projections.

All sides of core are surrounded by the molten metalAll sides of core are surrounded by the molten metaland are therefore subjected to much more severethermal and mechanical conditions and as a result thethermal and mechanical conditions and as a result thecore sand should be of higher strength than the

ldi dmoulding sand.

Desired characteristics of a core

Green Strength: A core made of green sand shouldGreen Strength: A core made of green sand shouldbe strong enough to retain the shape till it goes forbakingbaking.Dry Strength: It should have adequate dry strengthso that when the core is placed in the mould, itshould be able to resist the metal pressure acting onp git.Refractoriness: Since in most cases the core isRefractoriness: Since in most cases, the core issurrounded all around it is desirable that the core

i l h ld h hi h f imaterial should have higher refractoriness.Contd…

Permeability: Gases evolving from the molten metaly gand generated from the mould may have to gothrough the core to escape out of the mould. Hencethrough the core to escape out of the mould. Hencecores are required to have higher permeability.

P bilit N b Th t f fl f i iPermeability Number: The rate of flow of air passingthrough a standard specimen under a standard pressure is

d bili btermed as permeability number.The standard permeability test is to measure timep ytaken by a 2000 cu cm of air at a pressure typically of980 Pa (10 g/cm2), to pass through a standard sand980 Pa (10 g/cm ), to pass through a standard sandspecimen confined in a specimen tube. The standardspecimen size is 50 8 mm in diameter and a length ofspecimen size is 50.8 mm in diameter and a length of50.8 mm.

Then the permeability number R is obtained byThen, the permeability number, R is obtained byVHRAT

=

Where V= volume of air = 2000 cm3

pAT

Where V= volume of air = 2000 cm3

H = height of the sand specimen = 5.08 cmp = air pressure, g/cm2

A = cross sectional area of sand specimen = 20 268 cm2A = cross sectional area of sand specimen = 20.268 cmT = time in minutes for the complete air to pass through

Inserting the above standard values into the iexpression, we get

501.28R =.

Rp T

Calculate the permeability number of sand if it takes 1 min 25 s to pass 2000 cm3 of air at a pressure of5 g/cm2 through 25 s to pass 2000 cm3 of air at a pressure of5 g/cm through the standard sample.

25.0 /p g cm=1min 25 1.417 min

501 28T s= =

501.28 70.755 1.417

R = =×

IES 2007IES 2007What is permeability? Permeability is more important What is permeability? Permeability is more important 

in the basic process of sand casting than porosity. Give p g p y

one important reason for this feature.

[2 marks]

Collapsibility: At the time of cooling, casting shrinks, and p y g, g ,unless the core has good collapsibility (ability to decrease in size) it is likely to provide resistance against shrinkage ) y p g gand thus can cause hot tears.

For-2013 (IES, GATE & PSUs) Page 7

Friability: The ability to crumble should be a veryFriability: The ability to crumble should be a very

important consideration at the time of removal.p

Smoothness: Surface of the core should be smooth

for good finish to the casting.

Low Gas Emission

Core SandsUsed clay free silica sand.

Binders used are linseed oil, core oil, resins, dextrin,

molasses, etc.

l f l d f h dCore oils are mixtures of linseed, soy, fish and

petroleum oils and coal tarpetroleum oils and coal tar.

The general composition of a core sand mixture couldThe general composition of a core sand mixture could

be core oil (1%) and water (2.5 to 6%).( ) ( 5 )

Carbon Dioxide MouldingS di ili ( l SiO N O) i d bi dSodium silicate (water glass, SiO2:Na2O) is used as a binder.This is essentially a quick process of core or mouldpreparation.The mould is prepared with a mixture of sodium silicate andp psand and then treated with carbon dioxide for two to threeminutes such that a dry compressive strength of over 1.4y p g 4MPa is arrived.The carbon dioxide is expected to form a weak acid whichThe carbon dioxide is expected to form a weak acid, whichhydrolyses the sodium silicate resulting in amorphous silica,which forms the bondwhich forms the bond.The introduction of CO2 gas starts the reaction by formingh d d d b ( O O)hydrated sodium carbonate (Na2CO3 + H2O).

Contd…

The compressive strength of the bond increases withThe compressive strength of the bond increases with

standing time due to dehydration.

Because of the high strength of the bond, the core need not

be provided with any other reinforcements.

It does not involve any distortions due to baking and also

better dimensional accuracies are achievedbetter dimensional accuracies are achieved.

The sand mixture does not have good shelf life andThe sand mixture does not have good shelf life and

therefore should be used immediately after preparation.

IES‐2002Assertion (A): In CO2 casting process, the mould orcore attains maximum strength.Reason (R): The optimum gassing time of CO2through the mould or core forms Silica Gel whichthrough the mould or core forms Silica Gel whichimparts sufficient strength to the mould or core.(a) Both A and R are individually true and R is the(a) Both A and R are individually true and R is thecorrect explanation of A( )(b) Both A and R are individually true but R is not thecorrect explanation of A(c) A is true but R is false(d) A is false but R is true(d) A is false but R is true

G 2008 ( )GATE – 2008 (PI)In sand casting of a hollow part of lead a cylindrical coreIn sand casting of a hollow part of lead, a cylindrical core

of diameter 120 mm and height 180 mm is placed insideof diameter 120 mm and height 180 mm is placed inside

the mould cavity. The densities of core material and lead

are 1600 kg/m3 and 11,300 kg/m3 respectively. The net

force (in N) that tends to lift the core during pouring of

molten metal will be

( ) ( ) ( ) ( )(a) 19.7 (b) 64.5 (c) 193.7 (d) 257.6

Moulding Sand CompositionSand: Ordinary silica Sand (SiO2), zircon, or olivine

dsands.

Cl A bi di i d h ldiClay: Acts as binding agents mixed to the moulding

sandssands

Kaolinite or fire clay (Al O 2SiO 2H O) andKaolinite or fire clay (Al2O3 2SiO2 2H2O), and

Bentonite (Al O 4SiO H O nH O).Bentonite (Al2O3 4SiO2 H2O nH2O).

Water: Clay is activated by water.y y

Other AdditivesCereal binder up to 2% increases the strength.

Pitch if used up to 3% would improve the hot

strength.

Saw dust up to 2% may improve the collapsibility by

l l b i d i h bilislowly burning, and increase the permeability.

Oth t i l l h lt f l il hitOther materials: sea coal, asphalt, fuel oil, graphite,

molasses iron oxide etcmolasses, iron oxide, etc.

Moulding Sand PropertiesPorosity or Permeability: Permeability or porosity ofthe moulding sand is the measure of its ability tog ypermit air to flow through it.Strength: It is defined as the property of holdingStrength: It is defined as the property of holdingtogether of sand grains. A moulding sand should have

l h h h ld d llample strength so that the mould does not collapse orget partially destroyed during conveying, turning overor closing.Refractoriness: It is the ability of the moulding sandRefractoriness: It is the ability of the moulding sandmixture to withstand the heat of melt without showing

i f ft i f iany signs of softening or fusion.Contd…For-2013 (IES, GATE & PSUs) Page 8

Plasticity: It is the measure of the moulding sand to flow d  d       d i   i   d    if l  around and over a pattern during ramming and to uniformly 

fill the flask. Collapsibility: This is the ability of the moulding sand to decrease in volume to some extent under the compressive pforces developed by the shrinkage of metal during freezing and subsequent cooling. q gAdhesiveness: This is the property of sand mixture to adhere to another body (here  the moulding flasks)  The adhere to another body (here, the moulding flasks). The moulding sand should cling to the sides of the moulding boxes so that it does not fall out when the flasks are lifted boxes so that it does not fall out when the flasks are lifted and turned over. This property depends on the type and 

t  f bi d   d i  th   d  iamount of binder used in the sand mix.

Other SandsFacing sand: The small amount of carbonaceousFacing sand: The small amount of carbonaceousmaterial sprinkled on the inner surface of the mold

i i b f fi i h h icavity to give a better surface finish to the castings.Backing sand: It is what constitutes most of thegrefractory material found in the mould. This is madeup of used and burnt sandup of used and burnt sand.Green Sand: The molding sand that containsmoisture is termed as green sand. The green sandshould have enough strength so that the constructedg gmould retains its shape.Dry sand: When the moisture in the moulding sand isDry sand: When the moisture in the moulding sand iscompletely expelled, it is called dry sand.

IES‐2008

S ll t f b t i l i kl dSmall amount of carbonaceous material sprinkled

on the inner surface of mould cavity is calledon the inner surface of mould cavity is called

(a) Backing sand(a) Backing sand

(b) Facing sand( ) g

(c) Green sand( )

(d) Dry sand

Grain size numberASTM (American Society for Testing and Materials)grain size number defined asgrain size number, defined as

N -n12Where N is the number of grains per square inchvisible in a prepared specimen at 100X and n is thevisible in a prepared specimen at 100X and n is theASTM grain‐size number.L ASTM b f i i hi hLow ASTM numbers mean a few massive grains; highnumbers refer to many small grains.

IES‐2002In the grain ‐size determination using standard

charts, the relation between the given size

b d th b f i 'N'number n and the average number of grains N

per square inch at amagnification of 100 X isp q g

(a) N = 2n

(b) N = 2n‐l

(c) N = 2n + 1

(d) N = 2n + 1

Casting YieldThe casting yield is the proportion of the actual casting mass, w, to the mass of metal poured into the mould, W, expressed as a percentage. p p g

= ×Casting yield 100wWW

G i SGating System

Contd…

G ti S tGating SystemP i b i A ll f l h d i hPouring basin: A small funnel shaped cavity at thetop of the mould into which the molten metal ispoured.

Sprue: The passage through which the molten metal,f h b h h ldfrom the pouring basin, reaches the mould cavity. Inmany cases it controls the flow of metal into themould.

Runner: The channel through which the moltenmetal is carried from the sprue to the gate.

Contd…

Ingate: A channel through which the molten metal Ingate: A channel through which the molten metal enters the mould cavity. V S ll  i  i   h   ld   f ili    Vent: Small opening in the mould to facilitate escape of air and gases.

For-2013 (IES, GATE & PSUs) Page 9

Types of Gate or In‐gateTop gate: Causes turbulence in the mould cavity, it is prone

f d f bl d d hto form dross, favourable temperature gradient towards the

gate only for ferrous alloysgate, only for ferrous alloys.

Bottom gate: No mould erosion, used for very deep moulds,g , y p ,

higher pouring time, Causes unfavourable temperature

gradients.Parting Gate: most widely used gate easiest and mostParting Gate: most widely used gate, easiest and mosteconomical in preparation.

d f h d l fStep Gate: Used for heavy and large castings, size of ingatesare normally increased from top to bottom.

IES 2011In light metal casting, runner should be so designedthat:

1. It avoids aspirationI id b l2. It avoids turbulence

3. The path of runner is reduced in area so that3 punequal volume of flow through each gatetakes placetakes place

(a) 1 and 2 only (b) 1 and 3 only(c) 2 and 3 only (d) 1, 2 and 3

GATE – 2010 (PI)During the filling process of a given sand mould cavity by

lt t l th h h i t l f i lmolten metal through a horizontal runner of circular cross‐

section the frictional head loss of the molten metal in the

runner will increase with the

(a) increase in runner diameter

(b) decrease in internal surface roughness of runner

(c) decrease in length of runner(c) decrease in length of runner

(d) increase in average velocity of molten metal(d) increase in average velocity of molten metal

IES 2011IES 2011Match List –I with List –II and select the correct answer usinggthe code given below the lists :

List –I  List –IIList  I  List  II

A. Top gate 1. Heavy and large castings

B. Bottom gate 2. Most widely used and economical

C. Parting gate 3. Turbulence

D  St   t  U f bl t t   di t

Codes

D. Step gate 4. Unfavourable temperature gradient

A B C D A B C D(a) 3 4 2 1 (b) 1 4 2 3(a) 3 4 2 1 (b) 1 4 2 3(c) 3 2 4 1 (d) 1 2 4 3

IES‐1998A d i ldA sand casting mouldassembly is shown inthe above figure. Theelements marked Aand B are respectively(a) Sprue and riser(a) Sprue and riser(b) Ingate and riser(c) Drag and runner(d) Ri d(d) Riser and runner

GATE‐2002The primary purpose of a sprue in a castingmould is to(a)Feed the casting at a rate consistent with the rate(a)Feed the casting at a rate consistent with the rateof solidification

(b)A i f l l(b)Act as a reservoir for molten metal(c)Feed molten metal from the pouring basin to the( ) p ggate

(d)Help feed the casting until all solidification takes(d)Help feed the casting until all solidification takesplace

The goals for the gating system To minimize turbulence to avoid trapping gasses intothe moldthe moldTo get enough metal into the mold cavity before the

l lidifmetal starts to solidifyTo avoid shrinkagegEstablish the best possible temperature gradient in thesolidifying casting so that the shrinkage if occurs mustsolidifying casting so that the shrinkage if occurs mustbe in the gating system not in the required cast part.Incorporates a system for trapping the non‐metallicinclusions.

IES‐1998Which of the following are the requirements of an ideal gating system?

1. The molten metal should enter the mould cavity with as high a velocity as possible.high a velocity as possible.

2. It should facilitate complete filling of the mould cavity.I   h ld b   bl       h   b i   f  i      3. It should be able to prevent the absorption of air or gases from the surroundings on the molten metal while flowing through it.Select the correct answer using the codes given below:g g

(a) 1, 2 and 3  (b) 1 and 2  (c) 2 and 3  (d) 1 and 3

IES‐2009Consider the following statements:1 The actual entry point through which the molten 1.The actual entry point through which the molten metal enters the mould cavity is called ingate.2.Bottom gate in case of a mould creates unfavourabletemperature gradient.p g3.Sprue in case of a mould is made tapered to avoid air inclusioninclusion.Which of the above statements is/are correct?(a) 1 only (b) 1 and 2 (c) 2 and 3 (d) 1 and 3

For-2013 (IES, GATE & PSUs) Page 10

Types of Gating Systems

The gating systems are of two types:The gating systems are of two types:

Pressurized gating system

Un‐pressurized gating systemp g g y

Pressurized Gating SystemThe total cross sectional area decreases towards the

ld itmold cavityBack pressure is maintained by the restrictions in thep ymetal flowFlow of liquid (volume) is almost equal from all gatesFlow of liquid (volume) is almost equal from all gatesBack pressure helps in reducing the aspiration as thesprue always runs fullBecause of the restrictions the metal flows at highBecause of the restrictions the metal flows at highvelocity leading to more turbulence and chances ofmold erosionmold erosion.

Un‐Pressurized Gating SystemThe total cross sectional area increases towards the

mold cavity

Restriction only at the bottom of sprue

Flow of liquid (volume) is different from all gates

Aspiration in the gating system as the system never

f llruns full

Less turbulenceLess turbulence.

S D iSprue Designh h l h h h h h lSprue: Sprue is the channel through which the molten

metal is brought into the parting plane where it enters therunners and gates to ultimately reach the mould cavity.The molten metal when moving from the top of the cope tog p pthe parting plane gains in velocity and some low‐pressurearea would be created around the metal in the sprue.area would be created around the metal in the sprue.Since the sand mould is permeable, atmospheric air wouldbe breathed into this low pressure area which would thenbe breathed into this low‐pressure area which would thenbe carried to the mould cavity.

l h bl f hTo eliminate this problem of air aspiration, the sprue istapered to gradually reduce the cross section as it movesaway from the top of the cope as shown in Figure below (b).

Contd…

The exact tapering can be obtained by the equation of continuity  Denoting the top and choke sections of The sprue by continuity. Denoting the top and choke sections of The sprue by the subscripts’t’ and 'c' respectively, we get

A V A V= = cVA At t c cA V A V t ct

A AV

Contd…

Since the velocities are proportional to the square of the potential heads  as can be derived from the potential heads, as can be derived from Bernoulli's equation, 

= ct c

hA Aht c

th

Where H = actual Where H   actual sprue heightand ht = h + Hand ht   h + H

GATE‐2001The height of the down‐sprue is 175 mm and itsThe height of the down sprue is 175 mm and itscross‐sectional area at the base is 200 mm2. Thecross sectional area of the horizontal runner iscross‐sectional area of the horizontal runner isalso 200 mm2. Assuming no losses, indicate the

h i f h i (i d ) i dcorrect choice for the time (in seconds) required tofill a mould cavity of volume 106 mm3. (Use g = 10m/s2).(a)2 67 (b)8 45 (c)26 72 (d)84 50(a)2.67 (b)8.45 (c)26.72 (d)84.50

GATE‐2007A 200 mm long down sprue has an area of crossA 200 mm long down sprue has an area of crosssection of 650 mm2 where the pouring basin meets thed (i h b i i f h d )down sprue (i.e. at the beginning of the down sprue).A constant head of molten metal is maintained by thepouring basin. The Molten metal flow rate is 6.5 × 105

mm3/s. Considering the end of down sprue to be openmm /s. Considering the end of down sprue to be opento atmosphere and an acceleration due to gravity of104mm/s2 the area of the down sprue in mm2 at its end104mm/s , the area of the down sprue in mm at its end(avoiding aspiration effect) should be( ) ( ) ( ) ( )(a)650.0 (b)350.0 (c)290.7 (d)190.0

Contd…For-2013 (IES, GATE & PSUs) Page 11

Gating ratioGating ratio is defined as:   Sprue area: Runner area: 

Ingate area.

For high quality steel castings, a gating ratio of 1: 2: 2 or 

1: 2: 1 5 will produce castings nearly free from erosion  1: 2: 1.5 will produce castings nearly free from erosion, 

will minimize oxidation, and will produce uniform , p

flow. 

A gating ratio of 1: 4: 4 might favour the formation of 

oxidation defects.

IES‐2003A gating ratio of 1: 2: 4 is used to design the gatingsystem for magnesium alloy casting. This gating ratioy g y g g grefers to the cross∙ section areas of the various gatingelements as given below:elements as given below:1. Down sprue 2. Runner bar 3. IngatesTh f h b l i hThe correct sequence of the above elements in theratio 1: 2: 4 is(a) 1, 2 and 3(b) 1,3 and 2(b) 1,3 and 2(c) 2, 3 and 1(d)(d) 3, 1 an 2

IES‐2005

The gating ratio 2: 8: 1 for copper in gating systemThe gating ratio 2: 8: 1 for copper in gating systemdesign refers to the ratio of areas of:( ) S R I(a) Sprue: Runner: Ingate(b) Runner: Ingate: Sprue( ) g p(c) Runner: Sprue: Ingate(d) I R S(d) Ingate: Runner: Sprue

GATE‐2010

I     ti   t  th   ti     tIn a gating system, the ratio 1:2:4 represents

(a) Sprue base area: runner area: ingate area(a) Sprue base area: runner area: ingate area

(b) Pouring basin area : ingate area : runner area (b) Pouring basin area : ingate area : runner area 

(c) Sprue base area : ingate area : casting area (c) Sprue base area : ingate area : casting area 

(d) Runner area : ingate area : casting area(d) Runner area : ingate area : casting area

IAS‐1999Assertion (A): The rate of flow of metal through sprueis NOT a function of the cross‐sectional areas ofsprue, runner and gate.Reason (R): If respective cross‐sectional areas ofReason (R): If respective cross sectional areas ofsprue, runner and gate are in the ratio of 1: 2: 2, thesystem is known as unpressurised gating system.y p g g y(a) Both A and R are individually true and R is the correctexplanation of Aexplanation of A(b) Both A and R are individually true but R is not thecorrect explanation of Acorrect explanation of A(c) A is true but R is false(d) A is false but R is true(d) A is false but R is true

Risers and Riser DesignRi dd d i d i d f d li idRisers are added reservoirs designed to feed liquidmetal to the solidifying casting as a means ofcompensating for solidification shrinkage.To perform this function the risers must solidify afterTo perform this function, the risers must solidify afterthe casting.

d Ch ' l d h fAccording to Chvorinov's rule, a good shape for a riserwould be one that has a long freezing time (i.e., a smallsurface area per unit volume).Live risers (also known as hot risers) receive the lastLive risers (also known as hot risers) receive the lasthot metal that enters the mold and generally do so at ati h th t l i th ld it h l dtime when the metal in the mold cavity has alreadybegun to cool and solidify.

IES‐1994A i (A) I ld i i d i d d l dAssertion (A): In a mould, a riser is designed and placedso that the riser will solidify after the casting has solidified.Reason (R): A riser is a reservoir of molten metal whichwill supply molten metal where a shrinkage cavity wouldpp y g yhave occurred.(a) Both A and R are individually true and R is the correct(a) Both A and R are individually true and R is the correctexplanation of A(b) B th A d R i di id ll t b t R i t th(b) Both A and R are individually true but R is not thecorrect explanation of A(c) A is true but R is false(d) A is false but R is true( )

Chvorinov’s rulel l d f ( ) ( )Total solidification time (ts) = B (V/A) n

where  n = 1.5 to 2.0where  n   1.5 to 2.0[Where, B = mould constant and is a function of (mould 

t i l   ti   t i l   d  diti   f  ti ]material, casting material, and condition of casting]n = 2 and   triser = 1.25 tcastingriser 5 casting

⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟

2 2V V1 25or =⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠riser casting

1.25A A

or

( )= π 2

2

V D H / 4D

For cylinder of diameter D  ( )π= π +

2DA DH 2 4of diameter D and height H

IES 2011h l h b l fThe relationship between total freezing time t,

volume of the casting V and its surface area A,according to Chvorinov’s rule is :

V⎛ ⎞( ) Va t kAA

⎛ ⎞= ⎜ ⎟⎝ ⎠⎛ ⎞

2

( ) Ab t kV

⎛ ⎞= ⎜ ⎟⎝ ⎠

2

( ) Ac t kV

⎛ ⎞= ⎜ ⎟⎝ ⎠

Wh K i

2

( ) Vd t kA

⎛ ⎞= ⎜ ⎟⎝ ⎠Where K is a constant⎝ ⎠

For-2013 (IES, GATE & PSUs) Page 12

IES‐1998A spherical drop of molten metal of radius 2 mmp p

was found to solidify in 10 seconds. A similar drop

of radius 4 mmwould solidify in

(a) 14.14 seconds

(b) 20 seconds

(c) 28.30 seconds

(d) 40 seconds

GATE‐2003

With lidifi ti f t f 6 / 2 thWith a solidification factor of 0.97 x 106 s/m2, the

solidification time (in seconds) for a sphericalsolidification time (in seconds) for a spherical

casting of 200 mm diameter isg

(a) 539 (b) 1078 (c) 4311 (d) 3233

IES‐2006According to Chvorinov's equation, the

solidification time of a casting is proportional to:

(a) v2

(b) v

(c) 1/v

(d) 1/v2

Where, v = volume of casting

GATE – 2010 (PI)Solidification time of a metallic alloy casting is

(a) Directly proportional to its surface area

(b) Directly proportional to the specific heat of the

t t i lcast material

(c) Directly proportional to the thermal diffusivity of(c) Directly proportional to the thermal diffusivity of

the molten metalthe molten metal

(d)Inversely proportional to the pouring( ) y p p p g

temperature.

GATE‐2007

Volume of a cube of side 'l' and volume of a sphere ofVolume of a cube of side l and volume of a sphere of

radius ‘r’ are equal. Both the cube and the sphere are solidq p

and of same material. They are being cast. The ratio of the

solidification time of the cube to the same of the sphere is:

( ) ( ) ( ) ( )3 6 2 2 3 2 44 r 4 r 4 r 4 ra b c d

6 l 6 l 6 l 6 lπ π π π⎛ ⎞ ⎛ ⎞ ⎛ ⎞⎛ ⎞ ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ ⎛ ⎞

⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠ ⎝ ⎠⎝ ⎠ ⎝ ⎠ ⎝ ⎠ ⎝ ⎠ ⎝ ⎠

GATE ‐2011 (PI)GATE ‐2011 (PI)In a sand casting process, a sphere and a cylinderg p , p yof equal volumes are separately cast from the samemolten metal under identical conditions. Theheight and diameter of the cylinder are equal. Theratio of the solidification time of the sphere to thatratio of the solidification time of the sphere to thatof the cylinder is(a) 1 14(a) 1.14(b) 0.87( )(c) 1.31(d) 0.76( ) 7

GATE‐2009 (PI)( )A solid cylinder of diameter D and height equal to D, and a solidcube of side L are being sand cast by using the same materialcube of side L are being sand cast by using the same material.Assuming there is no superheat in both the cases, the ratio ofsolidification time of the cylinder to the solidification time of thecube iscube is

(a) (L/D)2

(b) (2L/D)2

( ) ( D/L)2(c) (2D/L)2

(d) (D/L)2

IES ‐ 2012The ratio of surface area of volume for a unit volume of 

friser is minimum in case of

( ) C li d i l  i  (a) Cylindrical riser 

(b) S h i l  i(b) Spherical riser

(c) Hemispherical riser (c) Hemispherical riser 

(d) Cuboids riser(d) Cuboids riser

For-2013 (IES, GATE & PSUs) Page 13

IES 2011 C ti lIES 2011 ConventionalA round casting is 20 mm in diameter and 50 mm ing 5

length. Another casting of the same metal is elliptical in

cross section, with a major to minor axis ratio of 2, and

has the same length and cross‐sectional area as the

round casting. Both pieces are cast under the same

conditions What is the difference in the solidificationconditions. What is the difference in the solidification

times of the two castings ? [10 – Marks]times of the two castings ? [10 Marks]

( ) ( )( )Area of ellipse

Circumference 3 3 3

ab

a b a b a b

π

π

=

⎡ ⎤= + − + +⎣ ⎦( ) ( )( )

( )2 2

Circumference 3 3 3

2 / 2 (approx.)

a b a b a b

a b

π

π

⎡ ⎤= + + +⎣ ⎦

= +

Conventional Question ESE 2003

Compare the solidification time of two optimum side –

f h l h h l d l hrisers of the same volume with one has cylindrical shape

and other is parallopiped [30 Marks]and other is parallopiped. [30 Marks]

Modulus MethodIt has been empirically established that if the modulus

f h i d h d l f h i bof the riser exceeds the modulus of the casting by a

factor of 1 2 the feeding during solidification would befactor of 1.2, the feeding during solidification would be

satisfactory.

MR = 1.2 Mc

Modulus = volume/Surface area

In steel castings, it is generally preferable to choose a

i i h h i h di i friser with a height‐to‐diameter ratio of 1.Contd…

22D Dπ

+ 2

4Dπ+

Conventional Question IES‐2008Conventional Question IES‐2008Calculate the size of a cylindrical riser (height and diameterCalculate the size of a cylindrical riser (height and diameter

equal) necessary to feed a steel slab casting of dimensions

30 x 30 x 6 cm with a side riser, casting poured horizontally

into the mould.

[Use Modulus Method][Use Modulus Method]

[10 ‐Marks][ ]

Caine’s MethodFreezing ratio = ratio of cooling characteristics of casting to the riser. ( )A( )

( )Casting

AVX

AV

=

The riser should solidify last so x > 1

( )RiserV

According to Caine X =a c

Y b+According to Caine X 

Y                  d   b        

Y b−

riserVY =               and a, b, c are constant. riser

castingV

Table: Constants in Caine’s Method Conventional Question IES‐2007Conventional Question IES‐2007Calculate the size of a cylindrical riser (height andy g

diameter equal) necessary to feed a steel slab

casting of dimensions 25 x 25 x 5 cm with a side

riser, casting poured horizontally into the mould.

[Use Caine’s Method]

[ F l b d ][ For steel a = 0.10, b = 0.03 and c = 1.00 ]

For-2013 (IES, GATE & PSUs) Page 14

ChillsE l hill f hi h h i hi h h lExternal chills are masses of high‐heat‐capacity, high‐thermal‐conductivity material that are placed in the mould (adjacent toth ti ) t l t th li f i ithe casting) to accelerate the cooling of various regions.Chills can effectively promote directional solidification ori h ff i f di di f i Th fincrease the effective feeding distance of a riser. They can oftenbe used to reduce the number of risers required for a casting.Internal chills are pieces of metal that are placed within themould cavity to absorb heat and promote more rapidlidifi i Si f hi l ill l d i hsolidification. Since some of this metal will melt during the

operation, it will absorb not only the heat‐capacity energy, butl h t f f i Si th lti t l b t falso some heat of fusion. Since they ultimately become part ofthe final casting, internal chills must be made from the samell th t b i talloy as that being cast.

IES‐1995

Di ti l lidifi ti i ti bDirectional solidification in castings can be

improved by usingimproved by using

(a) Chills and chaplets(a) Chills and chaplets

(b) Chills and padding( ) p g

(c) Chaplets and padding( ) p p g

(d) Chills, chaplets and padding.

GATE‐1998,2007

Chill d i ld tChills are used in moulds to

(a) Achieve directional solidification(a) Achieve directional solidification

(b) Reduce the possibility of blowholes(b) Reduce the possibility of blowholes

(c) Reduce freezing time(c) Reduce freezing time

(d) Smoothen metal flow for reducing splatter.(d) Smoothen metal flow for reducing splatter.

IAS 1994Chills are used in casting moulds to( ) A hi  di i l  lidifi i(a) Achieve directional solidification(b) Reduce possibility of blow holes( ) p y(c) Reduce the freezing time(d) I   h   h   f    f(d) Increase the smoothness of cast surface

CupolaCupolaCupola has been the most widely used furnace formelting cast iron.In hot blast cupola, the flue gases are used to preheat theIn hot blast cupola, the flue gases are used to preheat theair blast to the cupola so that the temperature in thefurnace is considerably higher than that in afurnace is considerably higher than that in aconventional cupola. Coke is fuel and Lime stone(C CO ) i l d fl(CaCO3) is mostly used flux.Cost of melting low.gMain disadvantages of cupola is that it is not possible toproduce iron below 2 8% carbonproduce iron below 2.8% carbon.Steel can be also prepared in cupola by employingduplexing and triplexing operations.

IES‐1997Assertion (A): Steel can be melted in hot blast cupola.Reason (R): In hot blast cupola the flue gases are used toReason (R): In hot blast cupola, the flue gases are used topreheat the air blast to the cupola so that the temperature inth f i id bl hi h th th t ithe furnace is considerably higher than that in aconventional cupola.(a) Both A and R are individually true and R is the correctexplanation of Ap(b) Both A and R are individually true but R is not thecorrect explanation of Acorrect explanation of A(c) A is true but R is false(d) A i f l b R i(d) A is false but R is true

IES ‐ 2012St t t (I) C l f i t l d fStatement (I): Cupola furnace is not employed formelting steel in foundryStatement (II): The temperatures generated within acupola are not adequate for melting Steel(a) Both Statement (I) and Statement (II) areindividually true and Statement (II) is the correcty ( )explanation of Statement (I)(b) Both Statement (I) and Statement (II) are(b) Both Statement (I) and Statement (II) areindividually true but Statement (II) is not the correctexplanation of Statement (I)explanation of Statement (I)(c) Statement (I) is true but Statement (II) is false( ) ( ) ( )(d) Statement (I) is false but Statement (II) is true

El i A FElectric Arc Furnace For heavy steel castings, the open‐hearth type of

f h l l f d ld b llfurnaces with electric arc or oil fired would be generally

suitable in view of the large heat required for meltingsuitable in view of the large heat required for melting.

Electric arc furnaces are more suitable for ferrousElectric arc furnaces are more suitable for ferrous

materials and are larger in capacity.g p y

Crucible FurnaceCrucible FurnaceSmaller foundries generally prefer the crucible furnace.The crucible is generally heated by electric resistanceor gas flame.or gas flame.

Induction FurnaceThe induction furnaces are used for all types ofThe induction furnaces are used for all types ofmaterials, the chief advantage being that the heatsource is isolated from the charge and the slag and fluxsource is isolated from the charge and the slag and fluxget the necessary heat directly from the charge insteadf th h tof the heat source.

For-2013 (IES, GATE & PSUs) Page 15

LadlesTwo types of ladles used in the pouring of castings.

Casting Cleaning (fettling)Impurities in the molten metal are prevented from reaching the mould cavity by providing a       g y y p g(i)  Strainer (ii) B tt   ll(ii) Bottom well(iii) Skim bob

GATE‐1996

Light impurities in the molten metal are preventedLight impurities in the molten metal are preventedfrom reaching the mould cavity by providing a( ) S i(a) Strainer(b) Button well( )(c) Skim bob(d) All f h b(d) All of the above

P i iPouring timeTime taken to fill the mould with top gate

Where   A = Area of mould A HH = Height of mouldA  A   f G t

Ag m

A.HtA 2gh

=

Ag = Area of GateHm = Gate height

g mg

Time taken to fill the mould with bottom gate Time taken to fill the mould with bottom gate 

( )2A ( )B m mg

2At h h HA 2g

= − −

GATE‐2005

A mould has a downsprue whose length is 20 cmA mould has a downsprue whose length is 20 cmand the cross sectional area at the base of thedownsprue is 1cm2 The downsprue feeds adownsprue is 1cm2. The downsprue feeds ahorizontal runner leading into the mould cavity of

l 3 Th i i d fill hvolume 1000 cm3. The time required to fill themould cavity will be(a)4.05 s (b)5.05 s (c)6.05 s (d)7.25 s

GATE‐2006In a sand casting operation, the total liquid head isa sa d cast g ope at o , t e tota qu d ead smaintained constant such that it is equal to the mouldheight The time taken to fill the mould with a top gateheight. The time taken to fill the mould with a top gateis tA. If the same mould is filled with a bottom gate,th th ti t k i t I th ti i d tthen the time taken is tB. Ignore the time required tofill the runner and frictional effects. Assumeatmospheric pressure at the top molten metal surfaces.The relation between tA and tB isA B(A) 2(B) 2

B A

B A

t tt t

=

=( )

(C)2

B A

AB

tt =2

(D) 2 2B At t=

( ) k dGATE – 2007 (PI) Linked S‐1I d ti f bIn a sand casting process, a sprue of 10 mm basediameter and 250 mm height leads to a runner5 gwhich fills a cubical mould cavity of 100 mm sizeTh l fl (i 3/ ) iThe volume flow rate (in mm3/s) is(a) 0 8 x 105 (b) 1 1 x 105(a) 0.8 x 10 (b) 1.1 x 10(c) 1.7 x 105 (d) 2.3 x 105

( ) k dGATE – 2007 (PI) Linked S‐2I d ti f bIn a sand casting process, a sprue of 10 mm basediameter and 250 mm height leads to a runner5 gwhich fills a cubical mould cavity of 100 mm sizeTh ld filli i (i d ) iThe mould filling time (in seconds) is(a) 2 8 (b) 5 78(a) 2.8 (b) 5.78(c) 7.54 (d) 8.41

Expression for choke area = 2mCA mm

cρt 2gHcρt 2gH

Where m = mass of the casting, kg = Density of metal, kg / m3ρ y , g /

t = pouring time   Effi i  f t   d i  th  f ti   f  t  

ρ

c = Efficiency factor and is the function of gate system  used 

H = Effective head of liquid metal= h for top gate p g

Contd…For-2013 (IES, GATE & PSUs) Page 16

hH=h‐ for bottom gatemh2

=h‐ for parting line gate 2

ch2hm2h

hmh

Ch

h

top gate                   parting line gate               bottom gate

mh

P i li

mh

top gate                   parting line gate               bottom gate

IES 2009IES 20092 marks2 marks

IAS‐2011 MainIAS‐2011 MainSk t h ld f t h ll t t bSketch a mould for two hollow components to be

cast On the diagram indicate runner gate risercast. On the diagram, indicate runner, gate, riser,

core, cope, sprue, pouring basin, sprue well, drag,p p p g p g

parting line.

[10‐Marks]

Casting Defects The following are the major defects, which are likely to 

doccur in sand castings:

G  d fGas defects

Sh i k   itiShrinkage cavities

Molding material defectsMolding material defects

Pouring metal defectsPouring metal defects

Mold shiftMold shift.

Gas DefectsA condition existing in a casting caused by thetrapping of gas in the molten metal or by mold gasestrapping of gas in the molten metal or by mold gasesevolved during the pouring of the casting.The defects in this category can be classified intoblowholes and pinhole porosity.p p yBlowholes are spherical or elongated cavities presentin the casting on the surface or inside the castingin the casting on the surface or inside the casting.Pinhole porosity occurs due to the dissolution ofhydrogen gas, which gets entrapped during heating ofmolten metal.

Sh i k C i iShrinkage CavitiesThese are caused by liquid shrinkage occurring during theThese are caused by liquid shrinkage occurring during thesolidification of the casting.T f hi f di f li id l iTo compensate for this, proper feeding of liquid metal isrequired. For this reason risers are placed at the

i l i h ldappropriate places in the mold.Sprues may be too thin, too long or not attached in thep y gproper location, causing shrinkage cavities.It is recommended to use thick sprues to avoid shrinkageIt is recommended to use thick sprues to avoid shrinkagecavities.

Molding Material Defectsg

Cuts and washesCuts and washes,

ScabScab

Metal penetrationMetal penetration,

Fusion, andFusion, and

SwellSwell

Cut and washesThese appear as rough spots and areas of excess metal, andare caused by erosion of molding sand by the flowingy g y gmetal.This is caused by the molding sand not having enoughThis is caused by the molding sand not having enoughstrength and the molten metal flowing at high velocity.Th f b k f b h h i fThe former can be taken care of by the proper choice ofmolding sand and the latter can be overcome by the

d f hproper design of the gating system.

S bScabThis defect occurs when a portion of the face of a mouldThis defect occurs when a portion of the face of a mouldlifts or breaks down and the recess thus made is filled bymetalmetal.When the metal is poured into the cavity, gas may bedi d i h h i l b k h ddisengaged with such violence as to break up the sand,which is then washed away and the resulting cavity filledi h lwith metal.

The reasons can be: ‐ too fine sand, low permeability ofp ysand, high moisture content of sand and uneven mouldramming.g

For-2013 (IES, GATE & PSUs) Page 17

Metal penetrationh l l h b dWhen molten metal enters into the gaps between sand

grains, the result is a rough casting surface.This occurs because the sand is coarse or no mold wash wasapplied on the surface of the mold. The coarser the sandppgrains more the metal penetration.

FusionThis is caused by the fusion of the sand grains with

the molten metal, giving a brittle, glassy appearance

on the casting surface.

The main reason for this is that the clay or the sand

ti l f l f t i th t thparticles are of lower refractoriness or that the

pouring temperature is too highpouring temperature is too high.

SwellSweUnder the influence of metallostatic forces, the moldwall may move back causing a swell in the dimensionwall may move back causing a swell in the dimensionof the casting. A proper ramming of the mold willcorrect this defectcorrect this defect.

InclusionsParticles of slag refractory materials sand orParticles of slag, refractory materials sand ordeoxidation products are trapped in the casting duringpouring solidification The provision of choke in thepouring solidification. The provision of choke in thegating system and the pouring basin at the top of themold can prevent this defectmold can prevent this defect

Pouring Metal DefectsThe likely defects in this category are

Mis‐runs andMis runs andCold shuts

A mis‐run is caused when the metal is unable to fillA mis run is caused when the metal is unable to fillthe mold cavity completely and thus leaves unfilledcavitiescavities.A cold shut is caused when two streams while meetingin the mold cavity, do not fuse together properly thusforming a discontinuity in the casting.forming a discontinuity in the casting.

Contd…

The mis‐run and cold shut defects are caused either byya lower fluidity of the mold or when the sectionthickness of the casting is very small. Fluidity can bethickness of the casting is very small. Fluidity can beimproved by changing the composition of the metaland by increasing the pouring temperature of theand by increasing the pouring temperature of themetal.

GATE‐2004

Mi i ti d f t hi h d tMisrun is a casting defect which occurs due to

(a) Very high pouring temperature of the metal(a) Very high pouring temperature of the metal

(b) Insufficient fluidity of the molten metal(b) Insufficient fluidity of the molten metal

(c) Absorption of gases by the liquid metal(c) Absorption of gases by the liquid metal

(d) Improper alignment of the mould flasks(d) Improper alignment of the mould flasks

GATE‐2009Two streams of liquid metal which are not hot

enough to fuse properly result into a casting defect

known as

(a) Cold shut

(b) Swell

( ) d h(c) Sand wash

(d) S b(d) Scab

Mold ShiftThe mold shift defect occurs when cope and drag

or molding boxes have not been properly aligned.

IES‐2001

S b i  Scab is a

(a) Sand casting defect(a) Sand casting defect

(b) Machining defect  (b) Machining defect  

(c) Welding defect(c) Welding defect

(d) Forging defect (d) Forging defect 

For-2013 (IES, GATE & PSUs) Page 18

IAS‐2004Match List‐I (Casting Defects) with List‐II (Explanation) and select the correct answer using the codes given below the lists:List‐I List‐IIList I List II(Casting Defects) (Explanation)A. Metallic projections 1. Consist of rounded or rough internal or exposed cavities     

including blow holes and pin holesincluding blow holes and pin holesB. Cavities 2. Formed during melting, solidification and moulding.C. Inclusions 3. Includes single folds, laps, scars adhering sand layers and 

oxide scaleoxide scaleD. Discontinuities 4. Include cracks, cold or hot tearing and cold shuts

5.Consist of fins, flash or massive projections and rough surfacessurfaces

Codes:   A  B  C  D A  B  C  D(a)  1  5  3  2 (b)  1  5  2  4(c) 5  1  2  4 (d)  5  1  3  2(c) 5  1  2  4 (d)  5  1  3  2

GATE‐2003Hardness of green sand mould increases with( ) I  i   i    b d 6 (a) Increase in moisture content beyond 6 percent(b) Increase in permeability( ) p y(c) Decrease in permeability(d) I  i  b h  i     d (d) Increase in both moisture content and permeability

IES‐1998Assertion (A): Stiffening members, such as webs and ribs, used on a casting should be liberally and ribs, used on a casting should be liberally provided. Reason (R): They will provide additional strength Reason (R): They will provide additional strength to a cast member.( ) B h A  d R   i di id ll     d R i   h  (a) Both A and R are individually true and R is the correct explanation of A(b) Both A and R are individually true but R is not the correct explanation of A p(c) A is true but R is false(d) A is false but R is true(d) A is false but R is true

IES‐2005In gating system design, which one of thefollowing is the correct sequence in which chokefollowing is the correct sequence in which chokearea, pouring time, pouring basin and sprue sizes

l l d?are calculated?(a) Choke area ‐ Pouring time ‐ Pouring basin – Sprue( ) g g p(b) Pouring basin ‐ Sprue ‐ Choke area ‐ Pouring time( ) Ch k     S P i  b i   P i   i(c) Choke area ‐ Sprue ‐ Pouring basin ‐ Pouring time(d) Pouring basin ‐ Pouring time ‐ Choke area ‐ Sprue( ) g g p

IES‐1997If the melting ratio of a cupola is 10: 1, then the coke requirement for one ton melt will becoke requirement for one ton melt will be(a) 0.1 ton(b) 10 tons(c) 1 ton(c) 1 ton(d) 11 tons

IES‐2009In which one of the following furnaces most of the non ferrous alloys are melted?non‐ferrous alloys are melted?(a) Reverberatory furnace(b) Induction furnace(c) Crucible furnace(c) Crucible furnace(d) Pot furnace

IAS‐2001Which of the following pattern‐materials are used in Precision Casting?in Precision Casting?1. Plaster of Paris2. Plastics3 Anodized Aluminium Alloy 3. Anodized Aluminium Alloy 4. Frozen MercurySelect the correct answer using the codes given below:(a) 1 and 2   (b) 2 and 4   (c)3 and 4   (d) 1 and 3(a) 1 and 2   (b) 2 and 4   (c)3 and 4   (d) 1 and 3

IAS‐2004Which one of the following gating systems is best suited to obtain directional solidification?suited to obtain directional solidification?(a) Top grating(b) Part‐line grating(c) Bottom grating(c) Bottom grating(d) Stepped grating

C t Al i i C dCast Aluminium CodeFour digit identification systemou d g t de t cat o systeFirst digit indicates alloy group

l1 – Aluminium, 99% or more2 – copper2  copper3 – Silicon, with copper and/or magnesium4 – silicon5 – magnesium5  magnesium6 – not used7 – zinc8 – tin8  tin9 – other elementsFor-2013 (IES, GATE & PSUs) Page 19

Cast Aluminium Code          Contd..S d di i id if h l i i llSecond two digits identify the aluminium alloy orindicate the aluminium purity.The last digit is separating from the other three by adecimal point and indicates the product form; that isdecimal point and indicates the product form; that is,castings or ingots

d f f h l ll d d bA modification of the original alloy is indicated by aserial letter before the numerical designation.Alloy A514.0 indicates an aluminium alloy casting withmagnesium as the principal alloy One modification tomagnesium as the principal alloy. One modification tothe original alloy has made, as indicated by the letter A.

IES 2011In the designation of Aluminium casting A514.0indicates :(a) Aluminium purity(b) Al i i(b) Aluminium content(c) Percentage of alloy element( ) g y(d) Magnesium Content

Ans. (d)s (d)

S i l C tiSpecial Castingp g

By  S K MondalBy  S K Mondal

Shell MouldinggThe sand is mixed with a thermosetting resin ise sa d s ed w t a t e osett g es sallowed to come in contact with a heated metal pattern(2000C)(200 C).A skin (shell) of about 3.5 mm of sand and plasticmixture adhere to the pattern.Then the shell is removed from the pattern.Then the shell is removed from the pattern.The cope and drag shells are kept in a flask with

b k t i l d th lt t l inecessary backup material and the molten metal ispoured into the mold.

Can produce complex parts.

A good surface finish and good size tolerance

reduce the need for machining.

Materials can be cast: CI, Al and Cu alloys.

Shell moulding processShell moulding process

Molding Sand in Shell MoldingMolding Sand in Shell MoldingThe molding sand is a mixture of fine grained quartz sand

and powdered bakelite.

Cold coating and Hot coating methods are used for

i h d i i h b k licoating the sand grains with bakelite.

Cold coating: quartz sand is poured into the mixer andCold coating: quartz sand is poured into the mixer and

then the solution of powdered bakelite in acetone andp

ethyl aldehyde are added. (mixture is 92% quartz sand,

5% bakelite, 3% ethylaldehyde )Contd…

Hot coating: the mixture is heated to 150oC– 180oC priorg 5 p

to loading the sand. In the course of sand mixing, the

soluble phenol formaldehyde resin is added. The mixer is

ll d l 8 C H i i ballowed to cool up to 80 – 90o C. Hot coting gives better

properties to the mixtures than cold methodproperties to the mixtures than cold method.

AdvantagesDimensional accuracy.

Smoother surface finish. (Due to finer size grain used)

Very thin sections can be cast.

Very small amount of sand is needed.

For-2013 (IES, GATE & PSUs) Page 20

LimitationsExpensive pattern

Small size casting only.

Hi hl li d h b b i dHighly complicated shapes cannot be obtained.

M hi ti t d i t i d d f h dliMore sophisticated equipment is needed for handling

the shell moldingsthe shell moldings.

ApplicationsApplicationsC li d d li d h d f i l d ICCylinders and cylinder heads for air‐ cooled IC

enginesengines

Automobile transmission parts.Automobile transmission parts.

Piston ringsg

IES 2010C id  th  f ll i   d t   f  h ll Consider the following advantages of shell mould casting:g

1. Close dimensional tolerance.2. Good surface finish.3  Low cost3. Low cost.4. Easier.4Which of these are correct?(a) 1, 2 and 3 only  (b) 2, 3 and 4 only( )      d    l   (d)        d (c) 1, 2 and 4 only  (d) 1, 2, 3 and 4

IES‐1996Consider the following ingredients used inmoulding:moulding:

1. Dry silica sand2.Clay3 Phenol formaldehyde3.Phenol formaldehyde4.Sodium silicateThose used for shell mould casting include(a) 1 2 and 4 (b) 2 3 and 4(a) 1, 2 and 4 (b) 2, 3 and 4(c) 1and 3 (d) 1, 2, 3 and 4

IES‐2005In shell moulding, how can the shell thickness be accurately maintained?be accurately maintained?

(a) By controlling the time during which the pattern i  i     i h  ld      is in contact with mould      

(b) By controlling the time during which the pattern ( ) y g g pis heated

(c) By maintaining the temperature of the pattern in (c) By maintaining the temperature of the pattern in the range of 175oC – 380oC

(d) By the type of binder used

IES‐2006Shell moulding can be used for:( ) P d i   illi  (a) Producing milling cutters(b) Making gold ornaments( ) g g(c) Producing heavy and thick walled casting(d) P d i   hi   i(d) Producing thin casting

IES 2007Which of the following are employed in shellWhich of the following are employed in shellmoulding?R i bi d M l H i il1. Resin binder 2. Metal pattern 3. Heating coils

Select the correct answer using the code giveng gbelow:(a) 1 and 2 only (b) 1 and 3 only(a) 1 and 2 only (b) 1 and 3 only(c) 2 and 3 only (d) 1, 2 and 3

IAS‐2007The mould in shell moulding process is made up

of which of the following?

(a) Gypsum + setting agents

(b) Green sand + clay

(c) Sodium silicate + dried sand

(d) Dried silica + phenolic resin

IAS‐1999Match List I (Moulding Process) with List II (BindingAgent) and select the correct answer using the codes

b l h lgiven below the lists:List I List II

A. Green sand 1. SilicateB. Core sand 2. OrganicC. Shell moulding 3. ClayD. CO2 process 4. Plaster of Parisp

5. PlasticCodes:A B C D A B C D(a) 3 2 5 1 (b) 3 2 4 1(c) 2 3 5 4 (d) 2 3 4 5( ) 3 5 4 ( ) 3 4 5

For-2013 (IES, GATE & PSUs) Page 21

Investment CastingInvestment casting process or lost wax processBasic steps:p1. Produce expendable wax, plastic, or polystyrene patterns.2 Assemble these patterns onto a gating system2.Assemble these patterns onto a gating system3. Investing or covering the pattern assembly with refractoryslurryslurry

4.Melting the pattern assembly to remove the pattern materiali i h ld h l f h5. Firing the mould to remove the last traces of the pattern

material6.Pouring molten metal7. Knockout, cutoff and finishing.g

Fig. Investment flask‐casting procedure

Ceramic Shell Investment CastingIn ceramic shell investment casting a ceramic shell isg

built around a tree assembly by repeatedly dipping a

pattern into a slurry (refractory material such as

zircon with binder).

After each dipping and stuccoing is completed, the

assembly is allowed to thoroughly dry before the nextassembly is allowed to thoroughly dry before the next

coating is applied.coating is applied.

IES 2009IES 20092 marks2 marks

AdvantagesTight dimensional tolerances

Excellent surface finish (1.2 to 3.0 μm )

Machining can be reduced or completely

li i t deliminated

High melting point alloy can be cast almost anyHigh melting point alloy can be cast, almost any

metal can be cast

Almost unlimited intricacy

Limitations

C tl tt d ldCostly patterns and moulds

Labour costs can be highLabour costs can be high

Limited sizeLimited size

Applications

A d k t tAerospace and rocket components.

Vanes and blades for gas turbinesVanes and blades for gas turbines.

Surgical instrumentsSurgical instruments

IES 2011The proper sequence of investment casting steps is :(a) Slurry coating – pattern melt out‐Shakeout – Stucco(a) Slurry coating pattern melt out Shakeout Stuccocoating(b) S i Sl i Sh k P(b) Stucco coating – Slurry coating – Shakeout – Patternmelt out(c) Slurry coating – Stucco coating – Pattern melt out –ShakeoutShakeout(d) Stucco coating – Shakeout – Slurry coating – Pattern

lmelt out

For-2013 (IES, GATE & PSUs) Page 22

GATE‐2006An expendable pattern is used inAn expendable pattern is used in(a) Slush casting(b) Squeeze casting(c) Centrifugal casting(c) Centrifugal casting(d) Investment casting

GATE‐2011 (PI)

Whi h f th f ll i tiWhich of the following casting processes uses

expendable pattern and expendable mould?expendable pattern and expendable mould?

(a) Shell mould casting(a) Shell mould casting

(b) Investment casting( ) g

(c) Pressure die casting( ) g

(d) Centrifugal casting

ISRO‐2010ISRO‐2010Investment casting is used forInvestment casting is used for

(a) Shapes which are made by difficulty using complex( ) p y y g p

patterns in sand casting

(b) Mass production

(c) Shapes which are very complex and intricate and

can't be cast by any other methodcan t be cast by any other method

(d) There is nothing like investment casting( ) g g

IES‐1992The most preferred process for casting gas turbine blades is:blades is:(a) Die moulding(b) Shell moulding(c) Investment moulding(c) Investment moulding(d) Sand casting

JWM 2010Consider the following materials :Consider the following materials :1. Wax 2. Wood3  Plastic3. PlasticWhich of these materials can be used as pattern in investment casting process ?(a) 1  2 and 3  (b) 1 and 2 only(a) 1, 2 and 3  (b) 1 and 2 only(c) 2 and 3 only  (d) 1 and 3 only

IES 2010Assertion (A): The investment casting is used forAssertion (A): The investment casting is used forprecision parts such as turbine plates, sewing

himachines etc.Reason (R): The investment castings have a good( ) g gsurface finish and are exact reproductions of themaster patternmaster pattern.(a) Both A and R are individually true and R is thecorrect explanation of A(b) Both A and R are individually true but R is NOT the(b) Both A and R are individually true but R is NOT thecorrect explanation of A( ) A i t b t R i f l(c) A is true but R is false(d) A is false but R is true

IES 2007IES 2007Consider the following statements in respect ofConsider the following statements in respect ofinvestment castings:

Th tt tt i / t j i d t t lk1. The pattern or patterns is/are not joined to a stalk orsprue also of wax to form a tree of patterns.2.The prepared moulds are placed in an oven and heatedgently to dry off the invest and melt out the bulk of wax.3.The moulds are usually poured by placing the moulds ina vacuum chamber. Which of the statements given abovea vacuum chamber. Which of the statements given aboveare correct?(a) 1 and 2 only (b) 1 and 3 only(a) 1 and 2 only (b) 1 and 3 only(c)2 and 3 only (d) 1, 2 and 3

IES‐2006Which of the following materials are used formaking patterns in investment casting method?making patterns in investment casting method?1. Wax 2. Rubber 3. Wood 4. PlasticSelect the correct answer using the codes given below:(a) Only 1 and 3 (b) Only 2 and 3(a) Only 1 and 3 (b) Only 2 and 3(c) Only 1, 2 and 4 (d) Only 2, 3 and 4

IAS‐1996Light and intricate parts with close dimensionaltolerances of the order of ± 0 005 mm aretolerances of the order of ± 0.005 mm areproduced by(a) Investment casting(b) Die casting(b) Die casting(c) Centrifugal casting(d) Shell mould casting

For-2013 (IES, GATE & PSUs) Page 23

Permanent Mould CastingThe process in which we use a die to make thepcastings is called permanent mold casting or gravitydie casting, since the metal enters the mold underdie casting, since the metal enters the mold undergravity.S ti i di ti i j t th lt t lSome time in die‐casting we inject the molten metalwith a high pressure. When we apply pressure ininjecting the metal it is called pressure die castingprocess.pGrey cast iron is used for mould material.

AdvantagesGood surface finish and dimensional accuracyGood su ace s a d d e s o a accu acyMetal mold gives rapid cooling and fine‐graint tstructureMultiple‐use molds.p

DisadvantagesHigh initial mold costgShape, size, and complexity are limitedMold life is very limited with high‐melting‐pointMold life is very limited with high‐melting‐pointmetals such as steel.Low melting point metals can be castLow melting point metals can be cast‐ Aluminum

Zi‐ Zinc‐ Magnesium alloys‐ Brass‐ Cast ironCast iron

Applications

Pi t / li d / dPistons/cylinders/rods

GearsGears

KitchenwareKitchenware

Die CastingMolten metal is injected into closed metal dies underj

pressures ranging from 100 to 150 MPa.

Pressure is maintained during solidification

After which the dies separate and the casting is ejected

along with its attached sprues and runners.

Cores must be simple and retractable and take the

f f i lform of moving metal segments

Die casting machines can be

Hot chamber

Cold chamber

Hot chamber machines areHot chamber machines areGood for low temperature (approx. 400°C)Good for low temperature (approx. 400 C)Faster than cold chamber machinesCycle times must be short to minimize metalcontaminationMetal starts in a heated cylinderA i f l i h diA piston forces metal into the dieThe piston retracts, and draws metal inp ,Metal: Lead, Tin, Zinc

Hot Chamber

Cold chamber machinesCasts high melting point metals ( > 600°C)Casts high melting point metals ( > 600 C)

High pressures usedg p

Metal is heated in a separate crucible

Metal is ladled into a cold chamber

The metal is rapidly forced into the mold before it 

lcools

Copper, Brass and Aluminium can cast.Copper, Brass and Aluminium can cast.

For-2013 (IES, GATE & PSUs) Page 24

Ad tAdvantagesE l   h  f   (   )Extremely smooth surfaces  (1 µm)

E ll t di i l Excellent dimensional accuracy

Rapid production rateRapid production rate

Better mechanical properties compared to sand Better mechanical properties compared to sand 

castingg

Intricate parts possiblep p

Minimum finishing operationsg p

Thin sections possible

LimitationsLimitationsHigh initial die costHigh initial die cost

Limited to high‐fluidity nonferrous metalsLimited to high fluidity nonferrous metals

Part size is limited

Porosity may be a problem

Some scrap in sprues, runners, and flash, but this can 

be directly recycled

A li iApplicationsCarburettorsAutomotive partsB h fiBathroom fixturesToysy

lCommonmetalsAlloys of aluminum, zinc, magnesium, and leadAlloys of aluminum, zinc, magnesium, and leadAlso possible with alloys of copper and tin

IES 2011d h f ll d f dConsider the following advantages of die casting over

sand casting :1. Rapidity of the process2 Smooth surface2. Smooth surface3. Strong dense metal structureWhi h f h d ?Which of these advantages are correct ?(a) 1, 2 and 3( ) , 3(b) 1 and 2 only(c) 2 and 3 only(c) 2 and 3 only(d) 1 and 3 only

IES‐2009Which of the following are the most suitablematerials for die casting?materials for die casting?(a) Zinc and its alloys(b) Copper and its alloys(c) Aluminium and its alloys(c) Aluminium and its alloys(d) Lead and its alloys

JWM 2010Assertion (A) : In die casting method smallAssertion (A) : In die casting method, smallthickness can be filled with liquid metal.Reason (R) : The air in die cavity trapped inside thecasting causes problems.g p(a) Both A and R are individually true and R is the 

t  l ti   f Acorrect explanation of A(b) Both A and R are individually true but R is not the ycorrect explanation of A (c) A is true but R is false(c) A is true but R is false(d) A is false but R is true

IES‐2005Which one of the following processes produces acasting when pressure forces the molten metalcasting when pressure forces the molten metalinto themould cavity?(a) Shell moulding (b) Investment casting(c) Die casting (d) Continuous casting(c) Die casting (d) Continuous casting

IES‐2006In which of the following aremetal moulds used?( ) G d ld(a) Greensand mould(b) Dry sand mould( ) y(c) Die casting process(d) L ldi(d) Loam moulding

For-2013 (IES, GATE & PSUs) Page 25

IES‐1995Assertion (A): An aluminium alloy with 11 % silicon isused for making engine pistons by die castingg g p y gtechnique.Reason (R): Aluminium has low density and additionReason (R): Aluminium has low density and additionof silicon improves its fluidity and therefore itscastability.y(a) Both A and R are individually true and R is the correctexplanation of Aexplanation of A(b) Both A and R are individually true but R is not thecorrect explanation of Acorrect explanation of A(c) A is true but R is false(d) A is false but R is true(d) A is false but R is true

IES‐1995Match List I with List II and select the correct answer taking the help of codes given below the lists:List I List II List I List II (Products) (Process of manufacture)A. Automobile piston in aluminium alloy 1. Pressure die‐castingp y gB. Engine crankshaft in spheroidal

graphite iron 2. Gravity die‐castingC Carburettor housing in aluminium alloy 3  Sand castingC. Carburettor housing in aluminium alloy 3. Sand castingD. Cast titanium blades 4. Precision investment 

castingh ll ld5. Shell moulding

Code: A B C D A B C D(a) 2 3 1 5 (b) 3 2 1 5(a) 2 3 1 5 (b) 3 2 1 5(c) 2 1 3 4 (d) 4 1 2 3

IAS‐2007Consider the following statements:

Zi  di   i  h  l   h1. Zinc die castings have low strength.2. In the die casting process, very thin sections or g p , ycomplex shapes can be obtained easily.Which of the statements given above is/are correct?Which of the statements given above is/are correct?(a) 1 only(b) 2 only(c) Both 1 and 2(c) Both 1 and 2(d) Neither 1 nor 2

IAS‐1996Assertion (A): Die casting yields a product of goodaccuracy and finish.accuracy and finish.Reason (R): Low melting alloys used in diecastingcasting.(a) Both A and R are individually true and R is the

l i f Acorrect explanation of A(b) Both A and R are individually true but R is not theycorrect explanation of A(c) A is true but R is false(c) A is true but R is false(d) A is false but R is true

IES 2011Consider the following statements :1 Hot chamber machine is used for casting zinc tin and1. Hot chamber machine is used for casting zinc, tin andother low melting alloys.

C ld h b hi i d f di i f2. Cold chamber machine is used for die casting offerrous alloys3. Rapid cooling rate in die casting produces highstrength and quality in many alloysstrength and quality in many alloys.Which of these statements are correct?(a) 1, 2 and 3 (b) 1 and 2 only(c) 2 and 3 only (d) 1 and 3 only(c) 2 and 3 only (d) 1 and 3 only

GATE‐2007Which of the following engineering materials isWhich of the following engineering materials isthe most suitable candidate for hot chamber diecasting?casting?

(a) Low carbon steel(b) Titanium(c) Copper(c) Copper(d) Tin

IES‐1995Assertion (A): Aluminium alloys are cast in hotchamber die casting machine.gReason (R): Aluminium alloys require high meltingwhen compared to zinc alloys.when compared to zinc alloys.(a) Both A and R are individually true and R is the correctexplanation of Aexplanation of A(b) Both A and R are individually true but R is not thecorrect explanation of Acorrect explanation of A(c) A is true but R is false

(d) A is false but R is true

GATE ‐2009 (PI)GATE ‐2009 (PI)Hot chamber die casting process is NOT suited forHot chamber die casting process is NOT suited for

(a) Lead and its alloy(a) Lead and its alloy

(b) Zinc and its alloy( ) y

(c) Tin and its alloy

(d) Aluminum and its alloy

C if l C iCentrifugal CastingProcess: Molten metal is introduced into a rotating sandProcess: Molten metal is introduced into a rotating sand,

metal, or graphite mould, and held against the mouldg p g

wall by centrifugal force until it is solidified

A mold is set up and rotated along a vertical (rpm is

reasonable), or horizontal (200‐1000 rpm is reasonable)

axisaxis.

The mold is coated with a refractory coating.The mold is coated with a refractory coating.

During cooling lower density impurities will tend to riseg g y p

towards the center of rotation.For-2013 (IES, GATE & PSUs) Page 26

Fig  True centrifugal castingFig. True centrifugal casting

PropertiesThe mechanical properties of centrifugally cast jobs arebetter compared to other processes, because the inclusionssuch as slag and oxides get segregated towards the centreand can be easily removed by machining. Also, they y gpressure acting on the metal throughout the solidificationcauses the porosity to be eliminated giving rise to densep y g gmetal.No cores are required for making concentric holes in theNo cores are required for making concentric holes in thecase of true centrifugal casting.

AdvantagesFine grained structure at the outer surface of thecasting free of gas and shrinkage cavities andcasting free of gas and shrinkage cavities andporosityF i f h ll i i i li d i hFormation of hollow interiors in cylinders withoutcoresCan produce a wide range of cylindrical parts,including ones of large sizeincluding ones of large size.Good dimensional accuracy, soundness, andl licleanlinessThere is no need for gates and runners, whichg ,increases the casting yield, reaching almost 100 %.

LimitationsMore segregation of alloy component during pouring under

the forces of rotationthe forces of rotation

Contamination of internal surface of castings with non‐Contamination of internal surface of castings with non

metallic inclusions

Inaccurate internal diameter

Shape is limited.

Spinning equipment can be expensive

Poor machinability

Common metalsIronsteelstainless steelll   f  l i i     d  i k lalloys of aluminium, copper, and nickel

GATE‐2002In centrifugal casting, the impurities areIn centrifugal casting, the impurities are

(a) Uniformly distributed(b) Forced towards the outer surface(c) Trapped near the mean radius of the casting(c) Trapped near the mean radius of the casting(d) Collected at the centre of the casting

GATE‐1993Centrifugally cast products have( ) L i i h hi h i(a) Large grain structure with high porosity(b) Fine grain structure with high density( ) g g y(c) Fine grain structure with low density(d) S i f l d h ki f h(d) Segregation of slug towards the outer skin of thecasting

GATE ‐2008 (PI)GATE ‐2008 (PI)In hollow cylindrical parts, made by centrifugal casting,y p , y g g,

the density of the part is

(a) maximum at the outer region

(b) maximum at the inner region

(c) maximum at the mid‐point between outer and inner

surfaces

(d) uniform throughout

IES‐2008h h f h f ll dWhich of the following casting processes does not

/do not require central core for producing pipe?1. Sand casting process2 Die casting process2. Die casting process3. Centrifugal casting processS l h i h d i b lSelect the correct answer using the code given below:(a) 1 and 2( )(b) 2 only(c) 2 and 3(c) 2 and 3(d) 3 only

For-2013 (IES, GATE & PSUs) Page 27

IES‐2009Which one of the following casting processes is

best suited to make bigger size hollow

symmetrical pipes?

(a) Die casting

(b) Investment casting

( ) h ll ld(c) Shell moulding

(d) C if l i(d) Centrifugal casting

IES 2007Which one of the following is the correctstatement?statement?In a centrifugal casting method(a) No core is used(b) Core may be made of any metal(b) Core may be made of any metal(c) Core is made of sand(d) Core is made of ferrous metal

IES‐1998Poor machinability of centrifugally cast iron pipe is due tois due to(a) Chilling(b) Segregation(c) Dense structure(c) Dense structure(d) High mould rotation speed

IES‐2009Which of the following are the most likelycharacteristics in centrifugal casting?characteristics in centrifugal casting?(a) Fine grain size and high porosity(b) Coarse grain size and high porosity(c) Fine grain size and high density(c) Fine grain size and high density(d) Coarse grain size and high density

IES 2007Match List I with List II and select the correct answer using the code given below the Lists:List I List IIList I List II(Casting Process) (Principle)A. Die casting 1.The metal solidifies in a rotating mouldB Investment casting 2 The pattern cluster is repeatedly dipped B. Investment casting 2.The pattern cluster is repeatedly dipped 

into a ceramic slurry and dusted with refractory

C Shell moulding 3  Molten metal is forced by pressure into C. Shell moulding 3. Molten metal is forced by pressure into a metallic mould

D. Centrifugal casting 4. After cooling, the invest is removed from the Casting by pressure jetting or g y p j gvibratory cleaning

Code:A B C D A B C D(a) 2 1 3 4 (b) 3 4 2 1( ) 3 4 ( ) 3 4(c) 2 4 3 1 (c)  3 1 2 4

IES‐2000Match List I (Process) with List II (Products/materials) and select the correct answer using the codes given b l hbelow the Lists:List I  List IIA. Die casting  1. Phenol formaldehydeB. Shell molding  2. C.I. pipesC. CO2 molding  3. Non‐ferrous alloysD. Centrifugal casting  4. Sodium silicateg g

Codes:A B  C  D  A  B  C  D(a)  1  3  4  2  (b)  3  1  4  2( ) 3 4 ( ) 3 4(c)  3  1  2  4  (d)  1  3  2  4

IAS‐2004Match List‐I (Name of the Process) with List‐II (Advantage) and select the correct answer using the codes given below the lists:answer using the codes given below the lists:List‐I List‐II(Name of the Process) (Advantage)A. Sand Casting 1. Large cylindrical parts with good qualityB. Ceramic mold casting 2.Excellent dimensional accuracy and surface

finishfinishC. Die casting 3. Intricate shapes and close tolerance partsD. Centrifugal casting 4. Almost any metal is cast and there if no limit to

h d hsize, shape and weight5. Good dimensional accuracy, finish and lowporosityp y

Codes:A  B  C  D A  B  C  D(a)  2  3  5  1 (b) 4  1 2 3

(c)  2  1  5  3  (d) 4 3 2 1

Semi‐centrifugal CastingCentrifugal force assists the flow of metal from a

central reservoir to the extremities of a rotating

symmetrical mold, which may be either expendable or

l i lmultiple‐use

R t ti l d l th f t t if lRotational speeds are lower than for true centrifugal

castingcasting

Cores can be used to increase the complexity of theCores can be used to increase the complexity of the

product. Fig. Semi‐centrifugal castingFor-2013 (IES, GATE & PSUs) Page 28

IAS‐2003Assertion (A): Semi‐centrifugal casting process issimilar to true centrifugal casting except that theg g pcentral core is used in it to form inner surface.Reason (R): In semi‐centrifugal casting process theReason (R): In semi centrifugal casting process theaxis of spin is always vertical(a) Both A and R are individually true and R is the correct(a) Both A and R are individually true and R is the correctexplanation of A(b) Both A and R are individually true but R is not the(b) Both A and R are individually true but R is not thecorrect explanation of A(c) A is true but R is false(c) A is true but R is false(d) A is false but R is true

CentrifugingUses centrifuging action to force the metal from a central

pouring reservoir into separate mold cavities that are

ff t f th i f t tioffset from the axis of rotation.

Low speedLow speed

May used to assist in the pouring of investment castingy p g g

trees.

Fig. Method of casting by the centrifuging process

IES‐2000Match List I (Type of casting) with List II (Working principles) and select the correct answer using the codes given below the Lists:Lists:List I List IIA. Die casting 1. Molten metal is forced into the die A. Die casting 1. Molten metal is forced into the die 

under pressureB. Centrifugal casting 2. Axis of rotation does not coincide with 

axis of mouldaxis of mouldC.  Centrifuging 3. Metal solidifies when mould is rotatingD. Continuous casting 4. Continuously pouring molten metal D. Continuous casting 4. Continuously pouring molten metal 

into mouldCodes:A B C  D A B  C D

( ) (b)(a)  1  3  2  4  (b)  4  3  2  1(c)  1  2  3  4  (d)  4  2  3  1

Dry Sand MoldingTo reduce gas forming materials air dried mould used.

Types:

1.Skin drying and

2.Complete mold drying

Slush CastingSlush casting is a variation of the permanent mold processin which the metal is permitted to remain in the mold onlyin which the metal is permitted to remain in the mold onlyuntil a shell of the desired thickness has formed.The mold is then inverted and the remaining liquid ispoured out.When the mold halves are separated, the resulting castingis a hollow shape with good surface detail but variable walls a o o s ape t good su ace deta but va ab e athickness.Frequently used to cast low melting temperature metalsFrequently used to cast low‐melting‐temperature metalsinto ornamental objects such as candlesticks, lamp bases,and statuaryand statuary.

IAS‐2004Which of the following are produced by slushcasting?casting?(a) Hollow castings with thick walls(b) Hollow castings with thin walls(c) Thin castings(c) Thin castings(d) Thick castings

IES 2011The method of casting for producing ornamental piecesare:(a) Slush and gravity casting(b) P d d l h i(b) Pressed and slush casting(c) Gravity and semi permanent mould casting( ) y p g(d) Semi permanent mould and pressed casting

IES ‐ 2012Th f ki h ll i f i lThe process of making hollow castings of non‐circularshape and desired thickness by permanent mouldwithout the use of cores is known as(a) Die casting (b) Slush casting(a) Die casting (b) Slush casting(c) Pressed casting (d) Centrifugal casting

For-2013 (IES, GATE & PSUs) Page 29

Squeeze CastingProcess:M l l i d i f di1. Molten metal is poured into an open face die.

2. A punch is advanced into the die, and to the metal.p ,3.Pressure (less than forging) is applied to the punchand die while the part solidifiesand die while the part solidifies.

4.The punch is retracted, and the part is knocked outwith an ejector pin.Overcomes problems with feeding the die andOvercomes problems with feeding the die, andproduces near net, highly detailed parts.

IAS‐2002Match List I (Casting Process) with List II (Applications) and select the correct answer using the 

d b l hcodes given below the Lists:List I  List II(Casting Process)  (Applications)A. Centrifugal casting 1. CarburetorB. Squeeze casting 2. PipesC. Die Casting 3. Wheels for g 3

automobiles4. Gear housings

Codes:  A B C A B C(a)  2 3 1 (b)  4 1 3(c)  2 1 3 (d)  4 3 1

Single Crystal CastingTh    i   ff i lThe process is effectively:1. Prepare a mold so that one end is a heated oven, and p ,

the other end chilled. The part should be oriented so that the cooling happens over the longest distancethat the cooling happens over the longest distance.

2. Cast metal into the mold3. Solidification will begin at the chill plate. These 

dendrites will grow towards the heated end of the de d tes g o to a ds t e eated e d o t epart as long dendritic crystals. The part is slowly pulled out of the oven  past the chill platepulled out of the oven, past the chill plate.

4. Remove the solidified part.

Creep and thermal shock resistance properties.Creep and thermal shock resistance properties.

IES 2009

2 marks

Plaster CastingProcess: A slurry of plaster, water, and various additives isadditives is pouted over a pattern and allowed to set. Thepattern is removed and the mould is baked to removeexcess water. After pouring and solidification, the mould isp gbroken and the casting is removed.Advantage: High dimensional accuracy and smoothAdvantage: High dimensional accuracy and smoothsurface finish, thin sections and intricate detail canproduceproduce.Limitations: Lower‐temperature nonferrous metals only:Commonmetals: Primarily aluminium and copper

Pit MouldingThis method is used for very large castings and is done onthe foundry floorthe foundry floor.

IES‐1996Which of the following pairs are correctly matched?

Pi   ldi F  l  j b1. Pit moulding ..................For large jobs.2. Investment moulding ... Lost wax process.g p3. Plaster moulding ……… Mould prepared in gypsumgypsum.(a) 1, 2 and 3 (b) 1 and 2(c) 1 and 3 (d) 2 and 3

Loam Moulding

M ldi l i ll ifi i ll d fMoulding loam is generally artificially composed of

common brick clay and sharp sandcommon brick‐clay, and sharp sand.

Loam means mudLoammeans mud.

LoamMoulding is restricted to forms which cannot beLoamMoulding is restricted to forms which cannot be

cast conveniently in any other process.

It is costly.

For-2013 (IES, GATE & PSUs) Page 30

IES‐1997Which one of the following pairs is not correctlymatched?matched?(a) Aluminium alloy piston …………Pressure die casting(b) Jewellery……………………….. Lost wax process(c) Large pipes Centrifugal casting(c) Large pipes ……………………..Centrifugal casting(d) Large bells ………………………Loam moulding

GATE‐1998List I List II (A) Sand casting  (1) Symmetrical and ( ) Sa d cas g ( ) Sy e ca a dcircular shapes only(B) Plaster mould casting  (2) Parts have hardened ( ) g ( )skins and soft interior(C) Shell mould casting  (3) Minimum post‐

i   icasting processing(D) Investment casting  (4) Parts have a tendency     

t  to warp(5) Parts have soft skin       

and hard interiorand hard interior(6) Suitable only for non‐

ferrous metalsferrous metals

GATE‐1992Match the following moulding/casting processes with the product:pMoulding/Casting processes Product(A) Slush casting (P) Turbine blade(A) Slush casting (P) Turbine blade(B) Shell moulding (Q) Machine tool bed(C) D   d  ldi (R) C li d  bl k(C) Dry sand moulding (R) Cylinder block(D) Centrifugal casting (S) Hollow castings 

l k l h dlike lamp shades(T) Rain water pipe(U) Cast iron shoe brake

GATE‐1996List I List II(A) Ri  f   i f  b d   F i(A) Rivets for aircraft body  1. Forging(B) Carburettor body  2. Cold heading( ) y g(C) Crankshafts  3. Aluminium‐based 

alloyalloy(D) Nails  4. Pressure die casting

5. Investment casting

IES‐2003Match List I (Products) with List II (Casting Process) and select the correct answer using the codes given below the Lists:Li  I Li  IIList I List II(Products) (Casting Process)A Hollow statues 1 Centrifugal CastingA. Hollow statues 1. Centrifugal CastingB. Dentures 2. Investment CastingC. Aluminium alloy pistons 3. Slush Castingy p 3 gD. Rocker arms 4. Shell Moulding

5. Gravity Die CastingCodes:A  B  C  D A  B  C  D

(a)  3  2  4  5 (b)  1  3  4  5( )        (d)       (c)  1  2  3  4 (d)  3  2  5  4

IES‐1993Match the items of List I (Equipment) with the items of List II (Process) and select the correct answer using ( ) gthe given codes.List I (Equipment)  List II (Process)List I (Equipment)  List II (Process)P ‐ Hot Chamber Machine  1. CleaningQ  Muller  2 Core makingQ ‐Muller  2. Core makingR ‐ Dielectric Baker  3. Die casting

d l lS ‐ Sand Blaster  4. Annealing5. Sand mixing

(a) P‐2, Q‐1, R‐4, S‐5  (b) P‐4, Q‐2, R‐3, S‐5(c) P‐4, Q‐5, R‐1, S‐2  (d) P‐3, Q‐5, R‐2, S‐1(c) P 4, Q 5, R 1, S 2  (d) P 3, Q 5, R 2, S 1

IAS‐2004Match List‐I (Name of the Casting Process) with List‐II (Process Definition) and select the correct answer using the codes given below the lists:List I List II      List‐I List‐II      (Name of the Casting Process) (Process Definition)A. Die casting 1.This process involves use of a mould made of

Dried silica sand and phenolic resin mixtureB. Electroslag casting  2. In this process, molten metal is forced by

Pressure into a metal mouldPressure into a metal mouldC. Centrifugal casting  3. This process employs a consumable electrodeD. Precision casting  4. This process involves rotating a mould while the 

l l d fmetal solidifies5. This process produces very smooth, highlyAccurate castings from both ferrous and nongferrous alloys

Codes:A  B  C  D A  B  C  D(a)  5  4  1  2 (b)  2  3  4  5(a)  5  4  1  2 (b)  2  3  4  5(c)  5  3  4  2 (d)  2  4  1  5

( )GATE – 2007 (PI)Match the listsMatch the lists

Group‐1 Group‐2Group 1 Group 2P. Sand Casting 1. Turbine bladesQ. Centrifugal Casting 2. IC Engine PistonsR  I  C i  L  b llR. Investment Casting 3. Large bellsS  Die Casting 4  Pulleys

(a) P 4 Q 1 R 3 S 2 (b) P 2 Q 4 R 3 S 1

S. Die Casting 4. Pulleys

(a) P – 4, Q – 1, R – 3, S – 2 (b) P – 2, Q – 4, R – 3, S ‐ 1(c) P – 3, Q – 4, R – 1, S – 2 (d) P – 3, Q – 2, R – 1, S ‐ 4 By  S K Mondaly

For-2013 (IES, GATE & PSUs) Page 31

Welding DefinitionWelding is a process by which two materials, usuallymetals are permanently joined together bymetals, are permanently joined together bycoalescence, which is induced by a combination of

d ll i l di itemperature, pressure, and metallurgical conditions.The particular combination of these variables canprange from high temperature with no pressure to highpressure with no increase in temperaturepressure with no increase in temperature.

Welding (positive process)Machining (negative process)F i i ( )Forming, casting (zero process)

Requirement for a high quality welding

1. A source of satisfactory heat and/or pressure,

2. A means of protecting or cleaning the metal, and

3. Caution to avoid, or compensate for, harmful

metallurgical effects.

l ifi i f ldiClassification of welding processesOxy fuel gas welding (OFW)y g g ( )Arc welding (Aw)Resistance weldingResistance weldingSolid state welding (friction welding, ultrasonic welding,forge welding etc )forge welding etc.)

Unique processq pThermit weldingLaser beamweldingLaser beamweldingElectroslag weldingFlash weldingInduction weldingElectron beamwelding

IES ‐ 2012Th d h ldi iThe advantage o the welding process is(a) It relieves the joint from residual stresses( ) j(b) It helps in checking of distortion of work piece( ) L b f l d ll b h i il d/(c) Large number of metals and alloys, both similar and/ordissimilar can be joined.

(d) Heat produced during the welding does not producemetallurgical changesmetallurgical changes.

Weldability / Fabrication ProcessesThe weldability of a material will depend on thespecific welding or joining process being consideredspecific welding or joining process being considered.For resistance welding of consistent quality, it is

ll h id i di lusually necessary to remove the oxide immediatelybefore welding.Fabrication weldability test is used to determinemechanical properties required for satisfactorymechanical properties required for satisfactoryperformance of welded joint.Th f h i i l iThe correct sequence of the given materials inascending order of their weldability isAluminum < copper < cast iron < MS

Contd…

Case of AluminiumThe oxide coating on aluminum alloys causes somedifficulty in relation to its weldability.y yIt also has high thermal conductivity and a very shorttemperature range between liquidus and solidus and whentemperature range between liquidus and solidus and whenliquid its viscosity is very low.Al i i i b b f l li hAluminium is poor absorber of laser light.During fusion welding, the aluminum would oxidize sog greadily that special fluxes or protective inert‐gasatmospheres must be employed.p p yFriction welding and TIG welding is good for aluminium.For aluminium AC current plus high frequency is mustFor aluminium AC current plus high frequency is must.

Case of Cast IronCast iron is more difficult to weld because of its highcarbon content and brittleness (poor ductility)(p y)Massive carbon deposits have a tendency to form inthe areas adjacent to the weld and high‐carbonthe areas adjacent to the weld, and high carbonmartensite tends to form in the heat‐affected zones.These microstructures are very brittle and may crackThese microstructures are very brittle and may crackspontaneously while welding is in progress or laterwhen load is applied to the workpiecewhen load is applied to the workpiece.Cast iron can be joined by the oxyacetylene brazingprocess and shielded metal arc welding (stick)process and shielded metal‐arc welding (stick)process.

h d h dSome cases preheating and/or post heating is required.

Case of Stainless SteelStainless steel is a difficult metal to weld because itcontains both nickel and chromium.The best method for welding stainless steel is TIGweldingwelding.The electric arc is also preferred for welding stainlesssteels A heavily coated welding rod which produce asteels. A heavily coated welding rod, which produce ashielded arc, is employed.Y d b j b f l iYou must do a better job of pre‐cleaning.Using a low arc current setting with faster travelg gspeeds is important when welding stainless steel,because some stainless steels are subject to carbidejprecipitation.

Contd…..

Case of Stainless SteelThe ferritic stainless steels are generally less weldablethan the austenitic stainless steel and require bothqpreheating and postweld heat treatments.Welds of ferritic stainless steel can be byWelds of ferritic stainless steel can be by

(i) autogenously (i.e. without the addition of fillermetal)metal)

(ii) with an austenitic stainless steel(iii) i hi h i k l fill ll(iii) using a high nickel filler alloy.(iv) Type 405 filler (low 11% Cr, low carbon and small

% l)0.2% Al)Welding process: TIG, MIG, Shielded‐metal arcg pwelding and Plasma arc welding

For-2013 (IES, GATE & PSUs) Page 32

IES 2010Assertion (A): It is generally difficult to weldAssertion (A): It is generally difficult to weldAluminum parts by normal arc welding process.Reason (R): Hard and brittle Aluminum‐oxide filmis formed at thewelded joints.j(a) Both A and R are individually true and R is the

t l ti f Acorrect explanation of A(b) Both A and R are individually true but R is NOT theycorrect explanation of A(c) A is true but R is false(c) A is true but R is false(d) A is false but R is true

IES‐2006Assertion (A): Aluminium has poor weldability.R  (R)  Al i i h  hi h  h l Reason (R): Aluminium has high thermal conductivity and high affinity to oxygen.(a) Both A and R are individually true and R is the 

correct explanation of Acorrect explanation of A(b) Both A and R are individually true but R is not the 

  l i   f A correct explanation of A (c) A is true but R is false( )(d) A is false but R is true

IES 2011During plasma arc welding of aluminium, improvedremoval of the surface oxide from the base metal isobtained with typical polarity of :(a) DC Straight(a) DC Straight(b) DC reverse(c) AC potential(d) Reverse polarity of phase of AC potential(d) Reverse polarity of phase of AC potential

IES 2011d h f llConsider the following statements.

Cast iron is difficult to weld, because of,1. Low ductility P  f i  2. Poor fusion 

3. Tendency to crack on cooling3 y gWhich of these statements are correct ?(a) 1  2 and 3 (a) 1, 2 and 3 (b) 1 and 2 only (c) 2 and 3 only (d) 1 and 3 only(d) 1 and 3 only

IES‐2006Fabrication weldability test is used to determine(a) Mechanical properties required for satisfactory 

performance of welded jointp j(b) Susceptibility of welded joint for cracking( ) S i bili  f  j i  d i(c) Suitability for joint design(d) Appropriate machining process( ) pp p g p

IES‐1999The correct sequence of the given materials in 

di   d   f th i   ld bilit iascending order of their weldability is(a) MS, copper, cast iron, aluminium( ) , pp , ,(b) Cast iron, MS, aluminium copper( ) C    i  MS   l i i(c) Copper, cast iron, MS, aluminium(d) Aluminium, copper, cast iron, MS( ) , pp , ,

IES 2010W ld bilit f f iti t i l t l d iWeldability of ferritic stainless steel used inautomotive exhaust system is improved byy p yselecting stainless steel electrode having lowcontent ofcontent of(a) Carbon (b) Nitrogen( ) ( ) g(c) Chromium (d) Carbon and Nitrogen

IES 2010Consider the following statements regardingConsider the following statements regardingwelded joints:

1. It is a permanent type of joint.2 It is reliable and economical for pressure vessel2. It is reliable and economical for pressure vesselconstruction.

f f f b l d l3. It is free from fabricational residual stresses.4. Such joints are suitable for static loading only.4. Such joints are suitable for static loading only.5. Welding is a versatile and flexible metal joining process.Which of the above statements are correct?(a) 1, 2 and 3 only (b) 2, 3 and 4 only(a) 1, 2 and 3 only (b) 2, 3 and 4 only(c) 1, 2, 3, 4 and 5 (d) 1, 2 and 5 only

IES ‐ 2012Whi h  f  h  f ll i  f  i   ld  bili   f Which of the following factors improve weld ability of steel?1. Low carbon content2  High carbon content2. High carbon content3. Good affinity content4. Poor affinity to oxygen( )    d  (b)    d   (a) 1 and 3 (b) 2 and 3 (c) 1 and 4  (d) 2 and 4

For-2013 (IES, GATE & PSUs) Page 33

Gas Flame Processes: W ldi C i d S i h iWelding, Cutting and Straightening

Oxy‐fuel gas Welding (OFW): Heat source is theOxy‐fuel gas Welding (OFW): Heat source is theflame produced by the combustion of a fuel gas andoxygen.

OFW has largely been replaced by other processes butit is still popular because of its portability and the lowit is still popular because of its portability and the lowcapital investment.

Acetylene is the principal fuel gas employed.Acetylene is the principal fuel gas employed.

Combustion of oxygen and acetylene (C2H2) in a ldi  t h  d    t  i    t   t   ti  welding torch produces a temp. in a two stage reaction. 

In the first stageg+ Heat

Thi   i       h   i   f  h   h C H O CO H+ → +2 2 2 22

This reaction occurs near the tip of the torch.In the second stage combustion of the CO and H2 and g 2occurs just beyond the first combustion zone.

2CO + O → 2CO + Heat2CO + O2 → 2CO2 + HeatH2 +   O2 → H2O + Heat

12

Oxygen for secondary reactions is obtained from the atmosphereatmosphere.

Three types of flames can be obtained by varyingth / t l ( /f l ) tithe oxygen/acetylene (or oxygen/fuel gas) ratio.If the ratio is about 1 : 1 to 1.15 : 1, all reactions are5 ,carried to completion and a neutral flame is produced.Most welding is done with a neutral flame It isMost welding is done with a neutral flame. It ischemically neutral and neither oxidizes or carburizesh l b i ld dthe metal being welded.

Oxy‐acetylene gas welding neutral flame

A higher ratio, such as 1.5 : 1, produces an oxidizingflame, hotter than the neutral flame (about 3300oC)but similar in appearance.ppUsed when welding copper and copper alloys butharmful when welding steel because the excess oxygenharmful when welding steel because the excess oxygenreacts with the carbon, decarburizing the region

d h ldaround the weld.

Oxy‐acetylene gas welding Oxidising flame

Excess fuel, on the other hand, produces a carburizingflame Carburizing flame can carburize metal alsoflame. Carburizing flame can carburize metal also.The excess fuel decomposes to carbon and hydrogen,

d h fl i ( band the flame temperature is not as great (about3000oC).Flames of this type are used in welding Monel (anickel‐copper alloy) high‐carbon steels and somenickel copper alloy), high carbon steels, and somealloy steels, and for applying some types of hard‐facingmaterialmaterial.

Oxy‐acetylene gas welding Carburizing flame

Metal FlameM S NHigh carbon steel RGrey cast iron N, slightly oxidizingAlloy steel NAluminium Slightly carburizingBrass Slightly oxidizingC B N li h l idi iCopper, Bronze N, slightly oxidizingNickel alloys Slightly carburizingL d NLead N

IES 2009 ConventionalExplain the three types of oxy‐acetylene flames.

Indicate with the help of sketches the various

zones, respective temperature ranges and

applications of each t pe of flameapplications of each type of flame.

[ 20  Marks][ 20 – Marks]

DiDiagramg

For-2013 (IES, GATE & PSUs) Page 34

d d i i iUses, Advantages, and LimitationsOFW i f i ldiOFW is fusionwelding.No pressure is involved.pFiller metal can be added in the form of a wire or rod.Fl b d l h f dFluxes may be used to clean the surfaces and removecontaminating oxide. The gaseous shield produced byvaporizing flux can prevent oxidation during welding,and the slag produced by solidifying flux can protecta d t e s ag p oduced by so d y g u ca p otectthe weld pool. Flux can be added as a powder, thewelding rod can be dipped in a flux paste or the rodswelding rod can be dipped in a flux paste, or the rodscan be pre‐coated.

Contd…

Exposer of the heated and molten metal to the variousp

gases in the flame and atmosphere makes it difficult to

prevent contamination.

Heat source is not concentrated, a large area of the

metal is heated and distortion is likely to occur.

Fl ldi i ill i i fi ld k iFlame welding is still quite common in field work, in

maintenance and repairs and in fabricating smallmaintenance and repairs, and in fabricating small

quantities of specialized products.qua t t es o spec a ed p oducts.

Oxy acetylene welding equipmentOxygen is stored in a cylinder at a pressure rangingfrom 13 8 MPa to 18 2 MPafrom 13.8 MPa to 18.2 MPa .Due to high explosiveness of free acetylene it is storedin a cylinder with 80‐85% porous calcium silicate andthen filled with acetone which absorb upto 420 timesp 4by its volume at a pressure 1.75 MPa .At the time of acetylene release if acetone comes withAt the time of acetylene release if acetone comes withacetylene the flame would give a purple colour.Another option is acetylene generator.

2 2 2 2 22 ( )CaC H O C H Ca OH+ → +

Pressure Gas WeldingPressure Gas WeldingPressure gas welding (PGW) or Oxyacetyleneg g ( ) y yPressure Welding is a process used to make buttjoints between the ends of objects such as pipej j p pand‐railroad rail.The ends are heated with a gas flame to aThe ends are heated with a gas flame to atemperature below the melting point, and the softmetal is then forced together under considerablemetal is then forced together under considerablepressure.Thi th f i t ll 'f f lidThis process, therefore, is actually a 'form of solid‐state welding.

IES 2010Th ti b t O d A t lThe ratio between Oxygen and Acetylenegases for neutral flame in gas welding isg g g

(a) 2 : 1 (b) 1 : 2(c) 1 : 1 (d) 4 : 1

GATE‐1994The ratio of acetylene to oxygen ise at o o acety e e to o yge sapproximately………. for a neutral flames used ingas weldinggas welding.(a) 1 : 1(b) 1 : 2(c) 1 : 3(c) 1 : 3(d) 1.5 : 1

GATE‐2003In Oxyacetylene gas welding, temperature at the inner cone of the flame is aroundinner cone of the flame is around(a) 3500°C (b) 3200°C (c) 2900°C (c) 2900 C (d) 2550°C

IES 2010Assertion (A): Oxidizing flame is used in gasAssertion (A): Oxidizing flame is used in gaswelding to join medium carbon steels having high

l i imelting point.Reason (R): In gas welding, oxidizing flame( ) g g, gproduces the maximum temperature compared toneutral and reducing flameneutral and reducing flame.(a) Both A and R are individually true and R is thecorrect explanation of A(b) Both A and R are individually true but R is NOT the(b) Both A and R are individually true but R is NOT thecorrect explanation of A( ) A i t b t R i f l(c) A is true but R is false(d) A is false but R is true

GATE‐2002The temperature of a carburising flame in gaswelding is that of a neutral or an oxidising flamewelding is that of a neutral or an oxidising flame.(a) Lower than(b) Higher than(c) Equal to(c) Equal to(d) Unrelated to

For-2013 (IES, GATE & PSUs) Page 35

IES‐2009By which one of the following methods gray casti i ll ld d?iron is usually welded?(a) TIG welding (b) MIG welding( ) g ( ) g(c) Gas welding (d) Arc welding

IES‐1998In oxy‐acetylene gas welding, for complete

b ti th l f i dcombustion, the volume of oxygen required perunit of acetylene is(a) 1(b) 1 5(b) 1.5(c) 2 (d) 2.5

IAS 1994In gas welding of mild steel using an oxy‐

t l fl th t t l t f t lacetylene flame. the total amount of acetyleneconsumed was 10 litre. The oxygen consumptionfrom the cylinder is(a) 5 litre(a) 5 litre(b) 10 litre(c) 15litre(d) 20 litre(d) 20 litre

IAS‐1995Assertion (A): If neutral flame is used in oxy‐acetylene welding, both oxygen and acetyleney g, yg ycylinders of same capacity will be emptied at the sametime.Reason (R): Neutral flame uses equal amounts ofoxygen and acetylene.( ) B h A  d R   i di id ll     d R i   h    (a) Both A and R are individually true and R is the correct 

explanation of A(b) B th A  d R   i di id ll  t  b t R i   t th  (b) Both A and R are individually true but R is not the 

correct explanation of A (c) A is true but R is false(c) A is true but R is false(d) A is false but R is true

IES ‐ 2012St t t (I) I ldi th t l t b j i d tStatement (I): In gas welding the metal to be joined getsoxidized or carburizedStatement (II): The neutral flame affects no chemicalchange on the molten metal.(a) Both Statement (I) and Statement (II) areindividually true and Statement (II) is the correcty ( )explanation of Statement (I)(b) Both Statement (I) and Statement (II) are(b) Both Statement (I) and Statement (II) areindividually true but Statement (II) is not the correctexplanation of Statement (I)explanation of Statement (I)(c) Statement (I) is true but Statement (II) is false( ) ( ) ( )(d) Statement (I) is false but Statement (II) is true

Oxygen Torch Cutting (Gas Cutting) Iron and steel oxidize (burn) when heated to atemperature between 8000C to 10000Ctemperature between 8000C to 10000C.High‐pressure oxygen jet (300 KPa) is directed againsta heated steel plate, the oxygen jet burns the metal andblows it away causing the cut (kerf).y g ( )For cutting metallic plates shears are used. These areuseful for straight line cuts and also for cuts up to 40useful for straight‐line cuts and also for cuts up to 40mm thickness.

Contd…

For thicker plates with specified contour, shearingcannot be used and oxy‐fuel gas cutting (OFC) isuseful.Gas‐cutting is similar to gas welding except torch tip.

Fig‐ differences in torch tips for gas welding and gas cutting

Contd…

Larger size orifice produces kerf width wider and largerdoxygen consumed.

At kindling temperature (about 870oC), iron form irong poxide.Reaction:Reaction:

3Fe + 2O2 → Fe3O4 +6.67 MJ/kg of ironh hThe other reactions:

2Fe + O2 → 2FeO + 3.18 MJ/kg of iron2 3 J g4Fe + 3O2 → 2Fe2O3 + 4.9 MJ/kg of iron

All exothermic reactions preheat the steelAll exothermic reactions preheat the steel.

Contd…

For complete oxidation 0.287 m3 oxygen/kg of iron iso co p ete o dat o 0. 87 o yge / g o o srequiredD t idi d t l bl th t lDue to unoxidized metal blown away the actualrequirement is much less.Torch tip held vertically or slightly inclined in thedirection of travel.direction of travel.Torch position is about 1.5 to 3 mm vertical from plate.

Contd…For-2013 (IES, GATE & PSUs) Page 36

The drag lines shows the characteristics of the movementf hof the oxygen stream.

Fi iti i   f  tti  t h i   f l    tti

Drag is the amount by which the lower edge of the dragline trails from the top edge

Fig‐ positioning of cutting torch in oxy‐ fuel gas cutting

line trails from the top edge.Good cut means negligible drag.

Contd…

If torch moved too rapidly, the bottom does not getffi i t h t d d l d hsufficient heat and produces large drag so very rough

and irregular‐shaped‐cut edges.If torch moved slowly a large amount of slag isgenerated and produces irregular cutgenerated and produces irregular cut.

Contd…

Gas cutting is more useful with thick plates.g p

F thi h t (l th thi k) ti i h ldFor thin sheets (less than 3 mm thick) tip size shouldbe small. If small tips are not available then the tip isinclined at an angle of 15 to 20 degrees.

Fig. Recommended torch position for cutting thin steel

IAS‐2011 MainIAS‐2011 MainD lf l t k t h f t lDraw a self explanatory sketch of oxy‐acetylene gas

cutting torch Briefly explain how cutting iscutting torch. Briefly explain how cutting is

effected.

[20‐Marks]

ApplicationUseful only for materials which readily get oxidized

and the oxides have lower melting points than the

metals.

Widely used for ferrous materials.

Cannot be used for aluminum, bronze, stainless steel

d lik t l i th i t id tiand like metals since they resist oxidation.

DifficultiesMetal temperature goes beyond lower criticaltemperature and structural transformations occurtemperature and structural transformations occur.

Final microstructure depends on cooling rate.

Steels with less than 0.3 % carbon cause no problem.

Contd…

For high carbon steel material around the cut shouldg

be preheated (about 250 to 300oC) and may post heat

also necessary.

Cutting CI is difficult, since its melting temp. is lower

than iron oxide.

If h i d i k l i fIf chromium and nickel etc are present in ferrous

alloys oxidation and cutting is difficultalloys oxidation and cutting is difficult.

IES‐1992The edge of a steel plate cut by oxygen cutting will

t h d d h th b t t iget hardened when the carbon content is(a) Less than 0.1 percent( ) p(b) Less than 0.3 percent( ) M h(c) More than 0.3 percent(d) Anywhere between 0.1 to 1.0 percent( ) y p

IES 2007Consider the following statements in respect of oxy‐acetylene welding:y g1. The joint is not heated to a state of fusion.2. No pressure is used.2. No pressure is used.3. Oxygen is stored in steel cylinder at a pressure of 14 

MPa.4. When there is an excess of acetylene used, there is a 

decided change in the appearanceg ppof flame.

Which of the statements given above are correct?g(a)  1, 2 and 3 (b) 2, 3 and 4(c) 1, 3 and 4 (d) 1, 2 and 4( ) , 3 4 ( ) , 4

For-2013 (IES, GATE & PSUs) Page 37

IES‐2001Oxyacetylene reducing flame is used while 

i   t th   ldi  carrying out the welding on(a) Mild steel (b) High carbon steel( ) ( ) g(c) Grey cast iron (d) Alloy steels

IES‐1992Thick steel plate cut with oxygen normally showsi f ki Thi t d f kisigns of cracking. This tendency for cracking canbeminimised by(a) Slow speed cutting(b) Cutting in two or more stages(b) Cutting in two or more stages(c) Preheating the plate(d) Using oxy‐acetylene flame

IES‐2005Consider the following statements:

I     ldi  th  t h  h ld b  h ld  t    l   f 1. In gas welding, the torch should be held at an angle of 30° to 45° from the horizontal plane.I     ldi   h  Si   f  h   h d d     h  2. In gas welding, the Size of the torch depends upon the thickness of metal to be formed.

h d ff b3. Drag in gas cutting is the time difference between heating of the plate and starting the oxygen gas for 

tticutting.Which of the statements given above are correct?(a) 1, 2 and 3 (b) 1 and 2(c) 2 and 3 (d) 1 and 3(c) 2 and 3 (d) 1 and 3

Powder CuttingCast iron stainless steel and others high alloy steels areCast iron, stainless steel, and others high alloy steels aredifficult to cut by oxy‐fuel cutting and we can use powder

icutting.By injecting a finely divided 200‐mesh iron powder intoy j g y pthe flame, a lower melting point eutectic oxide is formedat the cutting interface where additional iron‐oxygenat the cutting interface, where additional iron‐oxygenreaction is generated and cutting proceeds in a similar

f f l ttiway of oxy‐fuel cutting.The heat and the fluxing action of the burning irong gpowder enable the cutting oxygen stream to oxidize thebase metal continuously, just as in cutting carbon steel.base metal continuously, just as in cutting carbon steel.

GATE‐2009 (PI)GATE‐2009 (PI)Whi h f th f ll i d h ld b f d fWhich of the following powders should be fed for

effective oxy‐fuel cutting of stainless steel?effective oxy fuel cutting of stainless steel?

(a) Steel(a) Steel

(b) Aluminum( )

(c) Copper( ) pp

(d) Ceramic

lPlasma CuttingUses ionized gas jet (plasma) to cut materials resistant toUses ionized gas jet (plasma) to cut materials resistant tooxy‐fuel cutting,

h l l d b hHigh velocity electrons generated by the arc impact gasmolecules, and ionize them.The ionized gas is forced through nozzle (upto 500 m/s), andthe jet heats the metal, and blasts the molten metal away.j , yMore economical, more versatile and much faster (5 to 8times) than oxyfuel cutting produces narrow kerfs andtimes) than oxyfuel cutting, produces narrow kerfs andsmooth surfaces.HAZ i / ¼ h h f l iHAZ is 1/3 to ¼ th than oxyfuel cutting.Maximum plate thickness = 200 mm

l i ldiElectric Arc Welding 

l i ldiElectric Arc Welding

Fig  Basic circuit for arc weldingFig. Basic circuit for arc welding

Principle of ArcAn arc is generated between cathode and anode when

they are touched to establish the flow of current and

then separated by a small distance.

65% to 75% heat is generated at the anode.

If DC is used and the work is positive (the anode of the

i it) th diti i k t i ht l itcircuit), the condition is known as straight polarity

(SPDC)(SPDC).

Contd…For-2013 (IES, GATE & PSUs) Page 38

Work is negative and electrode is positive is reverseg p

polarity (RPDC).

SPDC conditions are preferred.

DC arc‐welding maintain a stable arc and preferred for

difficult tasks such as overhead welding.

For a stable arc, the gap should be maintained.

Contd…

ISRO‐2011ISRO‐2011I     ldi   t ti  i   i i  fIn arc welding, penetration is minimum for

( ) DCSP (a) DCSP 

(b) DCRP (b) DCRP 

( ) AC (c) AC 

(d)(d) DCEN

Manual arc welding is done with shielded (covered)electrodesBare‐metal wire used in automatic or semiautomaticBare metal wire used in automatic or semiautomaticmachines.N bl l t d ( t t ) i tNon consumable electrodes (e.g tungsten) is notconsumed by the arc and a separate metal wire is usedas filler.There are three modes of metal transfer (globularThere are three modes of metal transfer (globular,spray and short‐circuit).

Three modes of metal transfer during arc welding Major Forces take part in Metal Transfer(i) gravity force

(ii) Surface tension

(iii) electromagnetic interaction

( )(iv) hydrodynamic action of plasma

JWM 2010Assertion (A) : Bead is the metal added duringsingle pass of welding.single pass of welding.Reason (R) : Bead material is same as basemetal.(a) Both A and R are individually true and R is thecorrect explanation of Ap(b) Both A and R are individually true but R is NOT thecorrect explanation of Acorrect explanation of A(c) A is true but R is false(d) A is false but R is true

GATE‐1993In d.c. welding, the straight polarity (electrode negative) results innegative) results in(a) Lower penetration(b) Lower deposition rate  (c) Less heating of work piece(c) Less heating of work piece(d) Smaller weld pool

Arc welding equipments1. Droopers: Constant current welding machines

G d f l ldiGood for manual welding2. Constant voltage machinesg

Good for automatic welding

Contd…

Fig. Machine with different settings

Fig. Characteristic curve of a constant voltage arc‐welding machineFor-2013 (IES, GATE & PSUs) Page 39

FormulaFormula

V I 1V IOCV SCC

+ =OCV SCC

Requires a large current (150 to 1000 A) voltage isRequires a large current (150 to 1000 A), voltage is

between 30 and 40 V, actual voltage across the arcbetween 30 and 40 V, actual voltage across the arc

varying from 12 to 30 V.

To initiate a weld, the operator strike the electrode and

start arc.

IES 2010I ldi th l th h ld b l tIn arc welding, the arc length should be equal to(a) 4.5 times the rod diameter( ) 4 5(b) 3 times the rod diameter( ) i h d di(c) 1.5 times the rod diameter(d) Rod diameter( )

IES‐2005Consider the following statements:Consider the following statements:

1. In arc welding, 65% to 75% heat is generated at the danode.

2. Duty cycle in case of arc welding is the cycle of y y g ycomplete welding of work piece from the beginningbeginning.

3. Arc blow is more common with DC welding.

Which of the statements given above are correct?correct?(a) 1, 2 and 3  (b) 1 and 2( ) , 3 ( )(c) 2 and 3  (d) 1 and 3

IES‐2001

In manual arc welding, the equipment should g q p

have drooping characteristics in order to maintain

(a) Voltage constant when arc length changes 

(b) Current constant when arc length changes

(c) Temperature in the are constant 

(d) Weld pool red‐hot

IES‐2001In arc welding, d.c. reverse polarity is used to bear 

t   d t  igreater advantage in(a) Overhead welding( ) g(b) Flat welding of lap joints( ) Ed   ldi(c) Edge welding(d) Flat welding of butt joints( ) g j

IES‐1998The voltage‐current characteristics of a dc

t f ldi i t i ht ligenerator for arc welding is a straight linebetween an open‐circuit voltage of 80 V and short‐circuit current of 300 A. The generator settings formaximum arc powerwill bep(a) 0 V and 150 A (b) 40 V and 300 A( ) V d A (d) 8 V d A(c) 40 V and 150 A (d) 80 V and 300 A

IAS‐1999Open‐circuit voltage of 60 V and current of 160A

th ldi diti f ldi fwere the welding conditions for arc welding of acertain class of steel strip of thickness 10 mm. Forarc welding of 5mm thick strip of the same steel,thewelding voltage and current would beg g(a) 60 V and 80 A(b) V d 6 A(b) 120 V and 160 A(c) 60 V and 40 A( ) 4(d) 120 V and 40 A

IAS‐1998Assuming a straight line V‐I characteristics for a d   ldi   t   h t  i it  t    A dc welding generator, short circuit current as 400A and open circuit voltage as 400 which one of the following is the correct voltage and current setting for maximum arc power?p(a) 400 A and 100 V (b) 200 A and 200 V( )  A  d   V (d)  A  d   V(c) 400 A and 50 V (d) 200 A and 50 V

For-2013 (IES, GATE & PSUs) Page 40

GATE ‐2012 Same Q in GATE ‐2012 (PI)In a DC arc welding operation, the voltage‐arclength characteristic was obtained as V = 20 + 5Llength characteristic was obtained as Varc = 20 + 5Lwhere the arc length L was varied between 5 mmand 7 mm Here V denotes the arc voltage in Voltsand 7 mm. Here Varc denotes the arc voltage in Volts.The arc current was varied from 400 A to 500 A.A i li h i i hAssuming linear power source characteristic, theopen circuit voltage and the short circuit current forthewelding operation are(a) 45 V 450 A (b) 75 V 750 A(a) 45 V, 450 A (b) 75 V, 750 A(c) 95 V, 950 A (d) 150 V, 1500 A

( )GATE – 2007 (PI)Th DC f ldi h thThe DC power source for arc welding has thecharacteristic 3V + I = 240, where V = Voltage and3 4 gI = Current in amp. For maximum arc power atthe electrode voltage should be set atthe electrode, voltage should be set at(a) 20 V (b) 40 V (c) 60 V (d) 80 V( ) ( ) 4 ( ) ( )

GATE‐1992A low carbon steel plate is to be welded by the manualmetal arc welding process using a linear V Imetal arc welding process using a linear V ‐ Icharacteristic DC Power source. The following data are

il blavailable :OCV of Power source = 62 VShort circuit current = 130 AA l h LArc length, L = 4 mmTraverse speed of welding = 15 cm/sp g 5 /Efficiency of heat input = 85%V l i i V LVoltage is given as V = 20 + 1.5 L

Calculate the heat input into the workprice

Duty CycleThe percentage of time in a 5 min period that awelding machine can be used at its rated outputwelding machine can be used at its rated outputwithout overloading.Time is spent in setting up, metal chipping, cleaningand inspection.pFor manual welding a 60% duty cycle is suggested andfor automatic welding 100% duty cyclefor automatic welding 100% duty cycle.

Contd…

Required duty cycle   ⎛ ⎞= ⎜ ⎟

2IT TRequired duty cycle,  = ⎜ ⎟

⎝ ⎠a

aT T

I

Where ,T = rated duty cycleI = rated current at the rated duty cycleI = rated current at the rated duty cycleIo = Maximum current at the rated duty cycle

IFS‐2011IFS‐2011What is the maximum output current that can beWhat is the maximum output current that can bedrawn at 100% duty cycle from a welding power sourcerated at 600A at 60% duty cyclerated at 600A at 60% duty cycle.

[3‐Marks]

Electrode1. Non‐consumable Electrodes

C bl  El d2. Consumable Electrodes

Non‐consumable ElectrodesM d   f  b  G hi    TMade of carbon, Graphite or Tungsten.Carbon and Graphite are used for D.C.pElectrode is not consumed, the arc length remains constant  arc is stable and easy to maintainconstant, arc is stable and easy to maintain.

Contd…

Consumable ElectrodesProvides filler materials.Same compositionSame composition.This requires that the electrode be moved toward oraway from the work to maintain the arc andsatisfactory welding conditions.y g

Contd…

Consumable electrodes are three kinds:(a) Bare(b) Fl d li htl t d(b) Fluxed or lightly coated(c) Coated or extruded / shielded( )For automatic welding, bare electrode is in the form ofcontinuous wire (coil)continuous wire (coil).

For-2013 (IES, GATE & PSUs) Page 41

Electrode coating characteristic1. Provide a protective atmosphere.

S bili h2. Stabilize the arc.3. Provide a protective slag coating to accumulate3 p g g

impurities, prevent oxidation, and slow the cooling ofthe weld metalthe weld metal.

4. Reduce spatter.5. Add alloying elements.6 Affect arc penetration6. Affect arc penetration7. Influence the shape of the weld bead.8. Add additional filler metal.

GATE‐1994The electrodes used in arc welding are coated. This coating is not expected toThis coating is not expected to(a) Provide protective atmosphere to weld(b) Stabilize the are(c) Add alloying elements(c) Add alloying elements(d) Prevents electrode from contamination

Electrode coatingsl. Slag Forming Ingredients. asbestos, mica, silica,fluorspar titanium dioxide Iron oxide magnesiumfluorspar, titanium dioxide, Iron oxide, magnesiumcarbonate, Calcium carbonate and aluminium oxide.

2. Arc Stabilizing Ingredients. or ionizing agents:2. Arc Stabilizing Ingredients. or ionizing agents:potassium silicate, TiO2 + ZrO2 (Rutile), Mica,Calcium oxide sodium oxide magnesium oxideCalcium oxide, sodium oxide, magnesium oxide,feldspar (KAI Si3O8)

Contd…

3. Deoxidizing Ingredients. Cellulose, Calcium b  d l i   h  d i   d fl  carbonate, dolo‐mite, starch, dextrin, wood flour, 

graphite, aluminium, ferromanganese.

4. Binding Materials Sodium silicate, potassium silicate, gasbestos.

5. Alloying Constituents to Improve Strength of Weld

6. TiO2 and potassium compounds increase the melting rate of the base metal for better penetrationrate of the base metal for better penetration.

 I   d   id  hi h  d i i  7. Iron powder provides higher deposition rate.Contd… Contd…

The slag is then easily chipped.

Coatings are designed to melt more slowly than theCoatings are designed to melt more slowly than thefiller wire.

BindersAC arc welding used potassium silicate binders.

DC arc welding used sodium silicate binders.

Potassium has a lower ionization potential as compared

h dwith sodium.

IES 2007The coating material of an arc welding electrode

t i hi h f th f ll i ?contains which of the following?1. Deoxidising agentg g2. Arc stabilizing agent

Sl f i3. Slag forming agentSelect the correct answer using the code given below:g g(a) 1, 2 and 3 (b) 1 and 2 only( ) d l (d) d l(c) 2 and 3 only (d) 1 and 3 only

IES‐1997Assertion (A): The electrodes of ac arc welding arecoated with sodium silicate, whereas electrodes used,for dc arc welding are coated with potassium silicatebinders.Reason (R): Potassium has a lower ionizationpotential than sodium.( ) B h A d R i di id ll d R i h(a) Both A and R are individually true and R is the correct

explanation of A(b) B th A d R i di id ll t b t R i t th(b) Both A and R are individually true but R is not the

correct explanation of A(c) A is true but R is false(c) A is true but R is false(d) A is false but R is true

For-2013 (IES, GATE & PSUs) Page 42

IES‐2002Match List I with List II and select the correct answer:List I (Ingredients)  List II (Welding List I (Ingredients)  List II (Welding functions)A Sili A t biliA. Silica 1. Arc stabilizerB. Potassium oxalate 2. De‐oxidizerC. Ferro silicon  3. Fluxing agentD. Cellulose  4. Gas forming material4 g

Codes:A B C  D A B  C D(a)  3  4  2  1  (b)  2  1  3  4(a)  3  4  2  1  (b)  2  1  3  4(c)  3  1  2  4  (d)  2  4  3  1

Welding FluxAvailable in three formsGranularElectrode wire coating Electrode wire coating Electrode core 

Low Hydrogen ElectrodeLow Hydrogen ElectrodeThe basic coatings contain large amount ofThe basic coatings contain large amount ofcalcium carbonate (limestone) and calciumfluoride (fluorspar) and produce low hydrogenfluoride (fluorspar) and produce low hydrogen.But it can absorb moisture therefore coated lowhydrogen electrodes are backed before use to atemperature of 200oC to 3000C and stored in anp 3oven at 110oC to 150oCOther types of electrode release large amount ofOther types of electrode release large amount ofhydrogen, which can dissolve in the weld metal

d l d b i l kiand lead to embrittlement or cracking.

IFS‐2011IFS‐2011What is meant by low ‐hydrogen electrode ?What is meant by low  hydrogen electrode ?

[2‐marks]

W ldi P itiWelding Positions

Fig. The position of electrode for horizontal welding

Fig. Positioning of electrode for welding in vertically upward position

ldiWelding CurrentWelding current depends upon: the thickness of the welded metal  type of joint  welding speed  position of welded metal, type of joint, welding speed, position of the weld, the thickness and type of the coating on the l d   d i   ki  l helectrode and its working length.Welding current, I  = k. d, amperes;       d is dia. (mm)g , , p ; ( )

Welding VoltageThe arc voltage depends only upon the arc length

V = k1 + k2l   Volts1 2

Wh  l i   h    l h i     d k d k  Where l is the arc length in mm and k1 and k2 are constants,k1 = 10 to 12; and k2 = 2 to 3

The minimum Arc voltage is given byVmin = (20 + 0.04 l)   Volt

Arc LengthFor good welds, a short arc length is necessary,because:because:1. Heat is concentrated.2. More stable3 More protective atmosphere3. More protective atmosphere.

Contd…

A long arc results ingLarge heat loss into atmosphere.U t blUnstable arc.Weld pool is not protected.p pWeld has low strength, less ductility, poor fusion andexcessive spatterexcessive spatter.

For-2013 (IES, GATE & PSUs) Page 43

Fig. Arc Power Vs Arc Length

Arc length should be equal to the  diameter of the electrode size 

Bead width should be equal to three diameter of the electrode size q

GATE‐2002, ConventionalThe arc length‐voltage characteristic of a DC arc is given

by the equation: V = 24 + 4L, where V is voltage in volts

d L i l h i Th i land L is arc length in mm. The static volt‐ampere

characteristic of the power source is approximated by acharacteristic of the power source is approximated by a

straight line with a no load voltage of 80 V and a shortg g

circuit current of 600A. Determine the optimum arc

length for maximum power.

GATE‐2010 (PI)D i t d t l ldi ith di tDuring a steady gas metal arc welding with directcurrent electrode positive polarity, the welding current,

lt d ld d A V d 6 / ivoltage and weld speed are 150 A, 30 V and 6 m/min,respectively. A metallic wire electrode of diameter 1.2

i b i f d t t t t f / i Thmm is being fed at a constant rate of 12 m/min. Thedensity, specific heat and melting temperature of thei l t d k / 3 J/k oC d oCwire electrode are 7000 kg/m3, 500 J/kgoC and 1530oC,

respectively. Assume the ambient temperature to be 30oCd l h l h f l i F h idand neglect the latent heat of melting. Further, consider

that two‐third of the total electrical power is available forl i f h i l d Th l i ffi i (imelting of the wire electrode. The melting efficiency (in

percentage) of the wire electrode is(a) 39.58 (b) 45.25 (c) 49.38 (d) 54.98

GATE‐2008In arc welding of a butt joint, the welding speed isto be selected such that highest cooling rate isto be selected such that highest cooling rate isachieved. Melting efficiency and heat transferffi i d i l Th fefficiency are 0.5 and 0.7, respectively. The area of

the weld cross section is 5 mm2 and the unitenergy required to melt the metal is 10 J/mm3. Ifthe welding power is 2 kW, the welding speed ing p , g pmm/s is closest to(a) 4 (b) 14 (c) 24 (d) 34(a) 4 (b) 14 (c) 24 (d) 34

GATE‐2006In an arc welding process, the voltage and currentare 25 V and 300 A respectively The arc heatare 25 V and 300 A respectively. The arc heattransfer efficiency is 0.85 and welding speed is 8

/ Th h i (i J/ ) imm/sec. The net heat input (in J/mm) is(a) 64( ) 4(b) 797( )(c) 1103(d) 79700( ) 797

GATE‐2009 (PI)GATE‐2009 (PI)A t t t ldi f t lAutogenous gas tungsten arc welding of a steel

plate is carried out with welding current of 500 Aplate is carried out with welding current of 500 A,

voltage of 20 V, and weld speed of 20 mm/sec.g p

Consider the heat transfer efficiency from the arc

to the weld pool as 90%. The heat input per unit

length (in KJ/mm) is

(a) 0.25 (b) 0.35 (c) 0.45 (d) 0.55

ExampleCalculate the melting efficiency in the case of

ldi f t l ith t ti l f V darc‐welding of steel with a potential of 20 V anda current of 200 A. The travel speed is 5 mm/sp 5 /and .the cross‐sectional area of the joint is 20mm2 Heat required to melt steel may be takenmm2. Heat required to melt steel may be takenas 10 J/mm3 and the heat transfer efficiency as0.85.

Arc blow in DC arc welding

Contd…For-2013 (IES, GATE & PSUs) Page 44

A bl d i th ldi f tiArc blow occurs during the welding of magneticmaterials with DC.The effect of arc blow is maximum when weldingcorners where magnetic field concentration ismaximum.The effect is particularly noticeable when welding withp y gbare electrodes or when using currents below or aboveAgain the problem of arc blow gets magnified whenAgain the problem of arc blow gets magnified whenwelding highly magnetic materials such as Ni alloys,because of the strong magnetic fields set up by thesebecause of the strong magnetic fields set up by thesemetals.C U b l d ti fCause: Unbalanced magnetic forces.

Contd…

Effect of arc blowLow heat penetration.E i ldExcessive weld spatter.Pinch effect in welding is the result of electromagneticg gforcesWeld spatter occurs due toWeld spatter occurs due to

High welding currentToo small an electrode arc

Contd…

The effects of arc blow can beminimized with D.C.ldi bwelding by

Shortening the arc.gReduce currentR d i ld dReducing weld speed.Balance magnetic field by placing one ground lead atg y p g geach end of the work piece.Wrapping the electrode cable a few turns around theWrapping the electrode cable a few turns around thework piece.

IES‐2001Arc blow is more common in(a) A.C. welding(b) D.C. welding with straight polarity(b) D.C. welding with straight polarity(c) D.C. welding with bare electrodes(d) A.C. welding with bare electrodes

IES‐2001Pinch effect in welding is the result of(a) Expansion of gases in the arc(b) Electromagnetic forces(b) Electromagnetic forces(c) Electric force(d) Surface tension of the molten metal

ISRO‐2006Too high welding current in arc welding would result in(a) Excessive spatter under cutting along edges irregular(a) Excessive spatter, under cutting along edges, irregulardeposits, wasted electrodes(b) Excessive piling up of weld metal, poor penetration,wasted electrodes(c) Too small bead, weak weld and wasted electrodes(d) E i ili f ld l l i(d) Excessive piling up of weld metal, overlappingwithout penetration of edges, wasted electrodes

Gas shieldsAn inert gas is blown into the weld zone to drive away

other atmospheric gases.

Gases are argon, helium, nitrogen, carbon dioxide and

a mixture of the above gases.

Argon ionizes easily requiring smaller arc voltages.It is

d f ldi thi h tgood for welding thin sheets.

Contd…

Helium, most expensive, has a better thermal

conductivity, is useful for thicker sheets, copper and

aluminiumwelding, higher deposition rate.

The arc in carbon dioxide shielding gas is unstable,

l t i d idi d dleast expensive, deoxidizers needed.

It i h d th f th ldIt is a heavy gas and therefore covers the weld zone

very wellvery well.

Carbon Arc weldingArc is produced between a carbon electrode and the

work.

Shielding is not used.

No pressure

With or without filler metal

May be used in "twin arc method", that is, between

b ( hi ) l dtwo carbon (graphite) electrodes.For-2013 (IES, GATE & PSUs) Page 45

IES 2010Assertion (A): Straight polarity is alwaysAssertion (A): Straight polarity is alwaysrecommended for Carbon‐electrodewelding.Reason (R): Carbon arc is stable in straight polarity.(a) Both A and R are individually true and R is the(a) Both A and R are individually true and R is thecorrect explanation of A(b) h d d d ll b h(b) Both A and R are individually true but R is NOT thecorrect explanation of Ap(c) A is true but R is false(d) A i f l b t R i t(d) A is false but R is true

Tungsten Inert Gas welding (TIG)Arc is established between a non‐consumabletungsten electrode and the workpiecetungsten electrode and the workpiece.Tungsten is alloyed with thorium or zirconium forbetter current‐carrying and electron‐emissioncharacteristics.Arc length is constant, arc is stable and easy tomaintainmaintain.With or without filler.

Contd…

Very clean welds.

All metals and alloys can be welded. (Al, Mg also)

Straight polarity is used.

Weld voltage 20 to 40 V and weld current 125 A for

RPDC to 1000 A for SPDCRPDC to 1000 A for SPDC.

Shielded Gas: ArgonShielded Gas: Argon

Torch is water or air cooledTorch is water or air cooled.

Fig. TIG

GATE 2011Which one among the following welding processes used non – consumable electrode?(a) Gas metal arc welding(b) S b d    ldi(b) Submerged arc welding(c) Gas tungsten arc welding( ) g g(d) Flux coated arc welding

IES 2010In an inert gas welding process the commonly usedIn an inert gas welding process, the commonly usedgas is(a) Hydrogen(b) Oxygen(b) Oxygen(c) Helium or Argon(d) Krypton

ISRO‐2009ISRO‐2009Following gases are used in tungsten inertFollowing gases are used in tungsten inertgas welding(a) CO2 and H2

(b) A d(b) Argon and neon(c) Argon and helium(c) Argon and helium(d) Helium and neon

GATE‐2002Which of the following arc welding processes does not use consumable electrodes?not use consumable electrodes?(a) GMAW(b) GTAW(c) Submerged Arc Welding(c) Submerged Arc Welding(d) None of these

IES‐1994Which one of the following welding processes 

  bl   l t d ?  uses non‐ consumable electrodes?  (a) TIG welding( ) g(b) MIG welding( ) M l    ldi(c) Manual arc welding(d) Submerged arc welding.( ) g g

For-2013 (IES, GATE & PSUs) Page 46

IES‐2000Which one of the following statements is correct?(a) No flux is used in gas welding of mild steel(b) Borax is the commonly used flux coating on (b) Borax is the commonly used flux coating on 

welding electrodes( ) L  b   ldi   l       h b  (c) Laser beam welding employs a vacuum chamber 

and thus avoids use of a shielding method(d) AC can be used for GTAW process

Gas Metal Arc Welding (GMAW) or MIG A consumable electrode in a gas shield.A i b k i d i ll f dArc is between workpiece and an automatically fedbare‐wire electrode.Argon, helium, and mixtures of the two can be used.Any metal can be welded but are used primarily withAny metal can be welded but are used primarily withthe non‐ferrous metals.When welding steel, some O2 or CO2 is usually addedto improve the arc stability and reduce weld spatter.p y p

Contd…

Fast and economical.Fast and economical.A reverse‐polarity dc arc is generally used becausef i d i f d biliof its deep penetration, spray transfer, and ability

to produce smooth welds with good profile.

Fig. MIG

IES 2007In MIG welding, the metal is transferred into the f   f  hi h    f th  f ll i ?form of which one of the following?(a) A fine spray of metal( ) p y(b) Molten drops( ) W ld  l(c) Weld pool(d) Molecules( )

IES‐1997Consider the following statements:MIG  ldi    MIG welding process uses1.  Consumable electrode      2.non‐consumable electrode   3.  D.C. power supply  4. A.C. power supplyOf these statementsOf these statements(a) 2 and 4 are correct(b) 2 and 3 are correct(c) 1 and 4 are correct(c) 1 and 4 are correct(d) 1 and 3 are correct

IES 2010Assertion (A): Inert gas and bare electrode instead Assertion (A): Inert gas and bare electrode instead of flux coated electrode is used in the case of 

i  TIG  d MIG  ldi  automatic TIG and MIG welding processes.Reason (R): Better protection is provided by a cloud ( ) p p yof inert gas than the cover created by the flux.( ) B th A d R i di id ll t d R i th(a) Both A and R are individually true and R is thecorrect explanation of A(b) Both A and R are individually true but R is NOT thecorrect explanation of Acorrect explanation of A(c) A is true but R is false(d) A is false but R is true

IES ‐ 2012St t t (I)  DC  ith    l it  i   d i  MIG Statement (I): DC with reverse polarity is used in MIG weldingStatement (II):Use of DC with reverse polarity enables deeper penetration and a clean Surface(a) Both Statement (I) and Statement (II) areindividually true and Statement (II) is the correcty ( )explanation of Statement (I)(b) Both Statement (I) and Statement (II) are(b) Both Statement (I) and Statement (II) areindividually true but Statement (II) is not the correctexplanation of Statement (I)explanation of Statement (I)(c) Statement (I) is true but Statement (II) is false( ) ( ) ( )(d) Statement (I) is false but Statement (II) is true

Submerged Arc welding (SAW) A thick layer of granular flux is deposited just ahead of

a bare wire consumable electrode, and an arc is

maintained beneath the blanket of flux with only a few

ll fl b i i iblsmall flames being visible.

A ti f th fl lt M lt fl d flA portion of the flux melts. Molten flux and flux

provides thermal insulation slows cooling rate andprovides thermal insulation, slows cooling rate and

produce soft, ductile welds.p ,

Contd…For-2013 (IES, GATE & PSUs) Page 47

Most suitable for flat butt or fillet welds in low

carbon steel (< 0.3% carbon).

The process is not recommended for high‐carbon

t l t l t l l i isteels, tool steels, aluminum, magnesium,

titanium, lead, or zinctitanium, lead, or zinc.

Characteristic of submerged arc welding

High speeds, 

High deposition rates, 

Deep penetration, 

High cleanliness (due to the flux action).

AdvantagesWire electrodes are inexpensive.

No weld spatter.

Nearly 100% deposition efficiency.

Lesser electrode consumption. 

LimitationsExtensive flux handling,

Contamination of the flux by moisture.

Large‐grain‐size structures.

Welding is restricted to the horizontal position.

Chemical control is important

IES 2011The welding process in which bare wire is used aselectrode, granular flux is used and the process is, g pcharacterized by its high speed welding, is known as:(a) Shielded arc welding(a) Shielded arc welding(b) Plasma arc welding(c) Submerged arc welding(d) Gas metal arc welding(d) Gas metal arc welding

IES‐2006In which of the following welding processes, flux i   d i  th  f   f  l ?is used in the form of granules?(a) AC arc welding( ) g(b) Submerged arc welding( ) A     ldi(c) Argon arc welding(d) DC arc welding( ) g

IES‐2005Which of the following are the major characteristics of submerged arc welding?characteristics of submerged arc welding?1. High welding speeds.2. High deposition rates.3. Low penetration.3. o pe et at o .4. Low cleanliness.S l t th   t    i  th   d   i  b lSelect the correct answer using the code given below:(a) 2 and 3  (b) 1, 2 and 3(c) 3 and 4  (d) 1 and 2

IES‐2008Assertion (A): Submerged arc welding is notrecommended for high carbon steels, tool steels,g , ,aluminium, magnesium etc.Reason (R): This is because of unavailability of( ) ysuitable fluxes, reactivity at high temperatures andlow sublimation temperatures.( ) B h A d R d R i h l i(a) Both A and R are true and R is the correct explanation

of A(b) B th A d R t b t R i NOT th t(b) Both A and R are true but R is NOT the correct

explanation of A(c) A is true but R is false(c) A is true but R is false(d) A is false but R is true

For-2013 (IES, GATE & PSUs) Page 48

GATE‐1999For butt ‐welding 40 mm thick steel plates, whenthe expected quantity of such jobs is 5000 perthe expected quantity of such jobs is 5000 permonth over a period of 10 year, choose the best

i bl ldi f h f ll isuitable welding process out of the followingavailable alternatives.(a) Submerged arc welding(b) Oxy acetylene welding(b) Oxy‐acetylene welding(c) Electron beam welding(d) MIG welding

Atomic Hydrogen welding (AHW)An a.c. arc is formed between two tungsten electrodesalong which streams of hydrogen are fed to thealong which streams of hydrogen are fed to thewelding zone. The molecules of hydrogen aredissociated by the high heat of the arc in the gapdissociated by the high heat of the arc in the gapbetween the electrodes. The formation of atomichydrogen proceeds with the absorption of heat:hydrogen proceeds with the absorption of heat:

H2 = 2H ‐ 421.2 k J /molThi i h d bi f l lThis atomic hydrogen recombines to form molecularhydrogen outside the arc, particularly on the relatively

ld f f h k b i ld d l i hcold surface of the work being welded, releasing theheat gained previously:

2H = + 421.2 k J /mol. H2Contd…

Temperature of about 3700oCTemperature of about 3700oC.

Hydrogen acts as shielding alsoHydrogen acts as shielding also.

Used for very thin sheets or small diameter wiresUsed for very thin sheets or small diameter wires.

Lower thermal efficiency than Arc weldingLower thermal efficiency than Arc welding.

Ceramics may be arc welded.Ceramics may be arc welded.

AC used.

IES‐2005In atomic hydrogen welding, hydrogen acts as(a) A heating agent(b) One of the gases to generate the flame(b) One of the gases to generate the flame(c) An effective shielding gas protecting the weld(d) A lubricant to increase the flow characteristics of 

weld metal

R i t  W ldiResistance Welding

By  S K Mondal

Resistance Welding PrincipleBoth heat and pressure are usedBoth heat and pressure are used.Heat is generated by the electrical resistance of the

k i d h i f b hwork pieces and the interface between them.Pressure is supplied externally and is variedpp ythroughout the weld cycle.Due to pressure a lower temperature needed thanDue to pressure, a lower temperature needed thanoxy‐fuel or arc welding.

Contd…

They are not officially classified as solid‐state weldingThey are not officially classified as solid state welding

by the AmericanWelding Society.y g y

Very rapid and economical.

Extremely well suited to automated manufacturing.

No filler metal, no flux, no shielding gases.

Contd…

Overall resistance very low.

Very high‐current (up to 100,000 A)

Very low‐voltage (0.5 to 10 V) is used.

FIG. The fundamental resistance‐welding circuit

Fig. The desired temperaturedi t ib ti th

Fig. Typical current andpressure cycle for resistancedistribution across the

electrodes and the workpieces in lap resistance

pressure cycle for resistancewelding. The cycle includesforging and post heatingp p

welding. operations.

For-2013 (IES, GATE & PSUs) Page 49

Fig. The arrangement of the electrodes and the work in spotwelding, showing design for replaceable electrode tips.

IES 2007IES 2007Wh t i th i i l f i t ldi ?What is the principle of resistance welding?

Indicate where the resistance is maximum in spotIndicate where the resistance is maximum in spot

welding operation.g p

[ 2 marks]

Advantages1. Very rapid.

2. Fully automation possible.

3. Conserve material; no filler metal, shielding gases, or

flux is required.

4. Skilled operators are not required.

5.Dissimilar metals can be easily joined.

6. High reliability and High reproducibility.

Limitations1. High initial cost.

2. Limitations to the type of joints (mostly lap joints).

3. Skilled maintenance personne1 are required:

4. special surface treatment needed.

ApplicationThe resistance welding processes are among themost common technique for high volumejoiningjoining.

Different types1. Resistance spot welding

2. Resistance seam welding

3. Projection welding

4. Upset welding

5. Flash welding

6. Percussion welding

Resistance spot weldingThe process description given so far is called resistancespot welding (RSW) or simply spot weldingspot welding (RSW) or simply spot welding.This is essentially done to join two sheet‐metal jobs ina lap joint, forming a small nugget at the interface ofthe two plates.p

Heat input and Efficiency Calculations

Contd…

Electric ResistanceWeldingect c Res sta ceWe d g

l ’ l l blJoule’s law applicableQ = I2 Rt, JoulesQ I Rt, Joules

For-2013 (IES, GATE & PSUs) Page 50

IES‐2003In resistance welding, heat is generated due to the 

i t  b tresistance between(a) Electrode and workpiece( ) p(b) Asperities between touching plates( ) T  di i il   l  b i  i  (c) Two dissimilar metals being in contact(d) Inter atomic forces( )

IES‐2001The maximum heat in resistance welding is at the(a) Tip of the positive electrode(b) Tip of the negative electrode(b) Tip of the negative electrode(c) Top surface of the plate at the time of electric 

  i h  h   l dcontact with the electrode(d) Interface between the two plates being Joined( ) p g J

GATE‐2007T lli h h f hi k ld d i l j iTwo metallic sheets, each of 2.0 mm thickness, are welded in a lap jointconfiguration by resistance spot welding at a welding current of 10 kAand welding time of 10 millisecond. A spherical fusion zone extending

t th f ll thi k f h h t i f d Th ti f thup to the full thickness of each sheet is formed. The properties of themetallic sheets are given as:ambient temperature = 293 Kmelting temperature = 1793 Klatent heat of fusion = 300 kJ/kgdensity = 7000 kg/m3density = 7000 kg/m3

specific heat = 800 J/kg KAssume:(i) Contact resistance along sheet‐sheet interface is 500 micro‐ohm andalong electrode‐sheet interface is zero;(ii) No conductive heat loss through the bulk sheet materials; and(ii) No conductive heat loss through the bulk sheet materials; and(iii) The complete weld fusion zone is at the melting temperature.The melting efficiency (in %) of the process is( ) (b) 6 ( ) (d) 8(a) 50.37 (b) 60.37 (c) 70.37 (d) 80.37

GATE‐2009 (PI) Linked S‐1R i ldi f l h i i d iResistance spot welding of two steel sheets is carried out inlap joint configuration by using a welding current of 3 kA and

ld f l ld f la weld time of 0.2 S. A molten weld nugget of volume 20 mm3

is obtained. The effective contact resistance is 200 µΩ(micro‐ohms). The material properties of steel are given as:(i) latent heat of melting: 1400 kJ/kg, (ii) density: 8000kg/m3, (iii) melting temperature: 1520oC, (iv) specific heat:0.5 kJ/kgoC. The ambient temperature is 20oC.5 g pHeat (in Joules) used for producing weld nugget will be(assuming 100% heat transfer efficiency)(assuming 100% heat transfer efficiency)(a) 324 (b) 334 (c) 344 (d) 354

GATE‐2009 (PI) Linked S‐2R i ldi f l h i i d iResistance spot welding of two steel sheets is carried out inlap joint configuration by using a welding current of 3 kA and

ld f l ld f la weld time of 0.2 S. A molten weld nugget of volume 20 mm3

is obtained. The effective contact resistance is 200 µΩ(micro‐ohms). The material properties of steel are given as:(i) latent heat of melting: 1400 kJ/kg, (ii) density: 8000kg/m3, (iii) melting temperature: 1520oC, (iv) specific heat:0.5 kJ/kgoC. The ambient temperature is 20oC.5 g pHeat (in Joules) dissipated to the base metal will be(neglecting all other heat losses)(neglecting all other heat losses)(a) 10 (b) 16 (c) 22 (d) 32

GATE‐2005Spot welding of two 1 mm thick sheets of steel(density = 8000 kg/m3) is carried out successfully(density = 8000 kg/m3) is carried out successfullyby passing a certain amount of current for 0.1

d h h h l d Th l ldsecond through the electrodes. The resultant weldnugget formed is 5 mm in diameter and 1.5 mmthick. If the latent heat of fusion of steel is 1400kJ/kg and the effective resistance in the weldingJ/ g goperation in 200 , the current passing through theelectrodes is approximatelyelectrodes is approximately(a) 1480A (b) 3300 A(c) 4060 A (d) 9400 A

GATE‐2001Resistance spot welding is performed on twoplates of 1 5 mm thickness with 6 mm diameterplates of 1.5 mm thickness with 6 mm diameterelectrode, using 15000 A current for a timed i f d A i h i fduration of 0.25 seconds. Assuming the interfaceresistance to be 0.0001 , the heat generated toform theweld is(a) 5625 W‐sec (b) 8437 W‐sec(a) 5625 W sec (b) 8437 W sec(c) 22500 W‐sec (d) 33750 W‐sec

GATE‐2004Two 1 mm thick steel sheets are to be spot weldedat a current of 5000 A Assuming effectiveat a current of 5000 A. Assuming effectiveresistance to be 200 micro‐ohms and current flowi f d h d d i htime of 0.2 second, heat generated during theprocess will be(a) 0.2 Joule (b) 1 Joule(c) 5 Joule (d) 1000 Joules(c) 5 Joule (d) 1000 Joules

GATE‐1992For resistance spot welding of 1.5 mm thick steelsheets the current required is of the order ofsheets, the current required is of the order of(a) 10 A(b) 100 A(c) 1000 A(c) 1000 A(d) 10,000 A

For-2013 (IES, GATE & PSUs) Page 51

GATE‐2010Two pipes of inner diameter 100 mm and outerdiameter 110 mm each joined by flash buttdiameter 110 mm each joined by flash buttwelding using 30 V power supply. At the interface,

f i l l f h i hi h h1 mm of material melts from each pipe which hasa resistance of 42.4 Ω. If the unit melt energy is64.4 MJm‐3, then time required for welding inseconds is(a) 1 (b) 5 (c) 10 (d) 20

IAS‐2003Assertion (A): Spot welding is adopted to weld twooverlapped metal pieces between two electrodepp ppoints.Reason (R): In this process when current is switched( ) pon, the lapped pieces of metal are heated in arestricted area.( ) B h A d R i di id ll d R i h(a) Both A and R are individually true and R is the correct

explanation of A(b) B th A d R i di id ll t b t R i t th(b) Both A and R are individually true but R is not the

correct explanation of A(c) A is true but R is false(c) A is true but R is false(d) A is false but R is true

lIES 2007 ConventionalTwo steel sheets of thickness one mm are weldedTwo steel sheets of thickness one mm are weldedby resistance projection welding technique. A

t f A f d i d tcurrent of 30,000 A for 0∙005 second is made toflow. The effective resistance of joint can be taken

h h b d das 100 micro ohms. The joint can be considered asa cylinder of diameter 5 mm and height 1∙5 mm.y 5 g 5The density of steel is 0∙00786 gm/mm3. The heatneeded for welding steel is 10 J/mm3. Calculate theneeded for welding steel is 10 J/mm . Calculate theefficiency of welding. [20]

GATE – 2008 (PI)Aluminum strips of 2 mm thickness are joined togetherby resistance spot welding process by applying anby resistance spot welding process by applying anelectric current of 6000 A for 0.15 sec. The heat requiredfor melting aluminum is 2.9 J/mm3. The diameter andthe thickness of weld nugget are found to be 5 mm andthe thickness of weld nugget are found to be 5 mm and2.5 mm, respectively. Assuming the electrical resistanceto be 75 µΩ (micro – ohms), the percentage of totalenergy utilized in forming the weld nugget isenergy utilized in forming the weld nugget is

(a) 28 (b) 35 (c) 65 (d) 72( ) ( ) 35 ( ) 5 ( ) 7

Resistance seam weldingWeld is made between overlapping sheets of metal.

The seam is a series of overlapping spot welds.

The basic equipment is the same as for spot welding.

except that the electrodes are now in the form of

t ti di krotating disks.

Ti d l f t t f th l iTimed pulses of current pass to form the overlapping

weldswelds.

Contd…

Welding current is a bit higher than spot welding, tot h t i it f th dj t ldcompensate short circuit of the adjacent weld.

In other process a continuous seam is produced byp p ypassing a continuous current through the rotatingelectrodes with a speed of 1 5 m/min for thin sheetelectrodes with a speed of 1.5 m/min for thin sheet.

Contd…

Fig. Resistance seam welding

GATE – 2012 (PI)GATE – 2012 (PI)In resistance seam welding, the electrode is in theIn resistance seam welding, the electrode is in theform of a( ) li d(a) cylinder(b) flat plate( ) p(c) coil of wire(d) i l di(d) circular disc

Projection weldingLimitations of spot welding.

El d di i b i i d1. Electrode condition must be maintainedcontinually, and only one spot weld at a time.

2. For additional strength multiple welds needed.Projection welding (RPW) overcomes aboveProjection welding (RPW) overcomes abovelimitations.

Contd…For-2013 (IES, GATE & PSUs) Page 52

Dimples are embossed on work pieces at the weldlocations and then placed between large arealocations and then placed between large‐areaelectrodes, and pressure and current applied like spot

ldiwelding.Current flows through the dimples and heats themg pand pressure causes the dimples to flatten and form aweldweld.

Fig. Principle of projection welding, p j g(a) prior to application of current and pressure (b) and after formation of (b) and after formation of welds

Contd…

Projections are press‐formed in any shape.j p y p

Multiple welds at a time.p

No indentation mark on the surface.

Bolts and nuts can be attached to other metal parts.

Upset weldingMade butt joint compared to lap joint.

Pieces are held tightly and current is applied.

Due to pressure joints get slightly upset and hence its

name.

Useful for joining rods or similar pieces.

Contd…

Contd…

This is the process used for making electric resistance‐ld d (ERW) i i f l l f i blwelded (ERW) pipes starting from a metal plate of suitable

thickness.The plate is first formed into the shape of the pipe with thehelp of the three roll set as shown in Fig. above. The endsp gof the plate would then be forming the butt joint.The two rotating copper disc electrodes are made toThe two rotating copper disc electrodes are made tocontact the two ends of the plate through which thecurrent is passed The ends get heated and then forgecurrent is passed. The ends get heated and then forge‐welded under the pressure of the rolls.Th d f h i b ld d b f lThe ends of the pieces to be upset welded must be perfectlyparallel. Any high spots if present on the ends would getmelted first before the two ends are completely joined.

Flash WeldingIt is similar to upset welding except the arc rather than

resistance heating.

One pieces is clamped with cam controlled movable

platen and other with is fixed platen.

Contd…

Two pieces are brought together and the power supply isswitched on Momentarily the two pieces are separatedswitched on. Momentarily the two pieces are separatedto create the arc to melt the ends of the two pieces.Th i h i b h h d hThen again the pieces are brought together and thepower switched off while the two ends are fused underforce. Most of the metal melted would flash outthrough the joint and forms like a fin around the joint.g j jFaster than upset welding.

Percussion WeldingSimilar to flash welding except arc power by a rapid

discharge of stored electrical energy.

The arc duration is only 1 to 10 ms, heat is intense and

highly concentratedhighly concentrated.

Small weld metal is produced little or no upsetting andSmall weld metal is produced, little or no upsetting, and

low HAZ.

Application: Butt welding of bar or tube where heat

damage is a major concern.Contd…For-2013 (IES, GATE & PSUs) Page 53

Other Welding gTechniqueTechnique

Thermit WeldingHeating and coalescence is by superheated molten

metal obtained from a chemical reaction between a

metal oxide and a metallic reducing agent.

Used mixture one part aluminum and three parts iron

id d i it d b i f ( °C)oxide and ignited by a magnesium fuse. (1150°C).

8Al   F O → F     Al O  h t8Al+ 3Fe3O4 → 9Fe + 4Al2O3 + heat

Contd…

Temp. 2750°C produced in 30 seconds, superheatingp p p g

the molten iron which provide both heat and filler

metal.

Runners and risers are provided like casting.

Copper, brass, and bronze can be welded using a

diff i idifferent starting mixture.

U d j i hi k i i l iUsed to joint thick sections, in remote locations.

IES‐2000Consider the following processes:

G   ldi     1. Gas welding    2. Thermit welding3. Arc welding4 Resistance welding4. Resistance weldingThe correct sequence of these processes in increasing d   f th i   ldi  t t  iorder of their welding temperatures is

(a) 1, 3, 4, 2 (b) 1, 2, 3, 4(c) 4, 3, 1, 2 (d) 4, 1, 3, 2

Electro Slag WeldingVery effective for welding thick sections.

Heat is derived from the passage of electrical current

through a liquid slag and temp. 1760°C

Contd…

A 65‐mm deep layer of molten slag, protect andp y g p

cleanse the molten metal.

Water‐cooled copper molding plates confined the

liquid and moved upward.

Multiple electrodes are used to provide an adequate

l f fillsupply of filler.

Contd…

Applications: Shipbuilding, machine manufacture,

heavy pressure vessels, and the joining of large

castings and forgings.

Slow cooling produces a coarse grain structure.

Large HAZ.

Contd…

IAS‐2003Which one of the following is not an electric 

i t   th d  f  ldi ?resistance method of welding?(a) Electro slag welding( ) g g(b) Percussion welding( ) S   ldi(c) Seam welding(d) Flash welding( ) g

For-2013 (IES, GATE & PSUs) Page 54

IAS‐2000Consider the following welding processes:1. TIG welding  2. Submerged arc welding3. Electro‐slag welding 4. Thermit welding3. Electro slag welding 4. Thermit weldingWhich of these welding processes are used for welding hi k  i   f  l ?thick pieces of metals?(a) 1, 2 and 3  (b) 1, 2 and 4( ) , 3 ( ) , 4(c) 1,3 and 4 (d) 2, 3 and 4

Electron Beam WeldingA beam of electrons is magnetically focused on the

work piece in a vacuum chamber.

Heat of fusion is produced by electrons decelerate.

Allows precise beam control and deep weld

penetration.

h ld ( h b d)No shield gas (vacuum chamber used)

IES‐2004Assertion (A): In electron beam welding process,vacuum is an essential process parametervacuum is an essential process parameterReason (R): Vacuum provides a highly efficienthi ld ldshield onweld zone(a) Both A and R are individually true and R is the

correct explanation of A(b) Both A and R are individually true but R is not the(b) Both A and R are individually true but R is not the

correct explanation of A(c) A is true but R is false(c) A is true but R is false(d) A is false but R is true

IES‐2002In which one of the following welding techniques i     i t  i d?is vacuum environment required?(a) Ultrasonic welding( ) g(b) Laser beam welding( ) Pl     ldi(c) Plasma arc welding(d) Electron beam welding( ) g

IES‐1993Electron beam welding can be carried out in(a) Open air(b) A shielding gas environment   (b) A shielding gas environment   (c) A pressurized inert gas chamber(d) Vacuum

IAS‐2004Which one of the following welding processes 

i t   f  ll  H t Aff t d Z  (HAZ)?consists of smaller Heat Affected Zone (HAZ)?(a) Arc welding (b) Electron beam welding( ) g ( ) g(c) MIG welding (d) Thermit welding

Laser Beam WeldingUsed a focused laser beam provides power intensities

in excess of 10kW/cm2

The high‐intensity beam produces a very thin column

of vaporized metal with a surrounding liquid pool.

Depth‐to‐width ratio greater than 4: 1.

Contd…

Very thin HAZ and little thermal distortion.y

Filler metal and inert gas shield may or may not used.

Deep penetration.

No vacuum needed.

No direct contact needed.

Contd…For-2013 (IES, GATE & PSUs) Page 55

Heat input is very low, often in the range 0.1 to 10 J.p y g

Adopted by the electronics industry.

Possible to weld wires without removing the

polyurethane insulation.

Contd…

IES 2007Consider the following statements in respect of the laser beam welding:laser beam welding:1. It can be used for welding any metal or their 

combinations because of very high temperature of the combinations because of very high temperature of the focal points.

2 Heat affected zone is very large because of quick 2. Heat affected zone is very large because of quick heating.Hi h   i   i d t    th  3. High vacuum is required to carry the process.

Which of the statements given above is/are correct?(a) 1 and 2 only (b) 2 and 3 only(c) 1 only (d) 1, 2 and 3( ) y ( ) 3

IES‐2006Which one of the following welding processes 

i t   f  i i  h t  ff t d   (HAZ)?consists of minimum heat affected zone (HAZ)?(a) Shielded Metal Arc Welding (SMA W)( ) g ( )(b) Laser Beam Welding (LBW)( ) Ul i  W ldi  (USW)(c) Ultrasonic Welding (USW)(d) Metal Inert Gas Welding (MIG)( ) g ( )

GATE‐2012 (PI)Which of the following welding processes results inth ll t h t ff t d ?the smallest heat affected zone?(a) Shielded metal arc welding( ) g(b) Gas welding( ) L b ldi(c) Laser beam welding(d) Thermit welding( ) g

IAS‐2007Consider the following welding processes:1. Arc welding 2. MIG welding3. Laser beam welding 4. Submerged arc3. Laser beam welding 4. Submerged arc

weldingS l h i i i d f HSelect the correct sequence in increasing order of Heataffected zone (HAZ) using the codegiven below:(a) 1 2 3 4 (b) 1 4 2 3(a) 1 ‐ 2 ‐ 3 – 4 (b) 1 ‐ 4 ‐ 2 – 3(c) 3 ‐ 2 ‐ 4 – 1 (d) 4 ‐ 3 ‐ 2 – 1

IAS‐1999Match List I (Shielding method) with List II (Weldingprocess) and select the correct answer using the codesp ) ggiven below the lists:List I List II

l l ldA. Flux coating 1. Gas metal arc weldingB. Flux granules 2. Submerged arc weldingC CO Shi ld d l ldiC. CO2 3. Shielded metal arc weldingD. Vacuum 4. Laser beamwelding

El t b ldi5. Electron beamweldingCodes:A B C D A B C D(a) 1 2 5 3 (b) 1 4 2 5(a) 1 2 5 3 (b) 1 4 2 5(c) 3 5 1 4 (d) 3 2 1 5

Forge WeldingBlacksmith do this.

Borax is used as a flux.

The ends to be joined were then overlapped on the

anvil and hammered to the degree necessary to

produce an acceptable weld.

l d d h k ll f h k dQuality depends on the skill of the worker and not

used by industryused by industry.

Friction WeldingHeat is obtained by the friction between the ends of

the two parts to be joined.

One part is rotated at a high speed and other part is

axially aligned and pressed tightly against it.

Friction raises the temperature of both the ends. Then

t ti i t d b tl d th irotation is stopped abruptly and the pressure is

increased to joinincreased to join.

Contd…

Machine is similar to a centre lathe.Power requirements 25 kVA to 175 kVA.Th i l d d th t th dThe axial pressure depends on the strength andhardness of the metals being joined.Pressure 40 MPa for low‐carbon steels to as high as 450MPa for alloy steels.MPa for alloy steels.

Contd…For-2013 (IES, GATE & PSUs) Page 56

Very efficientVery efficient.Wide variety of metals or combinations of metals canb d h l lbe joined such as aluminium to steel.Grain size is refinedGrain size is refinedStrength is same as base metal.Only round bars or tubes of the same size, orconnecting bars or tubes to flat surfaces can join.g jOne of the components must be ductile.F i ti ldi i lid t t ldiFriction welding is a solid state welding.

Contd… Fig‐ friction welding process

GATE‐2007Which one of the following is a solid state joining process?process?(a) Gas tungsten arc welding(b) Resistance spot welding(c) Friction welding(c) Friction welding(d) submerged arc welding

GATE ‐2010 (PI)Two steel bars, each of diameter 10 mm, are coaxially

friction welded, end to end, at an axial pressure of 200

MP d i l d f ThMPa and at a rotational speed of 4000 rpm. The

coefficient of friction between the mating faces of thecoefficient of friction between the mating faces of the

rotating bars is 0.50. The torque is assumed to act at theg 5 q

3/4th radius of the rotating bar. The power (in KW)

consumed at the interface for welding is

(a) 12.33 (b) 16.44 (c) 18.50 (d) 24.66

IFS‐2011IFS‐2011Di   ith fi  th   i   t   i d f  Discuss with figure the various steps required for 

friction welding  mentioning at least two methods friction welding, mentioning at least two methods 

of control.

[5‐marks]

Ultrasonic Welding (USW)• USW is a solid‐state welding.Hi h f ( KH ) i li d• High‐frequency (10 to 200, KHz) is applied.

• Surfaces are held together under light normalg gpressure.

• Temp do not exceed one half of the melting point• Temp. do not exceed one‐half of the melting point.• The ultrasonic transducer is same as ultrasonicmachining.

Contd…

• Restricted to the lap jointW ld hi i l h f il d i h• Weld thin materials‐sheet, foil, and wire‐‐or theattaching thin sheets to heavier structural members.

• Maximum thickness 2.5 mm for aluminum and 1.0mm for harder metalsmm for harder metals.

• Number of metals and dissimilar metal combinationsd l b j i d h l iand non metals can be joined such as aluminum to

ceramics or glass.• Equipment is simple and reliable.• Less surface preparation and less energy is needed• Less surface preparation and less energy is needed.

Contd…

ApplicationsApplicationsJoining the dissimilar metals in bimetallicsJoining the dissimilar metals in bimetallics

Making microcircuit electrical contacts.g

Welding refractory or reactive metals

Bonding ultrathin metal.

Explosion WeldingDone at room temperature in air, water or vacuum.

Surface contaminants tend to be blown off the surface.

Typical impact pressures are millions of psi.

Well suited to metals that is prone to brittle joints

when heat welded, such as,

Aluminum on steel

Ti i lTitanium on steelContd…For-2013 (IES, GATE & PSUs) Page 57

Important factors are,C i i l l iCritical velocityCritical angleg

The cladding plate can be supported with tack weldedsupports at the edges or the metal insertssupports at the edges, or the metal inserts.

Contd…

Typically the detonation velocity should not exceed% f th i l it i th t l120% of the sonic velocity in the metal.

Contd…

High velocity explosives, 4572‐7620 m/s.TNTTNTRDXPETNPETNComposition BComposition C4Composition C4DatasheetPrimacordPrimacord

Medium velocity explosives, 1524‐4572 m/sAmmonium nitrateAmmonium perchlorateAmatolNitroguonidineDynamitesdiluted PETN

Contd…

AdvantagesAdvantages,Can bond many dissimilar, normally unweldablemetalsThe lack of heating preserves metal treatmentThe lack of heating preserves metal treatmentThe process is compact, portable, and easy to containInexpensiveNo need for surface preparationNo need for surface preparation

Contd…

DisadvantagesDisadvantages,The metals must have high enough impact resistance,

d d l ( l %)and ductility (at least 5%)The cladding plate cannot be too large.The cladding plate cannot be too large.Noise and blast can require worker protection, vacuumh b b i d i d/ tchambers, buried in sand/water.

Contd…

Typical applications:Typical applications:

Very large plates can be claddedVery large plates can be cladded.

Joins dissimilar metalsJoins dissimilar metals.

(titanium to steel, Al to steel, Al to Cu etc )(titanium to steel, Al to steel, Al to Cu etc.)

Join tube to tube sheets of large heat exchangers. Join tube to tube sheets of large heat exchangers. 

Contd…

GATE‐1992In an explosive welding process, the……….. (maximum/minimum) velocity of impact is fixed (maximum/minimum) velocity of impact is fixed by the velocity of sound in the……………… (fl / )  l   i l(flyer/target) plate material(a) Maximum; target( ) ; g(b) Minimum; target( ) M i  fl(c) Maximum; flyer(d) Minimum; flyer( ) ; y

IES 2011           S‐1 Contd…Match List –I with List –II and select the correct answer using the code given below the lists:using the code given below the lists:List‐I  List –II

A  L  b    C  b   li d f   ldi     f   l  A. Laser beam welding

1. Can be applied for welding or refractory metals like niobium, tantalum, molybdenum and tungsten.

B. Electron beam welding

2. A sound and clean welded joint is created due to rubbing of two parts against each other with d d d d hadequate speed and pressure producing intense heat raising temperature above melting point.

C. Ultrasonic welding

3. Clean heat source created much away from job, a narrow spot is heated, work chamber  operates in a high vacuum.

D. Friction  4. Clean heat source very quick heating, very small welding

4 y q g yfocal spot, no vacuum chamber is required.

For-2013 (IES, GATE & PSUs) Page 58

IES 2011             From S‐1Codes :

A B C D A B C DA B C D A B C D(a)  4  3 1 2 (b) 2 3 1 4(c) 4 1 3 4 (d) 2 1 3 4

IES‐2009Match List‐I with List‐II and select the correct answer using the code given below the Lists:List I List IIList‐I List‐II(Welding Process) (Application)

A. Laser welding 1. Uniting large‐area sheetsi i   ldi   i i  l  B. Friction welding  2. Repairing large parts

C. Ultrasonic welding 3. Welding a rod to a flat surfaceD. Explosive welding  4. Fabrication of nuclear reactor g

components                                                       5. Welding very thin materials

Code:(a) A B C D (b) A B C D

5  4  3  2 1 4 2 5

(c) A B C D (d) A B C D1 3 4 2 5 3 4 1

IAS‐2002Match List I, (Welding) with List II (Application) and select the correct answer using the codes given below the Lists:Li  I Li  IIList I List II(Welding) (Application)A. Explosive 1. Joining thick sheetsA. Explosive 1. Joining thick sheetsB. Ultrasonic 2. Manufacture of heat exchangesC. Thermit 3. Joining thin sheets or wires of 

similar/dissimilar metalssimilar/dissimilar metalsD. Projection 4. Joining hydraulic piston rods for 

agricultural machinery5. Joining rails, pipes and thick steel 

sectionsCodes:A B  C  D A  B  C  D(a)  2  5  1  3 (b)  4  5  1  3(c)  2  3  5  1 (d)  4  3 5  1

IFS ‐ 2009IFS ‐ 2009T l t f l i i d t i l t l tTwo plates of aluminium and stainless steel are to

be welded back to back to create a single plate ofbe welded back to back to create a single plate of

thickness equal to the sum of the thicknesses ofq

the two plates. Suggest the suitable process and

explain it in brief.

[ 10 – marks]

Autogeneous WeldingAutogeneous welding or fusion of the parent

t i l i i t hi ld ith t thmaterial in an inert gas shield without the useof filler metals.

Micro Plasma Arc Weld (PAW)Similar to GTAW except the plasma caused by the arc

is constricted by a water‐cooled orifice

Capable of high welding speeds where size permits

Argon is used as the shielding gas.

Diffusion WeldingIt i lid t t ldi hi h dIt is a solid state welding process which producescoalescence of the faying surfaces by the application of

d l t d t t ( b t t 8 %pressure and elevated temperatures (about 50 to 80%of absolute melting point of the parent materials) for ati i f l f i t t f htime ranging from a couple of minutes to a few hours.Produces high quality bonds with good strength withlittle or no distortion.Can join very dissimilar materials.Ca jo ve y d ss a ate a s.A solid filler metal may or may not be inserted.M t i l ld d f i ft d k t i d tMaterials welded for aircraft and rocket industry:Boron, Titanium, Aluminium, Ceramic, Composite,G hit M i tGraphite, Magnesium etc.

GATE – 2008 (PI)Which pair among the following solid state welding

processes uses heat from an external source?

P – Diffusion welding; Q‐ Friction welding

l ld ldR – Ultrasonic welding S – Forge welding

( ) P d R (b) R d S(a) P and R (b) R and S

( ) Q d S (d) P d S(c) Q and S (d) P and S

IAS‐2001Match List I (Welding processes) with List II (Features) and select the correct answer using the codes given below the Lists:

List I List IIA Ultrasonic welding 1 Gas heated to ionized condition      A. Ultrasonic welding 1. Gas heated to ionized condition      

for conduction of electric currentB. Electron beam welding  2. High frequency and high 

bintensity vibrationsC. Plasma arc welding 3. Concentrated stream of high‐

energy electronsenergy electrons4. Exothermal chemical reaction

Codes:A B C A B C(a)  1 2 4 (b) 4 3 1(c)  2 1 4 (d)  2 3 1

For-2013 (IES, GATE & PSUs) Page 59

JWM 2010Match List‐I with List‐II and select the correct answer using the code given below the lists :g g

List I  List IIA  Atomic  1  Two pieces are brought together and A. Atomic hydrogen welding 

1. Two pieces are brought together and power supply is switched on

B. Plasma‐arc welding 

2. Nugget is formed at the interface of two plateswelding  two plates

C. Spot welding  3. Gas is ionized

d

D. Flash welding  4. Inert gas shielded arc welding

Code:A B C D A B C D(a) 4 3 2 1 (b)  1  3 2 4(a) 4 3 2 1 (b)  1  3 2 4(c)  4 2 3 1 (d) 1  2  3  4

IES 2011 C ti lIES 2011 ConventionalDiscuss the process capabilities and applications of Gas

M t l A W ldi G t t A W ldi dMetal Arc Welding, Gas tungsten Arc Welding, and

Diffusion Bonding processesDiffusion Bonding processes.

[15 Marks][15 Marks]Brazing and SolderingBrazing and Soldering

Brazing and SolderingBrazing is the joining of metals through the use of heatand a filler metal whose melting temperature is above

b b l h l f h l b450°C; but below the melting point of the metals beingjoined.C i ith ldi d th b iComparison with welding and the brazing process

1. The composition of the brazing alloy is significantlydifferent from that of the base metaldifferent from that of the base metal.

2. The strength of the brazing alloy is substantially lowerthan that of the base metalthan that of the base metal.

3. Themelting point of the brazing alloy is lower than thatof the base metal so the base metal is not meltedof the base metal, so the base metal is not melted.

4. Capillary action or capillary attraction draws themolten filler metal into the joint, even against the flow ofj , ggravity.

B i h l di iBrazing process has several distinct advantages:advantages:

1 All metals can be joined1. All metals can be joined.

2. Suited for dissimilar metals.2. Suited for dissimilar metals.

3. Quick and economical.3. Qu c a d eco o ca .

4. Less defects.4

Contd…

Corrosion prone

Brazing metals are typically alloys such as,B i  b  (6 % C   %Z )Brazing brass (60% Cu, 40%Zn)Manganese bronzegNickel silverC   iliCopper siliconSilver alloys (with/without phosphorous)y ( / p p )Copper phosphorous

Contd…

Extremely clean surface needed.

Fluxes used are combinations of borax, boric acid,

chlorides, fluorides, tetra‐borates and other wetting

agents.

Contd…For-2013 (IES, GATE & PSUs) Page 60

A popular composition is 75% borax and 25% boricp p p

acid.

Sodium cyanide is used in brazing tungsten to copper.

Base materials not melted.

GATE‐2005The strength of a brazed joint( ) D   i h i  i    b   h    (a) Decreases with increase in gap between the two joining surfaces(b) Increases with increase in gap between the two joining surfacesjoining surfaces(c) Decreases up to certain gap between the two j i i   f  b d  hi h i  ijoining surfaces beyond which it increases(d) Increases up to certain gap between the two ( ) p g pjoining surfaces beyond which it decreases

IES‐2006Which one of the following is not a fusion welding 

?process?(a) Gas welding( ) g(b) Arc welding( ) B i(c) Brazing(d) Resistance welding( ) g

ISRO‐2010Which is not correct statement about the function ofWhich is not correct statement about the function offlux in brazing(a) To avoid thermal distortion and cracking(b) To dissolve surface oxide coatings which have formed(b) To dissolve surface oxide coatings which have formedprior to brazing( ) d f f d h b(c) To prevent oxides from forming during the brazingoperation on both the base metal and the brazingp gmaterial(d) To facilitate the wetting process by reducing the(d) To facilitate the wetting process by reducing theviscosity of the melt

Braze WeldingCapillary action is not required.

Edge preparation needed.

Can join cast iron.

Contd…

Done with an oxyacetylene torch.

Fig. Braze Welding

SolderingBy definition, soldering is a brazing type of operation

where the filler metal has a melting temperature

below 450°C.

Strength of the filler metal is low.

Soldering is used for a neat leak‐proof joint or a low

i t l t i l j i tresistance electrical joint.

Not suitable for high temp applicationNot suitable for high‐temp. application.Contd…

Effective soldering generally involves six importantsteps:

(1) Design of an acceptable solder joint,(1) Design of an acceptable solder joint,(2) Selection of the correct solder for the job,(3) Selection of the proper type of flux,(4) Cleaning the surfaces to be joined,(4) Cleaning the surfaces to be joined,(5) Application of flux, solder, and sufficient heat to

ll h l ld fill h j i b illallow the molten solder to fill the joint by capillaryaction and solidify, and

(6) Removal of the flux residue, if necessary.

For-2013 (IES, GATE & PSUs) Page 61

ld lSolder Metals

Most solders are alloys of lead and tin.

Three commonly used alloys contain 60, 50, and 40%

tin and all melt below 240°C.

Contd…

Solder FluxAmmonium chloride or rosin for soldering tin

Hydrochloric acid and zinc chloride for soldering

l i d igalvanized iron

S fl i d h ld b d ftSome fluxes are corrosive and should be removed after

useuse

Silver solders uses for higher temperature serviceSilver solders uses for higher‐temperature service,Electrical and Electronic purpose.

Difficulties with Grey Cast IronDifficulties with Grey Cast IronS ld i d b i diffi lt f t I dSoldering and brazing are difficult of grey cast Iron due

to surface contamination with graphite having a very lowto surface contamination with graphite having a very low

surface energy.gy

IES‐1994Match List ‐ I with List ‐ II and select the correct answer using the codes given below the Lists:g gList ‐ I (Filler)  List ‐ II (Joining process)A. Cu, Zn, Ag alloy  1. Braze welding.A. Cu, Zn, Ag alloy  1. Braze welding.B. Cu, Sn, alloy  2. BrazingC Pb  Sb  alloy  3 SolderingC. Pb, Sb, alloy  3. SolderingD.Iron oxide and aluminium powder 4. TIG welding of 

aluminiumaluminiumCodes:A B C  D A B  C  D(a)  2  1  3  ‐ (b)  1  2  4 ‐(a)  2  1  3  (b)  1  2  4(c)  2  1  3  4  (d)  2 ‐ 3 4

IAS‐1996Match List I with List II and select the correct answer using the codes given below the listsgList –I List‐II(Filler rod material)  (Joining process)A. Mild steel 1. MIG weldingB. Bronze  2. SolderingC. Brass  3. BrazingD. Lead and tin alloy  4. Thermit welding

B   ldi5. Braze weldingCodes:A B C D A B C D(a)  1  5 3 2 (b) 4  3  2 5(a)  1  5 3 2 (b) 4  3  2 5(c)  4  3  5 2 (d)  1 3 5 4

Welding design and defectWelding Problem Causes

Cracking of weld metal High joint rigidityCracking of weld metal High joint rigidityCracking of base metal Excessive stressesSpatter Arc blowSpatter Arc blowDistortion Poor joint selectionSlag inclusion Improper cleaning in multi-Slag inclusion Improper cleaning in multi

pass weldingPorosity Excessive H O N in the Porosity Excessive H2, O2, N2, in the

welding atmosphere or Damp electrodeselectrodes

Lamellar Tearing inclusions such as Mn Fe and S in the base metal and/or in the base metal and/or residual stress

IES‐2004Match List I (Welding problems) with List II (Causes) and select the correct answer using the codes given below the Lists:List I List IIA. Cracking of weld metal 1. Excessive stressesB C ki   f b   t l Hi h j i t  i iditB. Cracking of base metal 2. High joint rigidityC. Porosity 3. Failure to remove slag 

from previous depositp pD. Inclusions 4. Oxidation

5. Excessive H2, O2, N2, in h    ldi   hthe  welding atmosphere

Codes:A B C  D A B C D(a)  2  1  5  3  (b)  3  4  2  1(a)  2  1  5  3  (b)  3  4  2  1(c)  2  4  5  3  (d)  3  1  4  2

IES‐2003, ISRO‐2011Match List I(Welding Defects) with List  II (Causes) and select the correct answer using the codes given below the g gLists:List‐I List II( ldi f ) ( )(Welding Defects) (Causes)A. Spatter 1. Damp electrodesB Di i A  blB. Distortion 2. Arc blowC. Slag inclusion 3. Improper cleaning in 

multi‐pass weldingmulti‐pass weldingD. Porosity 4. Poor joint selectionCodes:A B C D A B C DCodes:A B C D A B C D(a)  4 2 3 1 (b)  4 2 1 3(c)  2 4 1 3 (d)  2 4 3 1(c)  2 4 1 3 (d)  2 4 3 1

For-2013 (IES, GATE & PSUs) Page 62

CracksCracks may be of micro or macro size and may appear inCracks may be of micro or macro size and may appear inthe weld metal or base metal or base metal and weld

t l b dmetal boundary.Different categories of cracks are longitudinal cracks,g gtransverse cracks or radiating/star cracks and cracks inthe weld crater.the weld crater.Cracks occur when localized stresses exceed the ultimatet il t th f t i ltensile strength of material.These stresses are developed due to shrinkage duringp g gsolidification of weld metal.

Cracks may be developed due to poor ductility of basemetal, high sulphur and carbon contents, high arc travelspeeds i.e. fast cooling rates, too concave or convex weldp gbead and high hydrogen contents in the weld metal.

Fig  Various Types of Cracks in WeldsFig. Various Types of Cracks in Welds

HAZ CrackingHAZ CrackingCracking in heat affected zone may be caused by:Cracking in heat affected zone may be caused by:

(i) Hydrogen in welding atmosphere(i) Hydrogen in welding atmosphere

(ii) hot cracking(ii) hot cracking

(iii) low ductility(iii) low ductility

(iv) high residual stresses(iv) high residual stresses

(v) brittle phase in the microstructure( ) p

Hydrogen Induced CrackingHydrogen Induced CrackingDue to the presence of moisture, grease, rust etc., ue to t e p ese ce o o stu e, g ease, ust etc.,hydrogen may enter the weld pool and get dissolved in the weld metal  the weld metal. During cooling hydrogen diffuses to the HAZ.Cracking may develop due to residual stresses assisted by hydrogen coalesence.hydrogen coalesence.The factors that determine the probability of hydrogen i d d  b ittl t  d  ki   f  ld induced embrittlement and cracking of weld are:

(a) Hydrogen content( ) y g(b) fracture toughness of weld and HAZ( )      hi h  h  j i  i   d      l   f (c) stress to which the joint is exposed as a result of the weld thermal cycle.

Residual stressThe residual stresses result from the restrained expansionand contraction that occur during localized heating andcooling in the region of weld deposit.The magnitude of residual stresses depends on the weldmentThe magnitude of residual stresses depends on the weldmentdesign, support and clamping of the components beingwelded their materials welding process used partwelded, their materials, welding process used, partdimensions, welding sequence, post weld treatment, size ofthe deposited weld beads etcthe deposited weld beads, etc.Residual stresses should not have a harmful effect on the

h f f ld d f istrength performance of weldments, reduces fatiguestrength, May cause distortion. This residual stress may

l h k f b l l dresult in the cracking of a brittle material and is notimportant as far as a ductile material.

PorosityP i l h h d i hPorosity results when the gases are entrapped in thesolidifying weld metal.These gases are generated from the flux or coatingconstituents of the electrode or shielding gases usedconstituents of the electrode or shielding gases usedduring welding or from absorbed moisture in thecoatingcoating.Porosity can also be controlled if excessively highwelding currents, faster welding speeds and long arclengths are avoided flux and coated electrodes arelengths are avoided flux and coated electrodes areproperly baked.

Fig. Different Forms of PorositiesFig. Different Forms of Porosities

Solid InclusionSolid InclusionSolid inclusions may be in the form of slag or any othernonmetallic material entrapped in the weld metal asthese may not able to float on the surface of theysolidifying weld metal.During arc welding flux either in the form of granules orDuring arc welding flux either in the form of granules orcoating after melting, reacts with the molten weld metal

i id d h i i i i h f f lremoving oxides and other impurities in the form of slagand it floats on the surface of weld metal due to its lowdensity.Slag inclusion can be prevented if proper groove isSlag inclusion can be prevented if proper groove isselected, all the slag from the previously deposited beadis removed too high or too low welding currents andis removed, too high or too low welding currents andlong arcs are avoided.For-2013 (IES, GATE & PSUs) Page 63

Fig  Slag Inclusion in WeldmentsFig. Slag Inclusion in Weldments

Lack of FusionLack of FusionLack of fusion is the failure to fuse together either theac o us o s t e a u e to use toget e e t e t ebase metal and weld metal or subsequent beads inmultipass welding because of failure to raise themultipass welding because of failure to raise thetemperature of base metal or previously deposited weldl t lti i t d i ldilayer to melting point during welding.Lack of fusion can be avoided by properly cleaning ofy p p y gsurfaces to be welded, selecting proper current, properwelding technique and correct size of electrode.welding technique and correct size of electrode.

Incomplete PenetrationI l i h h ld d h iIncomplete penetration means that the weld depth is notupto the desired level or root faces have not reached tomelting point in a groove joint.If either low currents or larger arc lengths or large rootIf either low currents or larger arc lengths or large rootface or small root gap or too narrow groove angles areused then it results into poor penetrationused then it results into poor penetration.

Imperfect Shape, Distortionsp p ,Imperfect shape means the variation from the desired shape andsize of the weld bead.size of the weld bead.During undercutting a notch is formed either on one side of theweld bead or both sides in which stresses tend to concentrate andit can result in the early failure of the joint. Main reasons forundercutting are the excessive welding currents, long arc lengths

d f l dand fast travel speeds.Underfilling may be due to low currents, fast travel speeds and

ll i f l d O l d lsmall size of electrodes. Overlap may occur due to low currents,longer arc lengths and slower welding speeds.E i i f t i f d if hi h t l ltExcessive reinforcement is formed if high currents, low voltages,slow travel speeds and large size electrodes are used. Excessiveroot penetration and sag occur if excessive high currents and slowroot penetration and sag occur if excessive high currents and slowtravel speeds are used for relatively thinner members.Distortion is caused because of shrinkage occurring due to largeDistortion is caused because of shrinkage occurring due to largeheat input during welding.

lIES 2011 ConventionalE  f  d f   d d     id l   i  Enumerate four defects caused due to residual stresses in welded joints.

[2 Marks]

Ans. 

1. Distortion

2. Cracking in the base metal

3. Lamellar Tearing

4. Reduction of fatigue strength

IES‐2004Consider the following statements:The magnitude of residual stresses in weldingThe magnitude of residual stresses in weldingdepends upon

D i   f  ld t1. Design of weldment2. Support and clamping of components3. welding process used4. Amount of metal melted / deposited4 pWhich of the statements given above are correct?(a) 1  2 and 4 (b) 1  2 and 3(a) 1, 2 and 4 (b) 1, 2 and 3(c) 1 and 3 (d) 2 and 3

GATE‐2003Match the followingWork material Type of joiningyp j gP. Aluminium 1. Submerged Arc WeldingQ. Die Steel 2. SolderingR. Copper Wire 3. ThermitWeldingS. Titanium sheet 4. Atomic Hydrogen Welding

5. Gas Tungsten Arc Welding6. Laser Beam Welding7. Brazing

(a) P ‐ 2   Q ‐ 5   R ‐ 1  S ‐ 3(b) P ‐ 6 Q ‐ 3  R ‐ 4   S ‐ 4(c) P ‐ 4 Q‐ 1   R ‐ 6   S ‐ 2(d)(d) P ‐ 5   Q ‐ 4 R ‐ 2  S ‐ 6

For-2013 (IES, GATE & PSUs) Page 64

IES‐2004Consider the following statements:Th   i   f  h  h   ff d   (HAZ)  ill i   i hThe size of the heat affected zone (HAZ) will increase with1. Increased starting temperatureg p2. Increased welding speed3 Increased thermal conductivity of the base metal3. Increased thermal conductivity of the base metal4. Increase in base metal thicknessWhich of the statements given above are correct?(a) 1, 2 and 3 (b) 1 and 3(a) 1, 2 and 3 (b) 1 and 3(c) 1 and 4  (d) 2 and 3

IES‐1992Weld spatter occurs due to any of the following 

texcept(a) High welding current( ) g g(b) Too small an electrode( ) A(c) Arc(d) Wrong polarity( ) g p y

JWM 2010Assertion (A) : Spatter is one of thewelding defectsAssertion (A) : Spatter is one of thewelding defects.Reason (R) : In submerged arc welding process,there is no spatter of molten metal.(a) Both A and R are individually true and R is the(a) Both A and R are individually true and R is thecorrect explanation of A(b) h d d d ll b h(b) Both A and R are individually true but R is not the

correct explanation of Ap(c) A is true but R is false(d) A i f l b t R i t(d) A is false but R is true

IES‐1998An arc welded joint is shown in the above figure. Th   t l b ll d 'B' i  th  fi  i  k  The part labelled 'B' in the figure is known as(a) Weld preparation ( ) p p(b) Penetration ( ) R i f  (c) Reinforcement (d) Slag( ) g

IES‐2004Assertion (A): A sound welded joint should not onlybe strong enough but should also exhibits a goodbe strong enough but should also exhibits a goodamount of ductilityReason (R): Welding process is used for fabricatingReason (R): Welding process is used for fabricatingmild steel components only(a) Both A and R are individually true and R is the correct(a) Both A and R are individually true and R is the correct

explanation of A(b) B th A d R i di id ll t b t R i t th(b) Both A and R are individually true but R is not the

correct explanation of A( ) A i t b t R i f l(c) A is true but R is false(d) A is false but R is true

IAS‐2003Tool material not suited to resistance welding is

(a) Aluminium oxide (b) Stellite( ) ( )(c) High speed steel (d) Masonite

GATE‐1996Preheating before welding is done to( ) M k   h   l  f(a) Make the steel softer(b) Bum away oil, grease, etc, from the plate surface( ) y , g , , p(c) Prevent cold cracks(d) P   l  di i(d) Prevent plate distortion

IES 2011Cold‐cracking in steel weldments depends on

1  Carbon equivalent1. Carbon equivalent2. Heat input3. Effective thickness3  Hydrogen content in weld pool3. Hydrogen content in weld pool

(a) 1, 2 and 3 only(b) 1, 2 and 4 only(c) 2  3 and 4 only(c) 2, 3 and 4 only(d) 1, 2, 3 and 4

GATE‐2001Two plates of the same metal having equalthickness are to be butt welded with electric arcthickness are to be butt welded with electric arc.When the plate thickness changes, welding is

hi d bachieved by(a) Adjusting the current( ) j g(b) Adjusting the duration of current( ) Ch i h l d i(c) Changing the electrode size(d) Changing the electrode coating( ) g g g

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IES ‐ 2012B i l ld i l b i d dBrittle welds are mainly obtained due to(a) Wrong electrode, faulty preheating and metal( ) g , y p ghardened by air(b) Faulty welds faulty sequence and rigid joints(b) Faulty welds, faulty sequence and rigid joints(c) Wrong speed, current improperly adjusted and faultypreparation(d) Uneven heat improper sequence and deposited(d) Uneven heat, improper sequence and depositedmetal shrinks

IES ‐ 2012Whi h  f  h  f ll i     i d  i h H  Aff d Which of the following are associated with Heat Affected Zone?1. Cold cracking2  Notch toughness2. Notch toughness3. Hydrogen embrittlement4. Stress corrosion cracking( )      d    l(a) 1, 2 and 3 only(b) 1, 3 and 4 only y(c) 2, 3 and 4 only (d)        d (d) 1, 2, 3 and 4

IES ‐ 2012St t t (I) H d i d d ki i th h tStatement (I): Hydrogen induced cracking occurs in the heateffected zone adjacent to fusion zone and classified as solidstate crackingstate crackingStatement (II):Hydrogen from burning of flux coatingpenetrates martensitic micro cracks preventing healing aspenetrates martensitic micro cracks preventing healing aswell as enlarging them.( ) B th St t t (I) d St t t (II) i di id ll(a) Both Statement (I) and Statement (II) are individuallytrue and Statement (II) is the correct explanation ofStatement (I)Statement (I)(b) Both Statement (I) and Statement (II) are individuallyt b t St t t (II) i t th t l ti ftrue but Statement (II) is not the correct explanation ofStatement (I)( ) S (I) i b S (II) i f l(c) Statement (I) is true but Statement (II) is false(d) Statement (I) is false but Statement (II) is true

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