Powder Coat scratching off with thumbnail

[Traffer]

Hi folks,
I have recently run into a problem. Last couple of batches of PC'd bullets ...scratching off with thumbnail. All kinds...Smoke's Clear, Translucent Copper, HF Red and some "Cardinal Silver"?
I did two layers this time one above the other (22lr bullets) and baked them at 400° for 30 minutes because of the extra layer. (air space between baking sheets)
The time before I did one regular layer 400° for 20 min. Same thing.
Bullets were not touched from mold to PC.
Could I have baked them too long? No sign of discoloring. They look great. Just no integrity to the coating. I am stumped...
Any ideas?

[Conditor22]

If you are water quenching the boolits after casting you may be contaminating the boolits
or you might be contaminating them somehow between casting and coating.
Your oven may not be reaching 400° you should test the temperature
Maybe you need to prewarm your boolits on top of the oven to remove possible moisture (make sure they are not too hot or you'll just get a glob of PC when you drop them in the container) If you can handling them barehanded your good
Manufacturers say to bake PC for XX min after either the metal temp reaches XXX° or the PC start flowing. IF the PC isn't baked long enough it won't reach a full cure and could be affected by smokeless gunpowder. I bake for 25 min in a preheated oven.
Are you using a convection oven or regular toaster oven? A toaster oven can't handle large batches.
A friend soaks his boolits in acetone, dips them out with a spoon onto a clean towel then filters the acetone with a coffee or paint filter so he can re-use it multiple times. After the boolits dry he warms them on the oven and gets perfect coverage even in75% + humidity.
I wouldn't suggest going 2 layers unless you needed to build up the boolits diameter. IF the first layer fails a second layer won't help
Cardinal Silver has always worked for me, it's the easiest to use PC.

[Traffer]

Well, this is what I found out:
I had the built in temp control and an add on thermometer which were both in perfect sinc. When one was 350 so was the other. 400 was 400 on both. So I figured it was very unlikely that they would both be off the exact same amount.
But I checked it with a different thermometer and got a very different reading. So I went and dug up an old faithful thermometer that I know is good...
Discovered that my toaster oven and the thermometer I had attached to it were BOTH OFF by 90° F. Unbelievable as it was, continued to test at different temps and sure enough from 75° to 100° off. I was actually baking them at 300° instead of what I thought was 400°.
That leads to another question...
Once the PC is baked and cured, can re-baking it make it re-flow and re-harden?
I'm afraid I am going to have to remelt a couple hundred bullets that I cast which are not baked well enough.

[cwlongshot]

I agree there is some contaminant at play here. I quench allot and make it a habit to always use fresh clean water. I also make it a habit NOT TO allow bullet contact with anything but my basket and large dedicated metal spoon.




Properly applied and baked PC will not easily come off.

[Dragonheart]

It is not a problem to recook, in fact that is the recommended method by the powder manufacturers to do a multi coat. It's called a "Partial Cure" where you do a first coat and cook until the powder obtains a smooth coat usually under 300 and then do a second coat and full cure.

However, even 300 degrees should have set the powder where a fingernail wouldn't scratch it off, so you may have a contamination issue also. I would just recook and see it that fixes the problem, if not it's contamination. Good luck.

[cwlongshot]

EDIT:

Yes i believe you can just rebake. In any even nothing lost in trying and testing.

Good luck!

CW

[popper]

You can re-cook, no problem. I've cooked for an hour for heat treating, no problem. IF they get cooked at too high a temp, the PC shrinks and peels off.

[Traffer]

As far as contamination...
The bullets were not quenched or touched by anything from mold to PC, except the soft cotton cloth I dropped them on out of the mold. There was no lube or release agent in the mold yada yada...
The only other thing I can think of is that I am now using dead soft lead. Could it be coming off because the lead is soft?
Will try rebaking them and see what happens.

[Conditor22]

Soft lead is not a problem, I've coated many round balls and mini balls for black powder

[fredj338]

I have never had PC flake or scratch off. I always smash test & the coating is solid. I bake @ 400 for 15m, water quench out of the oven, regardless of whos powder I use.

[marek313]

I noticed that some PCs claim they only need 10 mins at 350 to bake properly but as a rule I bake everything for 20 mins at 400 and then water drop at the end. The only time I saw PC flake off is when not baked hot enough and long enough which sounds like what you found. PC will turn darker as its baked longer unless your doing black but even then it will lose some shine before its unusable so you should be able to tell when its done. Batter bake it little longer then not long enough

[Traffer]

I think the problem is solved.
Started using a different toaster oven and thermometer.
One caveat:
I had some coated smokes clear that turned out milky white instead of clear. I rebaked them with the better heat control but they stayed milky white...and somewhat scratch-offy. I guess I will never know. The batches with new oven and thermometer are coming out correct.

[Petander]

The only other thing I can think of is that I am now using dead soft lead. Could it be coming off because the lead is soft?

.

A stupid question but how quickly after coating are you testing? My "dead soft" bullets are seriously soft for a couple of days after coating. Maybe you are actually scratching the soft lead and the coating comes off with the lead?

[Traffer]

Well I still have them so I went back and tested them again. SURE ENOUGH. The PC is hard. But with only a thin coat of PC, the lead underneath is scratching. Giving the appearance of having the PC scratch off. If I scratch without breaking the surface they are nice and hard. The ones with thicker coats are much more resistant.

[Smoke4320]

Traffer. Rebake them at the correct temp 400 degrees for 20 minutes then retest.
Pretty sure your issue will be corrected

[Traffer]

Traffer. Rebake them at the correct temp 400 degrees for 20 minutes then retest.
Pretty sure your issue will be corrected

I have already rebaked them correctly and can't seem to find the ones with clear on them. But that brings a question to mind:
You most likely do not know the answer to this but...
Since I swage the full bullet after powder coating (not just resize) I wonder what rebaking after swaging would do? Or even if there may be some benefit to deliberately underbaking them until after swaging then rebake them. I will have to experiment with that.
I have some that are swaged with questionable bake on them that I can toss in the next batch I PC. It will be a few days cuz wife and I are going on a trip for a week.

[Traffer]

I found the clear ones (not swaged) They have been rebaked at 400 for 20 min and have remained a bit milky colored and dull grey. But they are hard and not scratch-offy so all is well. The shiny one is a raw lead bullet. The grey one has clear PC. And the other one has different PC and has been swaged.

[Smoke4320]

Ok now we are getting somewhere ..
By swedging after powdercoating you are probably displacing too much lead and causing the coating to loose adhesion.. ( I did the same thing once sizing down 227 to 223. just too much leading shifting around and the coating would let loose)
I would try swedging FIRST then coating and if needed bumping in the swedging die for the final fit.

[Traffer]

I don't think that is it. The bullets only get swaged a couple of thousandths. And the powder coat was scratching off before I swaged them. I am convinced this has to do with at least 2 factors. One being my oven was off by 90° and some unknown factor. The good news is that it is not doing it anymore. If worse comes to worse I can melt the questionable bullets and recast them from that batch. I am sorry for troubling you and everyone else with this. I should have just figured it out myself. Most of the subsequent posts I made were just for clarification.
All other times I have used the same powder and process everything worked well. So this is no big deal.
Thanks for taking the time to try and figure out the problem for me. I will keep in mind that the swaging process can cause a problem with powder coat.
I will do more experiments when getting back from the trip. Will try to incorporate all the suggestions and see if I can narrow it down.

[Conditor22]

Oven temperature settings will vary greatly according to the surrounding ait temperature (due to the location and type of thermostats most tabletop ovens have)
I check my oven temp every time the surrounding temp changes and adjust the dial accordingly until I built and installed a PID takes the worry about temperature out of the equation.

When you say "swage" I would assume you mean size as in push through as sizing die.

All the powders I use say to bake at XXX° for XX min after a condition is met 1) the alloy/boolits reach XXX° or the PC starts to flow.

After reading that and some experimenting I bake all my PC'd boolits for 25 min @ 400° to ensure I get a complete cure.

IF you size before coating be 110% sure the die is completely free of any lube.