Caterpillar Service Welding Guide {0374, 0599, 0677, 0678, 0679} Caterpillar

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Introduction

Table 1

Revision	Summary of Changes in SEBD0512
06	Corrected Welding Symbols illustrations.
05	Added Expanded Mining Products and updated graphics.
04	Added confidentiality statement and Think Safety graphic.
03	Added serial number prefixes.

© 2016 Caterpillar All Rights Reserved. This guideline is for the use of Cat dealers only. Unauthorized use of this document or the proprietary processes therein without permission may be violation of intellectual property law.

Information contained in this document is considered Caterpillar: Confidential Yellow.

This Reuse and Salvage Guideline contains the necessary information to allow a dealer to establish a parts reusability program. Reuse and salvage information enables Caterpillar dealers and customers to benefit from cost reductions. Every effort has been made to provide the most current information that is known to Caterpillar. Continuing improvement and advancement of product design might have caused changes to your product which are not included in this publication. This Reuse and Salvage Guideline must be used with the latest technical information that is available from Caterpillar.

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Summary

The Service Welding Guide was developed by the Service Department and East Peoria Weld Engineering of Caterpillar Inc. The guide was developed to assist the technician in selecting the proper welding techniques to be employed. This fundamental information can be combined with the technician's welding abilities to utilize the optimum combination of factors affecting weld quality. These factors include welding process selection, recommended equipment, repair methods, types of joints and weld defects. The evaluation and application of these factors constitutes the proper service welding techniques. These techniques will produce welds in all joint positions on all types of steels.

The appendix of this booklet contains a list of reference books that have been proven to be useful to service welders. Further reading in these sources is suggested in areas of particular interest. The appendix also contains a glossary of welding terms used in this booklet.

Safety and Recommended Equipment

Illustration 1	g02139237

Safety Precautions

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Personal injury or death can result from an explosion. Applying heat to a tank which has held flammable liquids, even when empty, can result in residual flammable liquid or vapor igniting with explosive force. Do not weld or flame cut on any tank that has held flammable liquid without taking the proper precautions such as filling the tank with either carbon dioxide or water. Please refer to Special Instruction, REHS1841, "General Welding Procedures".

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Personal injury or death can result from fumes, gases and ultraviolet rays from the weld arc. Welding can cause fumes, burn skin and produce ultraviolet rays. Keep your head out of the fumes. Use ventilation, exhaust at the arc, or both, to keep fumes and gases from your breathing area. Wear eye, ear and body protection before working. Protect yourself and others; read and understand this warning. Fumes and gases can be dangerous to your health. Ultraviolet rays from the weld arc can injure eyes and burn skin. Electric shock can cause death. Read and understand the manufacturer's instructions and your employer's safety practices. Do not touch live electrical parts. See "American National Standard Z49.1, Safety in Welding and Cutting" published by the American Welding Society. American Welding Society 2501 N.W. 7th Street Miami, Florida 33125 See "OSHA Safety and Health Standards, 29 CFR 1910", available from U.S. Department of Labor. U.S. Department of Labor Washington, D.C. 20210

• Keep equipment and work area clean, dry, and neat. After using, put away tools.

• Be sure that work area has adequate ventilation.

• Always wear protective gloves and aprons, safety shoes, and heavy cotton clothing. Keep collars and shirt cuffs buttoned. Turn down trouser cuffs. Be sure that trouser legs extend below shoe tops.

• Wear a welding helmet or eye shield with proper filter plates when welding or cutting. Use a No. 4 or No. 5 filter for touch brazing, flame cutting, and gas welding. Use a No. 10 or No. 12 filter for arc welding.

• Keep a CO₂ or dry powder fire extinguisher within reach - especially when flame cutting or welding on or near machine engines.

• Remove all flammable materials, volatile liquids, and explosive gases from the welding area or shield adequately.

• Do not weld or cut on containers until you know that there is no danger of fire or explosion.

• Always drill a relief hole in a closed compartment, such as a fabricated track idler or track roller frame box section, before welding or cutting. Without performing this step, any moisture inside the compartment can vaporize, causing high pressure inside the compartment which may lead to an explosion.

• Never strike an arc on a cylinder of compressed gas or on any part of a track adjusting mechanism.

• Be sure that welding cables, electrode holders, and clamps are in good repair and properly insulated.

• Support large machine components such as scraper bowls and aprons, bulldozer blades, solidly before working under.

• Fasten oxygen and acetylene hoses cylinders securely in the vertical position before using. Observe all safety rules for handling compressed gas cylinders.

• Keep oxygen and acetylene hoses from being cut or burned. Inspect oxygen and acetylene hoses periodically for leaks and worn places. Check all connections for leaks before igniting flame. Do not use oil on oxygen fittings.

• Provide mechanical air movement over coated or painted surfaces being welded to dispel any toxic fumes that may be produced.

Other Recommended Equipment

Pneumatic Vibrator for slag removal

• Either chisel or needle type

Grinder, pneumatic, or electric

• 177.8 mm (7.00 inch) or 101.6 mm (4.00 inch) diameter - 36 grit and/or 24 grit

• both cup grinder and disc grinder

Electric Rod Oven for electrode storage if using shielded metal arc

• A practical approach is to use an airtight container with at least a 100 W light bulb permanently turned on.

Liquid penetrant kit for surface crack detection on ferrous and non-ferrous metals

Arc-Air for removing defective welds

• 3/8 inch and/or 1/4 inch carbon round or semi-round electrodes

• use dry air supply, no lubricant present

Oxyacetylene outfit with cutting and heating heads

• heavy-duty Oxyacetylene

Tempilstick crayons for determining temperature of metal

Leather weld clothing for operator

• Leather Gloves

• Fireproof Coat

• Apron or Chaps

• Leather Sleeves

Ceramic Weld Backing Material

• Grooved

• Round

• Triangle

Power Supplies and Electrodes

If Stick Electrode (SMAW) Shielded Metal Arc Welding

• 400 Amp to 600 Amp DC power source is recommended

• E7018 electrode

If Semi-Automatic (FCAW) Flux Cored Arc Welding

• 400 amp to 450 amp power source is recommended

• Shielding gas 75% argon 25% CO₂

• E71T-1 flux cored wire

If Semi-Automatic (GMAW) Gas Metal Arc Welding

• 400 amp to 450 amp power source is recommended

• Shielding gas 75% argon 25% CO₂ first choice, and straight CO₂ second choice

• (AWS) ER70S-3 solid wire

Considerations when using (GMAW) Gas Metal Arc Welding

Base metal cleanliness is more critical when using GMAW than when using SMAW. The fluxing compounds present in SMAW cleanse the molten weld deposit of oxides and gas forming compounds. Such fluxing slag is not present in GMAW.

GMAW is a gas shielded welding process and porosity may occur if too much or too little gas shielding flow is used. The gas shield can also be blown away by air movement, or by fans running in the welding area. The welder must not have too much or too little distance from the welding gun to the piece being welded. These are variables to consider when deciding whether to use GMAW or SMAW.

Stick Electrode Shielded Metal Arc Welding (SMAW)

Fundamentals of the Process

Definition

Shielded Metal Arc Welding is a process wherein coalescence is produced by heating with an electric arc a covered metal electrode and the work. Shielding is obtained from decomposition of the electrode covering. Pressure is not used and filler metal is obtained from the electrode.

Slang Names

1. Stick/Manual metal arc.

Process Principles

1. Heat source - heat of the arc.

2. Shielding gas - slag formed by the decomposition of the flux.

3. Filler metal - comes from the core wire.

4. Flux - contains deoxidizers/slag formed/ionizing elements to stabilize the arc/iron powder for higher deposition.

Methods of Application

1. Manual - most widely used - approximately 90%

2. Semiautomatic - firecracker - not used

3. Machine

4. Automatic - gravity

Electrical Requirements

Welding Circuit

Illustration 2	g03857225

Welding Current Types

1. A.C.

2. D.C.E.N. (straight) polarity

3. D.C.E.P. (reverse) polarity

Power Source Types and Characteristics

1. Generator (DC)

2. Transformer (AC)

3. Rectifier (DC)

4. Transformer Rectifier (AC/DC)

5. Alternators (AC)

Other Equipment Requirements

Extra Equipment Necessary

1. Helmet/gloves/leathers

2. Chipping hammer/wire brush

3. Grinder for repair

Setup of Equipment

Setup of equipment in preparation for welding is an important consideration. Both from the safety standpoint and for the speed and ease with which the weld can be made.

Welding should be done in a specially prepared welding area if at all possible. Carrying the work to the welder, is quicker, easier, and safer than carrying the welder to the work. If welding must be done in places other than the regular welding areas, extra attention should be given to safety precautions. Other workers in the area should be notified that welding will be going on.

Adequate ventilation and lighting and a source of sufficient power must be provided. The welding machine should be located close enough to the work to assure free and easy manipulation of the electrode holder and cable. Cable connections must be made soundly and the ground cable clamp must be attached securely to the work to assure an uninterrupted flow of current. The ground clamp must always be placed on the piece being welded.

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NOTICE
Current must never be allowed to flow through bearings, hydraulic cylinders, or other precision surfaces. Minute pits will form at the points of contact and cause excessive wear if current flows through bearings. Clamp the ground cable from the welder to the component that will be welded. Place the clamp as close as possible to the weld. This will help reduce the possibility of damage

The work should be positioned so the face and the axis of the weld will be within 10° of horizontal. In this position, higher amperages and deposition rates can be used. The puddle of molten metal is easier to control, and the welder is in a more comfortable position. In addition, more welding skill is required for welding in positions other than flat and horizontal.

Striking an Arc

An arc is struck by momentarily touching the work with the electrode. The electrode can stick to the work when the arc is struck. The sudden rush of current caused by the short-circuiting of the welding machine causes sticking. To avoid this sticking or freezing of the electrode, a motion similar to striking a match should be employed (Illustration 3). A longer than normal arc should be held until the parent metal is heated to the melting point making the proper size puddle of molten metal. When necessary to restrike an arc to continue an incomplete weld, strike the arc at the forward or cold end of the crater. Move the electrode rearward over the crater and then forward again to continue the weld. This procedure fills the crater and avoids porosity in the weld and trapping of slag.

Illustration 3	g03857242
Arcs must be struck carefully to keep electrode from sticking.

Controlling the Arc

The two primary factors involved in manipulating the arc are the length of the arc and the amperage of the welding current being used. The arc must be long enough so the diverging arc stream covers the width of the puddle and a good gas shield is maintained. Too long an arc will tend to swing sideways causing excessive spattering. Too long an arc will result in an imperfect gas shield, allowing elements in the air to come in contact with the molten metal. Too long an arc can cause an irregular weld bead with poor penetration (Illustration 4). Too short an arc, will not heat the parent metal sufficiently and may short out and cause the electrode to stick to the work. An arc of the proper length produces a steady transfer of metal from the electrode to the puddle with little splatter. An arc of the proper length has no tendency for the electrode to stick. An arc length equal to the core diameter of the electrode will usually produce these characteristics.

The proper amperage to be used will vary with different welding situations. Amperage depends on the type of material being welded. The type, and size of electrode will vary the amperage. In general the recommendations of the electrode manufacturer should be followed. Too low a welding current will not generate enough heat to melt the parent metal sufficiently. Low welding current will result in excessive piling up of weld metal and an overlapping bead with poor penetration (Illustration 4). Too high a current will cause excessive spattering, and irregular deposit of weld metal, and undercutting along edges of the weld (Illustration 4).

Illustration 4	g03857247
Arc length and welding current must be controlled for sound weld beads.

Deflection of the arc arising from concentrations of the magnetic field set-up in the work can be controlled in various ways:

• Place the ground connection at the start of the weld if back blow is a problem. Place connection at the end of the weld if forward blow is a problem.

• Weld toward a heavy tack or a weld already made.

• Hold as short an arc as possible so the force of the arc offsets the arc blow.

• Reduce the current, reverse the polarity, or switch to AC current.

Manipulating the Electrode

Once a good arc is established and maintained, the electrode must be held and moved properly. Assure a sound weld through the control of the puddle of molten metal. Primary factors here are electrode angle, travel speed, and weaving of electrode. Travel speed should be such that a flat or slightly convex bead is deposited. If travel speed is too fast, a small, irregular bead with a concave surface will result. If travel is too slow, a heavy convex bead with overlapping edges will result. Generally, reduce travel speed for vertical and overhead welding.

The quality of a weld can be affected to a large degree by the angle at which the electrode is held to the work. For normal flat welds, the electrode should be perpendicular to the surface of the joint and inclined in the direction of travel. The amount of inclination will affect the penetration, with greater inclination giving less penetration. Fillet welds require different electrode angles for successive passes, and the position of the joint will further affect angle requirements. Specific recommendations for individual types of welds will be made in the following sections.

Lay a weld deposit that is wider than can be obtained with a single bead. This is accomplished by weaving the tip of the electrode back and forth over the joint as the electrode travels along the joint. There are many weave patterns used in welding. The important requirements are that motion is uniform and the weaves are close enough together to assure good fusion at all points in the deposit. Again, specific recommendations will be made in the following sections.

In addition to widening the weld deposit, weaving helps to work impurities to the top of the puddle of molten metal. Weaving can be used to control contour and undercutting, as well as heat input and temperature in a joint. Control of heat input and temperature by weaving is especially useful in vertical and overhead welding. Disadvantages of weaving include the possibility of losing the gas shield and a possible increase in distortion from warping. Low hydrogen electrodes should not be wove more than two times the diameter of the electrode to avoid breaking the gas shield.

Certain environmental factors affect the welders ability to manipulate the electrode and control the puddle. The welding area should be orderly, lighted, and ventilated. A small fan located near the work area is desirable for welding in close or restricted quarters. The welding helmet should be kept clean of smoke and weld spatter.

All welding should be done from a comfortable position. The welder then can hold a steady arc and feed the electrode into the joint at a constant rate. Both hands should be free to grip the electrode holder and guide the electrode or steady the work as necessary. If the joint is in a hard-to-reach or awkward location, the electrode may be bent in such a manner that the proper electrode angle and arc length can be held from a more relaxed position (Illustration 5).

Illustration 5	g02581561
Electrodes can be bent for welding in hard-to-reach locations.

When the bead is started, hold a longer than normal arc until enough of parent metal melts to form the proper size puddle. Then the arc length is shortened and travel is begun (Illustration 6). At the end of the weld, the bead is stopped by shortening the arc and momentarily backing to fill the crater. Whip the electrode sharply backward to break the arc. If the bead must be stopped, whip the electrode to the side, leaving an unfilled crater in which to begin the bead. Check for proper electrode selection, arc control, and electrode manipulation by welding on scrap metal before welding the joint. The scrap metal should be in the same position as the joint.

Illustration 6	g02581563
Control of the arc is important at the start and finish of a joint.

Tack Welding

Tack welding permits accurate positioning of parts without special fixtures or clamping devices and controls distortion arising from cooling welds. Tack welds should be made with the same electrode and in the same manner prescribed for the final weld. All parts of a weldment should be tacked together before and final welds are made. The following procedure is recommended for making tack welds:

1. Hold the part in position and make the first tack weld on the end of the part so the part can be repositioned slightly, if necessary (Illustration 7). The first tack should be strong enough to hold the part in position.
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   Illustration 7	g02581576

2. Check the alignment with a level or a combination square (Illustration 8). Reposition the part if necessary.
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   Illustration 8	g02581596

3. Make a second tack weld in a place that will further restrain the part from being distorted when the final welds are made (Illustration 9).
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   Illustration 9	g02581598

4. Recheck alignment.

5. Make extra tack welds as required to hold the part in position while the final welds are being made (Illustration 9).

Tack welds must meet all the requirements for soundness that apply to final welds. Cracked tack welds must be gouged out and remade. Future cracking in the final weld will initiate if a cracked tack weld is not removed.

Flat and Horizontal Welding

A weld joint is in the flat position when both the axis of the joint and the face of the weld are within 10° of horizontal and the welding is performed on the top of the joint (Illustration 10). If the axis of the joint is within 10° of horizontal but the face is between 10° and 90° from horizontal, the joint is said to be in the horizontal position (Illustration 10).

Illustration 10	g02581616
Flat and Horizontal positions should be used when possible.

For normal flat welds, the electrode should be perpendicular to the surface of the joint and tilted slightly in the direction of travel (Illustration 11). For deeper penetration, the electrode should not be tipped in the direction of travel, hold electrode perpendicular to the face of the weld so the heat from the arc is directed down into the joint (Illustration 11). The weave pattern is the same as for normal flat joints.

For wide open gap joints with poor fit-up, where excessive heat in the joint would cause a melt-through, the electrode should be tilted slightly away from the direction of travel (Illustration 11). This angle directs the heat of the arc away from the center of the puddle of molten weld metal. This angle allows the metal to cool more rapidly. The wider weave pattern also helps the molten weld metal cool more rapidly.

Illustration 11	g02581696
Several electrode angles and weave patterns can be used for flat welding.

For horizontal fillet welds, the electrode should be held midway between the horizontal and vertical plates (45° work angle) on the first pass so an equal force from the arc is directed against each surface (Illustration 12). The second pass should be deposited against the horizontal plate to form a flat ledge on which the third pass can be laid. The second pass and all subsequent passes that do not contact the vertical plate should be made with a 20° work angle (Illustration 12). The third pass and all subsequent passes that do contact the vertical plate should be made with a 60° work angle. The electrode should always be tilted in the direction of travel (Illustration 13), making a 60° angle with the horizontal plate (30° lead angle).

Illustration 12	g02581756
Different work angles are needed on various passes for horizontal fillet welds.

The weave patterns for horizontal fillet welds utilize the force of the arc to wash up molten metal onto the vertical surface. This technique permits accurate forming of the weld deposit without undercutting (Illustration 13).

Illustration 13	g02581796
A 30° lead angle puts the electrode 60° from horizontal

For horizontal butt welds, the electrode holder should be held slightly below the joint so the electrode is directed slightly upward. The electrode again should be tilted in the direction of travel with a lead angle of about 10°. The electrode is directed upward so the force of the arc will hold the puddle of weld metal in position until puddle freezes. The weave patterns recommended for horizontal fillet welds (Illustration 13) should be used for horizontal butt welds, also. This pattern is done so molten metal can be washed up onto the upper surface to prevent undercutting.

Overhead and Vertical Welding

A weld joint in the overhead position when the axis of the joint is within 10° of horizontal and the welding is performed on the lower side of the joint (Illustration 14). If the axis of a joint is between 10° and 90° from horizontal, the joint is said to be in the vertical position (Illustration 14). An endpoint inclined at 30°, is closer to horizontal than vertical, classifying as a vertical weld. Problems encountered are essentially the same as problems of a joint that is upright.

Illustration 14	g02581816
Vertical and overhead welding is called out-of-position welding.

When working in the overhead and vertical positions, the welder must constantly take steps to counteract the effect of the force of gravity. The size of the molten metal puddle must be limited by reducing welding current, arc length, and deposition rate. Limiting the size keeps molten metal from dropping from the weld or running down over the work. The amount of slag shield must be reduced though proper electrode selection so the weld metal will freeze more quickly and in the proper location. The electrode must be held and moved in such a manner that the force of the arc holds the weld metal in position until solidification. All these factors reduce welding speed and make a sound weld more difficult to obtain.

Overhead welding requires a high level of skill from the welder. For overhead butt joints and overhead fillet welds where the face of the weld is horizontal, the electrode should be held perpendicular to the face and inclined slightly in the direction of travel (Illustration 15). For overhead fillets where the face or the weld is other than horizontal, the electrode should be held so most of the heat is directed onto the upper surface (Illustration 15). In each case, a circular or triangular weave pattern should be used to agitate the puddle to remove slag and impurities. A series of small beads is easier to run than a single large bead. Thorough cleaning is necessary after each pass because impurities will not float to the surface of the puddle with the overhead position.

Illustration 15	g02581836
Overhead butt and fillet joints require considerable skill from the welder.

Vertical welds may be made either upward or downward. Heavy joints are welded in the upward direction, while small joints on thin material should be welded downward. Welding downward requires less skill than welding upward. For both upward and downward vertical welding, the electrode should be held perpendicular to the face of the weld. Incline electrode downward (electrode holder below arc) regardless of direction of travel.

When making a fillet weld in the upward direction, build a small ledge or shelf on which to start the weld (Illustration 16). The shelf should be built to the desired width with a series of short passes. When the shelf is to the desired size, the first pass of the weld should be made, using a weave pattern consisting of a series of inverted V's with the highest point of the pattern in the root of the joint (Illustration 16). Heat will spread evenly to control the size of the puddle and allows impurities and flux to float downhill to the brim of the puddle. The bead should be small enough so all flux is kept in a molten or semi-molten state. The optional weave pattern (Illustration 16) gives a smoother bead. Greater care must be taken because slag can easily become entrapped in the center of the pattern.

After the first pass, enlarge the bead by using a weave pattern consisting of a series of horizontal passes with an upward swing at each end. The upward swing is used to tie the weld into the base metal without undercutting (Illustration 16). When low hydrogen electrodes are used, the weave pattern should be kept as narrow as possible to assure a good gas shield around the arc.

Illustration 16	g02581876
The proper weave pattern spreads heat and allows good removal of impurities.

Illustration 17	g03858149
Welding Positions

Electrodes

Electrodes used in arc welding can be classified according to operating characteristics, type of coating and characteristics of deposited metal. AWS specifications group electrodes in series (E45, E60, etc.) according to the minimum tensile strength of the deposited metal. The deposited metal from E80 electrodes, for example, has a minimum tensile strength of 80,000 psi in stress relieved condition. Each series is further subdivided according to welding position, coating composition, and welding current indicated by the last two digits in the classification number.

Illustration 18	g02582937
Electrodes formerly were marked according to a standard AWS color code.

Electrodes are usable within a range of amperages. With SMAW welding, the operator has a great amount of process control. The operator controls the arc length and uses a manipulating motion to control the arc. Specific weld settings are given in broad ranges. Welders normally listen for a frying or crackling sound, and making a visual inspection to confirm proper setting or make adjustments. Learning these skills is what makes an experienced welder.

E7018 Electrode Storage

These electrodes are to be purchased in hermetically sealed containers. After hermetically sealed containers are opened or after electrodes are removed from baking or storage ovens, the electrode exposure to the atmosphere should not exceed 4 hours, maximum. Electrodes that have been wet should not be used. Electrodes exposed to the atmosphere for periods less than 4 hours may be returned to the holding oven maintained at 121° C (250° F) minimum. After a minimum holding period of 4 hours at 121° C (250° F) minimum the electrodes may be reissued.

Electrodes exposed to the atmosphere for more than 4 hours must be baked for at least 2 hours between 260° C (500° F) and 430.0° C (800° F).

Place electrodes in a suitable oven at a temperature not exceeding one half the final baking temperature. Leave in oven for a minimum of one half hour. Increase the oven temperature to the final baking temperature. Final baking time shall start after the oven reaches final baking temperature.

Nominal electrode size reflects the diameter of the metal rod or core of the electrode. The overall diameter of the electrode with the coating will vary. As the rod diameter increases, the amperage necessary to produce a good weld will increase. Amperage ranges for different electrode types can vary, even if the diameters are the same. Recommended amperages for electrodes are sometimes printed on the box ends. If no recommended settings are found on the packaging, the manufacturer may provide literature with recommended amperages. Consult with an experienced welder to select a starting amperage and to get the desired weld bead shape and appearance.

Low hydrogen type electrodes (5, 6, or 8 as the far-right digit) will absorb moisture from the air if not stored properly. Electrodes are stored in ovens at a minimum temperature of 121° C (250° F). Electrode ovens are not to be used for food warming or storage of any other items.

Electrodes left out of heated storage ovens for longer than 2 hours must be reconditioned. Recondition in oven for at least 1 hour at 260° C (500° F), or 4 hours at 121° C (250° F). Porosity or hydrogen-induced cracking will result from improper storage and use of the low hydrogen electrodes.

Illustration 19	g02581897
Electrode storage oven

Illustration 20	g03858403
Label on electrode can

Illustration 21	g03857276
SMAW electrodes showing classification numbers

For electrode numbers with four digits, the two digits on the left denote tensile strength in the thousands of pounds. If the electrode number has five digits, the three digits on the left denote tensile strength. For both, the right-hand digit indicates the type of coating, and the second from the right indicates the recommended positioning for use.

Table 2

7018 Tensile Strength	Position	Coating Type (current)
60 (60,000)	1 - All	0 - Cellulose Sodium DC+
70 (70,000)	2 - Flat & Horizontal	1 - Cellulose Potassium AC DC+
80 (80,000)	3 - Flat Only	2 - Titanium Sodium AC DC-
90 (90,000)	4 - Not Vertical, Up	3 - Titania-Potassium AC DC+ DC-
100 (100,000)		4 - Titania-Iron Powder AC DC+ DC-
110 (110,000)		5 - Low Hydrogen - Sodium DC+
120 (120,000)		6 - Low Hydrogen - Potassium AC DC+
		7 - Iron Powder-Iron Oxide AC DC-
		8 - Iron Powder-Low Hydrogen AC DC+
		9 - Iron Oxide-Titania-Potassium AC DC+

Table 3

Welding Rod Classifications
F-1	High Deposition Group (EXX20, EXX24, EXX27, EXX28)
F-2	Mild Penetration Group (EXX12, EXX13, EXX14)
F-3	Mild Penetration Group (EXX10, EXX11)
F-4	Low Hydrogen Group (EXX15, EXX16, EXX18)

Table 4

Fourth Digit	Type of Coating	Welding Current
0	cellulose sodium	DCEP
1	cellulose potassium	AC or DCEP or DCEN
2	titanium sodium	AC or DCEN
3	titanium potassium	AC or DCEP
4	iron power titania	AC or DCEN or DCEP
5	low hydrogen sodium	DCEP
6	low hydrogen potassium	AC or DCEP
7	iron powder iron oxide	AC or DCEP or DCEN
8	iron powder low hydrogen	AC or DCEP
9	Iron oxide sodium	AC or DCEP
		DCEP - Direct Current Electrode Positive DCEN - Direct Current Electrode Negative

Mild Steel (Covered) Electrode Classification SMAW Process

Illustration 22	g02581942

Flux-Cored Arc Welding (FCAW)

Principle Features

The benefits of FCAW are achieved by combining three general features:

1. The productivity of continuous wire welding.

2. The metallurgical benefits that can be derived from flux.

3. A slag that supports and shapes the weld bead.

FCAW combines the characteristics of Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW), and Submerged Arc Welding (SAW).

Advantages of FCAW

Flux Cored Arc Welding has many advantages over the manual SMAW process and provides certain advantages over the SAW and GMAW processes. In many applications, the FCAW process provides high-quality weld metal at lower cost with less effort on the part of the welder than SMAW. These advantages can be listed as follows:

• High-quality weld metal deposit.

• Excellent weld appearance and smooth, uniform welds.

• Excellent contour of horizontal fillet welds.

• Many welds weldable over a wide thickness range.

• High operating factor, easily mechanized.

• High deposition rate, high current density.

• Relatively high travel speeds

• Relatively high electrode deposit efficiency.

• Economical engineering joint design.

• Visible arc, easy to use.

• Less precleaning required than GMAW.

• Up to four times greater deposition rate than SMAW.

• Higher tolerance for contaminants that may cause weld cracking.

• Resistant to underbead cracking.

Limitations of FCAW

• FCAW is presently limited to welding ferrous metals and nickel-based alloys.

• The process produces a slag covering which must be removed after each weld pass.

• FCAW electrode wire is more expensive on a weight basis than solid electrode wires, except for some high alloy steels.

• The equipment is more expensive and complex than required for SMAW. Increased productivity usually compensates.

• The wire feeder and power source must be fairly close to the point of welding.

• For gas shielded version, the external gas shield may be adversely affected by breezes and drafts.

• Equipment is more complex than equipment for SMAW so more maintenance is required.

• More smoke and fumes are generated (compared to GMAW and SAW).

Fundamentals of the process

Definition

The Flux-Cored Arc Welding process is where coalescence is produced by heating with an arc between a continuous filler material (consumable) electrode and the work. Shielding is obtained from a flux contained within the electrode. Extra shielding may or may not be obtained from an externally supplied gas or gas mixture.

Slang Names

1. FabCo - Fabshield-Inner Shield - Dual Shield.

Process Principles

1. Heat Source - an arc between a continuous filler metal electrode and the weld spot.

2. Shielding - is obtained from flux contained within the tubular electrode and with or without extra shielding from an externally supplied gas.

3. Filler metal - is obtained from a continuous-feeding tubular electrode.

4. Flux - will provide deoxidizers, ionizers, purifying agents, and sometimes alloying elements.

Illustration 23	g02581944

Methods of Application

1. Manual - not applicable.

2. Semiautomatic - most popular method of application.

3. Machine - widely used.

4. Automatic - widely used.

Metals Weldable

Table 5

Base Metal	Weldability
Cast Iron	Using Special Electrode
Low Carbon Steel	Weldable
Low Alloy Steel	Weldable
High and Medium Carbon	Weldable
Alloys Steel	Weldable
Stainless Steel-Selected	Limited Types

Thickness Range

Illustration 24	g02581946

Position Capabilities

• Grooves - all positions depending on size and type.

• Fillets - all positions depending on size and type.

• Limitations - would depend on the skill of the operator.

Electrical Requirements

Welding Circuit

Illustration 25	g02581957

Welding Current Types

• D.C.E.N. or D.C.E.P. depending on type of wire.

Power Source Types and Characteristics

• Constant voltage type with a flat volt amp curve.

• Constant speed system with a constant current machine. The wire feeder is a variable speed system.

Other Equipment Requirements

Extra Equipment Necessary

Welding guns - shielding gas - water cooling system. Welding guns are of two different types. The guns for externally gas shielded wires are identical to the guns for the Gas Metal Arc Process. For the self-shielding electrodes, the guns will contain wire guides that increase the electrical stickout, designed to preheat the wire.

Mid Steel (Flux Cored) Electrode Classification FCAW Process

Illustration 26	g02581956

Flux Cored Welding Electrode Classification

Table 6

AWS Classification	Shielding Gas	Current & Polarity	Tensile Strength Min.
E60T-7	None	DC Straight Polarity	67,000
E60T-8	None		62,000
E70T-1	CO2		72,000
E70T-2	None		72,000
E70T-3	None	DC	72,000
E70T-4	CO2	Reverse Polarity	72,000
E70T-5	None		72,000
E70T-6	None		72,000
E70T-G	Not Spec.	CO2	72,000

MIG (GMAW) Gas Metal Arc Welding

Fundamentals of the Process

Definition

The Gas Metal Arc Welding process uses the intense heat of an electrode arc to melt the filler metal and base metal. The consumable bare solid electrode wire is continuously fed into the arc. The deposited weld metal is formed from metal melted off the end of the electrode wire and transferred through the arc to the work. Shielding gas protects the weld from the contamination.

Slang Names

Microwave/MIG/Wire Welding/Carbon Dioxide Welding.

Process Principles

• Heat Source - electric arc between electrode (wire) and the work.

• Shielding - an external gas supply.

• Filler metal - fed automatically from a spool or reel.

• Flux - not applicable.

Illustration 27	g02581959

Transfer Modes with G.M.A.W

Illustration 28	g02581977

• Short circuiting - CO₂ or AR/CO₂, low amperage, and voltage, all positions

• Globular - CO₂ or AR/CO₂, higher amperage and voltage, flat and horizontal

• Spray - AR/O₂, high amperage and voltage, flat and horizontal

• Pulsed - AR/O₂, Various amperage levels, spray transfer, all positions.

Illustration 29	g03857283
Bead on plate penetration diagrams for various shield gases.

Position Capabilities

• Grooves - all position capabilities.

• Fillets - all position capabilities.

• Limitations - type of transfer/skill of operator/wire size.

Electrical Requirements

Welding Circuit

Illustration 30	g02581980

Welding Current Types

• D.C.E.P. - normal type of current used.

• D.C.E.N. - can be used with special electrodes.

• A.C. - has not been successfully used.

Power Source Types and Characteristics

• Constant Voltage - 100% duty cycle with a flat volt/amp curve.

Other Equipment Requirements

Extra Equipment Necessary

• Wire feed system.

• Welding gun and cable assembly.

Mild Steel (Solid) Electrode Classification GMAW, GTAW, and PAW

Illustration 31	g02581981

Air-Arc

Introduction

The air-arc process is most frequently used to gouge out defective welds in preparation for repair welding. The process can also be used to prep a joint prior to welding. The process is also referred to as the Aircair process, referring to the Aircair brand name. Caterpillar does not have a specification on the air-arc process.

Process and Materials

The air-arc process uses a carbon-graphite electrode, copper-colored, that is gradually consumed by the arc. The arc melts the metal to be removed and compressed air is used to blow the molten metal off the part. An electrode holder is used to clamp the electrode and to direct the compressed air down the electrode.

Illustration 32	g02581983
Electrode Holder

Illustration 33	g02581984
Air and Power Connection

The electrode holder is connected to compressed air using a quick-disconnect fitting. The electrical current is furnished by clamping the air-arc connector in the jaws of a stick-weld cable.

To enable air-arc gouging, individual machines have different switches that must be placed in the proper position. Air-arc is done with few changes from the normal production welding processes.

Amperage is the variable that is set by the operator, depending on the electrode size. To set amperage, control must be removed from the wire feeder boxes and given to the power source. A local/remote output switch on the front of the power source that is switched to the LOCAL position removes control. Once LOCAL control is selected, the amperage can be controlled using the rheostat output dial.

A toggle switch is used to select the voltage parameters for the power source. This switch is put in the CC mode, setting up the power source for constant current. On power sources that do not have constant current capabilities, the mode switch, if present, is left in the normal position.

The third and last switch to be changed is the process switch. This switch can be an unmarked switch on the front of the power source. When this switch is placed in the air-arc or stick position, the power source will immediately supply an open-circuit voltage capable of creating an arc.

Illustration 34	g02581986
Lincoln DC600 power source and switches for air-arc.

Unlike a stick electrode holder, the air-arc holder has a rotating disk with air ports that direct air down the electrode, and a valve to turn the air on or off. The air ports are located behind the electrode to force out the molten metal in front of the electrode. This necessitates moving the disk or repositioning the electrode each time the direction of travel is changed.

The electrode is always "hot" once the proper machine settings have been selected.

To start the gouging process, the air valve is opened and the electrode is touched to the work piece. The electrode is moved along the part to gouge a shallow channel in the part. Several passes may be required to complete the gouging.

Illustration 35	g02582827
Proper position of air ports and electrode.

Illustration 36	g02582836
New and used air-arc electrodes.

The dross or slag formed during the removal process must be removed before repair welding begins. The air-arc electrodes tend to leave carbon and copper deposits in the groove. Deposits will cause additional weld defects if not cleaned out prior to welding.

The only adjustable air-arc variables are the amperage and airflow. Airflow can be varied using the on-off valve. The air valve is normally used fully open, but can be partially closed to control airborne sparks and slag in tight areas. The air-arc process is tolerant of amperage variations, and the operator can use this fact to control the speed of metal removal and for following defects in the joint. The following table shows ranges for various size electrodes.

Air-Arc Operating Amperages

Table 7

Size	Min	Mid	Max
3/16	110	155	200
1/4	150	250	350
5/16	200	325	450
3/8	300	425	550

Automatic Welding

Summary

Automatic welding can deliver continuous, uniform, high-quality deposits at a rapid rate. Automatic machines for welding are not complicated. One can learn to operate the machines quickly and easily. Practice contributes to good results in automatic welding as in hand welding.

Cleanliness

Clean surfaces are essential for good welding. All foreign material such as oil, grease, water, paint, rust, and scale must be removed before the welding operation takes place. These substances generate gas when exposed to the heat of the affected zone. The gas can be trapped in the molten metal of the weld and cause porosity. Water or rust can also cause hydrogen embrittlement, which results in cracking of the deposit on the base material.

This bulletin reports on two types of automatic welding:

• Submerged arc welding

• Open arc welding

Submerged Arc Welding

Submerged arc welding is the fusion of a weld consumable to a base of metal by electrical means and mechanical means. Usually, the weld consumable is in the form of a coil of wire. The welding process results when an electric current is passed from the wire to the work that is being welded. This process creates an electrical arc. The wire is fed automatically as the current melts the wire. Submerged arc welding is used because the wire and the work are submerged in a granulated flux at contact.

Hard surfacing by any welding method requires the complete fusion of the added material to the base material. With normal techniques of submerged arc welding, the quantity of base material that is fused is twice as high as the quantity of wire fused.

Flux

Once in the molten state, the flux has four purposes:

• Conduct current and aid the welding operation.

• Prevent oxidation by keeping the molten metal submerged and away from the atmosphere.

• Retain the molten metal and help to form the bead.

• Keep metal molten to purge the dirt and long enough to clean the impurities from the surface of the base metal.

The depth of the flux influences the appearance and integrity of the finished weld. If the flux is too deep, a rough rope-like weld is likely to result. The gases that are generated during welding cannot readily escape and the surface of the molten metal is distorted intermittently. If the flux is too shallow, the zone of the weld will not be entirely submerged and flashing or splatter will be present. This will cause the appearance of the weld to be poor. The weld may be porous and the resultant rapid cooling may cause the surface to crack. The depth of the flux can be established by slowly decreasing the lever that controls the flux until the welding is submerged. This will allow the gases to escape around the welding wire. Sometimes, the gases will burn. Molten flux must not be disturbed in or around the zone of the weld.

Voltage and Current

Voltage

The voltage of the electrical arc determines the width or shape of a bead and has a moderate effect on the penetration of the weld. If the voltage of the electrical arc is increased, the bead will flatten. As the bead flattens, the amount of flux that is fused increases. This occurrence is due to the amount of area that is exposed to the flux. A rule of thumb is to increase the voltage to flatten the bead. As voltage increases, the consumption of flux also increases. In applications for hard surfacing, an increase of welding voltage also changes both the chemical and metallurgical characteristics of the deposit because arc blow causes a loss of certain alloys. The lowest voltage that will give an adequate contour of the bead should be used because the voltage of the electrical arc also adds heat to the component.

Current

The current or the amperage determines the penetration of a weld. The current or the amperage has a much greater effect on the rate of deposit than the voltage. The rate of burning of the wire increases rapidly as the current is increased. Use the highest amperage that is possible without adding too much heat or too much metal. A higher amperage increases the rate of deposit for the metal and efficiency. If too much metal is added some of the metal will not stay on the part.

Wire Polarity

Wire polarity affects the burning of the wire. The penetration of the wire is greatest if the wire is positive or if the wire is reverse polarity. By making the wire negative or straight polarity, the penetration is reduced. This indicates that the polarity of the electrical arc affects the distribution of heat. About 30% of the heat of the electrical arc is on the positive side and 70% is on the negative side. Therefore, if the wire is negative, the rate of burning of the wire increases greatly. Using negative wire decreases the amount of heat that is built up. Many tests show that the rate of deposit of wire can be increased by 25% or more by making the wire negative.

Again, this process has a disadvantage. Since penetration is reduced, dilution is reduced. The result may be an initial deposit that is not sufficient to provide a good bond. If the component is not properly cleaned prior to welding, do not use straight polarity on the first pass. The use of straight polarity will increase the possibility of picking up alloys from even neutral flux. This may increase the hardness of the deposit enough to cause cracking.

Dilution

The chemical composition of the first weld pass will not be the chemical composition of the welding wire. The chemical composition of the first pass will reflect the composition of the base material. The influence of the base material on the analysis of the weld is frequently termed "percent wire dilution".

Cracking

Care must be taken to prevent the weld from cracking. Aside from preheat, cracking of the weld can be avoided by preventing stress risers that are caused by an irregular width of the bead or a lack of bonding to the flanges. This is accomplished by maintaining the proper contours of fusion. Avoid notches while the weld bead is tied into the flange. Weld beads that change rapidly in width or show notches at the edges are due to faulty operating technique. These flaws will tend to crack transversely at the notches which act as effective stress risers. Cracking below the surface occurs if the weld bead tends to be excessively convex.

Cracking can be avoided by welding only as many parts as can be completed by the end of a work shift without allowing the parts to cool to room temperature.

Open Arc Welding

Open arc welding does not require flux. The electrical arc is shielded by an inert gas. This inert gas may be supplied by a substance in the core of the wire which generates the gas. This inert gas may also be from an outside source or from a combination of the two. This shield of gas must be protected from currents of air. If the gas is disturbed, the weld will splatter.

Open arc welding usually requires less attention from the operator. Submerged arc welding usually requires more attention. Usually, the light slag that is formed can be burned without the chipping that is sometimes necessary to remove fused flux.

The light from the electrical arc is not shielded by flux. Use a shield to protect the operator from flash. Open arc welding usually generates a considerable volume of smoke that must be removed from the welding areas.

Rate of Deposition

There are many variables that influence the rate of deposition. High rates of deposition are preferable to reduce the time that is required to recondition a component. One way to achieve high deposition is by using high amperage. Since high amperage results in high input of heat to the component, using high amperage to obtain high rates of deposition is limited.

The effects of reverse polarity and the effects of straight polarity on the rates of deposition have already been described. Straight polarity or negative wire will give a higher rate of deposition at a given amperage.

The wire diameter also affects the rate of deposition. The rate of deposition is affected by current density, which is determined by the area of the wire that is divided by the amperage. This effect can be used to increase deposition at a given amperage or this effect can be used to reduce heat input by maintaining a desired rate of deposition at a lower amperage. The advantages of the effects of greater density of the current of the smaller wire must be weighed against the added cost of the smaller wire to determine the most preferable wire size.

The rate of deposition can also be increased by increasing the distance between the tip of the welding gun and the work that is being welded. This change increases the distance between the current and the electrical arc and this distance causes the wire to preheat. Preheating reduces the energy of the electrical arc needed to melt the wire. This preheating often softens the wire and will cause the wire to wander over the surface that is being welded if the wire becomes too soft. This wander will become objectionable with most wires when the tip is more than 32.0 mm (1.25 inch) from the work

Welding Repair Methods

The preferred Welding process for repair of earth moving equipment is GMAW Gas Metal Arc Welding (MIG welding or FCAW Flux Cored Arc Welding). If these welding processes are not available or not practical, SMAW is the default process.

Considerations for Repair of Cracked or Defective Welds

• Selection of material and welding procedure.

• Select the welding repair process regarding base material cleanliness and the environmental conditions (indoors or outdoors).

• Develop a weld procedure that will include welding process, welding parameters, filler metal, welding sequence, and any other specific information concerning the welding joint technique.

• Weld repair process: use DC, reverse polarity (that is, electrode is positive (+), ground is negative (-) for either GMAW, FCAW, or SMAW.

• Before welding or arc airing, the area must be at least 21° C (70° F), and the surface must be dry and free of moisture, paint, and grease.

• Proper temperature can be accomplished by acclimating in a heated workshop or preheating.

• Do not let surfaces get above comfortable hand temperature to prevent distortion to bore surfaces. Bores can be cooled with compressed air to help prevent overheating.

• Protect finished bores and surfaces from spatter when welding or air arcing. Note - in proximity of finished bores and diameters

• Note about grounding - ground connection must be located where welding current will not arc through critical surfaces (for example, roller bearings, duo-cone seals, polished shafts/rods, etc.) and locate ground as close to work as possible to eliminate arc blow. Turn tractor disconnect key to off position before welding or air arcing.

• Remove flaw or crack completely using air arc method or by grinding. It is critical that flaw is removed or the repair could fail. Refer to "Crack Preparation" in this section.

• Use dye penetrant to confirm removal of flaw.

• Grind area that was air arced to remove slag and carbon deposits or residue.

• Reweld area where flaw was removed.

• Remove splatter from welded area and grind toes of welds to a smooth transition.

• Hammer peen the welds to improve the residual stress state.

In general, a weld repair will have, at best, the same fatigue life as the original detail. However, a repair made under difficult circumstances (poor access, out of position, outdoors, etc.) may have a shorter life.

Crack Preparation

1. Completely remove cracks with an air carbon arc torch or similar tool.

2. When a crack is removed with an air carbon arc torch or similar tool, make sure that the procedure does not cover up the cracks. A dye-penetrant can be used to check if the crack is removed down to solid metal.

   Note: All slag or foreign material must be removed from the crack before a check is made with a dye-penetrant.

   Show/hide table

   Illustration 37	g03857290
   Three types of groove angles.

3. Width (W) must be two times as wide as depth (D). If the crack extends through the plate, refer to Welding Procedure in this instruction.

4. The groove angle will vary depending on the procedure used to make the groove. V-grooves (1), U-grooves (2), or other radius preparation (3) can be used. See Illustration 37

Local Grinding

Toe grinding is normally done to improve the fatigue properties of the weldment by reducing the stress concentration at the weld toe detail. The grinding procedure should produce a smooth concave profile as shown in Illustration 38. Toe grinding can improve the fatigue strength of the weldment by 30% (a factor of 2.2 over the life of the weldment).

Illustration 38	g02582876
Toe grinding detail to improve fatigue life.

Types of Welds and Joints

The four types of welds commonly used in service work are the bead, the groove, the fillet, and the plug (Illustration 39). The bead is a weld deposited in an unbroken string on a surface. The groove weld is a weld made in the space between two surfaces to be joined. The fillet weld is a weld of triangular cross section that is used to join two surfaces at an angle. The plug weld is a weld made through a plate to join to another surface.

Illustration 39	g02582898
Four types of welds and four joint configurations are used.

Four types of joints are commonly employed in this type of welding: the lap joint, the T joint, the corner joint, and the butt joint (Illustration 39). These joints can be combined with variations in groove configuration to give the common surface welding joints shown in Illustration 40.

Illustration 40	g03857297
Joints can be combined with groove styles for many welds.

Illustration 41	g03858154
Seven basic groove welds

Illustration 42	g03858160
Some Typical Weld Joints

Illustration 43	g03858163

Welding Symbols

The weld symbol indicates the type of weld desired, and welding symbols are commonly understood by all welders. A summary of basic welding symbols published by the American Welding Society is shown in Illustration 44 and 45. Refer also to Sections I through VIII of the AWS Standard Welding Symbol Code.

Illustration 44	g03857304
American Welding Society Basic/Typical Welding Symbols Chart

Illustration 45	g03857314
American Welding Society Basic/Typical Welding Symbols Chart

A complete welding symbol, however, indicates the location, size, and finish of the weld and gives other specifications and information. A weld symbol placed below the reference line goes on the arrow side of the joint. A weld symbol placed above the reference line goes on the other side of the joint. The eight elements of the welding symbol are:

1. Reference line

2. Arrow

3. Basic weld symbols

4. Weld size

5. Supplementary symbols

6. Finish symbols

7. Tail

8. Specification

A typical complete welding symbol is shown in Illustration 46.

Illustration 46	g02582916
The welding symbol gives the location, the size, and the finish of weld.

Weld Defects

Repairing Cracks and Defective Welds

Cracks often develop in components that are used for unusually severe applications or are approaching the service life limit. Defective welds, on the other hand, are caused by careless welders who fail to use good welding techniques. The most common defects in welds are: underbead cracks, slag inclusions, porosity (gas holes and pockets), cold lap, undercut and slugged welds. The procedures for repairing cracks and replacing defective welds are similar.

Underbead cracks occur between the weld deposit and the parent metal or in the heat affected zone under the weld deposit in carbon steels. The cracks are caused by hydrogen gas being absorbed by the parent metal and being released as the metal cools. The gas builds up pressure in the minute voids of the parent metal and forces the metal to crack. Underbead cracking is the most common with steels having a carbon content more than 0.30%, but it often occurs when low carbon steels are welded in ambient temperatures below 0° C (32° F) without preheating to remove moisture.

Underbead cracks are not visible from the surface of the joint and can be detected only by X-ray or magnetic particle inspection. Using hydrogen electrodes that have been stored properly to keep dry will eliminate most underbead cracking.

Slag inclusion refers to entrapment of slag within the weld metal (Illustration 47). The inclusions arise mainly from failure to clean the weld deposit before the next pass is made. To slow of a travel speed also causes slag inclusions. The volume of slag becomes too large to be floated out of the puddle of molten metal.

Illustration 47	g03858168
Slag inclusions arise from failure to clean the weld deposit

Porosity usually is caused by the oxidation of foreign matter such as grease or paint that has been left on the joint (Illustration 48). The foreign matter is vaporized by the molten metal and forms gas pockets in the weld deposit. Porosity can also be caused by excessive moisture in any type of electrode coating or by excessive magnetic arc blow. Careful cleaning of joints prior to welding, using dry electrodes and controlling arc blow will prevent porosity.

Illustration 48	g03858170
Porosity is caused by oxidation of foreign matter on the joint.

Cold lap is caused by improper fusion of the weld metal to the parent metal, arising from insufficient heating of the joint members (Illustration 49). Instead of bonding to the parent metal, the weld deposit lies on top, causing a definite crack or void. Cold lap can be prevented by proper manipulation of the electrode to bring all parts of the joint up to a molten state. A slightly longer arc or higher welding current will also help to combat cold lapping by increasing the amount of heat used at the joint.

Illustration 49	g03858176
Cold lap is improper fusion of parent metal and weld.

An undercut is a groove melted in the parent near the toe of a weld that is not filled with weld metal (Illustration 50). Undercutting occurs most often in non-flat positions. Undercutting is caused by excessive heat in the joint, coupled with failure to wash up the weld metal onto the vertical plate. Prevent by reducing the welding current or shortening the arc and manipulating the electrode properly. Undercuts can be remedied by making another pass on the joint to fill the groove in the parent metal with weld metal.

Illustration 50	g03858179
Undercuts will arise from excessive heat in the joint.

A slugged weld is a weld that is made in a joint with a wide gap that has had small pieces of steel placed in the gap to fill up space (Illustration 51). The external appearance of a slugged weld may be perfect, but the joint is weakened by improper fusion of the slug to the parent metal. Poor penetration of the weld metal also weakens the joint. Besides being a shoddy practice, weld slugging contributes nothing at all to welding speed or electrode economy. If a back-up plate is used with a wide gap joint (Illustration 52), a larger electrode can be used. The joint can be welded properly in less time, if the slugs are added. Slugging a weld is a poor welding technique and should never be used in any type of service welding.

Illustration 51	g03858183
A slugged weld has small pieces of steel in the gap to fill up space.

Illustration 52	g03858188
A back-up plate will allow a wide gap joint to be welded properly.

Cracks and defective welds (except undercuts) must be removed completely, the resulting gap must be filled with a sound weld deposit to restore original strength to a component. Any portion of a crack that is left will initiate further cracking in the new weld. The best way to remove a crack or a defective weld is to grind out with a portable grinder. Gouging out with an Arc-air torch can also be used. The grinding or gouging must extend at least an inch past the visible ends of a crack. Remove all traces of the crack and any fatigued metal.

Reinforcing Plates and Hard Surfacing

Installing Reinforcing Plates

Machine components fail primarily because of a localized overstressed condition. This overstressing is caused either by overloading, which stretches, compresses or bends the member, or by repeated flexing which cracks the member without visible bending. The former may occur, for example, in a track roller frame, the latter in a scraper gooseneck. In either case, the stresses can be reduced by properly applying reinforcements to the weak section. Improper application may have the opposite effect. High stresses usually occur at definite, predictable locations in machine members, although the locations are not always apparent until a failure occurs.

The understanding and application of several basic rules will help in the successful design and installation of reinforcing plates:

Rule 1 - Avoid sudden changes in cross-sectional area. Notches, sharp corners, and abrupt changes in area create points of stress concentration. Reinforcements should be designed to enable loads to be transmitted smoothly through the reinforcements and from the reinforcement to the machine component (Illustration 53). Notches and cracks should be filled with weld metal. Corners should be curved with a generous radius, changes in width or thickness of plates should be gradual, ends should be tapered.

Illustration 53	g03858196
Changes in cross sectional area must be made smoothly and gradually.

Several examples of well-designed reinforcement plates are shown in Illustration 54. Note the tapered ends and rounded corners. Usually, tapered plates add the same strength to beams subjected to bending stresses as rectangular plates do. The tapered plates weigh about half as much as rectangular plates and require no more time to install.

Illustration 54	g03858208
Properly designed reinforcements have tapered ends and rounded corners.

Rule 2 - Place reinforcements as far as possible from the neutral axis for bending loads. The neutral axis of a beam is located on a line of zero stress, which is usually at or near the center of the beam. Reinforcing plates of a given thickness will be most effective when placed as far as possible from the neutral axis (Illustration 55). Note: Plates added to the top and bottom of a beam parallel to the neutral axis add considerable more strength than plates of the same thickness added to the sides of the beam.

Illustration 55	g03858211
Bending Load Reinforcements

Rule 3 - Use a circular or box section for torsional loads. Reinforcements for shafts subjected to torsional stresses should not be continuous around the shaft and should not run the full length that is in torsion (Illustration 56). Square sections should be reinforced by adding plates on all sides. Rectangular sections are strengthened by adding plates to the two opposite sides that are closest together. I-beams, channels, and angles should be reinforced in such a manner that the final section is boxed. In all cases, the circular or boxed section is much stronger in torsion and is preferred for torsional loads.

Illustration 56	g03858215
Torsional Load Reinforcements

Rule 4 - Consider the effect on the entire beam before adding a reinforcement. Relatively small reinforcing plates added to a beam may reduce the stresses directly under the plate, but tend to increase stresses at each end of the beam (Illustration 57). A long tapered plate is much better because it spreads the load uniformly through the beam instead of concentrating load in two spots.

Illustration 57	g02583257
Long reinforcing plates distribute the load evenly along the beam. Transverse welds at the end of reinforcing plates should be avoided.

Rule 5 - Avoid making transverse welds at the ends of reinforcements. Transverse welds create high stress areas that usually lead to cracking. Once a crack has formed, crack will progress across the beam and eventually cause a failure. The end of the reinforcing plate should be left open (Illustration 57). Again, the ends are tapered to spread the load over a greater area of the beam.

Rule 6 - Use gusset reinforcements to reduce stresses in sharp corners and other small areas. Gussets should be designed and installed so the forces are distributed and transmitted uniformly and are not concentrated in one spot. Gussets can be triangular or designed with a radius (Illustration 58). Gussets should not be welded in the sharp corners created by the machine components and the gusset. Welding in these areas creates localized overstressed conditions that originate cracks. The thickness of the gusset should be about the same as or slightly less than the thickness of the plates. If possible, the gusset should be welded on both the inside and outside.

Illustration 58	g02583296
Gussets reduce stresses in sharp corners and other small areas.

Controlling Heat Distortion

Illustration 59	g03858221
Members can be pulled into alignment by shrinking of the weld.

Distortion due to thermal expansion and contraction is a problem with all types of welds. There are three basic methods of minimizing distortion: peening, jigs and fixtures, and special welding techniques. With the first method, the weld metal is stretched immediately after being deposited by a series of hammer blows. Lack of precision is possible and the possibility of strain hardening the weld metal, limits peening application in service welding. When the work is clamped in a special jig or fixture, the clamping force overcomes the force of thermal contraction of the weld deposit. The deposit then stretches. This method, too, has limited application in service welding because of the expense of special jigs and the difficulty of clamping large components.

Special techniques in the positioning of welding members and special pass sequence is usually the simplest method for controlling distortion in service welding. Members can be positioned initially out of alignment, and the shrinking of the weld deposit can be relied upon to pull the member into proper position (Illustration 58). A pass sequence that builds up the deposit equally on each side of the joint will allow contractile forces to balance each other and prevent distortion (Illustration 60). Sufficient tack welding will greatly reduce distortion when the final weld is made. No attempt is made to eliminate the expansion and contraction. The forces are utilized to give the desired final shape to the joint.

Illustration 60	g03858232
A proper pass sequence allows contractile forces to balance each other.

The controlled expansion and contraction of metal has another application in service maintenance and reconditioning work - heat straightening. Large components such as track roller frames that are slightly bent can be straightened easily by controlled heating and cooling. The principle involved is based on upsetting the metal or making metal shorter and thicker in the area where heat is applied (Illustration 61). If the outer or convex side of the bend is heated, the heated area expands. If the inner or concave side of the bend is kept relatively cool, the heated area cannot expand lengthwise because of the rigidity of the cooler portion. The heated area then expands outward and becomes thicker. When the heated area cools, it contracts and effectively shortens the convex side of the bent beam. This shortening counteracts the bend and straightens the beam. If one heating and cooling operation does not bend the beam enough, the process can be repeated on either side of the original area.

Illustration 61	g03858239
If metal is forced to expand unevenly when heated, metal becomes "upset".

Selecting the Proper Reinforcing Steel

Many types of steels are available for use in reinforcing a machine operated under severe conditions. High-strength structural steel, heat-treated steel, and mild steel are recommended for various field reinforcements and reconditioning procedures. High-strength structural steel is a weldable steel with a minimum yield strength of 310 MPa (45,000 psi) and a minimum tensile strength of 480 MPa (70,000 psi). This type of steel is not heat-treated. E7018 electrodes are recommended for welding high-strength structural steel. Some heat treated steels that are considered weldable are also included. E11018 electrodes are recommended for the latter. A mild grade of hot rolled structural steel can also be used as reinforcing material. E60 Series electrodes are recommended for welding mild steel. SAE 1017, SAE 1018, SAE 1020, and SAE 1021 grades fall in this category and are produced by nearly all steel companies.

Rebuilding By Welding

Components of track roller frames on track-type machines (such as idlers) are often rebuilt by welding. In many cases, automatic welding equipment is best used for these operations.

Other components such as teeth and cutting edges, experience a marked amount of wear. It is more economical to replace these components as components become worn. In some instances it may be desirable to rebuild these parts by welding. Surfaces near cutting edges and members such as ripper shanks that run in the soil will wear away from the abrasive action of the soil. These surfaces can be restored to original dimensions by arc welding. The built-up weld deposit on restored surfaces must be strong enough to support a hard overlay deposit and hard enough to resist abrasion. Use E7018 electrodes on modern earthmoving machines where high strength steels are used. E7018 electrodes give the best weld buildup material. The material can be deposited in any position on any of the low and medium carbon steels.

Hard Surfacing

The service life of parts that are subjected to constant abrasion can be extended greatly by hard-surfacing the affected areas with beads of weld. Hard-surfacing is most commonly applied to rebuilt parts, but new components can be treated in the same manner. On parts such as bucket teeth that are exposed to severe wear, the entire area can be covered with a layer of hard-surfacing material. Since the material is hard and brittle, the layer should not be more than 3 mm (1/8 inch) thick. Otherwise hard-surfacing will tend to crack and break off. The leading edge of a cutting tool may break off if extended more than two beads away from the base metal (Illustration 62).

Illustration 62	g02583461
Service life of parts can be extended by hard-surfacing.

For most applications, a pattern of stringer beads of hard-surfacing material has been found to be more economical. In applications where heavy rocks are being handled, the beads should be placed parallel with the flow of abrasive material (Illustration 63). The parallel beads will support the rocks and protect the base metal while offering the least resistance to flow. Beads may be laid perpendicular to flow in areas that are covered completely. Surfaces exposed to the abrasive action of sand, soil, or small stones should be protected with stringer beads that are perpendicular to the flow (Illustration 63). The spaces between the beads will fill up with soil and the soft base will be protected. Another pattern used frequently is the diamond shaped pattern (Illustration 63). This pattern is designed to prevent dirt from packing between the stringer beads and is used where self-cleaning action is desired.

Illustration 63	g03858245
Different bead patterns are required for various applications.

Weld Toe Treatment for Fatigue Life Improvement

Introduction

This guide details the requirements for weld toe treatments needed to increase the fatigue life on existing welds for both new structures and repair of post production structures. The Gas Tungsten Arc Welding (GTAW) process (sometimes referred to as Tungsten Inert Gas [TIG] welding process), Toe Grinding (Burr Grinding), and Ultrasonic Peening are the variations described for weld toe dressing of welded components.

Application

Fatigue Life Improvement

The fatigue performance of fabricated structures involving fillet-welded attachments to highly stressed members is controlled by the fillet weld toe characteristics. Fatigue performance can be improved through alteration of the original, as-welded toe profile by different post weld treatment options.

Crack Initiation

The crack initiation phase is extended through the removal and reduction in size of surface and subsurface discontinuities and or introduction of compressive residual stresses into the crack-prone regions, thus improving the fatigue life of the component.

Unfavorable Weld Profiles

Stress concentrations are minimized by improving the transition from the base material to the weld toe and reducing unfavorable weld profiles, stress risers, and minimizing weld toe surface and subsurface discontinuities.

Toe Dress Options

TIG Toe Dress (TTD)

Illustration 64	g03858252

The TIG Toe Dress (TTD) process removes or reduces the surface and subsurface weld toe discontinuities by remelting the weld toe and adjacent base metal at the toe while increasing the weld toe radius. TIG toe dressing can be performed on any type of weld produced using an electric arc welding process such as Gas Metal Arc Welding (GMAW), Shielded Metal Arc Welding (SMAW), Gas Tungsten Arc Welding (GTAW), and others. Welds not made with an electric arc may be evaluated for TTD modification. Illustration 64 shows that the only acceptable weld starts, stops, and restarts for the TIG toe dress process that shall be used on the TIG toe dress weld. It is acceptable to use any one of the options, or combination of options shown in Illustration 64. The weld starts and stops should extend at least 6 mm (0.25 inch) beyond the specified toe treatment length, unless the weld terminates at that point, or part geometry impedes grinding beyond the specified treated length. If option "f" from Illustration 64 is used, then the weld overlap on the stop and start should be a minimum of 6 mm (0.25 inch). The TTD process is performed autogenously (without filler wire), but sometimes filler is used as a result of excessive undercut or a poor original weld bead profile. When using TTD, multiple weld passes may be deposited to achieve the minimum required radius. Filler metal may be added to repair excessive undercut if repair or rework is required. Only filler metal with the same classification as specified on the WPS (welding procedure specification) may be used. Toe treatment is required on all exposed weld toes of a multi-pass weld, unless specified otherwise on the engineering drawing.

Toe Grinding

The manual grinding process removes imperfections in the weld toe region and creates a smooth transition between the weld and base material. The cross-sectional thickness of the base material is slightly reduced by this process. Design consideration for the grinding effects of the cross-sectional thickness decrease shall be evaluated when specifying the Toe Grinding option. The minimum plate thickness allowed for Toe Grinding is 10.0 mm (0.40 inch). Any visible discontinuity at the weld toe should be weld repaired prior to Toe Grinding. To remove subsurface discontinuities at the weld toe, the minimum depth of grinding should be greater than 0.5 mm (0.02 inch) below the weld toe to base plate interface or until all traces of the original weld toe have disappeared, but no greater than the maximum 2 mm (0.08 inch) grinding depth. Grinding starts and stops shall extend at least 6 mm (0.25 inch) beyond the specified to treatment length, unless the weld terminates at that point, or part geometry impedes grinding beyond the specified treated length. Only steel carbide cutters are permitted for toe grinding. Abrasive grinding discs, stones, wheels, or cutters should not be used. When using the toe grinding process, the steel carbide cutter should have a minimum working diameter of 6 mm (0.25 inch) to ensure that the minimum toe radius is maintained.

Ultrasonic Peening

Equipment

Ultrasonic Generator/Controller - Range intensity must be on adequate setting for structures with 5 mm (0.20 inch) thick plate and thicker. The timer option must be turned off.

Ultrasonic Tool

Peening Head - The single 4 mm (0.16 inch) diameter peening head is recommended for easy and consistent operation.

Striker Pins - 4 mm (0.16 inch) diameter, 2 mm (0.08 inch) tip radius striker pins are recommended for optimum fatigue life improvement.

Air Supply Source - Air supply capable of supplying air capacity and 172-241 kPa (25-35 psi) or additional requirements of the ultrasonic peening manufacturer.

Air Regulator - Air regulator with variable flow adjustment of 172-241 kPa (25-35 psi) or additional requirements of the ultrasonic peening manufacturer.

Illustration 65	g03858277
Peen Depth Gage.

Peening Depth Groove Gage - 386-0542 Peen Depth Gage should be used for the measuring of a peen groove between 0.4 mm (0.016 inch) and 0.5 mm (0.020 inch).

Illustration 66	g03858291
Peen Depth Calibration Gage.

Peen Depth Calibration Gage - Use the 8T-0455 Liner Projection Tool Group (calibration gage) before each use of the peening depth gage to ensure accurate measurements. Always use the calibration tool to check the depth gage if the depth gage has been dropped or impacted.

Several ultrasonic peening suppliers are:

Applied Ultrasonics (www.appliedultrasonics.com)

AMERICAS
Corporate Office
5871 Old Leeds Roads, Suite 201
Birmingham, AL, 352103009
U.S.A.
(205) 951-7747
1 (877) 376-6491
info@appliedultrasonics.com

ASIA
Nippon Steel Technoresearch Corporation
KSP A101, Sakado 3-2-1, Takatsu-ku
Kawasaki City, 213-0012, Japan
81 (44) 814-3464
www.uit-nstr.co.jp

AUSTRALIA
Applied Ultrasonics Australia
Suite 8/9 Narabang Way
Belrose, New South Wales 2085
61 (02) 9986-2133
aussieinfo@appliediltrasonics.com

EUROPE
Applied Ultrasonics Europe
P.O. Box 8623
AP Rotterdam
The Netherlands
31 (347) 354-323

Illustration 67	g03858292
Applied Ultrasonics peening gun and ultrasonic generator.

Shockform (Sonats) (www.sonats-et.com)

SONATS (Headquarters)
2, rue de la Fonderie - BP 40538
44475 CARQUEFOU France
33 (251) 700-494

SONATS Inc. (North America HQ)
10 Gaston-Dumoulin, Suite 900
Blainville, Quebec, J7C 0A3
Canada
1 (450) 430-4224

SCHNÜR & HALLER
Ing. Schnür Haller KG
Untere Waldplätze 23
D 70569 Stuttgart Germany
49 (0) 711/687007-0
www.shkg.de

TRACOSA
4th Dobryninski per. 6/9
119049 Moscon Russia
7 (495) 237-6065

Illustration 68	g03858301
Shockform ultrasonic peening set-up and close view of a tip.

Integrity Testing Laboratory Inc. (www.itlinc.com)

80 Esna Park Dr., Units 7-9
Markham, Ontario
L3R 2R7
Canada
1 (866) 926-0802
info@itlinc.com

Illustration 69	g03858346
Integrity ultrasonic peening equipment.

Pfeifer Seil (www.pfeifer.de/en/germany-english/)

Dr.-Karl-Lenz-Strasse 66
D-87700 Memmingen, Germany
49 (8331) 937-0
complett@pfeifer.de

Illustration 70	g03858351
Pfeifer high frequency peening gun.

Weld Inspection Prior to Peening

Repair or remove weld undercut and weld spatter prior to ultrasonic peening to prevent stray peening marks and inconsistent peening groove depths from occurring.

Cleaning

Remove all mill scale, rust, silicates, and other debris from the weld toe area and adjacent weld areas. Use a wire brush prior to ultrasonic peening and during as metal flakes appear in the peened groove.

Ultrasonic Peening Technique

Skills required for peening are similar to manual welding skills. Using a 20-40 mm (0.8-1.6 inch) longitudinal weaving pattern insures adequate peening coverage and ease of operation. A single pin, 4.0 mm diameter peening head works the best for attachment components and small radii applications. Repeat ultrasonic peening until the desired groove depth of 0.4-0.5 mm (0.016-0.020 inch) is met.

Illustration 71	g03858362
Ultrasonic tool at proper angle during peening.

Peening Angles - The angle of the ultrasonic tool to the work piece (tool angle) is typically held at 80-90 degrees longitudinal to the weld toe while splitting the included angle between the base metal and weld (flank angle). These angles will change greatly while peening to vary the position of the peening head to base metal required for optimum transfer of compressive residual stresses to the weld toe area.

Ultrasonic Tool Manipulation - Follow the length of the weld area that requires toe grinding using a longitudinally oscillating motion. Oscillations should be between 20-40 mm (0.80-1.57 inch). This type of motion will help keep striker pins along the weld more consistent in depth and in line with the toe of the weld.

Peening Depth - The depth of the peened groove should fall into the range of 0.4 mm (0.016 inch) to 0.5 mm (0.020 inch) along the length of the weld toe. The full benefits of ultrasonic peening are realized after 0.4 mm (0.016 inch) is attained. After 0.5 mm (0.020 inch) of depth, ultrasonic peening is not detrimental but additionally benefits will not be gained.

Illustration 72	g03858370
Stray marking of base metal.

Peening Stray Marks - If the operator is not properly braced to guide the head and striker pins at the weld toe, it is easy to loose control of the head and cause unnecessary marks on the base material due to the vibrating nature of the process. This occurs when the striker pin pulls off the intended weld toe path during the peening process.

Ultrasonic Tool Air Supply Fitting - The fitting which fastens the air supply line must be connected with the air source to ensure that the working head receives adequate cooling and does not accidentally overheat the tool during operation. The air supply must be utilized during all peening operations.

Damaged Striker Pins - Chipped or flattened areas of the striker pins will cause the outside diameter of the pin to become non-uniform and will cause stress concentrations in the peen groove. Replace the striker pin when it becomes damaged.

Measurement Technique

Illustration 73	g03858373
Peen groove being measured with peen depth gage.

Use a simple, developed, low-cost Go/No-Go gage to measure the peened weld. Visually measure the maximum depth of the peened groove using a 0.1 mm (0.004 inch) incremental peen gage to between 0.2 mm (0.008 inch) and 0.5 mm (0.020 inch). Careful attention must be taken to insure accurate measurement. It is critical to maintain a peen depth of between 0.4 mm (0.016 inch) and 0.5 mm (0.020 inch) along the entire length of the weld to receive the full fatigue relief of ultrasonic peening. Run the gage along the peened groove so that gage is perpendicular to the groove. If the edge of the gage remains in full contact with the metal, then the depth indicated that on the gage has been attained. If light can be seen between the metal surface and the edge of the gage, then the indicated depth has not been attained.

Illustration 74	g03858375
Consistent peen groove depth.

Inspection

All weld lengths modified with the TIG toe dress, toe grinding, or ultrasonic peening process shall be visually inspected for acceptance. No visible discontinuities are permitted such as porosity, inclusions, lack of fusion, voids, overlap, and cracks. When the Toe Grinding process is used, reduction in the cross-sectional thickness of the base material shall not exceed 2.0 mm (0.08 inch). A minimum of 3.0 mm (0.12 inch) toe radius for the full length of the treated weld toe is required. A suitable radius gage shall be used to verify the TIG toe dressing (TTD) weld to the minimum radius requirements. Undercut on the TTD weld toes should not exceed 0.5 mm (0.02 inch) in depth. Undercut should be checked with a gage that has a minimum of 0.5 mm (0.02 inch) accuracy. The weld size shall be measured after the manufacturing process of the weld to ensure that throat size was not compromised during the weld toe treatment. Sharp transitions from the TTD to base metal and TTD to the original weld metal are not acceptable.

Illustration 75	g03858380
Radius gage capable of measuring the weld toe radius.

Appendix

Reference Books

Metals and How to Weld Them. Published by The James F. Lincoln Arc Welding Foundation, Cleveland, Ohio.

Procedure Handbook of Arc Welding Design and Practice. Published by Lincoln Electric Company, Cleveland, Ohio.

Welding Design and Fabrication. Published monthly by The Industrial Publishing Corporation, Cleveland, Ohio.

Welding Design and Fabrication Data Booke. Published biennially by The Industrial Publishing Corporation, Cleveland, Ohio.

Welding Engineer. Published monthly by the Welding Engineer Publications, Inc., Rochelle, Illinois.

Welding Handbook. Published by the American Welding Society, New York, New York.

Glossary

Arc Length - The distance from the end of the electrode core to the surface of the puddle of molten metal.

Arc Stream - Molten particles of electrode material flowing from the electrode to the puddle of molten metal.

Arc Welding - A process of fusion welding in which the heat from an electric arc is utilized to melt the adjacent surfaces of the pieces to be welded.

Axis (of a Joint) - A line through the weld deposit in a joint perpendicular to the cross section at its center of gravity.

Back Blow - Deflection of the arc away from the direction of travel. See Magnetic Arc Blow.

Back-up Plate - A plate placed behind a wide gap weld joint to retain the molten weld metal and insure complete penetration and fusion at the root of the weld.

Base Metal - See Parent Metal.

Cold Lap - A void between the weld deposit and parent metal caused by insufficient fusion.

Crater - The depression in a weld deposit caused by displacement of molten weld metal by the force of the arc stream.

Depth of Penetration - The distance from the surface of the parent metal to the root of the weld.

Electrode Angle - The angle that the electrode makes with the axis of the joint or the surfaces of the weldment members.

Flat Position - A joint position where both the axis of the joint and the face of the weld are within 10° of horizontal and the welding is performed on the top of the joint.

Flux - Fusible material used in welding to dissolve and facilitate removal of oxides and other undesirable substances.

Forward Blow - Deflection of the arc toward the direction of travel. See Magnetic Arc Blow.

Fusion - The melting together of parent metal and weld metal.

Fusion Welding - Welding by melting the adjacent surfaces of pieces to be joined and allowing the molten metal to mix.

Gas Shielding - The protection of molten weld metal from the air with a cloud of gas which is generated by the vaporization of materials in the electrode coating.

Gouging - Formation of a chamber or groove by melting and removing a portion of base metal.

Hard-surfacing - The deposition of weld metal on metal surface to obtain desired characteristics or dimensions.

Heat Treated Steel - Asteel that has been heated, quenched, and tempered, or otherwise treated in such a manner that its surface hardness is greater than in the annealed condition.

High-Strength Structural Steel - A weldable steel with a minimum yield strength of 310 MPa (45,000 psi) and a minimum tensile strength of 482 MPa (70,000 psi).

Horizontal Position - A joint position where the axis of the joint is within 10° of horizontal and the face of the weld is between 10° and 90° from horizontal.

Interpass Temperature - In a multiple pass weld, the lowest temperature should be measured 50.8 mm (2.00 inch) in from the start end of the preceding pass.

Low Hydrogen Electrode - An electrode containing no materials in the coating which will yield hydrogen gas upon vaporization.

Low Carbon Steel - Steel containing less than 0.30% carbon.

Lead Angle - The angle between the electrode and a line perpendicular to the axis of the joint.

Magnetic Arc Blow - Deflection of the arc from the intended path due to concentrations of magnetic force setup in the work by electric current.

Medium Carbon Steel - Steel containing 0.30% to 0.54% carbon.

Mild Steel - See Low Carbon Steel.

Neutral Axis - The line of zero stress in a beam, usually at or near the center of the beam.

Overhead Position - A joint position where the axis of the joint is within 10° of horizontal and the welding is performed on the lower side of the joint.

Overlap - Protrusion of weld metal beyond the bond at the top of a weld.

Parent Metal - The metal to be welded.

Pass - A single longitudinal progression of a welding operation along a joint.

Porosity - Gas pockets or voids in the weld metal.

Shielded Arc Welding - An arc welding process that employs an electrode coated with a material which, when heated, either decomposes to form a gas cloud, melts to form a slag covering over the weld, or both. The gas cloud and the slag protect the molten weld metal and the arc from elements in the air.

Slag - Non-metallic solid material composed of electrode flux and impurities from the joint. In a properly made weld, the slag will lie on top of the weld metal.

Slag Inclusion - The entrapment of slag in weld metal or between weld metal and parent metal.

Slugged Weld - A weld that has a piece or pieces of material added to it before or during welding resulting in a welded joint that does not comply with design or specification requirements.

Spatter - The metal particles expelled during welding which do not form part of the weld.

Tack Weld - A short weld made to hold parts of a weldment in proper alignment until the final welds are made.

Transverse Weld - A weld made at right angle to the axis of the beam.

Travel Speed - The rate at which the electrode is moved along the length of the weld.

Underbead Crack - A crack between the weld deposit and the parent metal or in the heat affected zone under the weld deposit.

Undercut - A groove melted in the parent metal, near the toe of a weld, that is not filled with weld metal.

Upsetting Metal - The process of shortening and thickening metal with the application of pressure. In heat straightening, the pressure is obtained from the thermal expansion of the heated metal.

Vertical Position - A joint position where the axis of the joint is between 10° and 90° from horizontal.

Warping - An undesirable change in the shape of a weldment due to the forces of expansion and contraction of the weld metal.

Weaving - Moving the tip of the electrode back and forth over the joint as the electrode travels along the joint to obtain a wider weld deposit and to control head input in the joint.

Weld Deposit - The material in a welded joint which was melted during the welding process. The weld deposit consists of both electrode metal and parent metal.

Weldment - An assembly whose components are joined by welding.

Work Angle - In horizontal fillet welds, the angle between the electrode and the vertical plate.