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1
Shielded Metal Arc Welding Principles
Objectives
2
1. List the percentage of usage of SMAW in the industry.
2. Name the components that make up the schematic representation of the shielded metal arc.
3. Know the maximum arc temperature of an SMAW electrode.
4. List the four constant current welding machines.
Objectives
3
5. List the common type and uses of constant current welding machines.
6. Name the power supply ratings.7. Name the characteristics of the four basic
types of welding machines.8. Choose the correct cable size based on
the application.9. List the welder’s safety equipment.
Shielded Metal Arc Welding (SMAW)
4
Manual arc welding
Also Called stick electrode welding Combustion and decomposition of electrode
creates gaseous shield
Protects electrode tip, weld puddle, arc, and highly heated work from atmospheric contamination
Heat for welding generated by electric arc established between flux covered consumable metal rod (electrode) and work
Additional shielding provided by covering of molten slag (flux)
SMAW
5
American Welding Society
Process Capability
6
Shielded metal arc welding one of most used of various electric arc welding processes
SMAW Advantages
7
Equipment less complex, more portable and less costly
Can be done indoors or outdoors, in any location and any position
Electrodes available to match properties and strength of most base metalsNot used for welding softer metalsNot as efficient in deposition
SMAW Operating Principles
8
Sets up electric circuitIncludes welding machine, work, electric
cables, electrode holder and electrodes, and a work clamp
Heat of electric arc brings work to be welded
and consumable electrode to molten stateHeat intense: as high at 9,000ºF at center
Welding Process
9
Electric arc started by striking work with electrode
Heat of arc melts electrode and surface of base metal
Tiny globules of molten metal form on tip of electrode and transferred by arc into molten pool on work surface
After weld started, arc moved along work
SMAW Operating Principle
10
American Welding Society
Welding Power Sources
11
Each type of power source has fundamental electrical differences that best suit particular processes
Welding machineMust meet changing arc load and
environmental conditions instantlyMust deliver exact amount of electric current
precisely at right time to welding arcAvailable in wide variety of types and sizes
Welding Power Sources
12
Also known as power supplies and welding machines
Two classificationsOutput slope
Whether constant current or constant voltagePower source type
TransformerTransformer rectifierInverterGenerator
Type of Output Slope
13
Two basic typesConstant current
Referred to as variable voltage
Constant voltageReferred to as constant potential
Output Slope
14
Relationship between output voltage and output current (amperage) of machine as current increased or decreasedAlso called volt ampere characteristic or
curveLargely determines how much welding
current will change for given change in load voltagePermits welding machine to control welding
heat and maintain stable arc
Output Slope
15
Indicates type and amount of electric current designed to produce
Each arc welding process has characteristic output slopeSMAW and GTAW require steep output slope
from constant current welding machineGMAW and FCAW require relatively flat
output slope from constant voltage power source
Submerged arc welding adaptable to either slop
Typical Output Slopes
16
Four Types of Power Source
17
Engine driven generatorsPowered by gas or diesel combustion engineCan be found with a.c. or d.c. electric motor
No longer being manufactured and rarely foundTransformer rectifiers
Use basic electrical transformer to step down a.c. line power voltage to a.c. welding voltage
Welding voltage then passed through rectifier to convert a.c. output to d.c. welding current
May be either d.c. or a.c. d.c. machines
Four Types of Power Source
18
A.C. transformersUsed to step down a.c. line power voltage to
a.c. welding voltageInverters
Increases frequency of incoming primary power
Constant current, constant voltage, or bothProduce a.c. or d.c. welding current
Power Sources
19
Important to select right power source for each job
Table 1 "Common types and uses of arc welding machines" should be studied
Study of job indicates whether a.c. or d.c.Shielded metal arc welding and gas tungsten
arc welding must use constant current machine
Gas metal arc prefers constant voltage machine
Constant Current Welding Machines
20
Used for shielded metal arc welding and gas tungsten arc weldingCurrent remains fairly constant regardless of
changes in arc lengthCalled drooping voltage, variable voltage, or
droopersLoad voltage decreases as welding current increases
Constant Current Output Slope
21
Constant current welding machinesSteep output slopeAvailable in both d.c. and a.c. welding
currentSteeper the slope, the smaller current
changeEnables welder to control welding current
in specific range by changing length of arc
Constant Current
Output Slope
22
Some jobs require steep volt ampere curve
Other jobs use less steep volt ampere curve
Open Circuit Voltage
23
Voltage generated by welding machine when no welding being doneMachine running idle
Arc voltage Voltage generated between electrode and
work during weldingLoad voltage
Voltage at output terminals of welding machine when arc is going
Combination of arc voltage plus voltage drop in welding circuit
Open Circuit and Arc Voltage
24
Open circuit voltage runs between 50 100 voltsDrops to arc voltage when arc struck
Arc voltagesRange: 36 volts (long arc) to 18 volts (short
arc)Determined by arc length held by welder and
type of electrode usedArc lengthened, arc voltage increases and
current decreases
Open Circuit and Arc Voltage
25
Open circuit voltage on constant current machines higher than on most constant voltage machines
Arc voltage depends on physical arc length at point of welding and controlled by welderShielded metal arc welding Gas Tungsten arc welding
Arc voltage much lower than open circuit voltage
Motor Generator Welding Machines
26
Usually supply only direct currentCan be made to supply a.c.
Most constant current typeUsed chiefly for shielded metal arc welding
and gas tungsten arc welding
Motor Generator Welding Machine
27
Hobart Brothers Co.
Sturdy steel lifting eye Large voltmeter Calibrated dial for easy,fine adjustment of heatand relation betweenvoltage and current
Outer wheel and dialfor selecting desiredwelding rangeStop button
Motor Generator Welding Machine
28
Hobart Brothers Co.
Ground cable connector Optional steel guard
Heavy duty ball bearings
Pressed steel bearing cap
Arc welded copper squirrel cage rotor
Motor stator
Heavy steel fan
Motor Generator Welding Machine
29
Hobart Brothers Co.
Steel frame
Fourpole "Multi Range" generator
Large commutator
Heavy duty metallic graphite brushes
Heavy duty ball bearings
Pressed steel bearing cap
Arc welded steel frame
Motor Generator Welding Machine
30
Hobart Brothers Co.
Removable steel covers
Heavy duty single unit steel shaft
Polarity switch
Welding cable connector
Large ammeter
Steel turret top with removable cover
Motor Generator Welding Machine for SMAW
31
The Lincoln Co.
Variablevoltagecontrol
Instruction on the Name plate
Polarity switch
Current control
Toggle switch
Constantvoltage
External Construction of d.c. Motor Generator Welding Machine
32
The Lincoln Electric Co.
Internal Construction of a D.C. Motor Generator Welding Machine
33
The Lincoln Electric Co.
Motor Generator Desirable Characteristics
34
Have forceful penetrating arcVersatile
Can be used to weld all metals that are weldable by arc process
FlexibleWith proper electrode, can be used in all
positionsDurable and have long machine life
Generators
35
Classified by type of motor that drives generator
Consists of a.c. motor, d.c. generator, and exciter built on single shaft
Miller Electric Mfg. Co. The Lincoln Electric Co.
Generators used in the field
Sizes
36
Determined on basis of amperageRange
100 ampere rated for home 1,500 ampere rated for use with automatic
submerged arc welding equipmentManual welding machine idle sometimesAutomatic power supply units 100% duty
cycleShould not be used at or beyond max over
extended period
Maintenance
37
Contacts of starter switch and control rheostat should be inspected, cleaned frequently and replaced when necessary
Brushes need frequent inspection for wearCheck commutator for wear or burning
Rewound and turned on latheMain bearings on shaft inspected and
greased at each 6 month periodClean old grease out of bearing housings
Start and Stop Buttons
38
Purpose of starting and stopping the motorStart button blackStop button redImportant buttons be engaged firmly
Polarity Switch
39
Electrode negative and electrode positive used in d.c. welding
DCEN (d.c. electrode negative)Electrode connected to negative terminal of
power source and work connected to positive terminal
DCEP (d.c. electrode positive)Electrode connected to positive terminal of
power source and work connected to negative terminal
Switch changes to either electrode positive or electrode negative
Volt Ampere Meters
40
Sometimes serve dual purposeCan indicate polarity as well as currentOthers, individual meters for volts and
amperesSome, single meter that indicates both volts
and amperesButton engaged to get individual readingsWould need second person for monitoring
Increased demand for additional devices so meters have been discontinued by some manufacturers
Current Controls
41
AmperageQuantity of currentDetermines amount of heat produced at weld
VoltageMeasure of force of currentDetermines ability to strike an arc and
maintain its consistencyTwo types of dual control generators
Tapped step current controlContinuously variable current control
Dual Tapped Current Control
42
Coarse adjustment dial selects current rangeCalled steps or tapsImpossible to secure current value between two
steps by setting dial between themFine adjustment dial trims current between steps
Whether set high or low depends on type and size of electrode, thickness of metal, soft or digging arc required, arc starting, restricting characteristics, and Position of welding
Dual Continuous Control
43
Coarse adjustment dial continuously adjusts current
Fine dial adjusts both current(amperage) and open circuit voltageOperator adjusts output slope for given current
setting by manipulating both coarse and fine adjustment dials together
Wheel or knob on both amperage and voltage setting devices gives welder continuous control of both
Engine Driven Generator
44
Miller Electric Mfg. Co.
Miller Electric Mfg. Co.
Capable of SMAW, GTAW,SMAW, FCAW and PAC.
Remote Control
45
Welding machines may be installed in remote part of plant
Welder may adjust current without leaving job
Timesaving on workWelder does not have to leave fabrication to
readjust current
Air Filters
46
Wear in arc welding machines costlyCost of replacement parts and laborLoss of production due to nonuse of machine
Bearing wear criticalMay be reduced through use of air filter fitted
on suction end of motor generator machineFilter cleaned regularly
High pressure air, commercial solvent or steam
D.C. Transformer Rectifier Welding Machines
47
Have many designs and purposesFlexibility one reason for wide acceptance
Deliver either DCEN or DCEPMay be used for:
Stick electrode weldingGas tungsten arc weldingSubmerged arc weldingMulti operator systemsStud welding
The Lincoln Electric Co.
Miller Electric Mfg. Co.
Transformer Rectifier Machines
48
Have two basic partsTransformer for producing and regulating
alternating current that enters machinerectifier that converts a.c. to d.c.
Third important part is ventilating fanKeeps rectifier from overheating
Design improves arc stability and makes it easy to hold short arc which is soft and steady
No major rotating parts so consume little power
A.C. D.C. Transformer Rectifier Welding Machines
49
Permit welder to select either a.c. or d.c. and electrode negative or electrode positive
SwitchPermits welder to use only transformer part of
machine for a.c. weldingFlipping switch then output current directed
through rectifier which converts it to d.c. welding High frequency arc starting devices, water/gas
flow controls, balance controls for a.c. operation, remote control often built into machine
A.C. D.C. Transformer Rectifier Welding Machines
50
The Lincoln Electric Co.
The Lincoln Electric Co.
Miller Electric Mfg. Co.
A 300 amp a.c. d.c.GTAW/SMAW
machine.Portable SMAW/GTAW
welding machine
A 300 amp modelshown in use
A.C. Transformer Welding Machines
51
Most popular a.c. welding machineFunction of transformer
Step down high voltage of input current to high amperage, low voltage current required for welding
Especially suitedfor heavy work
The Lincoln Electric Co.Miller Electric Mfg. Co
Advantages of a.c. Power Sources
52
Reduces tendency to arc blowCan use larger electrodes
Resulting in faster speeds on heavy materialsLower costDecreased power consumptionHigh overall electrical efficiencyNoiseless operationReduced maintenance
D.C. and A.C. D.C. Inverter Welding Machines
53
Portable, lightweight, and versatileMay be either constant current, constant
voltage or bothCan perform several different processes
Miller electric Mfg. Co.The Lincoln Electric Co.
Cost Comparisons: Arc Power Sources
54
Three main areas Cost of purchasing equipment (nearly equal)Operating efficiency
Motor generator machine: 52 65%Transformer rectifiers: 64 72%Inverters: 85%
MaintenanceMotor generator machine: replacing parts, lubricationTransformer rectifiers and inverters have no moving parts
Multiple Operator Systems
55
Can be installed away from work site and be connected to control panels close to welding operator
When using direct current, all welders must weld with same polarity
Miller Electric Mfg. Co.
• Most installations are d.c.• Power: 600 2,500 amperes• Cost less, saves space and
cable, lowers operating cost
Power Supply Ratings
56
Standards set The National Electrical manufacturers
AssociationOccupational Safety and Health
AdministrationProvide guidelines for manufacture and
performance of power sourcesRated by
Current outputOpen circuit voltageDuty cycle
– Efficiency of output – Power factor
Current Output
57
Rated on basis of current output in amperes
Amperage range200 amperes or less for light or medium workOver 2,000 amperes for submerged arc
welding
Open Circuit Voltage
58
Maximum allowable used for manual welding80 volts for a.c. or a.c. d.c. machines100 volts for d.c. machines
Very smooth output (less than 2% ripple)
Automatic machine weldingSome constant current machines rated up to
125Constant voltage types normally rated from
15 to 50
Duty Cycle
59
Percentage of any given 10 minute period that machine can operate at rated current without overheating or breaking downRating of 100% means machine can be used
at rated amperage on continuous basisRequired by continuous, automatic machine welding
Rating of 60% means machine can be used at its capacity 6 out of every 10 minutes without damageSatisfactory for heavy SMAW and GTAW
Efficiency
60
Relationship of secondary power output to primary power inputIndicated in percent
Determined by losses through machine when actually welding at rated current and voltage
Average efficienciesMotor generator welding machines: 50%Transformer rectifier: 70%Inverter: 85%
Power Factor
61
Measure of how effectively welding machine makes use of a.c. primary line powerPrimary power used divided by amount total
drawnExpressed in percent
Three phase d.c. transformer rectifiers: 75%
Single phase a.c. power units: 55%Welding machines can be purchased with
power factor correction
Power Cable
62
Conductors of ample capacity and adequately insulated for voltage transmit power
Necessary to ground frame of welding machinePortable cable with extra conductor fastened
to machine frame on one end and solid ground on other
Important cable adequately insulated with tough abrasion resisting insulationStand up under rough usage in welding
shops
Electrode and Work Cable
63
Required to complete electric circuit between welding machine and workElectrode cable (welding cable) attached to
electrode holderWork cable attached to work
Rubber covered multi-strand copper cable generally usedMust have high flexibility
The Lincoln Electric Co.
Cable Core Construction
64
Woven of thousands of very fine copper wire
Greater the number of strands the more flexible
ComponentsA. Wires stranded for extra flexibilityB. Paper wrapping around wires
allows conductor to slip withinrobber covering when bent
C. Extra strength from open braidedreinforcement of extra cotton cords
D. Special composition and curing of heavy rubber covering
Work Cable
65
Not necessary to have flexibility of electrode cableUsually same cable used
Important considerations Amperage of welding machine Distance from work
Larger cableGreater the amperage and greater the
distanceResistance increases as diameter of cable
decreases
Cable Lugs
66
Required on both electrode cable and work cableSoldered or fastened mechanicallyConnections MUST be tight and secure
Work Clamps
67
Variety of structures to be welded; many types of clamps may be usedCopper hook, heavy metal weight, C clamp Specialized work clamps
Lenco dba NLC. Inc.
Lenco dba NLC. Inc.
Spring loaded C clamp
Rotarytype
Lenco dba NLC. Inc.
This clamp stops twisting and turning of welding cable where work rotates. Clamp welded to part, thus permits work clamp to be attached in seconds. It is generally used in fabricating tanks, pressure vessels, and on weld positioners.
Quick Connector
68
Attached to ends of different lengths of cablesAllow quick and easy attachment to any length
cable
Lenco dba NLC. Inc.
This connector has cam type action that ensures positive stop and lock and cannot come loose or accidentally fall apart.
Metal Electrode Holders
69
Device used for holding electrode mechanically
Conveys electric current from welding cable to electrode
Insulated handle protects hand from heatJaws of holder grip electrode at any angleMade of metal with high electrical
conductivity and ability to withstand high temperatures
Lenco dba NLC. Inc.
Metal Electrode Holders
70
Jaws can be replaced with new onesShould be light in weight, well balanced
and have comfortable gripSize of holder must be in line with size of
welding machineFully insulated so stays cool even with high
duty cycles
Spring Type Electrode Holder
71
Lenco dba NLC. Inc.
Short stub Electrode Holder
72
Cable connections
Special extruded copper alloy body
High welding current conductanceOne ton pressure contact
Lifeguard insulation
Entirely insulatedBernard Welding Equipment Co.
Holds electrodes burned to very short stub.Twist type locking device permits electrode gripping power in excess of 2,000 pounds.
Angle head Electrode Holder
73
Jackson Products Co.
Available in sizes of 400 and 600 amperes
and takes electrodes from 1/16 through
5/16 inch in diameter.
Shorter and lighter than other holders
of comparable capacity.
Hand and Head Shields
74
Brilliant light caused by electric arc contains two kinds of invisible rays which injure eyes and skinUltravioletInfrared
Rays affect eyes within 50 feet; and skin any distance within 20 feet
Fibre Metal Products Co.
Hand shield so person may holdshield in front of face
Hand and Head Shields
75
Also called hood or helmetAttached to adjustable headband
Allows it to be moved up or down as wearer desires
Dependable protectionBoth hands free to grasp electrode holder
Partial protectionMust also wear leather or
nonflammable cap for adequateprotection
Fibre Metal Products Co.
Fibre Metal Products Co.
Hand and Head Shields
76
Constructed of heat resisting, pressed fiber insulating material
Shields fully molded at top and bottom to protect head and neck
Usually black to reduce reflection with window frame to hole protective lens Fibre Metal Products Co.
Wilson Products
Flip front welding helmet permits welder to inspect and brush weld without lifting the hood.
Chrome leather helmets ideal for hard to get into areas.
Head Shield Lens
77
Sizes: 2 x 4.5 or 4.5 x 5.25Colored to screen out ultraviolet, infrared
rays, and most of visible raysVariety of shades of color
Density depends on brilliance of arcVaries with size of electrode and volume of
currentSide exposed to weld pool protected by
clear polycarbonate plastic cover lensProtect costly filter lens from molten metal
spatter and breakage (replaced when pitted and clouded)
Auto darkening Electronic Filter Helmet
78
Useful when working close quarters, doing high production work, or avoiding inadvertent arc strikes
Single shade or variable shadesFilter can switch from light to dark
in less than 1/10,000 of a secondBattery powered
May have solar battery booster
Jackson Products Co.
.
Safety Glasses
79
Should be wornAlso behind hood to prevent
severe arc flash reaching eyesCan Absorb more than 99.9%
harmful ultraviolet raysWorn by others who work
with weldersLight in weight, well
ventilated, and comfortableLenses have light tint (Not
dark!) and tented side shields
© RobCrandall/The Image Works
Protective Clothing
80
Gloves to protect handsMade of leather or some other type of fire
resistant materialLeather capes, sleeves, shoulder
garments with detachable bibs, aprons
Split type apron if sitting downNo place to collect hot particles
High top shoesLeggings and spats
Department of Labor
Protective Clothing
81
100% cotton or woolThick enough to prevent
injurious untraviolet rays from penetrating to skin
Long sleevesShirts buttoned to neckShirttails tuckedCuffless pants long
enough to cover top of leather boots Miller Electric Mfg. Co.
Protective Clothing
82
Further Protection
83
Ear ProtectionFull ear muffs that cover entire ear or ear
plugsDangers
NoiseHot weld spatter or slag entering ear canal
Fume ProtectionAlways use proper ventilation to keep head
out of fume plume
http://www.aws.org/ American Welding Society
http://www.ewi.org/ Welding and Joining Information Network
http://www.lincolnwelding.com Lincon Electric (welding supply co.)
http://www.weldingengineer.com/ Welding Procedures and Welding Techniques http://www.efunda.com/processes/metal_processing/welding_inertgas.cfm
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References
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