The Art of Welding. William Galvery

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Figure 1-22 and 23 Back weld and backing weld

      A backing weld is applied to the bottom or root of a groove weld before the groove weld is applied. Because the root or bottom of the weld is made first it becomes a backing for the groove. The difference between a back and backing weld is the sequence of welding. Before the groove weld is completed the backing weld must be ground or gouged to sound weld. See Figure above.

       Backing Plates

      A backing plate contains the large weld pool when joining two thick sections that are accessible from only one side. It takes the place of a root pass. The backing plate also shields the weld pool from atmospheric contamination coming in from the back of the weld. Backing plates are usually tack welded to the two sections of the weld, but there are proprietary ceramic tapes and metal-glass tapes that perform the same function and do not need to be tacked into place. Copper and other materials are also used as backing plates. See Figure 1-24.

Figure 1-24 Weld backing plate

       Runoff Plates

      This is a made of the same material as the work being joined. The plate is tack welded to the joint at the start and/or end of the groove joint. The runoff plate contains a groove like the pieces being joined. It prevents the discontinuities caused by beginning and ending the welding process. See Figure 1-25.

Figure 1-25 Runoff plate or tab

       Multiple Pass Technique

      Use multiple passes of parallel weld beads when you are faced with making a large weld but the electrode deposition is much smaller than the weld width. See Figure 1-26.

Figure 1-26 Multiple passes to join thick material

What are some common welding positions?

      They are determined by the position of the axis of the weld with respect to the horizontal and whether they are made on plate or pipe. See Figure 1-27.

Figure 1-27 Groove weld (upper) and fillet weld positions (lower)

       Welding Positions for Pipe

      See Figure 1-28. Note the difference between welding positions A , and C: In position A, (1G) the pipe may be rotated about its longitudinal axis to provide access to any part of the weld joint allowing the welder the opportunity to weld the entire pipe in the flat (1G) position; in position C, (5G) the pipe is fixed and cannot rotate forcing the welder to weld upward or downward vertically, flat on the top and overhead on the bottom; position B is pipe in a vertical position and welded on the horizontal plane; pipe in D is on a 45° angle and all positions (flat, horizontal, vertical, and overhead) are welded when pipe is in this position; the final position is pipe at a 45° with a restrictor in place (the restrictor allows the welder to weld only from one side of the restrictor) making this the most difficult of all welding positions.

Figure 1-28 Pipe weld positions

       Slag Removal

      Remove slag between weld passes or the remaining slag will form inclusions within the weld metal and weaken it. Slag is usually removed with a slag hammer and wire brush angle grinders or pneumatic peening tools may also be used. Sometimes a wire wheel is used. Pipe welding, grinders and power wheels are used between each welding pass to assure a slag-free surface on which to begin the next pass.

       GENERAL TOOLS, MATERIALS AND SAFETY EQUIPMENT

      Each welding process requires specialized equipment to do the job. But welding, whether you use it for hobby purposes or to make home repairs, requires a number of common hand and power tools. Many of these СКАЧАТЬ