Author Topic: Powder coating front legs  (Read 547 times)

Offline Rene Holstebro

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Powder coating front legs
« on: Jan 29, 2018, 18:14:27 »
Iím having my bike frame powder coated but the guy says that I have to take the front legs completely apart because of the heat, Iím pretty sure that I didnít do that to an earlier project. Is it correct that I have to do that?
Cj360 77' Denmark

Offline clem

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Re: Powder coating front legs
« Reply #1 on: Jan 29, 2018, 21:09:27 »
Yes or your seals will melt and oil will boil.

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"After every war there are soldiers who refuse to surrender. To this day there are still thousands who cling to their 30+ year old motorcycles, thinking that the war is still on, refusing to concede that the four-strokes have won"

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Offline jetmechmarty

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Re: Powder coating front legs
« Reply #2 on: Jan 29, 2018, 21:30:46 »
You might consider having them hard anodized instead.  They'll be black and more resistant to wear.
Marty (in Georgia)

Offline jpmobius

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Re: Powder coating front legs
« Reply #3 on: Jan 29, 2018, 22:21:13 »
Yes, you need to have them completely taken apart as the powder coating process is high temperature.  Also, make sure the vendor is experienced with aluminum castings.  Castings are commonly quite porous, and residual oils need to be cooked out before being painted, otherwise they will boil out during the curing (baking) process ruining the job.  Additionally, the precision internal surfaces ( threads, bore, etc) need to be masked as there can be no trace of the coating on the machined surfaces for the part to work again.  I really like anodizing, but on castings, the outcome can be very unpredictable aesthetically (Some alloys tend towards dark, grey, or black(ish) no matter what color you wanted so if this is what you want, it might be the choice for you!).  Be aware that painting aluminum alloy, whether by spray can, high tech urethane, or powder coating, is an inherently difficult (nigh on impossible) task as aluminum starts to oxidize instantly upon exposure to the atmosphere, and this process becomes trapped under any sort of painting process. Eventually, this will disturb the cosmetic  (and ultimately the structural) properties.  This is why clear coating alloy parts eventually shows corrosion underneath.  In fairness, very well prepared parts will look good for quite a long time being painted (powder coating lasts longer by dint of its much tougher qualities), but for truly long term, any sort of "coating" has to alter the properties of the surface like anodizing does.  Anodizing creates a sort of oxidized layer out of the surface of the part and protects the part from further "corrosion".  Since there is no additional material added, the part fits back just like it did originally.  You could also passivate the part before painting, a chemical process, but this requires some dreadfully dangerous chemicals and is only done these days industrially when there is no other way to get the needed outcome.  For these reasons, personally, I paint parts myself with a 2 part urethane so I have control over the results.  Or, simply polish the aluminum and leave it bare.  Polished alloy does need maintenance, but it is fairly easy to hand polish once or twice a year once a really good polishing job is done the first time round.  Ultimately, this is the best long term solution as a permanent cosmetic solution because it is practical.  I have passivated parts (Chromic acid and cyanide - don't try this at home kids) and then painted them for a truly long term result, but one scratch and the protection is breached and you are back to square one.  So for me, if it has to have paint, I media blast, paint with epoxy as soon as possible (within minutes) and later paint.  Otherwise I polish.  I anodize wrought (made from extruded, not cast) alloy when needed only because I have sometimes had disappointing results with castings.  Mr. E has shown some excellent pics of corrosion under paint on some magnesium castings here:  The same thing happens with aluminum alloys (darn near all aluminum alloys have magnesium and vice versa, generally at a slower pace.
« Last Edit: Jan 29, 2018, 22:28:38 by jpmobius »

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Offline Rene Holstebro

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Re: Powder coating front legs
« Reply #4 on: Feb 07, 2018, 17:27:16 »
Thanks guys very Nice answers 😀😀 I decided to blast and paint the legs myself ad send the rest to powder coat, that way I donít have to take them apart and can do them myself every two years or so.
Regarding the anodising, I REALLY like the look but canít find anywhere that will make so little
Cj360 77' Denmark