An arc welding process with an arc between a covered electrode and the weld pool. The process is used with shielding from the decomposition of the electrode covering, without the application of pressure, and with filler metal from the electrode. See also FIRECRACKER WELDING.

The core of the covered electrode consists of either a solid metal rod of drawn or cast material or one fabricated by encasing metal powders in a metallic sheath. The core rod conducts the electric current to the arc and provides filler metal for the joint. The primary functions of the electrode covering are to provide arc stability and to shield the molten metal from the atmosphere with gases created as the coating decomposes from the heat of the arc.

The shielding employed, along with other ingredients in the covering and the core wire, largely controls the mechanical properties, chemical composition, and metallurgical structure of the weld metal, as well as the arc characteristics of the electrode. The composition of the electrode covering varies according to the type and purpose of the electrode.

Principles of Operation

Shielded metal arc welding (SMAW) is by far the most widely used of the various arc welding processes. It employs the heat of the arc to melt the base metal and the tip of a consumable covered electrode. The electrode and the work are part of an electric circuit, illustrated in Figure S-5. This circuit begins with the electric power source and includes the welding cables, an electrode holder, a workpiece connection, the workpiece (weldment), and an arc welding electrode. One of the two cables from the power source is attached to the work. The other is attached to the electrode holder.

Welding commences when an electric arc is struck between the tip of the electrode and the work. The intense heat of the arc melts the tip of the electrode and the surface of the work close to the arc. Tiny globules of molten metal rapidly form on the tip of the electrode, then transfer through the arc stream into the molten weld pool. In this manner, filler metal is deposited as the electrode is progressively consumed. The arc is moved over the work at an appropriate arc length and travel speed, melting and fusing a portion of the base metal and continuously adding filler metal. The arc is one of the hottest of the commercial sources of heat; temperatures above 5000°C (9000°F) have been measured at its center. Melting of the base metal takes place almost instantaneously upon arc initiation.

If welds are made in either the flat or the horizontal position, metal transfer is induced by the force of gravity, gas expansion, electric and electromagnetic forces, and surface tension. For welds in other positions, gravity works against the other forces.

The process requires sufficient electric current to melt both the electrode and a proper amount of base metal. It also requires an appropriate gap between the tip of the electrode and the base metal or the molten weld pool. These requirements are necessary to set the stage for coalescence. The sizes and types of electrodes for SMAW define the arc voltage requirements (within the overall range of 16to 40 V) and the amperage requirements (within the overall range of 20 to 550 A). The current may be either alternating or direct, depending on the electrode being used, but the power source must be able to control the level of current within a reasonable range in order to respond to the complex variables of the welding process itself.

Covered Electrodes

In addition to establishing the arc and supplying filler metal for the weld deposit, the electrode introduces other materials into or around the arc, or both.

Depending on the type of electrode being used, the covering performs one or more of the following functions:

(1)Provides a gas to shield the arc and prevent excessive atmospheric contamination of the molten filler metal

(2) Provides scavengers, deoxidizers, and fluxing agents to cleanse the weld and prevent excessive grain growth in the weld metal

(3) Establishes the electrical characteristics of the electrode

(4) Provides a slag blanket to protect the hot weld metal from the air and enhances the mechanical properties, bead shape, and surface cleanliness of the weld metal

(5) Provides a means of adding alloying elements to change the mechanical properties of the weld metal.

Functions (1) and (4) prevent the pickup of oxygen and nitrogen from the air by the molten filler metal in the arc stream and by the weld metal as it solidifies and cools.

The covering on shielded metal arc electrodes is applied by either the extrusion or the dipping process. Extrusion is much more widely used. The dipping process is used primarily for cast and some fabricated core rods. In either case, the covering contains most of the shielding, scavenging, and deoxidizing materials. Most SMAW electrodes have a solid metal core. Some are made with a fabricated or composite core consisting of metal powders encased in a metallic sheath. In this latter case, the purpose of some or even all of the metal powders is to produce an alloy weld deposit.

In addition to improving the mechanical properties of the weld metal, electrode coverings can be designed for welding with alternating current (ac). With ac, the welding arc goes out and is reestablished each time the current reverses its direction. For good arc stability, it is necessary to have a gas in the arc stream that will remain ionized during each reversal of the current. This ionized gas makes possible the re-ignition of the arc. Gases that readily ionize are available from a variety of compounds, including those that contain potassium. It is the incorporation of these compounds in the electrode covering that enables the electrode to operate on ac. To increase the deposition rate, the coverings of some carbon- and low-alloy steel electrodes contain iron powder. The iron powder is another source of metal available for deposition, in addition to that obtained from the core of the electrode. The presence of iron powder in the covering also makes more efficient use of the arc energy. Metal powders other than iron are frequently used to alter the mechanical properties of the weld metal.

The thick coverings on electrodes with relatively large amounts of iron powder increase the depth of the crucible at the tip of the electrode. This deep crucible helps to contain the heat of the arc and permits the use of the drag technique to maintain a constant arc length. When iron or other metal powders are added in relatively large amounts, the deposition rate and welding speed usually increase.

Iron powder electrodes with thick coverings reduce the level of skill needed to weld. The tip of the electrode can be dragged along the surface of the work while maintaining a welding arc. For this reason, heavy iron powder electrodes frequently are called drug electrodes. Deposition rates are high, but, because slag solidification is slow, these electrodes are not suitable for out-of-position welds.

Arc Shielding

The arc shielding action, illustrated in Figure S-6, is essentially the same for all electrodes, but the specific method of shielding and the volume of slag produced vary from type to type. The bulk of the covering materials on some electrodes is converted to gas b,y the heat of the arc, and only a small amount of sla,g is produced. This type of electrode depends largely on a gaseous shield to prevent atmospheric contamination. Weld metal from such electrodes can be identified by the incomplete or light layer of slag which covers the bead.

For electrodes at the other extreme, the bulk of the covering is converted to slag by the heat of the arc, and only a small volume of shielding gas is produced. The tiny globules of metal being transferred across the arc are entirely coated with a thin film of molten slag. This molten slag floats to the surface of the weld puddle because it is lighter than the metal. The slag solidifies after the weld metal has solidified. Welds made with these electrodes are identified by the heavy slag deposits that completely cover the weld beads. Between these extremes is a wide variety of electrode types, each with a different combination of gas and slag shielding.

Variations in the amount of slag and gas shielding also influence the welding characteristics of covered electrodes. Electrodes which produce a heavy slag can carry high amperage and provide high deposition rates, making them ideal for heavy weldmerits in the flat position. Electrodes which produce a light slag layer are used with lower amperage and provide lower deposition rates. These electrodes produce a smaller weld pool and are suitable for making welds in all positions. Because of the differences in their welding characteristics, one type of covered electrode usually will be best suited for a given application.

SMAW Capabilities and Limitations

Shielded metal arc welding is the most widely used process, particularly for short welds in production, maintenance and repair work, and for field construction. The following are advantages of this process:

(1) The equipment is relatively simple, inexpensive, and portable.

(2) The filler metal, and the means of protecting it and the weld metal from harmful oxidation during welding, are provided by the covered electrode.

(3) Auxiliary gas shielding or granular flux is not required.

(4) The process is less sensitive to wind and draft than gas shielded arc welding processes.

(5) It can be used in areas of limited access.

(6) The process is suitable for most of the commonly used metals and alloys.

SMAW electrodes are available to weld carbon- and low-alloy steels, stainless steels, cast irons, copper, and nickel, and their alloys, and for some aluminum applications. Low-melting metals, such as lead, tin, and zinc, and their alloys, are not welded with SMAW because the intense heat of the arc is too high for them. SMAW is not suitable for reactive metals such as titanium, zirconium, tantalum, and niobium because the shielding provided is inadequate to prevent oxygen contamination of the weld.

Covered electrodes are produced in lengths of 230 to 460 mm (9 to 18 in.). As the arc is first struck, the current flows the entire length of the electrode. The amount of current that can be used, therefore, is limited by the electrical resistance of the core wire.

Excessive amperage overheats the electrode and breaks down the covering. This, in turn, changes the arc characteristics and the shielding that is obtained. Because of this limitation, deposition rates are generally lower than for a welding process such as gas metal arc welding (GMAW).

Operator duty cycle and overall deposition rates for covered electrodes are usually less than provided with a continuous electrode process such as flux cored arc welding (FCAW). This is because electrodes can be consumed only to some certain minimum length. When that length has been reached, the welder must discard the unconsumed electrode stub and insert a new electrode into the holder. In addition, slag usually must be removed at starts and stops and before depositing a weld bead adjacent to or onto a previously deposited bead.

Equipment

Power Sources- Either alternating current (ac) or direct current (dc) may be employed for shielded metal arc welding, depending on the welding power supply and the electrode selected. The specific type of current employed influences the performance of the electrode. Each current type has its advantages and limitations, and these must be considered when selecting the type of current for a specific application. Factors which need to be considered are as follows:

(1) Voltage Drop. Voltage drop in the welding cables is lower with ac. This makes ac more suitable if the welding is to be done at long distances from the power supply. However, long cables which carry ac should not be coiled because the inductive losses encountered in such cases can be substantial.

(2) Low Current. With small diameter electrodes and low welding currents, dc provides better operating characteristics and a more stable arc.

(3) Arc Starting. Striking the arc is generally easier with dc, particularly if small diameter electrodes are used. With ac, the welding current passes through zero each half cycle, and this presents problems for arc starting and arc stability.

(4)Arc Length. Welding with a short arc length (low arc voltage) is easier with dc than with ac. This is an important consideration, except for the heavy iron powder electrodes. With those electrodes, the deep crucible formed by the heavy covering automatically maintains the proper arc length when the electrode tip is dragged on the surface of the joint.

(5) Arc Blow. Alternating current rarely presents a problem with arc blow because the magnetic field is constantly reversing (120 times per second). Arc blow can be a significant problem with d-c welding of ferritic steel because of unbalanced magnetic fields around the arc.

(6) Welding Position. Direct current is somewhat better than ac for vertical and overhead welds because lower amperage can be used. With suitable electrodes, however, satisfactory welds can be made in all positions with ac.

(7) Metal Thickness. Both sheet metal and heavy sections can be welded using dc. The welding of sheet metal with ac is less desirable than with dc. Arc conditions at low current levels required for thin materials are less stable on ac power than on dc power.

Constant-voltage power sources are not suitable for SMAW because with their flat volt-ampere curve, even a small change in arc length (voltage) produces a relatively large change in amperage. A constant-current power source is preferred for manual welding, because the steeper the slope of the volt-ampere curve (within the welding range), the smaller the change in current for a given change in arc voltage (arc length).

For applications that involve large diameter electrodes and high welding currents, a steep volt-ampere curve is desirable.

Where more precise control of the size of the molten pool is required (out-of-position welds and root passes of joints with varying fit-up, for example), a flatter volt-ampere curve is desirable. This enables the welder to change the welding current within a specific range simply by changing arc length. In this manner, the welder has some control over the amount of filler metal that is being deposited. Figure S-7 portrays these different volt-ampere curves for a typical welding power source. Even though the difference in the slope of the various curves is substantial, the power source is still considered a constant-current power source. The changes shown in the volt-ampere curve are accomplished by adjusting both the open circuit voltage (OCV) and the current settings on the power source.

Voltage- Open circuit voltage, which is the voltage set on the power source, does not refer to arc voltage. Arc voltage is the voltage between the electrode and the work during welding and is determined by arc length for any given electrode. Open circuit voltage, on the other hand, is the voltage generated by the welding machine when no welding is being done. Open circuit voltages generally run between 50 and 100 V, whereas arc voltages are between 17 and 40 V. The open circuit voltage drops to the arc voltage when the arc is struck and the welding load comes on the machine. The arc length and the type of electrode being used determine just what this arc voltage will be. If the arc is lengthened, the arc voltage will increase and the welding current will decrease. The change in amperage which a change in arc length produces is determined by the slope of the volt-ampere curve within the welding range.

Some power sources do not provide for control of the open circuit voltage because this control is not needed for all welding processes. It is a useful feature for SMAW, yet it is not necessary for all applications of the process.

Power Source Selection- Several factors need to be considered when a power source for SMAW is selected:

(1) The type of welding current required

(2) The amperage range required

(3) The positions in which welding will be done

(4) The primary power available at the work station

Selection of the type of current, ac, dc, or both, will be based largely on the types of electrodes to be used and the kind of welds to be made. For ac, a transformer or an alternator type of power source may be used. For dc, transformer-rectifier or motor-generator power sources are available. When both ac and dc will be needed, a single-phase transformer-rectifier or an alternator-rectifier power source may be used. Otherwise, two welding machines will be required, one for ac and one for dc.

The amperage requirements will be determined by the sizes and types of electrodes to be used. When a variety will be encountered, the power supply must be capable of providing the amperage range needed. The duty cycle must be adequate.

The positions in which welding will be done should also be considered. If vertical and overhead welding are planned, adjustment of the slope of the V-A curve probably will be desirable (See Figure S-7). If so, the power supply must provide this feature. This usually requires controls for both the output voltage and the current.

A supply of primary power is needed. If line power is available, it should be determined whether the power is single-phase or three-phase. The welding power source must be designed for either single-or three-phase power, and it must be used with the one it was designed for. If line power is not available, an engine-driven generator or alternator must be used.

Accessory Equipment

Electrode Holder- An electrode holder is a clamping device which allows the welder to hold and control the electrode. It also serves as a device for conducting the welding current from the welding cable to the electrode. An insulated handle on the holder separates the welder’s hand from the welding circuit as shown in Figure S-8. The current is transferred to the electrode through the jaws of the holder. To assure minimum contact resistance and to avoid overheating of the holder, the jaws must be kept in good condition. Overheating of the holder not only makes it uncomfortable for the welder, but also it can cause excessive voltage drop in the welding circuit. Both can impair the welder’s performance and reduce the quality of the weld. The holder must grip the electrode securely and hold it in position with good electrical contact. Installation of the electrode must be quick and easy. The holder needs to be light in weight and easy to handle, yet it must be sturdy enough to withstand rough use. Most holders have insulating material around the jaws to prevent grounding of the jaws to the work. Electrode holders are produced in sizes to accommodate a range of standard electrode diameters. Each size of holder is designed to carry the current required for the largest diameter electrode that it will hold. The smallest size holder that can be used without overheating is the best one for the job. It will be the lightest, and it will provide the best operator comfort.

Workpiece Connection- A workpiece connection is a device for connecting the workpiece lead to the workpiece. It should produce a tight connection, yet be able to be attached quickly and easily to the work. For light duty, a spring-loaded clamp may be suitable. For high currents, however, a screw clamp may be needed to provide a good connection without overheating the clamp.

Welding Cables- Welding cables are used to connect the electrode holder and the ground clamp to the power source. They are part of the welding circuit (See Figure S-5).The cable is constructed for maximum flexibility to permit easy manipulation, particularly of the electrode holder. It also must be wear and abrasion resistant. A welding cable consists of many fine copper or aluminum wires stranded together and enclosed in a flexible, insulating jacket. The jacket is made of synthetic rubber or of a plastic that has good toughness, high electrical resistance, and good heat resistance. A protective wrapping is placed between the stranded conductor wires and the insulating jacket to permit some movement between them and provide maximum flexibility. Welding cable is produced in a range of sizes from about AWG 6 to 4/0. The size of  the cable required for a particular application depends on the maximum amperage to be used for welding, the length of the welding circuit (welding and work cables combined), and the duty cycle of the welding machine.

If long cables are necessary, short sections can be joined by suitable cable connectors. The connectors must provide good electrical contact with low resistance, and their insulation must be equivalent to that of the cable. Lugs, at the end of each cable, are used to connect the cables to the power source. The connection between the cable and a connector or lug must be tight with low electrical resistance. Soldered joints and mechanical connections are used. Aluminum cable requires a good mechanical connection to avoid over-heating. Oxidation of the aluminum significantly increases the electrical resistance of the connection. This of course, can lead to overheating, excessive power loss, and cable failure. Care must be taken to avoid damage to the jacket of the cable, particularly for the electrode cable. Contact with hot metal or sharp edges may penetrate the jacket and ground the cable.

HelmetThe purpose of the helmet is to protect the welder’s eyes, face, forehead, neck, and ears from the direct rays of the arc and from flying sparks and spatter. Some helmets have an optional “flip lid” which permits the dark filter plate over the opening in the shield to be flipped up so the welder can see while the slag is being chipped from the weld. This protects the welder’s face and eyes from flying slag. Slag can cause serious injury if it strikes a person, particularly while it is hot. It can be harmful to the eyes whether it is hot or cold.

Helmets are generally constructed of pressed fiber or fiberglass insulating material. A helmet should be light in weight and should be designed to give the welder the greatest possible comfort.

Miscellaneous Equipment- Cleanliness is important in welding. The surfaces of the workpieces and the previously deposited weld metal must be cleaned of dirt, slag, and any other foreign matter that would interfere with welding. To accomplish this, the welder should have a steel wire brush, a hammer, a chisel, and a chipping hammer. These tools are used to remove dirt and rust from the base metal, cut tack welds, and chip slag from the weld bead.

The joint to be welded may require backing to support the molten weld pool during deposition of the first layer of weld metal. Backing strips or nonmetallic backing materials are sometimes used, particularly for joints which are accessible from only one side.

Materials

Base Metals- The SMAW process is used in joining and surfacing applications on a variety of base metals. The suitability of the process for any specific base metal depends on the availability of a covered electrode whose weld metal has the required composition and properties. Electrodes are available for the following base metals:

(1) Carbon steels

(2) Low-alloy steels

(3) Corrosion-resisting steels

(4) Cast irons (ductile and gray)

(5) Aluminum and aluminum alloys

(6) Copper and copper alloys

(7) Nickel and nickel alloys

Electrodes are available for application of wear, impact, or corrosion resistant surfaces to these same base metals.

Covered Electrodes

Covered electrodes are classified according to the requirements of specifications issued by the American Welding Society (AWS). Certain agencies of the Department of Defense also issue specifications for covered electrodes. The AWS specification numbers and their electrode classifications are shown in Table S-1. The electrodes are classified on the basis of their chemical composition or mechanical properties, or both, of their undiluted weld metal. Carbon steel, low- alloy steel, and stainless steel electrodes are also classified according to the type of welding current they are suited for and sometimes according to the positions of welding that they can be used. See ELECTRODE CLASSIFICATION.

Electrode Conditioning

SMAW electrode coverings are hygroscopic (they readily absorb and retain moisture). Some coverings are more hygroscopic than others. The moisture they pick up on exposure to a humid atmosphere dissociates to form hydrogen and oxygen during welding.

The atoms of hydrogen dissolve in the weld and the heat-affected zone and may cause cold cracking. This type of crack is more prevalent in hardenable steel base metals and high-strength steel weld metals. Excessive moisture in electrode coverings can cause porosity in the deposited weld metal.

To minimize moisture problems, particularly for low-hydrogen electrodes, they must be properly packaged, stored, and handled. Such control is critical for electrodes which are to be used to weld hardenable base metals. Control of moisture becomes increasingly important as the strength of the weld metal or the base metal increases. Holding ovens are used for low-hydrogen electrodes once those electrodes have been removed from their sealed container and have not been used within a certain period of time. This period varies from as little as half an hour to as much as eight hours, depending on the strength of the electrode, the humidity during exposure, and even the specific covering on the electrode. The time which an electrode can be kept out of an oven or rod warmer is reduced as the humidity increases.

The temperature of the holding oven should be within the range of 65 to 150°C (150 to 300°F). Electrodes that have been exposed too long require baking at a substantially higher temperature to drive off the absorbed moisture. The specific recommendations of the manufacturer of the electrode need to be followed because the time and temperature limitations can vary from manufacturer to manufacturer, even for electrodes within a given classification. Excessive heating can damage the covering on an electrode.

Applications

Shielded metal arc welding is the most widely used of the arc welding processes.

Materials- The SMAW process can be used to join most of the common metals and alloys. The list includes carbon steels, low-alloy steels, stainless steels, and cast iron, as well as copper, nickel, and aluminum and their alloys. Shielded metal arc welding is also used to join a wide range of chemically dissimilar materials.

The process is not used for materials for which shielding of the arc by the gaseous products of an electrode covering is unsatisfactory. The reactive (Ti, Zr) and refractory (Cb, Ta, Mo) metals fall into this group.

Thicknesses- The shielded metal arc process is adaptable to any material thickness within certain practical and economic limitations. For material thicknesses less than about 1.6 mm (1/16 in.), the base metal will melt through and the molten metal will fall away before a common weld pool can be established, unless special fixturing and welding procedures are employed. There is no upper limit on thickness, but other processes such as submerged arc welding (SAW) or flux cored arc welding (FCAW) are capable of providing higher deposition rates and economies for most applications involving thicknesses exceeding 38 mm (1-1/2 in.). Most of the SMAW applications are on thicknesses between 3 and 38 mm (1/8 and 1-1/2 in.), except where irregular configurations are encountered. Such configurations put an automated welding process at an economic disadvantage. In such instances, the shielded metal arc process is commonly used to weld materials as thick as 250 mm (10 in.).

Welding Position

One of the major advantages of SMAW is that welding can be done in any position on most of the materials for which the process is suitable. This makes the process useful on joints that cannot be placed in the flat position. Despite this advantage, welding should be done in the flat position whenever practical because less skill is required, and larger electrodes with correspondingly higher deposition rates can be used. Welds in the vertical and overhead positions require more skill on the welder’s part and are performed using smaller diameter electrodes. Joint designs for vertical and overhead welding may be different from those suitable for flat position welding.

Location of Welding

The simplicity of the equipment makes SMAW an extremely versatile process with respect to the location and environment of the operation. Welding can be done indoors or outdoors, on a production line, a ship, a bridge, a building framework, an oil refinery, a cross-country pipeline, or any such type of work. No gas or water hoses are needed and the welding cables can be extended quite some distance from the power source. In remote areas, gasoline or diesel powered units can be used. Despite this versatility, the process should always be used in an environment which shelters it from the wind, rain, and snow.

Weld Backing

When full penetration welds are required and welding is done from one side of the joint, weld backing may be required. Its purpose is to provide something on which to deposit the first layer of metal and thereby prevent the molten metal in that layer from escaping through the root of the joint.

Four types of backing are commonly used:

(1) Backing strip

(2) Backing weld

(3) Copper backing bar

(4) Nonmetallic backing

Backing Strip- A backing strip is a strip of metal placed on the back of the joint, as shown in Figure S-9 (A). The first weld pass ties both members of the joint together and to the backing strip. The strip may be left in place if it will not interfere with the serviceability of the joint. Otherwise, it should be removed, in which case the back side of the joint must be accessible. If the back side is not accessible, some other means of obtaining a proper root pass must be used.

The backing strip must always be made of a material that is metallurgically compatible with the base metal and the welding electrode to be used. Where design permits, another member of the structure may serve as backing for the weld. Figure S-9 (B) provides an example of this. In all cases, it is important that the backing strip as well as the surfaces of the joint be clean to avoid porosity and slag inclusions in the weld.

It is also important that the backing strip fit properly. Otherwise, the molten weld metal can run out through any gap between the strip and the base metal at the root of the joint.

Copper Backing Bar- A copper bar is sometimes used as a means of supporting the molten weld pool at the root of the joint. Copper is used because of its high thermal conductivity. This high conductivity helps prevent the weld metal from fusing to the backing bar.

Despite this, the copper bar must have sufficient mass to avoid melting during deposition of the first weld pass. In high production use, water can be passed through holes in the bar to remove the heat that accumulates during continuous welding. Regardless of the method of cooling, the arc should not be allowed to impinge on the copper bar, for if any copper melts, the weld metal can become contaminated with copper. The copper bar may be grooved to provide the desired root surface contour and reinforcement.

Nonmetallic Backing- Nonmetallic backing of either granular flux or refractory material is also a method that is used to produce a sound first pass. The flux is used primarily to support the weld metal and to shape the root surface. A granular flux layer is supported against the back side of the weld by some method such as a pressurized fire hose. A system of this type is generally used for production line work, and it is not widely used for SMAW.

Refractory type backing consists of a flexible, shaped form that is held on the back side of the joint by clamps or by pressure-sensitive tape. This type of backing is sometimes used with the SMAW process, although special welding techniques are required to consistently produce good results. The recommendations of the manufacturer of the backing should be followed.

Backing WeldA backing weld is one or more backing passes in a single groove weld joint. This weld is deposited on the back side of the joint before the first pass is deposited on the face side. After the backing weld, all subsequent passes are made in the groove from the face side. The root of the joint may be ground or gouged after the backing weld is made to produce sound, clean metal on which to deposit the first pass on the face side of the joint.

Safety Recommendations

The operator must protect eyes and skin from radiation from the arc. A welding helmet with a suitable filter lens should be used, as well as dark clothing, preferably wool, to protect the skin. Leather gloves and clothing should be worn to protect against bums from arc spatter.

Welding helmets are provided with filter plate windows, the standard size being 51 by 130 mm (2by 4-1/ 8 in.). Larger openings are available. The filter plate should be capable of absorbing infrared rays, ultraviolet rays, and most of the visible rays emanating from the arc. Filter plates that are now available absorb 99% or more of the infrared and ultraviolet rays from the arc.

The shade of the filter plate suggested for use with electrodes up to 4 mm (Y32 in.) diameter is No. 10. For 4.8 to 6.4 mm (3116 to 114 in.) electrodes, Shade No. 12 should be used. Shade No. 14 should be used for electrodes over 6.4 mm (1/4 in.).

The filter plate needs to be protected from molten spatter and from breakage. This is done by placing a plate of clear glass, or other suitable material, on each side of the filter plate. Those who are not welders but work near the arc also need to be protected. This protection usually is provided by either permanent or portable screens. Failure to use adequate protection can result in eye burn for the welder or for those working around the arc. Eye bum, which is similar to sunburn, is extremely painful for a period of 24 to 48 hours. Unprotected skin, exposed to the arc, may also be burned. A physician should be consulted in the case of severe arc burn, regardless of whether it is of the skin or the eyes.

If welding is being performed in confined spaces with poor ventilation, auxiliary air should be supplied to the welder. This should be done through an attachment to the helmet.  The method used must not restrict the welder’s manipulation of the helmet, interfere with the field of vision, or make welding difficult. Additional information on eye protection and ventilation is given in ANSI 249.1, Safety in Welding and Cutting, published by the American Welding Society.

From time to time during welding, sparks or globules of molten metal are thrown out from the arc.This is always a point of concern, but it becomes more serious when welding is performed out of position or when extremely high welding currents are used. To ensure protection from bums under these conditions, the welder should wear flame-resistant gloves, a pro- tective apron, and a jacket. It may also be desirable to protect the welder’s ankles and feet from slag and spatter. CuffIess pants and high work shoes or boots are recommended.

To avoid electric shock, the operator should not weld while standing on a wet surface. Equipment should be examined periodically to make sure there are no cracks or worn spots on electrode holder or cable insulation.

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