Stub Welding

Several years ago Carbines Engineering was asked to quote on the design and supply of a Rod repair system. The brief; to position a new stub and weld it to a pre-cut yoke, all this while the Rod/Yoke was still attached to the over head power and free conveyor. After moving outside the normal realms of welding procedure, a system was put forward and the client responded positively.

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The system relies on an in-house developed MIG/MAG Welding profile that could be referred to as Narrow Gap. It was noted that the normal procedure for welding a solid round MS rod to another of similar size was the “J” type welding profile, mainly because access was required for the shielding gas nozzle along with room for welding personnel to see what they were doing. If one didn’t need to take the nozzle very close to the weld (use a long wire stick-out) and the welder didn’t need to see what he was doing (use a welding robot) then the only issue left was weld penetration-fusion. If we look at what the application is,” mainly electrical conductivity”, along with enough strength to support 500kg at temperatures in excess of 1000 degrees. Then 1-2 mm of fusion was more that sufficient.

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These points, along with robot accuracy and seam finding led to the system now in operation. A 10mm wide gap to a depth of up to 50mm (stub diameter dependent), the robot now has less area to weld. Instead of the conventional “J” profile taking up to 45 minutes we now have only 7 minutes of welding time to complete the welding process per stub. The other main spin off for this process is one of contamination/porosity, “the less weld the less opportunity to create porosity”, destruction cross sectional testing of the welds has produced results that demonstrate less than 1% porosity with fusion in parts up to 3mm. Interestingly enough Ultra-Sonic testing was found to be unreliable due to the variety of steels and their sometimes-indefinable composition.

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Since the first 4 pin system, Carbines Engineering has now built systems for 2 pin, 3 pin and 6 pin. The most interesting of these being the 3 pin, as most engineers will realise, how do you position something correctly and still weld it? with a blind robot!. The answer, a very clever positioning jig, “the other half of this complete turnkey system”.