Chapter11

1. S hielded Metal Arc Welding Principles Chapter 11

2. Objectives

List the percentage of usage of SMAW in the industry.

Name the components that make up the schematic representation of the shielded metal arc.

Know the maximum arc temperature of an SMAW electrode.

List the four constant current welding machines.

3. Objectives

List the common type and uses of constant current welding machines.

Name the power supply ratings.

Name the characteristics of the four basic types of welding machines.

Choose the correct cable size based on the application.

List the welders safety equipment.

4. Shielded Metal Arc Welding (SMAW)

Manual arc welding

Heat for welding generated by electric arc established between flux-covered consumable metal rod (electrode) and work

Called stick electrode welding

Combustion and decomposition of electrode creases gaseous shield

Protects electrode tip, weld puddle, arc, and highly heated work from atmospheric contamination

- Additional shielding provided by covering of molten slag (flux)

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. 5. SMAW American Welding Society Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. 6. Process Capability

Shielded metal arc welding one of most used of various electric arc welding processes

7. SMAW Advantages

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 metals

Not used for welding softer metals

Not as efficient in deposition

8. SMAW Operating Principles

Sets up electric circuit

Includes welding machine, work, electric cables, electrode holder and electrodes, and a work clamp

Heat of electric arc brings work to be weldedand consumable electrode to molten state

Heat intense: as high at 9,000 F at center

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. 9. Welding Process

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

10. SMAW Operating Principle American Welding Society Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. 11. Welding Power Sources

Each type of power source has fundamental electrical differences that best suit particular processes

Welding machine

Must meet changing arc load and environmental conditions instantly

Must deliver exact amount of electric current precisely at right time to welding arc

Available in wide variety of types and sizes

12. Welding Power Sources

Also known as power supplies and welding machines

Two classifications

Output slope

- Whether constant current or constant voltage

Power source type

- Transformer

- Transformer-rectifier

- Inverter

- Generator

13. Type of Output Slope

Two basic types

Constant current

- Referred to as variable voltage

Constant voltage

- Referred to as constant potential

14. Output Slope

Relationship between output voltage and output current (amperage) of machine as current increased or decreased

Also called volt-ampere characteristic or curve

Largely determines how much welding current will change for given change in load voltage

Permits welding machine to control welding heat and maintain stable arc

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. 15. Output Slope

Indicates type and amount of electric current designed to produce

Each arc welding process has characteristic output slope

SMAW and GTAW require steep output slope from constant current welding machine

GMAW and FCAW require relatively flat output slope from constant voltage power source

Submerged arc welding adaptable to either slop

16. Typical Output Slopes Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. 17. Four Types of Power Source

Engine-driven generators

Powered by gas or diesel combustion engine

Can be found with a.c. or d.c. electric motor

- No longer being manufactured and rarely found

Transformer-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

18. Four Types of Power Source

A.C. transformers

Used to step down a.c. line power voltage to a.c. welding voltage

Inverters

Increases frequency of incoming primary power

Constant current, constant voltage, or both

Produce a.c. or d.c. welding current

19. Power Sources

Important to select right power source for each job

Table 11-1 "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

20. Constant CurrentWelding Machines

Used for shielded metal arc welding and gas tungsten arc welding

Current remains fairly constant regardless of changes in arc length

Called drooping voltage, variable voltage, or droopers

- Load voltage decreases as welding current increases

21. Constant Current Output Slope

Constant current welding machines

Steep output slope

Available in both d.c. and a.c. welding current

Steeper the slope, the smaller current change

Enables welder to control welding current in specific range by changing length of arc

22. Constant CurrentOutput Slope Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Some jobs require steep volt-ampere curve Other jobs use less steepvolt-ampere curve 23. Open Circuit Voltage

Voltage generated by welding machine when no welding being done

Machine running idle

Arc voltage

Voltage generated between electrode and work during welding

Load voltage

Voltage at output terminals of welding machine when arc is going

Combination of arc voltage plus voltage drop in welding circuit

24. Open Circuit and Arc Voltage

Open circuit voltage runs between 50-100 volts

Drops to arc voltage when arc struck

Arc voltages

Range: 36 volts (long arc) to 18 volts (short arc)

Determined by arc length held by welder and type of electrode used

Arc lengthened, arc voltage increases and current decreases

25. Open Circuit and Arc Voltage

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 welder

Shielded metal arc welding

Gas Tungsten arc welding

Arc voltage much lower than open circuit voltage

26. Motor Generator Welding Machines

Usually supply only direct current

Can be made to supply a.c.

Most constant current type

Used chiefly for shielded metal arc welding and gas tungsten arc welding

27. Motor-GeneratorWelding Machine Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Hobart Brothers Co. Sturdy steel lifting eyeLarge voltmeterCalibrated dial for easy, fine adjustment of heat and relation between voltage and current Outer wheel and dial for selecting desired welding range Stop button 28. Motor-GeneratorWelding Machine Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Hobart Brothers Co. Ground cableconnectorOptional steel guard Heavy-duty ballbearings Pressed steel bearing cap Arc welded coppersquirrel cage rotor Motor statorHeavy steel fan 29. Motor-GeneratorWelding Machine Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Hobart Brothers Co. Steel frameFourpole "Multi-Range" generatorLarge commutatorHeavy-duty metallic graphite brushes Heavy-duty ball bearings Pressed steel bearing cap Arc welded steel frame 30. Motor-GeneratorWelding Machine Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Hobart Brothers Co. Removable steel coversHeavy-duty single unitsteel shaft Polarity switchWelding cable connectorLarge ammeter Steel turret top withremovable cover 31. Motor Generator Welding Machine for SMAW Variable voltage control Instruction on theName-plate Polarity switch Current control Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Toggle switch Constant voltage The Lincoln Co. 32. External Construction of d.c. Motor Generator Welding Machine Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. The Lincoln Electric Co. 33. Internal Construction of a D.C. Motor Generator Welding Machine Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. The Lincoln Electric Co. 34. Motor Generator Desirable Characteristics

Have forceful penetrating arc

Versatile

Can be used to weld all metals that are weldable by arc process

Flexible

With proper electrode, can be used in all positions

Durable and have long machine life

35. Generators

Classified by type of motor that drives generator

Consists of a.c. motor, d.c. generator, and exciter built on single shaft

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Generators usedin the field Miller Electric Mfg. Co. The Lincoln Electric Co. 36. Sizes

Determined on basis of amperage

Range

100-ampere rated for home

1,500 ampere rated for use with automatic submerged arc welding equipment

Manual welding machine idle sometimes

Automatic power supply units 100% duty cycle

Should not be used at or beyond max over extended period

37. Maintenance

Contacts of starter switch and control rheostat should be inspected, cleaned frequently and replaced when necessary

Brushes need frequent inspection for wear

Check commutator for wear or burning

- Rewound and turned on lathe

Main bearings on shaft inspected and greased at each 6-month period

Clean old grease out of bearing housings

38. Start and Stop Buttons

Purpose of starting and stopping the motor

Start button black

Stop button red

Important buttons be engaged firmly

39. Polarity Switch

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

40. Volt-Ampere Meters

Sometimes serve dual purpose

Can indicate polarity as well as current

Others, individual meters for volts and amperes

Some, single meter that indicates both volts and amperes

- Button engaged to get individual readings

- Would need second person for monitoring

Increased demand for additional devices so meters have been discontinued by some manufacturers

41. Current Controls

Amperage

Quantity of current

Determines amount of heat produced at weld

Voltage

Measure of force of current

Determines ability to strike an arc and maintain its consistency

Two types of dual control generators

Tapped-step current control

Continuously variable current control

42. Dual Tapped-Current Control

Coarse adjustment dial selects current range

Called steps or taps

Impossible to secure current value between twosteps by setting dial between them

Fine adjustment dial trims current between steps

Whether set high or low depends on type andsize of electrode, thickness of metal, soft or digging arc required, arc starting, restricting characteristics, and Position of welding

43. Dual Continuous Control

Coarse adjustment dial continuously adjusts current

Fine dial adjusts both current(amperage) and open circuit voltage

Operator 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

44. Engine Driven Generator Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Capable of SMAW, GTAW, SMAW, FCAW and PAC. Miller Electric Mfg. Co. Miller Electric Mfg. Co. 45. Remote Control

Welding machines may be installed in remote part of plant

Welder may adjust current without leaving job

Timesaving on work

Welder does not have to leave fabrication to readjust current

46. Air Filters

Wear in arc welding machines costly

Cost of replacement parts and labor

Loss of production due to nonuse of machine

Bearing wear critical

May be reduced through use of air filter fitted on suction end of motor generator machine

Filter cleaned regularly

High pressure air, commercial solvent or steam

47. D.C. Transformer-Rectifier Welding Machines

Have many designs and purposes

Flexibility one reason for wide acceptance

Deliver either DCEN or DCEP

May be used for:

Stick electrode welding

Gas tungsten arc welding

Submerged arc welding

Multi-operator systems

Stud welding

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. The Lincoln Electric Co. Miller Electric Mfg. Co. 48. Transformer-Rectifier Machines

Have two basic parts

Transformer for producing and regulating alternating current that enters machine

rectifier that converts a.c. to d.c.

Third important part is ventilating fan

Keeps 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

49. A.C.-D.C. Transformer-Rectifier Welding Machines

Permit welder to select either a.c. or d.c. and electrode negative or electrode positive

Switch

Permits welder to use only transformer part of machine for a.c. welding

Flipping 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

50. A.C.-D.C. Transformer-Rectifier Welding Machines Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. A 300 amp a.c.-d.c. GTAW/SMAW machine. Portable SMAW/GTAW welding machine A 300 amp model shown in use The Lincoln Electric Co. The Lincoln Electric Co. Miller Electric Mfg. Co. 51. A.C. Transformer Welding Machines

Most popular a.c. welding machine

Function of transformer

Step down high voltage of input current to high amperage, low voltage current required for welding

Especially suited for heavy work

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. The Lincoln Electric Co. Miller Electric Mfg. Co 52. Advantages of a.c. Power Sources

Reduces tendency to arc blow

Can use larger electrodes

Resulting in faster speeds on heavy materials

Lower cost

Decreased power consumption

High overall electrical efficiency

Noiseless operation

Reduced maintenance

53. D.C. and A.C.-D.C. Inverter Welding Machines

Portable, lightweight, and versatile

May be either constant current, constant voltage or both

Can perform several different processes

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Miller electric Mfg. Co. The Lincoln Electric Co. 54. Cost Comparisons:Arc Power Sources

Three main areas

Cost of purchasing equipment (nearly equal)

Operating efficiency

- Motor generator machine: 52-65%

- Transformer-rectifiers: 64-72%

- Inverters: 85%

Maintenance

- Motor generator machine: replacing parts, lubrication

- Transformer-rectifiers and inverters have no moving parts

See Table 11-2 for more comparisons 55. Multiple-Operator Systems

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

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display.

Most installations are d.c.

Power: 600-2,500 amperes

Cost less, saves space and cable, lowers operating cost

Miller Electric Mfg. Co. 56. Power Supply Ratings

Standards set

The National Electrical manufacturers Association

Occupational Safety and Health Administration

Provide guidelines for manufacture and performance of power sources

Rated by

Current output

Open circuit voltage

Duty cycle

Efficiency of output

Power factor

57. Current Output

Rated on basis of current output in amperes

Amperage range

200 amperes or less for light or medium work

Over 2,000 amperes for submerged arc welding

58. Open Circuit Voltage

Maximum allowable used for manual welding

80 volts for a.c. or a.c.-d.c. machines

100 volts for d.c. machines

- Very smooth output (less than 2% ripple)

Automatic machine welding

Some constant current machines rated up to 125

Constant voltage types normally rated from15 to 50

59. Duty Cycle

Percentage of any given 10-minute period that machine can operate at rated current without overheating or breaking down

Rating of 100% means machine can be used at rated amperage on continuous basis

- Required by continuous, automatic machine welding

Rating of 60% means machine can be used at its capacity 6 out of every 10 minutes without damage

- Satisfactory for heavy SMAW and GTAW

60. Efficiency

Relationship of secondary power output to primary power input

Indicated in percent

Determined by losses through machine when actually welding at rated current and voltage

Average efficiencies

Motor generator welding machines: 50%

Transformer-rectifier: 70%

Inverter: 85%

61. Power Factor

Measure of how effectively welding machine makes use of a.c. primary line power

Primary power used divided by amount total drawn

Expressed 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

62. Power Cable

Conductors of ample capacity and adequately insulated for voltage transmit power

Necessary to ground frame of welding machine

Portable cable with extra conductor fastened to machine frame on one end and solid ground on other

Important cable adequately insulated with tough abrasion-resisting insulation

Stand up under rough usage in welding shops

63. Electrode and Work Cable

Required to complete electric circuit between welding machine and work

Electrode cable (welding cable) attached to electrode holder

Work cable attached to work

Rubber-covered multistrandcopper cable generally used

Must have high flexibility

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. The Lincoln Electric Co. 64. Cable Core Construction

Woven of thousands of very fine copper wire

Greater the number of strands the more flexible

Components

Wires stranded for extra flexibility

Paper wrapping around wires allows conductor to slip within robber covering when bent

Extra strength from open-braided reinforcement of extra cotton cords

Special composition and curing ofheavy rubber covering

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. 65. Work Cable

Not necessary to have flexibility of electrode cable

Usually same cable used

Important considerations

Amperage of welding machine

Distance from work

Larger cable

Greater the amperage and greater the distance

Resistance increases as diameter of cable decreases

See Table 11-3 to help choose the right size of welding cable 66. Cable Lugs

Required on both electrode cable and work cable

Soldered or fastened mechanically

Connections MUST be tight and secure

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. 67. Work Clamps

Variety of structures to be welded; many types of clamps may be used

Copper hook, heavy metal weight, C-clamp

Specialized work clamps

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Spring loaded C-clampLenco dba NLC. Inc. Lenco dba NLC. Inc. Rotary type Lenco dba NLC. Inc. This clamp stops twisting and turning ofwelding cablewhere work rotates.Clampwelded to part, thus permits work clamp to beattached in seconds.It is generally used in fabricatingtanks, pressure vessels, and on weld positioners. 68. Quick Connector

Attached to ends of different lengths of cables

Allow quick and easy attachment to any length cable

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. This connector has cam-type action that ensures positive stopand lock and cannot come loose or accidentally fall apart. Lenco dba NLC. Inc. 69. Metal Electrode Holders

Device used for holding electrode mechanically

Conveys electric currentfrom welding cable to electrode

Insulated handle protects hand from heat

Jaws of holder grip electrode at any angle

Made of metal with high electrical conductivity and ability to withstand high temperatures

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Lenco dba NLC. Inc. 70. Metal Electrode Holders

Jaws can be replaced with new ones

Should be light in weight, well-balanced and have comfortable grip

Size of holder must be in line with size of welding machine

Fully insulated so stays cool even with high duty cycles

71. Spring Type Electrode Holder Lenco dba NLC. Inc. Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. 72. Short-stub Electrode Holder Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Cable connections Special extruded copper-alloy body High welding current conductance One-ton pressurecontact Lifeguard insulationEntirely insulated Bernard Welding Equipment Co. Holds electrodes burned to very short stub. Twist-type locking device permits electrode- gripping power in excess of 2,000 pounds. 73. Angle-head Electrode Holder Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Jackson Products Co. Available in sizes of 400 and 600 amperesand takes electrodes from 1/16 through5/16 inch in diameter. Shorter and lighterthan other holders of comparable capacity. 74. Other Electric Arc processes

Generates heat for several major welding processes

Gas tungsten arc welding (GTAW)

Gas metal arc welding (GMAW)

Arc cutting utilizes much of same equipment as arc welding

75. Carbon Arc Welding

Welding heat comes from arc formed between base metal and carbon electrode or arc formed between two carbon electrodes

With or without addition of filler rod

Carbon electrodes available: 1/4, 5/16, 3/8 inch

Alternating current: 30-125 amperes

Metal electrode holders not suitable

Carbon electrode hotter than metal electrode

76. Twin Carbon Electrode Holder Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. The Lincoln Electric Co. Two leads are required because the arc is created between the two electrodes. Metal shield to protect welder's hand from intense heat. Larger than themetal electrodeholder Holder is water cooled 77. Atomic-Hydrogen Arc Welding

Process in which electric arc surrounded by atmosphere of hydrogen

Gas shields molten metal from oxidation and contamination from the air

Transfers heat from electrode to work

Arc formed between two electrodes

Temperature produced by arc: 7,500 F

Current supplied by a.c. welding transformer

Hydrogen supplied in cylinders

78. Atomic-Hydrogen Electrode Holder Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. General Electric Co. 79. Atomic-Hydrogen Arc Welding

Metal of same analysis as being welded can be deposited

Welds may be heat treated

Unusually smooth, ductile, nonporous and free from impurities

Surface free from scale

May weld hard-to-weld metals

Advantages: increased production, low operating cost, and low maintenance cost

80. Hand and Head Shields

Brilliant light caused by electric arc contains two kinds of invisible rays which injure eyes and skin

Ultraviolet

Infrared

Rays affect eyes within 50 feet;and skin any distance within20 feet

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Fibre-Metal Products Co. Hand shield so person may hold shield in front of face 81. Hand and Head Shields

Also called hood or helmet

Attached to adjustable headband

- Allows it to be moved up or down as wearer desires

Dependable protection

Both hands free to grasp electrode holder

Partial protection

Must also wear leather ornonflammable cap for adequate protection

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Fibre-Metal Products Co. Fibre-Metal Products Co. 82. Hand and Head Shields

Constructed of heat-resisting, pressed-fiberinsulating material

Shields fully molded at top and bottom toprotect head and neck

Usually black to reduce reflection withwindow frame to hole protective lens

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Fibre-Metal Products Co. Wilson Products Flip-front welding helmet permits welder toinspect and brush weld without lifting the hood. Chrome leather helmets ideal forhard-to-get-into areas. 83. Head Shield Lens

Sizes: 2 x 4.5 or 4.5 x 5.25

Colored to screen out ultraviolet, infrared rays, and most of visible rays

Variety of shades of color

Density depends on brilliance of arc

Varies with size of electrode and volume of current

Side exposed to weld pool protected by clear polycarbonate plastic cover lens

Protect costly filter lens from molten metal spatter and breakage (replaced when pitted and clouded)

84. Auto-darkening Electronic Filter Helmet

Useful when working close quarters, doing high production work, or avoiding inadvertent arc strikes

Single shade or variable shades

Filter can switch from light to dark in less than 1/10,000 of a second

Battery powered

May have solar battery booster

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. . Jackson Products Co. 85. Safety Glasses

Should be worn

Also behind hoodto prevent severe arc flash reaching eyes

Can Absorb more than 99.9% harmful ultraviolet rays

Worn by others who work with welders

Light in weight, well ventilated, and comfortable

Lenses have light tint (Not dark!) and tented side shields

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. RobCrandall/The Image Works 86. Protective Clothing

Gloves to protect hands

Made of leather or some other type of fire-resistant material

Leather capes, sleeves, shouldergarments with detachable bibs,aprons

Split-type apron if sitting down

No place to collect hot particles

High-top shoes

Leggings and spats

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. Department of Labor 87. Protective Clothing

100% cotton or wool

Thick enough to prevent injurious untraviolet rays from penetrating to skin

Long sleeves

Shirts buttoned to neck

Shirttails tucked

Cuffless pants long enough to cover top of leather boots

Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. MillerElectric Mfg. Co. 88. Protective Clothing Copyright The McGraw-Hill Companies, Inc.Permission required for reproduction or display. 89. Further Protection

Ear Protection