In resistance welding whether it is spot or seam welding build up on the face of the electrode is inevitable. It is caused by the heat generated on the electrode face and the chemical/metallurgical reactions that occur there. To reduce build up the process must be designed to maintain the face below red heat as much as possible. The process must reach red heat to make a weld. To accomplish this, the process must be designed to heat up to red heat, make the weld quickly and cool down quickly. Thus the electrode seam weld wheel face is at red heat a minimal amount of time. In roll spot seam welding there is some time/space between welds. In a liquid tight seam weld there is very little time between welds. There is not much cool time.
What can be done to protect the seam weld wheel?
• Water is always the first defense. Most operations provide flood cooling at the weld area.
• The next option is the seam weld wheel design. Look at the weld face to spread out the heat over a larger surface area.
• If buildup is a problem install a dresser that moves in and cleans the wheel between parts.
• If the machine is knurl driven make the knurl drive a dresser.
• Or remove/trade out the wheels at intervals and dress offline.
• Adjust the weld schedule to minimize time at temperature – don’t put in extra heat.
KNURLED WHEEL WITH COOLING TUBE
No matter what the material being welded stainless or steel the objective is the same “MINIMIZE TIME AT TEMPERATURE”.
Some dressing will be required during the seam welding or off line depending upon the heat being generated at the face of the electrode.
Reference: RWMA – Resistance Welding Manual Section 4