- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURE MECHANICS (CLF2300) Unit Title: ARC WELDING ___________________________________________________________________________ (CLF2301) Topic: ARC WELDING Time Years EQUIPMENT & SAFETY 2 Hours 1 / 2 / 3 / 4 ___________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome: #: (G-l) - Pass a safety test and demonstrate proper use of arc welding equipment. (G-10) - Change lens and head gear on a helmet. Special Material and Equipment: Arc welding helmet, leather gloves, aprons, coveralls, strikers, safety test, slag hammer, safety goggles References: Burke, Stanley R., & Wakeman, T. J. (1990). MODERN AGRICULTURAL MECHANICS (2nd ed.). Danville, IL: Interstate Publishers. 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) Giachino, Joseph W., & Weeks, William (1976). WELDING SKILLS AND PRACTICES (5th ed.). Available from: American Technical Society, Chicago, IL 60637 Hobart Brothers Company. (1978). TECHNICAL GUIDE FOR SHIELDED METAL ARC WELDING. Available from: Hobart Brothers Company, Troy, OH 45373 Evaluation: A passing score on the safety test. Unit exam or quiz by the instructor. TOPIC PRESENTATION: ARC WELDING EQUIPMENT AND SAFETY A. Introduction to Arc Welding 1. An arc welding machine joins two metals together by generating an electric arc between a coated metal electrode and a base metal. The heat of the electric arc melts the metal which mixes with the molten deposits of the coated electrode. The coating of the electrode produces a gas which shields the weld from the atmosphere and helps to maintain the weld shape. This coating is later removed in the form of slag. The slag coating over the weld insulates the hot weld from contaminants in the air during cooling. B. Equipment Used in Arc Welding 1. Power Supply a. The power supply of the arc welding apparatus must maintain a relatively constant current with only a slight change in voltage. b. Varying voltage and current will result in an uneven arc that creates splatters and uneven welds. c. There are three main types of power supplies. 1) Generators a) Generator powered arc welding machines run on direct current. b) These welding machines are commonly used in industry and are noisy, expensive to purchase, and costly to operate. 2) Transformers a) These machines are generally the cheapest to purchase and run on an alternating current. 3) Rectifiers a) The rectifier is a more versatile arc welding power supply that can be run on either direct or alternating current. 2. Ground Clamp a. The ground clamp completes the full electrical circuit so that enough heat will be available for the welding job. b. The ground clamp must be securely fastened to the metal being welded or to an adjoining workbench or piece of metal. 3. Electrode Holder (or Stinger) a. The stinger receives the amperage and directs it through the electrode to form the arc. b. The electrode holder should be well insulated, have a strong spring to firmly grasp the electrode, and a release lever to exchange the electrodes easily. 4. Cables a. The cables allow both the ground clamp and the stinger to be mobile. b. The cables should also be well insulated and protected from the heat during welding. 5. Electrode a. The electrode consists of an internal metal core and an outer coating called flux which shields the weld. The core melts into the molten base metal to produce the metal bond. b. There are several types and sizes of electrodes. Each will be discussed in detail in the next lesson. C. Protective clothing must be worn at all times when welding. The heat created during arc welding creates flying molten sparks and ultraviolet and infrared rays that can burn the skin. a. Leather Gloves 1) Gloves protect the hands from burns during welding. 2) The gloves should be made of thick leather and have long cuffs to protect the wrist and prevent sparks from falling into them. b. Leather or Cotton Sleeves 1) A NONFLAMMABLE material should be worn on the arms to protect from burns due to sparks and intense heat. c. Body Protection 1) Either a leather apron or coveralls or workshirt made of a flame retardant material will protect the body during arc welding. 2) All protective clothing should fit properly and be free of openings or rips into which a spark might enter or the intense heat might penetrate. d. Footwear. 1) Leather boots should be worn while arc welding. 2) Never wear open-toed shoes while working with hot metal or a welding apparatus. 6. Arc Welding Helmets and Shields - The brilliant light given off by the electric arc produces invisible ultraviolet and infrared rays which can severely burn the eyes and skin. NEVER LOOK AT THE ARC WITH THE NAKED EYE. Helmets and shields are equipped with special filtered lenses that reduce the intensity of the light and prevent the ultraviolet and infrared rays from reaching the eyes. a. The welding helmet is designed specifically for the purpose of arc welding. 1) The welding helmet fits on the head using a plastic adjustable headband. 2) The helmet leaves both hands free for working and positioning materials. 3) Many helmets have clear lenses under the filtered lenses that can be used when chipping slag. b. The hand shield is used for observing. 1) It is NOT advisable to use the hand shield when welding since one hand must be used to hold the shield in place. c. The protective lenses come in different shades depending on the type of welding to be done. Different types of welding use different amounts of voltage and current which determine the intensity of the light and the amount of ultraviolet and infrared rays produced. Spot welding requires the fewest amperes and thus requires the least amount of shading in the lens. Arc welding machines require from less than 30 to over 400 amperes. Lens shades range from number 5 (which provides the least amount of protection) to shade 14 (which provides the most protection). 1) Shade 5 is used for light spot welding. 2) Shades 6 and 7 are suitable for welding with up to 30 amperes. 3) Shade 8 is for welding with 30-75 amperes. 4) Shade 10 can be used when welding with 75-200 amperes. 5) Shade 12 is used when welding with 200-400 amperes. 6) Shade 14 is required when welding with over 400 amperes. d. Cover glasses are clear lenses that are used to stop flying slag or metal, thus protecting the filter lenses. There are 3 different types of cover glass currently available. 1) Clear, unbreakable plastic is the cheapest and lasts the longest. 2) Chemically treated glass is used to reduce pitting but it can be expensive. 3) Plain glass is very susceptible to breaking, pitting, and splatter sticks and is NOT recommended. e. Filter lenses must be changed if a crack or chip occurs in order to prevent ultraviolet and infrared rays from reaching the eyes. The shades of the lenses must also be changed. If the shade is too dark, the worker will be unable to see the work that is being performed. If the shade is too light, proper eye protection is not achieved. Many welding helmets have interchangeable lenses. The lens changing procedure is as follows: 1) Remove the lift-up mechanism on the helmet or the lens frame lock. 2) Slide the old filter lens out and insert the new one. 3) Reinsert the lift-up mechanism or the lens frame lock. 4) Put the helmet on and search for light leaks. If leaks are present, the lens must be readjusted. 7. Additional Welding Equipment a. Goggles - Goggles must be worn when chipping slag if a shell lens is not provided in the helmet. NEVER CHIP SLAG WITHOUT PROTECTIVE EYEWEAR. b. Tongs - The heat of the arc will heat all of the metal being welded. Always use tongs to carry or maneuver the metal stock. c. Slag Hammer or Chipping Hammer - The slag hammer is used to remove slag from the weld for proper cooling. d. Wire Brush - If a second pass is to be made with the arc, the wire brush must be used to remove all slag fragments from the welding area. If not removed, the weld will not be solid and residual stresses will result. C. Safety in Arc Welding SAFETY IN ARC WELDING* When arc welding, observe the following general safety practices. 1. Wear gloves and eye and face protection. The welder and all observers must wear welding helmets with a No. 10 or 12 filter lens. A welding cap or helmet with a hard hat is also recommended for head protection. When chipping slag or cleaning welds, wear a clear face shield or flip-up liftplate on the helmet. 2. Avoid electrical shock. Make certain that the electrode holder and all electrical connections and cables are properly insulated. Check to see that the welder is properly grounded. Do not dip the electrode holder in water to cool it because this practice may result in electrical shock. 3. Protect others. For small and practice welding jobs, work in a partitioned area to protect others from harmful rays. When prepared to strike the arc, inform all bystanders to cover their eyes. 4. Never weld in a damp area. Stand on a dry board or rubber mat if the floor or ground is damp or wet. 5. Never wear synthetic fiber clothing. Synthetic fibers are highly flammable. Wearing clothing made from wool or cotton is more satisfactory for welding because of their relatively high flash points. 6. Protect welding cables. Keep the cables from coming in contact with hot metal and sharp edges. Do not drive over cables. When welding, avoid wrapping electrode cables around your body. 7. Secure work. Use a welding table with a positioner to hold welds securely in place. Clamps and vises can be used to hold odd-shaped work or field work. Securing work will also prevent injury from accidental dropping of metal on your feet or body. 8. Dispose of electrode stubs properly. Keep a container in the work area in which to deposit electrode stubs. This prevents burns to shoes or falls due to stubs rolling underfoot. 9. Prevent burns. Never allow the hot electrode or electrode holder to touch bare skin. Avoid letting the electrode touch a grounded cable. Remove hot metal from the work area when you are finished welding to prevent burns to others. 10. Do not let the electrode stick. If the electrode sticks, cut off the switch, allow the electrode to cool, and then break it loose with your gloved hand. 11. Use both hands. To reduce fatigue, use both hands for welding. 12. Handle hot metal with pliers or tongs. Submerge hot metal completely in water to prevent steam burns. 13. Weld in a well-ventilated area. The fumes from lead, zinc, cadmium, and beryllium are toxic and may cause sickness or death. 14. Do not carry matches or lighters, and do not allow bystanders to smoke. Before welding, make sure the welding area is free of other flammables (gas, grease, etc.). _____________________ * Reprinted by permission of Interstate Publishers, Inc., from MODERN AGRICULTURAL MECHANICS, 2nd ed., by Stanley R. Burke and T. J. Wakeman. Copyright 1992 by Interstate Publishers, Inc. _____________________________________________________________ ACTIVITY: 1. Practice changing lenses and head gear in arc welding helmets. 2. Practice identifying and handling arc welding equipment, making sure that all safety procedures are followed and that suitable clothing is being worn. _____________________________________________________________ 7/23/91 DF/RRE/tf #%&C