Wilsons Sandbox

Esteemed MG-TABC group- Over the years, I've used Skip and Joe's procedure, sans the heat treat cycle. This approach is mainly for Older BMWs and Porsches, and is mainly due to the thicker cu washers on same. If the washers are without any gouges and any serious circular marks, I generally just lap them on a flat surface with a fine abrasive, clean them thoroughly, and reinstall them. I've never had any leaks, although I'm careful to avoid over-torquing them. Normally, I install new washers on the next repair cycle, as the washers tend to become a bit too thin after the 2nd use. I've never figured out which copper alloy is used for these washers, and suspect that, today, it is likely OFHC (oxygen-free, high-conductivity) copper. There is practically no end to the other alloys available, mainly having to do with the combination of strength and conductivity (both thermal and electrical). Typically, these issues are dictated by the mounting bases for large-current rectifiers: they must have the strength in the threaded base to take a significant torque, they must be able to conduct large currents, and they must maximize the conduction of heat to the heat transfer surface to which the rectifier is mounted. One of the alloys that I recall using in this application was Phelps Dodge 135, which was heavily laced with Chromium. Another alloy was AMZIRC (AMAX Metals), which contained Zirconium. Both had tensile strengths which were significantly higher than OFHC, and both had relatively high conductivities. In forming these alloys into the multiple forms used in the electronics industry, it was necessary to anneal them prior to the forming process, and to reanneal them if more than one forming step was required. This was usually done in a hydrogen atmosphere (to avoid oxidation) at around 1200 or 1300 deg. F. The time required depended on the size of the part. The quench was accomplished within the annealing furnace (still in the H2 atmosphere) by moving the parts into a cold zone. Following the forming operations, no further heat treat was generally required, as the cold-working created the desired hardness. The customer was quite picky about the "Hardness" because he didn't want his customers twisting off the threaded studs in his zeal to make sure that the proper contact was made with the heat dissipation surface. So, the issue of quenching the T-ABC washers after heating is mainly something that applies to copper alloys to rapidly stop the annealing process at the desired point in the phase diagrams governing the metal. Too much annealing, and the conductivity and/or the strength would be out of spec. The same applies to too little annealing: the part would not only have the wrong strength/conductivity properties, but might well also fail to "Flow" properly in the forming dies. OFHC doesn't care about all of this metallurgical hocus-pocus, as it is a pure, unadulterated copper without any oxygen inclusions (ie; oxides) Annealing our TABC washers doesn't require a sudden quench to arrest the process. It's just good, pure copper that has been work-hardened, and is now a nice, soft seal. Dropping the washer in a can of water might be a good idea from the standpoint of limiting the formation of copper oxide on the surface, however, and it's also a good idea from the standpoint of accidently dropping an item at 1300 deg (red heat) onto a pile of something combustible in your garage...next to the TABC, which is attached to your house. I also think that lapping the washers is a good idea, too. Regards, Bill Earhart, TC 0735 Hermosa Beach, Ca.