Bend Testers - Bend Specimen Cutting Fixtures - Coupons -Tensile Testers TT1 WELDING JOURNAL 21 decades if not abused. Abuse includes overheating due to excessive duty cycle operation, lack of adequate water flow, and internal water saturation due to water leaks or condensation. If your welding transformer is watercooled, check to make sure the smalldiameter internal copper water cooling tubes are not clogged, crushed, or leaking. If the machine has been run on city or well water, minerals can accumulate over the years just like excessive cholesterol clogs our arteries. Chemicals are available to clear clogs in water cooling lines, but sometimes the transformer needs to be disassembled so the water lines can be replaced. Shorted-out spot welding machine transformers can be rebuilt, but it’s best to send them to a specialist rather than your local electric motor repair shop. Secondary Connections Spot welding machines are designed to generate heat at the weld zone due to the resistance of the material being welded, but every other source of resistance — from the transformer out to the electrodes (tips) — should be minimized. This is significant because the welding transformer converts the incoming power of 220 or 440 V into extremely low secondary voltage, typically only 6–8 V, that “pushes” the high welding amperage through the welding machine’s secondary circuit. Any form of unwanted resistance in the loop restricts the flow of welding current to the work. Although it’s a lot of work, disassembling the welding machine’s copper secondary loop connections and removing the accumulated oxide is a task that should be done annually. If a connection in the welding machine secondary has gotten loose and arced out over time, the contacting surfaces will need to be remachined flat and smooth. Various conductive pastes are available that are designed to improve conductivity and reduce oxidation by coating the mating surfaces prior to reassembly. For the ultimate in conductivity, secondary connections can also be silver plated. If the flexible copper shunts that conduct electricity from the transformer to the moving part of the welding machine have broken copper sheets or show arcing at the connecting surfaces, they should be replaced. Replacement shunts are not extremely expensive and are usually the weakest link in conducting the necessary high welding current through the secondary. Pneumatic System As the metal reaches the molten state during the spot welding process, delivery of consistent force and fast forging followup is critical to good weld quality. Most spot welding machines used in production are air-operated, so check the air system for smooth operation. Air cylinders are simple to repair and relatively inexpensive to replace, so don’t ignore those important components. Also, check to make sure there is a working filter, regulator, lubricator (FRL), and gauge installed on the incoming air supply. Restriction of air to the welding machine through a clogged FRL can cause poor follow-up during the weld. This results in excessive metal expulsion (flash), reduced electrode life, and inconsistent weld quality. If in doubt, replace the FRL. Mechanical System On rocker arm spot welding machines, check for worn pivot points and replace bearings as needed. An easy way to check for problems is to grab the arm out at the end and shake it from side to side. There should not be much slack. On vertical press type spot welding machines, you can check the ram mechanism for wear with a similar side-to-side and front-to-rear method, but on machines with roller rams, it’s also advisable to remove the sheet metal that typically covers the ram area and look for wear on the ways and/or rollers — Fig. 3. Roller bearings can seize up and wear the ways. Once again, these mechanisms are relatively simple to repair. The old-style “quill” press welding machine rams typically seen on U.S.-made machines from the 1940s and some machines being imported today are often metal on metal and can be more challenging to repair if lubrication has been ignored over the years and wear is heavy. Rather than spending money to repair one of these rams, it might be time to scrap the machine and use the proceeds to buy a new one. That’s the saving grace of old spot welding machines — most of them are loaded with copper and, if salvaged properly, can provide a nice down payment on another machine. And, as always, an experienced spot welding machine dealer can help guide your decision-making process and provide the needed material to get your old spot welding machine back into production.◆ TOM SNOW is CEO, T.J. Snow Co., Inc., Chattanooga, Tenn., a member company of the RWMA, a permanent AWS standing committee. Send your comments and questions to Tom Snow at TomSnow@tjsnow.com, or mail to Tom Snow, c/o Welding Journal, 8669 Doral Blvd., Ste. 130, Doral, FL 33166. DO YOUR OWN TESTING www.fischerengr.com ! (937)754-1750 BT1B BT1C Visit our website for all sizes and models available BSC-1PLT Fig. 3 — A press-type resistance welding machine ram that needs to be repaired. For info go to www.aws.org/ad-index
Welding Journal | January 2013
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