|Welding is a
fabrication or sculptural process that joins materials (usually metals or
thermoplastics) by causing coalescence, often by melting the work-pieces and
adding a filler material to form a pool of molten material (the weld pool) that
cools to become a strong joint.
Welding is in contrast with soldering and brazing, which involve melting a lower-melting point material between the workpieces to form a bond between them, without melting the workpieces.
Of the many methods for joining metals, welding is one of the most convenient and rapid, as well as one of the most permanent. Welding has been used since ancient times through the process of forge welding where two pieces were heated to near melting temperature and hammered together. The roots of modern welding began in the late 19th century and progressed rapidly through two World Wars.
Today’s welding techniques and processes continue to develop to fit various needs, from simple steel brackets to nuclear reactors. For commercial enterprises, governmental agencies, and many other institutions around the world, welding is a widely accepted technique for the fabrication, maintenance, and repair of parts and structures.
You cannot become a proficient welder by reading a book--you need practice to build experience. However, you can gain a great deal of knowledge through study. For instance, by learning the correct equipment setting, set up method, or procedure from a book, you may eliminate many mistakes that otherwise would occur through trial and error.
This manual provides a background of basic information applicable to welding in general. Later manuals will provide more detailed information on various welding methods.
When you have completed this manual, you will be able to:
Forge welding, the earliest known form of welding, dates back to 2000 B.C.
A primitive process, forge welding joins metals by heating and hammering until the metals are fused together (Figure 1).
Forge welding still exists, but it is mainly limited to the blacksmith trade and to the artisans recreating replicas of historical metal implements and weapons.
Figure 1 — Example of forge welding process.
Today, there are multitudes of welding processes available. This manual will cover only a few, but they are the most common of the welding applications.
Figure 2 provides a list of processes used in modern metal fabrication and repair. Published by the American Welding Society (AWS), this list shows the official abbreviations for each process; for example, RSW stands for resistance spot welding and SMAW stands for shielded metal arc welding. The primary differences between the various welding processes are the methods by which heat is generated to melt the metal.
Arc welding is a process that fuses metal by heating it to a melting temperature with an electric arc created between an electrode and the metals being joined. The carbon arc welding (CAW) process is the oldest of all the arc-welding processes and is considered the beginning of arc welding. The Welding Society defines carbon arc welding as "an arc welding process which produces coalescence of metals by heating them with an arc between a carbon electrode and the work-piece. No shielding is used. Pressure and filler metal may or may not be used." It has limited applications today, but a variation called twin carbon arc welding is more popular, while yet another variation uses compressed air for cutting.
Figure 2 — Example of the multitude of welding processes.
Carbon arc welding has developed into the currently popular shielded metal arc welding (SMAW) process defined as "an arc welding process which produces coalescence of metals by heating them with an arc between a covered metal electrode and the workpiece. Shielding is obtained from decomposition of the electrode covering. Pressure is not used and filler metal is obtained from the electrode."
The most common types of welding are resistance welding (RW), oxyfuel gas welding (OFW), and arc welding (AW). Of the welding processes listed in Figure 2, shielded metal arc welding, also called stick welding, is the most common welding process. Your primary concern as a Steelworker will be gas and arc welding, the difference being in the method you use to generate the heat. Once you understand the theory of welding, you can apply it to most welding processes.
The oxyfuel gas welding process (OFW), shown in Figure 3, is one of the most popular welding methods. Heat is produced by mixing and burning oxygen with a combustible gas such as acetylene or MAPP (methylacetylenepropadiene).
Figure 3 — Example of oxyfuel gas welding (OFW).
Gas welding is widely used for maintenance and repair work because of the ease in transporting oxygen and fuel cylinders. Once you learn the basics and begin to practice OFW, you will find the process is adaptable to brazing, cutting, and heat treating.
Acetylene is a flammable fuel gas composed of carbon and hydrogen having the chemical formula C2H2. When burned with oxygen, acetylene produces a hot flame with a temperature between 5700°F and 6300°F. Acetylene is a colorless gas, but has a disagreeable odor that is readily detected even when the gas is highly diluted with air.
Acetylene can be safely compressed up to 275 psi when dissolved in acetone and stored in specially designed cylinders filled with porous material such as balsa wood, charcoal, finely shredded asbestos, corn pith, Portland cement, or infusorial earth. These porous filler materials aid in the prevention of high-pressure gas pockets forming in the cylinder. Acetone is a liquid chemical that dissolves large portions of acetylene under pressure without changing the nature of the gas. Being a liquid, acetone can be drawn from an acetylene cylinder when it is not upright.
You should not store acetylene cylinders on their side, but if they are, you must let the cylinder stand upright for a minimum of 2 hours before using. This allows the acetone to settle to the bottom of the cylinder. Acetone contaminates the hoses, regulators, and torch, and disrupts the flame.
Acetylene is measured in cubic feet. The most common cylinder sizes are 130-, 290-, and 330-cubic-foot capacity. A common standard size cylinder holds 225 cubic feet of acetylene.
MAPP (methylacetylene-propadiene) is an all-purpose industrial fuel having the high flame temperature of acetylene but the handling characteristics of propane. MAPP is a liquid sold by the pound rather than by the cubic foot, as with acetylene. One cylinder containing 70 pounds of MAPP gas can accomplish the work of more than six and one-half 225-cubic-foot acetylene cylinders; therefore, 70 pounds of MAPP gas is equal to 1,500 cubic feet of acetylene.
The total weight for a MAPP cylinder, which has the same physical size as a 225-cubicfoot acetylene cylinder, is 120 pounds (70 pounds of which is MAPP gas). MAPP cylinders contain only liquid fuel, with no cylinder packing or acetone to impair fuel withdrawal; therefore, the entire contents of a MAPP cylinder can be used. For heavy-use situations, a MAPP cylinder delivers more than twice as much gas as an acetylene cylinder for the same period.
MAPP produces a flame temperature of 5300°F when burned with oxygen, is not sensitive to shock, and is nonflammable in the absence of oxygen. There is no chance of an explosion if a cylinder is bumped, jarred, or dropped. You can store or transport the cylinders in any position with no danger of forming an explosive gas pocket.
MAPP gas is not restricted to a maximum working pressure of 15 psig, as is acetylene. In jobs requiring higher pressures and gas flows, MAPP can be used safely at the full cylinder pressure of 95 psig at 70°F. This characteristic allows MAPP to be excellent for underwater work.
The arc welding process uses an electric arc to join the metals being welded. This allows concentrated heat on the work material, a distinct advantage of arc welding over gas welding.
In gas welding the flame spreads over a large area, sometimes causing heat distortion. Concentrated heat, characteristic of arc welding, is an advantage because less heat spreads to the rest of the work material. While buckling and warping can still be a problem with both processes if unattended, they are less so with arc welding.
Heat concentration also increases the depth of penetration and speeds up the welding operation; therefore, you will find that arc welding is often more practical and economical than gas welding, particularly as the work material depth increases.
All arc-welding processes have three things in common: a heat source, filler metal, and shielding. In arc welding, you produce heat by arcing an electrical current between two contacts. The power source for the electrical current’s arc is a welding machine, or more commonly called a welder. This is also the same term for the person performing the operation, so do not confuse the two when communicating: “When a welder is welding, he or she is using the welder.” The welder (welding machine) can be either plug-in electric or motor-powered to produce the electricity. As a member of the Naval Construction Force (NCF), you need to become familiar with the two main types of arc welding processes: shielded metal arc welding (SMAW) and gas shielded arc welding (a generic term that covers a number of specific processes).
You perform shielded metal arc welding (Figure 4) with an arc between a coated metal electrode and the base metal. Once you establish the arc (called striking the arc), the molten metal from the tip of the electrode flows together with the molten metal from the base metal to form a sound joint. This process is known as fusion.
Figure 4 — Example of shielded metal arc welding (SMAW).
The coating from the electrode melts and forms a covering over the weld deposit, shielding it from contamination; hence, the name shielded metal arc welding. SMAW’s advantages are: 1) high-quality welds 2) made rapidly 3) at low cost. Additional information about shielded metal arc welding will be presented later in this manual.
The primary difference between shielded metal arc welding and gas shielded arc welding is the type of shielding used. In gas-shielded arc welding, both the arc and the molten puddle are covered by a shield of inert gas. The shield of inert gas prevents atmospheric contamination, thereby producing a better weld. Gas shielded arc welding is extremely useful because it can be used to weld all types of ferrous and nonferrous metals of all thicknesses.
GTAW or “TIG” (Figure 5) is one gas shielded arc welding process.
Figure 5 — Example of tungsten metal arc welding (GTAW) (TIG).
Features of TIG include:
GMAW or “MIG” (Figure 6) is a second gas shielded arc welding process.
Figure 6 — Example of gas metal arc welding (GMAW) (MIG).
Features of MIG include:
FCAW (Figure 7) is a third gas shielded arc welding process.
Figure 7 — Example of flux core arc welding (FCAW).
Features of FCAW include:
Spot welding (Figure 8) is a process in which contacting metal surfaces are joined by heat resistance to electric current flow. Work-pieces are held together under pressure by two shaped copper alloy electrodes. They simultaneously clamp and concentrate a welding current into a small "spot." Forcing a large current through the spot melts the metal (typically 0.5-3.0 mm thickness range) to form the weld without a filler metal.
Figure 8 — Example of resistance spot welding (RSW) equipment.
Which one is the right one for your project? There are no fixed rules. In general, the controlling factors are these:
Oxyfuel Gas welding (OFW) is widely used for maintenance and repair work in the field because of its flexibility and mobility. On the other hand, if you are tasked with repairing a critical piece of equipment made from aluminum or stainless steel, you should probably choose one of the gas shielded metal arc welding processes.
No matter which process you use, there is some basic information you need to know since it applies to all the processes. The remainder of this manual is devoted to this type of information. Study this information carefully; knowing it will allow you to follow welding instructions, read welding symbols, and weld various types of joints using the proper welding techniques.
|Test Your Knowledge
1. Welding is similar to soldering and brazing, in that you form a bond between materials by melting the workpieces.
- To Table of Contents -
To become a skilled welder, the first thing you need to learn is the technical vocabulary of welding. The next sections will present some of the basic welding terms. Once you understand the language of welding, you will be prepared to interpret and communicate welding information accurately.
When you weld two pieces of metal together, often you have to leave a space between the joint. The material you add to fill this space is known as the filler metal or filler material. There are two commonly used types of filler metals in welding: welding rods and welding electrodes.
Figure 9 — Typical use of welding rod (filler rod).
Welding rod (Figure 9), refers to a form of filler metal that does not conduct an electric current during the welding process. The only purpose of a welding rod is to supply filler metal to the joint. This type of filler metal is often used for gas welding. Electrode refers to the component in electric arc welding that conducts the current from the electrode holder to the metal being welded. Electrodes are classified into two groups: consumable and non-consumable.
Consumable electrodes not only provide a path for the current, they also supply the filler metal to the joint.
The electrode used in shielded metal arc welding is an example (Figure 10).
Figure 10 — Example of consumable electrode.
Non-consumable electrodes are used only as a conductor for the electrical current. The electrode in gas tungsten arc welding is an example (Figure 11). The filler metal for gas tungsten arc welding is a hand-fed consumable welding rod.
Figure 11 — Example of non-consumable electrode.
You will find additional information about filler rods and electrodes in other manuals of this manual, which cover specific welding processes.
Flux is a chemical cleaning agent that facilitates soldering, brazing, and welding by removing oxidation from the surface of metals to be joined. In high-temperature metal joining processes, the primary purpose of flux is to prevent oxidation of the base and filler materials.
Before performing any of the welding processes, you must ensure the base metal is clean. No matter how much the base metal is physically cleaned, it is not chemically clean; it still contains impurities called oxides, the result of oxygen combining with the metal and other contaminants within the base metal. Unless you remove these oxides with a proper flux, your weld may be faulty.
Flux is the material used to dissolve oxides and release trapped gases and impurities from the base metal. Thus, the reason flux is thought of as a cleaning agent is that it allows the filler metal and the base metal to be fused.
Different types of metals require different types of fluxes; therefore, you need to select a flux formulated for a specific base metal. Beyond that, you need to select a flux based on the expected temperature if you are soldering, brazing, or welding. When you are brazing, for example, you should select a flux that becomes liquid at the correct brazing temperature, so when it melts, you know it is time to add the filler metal. The ideal flux has the right fluidity at the welding temperature and thus blankets the molten metal from oxidation.
Table 1 — Typical Flux Selection Chart (Example)
|Flux Name||Base Metal||Recommended Filler Metal||Form||Applications / Description||Active Temp||Specification|
|Flux17||Stainless Steels, High Chrome Alloy and Carbides||Nickel Silver, Brass And Bronze, Low Silver Alloys||Powder||Carbide Tools, Restaurant Appliance Mining Tools||1400-2200° F||AWS Type 3D|
|Flux11||Cast And Malleable Iron||Low Fuming Bronze||Paste||Maintenance, Marine Engines||1500-2000° F||Mil-F-16136B|
|Flux800||Cast Iron||Cast Iron||Powder||All Cast To Cast Iron Joining||950-1300° F||N/A|
Fluxes are available in many different forms. Fluxes for oxyfuel gas applications, such as brazing and soldering, can be a paste, liquid, or powder. Paste and liquid fluxes can be applied to the filler rod and to the base metal with a brush. Powders can be sprinkled on the base metal, or the filler rod can be heated and dipped into the powder.
For shielded metal arc welding, the flux is a coating on the exterior of the electrode. In this case, as the electrode applies the filler metal, the flux combines with impurities in the base metal, floating them away in the form of a heavy slag, which shields the weld from the atmosphere.
Because of the wide variety of metal properties and different melting temperatures, no single flux is satisfactory for universal use; however, there are many good general-purpose fluxes for use with common metals. In general, a good flux has the following characteristics:
Nearly all fluxes give off fumes that may be toxic. Use ONLY in well-ventilated spaces, and remember: ALL welding operations require adequate ventilation whether a flux is used or not.
The weld joint is where two or more metal parts are joined by welding. The five basic types of weld joints are butt, corner, tee, lap, and edge.
A butt joint is used to join two members aligned in the same plane (Figure 12). This joint is frequently used in plate, sheet metal, and pipe work. A joint of this type may be either square or grooved. Some of the variations of this joint are presented later in this manual.
Figure 12 — Example of a butt joint.
Corner joints (Figure 13 View A) and tee joints (Figure 13 View B) are used to join two members located at right angles. In cross section, the corner joint forms an L-shape, and the tee joint has the shape of the letter T. Various joint designs of both types have uses in many types of metal structures.
Figure 13 — Examples of a corner joint and a tee joint.
Commonly used with torch brazing and spot welding applications, a lap joint, as the name implies, is made by lapping one piece of metal over another (Figure 14).
This is one of the strongest types of joints; however, for maximum joint efficiency, you should overlap the metals a minimum of three times the thickness of the thinnest
Figure 14 — Example of a member you are joining. lap joint.
An edge joint is used to join the edges of two or more members lying in the same plane. In most cases, one of the members is flanged, as shown in Figure 15.
Figure 15 — Example of an edge joint.
This type has some applications in plate work, but is more useful in sheet metal work. An edge joint should only be used for joining metals 1/4 inch thick or less that are not subjected to heavy loads.
While there are five basic types of joints, there are many possible variations and combinations of the five, some of which will be presented later in this manual.
There are many joint variations, but the parts of a joint are described by standard terms.
The root of a joint is that portion of the joint where the metals are closest to each other. As shown in Figure 16, the root may be a point, a line, or an area when viewed in cross section.
Figure 16 — Examples of the root of a joint.
The groove of a joint is an opening or space provided between the edges of the metal parts to be welded. The groove face is that surface of a metal part included in the groove; see Figure 17 View A
Figure 17 — Examples of groove face, root face, and root edge of joints.
A given joint may have a root face or a root edge.
The root face (refer again to Figure 17 View A), is that portion of the prepared edge of a part to be joined by a groove weld that has not been grooved; the root face has relatively small dimensions.
Essentially, a root edge is a root face of zero width; see Figure 17 View B.
Now look at Figures 3-17 Views C and D. In some joints, the groove face and the root face are the same metal surfaces.
The specified requirements for a particular joint are expressed in such terms as bevel angle, groove angle, groove radius, and root opening.
The bevel angle is the angle formed between the prepared edge of a member and a plane perpendicular to the surface of the member (Figure 18).
Figure 18 — Examples of bevel angle and groove angle.
The groove angle is the total angle of the groove between the parts to be joined. For example, if the edge of each of two plates were beveled to an angle of 30 degrees, the groove angle would be 60 degrees. This is often referred to as the included angle between the parts to be joined by a groove weld.
The groove radius is the radius used to form the shape of a J- or U-groove weld joint. It is used only for special groove joint designs (Figure 19). The root opening refers to the separation between the parts to be joined at the root of the joint, sometimes called the root gap.
Figure 19 — Examples of groove radius and root opening.
To determine the bevel angle, groove angle, and root opening for a joint, you must consider these factors:
As a rule, gas welding requires a larger groove angle than manual metal-arc welding.
The root opening is usually governed by the diameter of the filler material. This, in turn, depends on the thickness of the base metal and the welding position. Having an adequate root opening is essential for root penetration.
Figure 20 illustrates the terms root penetration and joint penetration of welds.
Figure 20 — Examples of root penetration and joint penetration of welds.
Root penetration refers to the depth that a weld extends into the root of the joint. Root penetration is measured on the centerline of the root cross section.
Joint penetration refers to the minimum depth that a groove (or a flange) weld extends from its face into a joint, exclusive of weld reinforcement.
Study Views A, C, and E. Often, the terms root penetration and joint penetration both refer to the same dimension. Notice View B, however; it shows the difference between root penetration and joint penetration. View D shows joint penetration only.
Weld reinforcement is a term used to describe weld metal in excess of the metal necessary to fill a joint (Figure 21).
Figure 21 — Example of face reinforcement and root reinforcement.
There are many types of welds. Some of the common types you will work with are: bead, groove, fillet, surfacing, tack, plug, slot, and resistance.
The first type of weld you will learn to produce is called a weld bead, also referred to simply as a bead (Figure 22).
Figure 22 — Example of weld bead.
A weld bead is merely a weld deposit produced by a single pass with one of the welding processes.
It may be narrow or wide, depending on the amount of transverse oscillation (side-to-side movement) you use. If you use a great deal of oscillation, the bead is wide; if you use little or no oscillation, the bead is narrow. A narrow weld bead made without much weaving motion is often referred to as a stringer bead; a weld bead made with side-to-side oscillation is called a weave bead.
Groove welds (Figure 23) are made in the groove between two members of a workpiece and are adaptable to a variety of butt joints of varying thicknesses.
Figure 23 — Examples of standard groove welds on varying thicknesses.
If two or more beads are deposited in the groove, the weld is made with multiplepass layers, as shown in Figure 24. As a rule, a multiple-pass layer is made with stringer beads (narrow) in manual operations.
Figure 24 — Example of multiple pass layers.
As a welder who is assigned welding tasks, you will frequently use groove welds in both single and multiple passes.
Buildup sequence is another term you need to be familiar with when making a multiple-pass weld.
Buildup sequence refers to the order in which you deposit the beads in the joint of a multiple-pass weld (Figure 25).
Figure 25 — Example of weld layer sequence.
Interpass temperature is another term you need to know. Often, welding instructions will specify an interpass temperature.
This term refers to the temperature you must allow the previous pass to lower to before applying the next pass.
When the effect of heat on metal is addressed later in this manual, you will be able to appreciate the significance of buildup sequence and the importance of controlling the interpass temperature.
A fillet weld is used to join two surfaces at approximately right angles to each other in a lap, tee, or corner joint. The shape of a fillet weld’s cross-sectional view is triangular (Figure 26).
Figure 26 — Examples of fillet welds.
Surfacing is a welding process used to apply a hard, wear-resistant layer of metal to surfaces or edges of parts as either a preventative to wear, or a remedy for already worn parts (Figure 27).
Figure 27 — Example of surfacing (hardfacing/wearfacing) welds.
It is one of the most economical methods of conserving and extending the life of machines, tools, and construction equipment.
Sometimes known as hardfacing or wearfacing, a surfacing weld is composed of one or more stringer or weaves beads.
A tack weld is a temporary weld made to hold parts of an assembly in proper alignment until the final welds are made (Figure 28).
Figure 28 — Example of tack welds.
Although the sizes of tack welds are not specified, they are normally between 1/2 to 3/4 inch in length, but never more than 1 inch in length.
In determining the size and number of tack welds you need for a specific project, you need to consider the thicknesses of the metals being joined and the complexity of the object being assembled.
Plug welds and slot welds are welds made through holes or slots in one member of a lap joint (Figure 29).
Figure 29 — Examples of plug welds and slot welds.
These welds are used to join the member with holes to the surface of another member exposed through the hole.
The hole may or may not be completely filled with weld metal.
These types of welds are often used to:
Resistance welding is a metal fabricating process in which the fusing temperature is generated at the joint by the resistance to the flow of an electrical current (Figure 30).
Figure 30 — Example of the resistance weld process.
This is accomplished by clamping two or more sheets of metal between copper electrodes and then passing an electrical current through them.
When the metals are heated to a melting temperature, forging pressure is applied either manually or automatically to weld the pieces together.
Resistance Spot Welding (RSW) and Resistance Seam Welding (RSEW) are two of the most common types of resistance welding processes (Figure 31).
Resistance spot welding is probably the most common. The material to be joined is placed between two electrodes and pressure is applied, with a charge of electricity sent from one electrode through the material to the other electrode.
Figure 31 — Examples of resistance spot welds and seam welds.
Spot welding is applicable to light gauge material; it is especially useful in fabricating sheet metal parts.
Resistance seam welding is similar to spot welding except the spot welds overlap to make a continuous weld seam (Figure 31).
This type of welding is most often used in industrial manufacturing.
In this process, the metal pieces pass between two roller-style electrodes (Figure 32).
Figure 32 — Example of the industrial resistance seam welding (RSEW) process.
As the electrodes (usually a copper alloy wheel) revolve, the current is automatically turned on and off at the speed the parts are set to move.
For you to produce welds that meet the job requirements, you need to be familiar with the terms used to describe a weld. Some terms may apply to multiple joint assemblies; some will be unique. Refer to both Figure 33 and Figure 34 for the weld terms.
Figure 33 — Terminology of a groove weld.
Face — the exposed surface of a weld on the side from which the weld was made.
Toe — the junction between the face of the weld and the base metal.
Root — the points at which the back of the weld intersects the base metal surfaces.
Leg — the portion of the weld from the toe to the root when looking at a triangular cross section of a fillet weld.
Throat — the distance from the root to a point on the face of the weld along a line perpendicular to the face of the weld. Theoretically, the face forms a straight line between the toes.
The terms leg and throat apply only to fillet welds.
Figure 34 — Terminology of a fillet weld.
In determining the size of a groove weld (Figure 33), you must consider such factors as the depth of the groove, root opening, and groove angle.
The size of a fillet weld (Figure 34) refers to the length of the legs of the weld. Unless specified otherwise, assume the legs are equal in size.
There are multiple styles and types of welding gauges available to measure and prepare material for welding, as well as gauges to check the parts of the completed weld as described in welding terminology. Figure 35 shows a few examples.
Figure 35 — Examples of various welding gauges.
A welding micrometer is a gauge used for determining the size of a weld. Figure 36 shows how the welding micrometer is used to determine the various dimensions of a weld.
Figure 36 — Examples of using a welding micrometer.
You need to be familiar with still more terms that are used to describe areas or zones of welds. As previously covered, fusion is the melting together of base and/or filler metal. See Figure 37.
Figure 37 — Examples of zone terminology in a weld.
The fusion zone is the region of the base metal that is actually melted.
The depth of fusion is the distance that fusion extends into the base metal or previous welding pass.
The heat-affected zone is another zone of interest to the welder. This zone is that portion of the base metal that has not been melted, but where the structural or mechanical properties of the metal have been altered by the welding heat.
Welding heat affects the mechanical properties of the base metal; therefore, it is very important for you to learn techniques to control this heat. For example, the intermittent weld is one technique often used to minimize heat input.
This technique and others will be presented as you progress through this manual. However, first consider some of the factors that affect the welded joint design.
|Test Your Knowledge
2. To become a skilled welder, the first thing you need to learn is _____.
- To Table of Contents -
The welded joint design is the term that includes all of the details of a joint, including the geometry and the required dimensions. The type of joint design best suited for a particular job will depend on many factors. Welded joints are designed primarily to meet strength and safety requirements, but you must also consider such questions as the following.
Another factor you must consider is joint efficiency; in welding, this is the ratio of the strength of a joint to the strength of the base metal expressed in percent. An efficient joint is one that is just as strong as the base metal, or 100 percent.
Normally, a designer or engineer determines the joint design and includes it in the project plans and specifications. Your understanding of how to interpret the joint design information is what will enable you to produce proper welds.
Earlier, this manual presented the five basic types of welded joints—butt, corner, tee, lap, and edge, and stated that every joint you weld would be some variation of them.
Now consider some of the variations of these welded joint designs and note the characteristics, efficiencies, and basis for a particular design.
Square butt joint — Figure 38
Figure 38 — Example of a square butt joint.
When you weld metals thicker than 3/16 inch, often it is necessary to use a grooved butt joint. The purpose of grooving is to give the joint the required strength. When you use a grooved joint, the groove angle must be adequate to allow the electrode into the joint; otherwise, the weld will lack penetration and may crack.
On the other hand, you also need to avoid excess beveling, as this wastes both weld filler metal and time. Depending on the thickness of the base metal, the joint design will call for either a single-groove (grooved on one side only) or double-groove (grooved on both sides) weld.
As a welder, you primarily use the single-V and double-V grooved joints.
Single-V butt joint — Figure 39
Figure 39 — Example of a single-V butt joint.
Double-V butt joint — Figure 40
Figure 40 — Example of a double-V butt joint.
To produce good quality welds using the groove joint you must:
When you follow these principles, you will produce better welds every time.
Other standard but less often used grooved butt joint designs include the bevel groove, J-groove, and U-groove, as shown in Figure 41
Figure 41 — Examples of additional grooved butt joint designs.
Figure 42 — Examples of corner joints.
The flush corner joint (Figure 42 View A) is designed primarily for welding 12-gauge or thinner sheet metal. It is restricted to lighter materials, because deep penetration is sometimes difficult and the design can support only moderate loads.
The half-open corner joint (Figure 42 View B) is used for welding materials heavier than 12-gauge. Penetration is better than in the flush corner joint, but its use is recommended only for moderate loads.
The full-open corner joint (Figure 42 View C) produces a strong joint, especially when welded on both sides. It is useful for welding plates of all thicknesses.
Figure 43 — Examples of tee joints.
The square tee joint (Figure 43 View A) requires a fillet weld that can be made on one or both sides. It can be used for light or marginally thick materials. For maximum strength, place considerable weld metal on each side of the vertical plate.
The single-bevel tee joint (Figure 43 View B) can withstand more severe loadings than the square tee joint because of better stress distribution. It is generally used on plates ½ inch thick or less, and where welding can be done from only one side.
The double-bevel tee joint (Figure 43 View C) is for use where heavy loads are applied and the welding can be done on both sides of the vertical plate.
Figure 44 — Examples of lap joints.
The single-fillet lap joint (Figure 44 View A) is easy to weld and the filler metal is simply deposited along the seam, but the strength of the weld depends on the size of the fillet.
It can be used for metal up to ½ inch thick that will not be subject to heavy loads
The double-fillet lap joint (Figure 44 View B) should be used when the joint will be subjected to heavy loads.
When welded properly, the strength of this joint is very close to the strength of the base metal.
Figure 45 — Examples of edge joints.
The flanged edge joint (Figure 45 View A) is suitable for plate ¼ inch thick or less and can sustain only light loads. Depending on the thickness of the workpieces, you can prepare for this joint as shown in either Figure 45 View B or C.
|Test Your Knowledge
3. Welded joints are designed primarily to meet _____.
- To Table of Contents -
You will do all your welding in one of four positions: (1) flat, (2) horizontal, (3) vertical, or (4) overhead. A fully qualified welder can make either fillet or groove welds in all of these positions. Figure 46 shows the various American Welding Society (AWS) positions used in plate welding.
Figure 46 — American Welding Society’s welding positions for plate.
The AWS uses a number/letter designation to identify the positions. For instance, the number designation indicates the position, or axis, of the weld, while the letter F indicates a fillet weld and the letter G indicates a groove weld. Thus, the 1G position refers to a groove weld in the flat position.
These number/letter designations refer to test positions, the positions a welder demonstrates a proficiency in to become certified during a welding qualification test.
As a welder, whether for your own professional development or for a project you are assigned to, there is a good possibility you will need to certify or perform a welding qualification test. Therefore, it is important that you have a good understanding and can apply the techniques for welding in each of the test positions.
It is important to note, however, that you do not have to qualify in all the positions initially. Qualifying in the various positions with different welding processes is a matter of steps. Figure 47 shows an example of a certification and a guide to its interpretation.
Figure 47 — AWS guide for interpreting certified welder card abbreviations.
Gravity affects the flow of molten filler metal in any of the positions, so use the flat position, if possible.
Although the terms flat, horizontal, vertical, and overhead sufficiently describe the positions for plate welding, they do not adequately describe pipe welding positions. Figure 48 shows the four basic test positions used in pipe welding. Notice that the position refers to the position of the pipe, not the position of welding.
Figure 48 — American Welding Society’s welding positions for pipe.
Test position 1G — the pipe is in the horizontal position. In this position, the pipe is rolled so that the welding is actually done in the flat position with the pipe rotating under the arc. This position is the most advantageous of all the pipe welding positions.
Test position 2G — the pipe is in the vertical position. The welding is then done in the fixed horizontal position.
Test position 5G — the pipe is in the horizontal position. However, unlike position 1G, in the 5G position, the pipe is not turned or rolled during the welding operation; thus the welding is more difficult.
Test position 6G — the pipe is at a 45-degree angle with the horizontal and the pipe is not rolled (Figure 49).
Figure 49 — Typical 6G certification test with GTAW (TIG).
Since the pipe is not rolled, welding has to be done in all the positions— flat, vertical, horizontal, and overhead. If you can weld pipe in this position, you can handle all the other welding positions.
There is no 3G or 4G test position in pipe welding, and since most pipe welds are groove welds, they are identified by the letter G.
|Test Your Knowledge
4. A fully qualified welder can make fillet or groove welds in four different positions.
- To Table of Contents -
One of the physical properties of a metal is its characteristic expansion when heated, and its contraction back to room temperature size when allowed to cool.
While some metals expand more readily than others, typically upon cooling, a metal contracts and tries to resume its original shape.
Figure 50 shows a bar that is not restricted in any way. When the bar is heated, it is free to expand in all directions. If the bar is allowed to cool without restraint, it contracts to its original dimensions.
Figure 50 — Example of unrestrained expansion/contraction with heating/cooling.
Figure 51 shows the results of heating and cooling metal under restraint.
When the bar is clamped in a vise and heated, expansion is limited to the unrestricted sides of the bar, in this instance vertically. As the bar begins to cool, it still contracts uniformly in all directions. As a result, the bar is now deformed; it has become narrower and thicker.
Figure 51 — Example of restrained expansion/contraction with heating/cooling.
Expansion and contraction forces act on the weld metal and base metal of a welded joint in the same way, although metal thicknesses will either exaggerate or diminish the effect.
However, when two pieces of metal are welded together, expansion and contraction are unlikely to be uniform throughout due to the difference in temperature from the actual weld joint out to the edges of the joint.
This difference in temperature leads to internal stresses, distortion, and warpage.
Figure 52 shows some of the most common difficulties you are likely to encounter if no controls are put in place during the weld preparation.
Figure 52 — Examples of distortion caused by welding.
See Figure 52 View A. When you weld a single-V butt joint, the highest temperature is at the surface of the molten puddle; this is where expansion and contraction are greatest. The temperature decreases as you move toward the root of the weld and travel away from the weld. Since the surface of the weld joint was the highest temperature, it contracts the most when the weld begins to cool, thus causing warpage or distortion.
Refer to Figure 52 View B. For a tee joint, the same principle applies with similar results but in a different axis orientation.
Refer to Figure 52 View C. Welding a bead on one side of a plate can warp it into a curve.
Refer to Figure 52 View D. Welding two plates together without proper tack welds can result in closed spacing and a loss of overall dimension.
When you expose a work-piece to heat buildup during welding, it will expand in the direction of least resistance. Conversely, when it cools, it will contract by the same amount. Therefore, if you want to prevent or reduce the distortion of the weldment, you have to use some method to overcome the effects of heating and cooling.
You can control the metal’s tendency to distort by expansion and contraction during welding by following some simple procedures.
To make good quality welds, proper edge preparation and fit-up are essential.
The faster a weld is made, the less heat is absorbed by the base metal. As you gain welding experience, it will become easier for you to minimize the heat by simply speeding up the welding process.
Often, regardless of your experience, you will need to use a welding technique designed to control heat input. An intermittent weld (sometimes called a skip weld) is one such technique you can use in lieu of one continuous weld. To make an intermittent weld:
Figure 53 shows examples of intermittent weld techniques.
Figure 53 — Examples of intermittent weld techniques.
Another technique to control the heat input is the back-step method (Figure 54).
When you use this technique, deposit short weld beads from right to left along the seam. Then move ahead and finish where you left off on the previous strip.
Figure 54 — Example of back-step welding techniques.
As previously covered, expansion and contraction rates are not uniform in a structure during welding because of the differences in temperature throughout the metal.
To control the differences in temperature, and thus the forces of expansion and contraction, you can preheat the entire structure before welding, and then following the welding, postheat to allow the structure to cool evenly and slowly. More about preheating and postheating will be presented later.
Keep distortion to a minimum by using as few weld passes as possible.
Limit the number of weld passes to the number necessary to meet the requirements of the job (Figure 55).
Figure 55 — Example of limiting the number of weld passes.
Holding the metal in a fixed position will prevent excessive movement from its tendency to expand and contract, so using jigs and fixtures can help prevent distortion.
A jig or fixture is simply a device used to hold the metal rigidly in position during the welding operation (Figure 56).
Figure 56 — Example of a welding jig.
Jigs can be temporarily developed for a unique part, or they can be an adjustable worktable that allows for various preparation positions.
Another alternative to adjust for distortion caused by expansion and contraction requires a certain level of experience and practice, but may be the simplest; just allow for it during fit-up.
To reduce distortion, angle the parts to be welded slightly in the opposite direction in which the contraction will take place.
When the metal cools, contraction forces pull the pieces back into position.
Figure 57 shows how distortion can be overcome in both the butt and tee joints.
Figure 57 — Examples of allowing for distortion for a butt and tee joint.
To be a good welder, you have to know more than how to do preparation, and be able to do more than lay a good bead. Many other factors must be considered, proper procedures being one of them. Later, additional techniques will be presented that you can apply to specific welding situations.
|Test Your Knowledge
5. Typically, upon cooling, a metal tries to _____.
- To Table of Contents -
Many factors are involved in the preparation of any welded joint. A welding procedure addresses those factors by providing the detailed methods and practices to prepare and perform a particular weldment. It identifies all the welding variables pertinent to a particular job or project. Generally, these variables include:
Welding procedures are used to produce welds that will meet the requirements of commonly used codes. The American Welding Society (AWS) produces the Structural Welding Code that is used for the design and construction of steel structures. It also publishes a number of other books specific to welding techniques for other metals.
As published, the AWS’s mission statement is: “The mission of the American Welding Society is to advance the science, technology and application of welding and allied joining and cutting processes, including brazing, soldering and thermal spraying.”
Another code that is used for the construction of steam boilers and pressure vessels is published by the American Society of Mechanical Engineers (ASME). These codes also provide a standardized guide of proven welding practices and procedures. As published, the ASME’s mission statement is: “To serve our diverse global communities by advancing, disseminating and applying engineering knowledge for improving the quality of life; and communicating the excitement of engineering.”
While you are not directly responsible for developing welding procedures, you could be assigned to a welding job that requires you to follow them. Those specifications will normally require the welding to be accomplished according to a specific code requirement, commonly one of AWS’s codes. If your unit is tasked to fabricate a welded steel structure, for instance, the specifications may require that all welding be accomplished according to AWS D1.1 (Structural Welding Code). The unit is then responsible for ensuring that the welders assigned to the job are qualified to produce the welds according to this welding procedure specification.
Using the Structural Welding Code and the project drawings and specifications, the welding inspector develops a welding procedure specification that meets the requirements of the job. This document assures that each of the variables can be repeated by qualified welders.
Once a welding procedure specification has been developed and qualified, the project’s welders are required to perform a Welding Performance Qualification test to meet the procedures. The weld specimens are then tested according to the requirements of the Welding Procedure Specification using either destructive or nondestructive tests. One destructive test is the guided-bend test; a nondestructive test would be an X-ray test.
When you are assigned to do a welding job, make a thorough examination of the drawings and specifications. Look carefully at the notes on the drawings. If specific codes are cited, inform the project supervisor so you can receive the training needed to perform the required welds.
As shown in Figures 3-58 and 3-59, a welding procedure specification is simply a document that provides details of the required variables for a specific welding application. ASME provides a suggested format with form QW-482.
Figure 58 — Example of welding procedure specification (QW-482 Front).
Figure 59 — Example of welding procedure specification (QW-482 Back).
|Test Your Knowledge
6. What organization produces the Structural Welding Code that is used for the design and construction of steel structures?
- To Table of Contents -
An engineer uses drawings or sketches to convey ideas to the skilled craftsman working in the shop. As a welder, you must be able to work from a drawing in order to fabricate metal parts exactly as the engineer designs them.
To read the drawings or sketches, you must know how engineers use lines, dimensions, notes, and views to communicate their ideas. This section briefly covers each of these drawing elements.
Figure 60 shows many of the different types of lines used in engineering drawings; each line has a specific meaning you must understand to interpret a drawing correctly.
Visible line (object line) — used to show the edges of objects visible to the viewer.
Look at one of the walls of the room you are in; you can see the outline of the walls, doors, and windows. These visible outlines or edges would be shown using visible lines drawn as described in Figure 60.
Hidden line — used to show the edges of objects concealed from the viewer.
Look at the wall again. Assuming the wall is wood frame, you know there are studs or framing members inside the wall that you cannot see. These invisible outlines or edges would be shown using hidden lines drawn as described in Figure 60.
The wall may also contain other items you cannot see, such as water pipes and electrical conduit, so as you can imagine, the more hidden lines there are, the more difficult it becomes to decipher what the hidden lines mean. However, there is another way these studs and other items can be “seen.”
Figure 60 — Example of engineering drawing’s line characters and uses.
Cutting or Viewing plane — used to reveal the edges of objects concealed from the viewer after an imaginary removal of layers causing the concealment.
Imagine you “cut away” the wallboard covering and replace it with a sheet of clear plastic through which the previously concealed studs, piping, and conduit are now visible. Now those items can be drawn using visible lines, rather than hidden lines.
Sectional view — the view as seen at the cutting plane.
Section drawing — used to reveal an object or view at the point of the cutting plane.
Section drawings are commonly used to show the internal components of a complicated object.
Section lines — used to show different types of materials.
These are drawn on the visible surfaces of a section drawing. Some types of section lines you are likely to encounter as a welder will indicate a metal type.
Engineers use lines to describe the shape (form) of an object and use dimensions to provide a complete size description. Two types of dimensions are used on drawings: size and location; their purposes are self-explanatory. Refer to Figure 6-61 for examples.
Figure 61 — Examples of
using location dimension and size dimension
in an orthographic drawing.
For obvious reasons, large objects are not drawn to their true size. Instead, the engineer or draftsman reduces the size of the object “to scale.” For example, when drawing a 40-foot tower, the drawing may be prepared using a scale of 1/2"= 1'-0". In this case, the height of the tower, on paper, is 20 inches.
The scale used to prepare working drawings is always noted on the drawing. It may be a fractional scale, such as the 1/2"= 1'-0" noted here, or a graphic scale, such as the one shown in Figure 61. Both numerical and graphic scales may be shown on construction drawings.
Never measure the dimension of an object directly from the drawing. These measurements are frequently inaccurate; a change in atmospheric conditions causes drawing paper to shrink or expand, and copying processes may render them inaccurate as well. To ensure accuracy, always use the size and location dimensions shown on the drawing. If a needed dimension is not shown on the drawing, check the graphic scale for accuracy, since it will always shrink or expand at the same rate as the drawing paper.
Drawing notes are used for different purposes and are either specific or general in nature.
Refer again to Figure 61 for an example of how specific notes are used. Two notes give the inside diameters of the holes, and they are used for size dimensioning. They are specific in that, by using a leader line, each note is referred to a specific hole or set of holes.
A general note provides additional information that does not apply to any one particular part or feature of the drawing. For example, the Figure 61 drawing could contain a general note saying: “All holes shall be reamed using a tolerance of ± 1/64 inch.” General notes often appear in the corners of drawings, so always remain alert for them.
Look at the drawing shown in Figure 62. This type of drawing is called a pictorial drawing. These drawings are frequently used to show, in a three-dimensional view, how an object should appear after it is manufactured.
Pictorial drawings are used as working drawings for a simple item, such as a metal washer, but for complex objects, such as shown in Figure 62, it becomes too difficult to provide a complete description in a pictorial drawing.
Common practice for complex objects is to prepare orthographic drawings to describe the object fully. Assume you are holding the object shown in Figure 62 so you are looking directly down at the top face of the object. The view you see is the top view; a drawing of that view is called an orthographic drawing.
Figure 62 — Example of a pictorial drawing of a steel part.
Obviously, an orthographic drawing of only the top view of the object is insufficient to describe the entire object; therefore, additional orthographic drawings of one or more of the other faces of the object are necessary.
The number of orthographic views needed to describe an object fully depends upon the complexity of the object. For example, a simple metal washer can be fully described using only one orthographic view, but an extremely complex object may require as many as six views (top, front, left side, right side, back, and bottom).
Typically though, most objects, such as the steel part shown in Figure 62, can be sufficiently described using three views: top, front, and right side.
Figure 63 is a typical orthographic drawing of the object in Figure 62 showing top, front, and right-side views.
Notice the placement of the views; this is a standard practice you should be aware of when reading orthographic drawings.
By this standard practice, the top view is always placed above the front view and the right-side view is placed to the right of the front view. When additional views are needed, the left side is always drawn to the left of the front view and the bottom is drawn below the front view.
Figure 63 — Example of orthographic views of pictorial viewed steel part.
Placement of the back view is somewhat flexible, but it is usually drawn to the left of the left-side view.
When reading and understanding the different orthographic views, sometimes you will find it helpful to prepare your own pictorial sketch.
Drawings are a form of communication that saves many words of explanation. Done properly, they help you understand all the necessary information you need to fabricate and assemble an object regardless of the complexity. It is important that you, as a Steelworker, learn to read drawings and become accustomed to their meanings.
Exercise special care when handling drawings. When they are in use, keep them on a rack or in another assigned storage place. Drawings are valuable, and they may be difficult or impossible to replace if lost or damaged.
Drawings contain special symbols to specify the weld location, type of joint, and size and amount of weld metal to be deposited in the joint. The American Welding Society (AWS) has standardized them. You will see them whenever you do a welding job from a set of prints, so you need to be familiar with all the elements of a standard welding symbol, and the location and meaning of the basic weld symbols.
A standard welding symbol The reference line is the foundation. Weld symbols, dimensions, and other data are applied to it. is: reference line + arrow + tail (Figure 64).
The arrow connects the reference line to the joint or area to be welded.
The direction of the arrow has no bearing on the significance of the reference line.
The tail of the welding symbol is used only when necessary to include a process, specification, or other reference information.
Figure 64 — Standard welding symbol.
Weld symbols refer to the symbols for a specific type of weld, such as fillet, groove, butt, surfacing, plug, or slot.
The weld symbol is only part of the information required in the welding symbol.
When used to disseminate information, the term welding symbol refers to the total symbol, which includes all the weld symbols needed to specify the weld(s) required
Figure 65 — Standard weld symbols.
Figure 66 shows how a weld symbol is applied to the reference line.
Figure 66 — Example of weld symbols applied to a reference line.
Notice that the vertical leg of the weld symbol is shown drawn to the left of the slanted or curved leg of the symbol.
Regardless of whether the symbol is for a fillet, bevel, J-groove, or flare-bevel weld, the vertical leg is always drawn to the left.
Figure 67 shows the significance of the weld symbol’s position on the reference line.
Figure 67 — Example of specifying weld location.
View A — fillet weld symbol on lower side of reference line (termed the arrow side) Weld on arrow side.
View B — fillet weld symbol on upper side of reference line (termed the other side) Weld on other side.
View C — fillet weld symbols on both sides of reference line Weld on both sides.
When only one edge of a joint is to be beveled, it is necessary to show which member is to be beveled (Figure 68).
Figure 68 — Example of arrowhead indicating bevel plate.
When such a joint is specified, the arrow of the welding symbol points with a definite break toward the member to be beveled.
Other weld symbols may be added to a welding symbol as necessary to communicate all the information needed for the weld.
However, regardless of the direction of the arrow, all information applied to the reference line on a welding symbol is read from left to right. (See Figure 69.)
Figure 69 — Example of locations for specific elements of a welding symbol.
Notice in Figure 69 that some specified information has designated locations.
The size, length, pitch (center-to-center spacing), groove angle, and root opening of a weld all have designated locations. These locations are determined by the side of the reference line on which the weld symbol is placed.
Figure 70 shows how dimensions are applied to weld symbols.
Figure 70 — Example of dimensions applied to weld symbols.
Figure 71 shows the meaning of various welding dimension symbols.
Figure 71 — Example of dimensioning welds and their meanings.
Refer to Figure 71 View A:
Refer to Figure 71 View B:
Refer to Figure 71 View C:
Besides the basic weld symbols, the welding symbol may include supplementary symbols. Figure 72 shows some of the most common. Contour symbols show how the face is to be formed; finish symbols indicate the method to use to form the contour.
A finish symbol (when used) shows the method of finish, C represents chipping, M means machining, and G indicates grinding, not the degree of finish.
Figure 73 shows how contour and finish symbols are applied to a welding symbol. This symbol indicates the weld is to be ground flush. Also, notice that the symbols are placed on the same side of the reference line as the weld symbol.
Figure 72 — Supplementary symbols.
Figure 73 — Finish symbol.
Refer again to Figure 72. Another supplementary symbol shown is the weld-all-around symbol. When this symbol is placed on a welding symbol, welds are to continue all around the joint.
Yet another symbol on Figure 72 is the field weld symbol, a black flag that points toward the tail of the welding symbol. For welds that cannot be made in the shop, for size, transportation, constructability, or other reasons, this symbol directs the welder to make the weld in the field, which could be “in situ” or on site.
If additional information is unnecessary, the welding symbol will not have a tail. However, when additional information is needed to specify a certain welding process, a type of electrode, or some other type of reference necessary to direct the weld process, the tail is added and the information is placed there (Figure 74).
Figure 74 — Examples of a welding symbol tail with additional information.
When you are fabricating a metal part, there are times when more than one type of weld is needed on the same joint; for example, a joint may require both a bevel groove weld and a fillet weld.
Figure 75 shows two methods of illustrating these weld symbols, either on the same reference line or on multiple reference lines. Note that in both welding symbol examples of the same information, the bevel groove weld (closest to the arrowhead) is to be completed first, followed by the fillet weld.
Figure 75 — Examples of symbols indicating multiple welds.
Figure 76 is an example of how a welding symbol may appear on a drawing. How would you interpret it? This figure shows a steel pipe column to be welded to a baseplate.
Figure 76 — Example of a typical welding symbol in use on a project.
For additional information about welding symbols, refer to Symbols for Welding and Nondestructive Testing, ANSI/AWS A2.4-86.
|Test Your Knowledge
7. As a welder, your only obligation is to know how to read weld symbols and you need not concern yourself with drawings.
- To Table of Contents -
Mishaps of varying degrees of severity can occur in welding operations, in part because of the nature of the work with metal, heat, confined vision, and construction in general. In some instances, they result in serious injury to the welder or other personnel working in the immediate area. In most cases, mishaps occur because of carelessness, lack of knowledge, and/or the misuse of available equipment.
Precautions applying to specific equipment are pointed out in the manual covering that equipment. This section will cover topics such as protective clothing, eye protection devices, and practices applicable to the personal safety of the operator and personnel working nearby.
Proper eye protection is of the utmost importance! This strong statement applies to the welding operator, helpers, chippers, inspectors, or any other personnel who are in the proximity of the welding and cutting operations. Eye protection is necessary because of the hazards posed by stray flashes, reflected glare, flying sparks, and globules of molten metal. Devices used for eye protection include goggles and helmets.
In addition to providing eye protection, helmets also provide a shield for the entire face and neck against sparks, flying metal and ultraviolet rays.
Flash goggles (Figure 77) are worn under the welder’s helmet and by persons working around the area where welding operations are taking place. This spectacle type of goggles has side shields and may have either an adjustable or nonadjustable nose bridge.
Figure 77 — Example of flash goggles with side shields.
Eyecup or cover type of goggles (Figure 78) is for use in fuel-gas welding or cutting operations. They are contoured to fit the configuration of the face. These goggles must be fitted with a shade of filter lens that is suitable for the type of work being done.
Figure 78 — Example of eyecup goggles for fuel-gas operations.
DO NOT substitute eyecup or cover type of goggles for an arc-welding helmet.
For electric arc-welding and arc-cutting operations, you must use a helmet with a suitable filter lens (Figure 79). This helmet serves three functions: 1) as eye protection, and as protection from 2) ultraviolet rays and 3) flying metal.
One helmet has an opening, called a window, for a flip-up filter lens 2 by 4 1/4 inches in size. When flipped up, another clear or light shaded lens provides additional eye protection from chipping or grinding operations.
Another helmet has a 4 1/2- by 5 1/4-inch window. The larger window affords a wider view and is especially useful when you are working in a confined place where head and body movement is restricted.
Figure 79 — Examples of welding helmets.
When welding in locations where other welders are working, you should wear flash goggles beneath your helmet to provide protection from the flashes caused by the other welders’ arcs. In addition, if you are not using the flip-up style of helmet, the flash goggles will serve as eye protection when chipping the slag from a previous weld deposit.
Welding goggles and helmets are made from nonflammable insulating material, with an exchangeable shaded filter lens and a protective clear cover lens.
The purpose of the clear cover lens is to protect the filter lens against pitting caused by sparks and hot metal spatter. The clear lens must be placed on the outside of the filter lens. You should replace the clear lens when it impairs vision.
Filter lenses are available in a variety of shades designated by number; the lower the number, the lighter the shade; the higher the number, the darker the shade.
The filter lens shade number selected depends on the type of work and somewhat on the preference of the user. Remember, a filter lens serves two purposes.
Table 2 — Recommended Filter Lenses for Various Welding Operations
|Up to 4||Light electric spot welding or for protection from stray light from nearby welding.|
|5||Light gas cutting and welding.|
|6-7||Gas cutting, medium gas welding, and arc welding up to 30 amperes.|
|8-9||Heavy gas welding, and arc welding and cutting, 30-75 amperes.|
|10-11||Arc welding and cutting, 76-200 amperes.|
|12||Arc welding and cutting, 201-400 amperes.|
|13-14||Arc welding and cutting exceeding 400 amperes.|
Rule of thumb: when selecting the proper shade of filter lens for an electric arc welding helmet, place the lens in the helmet, look through it at an exposed bare light bulb, and see if you can distinguish its outline. If you can, use the next darker shade lens and repeat the test. When you no longer see the outline of the bulb, the lens is of the proper shade.
Remember, you should perform this rule of thumb test in the same lighting conditions as the welding operation will be performed. Welding in a shop may require a shade lighter lens than if you are going to do the same in bright daylight, perhaps on the work site. When testing for the proper lens shade to work in field operations, look at a bright reflective object.
A variety of special welder’s clothing is available to protect parts of the body.
The clothing selected varies with the size, location, and nature of the work you need to perform. During any welding or cutting operation, you should always wear flameproof gauntlets, that is, five-finger gloves for gas welding and cutting, or two-finger gloves (or mitts) for electric arc welding. Both types of gloves protect your hands from heat and metal spatter (Figure 80).
Figure 80 — Examples of welding gloves and mitts.
The two-finger gloves have an advantage over the five-finger gloves: they reduce the danger of weld spatter and sparks lodging between the fingers. They also reduce finger chafing from the inside seams, which sometimes occurs when five-finger gloves are worn for electric arc welding.
Many light-gas welding and brazing jobs require no special protective clothing other than gloves and goggles. Nevertheless, even in these taskings, it is essential you wear your work clothes properly. Sparks seem to have an affinity for and are very likely to lodge in pockets, rolled-up sleeves, and cuffs of trousers or overalls.
You should leave your sleeves rolled down and buttoned, as well as your shirt collar. Do not cuff your trousers on the outside, and eliminate any pockets from the front of overalls and aprons that do not have button-down flaps. Be sure all your clothing is free of oil and grease. Wear high-top safety shoes; low-cut shoes are a hazard. Sparks and molten metal can lodge in them, especially when you are sitting down.
Medium- and heavy-gas welding, all-electric welding, and welding in the vertical or overhead welding position require special flameproof clothing made of leather or other suitable material (Figure 81). This clothing is designed to protect you against radiated heat, splashes of hot metal, or sparks. They afford a choice of protection depending upon the specific nature of the particular welding or cutting job This clothing consists of aprons, sleeves, combination sleeves and bib, jackets, and overalls.
Figure 81 — Examples of welder’s protective clothing.
If leather protective clothing is not available, wear woolen clothing instead of cotton. Woolen clothing is not as flammable and helps protect you from the changes in temperature caused by welding. If cotton clothing is unavoidable, it should be chemically treated to reduce its flammability.
Area awareness can also be termed situational awareness. It really is a matter of staying attentive and cognizant of your surroundings. That includes remaining alert to those working around you whether you are in the shop or in the field.
Welding by its very nature is a narrowly focused task, and when the welding helmet is down you have no peripheral vision. Before you drop the hood, know what is going on in the immediate area and always have an alternate position to which you can move. If the tasking does not allow this, a welder’s helper can assist with an overall view of any changing conditions around you until the confined tasking is completed. Know your surrounding at all times.
- To Table of Contents -
Modern welding is just over 100 years old. The continuing changes in equipment and technologies have advanced from the beginnings of carbon arc to the multiple processes available today. As a professional welder, you are, or will be, the expert on metals. Learning to weld, practicing, and becoming proficient at it will serve you well when you eventually transition. Certified welders are always in demand on multitudes of projects. The key word is “certified”; that means 1) in the positions 2) with the equipment 3) with plate and pipe. Practicing for proficiency and applying your ability as often as possible will improve your skills and opportunities.
- To Table of Contents -
1. The source of heat for the forge welding process is a flow of electricity between two contacts.
2. In welding terms, RSW means _____.
3. The source of heat for electric arc welding is _____.
4. The primary advantage of using shielded metal-arc welding is that it produces high-quality welds rapidly at a low cost.
5. What is the primary purpose of the gas in gas shielded arc welding?
6. When welding two pieces of metal together, you will often need to leave a space to be filled in. What material is added during the welding phase?
7. The two types of filler metals commonly used in welding are welding rods and welding electrodes.
8. A common property of a welding rod and a welding electrode is that both are used to conduct electricity.
9. Into what categories are electrodes classified when they are divided into groups?
10. What term refers to materials that are used to dissolve or facilitate the removal of oxides and other undesirable substances formed during welding?
11. A good flux does NOT have to _____.
12. In which of the following forms are fluxes produced?
13. What are the five fundamental types of joints?
14. What type(s) of welded joint should you use when two members are at right angles to each other?
Refer to the figure below for questions 15-17.
15. What location(s) indicate(s) a corner joint?
16. What location(s) indicate(s) a tee joint?
17. What type of joint is E?
18. How large, in degrees, is the groove angle when the edges of each of two joints that are to be joined are beveled to an angle of 45 degrees?
19. Which factors must you consider to determine the bevel angle, groove angle, and root opening for a weld joint?
20. What term refers to the depth that a groove weld extends into the root of a joint?
21. What type of weld bead is made by using a side-to-side oscillation?
22. What factor in the welding process does the term “buildup sequence” refer to?
23. What type of weld has a triangular cross section?
24. What type of weld has a circular cross section made by applying filler metal through a prepunched or precut hole?
25. What type of weld is used to apply a hard wear-resistant layer of metal to surfaces or edges of worn-out parts?
26. What type of weld should you use temporarily to hold two parts in proper alignment for the final weld?
27. The junction between the face of the weld and the base is known as the _____.
28. The exposed surface on the side from which the weld is made is known as the _____.
29. The portion of the weld from the toe to the root is known as the _____.
30. Why is the term “heat-affected zone” important to a welder?
31. What term is used to describe the details of a joint that includes both geometry and required dimensions?
32. What butt joint is NOT recommended when metals are subject to fatigue or impact loads?
33. Which of these butt joints is recommended as an excellent joint for all load conditions?
34. What corner joint is used primarily for welding 12-gauge or lighter sheet metal?
35. What tee joint is used in locations where heavy loads are applied?
36. What factor determines the strength of a single-fillet lap joint?
37. All welding is done in one or more of four positions.
38. The American Welding Society (AWS) number/letter designation 1F indicates a _____.
39. What welding position should a welder use anytime conditions allow, due to the effects of gravity on welding?
40. In pipe welding there are four basic test positions that refer to the position of the pipe and not to the position of the welding.
41. What welding position(s) do you use for pipe welding when welding in the 6G position?
42. What factor causes internal stresses, distortion, and warpage when two pieces of metal are welded together?
43. When exposed to the heat buildup of welding, all metals expand in the path of least resistance.
44. You should space tack welds at least 12 inches apart and _____ to aid in controlling distortion.
45. Why is an intermittent weld (often referred to as a skip weld) used?
46. To control the forces of expansion and contraction during welding operations, you can heat the entire structure before welding.
47. What devices should you use to prevent excessive movement of metal parts during a welding operation?
48. Which of these variables must be considered when identifying the correct welding procedure?
49. When assigned a welding job, you should make a thorough examination of the drawings and specifications. In what section of the specifications should you look for welding codes?
50. What type of line is used to show the edges of an object that are visible to a viewer?
51. What type of line is used on a drawing to show the edges of concealed studs, pipes, and electrical conduit?
52. What type of line is used on a drawing to show different types of materials?
53. Which of these drawings is used to show internal components?
54. A general note is used to provide additional information that applies to one particular part or feature of a drawing.
55. The dimensions of an object should be measured (scaled) directly from the drawing.
56. What do you call a drawing that shows how an object will appear after being manufactured?
57. What type of drawing is used to show a complex object completely?
58. Which of these features make(s) up the standard welding symbols of the American Welding Society (AWS)?
59. The term “welding symbol” refers to the total symbol, which includes all the information needed to specify the weld(s) required.
60. What type of symbols is used with weld symbols to show how the face of the weld is to be formed?
61. What type of symbol is used to indicate the method to use for forming the contour of the weld?
62. What eye protection device is designed for wear under the welder’s helmet?
63. For which of the following reasons is a welding helmet worn?
64. When you are welding with a current of 300 amperes, what lens filter is best for eye protection?
65. Which of these indications can determine whether the lens is the proper shade when using a light bulb to test a filter lens?
66. What type of leather gauntlets is recommended for arc welding?
67. What items of safety gear are best suited for overhead welding?
68. Which of the following clothing materials is least likely to catch fire from welding sparks?
- To Table of Contents -
Copyright © David L.
All Rights Reserved