Page 46 - MetalForming-Aug-2018-issue

Welding Well
creating the potential for a catastrophic failure the next time the water is turned on.
Go With the Flow
Research has proven that water chilled to 55 to 60 F and circulated through the spot-welding tips will improve electrode life. Therefore, in the ideal world, and if one doesn’t mind the potential for condensation dripping off of electrodes, two chillers per machine would be nice, with one set to a low temperature and connected to the machine’s secondary circuit and a second chiller set to a temperature exceeding the dew point, cooling the transformer and control.
However, if using just one chiller to remove heat generated by the machine, compromises are necessary. That’s when water flow should be as high as possible. For this reason, select a chiller with a properly sized pump, and plumb the system to minimize head pressure
caused by running overhead water lines.
Installing petcocks for each circuit, along with inline water flow meters or visual indicators, makes it easier to balance the water flow.
Chiller Sizing
The ideal setup: Connect to just one new machine, or a group of similar machines located close together, and run water lines on the floor.
Selecting the proper refrigeration capacity of a resistance-welder chiller is not always an exact science, since the welder or group of welders to be cooled may not run continuously. How- ever, a good rule of thumb for standard single-phase AC resistance welders is to specify 1 ton of refrigeration for each 100 KVA of welding capacity.
MFDC (inverter type) resistance welders require additional heat-removal ability to cool the secondary diodes. A good rule of thumb here: 3 tons of
refrigeration for every 150 KVA of weld- ing capacity.
Reservoir tanks typically built into a chiller serve as a thermal flywheel, helping to prevent short cycling of the refrigeration compressor.
When choosing a large chiller to serve several welders or even an entire plant, consider a multicompressor sys- tem. This allows the system to ramp up and down automatically to meet the required cooling capacity.
With continuing droughts world- wide and the possibility of future wars over water rather than oil, buying self- contained chillers for use with your resistance welders could be one small way to help save the world. At the very least, it can improve your resistance- welding process and save money. MF
Snow acknowledges and appreciates input for this article from Raschell Hick- mott of Dimplex Thermal Systems, Roger Hirsch of Unitrol Electronics and Don DeCorte of RoMan Manufacturing.
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