- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS (CLF2250) Unit Title: OXYACETYLENE WELDING ___________________________________________________________________________ (CLF2257) Topic: OXYACETYLENE HEATING OF METAL Time Year(s) 3 Hours 1 / 2 / 3 / 4 ___________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the students will be able to: Learning Outcome #: (F-15) - Observe phase change of metals when they are subjected to heat. Special Material and Equipment: References: Cooper, Elmer L. (1987). AGRICULTURAL MECHANICS: FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar Publishers. Davies, A. C. (1972). THE SCIENCE AND PRACTICE OF WELDING. London: Cambridge University Press. Phipps, Lloyd J., & Reynolds, Carl L. (1990). MECHANICS IN AGRICULTURE (4th ed.). Danville, IL: Interstate Publishers. Resources: Deere & Company. (1987). WELDING (6th ed.) (Fundamentals of Service (FOS) Series). Available from: John Deere Technical Services, Dept. F, John Deere Road, Moline, IL 61265 (Available in Spanish) Evaluation: Quiz by instructor. TOPIC PRESENTATION: Oxyacetylene Heating of Metal A. Applications for Oxyacetylene Heating of Metal 1. Expansion and Contraction: a. Metal expands when it is heated and contracts when it is cooled. b. Oxyacetylene equipment with a rosebud tip and neutral flame can be used to heat tight-fitting metal parts (such as the ring gear on a flywheel) so they expand and loosen enough to be more easily separated. 2. Bending and Shaping a. To bend, straighten, or shape metal with an oxyacetylene torch, attach a rosebud tip and adjust a neutral flame. b. Keeping the inner cone back away from the surface, heat the metal evenly by moving the flame around. c. When the metal begins to glow bright red, bend or form the piece of metal with a hammer, vise, or press. 3. Flame Hardening a. Flame hardening is a process whereby mild steel is heated to a cherry red glow and then quenched in water or oil to harden it. b. Use a rosebud tip and a neutral flame. 4. Tempering a. Tempering is the process used to reduce the hardness and brittleness of steel and to relieve its internal stresses. b. This is accomplished by reheating quenched steel to a glowing cherry red and cooling it when the desired oxide color on the polished surface is obtained (blue being the most common tempering temperature). 5. Annealing a. Annealing is the process used to soften steel and remove internal strains. b. This is accomplished by heating the steel to a uniform glowing dark-red color and then allowing it to cool slowly out of contact with the air to prevent oxidation. B. Temperature and Oxide Colors of Heated Iron and Steel 1. Temperature-Color Relationship a. Iron and steel emit visible light as they are heated. b. The color of the light emitted is related to the metal temperature and can serve as a rough guide to temperatures for forging and heat treating. c. Quenched steel that has been polished and reheated for tempering will produce an oxide film on the polished surface. d. The color of the oxide film indicates the temperature to which the steel has been reheated and can serve as a guide to the degree of tempering accomplished. 2. Oxide colors for tempering a. 430 degrees Fahrenheit = Yellow b. 470 degrees Fahrenheit = Straw c. 500 degrees Fahrenheit = Brown d. 540 degrees Fahrenheit = Purple e. 570 degrees Fahrenheit = Blue 3. Light colors for forging and heat treating a. 870 degrees Fahrenheit = Black red b. 975 degrees Fahrenheit = Dark red c. 1450 degrees Fahrenheit = Cherry red d. 2000 degrees Fahrenheit = Yellow e. 2300 degrees Fahrenheit = White f. 2550 degrees Fahrenheit = Sparks flying C. Hot Metal Working with Oxyacetylene Equipment 1. Project: offset screwdriver 2. Principles applied: forging, hot bending, and heat treating 3. Material and tools required: a. Nine-inch length of heat-treatable steel round stock b. Oxyacetylene torch with a rosebud heating tip attached c. Pliers, hammer, anvil, vise, grinding wheel, wire wheel, oil-quench bath, and water-quench bath 4. Procedure a. Heat the end of the material to a cherry red with the torch. b. Forge the material into a screwdriver shape, hammering near the edge of the anvil (not on the vise). c. Heat the end of the material to a cherry red again and bend the offset near the tip with the vise, then cool in water. d. Repeat steps a through c on the other end. (Make the blades at 90 degrees to each other with bends on the same plane.) e. Reheat one end to a cherry red; hold it at that temperature for about 30 seconds, then quench it in oil by shoving the whole end quickly under the oil to avoid igniting the fumes. f. Polish the oil-quenched end, then grind the tip square and flat. g. Temper the polished end by carefully adding heat to the material above the tip end and allowing the heat to slowly flow to the tip. h. Watch the oxide colors form on polished surface being heated. When the straw/gold color reaches the tip, quickly quench the end in water. i. If the straw color passes the tip, repeat steps e through h. j. Repeat steps e through i on the other end. _________________________________________________________ ACTIVITY: 1. Complete the offset-screwdriver project. _________________________________________________________ 7/1/91 OLR/tf #%&C