What causes powdercoat to fisheye, like outgassing? I have a set of wheels at the powdercoater, and all four are doing the same thing. They were cleaned and blasted, prior to coating. They are two different pairs of wheels, from different foundries. One pair came from So Cal, and the other was cast in Italy. They are going to give them another try, but I am concerned that I am going to end up painting them. Any ideas?
My understanding is that some casat aluminum is difficult to powder coat due to it's porous nature. I had some Offennauser aluminum valve covers done several year ago and the job was less than great.
It's not so much porous castings as what has gotten into the porosity. I learned the hard way that with aluminum castings that have been in service, if there's the slightest trace of corrosion anywhere to pre-bake the part at flow-out heat for at least 1/2 hour after blasting and repeat the blast after heating. I've had a few bits that needed several passes before being ready to coat. Tell them to strip them, bake them, check very carefully for any signs of corrosion 'boiling' out of the casting after baking, then re-blast. If you get anything more than a minor trace after baking, I'd quick blast, then repeat at least one more time.
And I should also note that it may not even be corrosion. I've had issues with parts exposed to various automotive fluids, sometimes residue can get trapped in the metal. I had a Harley engine side cover that took 5-6 tries before I got a clean job.
As Usual Crazy Steve probably hit it spot on = Contamination. If they came used I'd suspect that they may have had silicone spray on them at one time. Back in the 70's I was working at the Pontiac dealership in Yakima and The bodyman who was working on a Trans AM in the stall on the other side of the wall came in asking if I had sprayed anything silicone in the past couple of hours. I said Nope but the Boss's buddy was dinking with his step van 15 Ft away from where you were working when I went out to the snack truck on break and was spraying silicone on the hinges. That guy used to show up and hang around about 3 days a week but I never saw that step van on the property after that. I've talked to painters who had jobs fisheye because they figured that someone had used silicone wax on the car before too. That was before folks were having stuff powder coated in that late 70's early 80's time frame.
Silicone/ oil contamination. Unfortunately you’ll have to blast it clean and start over. Otherwise you’ll chase that contamination/ fish eyes until the cows come home. Sent from my iPhone using H.A.M.B.
Food for thought here....... Aluminum= porous. If the coater has had some experience with this situation before,- A hot jet wash first. Then a pre heat cycle to outgas/burn any remaining contaminants, then maybe a good shot blast... Aluminum likes to hold on to the gremlins, and it's tough to be totally clean when coating. Been /done/suffered, but persevered......... maybe ask? Hope it turns out!
The shop is doing them over. I am concerned that it is going to be a cycle so endless that the wheels will be too thin to use, before a clean finish has been achieved.
25 years ago when I owned a powder coating shop it was normal to pre bake any suspect items like aluminum castings, lugged motorcycle frames, or anything that might have absorbed oil or water. That drove the gas out before coating and eliminated most of that sort of problem.
You shouldn't have any problems if they're baked once or twice. The side cover was problematic because it had absorbed oil over time; if I didn't know better, I would have sworn that whole cover was made out of oillite bushing material...
It’ll be fine, if it’s a good shop they’ll Strip the powder and start over. I remember the first time I encountered this. It was for a set of chrome Harley side covers. Sanded and re coated them 4 times! Fish eyes kept moving and re appearing. Finally called the guy up and turned out he waxed the bike before he brought the parts in . If we knew that we would have done a more aggressive prep from the get go. We stripped the powder, heavily blasted the chrome (without burning through it) and they came out perfect in one shot. The other guys are right with porous materials, it’s never a bad idea to pre-bake but a thorough blast and solvent cleaning should be used in addition
They did re-do it, and they are fine now. I feel better equipped to ask for a pre-bake beforehand now.
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