viii Technical Terms list the key terms to be learned in the chapter. Guided Tour Chapter 6 Math Applications for Welders After studying this chapter, you will be able to: Learning Objectives acute triangle area base caliper centimeter (cm) circle circumference diameter equilateral triangle height hypotenuse International System of Units (SI metric units) meter (m) millimeter (mm) obtuse triangle parallelogram perimeter pi Pythagorean theorem radius rectangle right angle right triangle square surface area trapezoid triangle US customary system volume Technical Terms • Measure using both the US customary system and the SI metric system. • Convert lengths from US customary units to SI metric units and from SI metric units to US customary units. • Calculate the perimeter of common shapes. • Calculate the area of common shapes. • Calculate the volume of common shapes. • Calculate the perimeter and area of a circle and the volume of a cylinder. • Convert welding values from US customary units to SI metric units and from SI metric units to US customary units. Copyright Goodheart-Willcox Co., Inc. 75 Click on the activity icon or visit www.g-wlearning.com/welding/6938 to access online vocabulary activities using key terms from the chapter. Learning Objectives clearly identify the knowledge and skills to be obtained when the chapter is completed. cleaned with steam or degreasers. Porous metals such as cast iron are heated to 400°F–600°F (200°C–315°C). Heating to these temperatures vaporizes grease and oil in the porous areas. Preheating Some metals must be preheated prior to surfacing. Preheating to a specifi c temperature prepares the metal for surfacing. It ensures a complete bond between the base metal and surfacing material. Preheating recommendations for several metals are listed below. • Cast iron: 500°F–700°F (260°C–370°C). • Low and mild carbon steel: preheating is not required except for heavy sections. • Manganese steel (steel containing 12–14% manganese): 200°F (93°C). Do not heat above 500°F (260°C). Caution Before preheating an unknown base metal, be certain that it is not manganese steel. Preheating manganese steel affects the corrosion resistance and mechanical properties of the metal. Surfacing with Shielded Metal Arc Direct current electrode positive (DCEP) polarity is generally used when surfacing with a shielded metal arc. The equipment used for surfacing is the same as that used for shielded metal arc welding. However, different electrodes are used. Surfacing materials may be applied over areas of a part or over the entire surface of a part. They can be applied as stringer or weave beads. Deep penetration of the surface is not required or desired. Figure 14-1 shows an example of completely covering a small area of a part with hardfacing materials. Figure 14-2 shows examples of patterns of well-spaced beads covering larger areas of parts. After the part has been cleaned and preheated (if necessary), the process of surfacing with a surfacing electrode is the same as welding with a SMAW electrode. An arc is struck in the same manner as in SMAW. However, a long arc is maintained for surfacing. The long arc is needed to spread the heat over a larger area. Penetration is reduced by spreading the heat out. Higher amperage may be required for a surfacing electrode compared to a welding electrode for a given electrode diameter. A surfacing electrode is held at approximately a 0° work angle (90° to the base metal). A drag travel angle of approximately 45° is used. An oscillating (forward and back) motion is recommended for stringer beads. See Figure 14-10. This oscillation will create more build up as seen in Figure 14-2. A weaving or circular motion is used to create wider weld beads. See Figure 14-11. A weave or circular bead should not be wider than six times Goodheart-Willcox Publisher Figure 14-11. A circular motion suggested for beads that are from 3/4″–1 1/44″ (20 mm–30 mm) wide. Goodheart-Willcox Publisher Figure 14-10. Use a forward and backward oscillating motion when applying material with a SMAW electrode. Oscillatingg motionn Chapter 14 Surfacing 203 Copyright Goodheart-Willcox Co., Inc. g d not b e wi d er th an six times Goodheart- Willcox Pu blisher r motion iis s sugge sted for beads ″ (20 mm–30 mm) wide. ″ G oodheart-Willcox Publisher r ward and backward oscillatin g hhardfacingg ardfacin material with a SMAW Oscillat in ing ng motion on the safety cap. The other hand is used to roll the cylinder in the direction of travel. Cylinders fi lled with gases under pressure must be stored in an upright position. They should be fastened to a wall, column, or hand truck with chains or steel straps. Fusible Plugs Fusible plugs prevent acetylene cylinders from exploding in a fi re. A fusible plug is a steel plug fi lled with a metal that melts at about 212°F (100°C). The plug is externally threaded and is screwed into an opening at the top or bottom of the acetylene cylinder, Figure 24-6. In case of a fi re, the center of the fusible plug melts. This allows the acetylene to escape slowly. Although the gas escapes and burns, the tank will not explode. Acetylene Cylinder Valve An acetylene cylinder valve controls the fl ow of gas from the cylinder. A handwheel or a cylinder valve wrench is used to open and close the valve. See Figure 24-7. An acetylene cylinder valve is usually opened only 1/4–1/2 turn for suffi cient gas fl ow. This allows it to be closed quickly in case of an emergency. Warning The handwheel or valve wrench should always remain on the cylinder valve when the cylinder is in use. Acetylene Safety Precautions Acetylene can be very explosive if not handled safely. Always refer to the manufacturer’s instructions when handling or using equipment. • Acetylene gas is unstable at pressures above 15 psig (103 kPa). • Avoid contact between acetylene and copper, silver, or mercury. Also avoid contact with the salts, compounds, and high concentrations of these metals. Under certain conditions, acetylene and these metals can form explosive compounds. • Fusible plugs melt at approximately 212°F (100°C). • Concentrations of acetylene between 2.5% and 80% by volume in air ignite easily and may cause an explosion. • Acetylene has a garlic-like odor. Acetylene may displace air in a poorly ventilated space. Adequate ventilation is essential. An area must contain at least 18% oxygen to prevent dizziness, unconsciousness, or possibly death. • Smoking, open fl ames, unapproved electrical equipment, or other ignition sources are not permitted in acetylene storage areas. • Do not place cylinders beneath overhead welding or cutting operations. Hot slag (metal) may fall on them and melt a fusible plug. • Keep the handwheel or valve wrench on the cylinder valve while the cylinder is in use. Goodheart-Willcox Publisher Figure 24-7. A—Handwheel used to regulate the flow of acetylene. B—An acetylene cylinder with the acetylene valve wrench in place. Goodheart-Willcox Publisher Figure 24-6. Fusible plug on an acetylene cylinder. The valve is depressed and has internal threads. This type of cylinder is known as a POL (Prestolite) cylinder. Acetylene cylinder valve with square shaft Fusible plug A B Chapter 24 Oxyfuel Gas Cutting and Welding: Equipment and Supplies 355 Copyright Goodheart-Willcox Co., Inc. Safety Concerns are presented in bold red type throughout the book to make you aware of things that could potentially endanger the safety of you or people around you. Cautions alert you to practices that could potentially damage equipment or instruments. G-W Learning Companion Website Activity Icon identifies related content available on the G-W Learning companion website. Warnings alert you to potentially dangerous materials and practices.