Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

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pete
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by pete »

I've worked around but have not had any hands on experience with ball mills used to crush rock down to about 100 mesh during ore extraction in copper / gold mines for many years. There's also what are called rod mills that use long lengths of steel rods to crush the ore while the mill is rotating. Either type uses hardened steel and there constantly reloading fresh balls or rods to keep up to the old ones wearing out to nothing. The rods or balls rub against each other so even if your doing softer material than rock there still can be a high wear rate. Zinc / aluminum or other softer material likely won't work for long and may or may not cause you contamination issues. I think if it were me? I'd maybe visit some large equipment repair companys and see if you can pick up some large scrap ball or roller bearings. Tracked equipment uses a lot of them. Abrasive saw cut the inner race out and you'll have very hard balls or rollers at a cheap cost and a bit of work. A bit more information is needed though. What material are you trying to run through that ball mill? Rpm is crtical on mills of that type since too slow and the process takes forver, too fast and the balls won't fall due to gravity. There's other materials used for machine part deburring such as ceramic stones that might work for you depending on what your ball milling. Even milling of soft wheat to make flour the old way used hard grinding stones to mill it. I'm still only guessing, but in my honest opinion I just don't think your chosen casting material is going to work very long or all that well. It's the hammering of the hard and heavy as possible material falling against the softer material to be ground that does the work so that's why they use something as heavy and durable as possible that can be found at an economical price.
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Harold_V
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by Harold_V »

What pete said. If the speed of a ball mill isn't correct, grinding is accomplished by attrition instead of hammering, the result of the balls falling from the apex of the curve of the ball mill. Without the dropping of the balls/rolls, grinding is quite slow.

I had one large piece of ore that was introduced to my ball mill and it was reduced to powder only after many hours of running, which clearly showed the relationship of size of the feed stock and the size of the balls in use.

The rollers I spoke of that were used in my ball mill were from large bearings, as were the smaller balls I used. I was fortunate to find a source for used balls (from ball mills), which was the source of the larger balls I used. Too small for large ball mills, but a perfect fit for mine.

The level of noise produced by a properly operating ball mill is hard to imagine. I had to wear ear protection while mine was in operation.

H
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pete
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by pete »

You should hear what multiple 30'-40' diameter balls mills sound like Harold. And today most large ball mills are using rubber faced internal cast steel liners on there mills to try and keep the abrasive wear down. Secondary is a real noise reduction, but there still more than loud. We used a variety of sizes for the balls since there were a variety of different ball mills being used depending on exactly where there location was in the process line they were. Anywhere from 2" up to around 8" in diameter. Anything entering the mills was 6" or minus that for size, and that all got reduced to 100 mesh per square inch or smaller. And doing 60,000 tons a day is only a medium sized mill today. When they shut the mills down to do repairs or liner changes it's not at all uncommon to hear a steel ball explode inside the mill from stress and internal heat build up, and that's after still using water to cool and help move the fine rock through mills and throughout the whole process. Proper and efficient ball milling is a pretty scientific process and it's not quite as simple as it seems.
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by Bentworker »

If you decide you want to go with graphite you might check ebay for Cadweld molds. Cadwelding is not as popular as it once was for electrical contractors and electric utilities, alot of the old molds get pitched in the trash or resold. Might be a good cheap source of graphite.
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CaptonZap
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by CaptonZap »

Since you sound like you are conversant with metal casting, green sand casting would probably be a way to go.
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CaptonZap
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by CaptonZap »

PS.
With a suitable sized flask, you could pour six or more at a time. Since the ball mill will not care if they are perfectly round, or cylindrical, you don't need a perfect surface on them. KBond sand, http://castinghobbyfaq.bareboogerhost.com/kbond.shtml, can be made in small batches, or traditional green sand might already be in your inventory.

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Glenn Brooks
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by Glenn Brooks »

I was thinking of large steel ball bearings when I read Earlgo's post. Would 1" steel
balls work? If you use rollers, I'll bet junk yard axle material would work great. Cut into "1-2" diameter, cut into 1" lengths. I've found used shafting often is either work hardened through use or, if mechanical shafting, some form of high grade steel due to the original design conditions it was used. Sometimes junk yard materials can be good by default!

Very interesting project!

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RogueRose
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by RogueRose »

Harold_V wrote: Sun Sep 24, 2017 1:47 am
RogueRose wrote:I am curious as to what you think about using cylinders vs spheres as the cylinders would be easier to make.
I have limited experience with ball mills, having built one to reduce ½"- crushed gold ore to less than 200 mesh. For that process, I used a combination of balls and rollers, all steel. Ball size varied from about 1½" to about 5/8", and rollers were no larger than 3/4" diameter and about an inch long, no longer. For me, it worked exceedingly well.

Ball mill.jpg

You're going to get considerable wear with soft materials, perhaps contaminating the substances you wish to mill. You might be well served to explore other options if that would be troublesome.

H
I missed this post some time ago and am very interested in making a ball mill (or some other type of mill like a planetary mill - these are AWESOME!!). What is the container made of, the vessel that holds the grinding medium and material to be ground? I've seen some made of ceramic which seem to be the best choice but I would suspect that they are a little more expensive and then I guess there is the option of steel (of which there are almost countless choices in type, a hardened steel would be best).

I've seen people create make-shift mills with old glass pickle jars or even plastic peanut butter or mayonnaise jars so they are probably made of PETE plastic. I've used old paint cans, the gallon cans made of thin steel that were grinding aluminium with steel balls. The walls eventually were eaten through (in a couple places) with about 20-30 hours of usage so that didn't work out too well. I have cut a 5 gallon bucket into a strip that would fit on the inside of the container and the edges fit just about perfectly. I think the material is resilient enough to withstand the abrasion of the aluminium and steel but would like to come up with a better solution.

Grinding medium has been one of the more difficult things to find without breaking the bank. I'm torn between using larger sizes (like 1/2" - 1" bearings) or smaller sizes like 5mm - 12mm (just under 1/4" and 1/2") and settled on 10mm due to price of $10 for 100. I also have steel BB's which are .177". Now I'm wondering if it would be best to have a mixture of all sizes so that the small ones fill in the gaps between the larger ones. It seems that the grinding happens where the material comes in contact with the grinding balls.

Then there is the option of buying long rods, either smooth or threaded, and cutting pieces into desired size. IDK if these rods would be better than balls or maybe better in conjunction with balls.

Anyway, I don't mean to hijack my own thread, but this is another topic I am interested in. Maybe I need to start a thread dedicated to this..
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Harold_V
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by Harold_V »

It is important that you understand the relationship between feed size, drum speed and ball size. If you ignore those things, you will experience less than good results unless you are very fortunate and happen to hit on a good combination. Wall thickness of your mill is important, too, just like using an anvil. If you use a can, for example, you get almost NO hammering. Same thing if you run the wrong speed. It isn't the intimate contact of the balls (or rods) with the material that does the grinding--it's the dropping of the balls, hitting the material against the housing (anvil).

If you disregard these things, what ever you hope to mill will be reduced only because of rubbing, which is a very long and slow process, and is just as destructive on the mill as it is the material.

H
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pete
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by pete »

Limited grinding action happens when the material your grinding is worked against the harder balls or rods. However that's not how a ball or rod mill actualy works. It's the drums speed of rotation that lifts the balls or rods almost to the apex of the drum and then the balls or rods falling due to gravity that does the majority of the work. It's like a whole bunch of hammers working against the material and slowly crushing it's size down to what's wanted. BBs aren't going to work, there's a relationship between the drum size and the ball size and the hardness of the material your milling. Harder material obviously takes a harder hit to start reduceing it's size, that harder hit takes a bigger drum size to lift the balls or rods higher so they fall farther and that's what gives the harder hit. I'd suggest you go back and reread everything that's already been posted here since all your questions have been answered already. And afaik you still haven't said what your trying to mill.
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