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I powder at 185c for 30 min, 200c for more hard wearing parts and only in black, 200 should definitely not warp 4mm steel or aluminium.

Thanks guys. I guess I'll just double check the surfaces and thickness when I get home (no point in sending off discs that are pretty much done), then I'll pack them up and send them off.

wrote:

The powder coating heat is only 200 C°/30 minutes, so you are on the save side for the steel rotor but the alu carrier...Who knows more about....?

I would definitely look into the possibility that baking the aluminum hub/carrier might remove any heat treating strengthening.  I have no idea what alloy might be used on these rotors, or what the critical temperature might be, but I think it's worth looking in to.

A friend of mine worked for Dodge, and he said that they had some fancy aluminum wheels powder coated for a test car.  I guess no one thought about the fact that the powder coating process could remove the heat treatment hardness.  The wheels deformed under load on the track.  I think they started to rub on the brakes before anything catastrophic happened.

Here is a document with a bunch of temperatures listed for different alloys...  It looks pretty complicated.
materialsdata.nist.gov/bitstream/handle/...quence=3&isAllowed=y

wrote:

I would definitely look into the possibility that baking the aluminum hub/carrier might remove any heat treating strengthening.  I have no idea what alloy might be used on these rotors, or what the critical temperature might be, but I think it's worth looking in to.

A friend of mine worked for Dodge, and he said that they had some fancy aluminum wheels powder coated for a test car.  I guess no one thought about the fact that the powder coating process could remove the heat treatment hardness.  The wheels deformed under load on the track.  I think they started to rub on the brakes before anything catastrophic happened.

Here is a document with a bunch of temperatures listed for different alloys...  It looks pretty complicated.
materialsdata.nist.gov/bitstream/handle/...quence=3&isAllowed=y

Thanks, I'll look into that. Thinking about it some more, I'd assume even the inner carrier would reach 180-200°C under heavy braking (at least around the outer edges). Am I wrong?

Not the temperature under heavy breaking but the heat and long time of the powder coating process remove heat treatment hardness of the disk carrier.

I wouldn't think that they would use discs that have heat sensitive parts, regardless of how long the exposure needed to be to cause problems.
Having said that, I think I'll save myself some money and just paint the discs when I paint the engine on my other build. The discs aren't in really good condition so I'll be looking for replacements in the next couple of years anyway. 

Aluminium heat treatment is a process by which the strength and hardness of a specific subset of aluminium alloys, namely the wrought and cast alloys that are precipitation hardenable, are increased, annealing may be required for parts that have experienced strain hardening during their forming process, the inner carrier would be sheet aluminium that was either punched out or laser. The typical aluminium heat treatments are annealing, homogenising, solution heat treatment, furnace temperatures can range from 240(115°c) to 1000°F(537°c). Powder coating is effective at 180 degrees. Paint is the safe option though and the one i go with myself. Personably i dont think it would alter the hardness, i was a powder coater for years and we used to make 4mm hanging brackets for thermo king that were powder coated and never a problem but the safe option is always the better one.
 

Finally getting the brake calipers ready to send off to the powder coaters. Does anyone know if the rear master cylinder on the A1 was painted or not? I've seen them in black and also just blank aluminium.

I thought they were painted black on the A model, since the bottom of the rear MC was visible below the side cover.  The rear MC was natural on the Z1R as it was hidden behind the larger side cover.  The FSM shows a black painted rear MC in the '77 A1 disassembly section.

Black on my A1

Yep, black master cylinders matter!!!

We had a customer that had a sports car with knock offs - the single nut hubs to hold the wheel on.  No matter how tight he got them, they would come loose on the race track.  It was finally determined that the heat the wheel was reaching would cause the powder coating to soften, causing the wheel nut to loose it's torque.  Simply removing the powder coating from the surface the wheel nut tightened against on the rim solved the problem.  So it is never a good idea to powder coat a surface that have something torqued against that will see high temperatures.  Wheels, brakes, etc.  Always have the mating surfaces masked from the coating.