Contact Pad Maintenance
Contact pads are the most replaced copper pieces within a secondary system. Maintenance used to reduce the possibility of arcing a contact pad can be very economical. Costly repairs and replacements can be avoided with proper cleaning and inspection.
Understanding Your Contact Pads
New style arms use contact pads to transfer the power from the head of the arms to electrodes. Clamp bands pull electrodes towards the arm heads and compress electrode into a contact pad. Contract pads undergo pressure from clamping electrode sticks which aids in preventing slippage during operation. Cooling water cycles through the pads to prevent overheating.
Contact Pad Inspection
1) Dirt and Buildup
The connection between a contact pad and electrode is crucial to prevent arcing. Dirt and buildup between the electrode creates a small insulative barrier and poor conductivity. Most contact pad failures are a result of unclean contact surfaces. Buildup from a furnace and graphite from the electrode stick packs onto the surface. Develop a cleaning routine to prolong the lifespan of your pads. Frequency of cleaning routines are highly dependent on a mill’s environment, metal grades, and overall furnace system construction. A portable sand blaster should be used for cleanup of the contact pads’ surface.
2) Arc Damage
Arc damage commonly comes from dirt and buildup but may also be a result of poor clamping pressure (see maintenance module Hydraulics for more info on failing clamping pressure). Arcing can be seen as rough pitting or gouging within a contact pad’s surface. Filling in arced sections of a pad with copper grease is not recommended as a repair. Copper grease is used to prevent against corrosion and also acts as an anti-seize. Copper grease is not capable of transmitting power used by EAFs. Arc damage must be repaired by an experienced mill repair shop such as Erie Copper Works. Using a pad with arc damage may result in far more sever arcing and costly repairs. Inspect your contact pads for arcing damage during each cleaning cycle.
3) Back Arc Damage
Arc damage on the back of pads is a commonly a result of a gap between the pad and arm head. Ensure the back of the pad is clean before installing. During installation, check for a tight connection between both copper surfaces; no gaps should be visible. Tighten the hardware to secure the pad based on the OEM’s specifications. The seals should compress and NOT interfere with the mating of the two surfaces. If you find arcing on the backside of a pad we can repair both your arm’s head and the contact pad.