Shielded Metal Arc Welding Principles Chapter 11

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.

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 welder’s safety equipment.

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.

SMAW American Welding Society Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

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

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 welded and consumable electrode to molten state Heat intense: as high at 9,000ºF at center Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

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

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

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

Type of Output Slope Two basic types Constant current Constant voltage Referred to as variable voltage Constant voltage Referred to as constant potential

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.

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

Typical Output Slopes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

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

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

Constant Current Welding 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

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

Constant Current Output Slope Some jobs require steep volt-ampere curve Other jobs use less steep volt-ampere curve (A), (B) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

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

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

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

Motor-Generator Welding Machine Hobart Brothers Co. Sturdy steel lifting eye Calibrated dial for easy, fine adjustment of heat and relation between voltage and current Outer wheel and dial for selecting desired welding range Large voltmeter Stop button Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Motor-Generator Welding Machine Hobart Brothers Co. Ground cable connector Optional steel guard Pressed steel bearing cap Heavy-duty ball bearings Arc welded copper squirrel cage rotor Motor stator Heavy steel fan Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Motor-Generator Welding Machine Hobart Brothers Co. Steel frame Fourpole "Multi-Range" generator Heavy-duty metallic graphite brushes Large commutator Arc welded steel frame Heavy-duty ball bearings Pressed steel bearing cap Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Motor-Generator Welding Machine Hobart Brothers Co. Steel turret top with removable cover Removable steel covers Large ammeter Heavy-duty single unit steel shaft Polarity switch Welding cable connector Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Motor Generator Welding Machine for SMAW Instruction on the Name-plate The Lincoln Co. Variable voltage control Polarity switch Constant voltage Toggle switch Current control Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

External Construction of d.c. Motor Generator Welding Machine The Lincoln Electric Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Internal Construction of a D.C. Motor Generator Welding Machine The Lincoln Electric Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

Generators Classified by type of motor that drives generator Consists of a.c. motor, d.c. generator, and exciter built on single shaft The Lincoln Electric Co. Miller Electric Mfg. Co. Generators used in the field Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

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

Start and Stop Buttons Purpose of starting and stopping the motor Start button black Stop button red Important buttons be engaged firmly

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

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

Current Controls Amperage Voltage Two types of dual control generators 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

Dual Tapped-Current Control Coarse adjustment dial selects current range Called steps or taps Impossible to secure current value between two steps by setting dial between them Fine 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 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

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

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

Air Filters Wear in arc welding machines costly Bearing wear critical 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

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

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

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

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

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

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

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 Miller electric Mfg. Co. The Lincoln Electric Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

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 Miller Electric Mfg. Co. Most installations are d.c. Power: 600-2,500 amperes Cost less, saves space and cable, lowers operating cost Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

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

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 from 15 to 50

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

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%

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

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

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 multistrand copper cable generally used Must have high flexibility The Lincoln Electric Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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 of heavy rubber covering Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

See Table 11-3 to help choose the right size of welding cable 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

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.

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 Rotary type 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. Lenco dba NLC. Inc. Lenco dba NLC. Inc. Spring loaded C-clamp Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Quick Connector Attached to ends of different lengths of cables Allow 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. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Metal Electrode Holders Device used for holding electrode mechanically Conveys electric current from 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 Lenco dba NLC. Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

Spring Type Electrode Holder Lenco dba NLC. Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Short-stub Electrode Holder One-ton pressure contact High welding current conductance Special extruded copper-alloy body Cable connections Entirely 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. Lifeguard insulation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Angle-head Electrode Holder Shorter and lighter than other holders of comparable capacity. Jackson Products Co. Available in sizes of 400 and 600 amperes and takes electrodes from 1/16 through 5/16 inch in diameter. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

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

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

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: 7,500ºF Current supplied by a.c. welding transformer Hydrogen supplied in cylinders

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

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

Hand shield so person may hold shield in front of face 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 within 20 feet Fibre-Metal Products Co. Hand shield so person may hold shield in front of face Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Hand and Head Shields Also called hood or helmet Dependable protection 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 or nonflammable cap for adequate protection Fibre-Metal Products Co. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Hand and Head Shields 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. Chrome leather helmets ideal for hard-to-get-into areas. Wilson Products Flip-front welding helmet permits welder to inspect and brush weld without lifting the hood. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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)

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

Safety Glasses Should be worn Also behind hood to 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 © RobCrandall/The Image Works Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Protective Clothing Gloves to protect hands Made of leather or some other type of fire-resistant material Leather capes, sleeves, shoulder garments with detachable bibs, aprons Split-type apron if sitting down No place to collect hot particles High-top shoes Leggings and spats Department of Labor Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Protective Clothing 100% cotton or wool Miller Electric Mfg. Co. 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.

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

Further Protection Ear Protection Flume Protection Full ear muffs that cover entire ear or ear plugs Dangers Noise Hot weld spatter or slag entering ear canal Flume Protection Always use proper ventilation to keep head out of fume plume