sandblasting an alloy wheel can warp it?

[RuBiCaNT]

@LAFENGAS

Let’s rule out powdercoating as having anything to do with weakening rims. We know it’s not the powdercoat itself, it’s the temperature the metal is heated to. I can give exact numbers for every rim alloy, both aluminum and steel.

I’ll try breaking it down.

What Process “SOFTENS” the metal? The Answer is Annealing. You can’t say ‘weaker’ because softer doesn’t mean weaker. For instance, hardened steels are very hard, but brittle. You can break them with impact.

In order to determine the Annealing temperature you need to look at it’s TTT Diagram (Transformation, Time, and Temperature) to determine the Critical temperature. At this point, you’re looking at the metal under a microscope and seeing how the actual grain structure is affected.

Once you find the Critical temperature of the specific alloy, it should be heated about 100°F (rule of thumb) above the critical point for a period of time (in hours). This changes the grain structure of the metal (to what’s called an austenitic structure) Once this critical temperature reached for a period of time, it is then air cooled to slowly bring it down to room temperature. That’s the ‘generic’ annealing process.

Now…to put things in prespective. Carbon steels with a low carbon content ( less then .12% carbon, i.e. tool steels) their critical temperature is 1600°F to 1700°F. The higher the carbon content, the lower the critical point… as low as 1400°F for the lowest critical point temperature.

I don’t know the specifics for aluminum off-hand. What you would do is find an aluminum alloy, find it’s TTT diagram and find the critical temperature. I believe the annealing range for aluminum is about 700°F - 1200°F

Powdercoating oven is typically 300°F - 500°F

Great post, Josh!!

[Jeller]

Thanks Josh, I will be looking to get my stock wheels powdercoated sometime over the summer :tup:

jeller

[66impalass]

@newman

sandblasting can be pretty harsh, i know it’s apples and oranges, but i have seen 3/8 stainless steel plate warped by a blaster…

sandblasting can realign surface grain structures and will cause VERY non-uniform heat concentrations.

missed the whole sandbalsting part, just was going on media in general. You would have to sit in one place or not know how clean to warp materials with media. Can it be done, yes, can it be done with a proper technique, shouldn’t be

also fin the specific material that you rim is made out of, aluminum is not the correct answer

Online Materials Information Resource - MatWeb

[newman]

trying to dig up the info, lotus says their wheels should not be heated above 150C (cast) and 175C (forged) for more than 15 minutes… PC temps can get close to this… However, depending on whether it is a convection oven or IR oven, the internal temps will vary greatly.

[LAFENGAS]

@newman

trying to dig up the info, lotus says their wheels should not be heated above 150C (cast) and 175C (forged) for more than 15 minutes… PC temps can get close to this…

don’t forget the industry standard 2.5 safety factor.

Out of curiosity, why should they not be heated above 150°C? Does it say? Is it because the current finish can’t withstand it? There could be several reasons why, not necessarily linked to wheel failure.

[newman]

it does not say, it could be wheel finish. there are alot of OEM powdercoated wheel manufacturers…

[MaximaSE98]

so use aircraft stripper on them instead…then clean them up good so powdercoat stays