Please read- Repainting alloy wheels

[missmetallurgist]

Please please be careful if you are thinking of having your alloy wheels repainted.

Many wheels are made from an aluminium casting alloy which is solution heat treated- this means that on initial manufacture, it uses the paint baking process to strengthen the wheel to the required range (aging).

If these wheels are reheated later in their life (eg during repainting) this 'overages' the material and DRAMATICALLY lowers it's strength. This can occur at process temperatures as low as 150°C.

I have seen wheels where the centre hub has become detached from the rim by fracture through all spokes.
On a car, the occupant is fairly protected- not on a bike!

If you have repainted wheels, please check for cracks; if you are thinking about repainting, please check with the OEM dealership for information on the effect of temperature on your wheels.

I don't intend to scare people, just please be aware that metals are affected by many things you may not have thought of.

I would appreciate any comments on this post.

>>> Edited by missmetallurgist on Thursday 13th May 18:08

[big_treacle]

Wow, that's the most dramatic first post ever!
Interesting reading tho. Be interested to know how many repainted wheels do fall apart

[ultimasimon]

Hi Liz and welcome. Thats a very interesting observation. I have a friend who is currently doing up an old TZR 250 bike and is thinking about having the wheels done, so I will pass this information on to him.

I wonder how many other people have never heard of this? It makes perfect sense too so I am suprised no ones ever thought about it, or is it just me?

[alfa145uk]

So is it structurally ok to shotblast them or do you need to rub down by hand?

Then I presume it's ok to use cellulose/2pac, let the paint cure naturally then lacquer - as that way they are not being baked?

[matt_t16]

missmetallurgist said:

Please please be careful if you are thinking of having your alloy wheels repainted. Many wheels are made from an aluminium casting alloy which is solution heat treated- this means that on initial manufacture, it uses the paint baking process to strengthen the wheel to the required range (aging). If these wheels are reheated later in their life (eg during repainting) this 'overages' the material and DRAMATICALLY lowers it's strength. This can occur at process temperatures as low as 150°C. I have seen wheels where the centre hub has become detached from the rim by fracture through all spokes. On a car, the occupant is fairly protected- not on a bike! If you have repainted wheels, please check for cracks; if you are thinking about repainting, please check with the OEM dealership for information on the effect of temperature on your wheels. I don't intend to scare people, just please be aware that metals are affected by many things you may not have thought of. I would appreciate any comments on this post. >>> Edited by missmetallurgist on Thursday 13th May 18:08

Think your refering to powder coating not painting. Low bake ovens operate at no more than 70 degrees and usualy a lot lower. Repainting then low baking won't cause an issue and its only cheap wheels that tend to be manufactured in the way described. Shotblasting can result in a stronger wheel, if done correctly.

TBH if the wheels are in enough of a state to require a big refurb just chuck them and start again with a decent set. You don't take risks on tyres so why take risks with the kit holding them to your car.

Matt

[TonyOut]

Talk about making an entrance

[wedg1e]

Hmmm. I've seen a wheel (or two) that had the centre hub fracture out from the spokes. The car concerned was a British open 2-seater. The wheel had undergone the usual design and metallurgical testing and was OK'ed for production. Then several crashes occurred where of course everyone assumed the driver was at fault. Eventually someone dug a bit deeper and proved that the stresses induced on the road exceeded those that were allowed for or computer-modelled or destructively tested for. One quiet redesign later and all is now well.

The joys of working in the NDT industry, you get to find out all sorts of things...

Ian