366 Modern Welding Copyright Goodheart-Willcox Co., Inc. 4. After the acetylene is regulated, turn on the oxygen torch valve slowly, as shown in the following figure. Adjust the oxygen torch valve until a neutral flame is obtained. Goodheart-Willcox Publisher 5. Some fine adjustments of both the acetylene and oxygen torch valves may be required to obtain the desired neutral flame. See Figure 13-2. Refer to Figure 13-3 for a detailed view of the flames. The correct quantities of gases for smaller tip sizes can also be detected by listening to the torch flame. When the gas mixture is correctly adjusted, the flame should emit a soft purr, not a sharp irritating hiss. Note If the torch burns with an irregular contour (feather) to the cone, the flame is called a carburizing flame. There is an excess of acetylene. If the inner cone has a very sharp point and if it hisses excessively, it usually means that too much oxygen is being used. This is called an oxidizing flame. See Figure 13-3. Procedure Lighting and Adjusting a Welding Torch Flame 1. Open the acetylene torch valve approximately 1/16 turn. Goodheart-Willcox Publisher 2. Light the acetylene at the torch tip, using a spark lighter. Goodheart-Willcox Publisher 3. Open the acetylene torch valve until the flame becomes turbulent (rough) about 3/4″–1″ (19–25 mm) from the end of the tip, as shown in the following figure. With the correct amount of acetylene, the flame no longer smokes or releases soot. Look at Figure 13-11 and compare the flames. Goodheart-Willcox Publisher 13.2.8 Shutting Down an Oxyacetylene Welding Outfit The flame must be turned off whenever the oxy- acetylene torch is not in your hand. Turn the flame off by closing the acetylene torch valve and then the oxygen torch valve. The process for shutting down a cutting outfit is nearly the same as shut- ting down a welding outfit. The process is com- pletely illustrated with photographs in Chapter 15, Oxyfuel Gas Cutting. Copyright Goodheart-Willcox Co., Inc. 716 Modern Welding Summary • Surfacing is the application by welding, brazing, or thermal spraying of a layer, or layers, of material to a surface. • A surfacing material is applied to resist wear, improve performance, improve physical strength, increase dimensional size, protect the base material from chemical corrosion, or improve appearance. • Surfacing variations include the following: • Cladding: application of surfacing materials to improve corrosion- or heat-resistance. • Hardfacing: application of surfacing material to reduce wear. • Buttering: application of metal on one or more surfaces to provide metallurgically compatible weld metal for the subsequent application of a dissimilar metal. • Buildup: addition of surfacing material to achieve required dimensions. • In thermal spraying, fi nely divided metallic or nonmetallic surfacing materials are deposited in a molten or semi-molten condition on a substrate. • Thermal spraying processes used for surfacing are fl ame spraying (FLSP), arc spraying (ASP), detonation fl ame spraying (DFSP), and plasma spraying (PSP). • A material used to prevent a wear problem must be chosen for its ability to prevent wear from one or more of the following: abrasive wear, surface fatigue, corrosive wear, and galling or adhesion. • A large variety of hardfacing materials are available for SMAW, FCAW, and SAW processes. GTAW and oxyfuel can also be used. • Spalling (breaking off of surfacing material from the base metal or a previous hardfacing layer) results from poor surfacing procedures. Material to be surfaced must be properly cleaned and previous hardfacing must be removed. • Thermal spraying can be used to deposit almost all metals and many alloys to other metal surfaces. • The pattern used to deposit hardfacing can be adjusted to match the specifi c application. • Not all metals must be preheated before surfacing materials can be applied, but preheating is advisable with alloy steels. • Both thermal spraying and hardfacing (using a solid rod), can be done with the oxyfuel gas process. • Flame spraying involves melting surfacing or cladding materials in an oxyfuel gas fl ame. The molten materials are transferred to the surface of the part. The surfacing or coating material may be in the form of wire, rod, or powder. • The methods used to spray material in surfacing processes include electric arc spraying, detonation fl ame spraying, and plasma arc spraying. • Completed thermal sprayed surfaces are generally inspected visually for defects and oil or other contaminants. Visible defects must be removed and the surfacing material reapplied. • Safety precautions specifi ed for gas welding, arc welding, welding on containers, and similar applications also apply to metal surfacing. Earplugs or earmuffs should be worn for arc spraying, detonation spraying, and plasma arc spraying processes. Technical Terms abrasive wear bond coat buildup buttering chemical corrosion cladding detonation fl ame spraying detonation fl ame spraying gun electric arc spray method fl ame spraying hardfacing hardness high velocity oxyfuel (HVOF) spraying impact wear spalling surfacing thermal spraying wear Review Questions Answer the following questions using the information provided in this chapter. Know and Understand 1. Which of the following statements about surfacing is false? A. Surfacing may be done with welding, brazing, or thermal spraying. B. Surfacing adds a layer or layers to a material. C. Surfacing involves making a joint. D. Surfacing is done to obtain desired properties or dimensions. Copyright Goodheart-Willcox Co., Inc. Chapter 27 Metal Surfacing 717 2. The application of surfacing materials to improve corrosion- or heat-resistance is called _____. A. buildup B. cladding C. hardfacing D. buttering 3. A form of surfacing in which surfacing material is deposited to reduce wear is called _____. A. spalling B. buildup C. buttering D. hardfacing 4. True or False? The surface materials used in thermal spraying may be metallic or nonmetallic. 5. A rubbing or scraping action describes _____. A. impact wear B. surface fatigue C. corrosive wear D. abrasive wear 6. True or False? Either DCEP polarity or AC can be used for hardfacing. 7. Surfacing with GTAW is done with _____. A. DCEN polarity and a ceriated electrode B. DCEP polarity and a lanthanated electrode C. DCEN polarity and a thoriated electrode D. DCEP or AC polarity and a pure tungsten electrode 8. The thermal spraying process that propels the surfacing material to the surface with the highest velocity is _____. A. plasma spraying B. electric arc spraying C. detonation fl ame spraying D. fl ame spraying 9. True or False? A transferred arc is used for plasma spraying. 10. True or False? A bond coat is the fi nal layer of surfacing to be applied. Apply and Analyze 1. What is thermal spraying? 2. What factors should be considered when evaluating whether a part should be surfaced? 3. What are two ways of helping to prevent spalling? 4. Why is a basket weave pattern used to apply hardfacing alloys to many parts used for digging? 5. In what two ways can powder be delivered to the fl ame during the fl ame spraying process? 6. For fl ame spraying with powdered surfacing materials, why should oxygen not be used as the carrier gas? 7. In fl ame spraying, why is the spraying rate critical with powders? 8. Explain how porous and nonporous surfaces should be cleaned before surfacing material is applied. 9. What types of defects may be found on thermal sprayed surfaces? 10. Hearing protection must be worn during which three thermal spraying processes? Critical Thinking 1. Some metals must be preheated before they are surfaced others do not require preheating (as discussed in section 27.2.1). Why do you think some metals must be preheated in order to form a complete bond, while others bond completely without preheating? 2. Surfacing is defi ned by the American Welding Society as “the application by welding, brazing, or thermal spraying of a layer, or layers, of material to a surface to obtain desired properties or dimensions, as opposed to making a joint.” The AWS defi nition of surfacing is different from that used in common language outside the fi eld of welding. Think of at least two other words defi ned by the AWS that have a different meaning in a professional we lding setting than in common language. Experiment 1. Preheating the base metal is important in many surfacing processes. A specifi c preheat temperature is required for different base metals. Use temperature-indicating crayons to quickly determine the temperature of a base metal. Raise the temperature of various thicknesses of steel plate to approximately 2200°F (1200°C). Then, preheat various thicknesses of cast iron to 500°F–700°F (260°C–370°C). Using temperature- indicating crayons, note the different lengths of time required to successfully preheat different materials and various thicknesses of base material. Notes call attention to useful information. Tables present data such as welding variables and other useful information in an easy-to-read format. Summaries feature provides an additional review tool for you and reinforces key learning objectives. Review Questions allow you to demonstrate knowledge, identifi cation, and comprehension of chapter material. 220 Modern Welding Copyright Goodheart-Willcox Co., Inc. An increased electrode extension distance preheats the electrode wire. If the electrode extension is not suffi cient, the electrode wire will not be preheated enough. Figure 8-44 lists proper electrode extensions for GMAW and FCAW processes. A long extension may cause too much fi ller metal to be deposited with low heating by the arc. This may cause shallow penetration and a high-crowned weld bead shape. In spray transfer, if the extension is too short, proper preheating of the welding wire does not occur. In FCAW–S, the proper electrode extension is important. If the welding wire is not properly pre- heated, the fl ux will not produce the shielding gas necessary to protect the welding area. 8.7 Welding Techniques Most arc welding processes require the welder to con- trol the arc length, welding speed, gun angle, and gun motions to obtain a good weld. In GMAW and FCAW, the arc length remains constant and is determined by the arc voltage set on the welding machine. While gas metal or fl ux cored arc welding, the welder must watch and control the distance from the nozzle or con- tact tip to the work. Refer to Figure 8-43. By control- ling the nozzle-to-work distance, the welder controls the electrode extension distance. The welding speed affects the bead width and pen- etration. A slower weld speed produces a wider bead and deeper penetration. Gun angle also affects the bead width and penetration. The welder can use weave motions and change the gun angle as needed to obtain the desired weld pool. The terms forehand, backhand, and perpendicular are used to describe the angles at which the gun can be held in relation to the weld bead. In forehand welding, the tip of the electrode points in the direction of travel. This is often referred to as a push angle or push travel angle. In backhand welding, the electrode tip points away from the direction of travel. This is often called a drag travel angle. Perpen- dicular welding is done with the electrode at a 90° angle to the base metal. This is a travel angle of zero. Figure 8-45 shows the effects of these various angles. GMAW and FCAW Electrode Extensions Process Method Electrode extension GMAW Short circuiting 1/4″–1/2″ (6 mm–13 mm) GMAW Spray transfer 1/2″–1″ (13 mm–25 mm) FCAW Gas-shielding 3/4″–1 1/2″ (19 mm–38 mm) FCAW Self-shielding 3/4″–3 3/4″ (19 mm–95 mm) Goodheart-Willcox Publisher Figure 8-44. Recommended electrode extension distances for GMAW and FCAW. Forehand Perpendicular Backhand 25° drag travel angle 25° push travel angle Direction of travel Direction of travel Direction of travel Goodheart-Willcox Publisher Figure 8-45. Effects of the welding gun angle on the bead. Notice that the backhand angle gives the deepest penetration. Procedures provide clear instructions for hands-on service activities. You can refer back to these procedures easily. Many procedures are illustrated to aid in comprehension. Illustrations and photos clearly and simply communicate the specifi c topic. Technical Terms list the key terms to be learned in the chapter. Experiments provide opportunities to apply knowledge gained from the chapter to further explore the world of welding.