Ball Mill Media - alloy and shape

[otto]

OK, I've done a bunch of searching and reading and reading and searching and found some general direction but not much in the way of any thing specific. I've got a ton of lead and the attendant alloys and I'll be casting my own mill media. Here's my questions:

 

I've come into a pile of foundry type (very hard) and I am planning on casting a few buckets of mill media in straight foundry metal. I'm thinking there's an advantage in the hardness of the media as opposed to anything softer (as in reduced hardness with straight lead). My question is: will the straight foundry metal be too brittle? Is it heavy enough in relation to? Any plusses or minuses other than the expense of diluting the harder alloy? Just looking for opinions based on experience....

 

Next is the shape of the media. Balls are standard but cylpebs are popular in zircon options. I have the ability to cast balls, eggs, teardrops, pyramids, coins and "cylpebs". Any opinions on media shape in relation to effectiveness?

 

Thanks for the input and perhaps (if I have the time) I can run my own trials with different shapes and record the outcome but my time is pretty limited right now.

 

Of course if I can steal a barrel of zirc media this will all be moot; but until then....

 

Thanks for any opinions,

 

/m

[Bobosan]

otto,

 

Perhaps the attached .xls spreadsheet will help with your search on alloying. Foundry type is located midway down in the chart.

 

Media shape more often used with lead is spherical, probable reason being it is the most common casting shape with a smooth surface. Other shapes have been tried with other media types (copper pipe filled with lead, brass rod, etc.) with success. Trials with different shape lead media have not been performed as far as I know.

Lead Alloy Calculators 070612.xls

[MrB]

That .xls is great guide.

However, i used one of those lead hardness testers, and wheel weights seam to vary in hardness depending on the source.

Cant confirm with any other kind, but both stick-on, and clip-on was at-least a 2point sliding range, where stick-on was 6-8 and clip-on were 11-13.

My source was mainly weights for large vehicles, think semi-trailer combinations. (Swiftly stolen from the junkbin at the family workshop. Every other source have pretty much ran dry at this time. Which sucks. Buying lead for media is such a let-down.)

B!

[otto]

Thanks for the file bobosan. It will be handy even though I've familiarized myself with most of the usual alloys and their properties.

 

Seems like most of the alloy sense come from the bullet casting guys that are looking for something other than what might be the best milling media. Maybe someone that does a bit of each will chip in. I guess what I'm really looking for is any first hand experience in milling with different shapes (I've seen the copper filled with lead) and/or using a straight harder alloy as opposed to diluting it with lead.

 

I'm thinking if I absorb the expense of the undiluted alloy it will repay in a more efficient media; harder (plus) but not as heavy (minus) and guaranteed non-spark. So the bottom line is: harder and lighter or heavier and softer?

[Bobosan]

I do both...casting for shooting and milling. Your foundry type lead is plenty hard for milling but very risky to use as projectiles due to extreme hardness. Reduced hardness could be done with a pure lead percentage mix as your foundry lead already contains a large amount (23%) of antimony. Most boolit casters use clip on wheel weight lead that is water quenched for additional hardness. According to the chart, 3% antimony allows water quenched lead enough hardness for firearm use. .

 

For milling purposes, I use 75% clip on wheel weights plus 25% linotype, water quenched. Plenty hard for milling use, heavy and little wear. If I had pure lead it would be reversed, 75% lino to 25% clip on lead.

 

You can get your desired weight and hardness by working the ratios.

 

edit - to answer your original post, try the straight foundry lead as mill media. I believe it should do just fine. If not, you can always recast to a softer mix.

Reason we like the harder media is to reduce wear and deposit of lead contaminant in the composition. The harder media also mills more efficiently as long as the mill itself is optimized for peak performance.

Edited August 31, 2014 by Bobosan

[Arthur]

Balls and cylinders are the most usual media shapes, balls will usually tumble well but they grind to a range of particle sizes, rods or cylinders tumble less well (ultimately long rods will twist and knot up before wrecking the jar) but will grind to a narrower range of particle sizes.

[Arthur]

The original reason for "Typemetal" was that it expanded on solidifying so it filled the moulds accurately giving a cleaner impression of the type.

[otto]

bobosan, I used your alloy chart this morning and discovered I gain hardness faster than I lose weight with alloys. Seems to me I should use the hardest alloy I can cast for media. Whatever I choose will better than anything softer but never as hard as Zirc M, though it will always be heavier than that.

 

Arthur, the expanding on solidifying observation is helpful, I was going to make my own cylinder molds from some aluminum bar. I was hoping to be able to use one piece and just tap them out, but unless I polish the inside that seems unlikely. Now I'm thinking a two piece in the event I have to use a press to get the buggers out. Probably better polish 'em good anyway...

 

I poured a couple hundred balls in a Hilts .50 round ball mold yesterday. Very tight in the mold, I know now why they say "soft lead only" for lure molds in aluminum. It's only a matter of time before it gets dinged up from prying pieces out. That foundry stuff is unbelievably hard compared to the lead and WW stuff I've been used to. If I snap the sprues right away it's not too bad, but if they sit for 10 minutes or so I can barely break 'em without using a tool.

 

One last question: I wasn't going to water quench based on their natural hardness but now I'm thinking I can gain that much more. Is there a tipping point where I cross over to issues with brittleness resulting in chipping or breakage in a mill? I know brittleness in bullets is an issue but I'm not driving this stuff @ 2000 + fps. And would I have to quench right out of the mold or can I get 'em back up to 500 degrees or so in an oven and do it from there?

 

I probably should have started this in the tools/tooling section....

[Bobosan]

I would use your foundry stuff just as it is without quenching. The brittleness should not be an issue for milling media. As you pointed out though, it may give you fits getting the piece out of the mold. You could use a mix of foundry and pure lead to ease the mold release problem and then water quench to bring hardness back up.

 

What kind of mill jar are you planning to use?

[Arthur]

http://en.wikipedia.org/wiki/Type_metal

 

Just don't assume that lead wheel weights are really lead -the UK now uses other metals your country may use lead or other metals.

[otto]

I've been using an old Sears rock tumbler. I has a hexagonal rubber lined jar similar to the Thumblers model.

 

I am in the process of building an actual mill with a 6" PVC jar. My design will accommodate both larger and smaller jars but a 6" x 12" will be the standard and give me almost a gallon of capacity. That should be fine for now.

 

I've been hanging out here for a couple years just reading and learning. Haven't made much yet, just working on getting the correct knowledge, proper tools and safety equipment. Events of last year made me think very hard about whether I wanted to pursue this or not. I invested in some pretty heavy duty PPE for certain manufacturing processes and I'm reasonably confident that if something unplanned happens I'll at least be protected. There's so much great information here it's pretty difficult to get down a wrong road if you read, heed and proceed with caution.

[Bobosan]

I've been using an old Sears rock tumbler. I has a hexagonal rubber lined jar similar to the Thumblers model.

 

I am in the process of building an actual mill with a 6" PVC jar. My design will accommodate both larger and smaller jars but a 6" x 12" will be the standard and give me almost a gallon of capacity. That should be fine for now.

 

I've been hanging out here for a couple years just reading and learning. Haven't made much yet, just working on getting the correct knowledge, proper tools and safety equipment. Events of last year made me think very hard about whether I wanted to pursue this or not. I invested in some pretty heavy duty PPE for certain manufacturing processes and I'm reasonably confident that if something unplanned happens I'll at least be protected. There's so much great information here it's pretty difficult to get down a wrong road if you read, heed and proceed with caution.

 

The rubber lined barrels operate quietly compared to PVC but many millers use it. Those hex barrels are more efficient IMHO as the flat sides act similar to drop bars inside the jar.

 

+1 on your last paragraph.

[otto]

I've thought of the sound issue regarding that and when I had the Sears unit loaded with cartridge cases it was modestly noisy in the basement. I live in the country and where the BP mill will be placed the noise won't bother anyone.

 

Another question now occurs. If I were to continue to use that rubber lined drum, and I may from time to time depending on, what measurement would I use to determine the critical speed? I know that the shape offsets some of the lifting issues but @ 22 rpm I expect that a faster speed cuts process time.The liner is 7.5" across the "points" and 6.375 across the "flats".

[Bobosan]

Maybe the following link will help.

 

http://www.pauloabbe.com/size-reduction/resources/mill-speed-critical-speed

 

For the 15lb Thumbler drum, critical speed is roughly 100 - 109 rpm using .500 media size and varies on what part of the drum inside you use for calculation. Desired jar rpm is usually 55% - 75% of critical speed, average 65% commonly used.

Edited September 1, 2014 by Bobosan

[Mumbles]

You might need to use some trial and error on a hex jar. I've heard the normal optimum speed calculations are quite off, since they're based on a round jar. I generally hear values in the 30-40rpm region. Luckily with homemade mills, it's as easy as swapping out pulleys.