Motorcycle Forums

powdercoating

Shocking but thanks for the report,it must be a chemical reaction ,but a couple of years to come about.

Have seen

corrosion underneath powder coating, from moisture seeping under from damaged areas of coating, then the coating cracks and flakes off, so possibly salt induced corrosion in an existing fault. But actual cracks in the alloy point more to damage from impact, either before or after coating, was this a repaired wheel, ie. rim damaged and repaired? Coating temperatures are not usually excessively high, however there is a possibilty in some types of castings of heat releasing stresses in the material from the casting process

Wheels have been steadily getting lighter as manufacturing techniques have improved and demand for lighter sportier bikes carries on, wheels making a very notable difference to handling as they are lightened, and our roads have been getting more and more unfit for purpose, potholes bumps and so on.

cracks

As smoto5 says, it could be cracks in the coating,

but looking at photo 1, it looks to me like the metal is cracked, if you look closely at the greyish "crack" at the base of the spoke you can see a fine dark line in the centre of the greyish area, this looks like a crack to me, the greyish bit is the metal under the coating and the coating is chipped off along either side of the crack, as the wheel flexes through torque and load stress's the metal either side of the crack will move, and as the two edges of the crack move independently of one another the coating along those edges gets chipped off exposing the crack in the centre.

Having said all that if you can't tell if it's cracked or not visualy, then you need to get it tested, there are various techniques that would determin if the metal is cracked or not.

Not sure how much heat is applied to the wheel during the coating procedure, but If there were minute cracks in the original wheel, application of enough heat would definitely "open them up" make them larger and more noticeable.

it's worth noting too that by heating any metal above certain temperatures will change the properties of the material, which can lead to localised hardening and embrittlement, causing cracks, or even softening and weakening. the same applies to cooling after heating too.

BritChopper

is a forum with a whole host of clever people that have had all sorts of things powdercoated, and the concensus is that the wheel may have been faulty before the powdercoat was applied, and that the heating has just shown up the damage.

A word with aerocoat might help clear up any confusion on the process???

Cracks in powdercoated wheel.

I just saw this, I dunno if I'm too late to post this but here goes for my first forum post. Theyre some scary cracks. I would be surprised if it was due to a 'chemical reaction' between the aluminium and the coating. If the P/C process was suitable for aluminium, I would be surprised if the heat from the process had much to do with it either, but it depends what type of plastic they were coating it with which would dictate what temp they were taking it to. I'm no P/C expect but if the coating was PVC the temp probably wouldnt be much more than 100C. The wheels are most likely cast aluminium which should be fine at this temp.  Heat treatment is complex; (much) higher temps could anneal and soften aluminium but on the other hand it could ‘artificially age’ or precipitation harden it and make it stronger, it all depends on what type of aluminium alloy it is and there are hundreds.  To a cast alloy it probably wouldnt make a great deal of difference, theyre generally not very strong anyway.  'Crackfinder' is right, there are embrittling mechanisms too which are very alloy-specific, but generally aluminium is not too sensitive to cooling rates. But I’m not thinking that this is a strength issue; it doesn’t look like an overload failure. It doesn’t look like corrosion has travelled under the coating much either.  By the position and appearance, it almost looks like a fatigue crack to me. If this coating is not very flexible, it may have cracked as the wheel flexed, and if the coating was adhered strongly to the metal, the crack might have carried on into the metal. It could have happened due to tensile stresses in the coating.  It is common practice to ‘peen’ the surface of a critical component to impart compressive stress to improve fatigue strength, so you can imagine that any tensile stress would make matters worse.  I suppose it could be stress-corrosion cracking, which would require a crack in the paint too.  Either one is a gradual process. Dont get me wrong, I’m not saying that is the cause, I’m just saying it could be.  Send me the wheel and I’ll have a look at it for you!!  Pity the original post was 2 years ago!!  Dammit, I want to know now!