Welding Essentials. William Galvery
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 4–20-21.
Why are weld backing plates used and what materials are used for them?
A backing plate is used to contain 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 weldment. 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 4–22.
Figure 4–22Weld backing plate
What is a runoff plate or tab and why are they used?
It is a plate of the same material of the work being joined which 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 4–23.
Figure 4–23Runoff plate or tab
How can a large weld be made when the electrode deposition is much smaller than the weld width?
By using multiple passes of parallel weld beads. See Figure 4–24.
Figure 4–24Multiple passes to join thick material
Slag Removal
Why is slag removal between weld bead applications important?
Slag must be fully removed 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.
Welding Cable Sizing
How do you determine what size welding cable is adequate for a task?
For copper cables, look up the cable size required in welding lead sizing chart based on the power supply-to-work distance and the current setting in Table 4–1. Tables are also available for aluminum conductors.
Table 4–1 Copper welding lead sizing
Work-Lead Connections
What are the common designs of work-lead connections?
•Spring-loaded
•Screw-clamp
•Magnetic attachment
•Tack welded connectors
See Figure 4–25.
Figure 4–25Work-lead connection methods include: spring-loaded, screw-type, magnet type, and tack-welded connections
Why is it important to have a good work-lead connection?
A poor work-lead connection will generate heat between the connection and the work. It is best to make a solid connection on freshly cleaned base metal. Use a grinder or wire wheel to get through rust, paint, and mill scale. If the welding electrode holder overheats, this is an indication of a poor work-lead connection.
Welding Hand Tools
What hand tools is the welder likely to need?
•Chipping hammer to remove welding slag
•Wire brush for cleaning welds
•Hammer and cold chisel to break tack welds
•Pliers for moving hot metal safely
•Wire cutters to trim electrode wire (GMAW and FCAW only)
See Figure 4–26.
Figure 4–26Various hand tools
Safety Equipment
•Welding helmet with the proper lens shade for the process and amperage.
•Leather capes and sleeves or jacket called skins or leathers, to protect the welder’s clothing from sparks, especially while welding overhead.
•Welder’s cap to protect from sparks getting behind the welding helmet and into the welder’s hair. See Figure 4–27.
Figure 4–27Welding safety equipment
•Breathing apparatus to provide the welder with fresh air in confined spaces with inadequate ventilation. Safety glasses under the welding helmet.
What is and what are the advantages of the electronic faceplates?
•An electronic faceplate or lens is one of the most recent and important safety devices developed in the welding industry. These devices are designed to be clear, or nearly clear, then darken the instant arc is established; when purchasing be aware of the time the lens takes to darken 1/25,000 of a second or faster is recommended.
•The welder does not need to raise and lower his helmet when performing a series of welds: he can always see where he is with the helmet down.
•The beginner does not have to master holding his electrode steady when he drops his helmet. This permits beginners to perform better welds earlier in their training.
•Electronic faceplates offer continuous eye protection from infrared radiation coming off red-hot metal even when they are not in the darkened mode. It is just easier on the eyes and the welder is less likely to incur eye injury from inadvertent arc strikes.
Safety
What is the authoritative source of welding safety information?
Consult the AWS (American Welding Society) booklet Safety in Welding Cutting and Allied Processes, Z49.1.
What safety issues must we remember with SMAW, GMAW, FCAW, and GTAW?
•Protection of face and eyes from sparks and radiation with a helmet and lens of appropriate shade number (darkness).
•Protection