A STUDY ON CASTING

METHODOLOGY AND DEFECTS

OF STEEL CASTINGS

AT PEEKAY STEELS Pvt. Ltd

PRESENTED BY

AKHIL VAS (404)

AKHIL NATH R (406)

JAI SHANKER S (427)

ASISH JO MATHEW (415)

GUIDED BY

SHAJAN S

ASSISTANT PROFESSOR

SCTCE

1

CONTENTS

• OBJECTIVE OF STUDY

• INTRODUCTION TO CASTING

• METHODOLOGY

• PHASE 1:INDUSTRIAL CASTING METHODOLOGY

• PHASE 2: DEFECT STUDY USING RADIOGRAPHY

TESTING

• CONCLUSIONS

• REFERENCES

2

OBJECTIVE OF STUDY

To study in depth the industrial casting methodology

adopted by Peekay steel Pvt. Ltd

To study casting defects by using radiography testing

method and find ways to minimize the defects by conducting

various experiments.

3

INTRODUCTION

•Casting is one of the oldest manufacturing processes, dates

back to 4000 B.C. when copper arrowheads were made.

•Casting processes basically involve the introduction of a

molten metal into a mold cavity, where upon solidification,

the metal takes on the shape of the mold cavity.

•Example of cast parts: frames, structural parts, machine

components, engine blocks, valves, pipes, statues, ornamental

artifacts etc.

•Casting sizes range form few mm (teeth of a zipper) to 10 m

(propellers of ocean liners).4

CASTING TERMS

5

METHODOLOGYMethodology adopted in the project work.

Stages Description Methodology adopted

STAGE 1

study of casting process

and defects.

Background study of

casting process and

defects is done basically

by referring the books and

websites.

STAGE 2

Study about Peekay steel’s

equipments and methods

used in casting process.

Information about the

company is collected

through their website and

by having a complete plant

visit.

STAGE 3

Study of the casting

methodology adopted to

produce a gate valve.

The proceedings at each

department is thoroughly

followed. The discussions

with the engineers and

other workers have

contributed much to collect

the information.

6

STAGE 4

Making of the casting

prototypes for conducting

the experiments.

With help of R&D

department the

required no. of

prototypes are made.

STAGE 5

Study of the radiography

testing devices, principle,

film processing and film

interpretation.

By referring books,

pdfs , websites and

information collected

from the NDT

department.

STAGE 5

Study of various factors

which affect certain

defects by radiography

testing.

Experiments are

conducted and defects

are analyzed using

radiography method.

Pareto charts are

plotted and results

with conclusions are

obtained.

7

PHASE 1

INDUSTRIAL CASTING

METHODOLOGY

AT PEEKAY STEEL Pvt. Ltd

8

VARIOUS DEPARTMENTS COORDINATING

THE CASTING PROCESS ARE:

METHODS AND DEVELOPMENT

PATTERN SHOP

MOULDING SHOP

MELTING DEPARTMENT

HEAT TREATMENT DEPARTMENT

FETTLING DEPARTMENT

QUALITY CONTROL

MACHINE SHOP

9

METHODS AND DEVELOPMENT•Pro - CAST Simulation software is used for the modeling of thermal

heat transfer including radiation with few factors, liquid flow, including

mold filling and also porosity modeling.

•This department also takes care of the pattern allowances, runner and

riser design, gating system design and prepares the product data sheet for

the moulding.

•The different allowances provided are:-

•Shrinkage allowance

•Draft allowance

•Machining allowance

•Shake allowance

10

GATING SYSYTEM

11

Gating system design

• The liquid metal that runs through the various channels in the

mould obeys the bernoulli’s theorem which states that the total

energy head remains constant

• Another law which is useful in understanding the gating system

behaviour is the law of continuity.

A1V1=A2V2

Goals of Gating System

• To minimize turbulence to avoid trapping gasses in the mold.

• To get enough metal into the mold cavity before the metal starts to

solidify

• To avoid shrinkage

• Incorporates a system for trapping the non-metallic inclusions12

Choke Area

•Choke area is the main control area which meters the metal flow into the

mould cavity, so that the mould is completely filled within the calculated

pouring time.

•the choke area happens to be at the bottom of the sprue and hence, the first

element to be designed in the gating system is the sprue size and its

proportions.

•Choke area = W

dtc(2gh)1/2

Where A = choke area, mm2

W = casting mass, kg

t = pouring time, s

d = mass density of the molten metal, kg/mm3

g = acceleration due to gravity, mm/s2

H = effective metal head (sprue height),

C = efficiency factor which is a function of the gating system.

13

Efficiency coefficients, C for various types of gating systems

effective sprue height ,H

14

Sprue

•Sprue is the channel through which the molten metal is brought into the

parting plane, where it enters the runners and gates to ultimately reach the

mould cavity.

•The molten metal when moving from top of the cope to the parting plane

gains in velocity, and as a consequence, requires a smaller area of cross

section for the same amount of metal to flow at the top.

•If the sprue were to be straight-cylindrical then the metal flow would not

be full at the bottom, but some low-pressure area would be created around

the metal in the sprue.

•Since the sand mould is permeable, atmospheric air would be breathed into

this low-pressure area, which would then be carried to the mould cavity.

•To eliminate this problem of air aspiration, the sprue is tapered to gradually

reduce the cross section as it moves away from the top of the cope.

15

•The exact tapering can be obtained by the equation of continuity.

Denoting the top and choke sections of the sprue by the subscripts t and c

respectively, we get:

AtVt = AcVc

At = AcVc

Vt

16

Runner and riser design•The gating ratio refer to the proportion of the cross-sectional areas

between the sprue, runner and in-gates, and is generally denoted as

sprue area : runner area : and in-gate area.

•By assuming a gating ratio say 1:2:1 the runner area is obtained.

•RISER diameter is six times modulus of cast

•Modulus of cast is the ratio of volume to surface area

17

PATTERN SHOP•This department works in close relation with the methods and development

dept.

•They receive the pattern design with all the allowances ,and modifications

to be made in the existing pattern.

•The pattern is then made accordingly using mainly teak wood ,it is finished

and coated with aluminium paint to avoid contact of wood with moisture.

•The chill positions are identified and marked with black paint as several

cross marks in a square.

•Different types of patterns generally used are:

i. Single piece pattern

ii. Split pattern

iii. Match plate pattern

iv. Loose piece pattern

v. Sweep pattern and skeleton pattern

18

Pattern materials•The usual pattern materials are wood, metal and plastics.

•The most commonly used pattern material for very large castings is wood,

the main reason being the easy availability and the low weight, it can be easily

shaped and is relatively cheap.

•The main disadvantage of wood is its absorption of moisture as a result of

which distortions and dimensional changes occur.

•Because of their durability and smooth surface finish, metal patterns are

extensively used for large-scale casting production and for closer dimensional

tolerances.

•Though many materials such as cast iron, brass etc. can be used as pattern

materials, aluminium and white metal are most commonly used.

19

MOULDING SHOP•A large variety of moulding materials are used in foundries for

manufacturing moulds and cores. They are:

a) moulding sand

b) system sand (backing sand)

c) rebonded sand

d) facing sand

e) parting sand

f) core sand.

•The properties that are generally required in moulding materials are the

following:

a) Refractoriness

b) Green strength

c) Dry strength

d) Hot strength

e) Permeability

f) Collapsibility

g) Adhesiveness

h) Cohesiveness

20

MOULDING SAND COMPOSITION

•The main ingredients are :

a) Silica grains (SiO2)

b) Clay as binder

c) Moisture to activate the clay and provide

plasticity.Sand preparation•For the uniform mixing of various sand ingriedients mullers are normally

used.

•Two types are : batch type and continuous type.

•A batch muller consists of one or two muller wheels and equal number of

plough blades, all of them connected to a single driving source.

•A continuous muller consists of two bowls with wheels and ploughs, such

that sand, clay, and moisture are fed through a hopper into one of the

bowls which after getting mulled moves into the second one and then

finally out.

21

MOULD MAKING PROCEDURE

No bake Moulding Process

•No bake is a casting process that involves the use of chemical binders (furan

or urethane) to bond the moulding sand in place of clay, which is normally

used in green-sand moulding.

•APNB (Alkaline Phenolic No Bake) moulding process is employed.

•A mixer is then used to thoroughly blend the sand with the chemical binder

and a catalyst.

•The chemical-mixed sand is then poured into the moulding flask fitted with

the cope/drag-pattern plate that is complete with the necessary gating and

risering system as designed.

•Each mould half is then compacted to form a strong and dense mould.22

•After a specified period of time (usually 3 to 6 hrs depending upon mould

size) the sand mixture hardens to form the mould halves and the cope/drag-

pattern plates are removed.

•Cores can also be made using the same process.

•After the sand has set, a mould-wash may be applied.

•The cores are set into the drag and the cope is closed over the cores to

complete the mould.

ADVANTAGES

Possibility for reclamation of used sand and control on bench life and strip

time of mixed sand went in favor of the system.

good dimensional tolerances (± 0.125–0.375 mm) because of the high

strength of the mould.

No bake mould can withstand the pressure exerted by the molten metal

during casting. 23

24

MELTING DEPARTMENT

•Electric induction furnaces are used.

•Scrap & other melting components of the highest

quality are made use of.

•Within the furnace there is a coil of copper tubings.

•AC current is passed through the coil and an em field

is produced which induces an electric current in the

scrap metal.

•This induced electric current heats up the metal and thus molten metal is

obtained.

•Heating temp. can be adjusted by adjusting the frequency of induction furnace

•Method of Pouring: Lip Pouring and Bottom Pouring.25

AOD (ARGON OXYGEN DECARBURIZATION)

•Stainless steel refining process.

•In AOD process first scrap metal is melted in the furnace. It is then

poured to AOD vessel where it is decarburized and refined.

•Oxygen for decarburization is mixed with argon or nitrogen inert gasses.

•Argon dilution minimizes the oxidation of valuable elements like

chromium

26

Degasification process•It is the process of removing dissolved hydrogen from the molten metal.

•dissolved hydrogen creates porosity.

•The inert gas when purged through the melt collects the soluble

hydrogen atoms, allowing a hydrogen molecule to form inside the lower

pressure of the collector gas bubble.

•As these bubbles break, aluminium is lost to oxidation by the furnace

gases and entrapment in dross.

HEAT TREATMENT• ANNEALING is a generic term

denoting a treatment that consists of

heating to and holding at a suitable

temperature.

• It is followed by cooling at an

appropriate rate, primarily for the

softening of metallic materials.

• Steels may be annealed to facilitate

cold working or machining, to improve

mechanical or electrical properties, or

to promote dimensional stability.

• In plain carbon steels,

annealing produces a ferrite-pearlite

microstructure . 27

• QUENCHING refers to the process of rapidly cooling metal parts

from the austenite structure or solution treating temperature.

• It lies within the range of 815 to 870 °C (1500 to 1600 °F) for steel.

• Stainless and high-alloy steels may be quenched to minimize the

presence of grain boundary carbides or to improve the ferrite

distribution.

• But most steels including carbon, low-alloy, and tool steels, are

quenched to produce controlled amounts of martensite in the

microstructure.

28

FETTLING• It is the complete process of the

cleaning of the casting.

• It involves removal of the cores ,

gates,risers,cleaning of the cast

surface and chipping of any of the

unnecessary projections on the

surfaces.

• Core can be removed simply by

knocking of it with an iron bar or

by means of a cone vibrator.

• Gates and risers can be removed by hammering, chipping, hack

sawing, or by flame or arc cutting.

• Fins and other small projections can be removed by means of hand

tools

29

SHOT BLASTING

• Shot blasting is a method used to clean, strengthen (peen) or polish

metal.

• Shot blasting is used in almost every industry that uses metal, including

aerospace, automotive, construction, foundry, shipbuilding, rail, and

many others.

• Centrifugal wheel blasting is the more common blast cleaning

technique as well as the most economical and environmentally friendly

method.

• The turbine delivers abrasive shot by centrifugal force in a specific and

controlled direction, speed and quantity.

• Shot blasting machines may use one or a multitude of turbines

positioned in such a way that the abrasive blast pattern covers the entire

surface of the material to be shot cleaned.

30

QUALITY CONTROL•The properties of the casting are

studied in order to determine the

soundness of the casting.

•Also it is the duty of this dept. to

ensure that the casting is within the

quality specifications of the customer.

• two types of test are conducted :

Destructive and nondestructive

testing.•Destructive testing involves: hardness test, tensile

strength test etc.

•Non destructive involves : Visual and Optical Testing

(VT), Magnetic Particle Testing (MT) , Electromagnetic

Testing (ET) or Eddy Current Testing, Radiography (RT) ,

Ultrasonic Testing (UT). 31

MACHINE SHOP

•The final finishing is done in this dept.

•Several high tech equipments like CNCs,

LECO gas analyser, hydro analyser etc. with

High capacity to machine parts upto 20 T.

32

PHASE 2

DEFECT STUDY USING

RADIOGRAPHY TESTING

33

RADIOGRAPHY

• Radiography today is one of the most important, most

versatile, of all the non-destructive test methods used by

modern industry.

• Employing highly penetrating x-rays, gamma rays, and other

forms of radiation that do not damage the part itself.

• It is equally apparent in cost reductions. And it is found be in

a value such that it is profitable for the user.

• Objects radiographed range in size from micro miniature

electronic parts to mammoth missile components.

34

PRINCIPLE OF RADIOGRAPHY

35

RADIOGRAPHY TESTING

MACHINE

30 Ci / Item No:ENK-IRS-024

•Iridium-192 sources are constructed using iridium metal discs or

pellets confined within welded stainless steel capsule.

•Cobalt-60 sources are constructed using compression fused cobalt

metal pellets confined within welded titanium and stainless steel

capsules.

36

TESTING PROCESS

• A radiograph is a photographic record produced by the passage of x-rays

or gamma rays through an object onto a film.

• When film is exposed to gamma rays, an invisible change called a latent

image is produced in the film emulsion.

• The areas so exposed become dark when the film is immersed in a

developing solution, the degree of darkening depending on the amount of

exposure.

• After development, the film is rinsed, preferably in a special bath, to stop

development.

• The film is next put into a fixing bath, which dissolves the undarkened

portions of the sensitive salt. It is then washed to remove the fixer and

dried so that it may be handled, interpreted, and filed either manually or

automatically. 37

CASTING DEFECTSMost common casting defects are:

1. Blow holes and open blows

2. Air inclusions

3. Shrinkage

4. Cavities

5. Hot tears

6. Sand inclusions

7. Mis runs and cold shuts

8. Metal penatration

38

Radiographic Interpretation of Casting Defects

o Gas porosity or blow holes are

caused by accumulated gas or air

which is trapped by the metal.

o These discontinuities are usually

smooth-walled rounded cavities of a

spherical, elongated or flattened

shape.

o If the sprue is not high enough to

provide the necessary heat transfer

needed to force the gas or air out of

the mold, the gas or air will be trapped

as the molten metal begins to solidify.

o Blows can also be caused by sand

that is too fine, too wet, or by sand

that has a low permeability so that gas

cannot escape..

39

o Sand inclusions and dross are

nonmetallic oxides, which appear

on the radiograph as irregular,

dark blotches.

o These come from disintegrated

portions of mold or core walls

and/or from oxides (formed in

the melt) which have not been

skimmed off prior to the

introduction of the metal into the

mold gates

.

40

shrinkage

o Shrinkage is a form of discontinuity

that appears as dark spots on the

radiograph.

o Shrinkage assumes various forms, but

in all cases it occurs because molten

metal shrinks as it solidifies, in all

portions of the final casting.

o Shrinkage is avoided by making sure

that the volume of the casting is

adequately fed by risers which

sacrificially retain the shrinkage.

o There are at least four types of

shrinkage: (1) cavity; (2) dendritic; (3)

filamentary; and (4) sponge types.

Some documents designate these types

by numbers, without actual names, to

avoid possible misunderstanding

41

cracks

42

Cracks are thin (straight or jagged) linearly disposed discontinuities that occur after the melt has solidified. They generally appear singly and originate at casting surfaces.

DEFECT ANALYSIS USING

RADIOGRAPHIC TESTING

• The experiment is conducted on a prototype of a gate valve.

• The material used is ASTMA 995/CD3MWCuN .

• Its composition as obtained from sparks spectroscopy test is shown in the table..

Carbon 0.027%

Manganese 0.9%

Silicon 0.87%

Phosphorus 0.029%

Sulfur 0.026%

Nickel 7.2%

Chromium 24.3%

Molybdenum 3.7%

Copper 0.7%

Tungsten 0.69%

Nitrogen 0.28%

43

44

45

CASTING DEFECT ANALYSIS ON A

RANGE OF POURING TEMPERATURE

• Aim: To create three casting models poured at three

temperatures(1560,1590,1620)and to conduct RT defect

analysis of the same.

• Materials required:cope,drag,rand York chromite

grade4B_60B,runner,riser,muller,binder,hardner(h740,h8

00),patern,core,chaplets,induction furnace, radiographic

testing machine, radiographic film.

46

• Procedure: Required mould is created by following APNB method. The molten metal is poured into the mould at three different temperatures and the prototypes are created.This prototypes are tested with radiographic technique and the result are find out and recorded.

OBSERVATIONS:

47

48

49

INFERENCE

• Air inclusions increases with increase in pouring temperature

because as the pouring temp increases the air aspiration of the molten

metal is also increased as more voids are created as temp increases.

• Shrinkage defects shows a narrow decrease as the pouring temp

increases because as temp increases viscosity of the fluid is

decreased which results in increase in fluidity. As fluidity increases

the rate of compensation of the metal from the riser to the mold

cavity increases

• It is observed that there is a drastic increase in the total defect as

temp is increased, so an optimum pouring temp is to be found out to

reduce casting defects

DEFECT ANALYSIS ON A CAST WHICH IS MANUFACTURED WITHOUT

PERFORMING DEGASIFICATION

• Aim: To create a casting models ,which is manufactured without performing de gasificaton and to conduct RT defect analysis of the same

• Materials required:cope,drag,rand York chromate grade4B_60B,runner,riser,muller,resin,binder(h740,h800),pattern,core,chaplets,induction furnace, radiographic testing machine, radiographic film.

Procedure: Required mould is created by following APNB method. The molten metal is poured into the mould without performing AOD and the prototype is created.This prototype is tested with radiographic technique and the result is found out and recorded.

OBSERVATION:

52

53

INFERENCE

• Air inclusions increases as the model is prepared without degasification. Due to the presence of gases such as hydrogen which inhibits air inclusions.

• Presence of cracks is also an effect of lack of degasification.

DEFECT ANALYSIS ON CAST WHICH IS RAPIDLY COOLED

• Aim:To create a casting model and to conduct chilling of the model, and to conduct RT defect analysis of the same

• Materials required:cope,drag,rand york chromite grade4B_60B,runner,riser,muller,resin,binder(h740,h800),patern,core,chaplets,induction furnace,radiographic testing machine,radiographic film.

55

Procedure: Required mould is created by following APNB method. The molten metal is poured into the mould and the prototype is created.The model is then chilled using a pressurised air blower.This prototype is tested with radiographic technique and the result is found out and recorded

OBSERVATIONS:

56

57

INFERENCE

• Due to rapid cooling there is an increase in the no of

voids as a result an increase in air inclusion is observed.

• Due to its fine grain structure there is an increase in its

shrinkage.

CONCLUSION

• The pouring temperature must be made as low as

possible inoder to reduce air inclusion.but it should not

fall beyond a particular level since the metal starts to

solidify while flowing through the spure.

• It is preferred to use de gasification since it reduce the

defects considerably. And as a result it eventually reduces

defect curing cost.

• Rapid cooling is only preffered when high strength is

needed.

59

REFERENCES

60

•Blair, M., Monroe, R., Hardin, R.A., and Beckermann, C., “A New

Standard for Radiographic Acceptance Criteria for Steel Castings,” in

Proceedings of the 62nd SFSA Technical and Operating Conference,

Paper No. 5.5, Steel Founders' Society of America, Chicago, IL, 2008.

•Steel Castings Handbook Supplement 2 ,Summary of Standard

Specifications

For Steel Castings – 2009.

•CASTINGS HANDBOOK Supplement 8, High Alloy Data Sheets

Corrosion Series, Steel Founders' Society of America 2004

•Standard Reference Radiographs for Steel Castings Up to 2 in. (51 mm)

in Thickness , ASTM.

•K. SIEKAŃSKI , S BORKOWSKI, ANALYSIS OF FOUNDRY

DEFECTS AND PREVENTIVE ACTIVITIES FOR QUALITY

IMPROVEMENT OF CASTINGS,2003.