Low Cure PC Paint Question

[18Bravo]

My oven seems to fluctuate when it gets up around the 400 degree mark. Plus or minus 25 degrees in not uncommon. While I don't think this is a real issue for baking the PC it is still a bit bothersome. I've taken Smokes advice and extended the bake time from 10 to 16 minutes to compensate for the temp changes. The problem I've incurred is that soft lead, 8 to 9 BHN, will slag at these higher temperatures if not constantly monitored.

Several paints, Specifically RAL paints, have a lower cure temp of 340 to 350 degrees. 10 minutes is still the recommended bake time. My oven will hold these temperatures without issue for hours. A lower temp would hopefully alleviate the slagging issues with the softer lead alloys. So here's the question...Do low cure paints work with the same effectiveness as those that bake at higher temperatures?

[bangerjim]

Pure lead shold NOT even come close to sagging at 400F. Pure melts muchhotter than the harder alloys we use. Pure melts ad 622F!

Sagging is caused by using a standard oven with hot spots over the heating coils. Convection ovens give an even heat.

I have only used 400F for 10 min powders (MOST commerciasl powders) and they all work prefectly in a good convection style oven. No run, no drips, no sags, no errors.

Check the temp profile of you oven.

banger

[18Bravo]

Pure lead shold NOT even come close to sagging at 400F. Pure melts muchhotter than the harder alloys we use. Pure melts ad 622F!

Sagging is caused by using a standard oven with hot spots over the heating coils. Convection ovens give an even heat.

I have only used 400F for 10 min powders (MOST commerciasl powders) and they all work prefectly in a good convection style oven. No run, no drips, no sags, no errors.

Check the temp profile of you oven.

banger

banger,
Yes it quite possible the oven has a hot spot. However I have read posts on this forum concerning slagging issues. I'm not inferring that the lead is actually melting. I have a thermometer in the oven that has been check for accuracy. If you look at this link,http://www.lasc.us/castbulletnotes.htm, there is mention that WW will begin to get "slushy" at 463 degrees while pure led has a melting temp of 621 degrees. If WW get "slushy" at 463 it is probably possible for "saggy" at say, 425 degrees. With all that said, in your experience, can I use low cure temp PC paint and achieve the same results of the higher cure temp paints?

[Smoke4320]

18Bravo
if you are getting up to 425 in fluctuations why not try a small batch at say 380 degrees that way your hi will be 405

my convection oven will vary 20 degrees from switch on to switch off so I set it at 375 (it will hit 395 and switch off) and bake 16 minutes.. so far all my bullets shoot just fine I shoot mostly 50/50 with 2 % HSB

PS all my Powders except 1 are RAL and none I have found have a cure temp at less than 375 .. Might be some out there I just have not seen them yet

PS I rejected any that would not dry tumble so I was not concerned with their cure temps

[Smoke4320]

PS Bangerjim is also correct about the hot spots ..
my very first batch of bullets ending up a puddle in certain spots on the tray while others were fine.. 2nd nearly the same thing..
Got a convection oven then watched the temps several times till I had its on off points figured out then all was fine

[18Bravo]

Smoke,
Thanks for the advice. Curiosity and a desire to learn this new technique has led to a lot of unanswered questions. Just looking around at powders, I've seen cure temps range from a low of 340 degrees to the normal 400 degrees. Obviously a lower cure temperature would have its advantages IF the boolit reacted the same way as those baked at higher temperatures. I've taken your advise in the past with good results so I see no reason not to accept it again. Thank you.

[Smoke4320]

I am by no means an expert on all things powdercoating.. I learned and am still learning everyday..
There are so many variables to this process.. We post what seems to work for us then those have to be modified to fit Your situation ..
Couple of Things do seem to be consistant .. a convection oven with fan ON gives a better almost slick finish (when the proper temp is reached) std ovens in a lot of cases do have hot spots and cause consistency issues..
You have to find your ovens actual temp (not what dial or display says) plus its switch on and off points then work your cure times from there..
adding 3 to 6 minutes extra (when proper temps are met) does not seem to hurt anything at all

[RP]

Gremlin posted over in the oven temp poll thread about adding some clay tiles or bricks to you oven to even out temps for the most part. Post 21 I think it was. Stating they act as a heat sink this may fix your problem.

[prs]

Well, let me toss in a monkey wrench. I do not preheat the convection oven. With a new powder, I set the oven dial to where I have observed it register 400F on my oven thermometer. I watch the bake until the powder goes glossy. Then I set the timer to 15 minutes. I figure the metal shell of the oven is going to lose heat fast and that I can take advantage of even that first warming to let the lead soak-up the heat and become heated through out instead of just at the surface. My convection toaster style oven handles 7+ pounds of boolits easily and that about all of my 45ACPs that will fit on the two trays. Typically, it takes about 10 minutes to go glossy and 25 minutes overall for most powders. I have noticed no ill effects, other than electric waste, in baking up to 35 minutes total. I think the lead itself is a pretty good heat sink, if you actually get it hot through and through.

prs

[bangerjim]

Preheat or not.......up to you.

I preheat my convection to 400F, put 2 full trays of boolits in, wait until all the powder turns shiny, and the bake for ONLY 10 min. All are perfect, hammer-test proven, and look great. This baking for 20-40 minutes I read about is really not needed, but if you feel warm fuzzies doing it, when you could be doing 1-2 more batches of boolits, then bake for much longer. Most powders have specs of ~10 min, so why not use it. If it is good enough for the chemists and designers of the powders and the commercial powder coaters that do this for a living, it is good enough for my simple little boolits. And if all my boolits pass the hammer testing I do (pound into a cube!), I have no complaints.

But from what I have read, extra time at the specified powder's temp does not hurt the ingetrity of the powder. Just wastes your time and money.

Good coating!

[popper]

18bravo - shouldn't get any sag or slump @ 400 at all unless you have hot spots in the oven. Tin will lower the slump temp. I cooked a bunch (30 cal rifle) with Smoke's powder yesterday @ 425F. Worked fine. I've done the same with HF powder, no problem. Now if you approach 450F, I'd be concerned. My oven is a convection/PID home brew and works fine.