Re: Numerous Ball Mill Questions


<steve.g.hall@xxxxxxxxxxx> wrote in message
news:1153079138.595144.192620@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

First, I have noticed that 440c stainless balls are readily available.
I know this is one of the hardest stainless alloys, and is also very
corrosion resistant, frequently being used for knife blades. Will
nitrates attack this alloy? How about chlorates and perchlorates?

Nitrates will slowly attack 440c or 316 stainless, but simply washing the
media between uses will keep it pristine.


Secondly, I have seen that many people "roll their own" PVC milling
jars from PVC pipe and plumbing parts, due to the low cost and great
availability. I have noticed that PVC can generate and hold large
static electric charges. There is also the well known property of PVC
that causes it to shatter into dangerous shrapnel in the event of a
'mishap'. Would it be safer to use some type of HDPE plastic, such as a
large HDPE bottle, for BP milling?

HDPE would be safer in the event of explosion, but it's slippery. HDPE jars
usually require the use of lifter bars to guarantee the media will not slip
in the jar.

Also, I have seen ball mills and ball mill 'jars' that are made from
metal, with a plastic or hard rubber liner. They are generally six
sided rather than round, and the manufacturer claims that this promotes
much faster and more efficient milling action. Any comments on this?

The hexagonal geometry is simply another way to effect the function of a
lifter bar. If the media cascades properly in a round jar without lifters,
it will mill as efficiently (as fast) as a hex jar or a round one with
lifters.

Would anyone else worry about the outcome of a BP explosion in a metal
milling vessel, or is the chance of this so remote with brass or lead
media as to be of no concern? Personally, I would feel safer with a
HDPE jar.

The media isn't so much of a projectile hazard. The jar is. Don't use
metal containers for milling BP.
Don't expose your body to PVC jars, either. We blew up a 6" jar
deliberately. The 3/4" lead media traveled only a short distance. PVC
shards flew over 100' from the blast.

I was also wondering what sized media would be optimum for a 6" and a
9" diameter ball mill. I assume 1/2" to 5/8" media would be fine.

1/2" to 5/8" is perfect for a 6" jar, and will work nicely in larger sizes.
Reduce the media size as the jar size goes down, consistent with keeping the
media particles heavy enough to crush the material you are grinding.

LLoyd


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