Welding Shielded Metal Arc Welding

Good morning everyone I am Mrs Makubo (Maphalla) Welding lecturer Downloaded from hlayiso.com

SHIELDED METAL-ARC WELDING Contents of this module 1.SAFETY PRECAUTIONS 2.. KNOWLEDGE OF SHIELDED METAL-ARC WELDING AND EQUIPMENT 3.. SHIELDED METAL-ARC WELDING: PRACTICAL 4 FILLET WELD 2F 5. BUTT WELD 1G 6. COMBINATION OF WELDS AS PER DRAWING Downloaded from hlayiso.com

Outcomes  On completion of this elements you will have attained the basic knowledge about shielded metal arc welding and equipment  You will have the ability to strike an arc and run a weld bead on mild –steel plate  You will have attained the necessary ability to do a butt weld in the down hand position  You will have attained the necessary ability to do fillet weld joint in the down hand positions How well you must do it  There must be no surface porosity evident in the weld bead. there may be no crater cracks evident at the end of the weld bead.  All safety precaution must be adhered to  Undercutting may not be evident, no surface porosity may be evident,  Penetration must be according to drawing or sample Downloaded from hlayiso.com

Introduction  Arc welding, or electric-arc welding, is a process that is widely used today. It is a fusion process because it melts the base metal being joined. This method is used in the locomotive, boiler-making, structural and other branches of engineering. The welder using the electric-arc welding process has a special holder which grips the electrode. As the welder brings the electrode close to the base metal, an arc is created by an electric current that flows between the electrode and the base metal. The arc, which is very hot  (approximately 3 539C°) causes the base metal and electrode to melt. The molten metal from the electrode then flows into the joint. Downloaded from hlayiso.com

SAFETY RULES FOR SHIELDED METAL-ARC WELDING 1 Always wear a welding helmet with the correct grade of filter lens 2 Check lens for cracks before starting to weld. 3 Wear fire-resistant clothing at all times. 4 Before you start welding, make sure that others are protected from the rays that will be given off by the electric arc. 5 Never strike an arc near an unprotected person because he might get “arc eyes”. 6 Switch the welding machine OFF when not in use. 7 Never do any welding in damp or wet areas. 8 Do not throw stump of the welding electrode on the floor, use a metal container. Downloaded from hlayiso.com

SHIELDED METAL ARC-WELDING MACHINES  1) An AC (alternating current) machine.  2) A DC (direct current) machine.  3) An AC/DC machine (combination of the two machines) Downloaded from hlayiso.com

Equipment's ELECTRODE HOLDERS Electrode holders are used to grip the electrode and to provide an insulated handle. Holders come in a variety of shapes and sizes. Figures 3 and 4 show two of the common types that are used. The size of the holder required depends on the maximum amperage to be used. The important point is that the holder should be lightweight, yet capable of carrying sufficient current to avoid overheating. FIGURE 3 Downloaded from hlayiso.com

. EARTHING CLAMPS The earthing clamp is fastened to the piece of metal to be welded or onto the welding table, thus completing the welding circuit when electrode is touched to the metal. An earthing clamp with springs is the most convenient and provides the easiest method of securing the earthing clamp to the base metal. See drawing below. Downloaded from hlayiso.com

CHIPPING HAMMER Although not safety equipment, the chipping hammer and wire brush are essential parts of the welder’s equipment. All welds should be chipped and brushed on completion. These tools come in a wide variety of shapes and sizes. They should be used frequently and always be kept in a good condition. See figure below for a typical chipping hammer and ire brush. Downloaded from hlayiso.com

Wire brush Downloaded from hlayiso.com

POLARITY  An electric current causes a magnetic force around a current-carrying conductor. Because the lines of MAGNETIC force end at the negative and positive terminals of an electric current, the terminals may be called the negative pole and the positive pole. From this we obtain the word polarity by which we may know the direction of the current flow. Polarity can be obtained only on a DC welding machine. It cannot be obtained on an AC welding machine because of the current reversal. When the electrode is connected to the positive terminal of the welding machine, the machine is on positive polarity. See Figure 8. When the electrode cable is connected to the negative terminal of the welding machine, the welding machine is on negative polarity. In the American industry, positive and negative polarity are referred to as reverse and straight polarity respectively, in British industry the opposite applies. Most welding machines are marked with a + and - sign. It is not necessary to change the cables. On most welding machines, this is accomplished by moving a lever or dial on the front of the welding machines. Downloaded from hlayiso.com

. + - ELECTRODE CABLE A. REVERSE (POSITIVE) POLARITY + - ELECTRODE CABLE Downloaded from hlayiso.com B. STRAIGHT (NEGATIVE) POLARITY

Self assessment  What are the 5 basic pieces of safety clothing that you must wear during the SMAW?  Name at least 4 safety precautions that you must adhere to during the SMAW Process ?  What type of rays cause EYE FLASH during the arc welding process?  Why is it not advisable to wear clothes made of cotton material during arc welding?  Describe what alternating current means.  What are the 3 types of electric arc-welding machines we use in the welding industry.  Why can’t you change the polarity on an AC welding machine? Downloaded from hlayiso.com

The focus was on safety ,basic of shielded metal arc welding ,equipment and the polarity  The next presentation will focus on (electrodes Identification because there are so many different types of electrodes on the market it can be very confusing to choose the correct one for the work to be done .as a results ,aws has established a numbering system which is used by welding industry they uses codes such as E6014,E10014 and E6011.so will discuss it tomorrow Downloaded from hlayiso.com