A:While it is always possible that a welding control can have a problem, I doubt this is the case here. There are two things to look for. 1. Water problems. If cooling water flow is low, or water temperature is too high, heat will build up in the electrodes, holders, and other water-cooled components in the welding machine secondary. This raises the resistance of these components and lowers the current in the weld. The most common problem I see is that a water tube in the electrode holder is missing, or the cooling tube does not go all the way to the bottom of the hollow of the electrode. In this case, the electrode will get hot enough to turn purple, and the resistance goes quite high. Letting the welding machine “rest” allows this hot copper to cool down and lowers resistance. Fig. 1 — Badly arched lower welding machine arm where it attached to the machine’s secondary pad. Loose bolts caused this damage. 2. Welding machine secondary component problems. Any connection in the welding machine secondary (exposed copper components at the front of the welding machine) that has high resistance will heat up during welding and increase this resistance. Another person contacted me recently with this exact problem on a 250-kVA aircraft welding machine. I suggested he check the secondary connections and he found the lower arm connection to the weld transformer secondary pad was loose and had arched as shown in Fig. 1. Because the connection was so badly pitted, the surfaces had to be machined and silvered. Once this was done and the bolts tightened, the welding machine produced the same current over the entire shift. Q: I weld stainless steel cross wires — Fig. 2. Just by accident, we discovered we can increase the strength of a weld by lowering the welding pressure regulator. Will this cause a problem? A: First, let’s see what is causing the increased strength. If you lower the RWMA Q&A 22 WELDING JOURNAL / JULY 2016 BY ROGER HIRSCH Q: We are welding 14gauge steel making about 25 welds a minute. We can get very good welds for the first 50 or so pieces, then the welds start to weaken. If we stop welding for about a half hour, the welds start off well and then again become weaker after about 50 pieces. Does this sound like a problem with the welding control? For info, go to aws.org/adindex
Welding Journal | July 2016
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