Technical information provided by The Lincoln Electric Co.

Welding shops require many types of equipment, including power supplies, guns, torches, wire feeders, flux-handling devices, and accessories such as cables and ground clamps, as well as consumables—filler metals, fluxes, and shielding gases. For brazing, shops employ furnaces and custom-built fixtures.

Shielded-Metal-Arc Welding ( SMAW, STICK )
AWS (American Welding Society) A5 specifications set standards for electrodes for SMAW of carbon, stainless, and low-alloy steels; aluminum, copper, and nickel and their alloys; and weld-surfacing. Designations for covered electrodes carry the prefix 'E'. Packaged to AWS specifications, electrodes come in boxes, cans, or other containers, labeled with their AWS specification and trade name, quality-control (heat or lot) number, supplier name, diameter and length, and weight of contents. Specifications require that every electrode be marked for identification near with its numeric designation the grip end.

To select a covered SMAW electrode, consider these factors, in approximate order of importance.

1. Mechanical properties of the base material. Tensile strength and yield strength of the weld metal should equal or exceed that of the base material. Ductility and toughness at low temperatures may also be important. High-temperature service requires resistance to creep. Shock loading requires impact resistance. In general, weld metal should exceed base-material properties.
2. Composition of the base material. For stainless steels, low-alloy steels, nickel and copper alloys, and materials that serve in corrosive atmospheres, chemical composition is important. Consider the possibility of electrochemical corrosion between base and weld metal of different compositions.
3. Welding position. The first performance characteristic to consider. High-cellulose coatings, like those on E6010 and E6011 electrodes, generate a light slag that makes for rapid solidifying of the weld metal, good for outof-position welds. Also good are rutile-fluxed electrodes-E6012 and E6013that hold out-of-position weld metal in place as it solidifies.
4. Welding current. Covered electrodes run on AC, DC, or both. When welding DC, the positive lead typically connects to the electrode (DCEP, or reverse polarity). Some suppliers design electrodes that weld with the electrode negative (DCEN, or straight polarity). Assure the electrode will perform with the available current.
5. Joint design and material thickness. Some electrodes create an arc that penetrates deeply, performing well on thick sections with narrow grooves or no bevel. Poor fit-up calls for electrodes that can bridge wide gaps.
6. Efficiency. Meeting all other conditions, engineers select the electrode that gives the highest deposition rate. For heavy-section joints, use powder-metal-addition fillers.

Designating electrodes for carbon and low-alloy steels, following the prefix 'E', to signify a SMAW electrode, come two or three digits to indicate minimum tensile strength in 1,000 PSI units; a digit indicating usable current and electrode-coating type; and, in some cases, a hyphen followed by a letter and number suffix to denote weld-metal composition. Example: E7010-A1 is a SMAW electrode (E), of 70,000-PSI tensile strength (70), for use in all welding positions (1), having a high-cellulose-sodium coating for use with DCEP (0). -A1 indicates a particular composition listed in the A5 specification. A -1 suffix, as in 7018-1, indicates high impact toughness at a temperature lower than specified for a standard E7018 electrode.

Low-hydrogen types. These basic-coated electrodes, EXX15, EXX16, EXX18, EXX28, and EXX48, are formulated with low-moisture-retaining coatings and manufactured to contain low levels of hydrogen. Hydrogen-controlled electrodes minimize risk of hydrogen-induced cold cracking when welding high-tensile steels on restrained structures. Fabricators use these electrodes to reduce or avoid the need for pre-or postweld heat treatment to drive hydrogen from weld metal. Weldmetal diffusible hydrogen content varies from 1 to 16 ml/100 g. Optional designators H16, H8, and H4 set decreasing limits on hydrogen content in deposited weld metal. An optional electrode designator, 'R', indicates an electrode that is moisture resistant; it will not absorb water in excess of a specified limit after exposure to humidity. Low-hydrogen electrodes should be used in dry condition and may require baking after exposure to the atmosphere.

High-deposition electrodes.

These contain iron-powder additions in the coating to raise deposition rate. Designations: EXXX4, EXXX7, EXXX8.

For fastest deposition, use the largest diameter possible for an applicationthe thicker the electrode, the greater its current-carrying capacity and the higher the deposition rate. Welding out of position and over-head, select a small-diameter electrode to enable welders to reach into narrow root openings.

Gas-Metal-Arc Welding (GMAW , MIG)
GMAW typically uses solid wire, spooled or reeled, for continuous feeding to the gun; diameter, 0.030 to ¹ /16 in. typically, although wires as small as 0.020 in. and as large as ¹ /8 in. are sometimes used. AWS lists specifications for filler wires of copper and its alloys, aluminum and its alloys, surfacing alloys, nickel and its alloys, titanium and its alloys, carbon and low-alloy steels, magnesium alloys, stainless steel, and zirconium and its alloys.

For special applications, manufacturers offer metal-cored wires for GMAW. These are composite electrodes comprised of a metal sheath with a powder-metal core. They are often confused with flux-cored wires, which form a slag that completely covers the weld-bead face; metal-cored wires produce very little slag. A major advantage of metal-cored wires is the ability to manufacture special-ized-alloy compositions not easily available or producible in solid-wire form. Modifying the composition of the powder-alloy core allows the wire manufacturer to customize wire formulations to metallurgical, compositional, or physical properties per customer demand. Horizontal-fillet welds made with metal-cored GMAW can deposit weld metal at rates up to 20 percent higher than with solid wire. Alloying elements, such as silicon, in the powder-metal core improve sidewall wetting and reduce weld-bead convexity by reducing surface tension of the molten weld pool. For this reason, flat and horizontal welds deposited with metal-cored wires have better appearance than weld metal deposited with flux-cored and solid wires. Compared to solid wires, metal-cored wires also result in higher current density, for increased penetration; a wider operating window with respect to welding-process variables; better sidewall melting; and less lack of fusion.

Flux-Cored-Arc Welding ( FCAW )
This process is a variation of GMAW. Electrodes comprise a metal sheath surrounding a core of fluxing and alloying compounds. Self-shielded (FCAW-SS), it uses gas generated by breakdown of a powder-flux core inside the wire to shield the weld. Gas shielded (FCAW-GS), external gas supplies shielding.

The compounds in the electrode perform essentially the same functions as the coating of a covered electrode used in SMAW: to form a floating slag coating on the weld pool to protect the weld as it solidifies; deliver deoxidizer and scavengers to help purify the weld; deliver arc stabilizers to minimize spatter; add alloying elements to the weld, for optimum mechanical properties; and provide shielding gas.

Filler-metal selection for FCAW depends on base-metal composition, cleanliness of base metal, thickness, and service. AWS specifications: A5.20, Specification for Carbon Steel Electrodes for Flux-cored Arc Welding, for low-carbon steel up to 0.15 C and mild steel 0.15 to 0.29 C; A5.29, Specification for Low Alloy Steel Electrodes for Flux-cored Arc Welding, for steel of higher carbon content and the low-alloy types; A5.22, Specification for Flux-cored Corrosion-Resisting Chromium and Chromium-Nickel Steel Electrodes, for stainless steels.

Gas-Tungsten-Arc Welding (GTAW , TIG)
GTAW uses an arc between a nonconsumable electrode and the work. It joins with or without filler metal. AWS A5.12 lists electrode types and sizes. All are tungsten, some with thoria, zirconia, ceria, or lanthana added. Thoria provides higher current-carrying capacity than pure tungsten with less contamination of the weld pool. Other benefits: better arc starting, greater arc stability. Zirconiated electrodes perform well with alternating current: the arc is stable, the electrode retains a balled end during welding, and has current-carrying capacity of thoriated electrodes. Zirconiated electrodes resist contamination and minimize tungsten contamination of weld metal.

Electrodes come 3 to 24 in. long, 0.01- to 0.25-in. diameter. Colored markings—bands or dots—indicate composition: pure tungsten, green; 1-percent thoriated, yellow; 2-percent thoriated, red; ceriated, orange; lanthanted, black.

Filler metal. GTAW does not usually require addition of filler metal, but filler is commonly added when base-metal thickness is greater than ¹ /8 in. Filler metal for carbon steel are described in A5.18, and for low-alloy steels in A5.28.

Submerged-Arc Welding ( SAW )
Flux. AWS specifications A5.17 and A5.23 describe fluxes for SAW. AWS designation of fluxes precedes that of the wire when identifying a combination for a welding procedure. For example, the designation F7A2-EM12K indicates a flux (F) that will provide, with a given wire designation, tensile strength of 70,000 PSI (7), in the aswelded condition (A), and impact properties of 20 ft-lb at -20 F (2). A designation containing a P rather indicates the flux properties after post-weld heat treatment.

Fused fluxes are melted in a furnace, chilled, then crushed and screened for size. They recycle without alterations in particle size or composition. Bonded fluxes are powdered materials mixed dry and bonded together with a silicate, pelletized, baked, broken up, and screened for size: the process permits easy addition of deoxidizers and alloying elements. Bonded fluxes allow thicker flux layers when welding. Disadvantages of bonded fluxes are their absorption of moisture and alterations during handling in particle size and composition due to particle segregation. Agglomerated fluxes are similar to bonded fluxes except that they use a ceramic binder. They require higher baking temperatures during manufacture. Mechanically mixed fluxes are combinations of two or more bonded or agglomerated fluxes. They allow special flux mixtures for critical welds, but they may separate during storage, use, and flux recovery.

Three-parts new flux mixed with one-part recovered flux works well. Consult the flux manufacturer for proper proportions.

Fluxes classify as basic, acid, or neutral. Fluxes that contain oxides and break up easily during welding are basic. These provide oxidizing action and alloy with the weld metal to obtain desired mechanical properties. Acidic oxides break up slightly, for the same reasons. Welding voltage must remain within the range specified by the manufacturer of acidic and basic fluxes. Excessive arc voltage increases the alloying of flux constituents with the weld metal. Neutral fluxes do not oxidize alloying elements or add alloying elements to the weld. As amperages increase, flux-particle size should decrease. Excessive current for a particle size produces unstable arcs and uneven weldbead edges.

Weld wire. SAW uses electrodes of continuous wire, solid or flux-or metal-cored. Selection depends on base-metal composition and thickness, flux, joint design, and cleanliness. AWS specifications A5. 17 and A5.23 detail filler materials for SAW of carbon and low-alloy steels; A5.9 and A5.14, filler metals weld corrosion-resisting stainless steels and nickel alloys, respectively.

Hardfacing Electrodes
Hardfacing welds a wear-resistant material to a substrate-base material that is commonly mild, alloy, or stainless steel. Hardfacings can be deposited manually using SMAW electrodes; semiautomaticaly using solid wire and self-shielded flux-cored electrodes; or automatically by submerged-arc welding. The method chosen depends on the size and accessibility of the area to be surfaced.

Select hardfacing materials based on weld-deposit microstructure and the wear situation the part will encounter, with consideration given to thermal treatments applied to the material before and after hardfacing. Deposit chemistry can be crucial in attaining the desired corrosion resistance or wear properties, or for minimizing the risk of solidification cracking. Acceptable deposit chemistry is achieved through the initial choice of consumables, using wire analysis and flux composition, and by specifying the number of weld passes needed to reduce parent-metal dilution to within acceptable limits. With the submerged-arc process, the flux and electrode govern the characteristics of the applied hardfacing. For example, those fluxes neutral to manganese and silicon are not necessarily neutral to carbon and chromium, elements that matter most in hardfacing.

Hardfacing alloys contain as base elements typically iron, nickel, or cobalt, to which metallurgists add varying amounts of carbon, chromium, molybdenum, tungsten, silicon, manganese, vanadium, and boron. To raise hardness, the primary property for wear resistance, alloy designers add elements that either form hard constituents (carbides, borides, or Laves phase), or that strengthen the matrix by going into solid solution. Carbon content determines toughness and abrasion resistance—as carbon rises, abrasion resistance increases and toughness drops. Chromium forms carbides, increases corrosion resistance, and adds high-temperature strength. Tungsten, a potent carbide former, also boosts high-temperature strength, as does cobalt. Tougheners include nickel and manganese. Boron forms hard wear-resistance borides.

Iron-base alloys, the most widely used hardfacing materials, combine versatility with moderate cost. They achieve wear resistance by forming carbides and martensite, a hard matrix structure that forms on quenching and toughens with tempering. Pearlitic alloys, usually containing less than 0.30 percent carbon, are comparatively soft and ductile.

Nickel-base alloys resist corrosion and heat better than iron-base alloys. They come in three types, depending on the hard phase (boride, carbide, or Laves) that forms on cooling. In boride-containing alloys, large amounts of chromium borides provide wear resistance.

Cobalt-base alloys provide more high-temperature corrosion resistance than iron-base and nickel-base grades. Carbides or Laves-phase give wear resistance.

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Power Supplies

Welding power supplies take alternating or direct current from a power line or portable generator and convert it to current usable at the welding arc. Check National Electrical Manufacturers Association (NEMA) Standards Publication EW1, Electric Arc Welding Power Supplies, and manufacturers' literature for construction and performance requirements of individual machines.

Among types of power supplies, alternating-current (AC) transformers are least costlymost use 230 V single-phase input power. Direct-current (DC) transformer-rectifiers convert AC to DC, using single-or three-phase power to produce constant voltage (CV) or variable voltage (VV). AC-DC transformer-rectifiers can AC and DC weld.

Transformer-rectifiers have moveable parts that tend to wear out. However, these machines can produce some of the best arc characteristics.

A silicon-coated-rectifier (SCR) power source, electronically voltage-controlled, has no real moving parts other than the primary current contactor and cooling fan—the only parts that will wear out. If a fabricator requires pulsed welding, the SCR power source starts to show its limitations and inverters become the power supply of choice.

AC-DC inverters, which convert AC input frequency to very high frequencies—up to 1,000 times that of input frequency—allow transformers and other components to be small in size and the power supply to be relatively lightweight. This high operating frequency enables the inverter to precisely control output power and to deliver smooth arc initiation with minimal or no spatter. Current ripple is low for a very stable arc, even at low amperages. And the improved arc control can, in some cases, minimize electrode overheating and fume emissions. Finally, the smallish transformer allows for more efficient use of primary power compared to conventional power supplies.

Multiple-operator power supplies use a high-amperage high-voltage power source to feed power to more than one welding station. Where line power may be unavailable, as in the field, contractors operate engine-driven generators powered by natural gas, propane, or diesel fuel.

Power Supplies By Welding Process
A manual process, shieldedmetal-arc welding (SMAW) requires a CC power supply, 25 to 500 amperes, 15 to 35 volts. Given the correct electrode, almost any CC welding machine, AC or DC, can be used for shielded-metal-arc welding, depending on the composition of the electrode coating.

Gas-metal-arc welding (GMAW) calls for continuous filler-metal wire-shielding gas protects the weld pool as wire feeds into the arc. The process requires direct current-arcs generally run at 15 to 35 volts, 30-600 A. Specify a CC machine that gives constant melt rate and variable wire feed. Inverters for GMAW feature electronic control of inductance, enabling the welder to fine-tune the arc for minimal spatter and optimum weld-bead wetting action.

Welding-site conditions and weld-ing-wire diameter govern efficiency and size of power supply required for a job. Select a 100-A unit that runs from single-phase 115-V input for low-duty-cycle welding of sheet to ¹ /8 in. thick, feeding wire to 0.030-in. diameter. Medium-duty power supplies, 150-200 A, normally take single-phase 220-V input to weld steel to ³ /16 in. and 0.035-in. wire at low-duty cycles. For high-duty cycles, as in mechanized welding, select a 250-A machine, single or three-phase input at various volt-ages-these weld material to ¹ /2 in. thick with wire as large as 0.045-in. diameter. Taking three-phase input only and wire up to ¹ /16-in. diameter, 400-A units serve for mechanized continuous-welding applications.

For pulsed GMAW, shops use inverter and transistor power sources, constant-current or constant-voltage, that offer independent setting of pulse parameters. They employ synergic controls preprogrammed for a range of wire-feed speeds-the operator sets only one dial, for average current.

For flux-cored-arc welding, shops use CV or CC types, 300 to 1,500 A, 25 to 50 V, rated 60- to 100-percent-duty cycle. CV types are more popular because wire-feed speed, set before welding, controls welding current. CC types require a variable-speed or voltage-sensing wire feeder.

Gas-tungsten-arc welding (GTAW) requires a constant-current (AC or DC) power supply with a steep volt-amp curve to minimize current change for variation in voltage or arc length. They come rated to 1,500 A , 10 to 75 V, at 40- to 100-percent-duty cycle. Most GTAW power supplies come equipped with high-frequency circuitry for arc initiation and stabilization, gas valves, and cooling-water valves for high-current welding. High-frequency arc start is useful when the maximum open-circuit voltage allowed by NEMA standards, 80 to 100 V, will not establish and maintain a stable arc.

For AC-GTAW of Aluminum Alloys, ... most of the significant advances focus on new ways to manipulate the AC wave form. These advances largely result from using inverter-based power sources, which allow a welder to extend the balance control, adjusting output frequency and independently controlling current in each AC half cycle. New inverter-based GTAW machines extend EN balance control, allowing duration from 50 to 90 percent. Making the EN portion of the cycle last longer:

• Allows greater weld penetration
• May permit increasing travel speeds by as much as 20 percent.
• Narrows the weld bead
• May permit using a smaller-diameter tungsten electrode to more precisely direct the heat or deposit a narrower weld bead
• Reduces the size of the etched zone for improved cosmetics.

Less EN time improves cleaning action to remove heavier oxidation, lessens penetration, and widens the bead profile.

Inverter-based machines also let operators adjust welding-output frequency from 20 to 250 Hz. Decreasing frequency produces a broader arc cone, which widens the weld-bead profile and better-removes impurities from the surface of the workpiece. It also transfers the maximum amount of energy to the workpiece, ideal for work requiring heavy metal deposition.

Increasing frequency produces a tight, focused arc cone. This narrows the weld bead, helpful when welding in corners and on root passes and fillet welds. Independent amperage control of the EN and EP portions of the AC cycle allows the operator to fine-tune the amount of energy directed into the workpiece, as well as take heat off of the tungsten electrode. A basic, professional-quality AC GTAW power supply lets the operator adjust four variables: amperage, balance control, and shielding-gas pre-flow and post-flow time.

Saw Uses CV or CC Power Supplies, ... 200 to 1,500 A, 28 to 44 V, at 60-to 100-percent-duty cycle. Automatic units commonly use up to 1,500 A on one wire. Cv welding machines that offer variable-slope control give the welder extra adjustability, and can extend the usefulness of the machine to weld a range of material thicknesses and types.

Selection of Power Sources
When choosing a power source, start by checking NEMA specs. NEMA Class I arc-welding power sources deliver rated output at 60-, 80-, or 100-percent-duty cycle: Class II units, 30-, 40-, or 50-percent; and Class III, 20 percent. First consider capacity and kind of current needed for the job. Rely on the manufacturer's rating as being conservative: don't buy more capacity than needed. Choose lowduty-cycle machines only for maintenance or for intermittent welding. If portability is important, consider inverter units.

With the advent of the CE-mark requirements in Europe, many manufacturers now design to the International Standard IEC 974-1. One of the requirements of this standard is to place an IP rating on the nameplate of the machine to indicate the degree of protection provided by the enclosure to avoid damage from water and foreign objects.

Purchasers of power supplies must consider the power they will be putting into the machines which operate from line power or some other source of electricity. Ratings list voltage, number of phases, frequency, and current level when the power source is running at rated output. Most motor-generator sets require three-phase AC power.

Features and Options
Power supplies are capable to "talk to each other," useful when a company wants to input the same welding procedures into several machines at once or monitor the welding consistency and performance of several machines from a single location through serial-data communications. Fabricators can take some of their machines and connect them to a personal computer to monitor performance, and download welding parameters to the machines from a memory card for fast setup. High-end machines will calculate the pounds of weld wire used per machine. The machine can also be prepped to constantly monitor and average the welding current and voltage used, so that fabricators can set limits on the machine and track how many times welding parameters fell in or out of these limits.

Remote control of current and voltage is a plus if the welding operator is located away from the power source.

Robotic and automatic applications generally require high-duty-cycle power supplies, and controls and connections for interfacing to the robot or automatic fixture.

Supervisory control of the process will prevent the welder from changing the welding procedures. Here, select a power supply or controller that enables the supervisor to program the procedures, then lock them into the control memory. Some power supplies or controllers offer the welder limited control of the process.

Input power to power supplies can be single-and/or three-phase, with voltage from 115 to 575 V and input frequencies of 50, 60, or 50/60 Hz. Note that many inverter power supplies are designed to operate on both single-and three-phase input, and have automatic input-voltage selection and linking.

Production vs. repair applications In general, production applications require high-duty-cycle power supplies, and repair applications can use low-duty-cycle portable units.

Lift-arc GTAW Many DC power supplies are equipped with a lift-start feature for, a variation of scratch starting, GTAW welding. When the welder touches the tungsten electrode to the workpiece, a small amount of current—15-20 A—flows. When he lifts the electrode from the work, the arc starts softly and the machine switches to the set weld-current value. This low-current starting minimizes weld contamination caused by touching the tungsten to the workpiece and eliminates the need for high-frequency starting.

Duty-Cycle Rating
Power-supply rating depends on the type and thickness of the workpiece and the length of time it takes to deposit the longest weld on the thickest material. Duty cycle is the key factor to consider when selecting a power source. Once the engineer has determined the current and voltage needed to accomplish the weld, he then reviews duty-cycle requirements.

Duty-cycle rating is the percentage of time during a 10-minute period a power supply can operate at rated output amperage without overheating. A 300 A machine at 60-percent-duty cycle can weld for six minutes at 300 A during a 10-minute period. After six minutes, the welder must rest the machine for the next four minutes to avoid overheating the unit.

Welding Torches and Guns
Used for shielded-metal-arc welding, torches (electrode holders), manually controlled, grip ends of electrodes, also called rods-pinch type and collet type are common.

GMAW and FCAW guns come in pistol-grip, goose-neck, and in-line styles, the latter used for mechanized welding. Knowing the wire diameter, select a gun rated slightly higher than the welding current to be used. Duty-cycle ratings are usually given for CO2 shielding—air or CO2 cooling are usually sufficient for welding at up to 600 A at less than 100-percent duty. Higher amperages require water cool-ing—high-amperage guns come with tubing for water cooling. Hand-held, mounted on a robot arm, or fixed within a mechanized welding setup, guns guide filler wire and shielding gas into the weld puddle.

GTAW torches come air-cooled and water-cooled. Their heads align in-line with the body or at 90, 120, or 135 degrees to it. Nozzles, specified by inside diameters, run ¹ /4 to ⁵ /8 in. Vendors offer special designs: longer to give improved accessibility to the weld joint, or wider to extend shielding gas coverage.

Saw guns come in three types-side, concentric, and deep-groove flux delivery.

In oxyfuel welding (ofw), heat comes from burning gases, rather than arcs. Torches hold separate tubes for fuel gas and oxygen, blended in a mixer assembly. A torch assembly comprises a handle (aluminum, stainless steel, or brass); a mixing chamber; and a brass welding tip or cutting head. Light-duty torches weld sheet metal to 3/16 in. thick; medium, to 1 /2 in.; heavy, ¹ /2 in. and up. Specifying tips by orifice diameter or drill size, manufacturers recom-mend tip sizes based on material and thickness to be welded.

Wire Feeders
GMAW, GTAW, and SAW guns require wire feeders, constant-speed and constant-voltage models, to guide the electrode wire smoothly and continuously into the arc.

Integral with small power supplies or as separate units, these devices push or pull some do both filler wire into the welding gun at speeds from 50 to 900 in./min. Useful features and options: pre-and post-weld gas flow to cover the weld pool at arc-start and ³ /16 in. thick; meto-stop; fine feed-speed calibration; gas purge to clear the gun and cable assembly of air before welding; cold-inch switch to feed wire while electric circuit is inactive; burn-back control to forestall jamming of wire in gun when arc goes out; and digital readouts of settings and speeds. For aluminum welding, look for push-pull setups where the pushing wire feeder can control run-in and crater fill.

Microprocessor-based programmable wire feeders with digital motor-speed control and tachomoter feedback deliver optimum arc control, particularly useful for pulsed welding. Shops can store several synergic-pulsed programs, usually factory-set, in the wire-feeder memory so that the operator simply selects wire and shielding-gas type and the wire feeder does the rest. On some models, operators can customize programs and controls.

Some of these wire feeders feature digital communication to synchronize wire feeder and power supply, to ensure consistent performance even if the two components are separated.

Some suppliers are offering wire feeders redesigned to satisfy CE and NEMA standards.

For outdoor work, select a model housed in an impact-resistant plastic case; the toughest models on the market are steel-reinforced and flame retardant. For work in particularly dusty or dirty conditions, look for models with covered drive-roll assemblies. Where welders are required to switch among two wires of different sizes or types, opt for dual-wire models.

Cables and Accessories
Cables, large-diameter sheathed wires, conduct electricity, linking power sources to work and electrode holders. Along its route, the current passes through lugs, connectors, and splices. Welding cable is generally of drawn annealed strands of copper, 30 or 34 AWG (American Wire Gage). Though 30-gage cable is more common, choose the finer 34-gage wire if you need maximum flexibility.

When specifying cables, remember to distinguish between ground and work cables. The work lead carries current from the power source to the work; the ground lead carries current to ground, from which it completes the circuit to the source.

Some cable is of aluminum wire, lighter and less costly than copper. Specifiers prefer aluminum cable for low-duty-cycle welding; where flexibility is not critical; and where price, weight, and theft (copper attracts thieves) are considerations. Selecting cable, consider ampere draw, current that flows through the cable; distance current will flow from the power supply to the arc; and duty cycle or operator factor. Also consider exposure to atmospheric influences, such as sunlight, ozone, and water; and possibility of exposure to flame and hot metal.

Connectors for welding cable are of brass, copper, or forged copper alloy. They come in sizes for cable 4 through 4/0 AWG. Also called ground clamps, ground connectors ensure strong positive electrical contact, attach and detach easily, and stand up to rough use.

Constructed of drawn-copper strands, insulated welding cables carry currents to 1,000 A.

Gas hoses, with accessories such as connectors and clamps, route shielding gas from the source, cylinder or tanks, to the welding gun. Water hoses for cooling high-amperage guns feed from a city-water tap or a tank.

GTAW accessories include cables — diameters depend on current-output capacity of the power supply, its duty cycle, and the distance from the power supply to the work. The GTAW torch holds the tungsten electrode and conveys the shielding gas to the arc. Torches may be aircooled (to 150 A) or water-cooled (above 150 A) and come rated by current-carrying capacity at 100-percent-duty cycle. Cup-nozzle i.d. is given in sixteenths of an inch--a No. 5 cup measures ⁵ /16-in. i.d. SAW accessories comprise gravity hoppers, which deliver flux to concentric (hand-held) guns. Forced-air systems feed flux for semiautomatic SAW, pushing flux through a hose to the gun: 30 PSI is enough pressure for a 15-ft. hose; longer hoses require more pressure. Most wire feeders used for GMAW work for SAW. Units that vary wire-feed speed with changes in arc voltage work with CC power supplies; CV power supplies take constant-feed-speed wire feed-ers. Dual-wire SAW requires special drive heads to feed two wires of the same diameter with one gun into the weld pool from a common power supply.

Oxyfuel welding requires two gas cylinders (oxygen and fuel gas), gas-flow regulators, hose, check valves, and flashback arrestors. Built to withstand high pressures, gas cylinders hold oxygen and fuel gas such as acetylene and propane.

Gages used on the high-pressure side of a regulator come in 0-3,000 and 0-4,000-PSI ranges. Ranges for low-pressure-side gages: 0-15, 0-30, 0-60, 0-100, 0-200, 0-400, and 0-600 PSI. High-pressure gages for gases at 1,500 PSI and greater should be equipped with flow restrictors to moderate flow into the gage when flow begins.

Installed between hoses and torch or between hoses and regulators, check valves prevent reverse flow of gas. Mounted on regulator outlets, flashback arrestors stop flashback, a high-pressure flame that runs from the torch tip back into the cylinder.

Hoses for OFW are limited to working pressures of 200 PSI. Four sizes are standard, from ⁵ /16- to ⁵ /8- in. inside diameter. Larger diameters offer less resistance to gas flow-they should be used when installations call for long hoses. Flexible and easy to handle, small-diameter hoses allow welders to maneuver around complex weldments with intricate details.

Pressure gages for gases at 1,500 PSI and higher should be equipped with flow restrictors to moderate flow into the gage when flow begins. Regulators come with threaded connections, stipulated by CGA specifications for attachment directly to gas containing cylinders. Most fuel-gas regulators carry left hand threads; oxygen connections are right-handed.

Brazing Equipment and Consumables
Brazing joins materials, both metals and nonmetals, through application of heat and a filler metal that melts at a temperature below the melting point of the materials being joined. Process equipment includes torches, furnaces (vacuum or controlled atmosphere), induction coils, dip baths, and heating devices, for resistance brazing.

Brazing torches are the same as those used for gas cutting and welding operators fit brazing tips at torch ends. All commercial gas mixtures can be employed as fuel; oxyacetylene and oxygen-natural gas are used most often.

Brazing fillers come in wire, foil, rod, preforms, or paste, covered by AWS specs. Filler metals include Bag fillers (ferrous parts); or BCuP, BCu, or RBCuZn fillers for brazing copper parts. Baths for brazing carbon and low-alloy contain fluxing agents such as borax or cryolite.

Powered by electricity, gas, or oil, brazing furnaces provide air-tight chambers holding a vacuum or a controlled atmosphere of high-purity gas, inert or reducing. The AWS Brazing Handbook specifies 12 atmospheres for furnace brazing. lnduction brazing employs electrically powered induction coils to surround and heat joint sites.

For dip brazing, brazements sit in a heated bath, either of molten filler metal or a flux bath of molten salt-brazing alloys come as preplaced filler-metal preforms.

Resistance brazing places the workpiece, with filler metal preplaced, in an electrical circuit. Electrodes contact the brazement to conduct heat into the work, or resistance of the brazement material generates heat. Electrodes are of copper alloys—RWMA (Resistance Welding Manufacturers Association) Class 2 chromium-copper and Class 14 refractory electrodes or of carbon-graphite or electrographite. Common fillers include BAg-1, -1A, -2, -7, -8, and -18, and BCuP 2, and -5. Refer to the AWS Brazing Handbook for classifications of brazing fluxes.