Curing Times and Temps

[Fireblade]

Hello all, I have a question that I have been wondering in my mind for a while now. How long do you actually cure a part in a oven? And at what temp? Is this temp the part temp or the oven temp? Here is what I have found from experience doing this. First off, I used to preheat my oven to 450degrees, then place my coated part in, let it flow out, then drop the temp to 400degrees, and let it go for 20 minutes. Pull the part out, I compared this to "Professional" shops jobs, and the powder on my parts came off alot easier than theirs. So I toyed around, and I tried this, I would preheat the oven to 340 degrees, place the coated part in the oven, then wait, I would check the part temperature every 5 mins waiting for it to achieve a 320 degree part temperature, then I would set my timer for 30 minutes. I just recently did this on a set of Harley heads. I have been told that if you bake aluminum (mainly t-6061) past 350 degrees, it could cause a chemical change in the aluminum itself and weaken it. Now after I did the cook process the second way, my parts seem to have a much more durable coating on them. What is the right way to do this cure thing? Now the Harley heads are cast aluminum, and quite a decent size, so they heat up slower then a thin gauge steel or something like that would. Here is another question, I am building a large oven myself. If I put heavy cast pieces in it, with smaller objects, would this make for a over baked finish on the small parts and underbaked finish on the large parts? Thanks for any info on this. I am kinda confused, I have done many parts, some turned on good, others I was dissappointed with. I want to to have a definitive answer to this cure thing to ease my mind. THANK YOU!

[warchild]

Curing Times and Temps

Im not a pro at powder coating yet. but i have been powder coating dirt bikes heads and jugs for a bike shop. they have had no problems with anything i done. After i powder coat the motor part i put it in the oven Then i turn on the oven to 400deg. with no pre heat. i leave it in there for 21min. then turn the oven off and leave it in there for another 20min. and don"t open the door till then. That is how i do it. for me thats the best i ever had anything to come out. im going to be working on Harley's too. i would like to know more about the Aluminum chemical change with the high heat. and how hot does a harley motor get when it's running. about as hot i would guess or around 300-350deg. i got a Harley and the motor on it is powder coated.

[Fireblade]

I don't own a Harley, but as you said, they come with powdercoated heads now. I was told by a guy I do work for, that they get to maybe a little over 300 degrees. Have you ever done an MEK test on your pieces after you cooked them? Or even tried a destruction test with them? If you don't know, take a q-tip, and dip it in some MEK, then rub the part in a inconspicuous area 20 times, back and forth, a stroke forward, then a stroke back, counts as 1 time. The coating should not come off easily onto the Q-tip head. This would show a complete cure. Now about the destruction testing, I just try to beat on the coating and see how easily it dents or mars. I have no "real" way of comparing it, except for just what I deem acceptable. I like a finish that is VERY durable, and so far I have not seen that with the lower cure times. But yes, with the aluminum, you have t be careful with it, I have not had a problem with anything I have ever done, but you don;t want to find out the hard way either.

[DALE]

temp and time

Times vary depending on temp and size and chemistry. I go simply on surface temp of part.Remember you will get better results with the lower temps and longer times, this keeps the powder in it's liquid state longer and allows for more flow out and less orange peel.Too high of a temp and the powder cures before it has time to flow out fully. Always preheat, this causes the oven to heat soak and the temps become more stable.Turning the oven off and allowing to cool slowly helps keep the finish from hazing over, if this does happen alot of the time you can take a clean dry rag and lightly rub it out to remove haze. This happens mainly with polyester powder.Most all types of powder will begin to flow at about 300F. As a general rule increase time in oven by 5 min for every 25F decrease in temp. These are surface temp readings.10min at 400F , 15min at 375, 20 min at 350, 25 min at 325, 30 min at 300. The oven style can change these slightly. Multiple layer coatings are different.

[Fireblade]

Ok, the times you posted on the last message seem to be the ones that work best for me. Even though others have said differently, including other manufacturers of powder coating products, so I will stick with what I have been doing. Now, as to what you said about multiple coats? Why are they different and what is to be done differently with them?

[DALE]

Remember times and temps are not set in stone, use what works.Different powder chemistries require different settings.Multiple coats vary depending on manufacturers.Some say cure till flow out then remove and cool before fully cured others require you fully cure each coat seperately.2 coats is easy any more than that and it gets tricky for a nice finish.