Is it possible to overbake?

[Black Jaque Janaviac]

Is it possible to bake the bullets too long? Or too hot?

I just recently experienced my first powder coats that failed the hammer test. For years they all passed the hammer test so the only "failures" were from poor coverage not failure to cure.

The first time I had a failure to cure I didn't get good coverage with the first coat so I gave them a second coat. On the second coat I failed to start my timer so they baked well passed the 25 minutes I usually set them for. When I pulled them from the oven they looked well coated but had not-so-glossy coating and some of the bullets that were directly over the heating elements had very slight slumpage (almost looked like it could have been fixed by sizing). Before sizing I gave one the hammer test and to my horror the paint flaked off the out edge as the bullet flattened. I found a reject bullet from this batch that had been given the first coat with the others but I rejected it before putting a second coat on it. That bullet passed the hammer test.

Now just yesterday I made a batch of roundballs and coated them (one, good coat). This time I stopped the oven shortly after the 25 minute timer. After they cooled I hammer tested one and it failed. Granted since these will all be surrounded by a cotton patch when loaded in a muzzleloader I don't need to re-melt these, but still - I wonder what's up.

I've tested the oven with an oven thermometer and it's accurate. The 400° setting produces a 400° reading on the thermometer just as it has for years.

I read this forum for quite some time and I've never read anyone having problems with baking too long. Too hot produces melted bullets, but I have not read of bad consequences from baking too long. Is it possible? If so where's the margin? If 20-30 minutes in a pre-heated oven seems to be the standard recommendation, has anyone gone past that for say 45 minutes? an hour? an hour and a half? What happens?

[bangerjim]

I always use 400F for TEN (10) minutes. no more no less. That's after the powder turns shiny. Perfect coats every time with anything from HF red to several of Smokes powders. I have never gone as long as you since I started doing this back in 2013. There is no reason to. Most powders I have seen & used state 400F for 10 minutes. Where did you come up with this 25 minute bake requirement???????

You never did tell us the brand/color of powder(s) that are giving you problems.

banger

[popper]

too hot! When they get close to slump temp the alloy starts to 'bead' up and PC loses it's grip. above cook temp and below slump, the PC loses it's 'cure' and will come off in strips. I cook at proper temp for an hour, no problem.

[Black Jaque Janaviac]

I always use 400F for TEN (10) minutes. no more no less. That's after the powder turns shiny. Perfect coats every time with anything from HF red to several of Smokes powders. I have never gone as long as you since I started doing this back in 2013. There is no reason to. Most powders I have seen & used state 400F for 10 minutes. Where did you come up with this 25 minute bake requirement???????

You never did tell us the brand/color of powder(s) that are giving you problems.

banger

I am using Smokes.

I don't know where I came up with the 20+ minute bake time. But it seems to be referenced in many threads although, now that I look back it doesn't seem to be you stating the 20+ minute bake time.
https://castboolits.gunloads.com/showthread.php?171403-Powder-Coating-Boolits

[Black Jaque Janaviac]

too hot! When they get close to slump temp the alloy starts to 'bead' up and PC loses it's grip. above cook temp and below slump, the PC loses it's 'cure' and will come off in strips. I cook at proper temp for an hour, no problem.

400° is too hot? What do you usually bake at?

[KenH]

Per most of the manuf'ing folks (and Smoke) it says 400°F for 20 minutes. That's putting a cold bullet in a preheated oven. I'm thinking if you watch the bullets you'll find that's pretty close to the 10 minutes AFTER the powder has started to melt giving it a shiny look.

[Jaaymar]

I am familiar with powder coating steel and other metals but not lead (nowhere to cast).

I remember having issues with a second coat on steel.
The issue was that the static could not build up to get an adequate coating on the material. We used an electrostatic system.
Never rebaked the parts with a second coat so not sure if the material will not stick to itself after it cures.
Like casting silicone rubber (2 part, not calk) after it cures nothing will stick to it.
It is a thermoset polimer so it may or may not stick to an already cured surface.

Jaaymar

[Driver man]

I bake for 30 minutes at 400 deg from a preheated oven and get perfect results but that was not always the case. I found that the tray I stand the boolits on originally was to thin and I would get occasional slump with the coating failing the hammer test. I reasoned that the oven ambient temperature might reach 400deg but the radiant temperature from the heating elements must be heating the oven tray to reach much higher temperatures in order to cause the boolit slump (melting) I was experiencing. I found a heavier duty oven tray and also shielded the elements and have since had perfect results. I use Smokes powder and also preheat the boolits (just warm to the touch) and have done thousands.

[BK7saum]

Also, bullet size/weight affects cure time. A heavy bullet takes longer to get to 400, but a smaller bullet such as your round ball, got there quicker and thus cooked longer and maybe hotter. If your conditions are good, but on the edge of too hot with say a .44 cal 265 or 300 grain bullet, the round balls might have gotten too hot. Nothing changed in the oven but the size/mass of what you are coating.

[FrankJD]

YES! Been there, done that!! Too hot and too long!!!

[slim1836]

Is your oven a convection oven? You may be getting hot spots in areas.

Slim

[Smoke4320]

Per most of the manuf'ing folks (and Smoke) it says 400°F for 20 minutes. That's putting a cold bullet in a preheated oven. I'm thinking if you watch the bullets you'll find that's pretty close to the 10 minutes AFTER the powder has started to melt giving it a shiny look.
That is the reasoning. 20 to 25 minutes putting cold 100 to 200 grn bullets into preheated oven.
Larger bullets will take more time to get up to the shiny stage before the "10 minute " cure time starts. 250 to 300 might be as long as 30 minutes. Ect, ect

[charlie b]

I believe that's why Eastwood has the additional time for baking. 450F until the powder gets 'shiny', then 20min at 400F. The first part for me always took about 3min.

Now days I put them in for 23min at 400F using Smoke's powder. Same results. Shiny after about 3min. The coating still does it's job even with gas checked rifle bullets at 2400fps. Plain base at 1500fps.

[mnewcomb59]

I use an oven thermometer and a convection oven.

Baking Smoke's powders at 400 for 20 minutes gave me some problems with high nitro powders like Titegroup. Smoke's carolina blue turns green and soft after a year or so on the bullet bases. Recent tests of 25 minutes show no such problem so I have been baking longer. My problem happened with relatively small bullets (125 gr) , which would have reached part metal temp of 400 relatively soon.

I bake all bullets 25 minutes now. I have also experimented with water dropping after PC and the longer bake time gives more effect on AC alloy and WD bullets lose less hardness when WD again after PC if they were baked longer.

400 is the bottom end of any heat treating effects and is good for an additional 1-3 BHN depending on antimony percentage. I have successfully baked as high and long as 425 for 25 minutes and the PC looks great and passes smash and nitroglycerin exposure tests. 425 really gains some hardness over 400.

[Budzilla 19]

High velocity rifle boolits get a one hour bake at 425*f , pistol boolits 25-30 minutes at 425*f.
This is after the powder coat paint becomes glossy. Then both styles are splashed in ice water after baking. Works for me. Hammer test has never failed.

[GregLaROCHE]

I put my boolits into a cold oven, turn it to 400F and the timer for 45 minutes and forget about them. Works every time for me. If you are using higher temperatures, that my cause the powder to break down.

[Taterhead]

If there's such a thing as baking too long then I haven't seen it. I heat treat after coating and sizing. Coated bullets spend an hour at about 415-420F then quenched (Smoke's powders). Zero issues whatsover and no difference between the coating before or after the heat treat. Well into 5 digits of quantity this way.

Probably has something to do with what was going on between coat 1 and 2.

[FrankJD]

I intentionally "overbaked" 35 min @ 435F. Cooked and singed the Eastman Gloss Clear powder.

[brassrat]

I generally set for 15 minutes at 400* on cold oven and works fine. When its hot, I bring it down to 10 or so. Getting them to coat is a pain but not baking. Never tested them.

[oley55]

If there's such a thing as baking too long then I haven't seen it. I heat treat after coating and sizing. Coated bullets spend an hour at about 415-420F then quenched (Smoke's powders). Zero issues whatsover and no difference between the coating before or after the heat treat. Well into 5 digits of quantity this way.

Probably has something to do with what was going on between coat 1 and 2.

What method have you used to measure the BHN of you heat treated/PC'd boolits?

[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!