Is it possible to overbake?

[charlie b]

Look at some of the manufacturer's sites about bake time. Some have time/temp charts that show the effect of different temps on the time to cure as well as maximum temps. Almost all of them had a decent cure time at 400F and there did not seem to be a max time at 400F. The higher cure temps had max times associated with them. Longer than max time at higher temps would result in a poor/damaged coating.

FWIW, the reason for the time/temp charts is production. High volume lines will use the cure temp that gives them the fastest cure time.

Make sure your oven runs at the correct temp. Know that there will be hot or cold spots in the oven, which is why a convection type is better. If you are running larger batches (basketful of bullets) then you will need a longer bake time (thermocouple in the center of the basket is highly recommended).

I'd rather not worry about it so I set the timer on my little convection oven for 23min (preheated), slide the tray of bullets in and let cook at 400F. Note: all of my bullets are cast in a single layer on the tray, most standing on the bullet base.

[renoce]

I have always set the oven at 400 degrees but I don't know how accurate that really is. I have always used the 20 mins as a time. Now sometimes I do go over by a min or two, but have never noticed any adverse issues. I have had good results.

[William Yanda]

" some of the bullets that were directly over the heating elements had very slight slumpage"

I think you have answered your own question.

Out of curiosity, why would you powdercoat round balls?

[res45]

I primarily use Eastwood and Smokes powders, and I have a few colors from the Powder Coat Store as well. I always preheat my convection oven for about twenty minutes or until the oven beeps and use a Taylor glass tube oven thermometer to verify my ovens temperature, which in my oven requires a 425 degree setting to achieve a constant 400 degree temperature.

Powder Coat Store instructions state, Cure Schedule: 10 minutes at 400 Degrees (Part Metal Temperature) I cure those bullets for 15 min. All the Eastwood powders I use state to cure at a temperature of 400 degrees F for 20 minutes after flow out/gloss over begins, which in my oven takes about five minutes, so total oven time is 25 min. For bullets where no expansion is required, I just water quench them right out of the toaster oven.

[popper]

Over-temp is BAD. Overtime is NOT bad. Once cured, only high temp will destroy the cross-linking.

[Kraschenbirn]

Just had an inadvertent 'overbake' this afternoon. 124 gr. 9mm RNFPs @ 420 degrees (oven thermometer) for 40 minutes (?). Put a tray in the oven, started timer, got busy doing something else, timer battery died, so I'm only guessing at how long boolits were actually in oven. No visible 'slump' and 'smash test' looks good. Gonna load and shoot 'em.

Bill

[David2011]

I recently saw a post from Smoke4320 on this subject. He inadvertently overbaked and said that the powder flowed better. I let my last couple of batches go 25 minutes after the powder started to melt and they turned out very well.

My oven is an Oster convection oven and I’m using relatively heavy baking pans. Most likely they came from Walmart. They seem to prevent concentrations of heat better than the real thin cookie sheets.

[Smoke4320]

20 to 30 minutes overtake will not hurt anything. In some cases it will actually allow the powder to flow better and make a more even finish..
Overtemp can cause multiple issues.. bullet slump, pretty puddles, ect

[Shuz]

FWIW--I have had excellent results with Smoke's Traffic Purple by laying the powder coated boolits on a piece of 1/4" screen cloth after they have been shaken in a vegetable type strainer to remove excess powder. I then place the tray and screen cloth with the boolits just laid out and vibrated by hand so that there is minimal touching of each other. I then stzrt with a cold oven and heat for 45 minutes. Boolits come out perfectly coated, even where they touch the screen cloth. I have 2/ ea oven thermometers on the tray. One reads 400 degrees and the other reads 450. I don't know which is correct, but I sure like the results!