Ball mill question

[braddsn]

I have been ball milling my bp the same way for a couple years now. What I am wondering is, 1) Is my setup optimum and charged properly, and 2) Am I running my mill long enough? First, I built my ball mill with the plans Ned has over on FW. It's a heavy duty mill that uses a Thumler's barrel, turns at around 65 rpm's. It is half-full of 50 cal. lead balls. I charge with 600g KNO3, 120g ERC, 80g Sulfur, and 32g Dextrin. I run the mill for 2 hours. Feel free to critique, any input is appreciated. What say you Lloyd?

[Livingston]

Brad Ned built his mill based on Lloyds book if im not mistaking

[lloyd]

Livingston is correct. Ned went further to actually quantify the amount of raw, granular materials needed to compact back to the 25% 'fill factor' at the end of milling.

 

Ned and I are good friends. But even if we weren't, I would be forced to say that his layout with the Thumbler's Tumbler jar works just fine.

 

Lloyd

[braddsn]

Lloyd, how do my numbers look? I just want to know if in fact I am optimally charging my barrel. Thanks.

[lloyd]

Well, I can say that 50% full of the lead media is correct. But I cannot tell you whether or not the 600g of constituents is correct unless I know the gross capacity of the jar, OR that it's the same Thumblers' jar model that Ned is using.

 

IF it's a 1-gallon jar, or if you're using the same model as Ned, then (IIRC) a 600g charge is optimal according to Ned's testing.

 

Your charge is 832g. That sounds a little much to me, but longer milling would probably still reduce it adequately.

 

Please remember that all the figures I ever quoted were "optimal" according to the ball milling industry. Deviations from those quantities can still work, at the cost of milling efficiency (but not necessarily 'terminal fineness'). SEVERE over-charging will limit the fineness of grind, but my opinion is that an 800g charge wouldn't do that; just that it would take longer to mill.

 

Lloyd

Edited February 7, 2017 by lloyd

[Mumbles]

I am of the opinion that the optimal charge is going to be somewhat dependent on your materials as well. I'm particularly thinking of the charcoal. It's amazing how big of a difference different varieties can have.

 

I'd wonder if you could just measure the volume of say 1qt of gently sifted milled BP to get an idea of how close we are getting.

[lloyd]

That might be a way to estimate it, Mumb!

 

But, um, measuring the volume of 1qt should result in a volume of 1qt, no?

 

Heh! I'm betting you meant WEIGH 1qt of gently-sifted milled BP! <grin>

 

Lloyd

[braddsn]

Got ya, thanks for the input guys. Sounds like I am not too far off from being pretty efficient. I mill for 2 hours at the moment, I may try to bump it up to 3 or 4 hours and see if it makes a difference. I am pretty satisfied with my bp, but I also think it could improve some. It takes about 14% of shell weight to get a 4 incher up to 400 ft. I would like to be at more like 10%. When the 4th gets close and I go to lift all of my shells (around 400 of them), a few percent makes a big difference as to how much lift I have to make. I know that there are more variables, like exactly how the charcoal is cooked. I plan on trying Poplar, Sassafras, Black Willow, and Tree of Heaven soon to see how they compare to ERC.

[lloyd]

I lift 4" shells with 6.25%-8.25%... hmmmm...

 

Lloyd

[a2l]

As I want to get back into the hobby and build a durable ball mill this time I got a couple questions for the knowledgeable ones here.

Sorry to hijack this topic but I can't post a new one since I'm a new member :-(

Here goes:

 

1) I have an 18mm rod lying around that I can use as axis but there exists no heater hose with that diameter. So I had the idea: would shrink tube work instead? There are ones with glue on them already. I'm not sure if the grip would be sufficient. What do you think?

2) For a jar I had in mind to use this one:

http://www.curtec.com/uploads/Product%20thumbs/7004.jpg

It's used for canoeing and it's got a nice diameter of 8 inches, and volume 0.8 gallons. it's made from HDPE so what I wonder is: is this dangerous in terms of static electricity?

I've yet got to feel it in my hands to see if it seems durable enough, since I know HDPE jars can be... squishy.

If the wall of the jar is thick enough, would this jar be a good idea?

Thanks guys!

[lloyd]

A2I,

Heat-shrink tubing will not provide enough surface friction to do the job. Think of the rubber hose as a "tire". It has to grip.

 

You could use the self-sealing sort of heat-shrink to build the rod up to the correct diameter to fit (say) 20mm i.d. tubing, though.

 

But - um - why not just buy a shaft of the appropriate diameter? Is it that you already have the bearings?

 

In addition, HDPE is kind of 'slippery', and would probably compound your problems, unless you have good friction on the roller cover.

 

HDPE would be no more of a static risk than the PVC most folks use for their jars. Remember: All static generated within that jar will STAY in that jar, because it's a "closed system". If you're milling black powder, it's conductive-enough to equalize all charges inside.

 

Now, please understand that the whole jar could become charged to a high potential relative to the rest of your environment. It's always a good idea to use proper 'static management' behaviors in a pyro shop, and properly draining an object of its charge before opening it is one of the necessary practices.

 

Lloyd

[a2l]

Thanks Lloyd, appreciate it!

I guess there's no shortcuts, I'll buy a 5/8" rod. It was more that I'd have to buy new stuff instead of using what I already had. Plus it was already at appropriate length, so I'd not have to let it be cut. I liked your idea of building up of the shaft though!

And thanks for the static advice. I'll ground myself and the jar before opening it.