- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS (CLF2250) Unit Title: OXYACETYLENE WELDING ___________________________________________________________________________ (CLF2253) Topic: OXYACETYLENE FUSION WELDING Time Year(s) 5 hours 1 / 2 / 3 / 4 ___________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the students will be able to: Learning Outcome #: (F-5) - Run a bead with the oxyacetylene equipment with and without filler rod. Special Material and Equipment: Oxygen and acetylene cylinders, regulators and hoses, torch, tips, open-end wrench, striker, protective clothing, gloves, goggles. References: Cooper, Elmer L. (1987). AGRICULTURAL MECHANICS: FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar Publishers. 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 Fusion Welding A. Oxyacetylene Fusion Welding Definition and Applications 1. Definition a. Fusion welding is the joining of metal pieces by melting them together. b. This is accomplished by heating the adjoining edges of metal to their melting point, allowing them to flow together, and then cool to harden as one piece. 1) The combustion of the oxygen-acetylene gas mixture provides the heat for fusion. 2) The flame from the combustion shields the weld from atmospheric contamination. 3) A filler rod may be used to provide additional metal to help the two metal pieces join. 4) The basic skill required in fusion welding is to form, maintain, and move a puddle of molten base metal along the weld, keeping it uniform in both size and shape. 2. Applications a. Fusion welding is used extensively for joining steel. b. Oxyacetylene fusion welding is usually applied only to thin steel. B. Oxyacetylene Welding Terminology 1. Forehand Welding a. The filler rod precedes the torch in the direction of the weld. b. The filler rod and torch tip are both manipulated in opposite rotating directions. c. This is the best technique for welding metal up to 1/8 inch thick. 2. Backhand Welding a. The torch tip precedes the filler rod in the direction of the weld. b. Little or no manipulation of the torch tip and filler rod is required. c. This is the best technique for welding metal over 1/8 inch thick. 3. Welding Angles a. Work angle is the angle of the torch or filler rod perpendicular to the direction of the welding bead. b. Lead angle is the angle of the torch or filler rod parallel to the direction of the welding bead. 4. Base Metal (the metal to be welded) 5. Filler Rod a. It is a rod or wire of filler metal of the same composition as the base metal. b. A mild steel rod is used to weld mild steel; an aluminum rod is used to weld aluminum, etc. c. The diameter of the filler rod should equal the thickness of the base metal or bead. 6. Bead is the appearance of the finished weld, normally viewed as neat ripples formed by the metal while it was in its semiliquid state. 7. Tack Weld a. Tack welds are small, spaced welds along the weld joint made before running the continuous bead along the same joint. b. Tack welds prevent expansion or contraction of the weld joint during continuous welding. C. Oxyacetylene Fusion Welding Procedures 1. Running a bead without filler rod (pushing a puddle) a. Prepare a piece of mild steel 1/8 inch thick. b. Use an 0 or 00 welding tip. c. Adjust the working pressures to about 3 psi for acetylene and 10 psi for oxygen. d. Wear appropriate protective gear, then light and adjust the torch to a neutral flame. e. Hold the torch at a 90 degree work angle and a 30 degree to 45 degree lead angle, with the inner cone of the flame 1/16 to 1/8 inch above the base metal. f. Hold that position over a spot just inside the right edge of the base metal until a molten puddle is established. g. Move the torch in a series of arcs or circles to make the puddle circular in shape and about 1/4 inch in diameter. h. Advance the torch from right to left across the base metal at a speed that will maintain a uniform puddle size and shape. 1) If advanced too rapidly, the puddle will become too small and may be lost completely. 2) If advanced too slowly, the puddle will become too large and may burn through the base metal. 2. Running a Bead with a Filler Rod a. The steps are the same as above until the molten puddle is formed. b. Once the puddle is formed, dip the end of the 1/16 inch diameter steel filler rod into the puddle and begin moving the torch in a series of vertical ovals, while at the same time moving the rod up and down, in and out of the puddle. 1) As the flame rises, the rod lowers, and vice versa. 2) Do not allow molten metal to drip from the end of the filler rod, but add the filler metal directly by dipping the end of the rod into the puddle. c. As the torch is advanced from right to left, maintain uniform bead width and height with a smooth ripple effect. 1) If advanced too rapidly, the bead will become narrow and have the appearance of having been deposited on top of the base metal. 2) If advanced too slowly, the bead will become too large and may burn through the base metal. D. Oxyacetylene Welding Problems 1. Backfire (popping noise) a. Backfire is a momentary burning back of the flame into the tip ending with a loud pop (explosion at the tip). c. The causes can include the following: 1) Insufficient gas velocity (open torch valves more). 2) Overheated tip (hold tip farther away from the work or change the lead angle). 3) Inadvertently moving the torch tip into the molten puddle (clean out the tip). 4) Sparks flying into the tip. 5) Improper seals or grommets within the torch (examine and replace). 2. Flashback (popping with shrill squealing or hissing) a. Flashback is an explosion occurring at the tip accompanied by gases burning back into the hoses and regulator. b. The symptoms are as follows: 1) The flame goes out with a pop. 2) A loud squealing or hissing noise occurs. 3) Black smoke and sparks emerge from the tip. c. The action required to remedy the problem is as follows: 1) Quickly close the torch valves and shut down the regulators and cylinder valves; allow the apparatus to cool. 2) Do not relight until the cause has been found and remedied d. Possible causes could by any of the following: 1) Clogged tip 2) Improper oxygen-acetylene gas mixture ratio 3) Loose connections 4) Kinked hose _________________________________________________________ ACTIVITY: Make a bead with and without a filler rod. _________________________________________________________ 6/28/91 OLR/sg #%&C