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How do I protect our copper wires from over annealing

I produce bare copper flexible conductors made of stranded and braided annealed copper wire. When the same is used by manufacturers of carbon brushes, they have to leave the carbon brush with the conductor in a vacuumed or inert gas oven of about 700 °C for some time. My problem is that sometimes the coppers are over annealed and cause destruction of the copper. It is surprising that sometimes this does not happen even though the curing condition is exactly the same. Now I would like to know what could be the reason and how can I correct the quality. Could it be due to copper quality which might be different from one to another? Could it be due to different coppers made in different systems such as upcast and continuous casting, or could the pre annealing of the single wires have any effect.

Thanks,

Mahmoud Tehranchi
technical manager - Tehran, Iran
2003

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You may very easily have different alloys, even tho they are somewhat similar. Some (possibly all) copper anneals on a rapid cool down from heat and hardens on a slow cool down from heat. Possibly load size or lunch break or end of the shift caused a load to be rapidly cooled. Just a thought. It might also have someone that is an expert chime in to point out any errors in my thought pattern (guesses).

James Watts
- Navarre, Florida
2003

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February 25, 2008

On the subject of annealing of Copper Wires used in Carbon Brushes, we face two issues (possibly related).

After the Brushes are compacted they are heated to about 600 °C. We find a small percentage of Brushes where the wires come off the Brush easily. The occurrance is about one pieces in 50,000 or more. More of a random occurrance. Could this be related to hot spots in the copper wire. One theory is on heating and cooling the prestressed copper wire spot anneals and shrinks loosening the joint.

Is there a method to check the hardness or flexibility of the stranded copper wire?

Suresh Rajagopalan
- Chennai, India