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Ball Mill Barricade


LiamPyro

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I have recently been re-configuring my pyro workshop, stocking up on supplies, and gathering formulas and information. One thing that came up is where to run my mill and how to barricade it. I have a 3lb Harbor Freight rock tumbler with a modified drive shaft and will be using ceramic media with it. In the past, I've run my mill in my basement, which I now realize is unsafe. Also, I was using chrome-plated steel as media and it began to rust, meaning that either the coating wore off or it never had a coating in the first place. I stopped using it for obvious reasons.

 

Now, back to the milling location. I have been trying to find a good place to run it that will reduce the effects of an accidental explosion. There is a large hillside above my house, but it is thick with trees, bushes, and dry grass that could easily catch fire in the event of an explosion. The other option is next to my house, between a dirt rise and the side of the building. I figure if I dig a nice deep hole and surround it with sand bags with a piece of plywood or something on top, it should absorb much of the blast and direct the rest of it upwards. Also, it would contain most of the milling media and any shrapnel. Would this work? Also, the main concern besides safety is not having the police called. Is there any way I can reduce the noise that would be produced in the event of an explosion? I have no clue how loud 100 grams of mill dust in a rubber drum would be, but I'm sure it would make a bit of a boom.

 

If there is already a topic discussing this issue in-depth, then if someone could put a link to it that would be great. Otherwise, I think this is a relevant problem that isn't discussed much and certainly needs a thread of it's own.

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I think for sound you have to contain the blast pressure / wave completely and then just vent it slowly e.g.:

I'd go for tyre lined pit with wooden lid covered with sandbags and a long vent line coming out of bottom of pit and going at least few meters at that depth.

 

Also, blasts under water get absorbed quite well, but that would ruin the mill (e.g. if placed in watertight container and that submerged).

Edited by deer
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That's a very good idea, but why use tires to surround the pit? Is there any reason why sandbags wouldn't work as well? I like the idea of having a vent, I think I'll incorporate that into my design. Thanks for replying!
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The idea with tires is to contain and direct the force. I've used a similar concept, with a buried pair of cement pipes. If it goes up, it really goes, up, so to speak. I "close" the milling pit with a couple of rigid glass-wool insulating boards, keeping the noise down, but i dread the day i have to clean up after an accident. There will be bits of board everywhere. But it's so soft it's hard to get hurt by even if your standing close, and the stuff that gets thrown out (mill parts, media, so on) will be directed in a quite steep upwards angle. I cant make the pit deep enough to make it "perfect" but the shrapnel shouldn't be able to leave the property, so the velocity of the returning bits should be low. As in close to terminal, which while quite possibly painful, shouldn't be able to cause actual trauma.

 

Sandbags should work, the finer the sand, the better. Less mass to be hurt by, when it gets shot everywhere.

B!

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Alright, I think I'll go with a pit surrounded by dirt sandbags with a sheet of tin roofing or plywood on top. I might add some kind of vent in the dirt around the pit to help dissipate the hot gases that would be produced in the explosion. Would it be a good idea to pile sandbags on top of the cover to help contain the blast? Or does this make it more dangerous? Thanks for the good suggestions!!
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Your main concern should be shrapnel and stuff getting caught on fire. I'd add the bags to ensure the plywood doesn’t go flying and to stop any lead balls which might penetrate it.

 

As for tyres - basically because discarded ones can be had for free, they're rugged, flexible and come in various sizes. You'd need something to line the pit anyway.

And if you leave some gap, between the tyre and pit walls, they can even act to absorb some of the blast. It's their original purpose after all - to inflate and amortise bumps.

 

Just keep in mind, that if they get caught on fire, you'll be producing huge black smoke pillar.

Edited by deer
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I see, thanks for explaining. How easy is it for tires to catch fire? Would smoldering debris make them burst into flames?
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Oh.. that was so long ago I don't even remember. I think it was fairly difficult and you had to throw them in a camp-fire to actually start them burning, but when they get going it's quite intense. AFAIK ground up tyre rubber is even used in some black smoke compositions. Just grab a strip of exploded tyre somewhere along the road and test it.

 

They even do this and its fine:

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Tire rubber will burn, but it wont catch fire from an explosion of the sort we speak of here. The fireball from a BP wont set fire to a Styrofoam cup, the heat just doesn't last long enough. A slow burn, is a whole different thing.

B!

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Gotcha. And one last thing, how deep should the hole be? I was thinking about 1.5 to 2 feet deep, is there any reason to have it a different depth? Also, as far as the width goes... should I make it wider to allow somewhere for the blast of a potential explosion to go, or is it fine just to have it large enough to comfortably fit the mill?
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The wider it is, the deeper it should be. Your trying to force whatever gets shot out in an accident to go as straight up as possible. My "Pit" is about 1 meter deep, and 1.2m wide. Ideally it should be more like 2 meters deep, or, only half as wide. Well, ideally it should be only wide enough to fit the mill, and deep enough to make everything go straight up, but anyway, thats the setup i got, and what i wish i had.

 

The reason is ballistics. Something trown out at an angle maintains it speed a lot better then whats thrown straight up. A good size milling media that went straight up, and comes back down will just hurt when it hits you in the head, where the return trip ends. If it goes 100 meters straight up, or 2 kilometers doesn't matter, on the way down it has the same top speed. Where as something thrown out at an angle will arc back to earth, and will maintain a larger portion of it's energy, and just might end up killing someone a kilometer away. Very unlikely, yes, i agree, but in the same way as it prevents lethal damages, it limits every other kind of damage as well. A loud noise might be easier to explain, then the broken windows on the neighboring properties.

B!

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Cool, I had never thought about how the dimensions of the hole would affect the media and shrapnel. I had been focusing more on absorbing the blast. Thanks for your help!
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