Ok, so I am fairly new to powder coating, and have run into a problem, that I can not find a solution for! I am chrome powder coating my valve covers and upper intake, so I can do them in transparent blue. No matter what I try, I am getting bubbles after the parts are oven cured.

The valve covers came out better, with only a few bubbles here and there:




Here is the process I am using:

• 
  
• The parts were hot tanked to remove all paint, grime ect.
  
• I then cleaned the parts with mineral spirits to ensure no contaminants were on them. (I used 2 clean rags to handle them from that point)
  
• I heated the parts to temperature, to ensure they were completely dry
  
• I powder coated the parts
  
• I then immediately put them in the oven at 350 for 15 minutes after flow out. Took about 10 minutes for the part to flow out, and another 15 from that point.

When opening the oven, the parts are speckled with tiny bubbles all over the place! I have done this 3 times now! The first time it happened, I sanded them down smooth again, and re-powder coated them. The bubbles returned, but not as bad, I sanded down the bubbled areas, and powder coated again... Then the third, and last time up till now...this was the last result:



This is what the blemishes look like close up:



I am not sure what is causing the bubbles... I see no way that the part could be any cleaner, with hot tanking it, washing it with dawn, cleaning with mineral spirits, and finally heating to make sure it is dry before powder coating.

Any help and advice is great appreciated!

[This message has been edited by JohnWPB (edited 03-04-2012).]

Sand an re-clean the parts. Heat them up to a VERY high temperature to make sure and burn off the mineral spirits. Then try again. My guess is that the mineral spirits are getting into the pores of the aluminum and not allowing the material to stick. I believe the intake and valve covers are different finishes from the factory so the intake may be a little more porous than the covers.

[This message has been edited by IMSA GT (edited 03-04-2012).]

it could be something with the aluminum thats causing the bubbles. I powdercoat every day at work and some stuff theres just nothing you can do its always going to bubble it could also be something with the paint. ive never tried but you could try wet sanding the bubbles out. i dont know how thick you put it on but id probably start with 400 then use 600 and finish with 1200 then use a mini buffer wheel with some compound to bring back the shine. should be worth a try.

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I heated the parts up to 450 after the mineral spirits to dry them out / burn anything off. All the powder coat manufacturers say to clean the parts just before coating with mineral spirits and then make sure they are thoroughly dry.

As for the different materials, I had to do the valve covers a couple times as well. I still have some bubbles in them as well. It's really frustrating to take the time and $100 to have the parts hot dipped, totally cleaned, and then the hours of grinding and sanding on the plenum to try to get it smooth to have this happen.

I've been fooling around with powder coating too. I've never had that problem. I always clean with brake cleaner prior to coating.

DF

It certainly looks like you have contaminates somewhere, either on the part, or in the powder itself.

Brad

Hey John, It looks like you are getting out gassing of some old oils and such. When you heated it to 450, how long did you bake it at that temp?
I would bake them for a good long time to cook off any contaminates. G/L Ray

Boy do I recognize that! I have done a lot of Fiero intakes, seen this often. Your parts are outgassing due to porous alluminum. The hot tank likely caused/contributed to this problem.

What to try: Strip off the powder. Put the covers in the over and turn on the clean cycle. When the door locks set the timer to 17 minutes. After you remove them I always sandblest the covers. DO NOT EVER wipe a part with a cloth towell. I blow the parts clean only. I do not solvent wash the parts, it just causes reactions. Coat them again.

If it happens again, start over again. Do the above, then put the covers in the oven at 450 for at least a couple hours. Hopefully it will burn out the contaminants in the pores. Coat again.

If it happens again: Start over and do everything above again. Heat the covers to about 250 and coat them hot.

If it happens again, toss them and start with a non-contaminated set. Stay far away from chemical stripping on the next set.

Aaron

Thanks to everyone that responded! This is a learning experiene to me for sure in powder coating....

quote Originally posted by Electrathon: Boy do I recognize that! I have done a lot of Fiero intakes, seen this often. Your parts are outgassing due to porous alluminum. The hot tank likely caused/contributed to this problem.

Well, thank you! It is nice to actually know what is causing it now!

I didn't know if it was, as someone mentioned, something in the powder itself, laying it on incorrectly, the temperature & cure time ect. Now that I know what the problem is, I should be able to tackle it better. I will try baking the part for a long time at a high temperature and give the powder another go. It makes sense that the hot tanking could have gotten it's high pressure liquid deep in the pores of the aluminum.

quote Originally posted by Electrathon: Boy do I recognize that! I have done a lot of Fiero intakes, seen this often. Your parts are outgassing due to porous alluminum. The hot tank likely caused/contributed to this problem. What to try: Strip off the powder. Put the covers in the over and turn on the clean cycle. When the door locks set the timer to 17 minutes. After you remove them I always sandblest the covers. DO NOT EVER wipe a part with a cloth towell. I blow the parts clean only. I do not solvent wash the parts, it just causes reactions. Coat them again. If it happens again, start over again. Do the above, then put the covers in the oven at 450 for at least a couple hours. Hopefully it will burn out the contaminants in the pores. Coat again. If it happens again: Start over and do everything above again. Heat the covers to about 250 and coat them hot. If it happens again, toss them and start with a non-contaminated set. Stay far away from chemical stripping on the next set. Aaron

Great advice and glad I know this now.

I've also heard silver is a major PITA (so maybe chrome as well?) when it comes to powdercoating. Guy I know that runs a shop was to the point that he just wanted to decline anything in silver.

I have likely done 50 sets of these. When I started I would do it for $20 less if they arrived stripped. No one ever sent one totally clean. Most gave up right off. The hardest ones were the ones that arrived after chemical stripping. For some reason the upper plenum was more prone to it, usually in the ribs between the raised flat areas.

If I was doing this set in transparent blue I would do them in alluminum powder instead of chrome. It is easier to apply and would likely look the same finished. I always "grain" the fins. I mask them off and then belt sand (directionally) the ribs.

My process would be to mask the fins, coat in alluminum. Mask again and coat with color. Grain the fins and then clear. You likely will have to do all but the first coat hot. Usually the top coats do not adhear unless heated. If it looks good without the clear would leave it off. Some colors reqiure it though.

[This message has been edited by Electrathon (edited 03-05-2012).]

quote Originally posted by Electrathon: .. The hot tank likely caused/contributed to this problem. ..

I disagree with that. I have done many parts with this method and never had any problem. Now I have never used mineral spirit to clean. I always use a good degreaser for last step. But the outgasing is definitely contaminants coming out. On VC and plenum I always mask the fins as those look better polished.

I was going to guess that there is water in the air line. Change the water seperator filter.

quote Originally posted by revin: I was going to guess that there is water in the air line. Change the water seperator filter.

That will do it but he's not using an air gun unit.

quote Originally posted by Alex4mula: That will do it but he's not using an air gun unit.

Yea, I forgot to mention that part hahah! It is a Craftsman electric powder coating gun.

@Alex, THANK YOU! ! ! The headlight buckets you helped me powder coat at your house came out great! Now that I have my own little set up here, I won't have to call you every time I need something coated

quote Originally posted by Electrathon: Boy do I recognize that! I have done a lot of Fiero intakes, seen this often. Your parts are outgassing due to porous alluminum. The hot tank likely caused/contributed to this problem. What to try: Strip off the powder. Put the covers in the over and turn on the clean cycle. When the door locks set the timer to 17 minutes. After you remove them I always sandblest the covers. DO NOT EVER wipe a part with a cloth towell. I blow the parts clean only. I do not solvent wash the parts, it just causes reactions. Coat them again. If it happens again, start over again. Do the above, then put the covers in the oven at 450 for at least a couple hours. Hopefully it will burn out the contaminants in the pores. Coat again. If it happens again: Start over and do everything above again. Heat the covers to about 250 and coat them hot. If it happens again, toss them and start with a non-contaminated set. Stay far away from chemical stripping on the next set. Aaron

What he said

Same happened to me; did a lil research and did the above. Problem solved...

I will try to get the powder coat removed, and bake the part at a nice high temperature, for a nice long time, and give it another go.

Thanks to everyone for all the advice! ! ! !

What are you using for an oven? Also, how are you going to strip it?

[This message has been edited by Electrathon (edited 03-06-2012).]

quote Originally posted by Electrathon: What are you using for an oven? Also, how are you going to strip it?

LOL! This is kinda crazy.... I just need to do a few parts and then am done with it. So I did not need a long term oven, like the Harbor Freight one for $500. I am using an old half-height filing cabinet I picked up at the thrift store for $5. I used one of the drawers and sealed the bottom of the cabinet, and the other door to use as the "door" to the oven. I also bought a large toaster oven for $20, and ripped out all of the internals. I then transferred the 4 heating elements and controls to the filing cabinet. It is far from insulated, but I have it set on a couple of bricks and can easily maintain a nice steady temperature up to 400 degrees. It also gets up to temperature in a pretty short 10 minutes or so.

As for stripping the part, I am gonna have to probably take it and get is sandblasted somewhere this time instead of chemically stripped.

I was worried you were doing this in the kitchen. I have an old oven I bought for $5 I think at a garage sale. Far better quality than the Harbor freight oven you are talking about. I also have one that is about the size of a refrigerator. We made a sheet metal box (it is insulated) and used the controls out of another oven to make it work.

If it makes you feel better I powder coated a dogbone tonight and it is covered with outgas blisters. Going to have to strip it and start over.

quote Originally posted by Electrathon: I was worried you were doing this in the kitchen. I have an old oven I bought for $5 I think at a garage sale. Far better quality than the Harbor freight oven you are talking about. I also have one that is about the size of a refrigerator. We made a sheet metal box (it is insulated) and used the controls out of another oven to make it work. If it makes you feel better I powder coated a dogbone tonight and it is covered with outgas blisters. Going to have to strip it and start over.

I agree fully, buy a used oven, cheaper and better.

Also before coating, I clean the item with flammable break cleaner, it works great. Non-flammable will leave a film. BTW wear clean gloves, latex surgical gloves are good. I then blow it clean with air hose and hit it with my propane torch to make sure there's no hand or other oil it anywhere. It's now ready to be coated.

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