Powder Caking in the mill

[Eagle66]

I just did my first BP run in my new ball mill, and ran into the problem of the powder caking in the mill.

 

I have a 1 gallon jar with 30# of 1/2 inch lead ball media, which fills the jar half full. The total powder charge is 600gm, about 1 qt in volume. The KNO3, S, & willow coal were all airfloat milled before mixing. I ran it 3 hrs @70rpm. Air temperature was in the mid 20'sF. I ended up with a lovely cake in the bottom of the jar. When I chipped the cake out of the jar, it broke up pretty well and looked quite uniform and just a touch lighter color than the "raw" mix. A lump of it burned with a very nice flash.

 

So. I have several questions about this.

 

1. What can I do to salvage the batch? Maybe it's good and all I need to do is break up the lumps, run it through my 100 screen, moisten and corn it? Maybe not.

2. If not, should I mill it again and how long?

3. What can I do to prevent it in the future? From what I've read here, moisture in the mix is probably the problem. How can I dry it out before mixing?

 

BTW, this lot & the next 2 will go to feed my BP guns, but I fear that the problem might come up again when the powder is for fireworks.

 

Thanks in advance for your help.

 

Mark

[schroedinger]

There are two reasons for it doing that.

 

You had some moisture in xour powders. If that happend dry itand mill it again. Next time dry your chemicals before millung.

If y8ur chemicals where dry, then be happy:

Finished BP is known to start sticking to the walls. So if that happens, you shoukd have supperior bp

[dan999ification]

Yep it's wet, most likely the nitrate or charcoal usually the charcoal. A slow cooker or crockpot will dry them just fine. Weigh before an after you may be suprised, I was.

 

You can Just break up the cake and re mill it for a few minutes to get powder. If its fast enough screen it and use your normal process to granulate.

 

Dan.

[LambentPyro]

During your mill session, take the jar out once in a while and smack the bottom and the sides with a rubber mallet. If it cakes up down there, it's technically not milling and your grinding your media up and wasting time and electricity.

[FlaMtnBkr]

Even with dry chemicals it will clump eventually. Super fine powders often pack down under it's own weight and lock together into rock hard pieces. A lot of times clumping is an indication the run is done.

 

If using in a gun you should qualify your powder in some way. It is easy to make powder that is hotter than the commercial stuff you would buy. I would put the minimum charge the rifle recommends and chronograph it and see how it compares to your standard charge. Even before that you can get a feel for how it compares. If you have a 3" fireworks mortar put 4 or 5 g in and a baseball and time it. Use the same weight of powder and do a couple times and average the time. Then do the same for your commercial powder and see how they compare.

 

If your powder is acceptable I would make a few batches and then put it all in the mill jar minus the media and mix the various batches together. If you press and corn you can also add some graphite and polish your powder for pretty grains. Just put on a fine screen when done and get rid of any fines that may break off.

 

I also would put some on a piece of paper and light it with a fuse. Good powder won't burn the paper much and won't leave a ton of residue. I'm sure you know you need to clean the gun out after shooting or you will have a rusty mess. Quite a bit worse than BP substitutes like Pyrodex as the BP residue pulls water out of the air and keeps the metal wet.

 

Just some things to think about.