Tricks to minimize outgas?

[tomg552001]

Anyone have any tricks to minimize out gas on cast aluminum parts? I'm thinking the best is to cure longer at a lower temp to keep it liquid as long as possible and pray that a lot of the bubbles even themselves out. Any suggestions would be greatly appreciated.

[Hemi-T]

On aluminum parts where outgassing is possible:

1) sandblast
2) bake in the oven at cure temp to outgas
3) remove, cool, and coat with powder
4) cure powder

I've had good luck with doing it this way.

Hemi-T

[tomg552001]

Wow i never tried that. I figured that cooling it back down would cancel out the whole curing without powder process. I will give this a try. I have tried a lot of things but it seemds that there is always some in cast aluminum. My best results, even though its more work is to pre cure, coat with powder, cure, cool, west sand outgas, than re-coat. Thanks for the tip, i'll try it.

[rivermasternc]

Tom:

Hemi-T is right on. This is also the strategy you will want to try for zinc die castings, although zinc is normally more troublesome than aluminum. If all else fails, discuss a special formulation of the powder with your powder supplier. Two things they will consider will be a self healing (longer flow state) or lower cure temperature material.

-Scott

[tomg552001]

Ok so i tried this method today and still can not figure out where i am going wrong. Could you guys give me some temp and time recommendations? I attempted this on a cast aluminum nissan valve cover, approxiamtely 22 inches long, 8 inches wide and 3 inches tall with a weight of about 10-15lbs. I outgassed it for 20 minutes at 450 degrees, cooled it down, than powder coated it, than cured for 20 minutes at 375 and still got outgas pretty heavily. I am using TGIC powders and blasting with alum oxide/glass bead mix, followed by a pretreatment solution, than outgas, powder coat and finally cure. Any suggestions on how long i should out gas at waht temp and what temp should i cure at for how long? I havnt purchased a infrared temp gun but will most likely shortly. Thanks in advance for the expertise.

[Hemi-T]

What is "pretreatment solution"? I used brake cleaner (not the orange based stuff) to degrease my aluminum valley cover inside and out, then sandblasted with silica, then baked at 450 degrees for 15 minutes to outgas, then cooled and powder coated as normal. No problems. It has been on a running engine using synthetic oil for 3 years before being powder coated.

Hemi-T

[tomg552001]

Hmm, its something i purchased from columbia coatings. It's a paint/powder coat prep that they sell.

[Hemi-T]

Try coating a similar part without using the pretreatment and see if you get the same results. I would be suspicious of something that says it works for paint and powder coating. They're different beasts. Any contamination could potentially cause outgassing. The brake cleaner I use is extremely volatile, and vaporizes completely in seconds even without heat, but I still preheat to outgas aluminum parts anyway. Good luck!

Hemi-T

[rivermasternc]

Why would any "pretreatment solution" be needed for an aluminum substrate if you are grit blasting? I can see a phosphate solution on a steel part to reduce rust creep.

[tomg552001]

I was under the understanding that it helped dissolve any surface oils such as from my hands after touching it etc. How are my times and temps? Any suggestions on that?

[rivermasternc]

Tom:

The time/temperature should be OK. Drop the temp a bit if you want to try a longer time. Say 375F for 30 mins. Aluminum is not very tolerant of a lot of thermal processing.

Handle the parts with cotton gloves after blasting. If they need degreasing, do that before blasting. I would skip the "pretreatment solution", particularly as a last step. If you have some grit material embedding in the surface, knock that off gently with some 320 grit 3M wet/dry abrasive paper (use dry). Try to not sand the blast profile down, you just want to knock that embedded grit out. If no embedded grit, do not sand at all.

-Scott

[DALE]

Tom

Okay first thing, don't waste your time talking to your powder manufacturer for a different formula,as a hobbiest it's not gonna happen.
Next media blasting is a great way to physically clean the surface you just need to remove blasting residue afterwards.For aluminum soapy water works fine with a clean rinse then dry in oven and outgass at same time.
Third you can bring most powder cure temps down to 300-325 and add ten min to time, stay above 300 for the whole process. This lower temp should be your ticket to success. Be sure you have a thermometer in oven for accuracy, don't trust knobs they are usually generally set unless you have an industrial oven.

[tomg552001]

Thanks for the info guys. So would say 30 minutes at 350 be good or should i go even lower for a longer period of time? Most of the pieces im powder coating are about the size of the part i mentions before. I do use a in oven thermometer to keep track of temp aswell.

[DALE]

If the part is still giving you trouble go down to 325. 25degrees makes alot of difference in cure cycle.

[dsacco1013]

tOM, i WAS WONDERING WHAT WAS YOU OUTCOME?... Caps lock

Dave