- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURE MECHANICS (CLF2300) Unit Title: ARC WELDING ______________________________________________________________________________ (CLF2303) Topic: AWS CLASSIFICATION SYSTEM Time Years FOR ELECTRODES 2 Hours 1 / 2 / 3 / 4 ______________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome: #: (G-3) - Be familiar with the American Welding Society (AWS) classification for electrodes. Special Materials and Equipment: Samples of electrodes 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: Correct identification of various electrodes TOPIC PRESENTATION: AWS CLASSIFICATION SYSTEM FOR ELECTRODES A. What are electrodes an how are they selected for various welding applications? 1. Shielded electrodes are thin metal rods having approximately the same composition as the metal to be welded. They are coated with a wide variety of types of flux. 2. Electrodes are designed not only to weld different metals but also to use AC, DC reverse, or DC straight polarity electric current. 3. Electrodes come in various diameters; the larger the diameter the higher the amperage required to properly use the electrode. 4. It is very important that the appropriate electrode be selected for a given welding operation. Poor electrode selection will cause difficulty in completing a good welding job. 5. Electrodes are classified into five main groups: 1) mild steel, 2) high-carbon steel, 3) special alloy steel, 4) cast iron, and 5) non-ferrous. B. The American Welding Society (AWS) has developed the following electrode classification system: 1. What does the classification E-70 1 8 on an electrode mean? a. The E means that the electrode is used for electric arc welding. b. The first two digits indicate the tensile strength in thousands of pounds per square inch (i.e., 70 means 70,000 psi). c. The fourth digit indicates the special characteristics of the electrode, such as type and general content of the coating, weld quality, amount of penetration, and the type of arc or electrical current. The fourth digit may be any number between 0 and 8. It is important to note that the fourth digit cannot be considered individually but must be considered in conjunction with the third digit in order to identify both the polarity and position of the electrode. C. Selecting the Correct Electrode 1. The electrode should produce a weld metal with approximately the same metallurgical properties as the parent metal. A top quality weld should be as strong as the parent metal. 2. In selecting the best electrode for a particular welding situation, the aim is to choose one that will provide good arc stability, fast deposition, maximum weld strength, minimum splatter, easy slag removal, and a smooth weld bead. To achieve these characteristics from an electrode, the following factors should be considered: a. Electrode Diameter - Generally, an electrode with a diameter larger than the thickness of the base material should not be used. If it is done, welding must be done at a very high speed and this requires considerable skill in order to obtain a sound weld. When making a vertical or overhead weld, a fast freeze type electrode with a diameter of 1/8" would normally be used. Regardless of the base metal size, an electrode diameter of 3/16" is the maximum size used. Electrode diameter is also determined by joint design such as a joint with a narrow gap or V-groove base metal plates. When this is a factor, use a small diameter electrode to do the root pass or the first weld bead. b. Joint Design - This is another important factor to consider when choosing an electrode. 1) When welding a joint that is not beveled at the proper angle to allow easy penetration, consider using a deep penetrating, fast freeze electrode, for example, E-6010 or E-6011. The opposite of this situation would be an open or poorly fit joint where a good choice of electrode would be E-6012 or E-6013. c. Welding Position - The welding position to be used during the deposition of the weld metal is a very important factor when selecting an electrode. Electrodes with a number 1 as their third digit will give better results in both the flat and the horizontal positions and a 3 will give good results in the flat position. Electrodes with a 2 or a 3 as their third digit are not recommended for welding in an overhead position. d. Type of Welding Current - This is another factor to consider when choosing an electrode. Some electrodes are designed for AC and DC straight or DC reverse polarity while others are designed to function properly using either AC or DC current. Information regarding current is generally written on the outside of the package and does not have to be figured from the AWS classification number. _________________________________________________________________ ACTIVITY: 1. Select six different arc electrodes and outline in writing each of their characteristics. 2. Weld a bead with each of the six arc electrodes and describe in writing how each electrode reacts during the welding process. 3. Weld various beads using DC straight, DC reverse, and AC type currents. _________________________________________________________________ 7/23/91 Df/RRE/tf #%&C