SHIELDED METAL-ARC WELDING AND WEARFACING

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CHAPTER 7SHIELDED METAL-ARC WELDINGAND WEARFACINGrequires a number of accessories that include a combination chipping hammer and wire brush, welding table(for shopwork), C-clamps, and protective apparel.The shielded metal-arc welding process, referred toas metallic-arc welding, arc welding, or stick welding,is extensively used in welding ferrous and nonferrousmetals. It has many applications for producing a vastassortment of metal products. Shielded metal-arc welding is found in the ship building industry and in theconstruction industry for fabricating girders, beams, andcolumns. Because it is easy to use and portable, shieldedmetal-arc welding is universally used in the repair andservicing of equipment, machinery, and a host of otheritems.Before we discuss the different types of weldingmachines, you must first have a basic knowledge of theelectrical terms used with welding.Electrical TermsMany terms are associated with arc welding. Thefollowing basic terms are especially important.ALTERNATING CURRENT.— Alternating current is an electrical current that has alternating negativeand positive values. In the first half-cycle, the currentflows in one direction and then reverses itself for thenext half-cycle. In one complete cycle, the currentspends 50 percent of the time flowing one way and theother 50 percent flowing the other way. The rate ofchange in direction is called frequency, and it is indicated by cycles per second. In the United States, thealternating current is set at 60 cycles per second.MANUAL SHIELDED METAL-ARCWELDINGArc welding provides you the ability to join twometals by melting them with an arc generated betweena coated-metal electrode and the base metal. The temperatures developed by the arc can reach as high as10000 F. The arc energy is provided by a power sourcethat generates either direct or alternating current. Theelectrodes that carry the current produce a gas thatshields the arc from the atmosphere and supplies fillermetal to develop the weld shape.AMPERE.— Amperes, sometimes called “amps,”refers to the amount of current that flows through acircuit. It is measured by an “amp” meter.ARC-WELDING EQUIPMENTCONDUCTOR.— Conductor means any materialthat allows the passage of an electrical current.A wide variety of welding equipment is available,and there are many differences between the makes andmodels of the equipment produced by the manufacturers. However, all types of arc-welding equipment aresimilar in their basic function of producing the high-amperage, low-voltage electric power required for thewelding arc. In this discussion, we are primarily concerned with the typical items of arc-welding equipment,rather than the specific types. For specific informationabout the equipment your battalion or duty station hasavailable, consult the manufacturer’s instruction manual. For additional operational information and safetyinstruction, have your leading welding petty officerexplain the operation to you.CURRENT.— Current is the movement or flow ofan electrical charge through a conductor.DIRECT CURRENT.— Direct current is an electrical current that flows in one direction only.ELECTRICAL CIRCUIT.— Electrical circuit isthe path taken by an electrical current flowing througha conductor from one terminal of the source to the loadand returning to the other terminal of the source.POLARITY.— Polarity is the direction of the flowof current in a circuit. Since current flows in one direction only in a dc welder, the polarity becomes an important factor in welding operations.The basic parts of a typical shielded metal-arc welding outfit include a welding machine, cables, electrodeholder (stinger), and electrodes. The Steelworker alsoRESISTANCE.— Resistance is the opposition ofthe conductor to the flow of current. Resistance causeselectrical energy to be changed into heat.7-1

127.517Figure 7-1.—A 300 amp ac/dc portable weldingmachine.Figure 7-2.—An ac arc-welding transformer.1. Machines rated 150 and 200 amperes—30 voltsare for light-shielded metal-arc welding and for inertgas arc welding. They are also for general-purposejobs or shopwork.VOLT.— A volt is the force required to make thecurrent flow in an electrical circuit. It can becompared to pressure in a hydraulic system. Volts aremeasured with a volt meter.2. Machines rated 200,300, and 400 amperes—40volts are for general welding purposes by machine ormanual application.Power SourceThe power source used in arc welding is called awelding machine or a welder. Three basic types ofwelding machines are presently in use: motorgenerators, transformers, and rectifiers.3. Machines rated 600 amperes—40 volts are forsubmerged-arc welding or carbon-arc cutting.ALTERNATING-CURRENT TRANSFORMERWELDING MACHINES.— Practically all thealternating current (at) arc-welding machines in useare the static-transformer type, as shown in figure 72. These types of machines are the smallest, leastexpensive, and the lightest type of welders made.Industrial applications for manual operation usemachines having 200, 300, and 400 ampere ratings.Machines with a 150-ampere rating are used in lightindustrial, garage, and job/shop welding.The transformers are usually equipped with arcstabilizing capacitors. Current control is provided inseveralwaysbytheweldingtransformermanufacturers. One such method is an adjustablereactor that is set by turning a crank until theappropriate setting is found. Another method is byplugging the electrode cable into different socketslocated on the front of the machine.One major advantage of ac transformers is thefreedom from arc blow, which often occurs when weldingwith direct-current (dc) machines. Arc blow causes the arcto wander while you are welding in corners on heavymetal or using large coated electrodes.MOTOR-GENERATORWELDINGMACHINES.— These types of welding machines arepowered by electrical, gasoline, or diesel motors. Thediesel and gasoline motors are ideal for use in areaswhere electricity is not available. Portable gas/dieselwelding machines are part of the equipmentallowance for Naval Mobile Construction Battalions.These machines usually have the capability ofgenerating alternating or direct current. On thenewer machines, when you are welding in the directcurrent mode, the polarity can be changed by turninga switch. Some of the older machines requirereversing the cable connections. One of theadvantages of a direct-current (dc) welding generatoris that you have the choice of welding with eitherstraight or reverse polarity. The welding machine, asshown in figure 7-1, consists of a heavy-duty, ac/dc300 amp generator powered by a diesel engine. Thegenerator is also capable of producing 3 kilowatts of60 cycle ac power.Welding machines are made in six standardizedratings for general purposes and are listed as follows:7-2

Table 7-1.—Cable Size Selection Guidepolarity current. By flicking a switch, the welder canselect the current that best suits the job. Figure 7-3 showsan example of a combination ac/dc rectifier.CablesWelding cables carry the current to and from theworkpiece. One of the cables runs from the weldingmachine to the electrode holder and the other cableconnects the workpiece to the welding machine. Thecable that connects the workpiece to the welding machine is called the ground. When the machine is turnedon and the operator touches the electrode to the workpiece, the circuit is completed, current begins to flow,and the welding process commences.The welding cables must be flexible, durable, wellinsulated, and large enough to carry the required current.Only cable that is specifically designed for weldingshould be used. A highly flexible cable must be used forthe electrode holder connection. This is necessary so theoperator can easily maneuver the electrode holder during the welding process. The ground cable need not beso flexible because once it is connected, it does notmove.Two factors determine the size of welding cable touse: the amperage rating of the machine and the distancebetween the work and the machine. If either amperageor distance increases, the cable size also must increase.(See table 7-1.) A cable that is too small for the amperageor the distance between the machine and the work willoverheat. On the other hand, larger size cables are moreFigure 7-3.—Combination ac, dc transformer-rectifier arc welder.RECTIFIER WELDING MACHINES.— Rectifier welders are single-phase or three-phase transformers that have selenium or silicon rectifiers added torectify (change) the output current from alternating todirect current. Most of these machines have the capability of producing either ac or dc straight or reverse7-3

difficult to handle, especially if you are working on astructure that requires a lot of moving around. The bestsize cable is one that meets the amperage demand but issmall enough to manipulate with ease.As a rule, the cable between the machine and thework should be as short as possible. Use one continuouslength of cable if the distance is less than 35 feet. If youmust use more than one length of cable, join the sectionswith insulated lock-type cable connectors. Joints in thecable should be at least 10 feet away from the operator.Figure 7-4.—C-clamped ground cable.Electrode HolderAn electrode holder, commonly called a stinger, isa clamping device for holding the electrode securely inany position. The welding cable attaches to the holderthrough the hollow insulated handle. The design of theelectrode holder permits quick and easy electrode exchange. Two general types of electrode holders are inuse: insulated and noninsulated. The noninsulated holders are not recommended because they are subject toaccidental short circuiting if bumped against the workpiece during welding. For safety reasons, try to ensurethe use of only insulated stingers on the jobsite.Figure 7-5.—A spring-loaded ground clamp for the ground lead.Electrode holders are made in different sizes, andmanufacturers have their own system of designation.Each holder is designed for use within a specified rangeof electrode diameters and welding current. You requirea larger holder when welding with a machine having a300-ampere rating than when welding with a 100-ampere machine. If the holder is too small, it will overheat.Ground ClampsFigure 7-6.—Bolted and tack-welded ground clamps.The use of a good ground clamp is essential toproducing quality welds. Without proper grounding, thecircuit voltage fails to produce enough heat for properwelding, and there is the possibility of damage to thewelding machine and cables. Three basic methods areused to ground a welding machine. You can fasten theground cable to the workbench with a C-clamp (fig. 74), attach a spring-loaded clamp (fig. 7-5) directly ontothe workpiece, or bolt or tack-weld the end of the groundcable to the welding bench (fig. 7-6). The third waycreates a permanent common ground.part of the welder’s equipment. After initial cleaning anda weld bead has been deposited, the slag cover must beremoved before additional beads are added. The chipping hammer was specifically designed for this task.The chipping operation is then followed by more brushing, and this cycle is repeated until the slag has beenremoved. When the slag is not removed, the result isporosity in the weld that weakens the weld joint.Cleaning can also be accomplished by the use ofpower tools or chemical agents. If these items are used,it is essential that all safety precautions are followed.Cleaning EquipmentSafety EquipmentStrong welds require good preparation and procedure. The surface area of the workpiece must be free ofall foreign material, such as rust, paint, and oil. A steelbrush is an excellent cleaning tool and is an essentialArc welding not only produces a brilliant light, butit also emits ultraviolet and infrared rays that are very7-4

dangerous to your eyes and skin. In chapter 3, personalsafety items, such as helmets, lenses, and gloves, werecovered. An important item that needs to be coveredhere is welding screens. The welder not only has toprotect himself but he also must take precautions toprotect other people who may be working close by.When you are welding in the field, you must install awelding screen around your work area. It can be anelaborate factory-manufactured screen or as simple asone constructed on site from heavy fire-resistant canvas.literature and check with your senior petty officer orchief on the items that you do not understand. Machinesetup involves selecting current type, polarity, and current settings. The current selection depends on the sizeand type of electrode used, position of the weld, and theproperties of the base metal.Cable size and connections are determined by thedistance required to reach the work the size of themachine, and the amperage needed for the weld.Operator maintenance depends on the type of welding machine used. Transformers and rectifiers requirelittle maintenance compared to engine-driven weldingmachines. Transformer welders require only to be keptdry and a minimal amount of cleaning. Internal maintenance should only be done by electricians due to thepossibilities of electrical shock Engine-driven machines require daily maintenance of the motors. Inmostplaces you will be required to fill out and turn in a dailyinspection form called a “hard card” before starting theengine. This form is a list of items, such as oil level,water level, visible leaks, and other things, that affectthe operation of the machine. Transportation departments are the ones who usually handle these forms.WARNINGNever look at thes welding arc withoutproper eye protection. Looking at the arc withthe naked eye could result in permanent eyedamage. If you receive flash burns, they shouldbe treated by medical personnel.Another area often overlooked is ventilation. Welding produces a lot of smoke and fumes that can beinjurious to the welder if they are allowed to accumulate.This is especially true if you are welding in a tank orother inclosed area. Perm