Ball mill under an iron dome

[poisonkiller]

Is it safe to put my (home-made) ball mill under an iron dome? The dome perfectly fits onto my ball mill (there's room above the mill) and I can barely push my fingers under it. I'm asking, because maybe in case of an accidental explosion it might fly off and cause more harm, than flying media would cause.

By the way, I would put it in a hole in the ground, but because the climate around here is quite moist, the hole would eventually turn into mud. And before making a waterproof hole, which would need some work, I want to explore the dome option first.

 

If I can, I'll attach some pictures of it later.

[TheSidewinder]

Safe?

 

In a word: no.

 

A ball mill explosion would send that dome flying in god-knows-what-direction.

 

And that assumes it doesn't shatter it first.

 

 

Go with the other option: Dig a hole and make it as waterproof as it needs to be.

[poisonkiller]

How unfortunate, it looked really good and blocked most of the noise as well.

[Swede]

This is a topic that doesn't get discussed too often... how to locate and operate a ball mill. Black powder and some star comps are about the only things that should be milled with the exception of lone chemicals, so the worst case should be a load of fast BP exploding in a jar full of heavy media. A big hobby jar might hold a kilogram of BP, a significant and powerful force.

 

A hole would be best, channeling the blast upward, with some sort of covering that would not fragment, but that might slow or deflect the media, which is probably going to be the greatest danger.

 

Lacking a hole what would be considered reasonably safe? Would a cinder-block structure lined with 3/4" plywood suffice? Maybe 2 plywood layers with foam board between them? With the sandwich glued to the cinder blocks with construction adhesive, it would form a sort of composite blast chamber that would soak up the energy, while not in itself breaking up into dangerous projectiles.

 

I use a pit for BP and other comps, but I suspect a lot of guys don't, and it might be worthwhile to toss out some ideas to secure a ball mill.

[NightHawkInLight]

This is a topic that doesn't get discussed too often... how to locate and operate a ball mill. Black powder and some star comps are about the only things that should be milled with the exception of lone chemicals, so the worst case should be a load of fast BP exploding in a jar full of heavy media. A big hobby jar might hold a kilogram of BP, a significant and powerful force.

 

A hole would be best, channeling the blast upward, with some sort of covering that would not fragment, but that might slow or deflect the media, which is probably going to be the greatest danger.

 

Lacking a hole what would be considered reasonably safe? Would a cinder-block structure lined with 3/4" plywood suffice? Maybe 2 plywood layers with foam board between them? With the sandwich glued to the cinder blocks with construction adhesive, it would form a sort of composite blast chamber that would soak up the energy, while not in itself breaking up into dangerous projectiles.

 

I use a pit for BP and other comps, but I suspect a lot of guys don't, and it might be worthwhile to toss out some ideas to secure a ball mill.

I am in the process of setting up a new workshop and haven't gotten quite so far as the mill setup. I have a large plastic tub with 1/4" walls that was the shipping cover for a large engine. I plan on using that hinged on a plywood base with perhaps a sliding lock. In the event of an explosion it likely would shatter, but I intend for it to be more of a protection from the elements. My mill jars are rubber so ignition would not result in much of a concussive explosion compared to other more rigid confinement.

 

I very highly doubt that heavy lead media would fly at a velocity capable of causing any injury at all out of a semi soft container. If you are using a jar such as PVC that can withstand much more pressure before shattering it may fly moderately fast, but I would be more worried about the PVC itself. Media within a jar has much less gas wanting to push it out of the way, and a much more aerodynamic shape to allow gas to flow around than do the walls of the jar itself.

[Bananaphone69]

Securing ball mills has always been a topic of discussion, and all ideas are worth examining, but to be honest, I read this and laughed...

[mike_au]

I used something similar on my first mill.

 

It was built on top of a small wooden table, I had a heavy steel box which would fit over it nicely in one direction but overhang by about 10-15cm on each end in the other direction.

 

I figured that if anything went up inside the relatively large gap at each end would be enough to the gases that would cause it to go flying off, and it should catch most of the shrapnel.

 

My new mill uses a timber lined steel frame which I think is a better solution, but I still suspect that the old one would have been OK.

 

If I ever decide that I don't want the box anymore (not likely, it is a really nice powdercoated, waterproof thing) I will take it out into a big field and test my theory.

[lostfido]

It just so happens that I am working on my lawn irrigation system this morning also.

Has anyone thought about using the large valve box for sprinklers as there ball mill containment system?

 

All you do is dig a whole and set the box in. Then you put the remaining dirt back around the box and tamp it down.

The cover fits tight enough to keep out the critters but loose enough that you can remove it by hand.

 

I have the 6lb mill from Harbor Freight and it would easily fit in this box.

 

What do you think?

[optimus]

I thought of anvil lifting when I saw this thread...

 

The op might want to check out a few anvil vids for a reminder of the power of BP : )

 

Seriously though, I do remember reading that the (lead) media didn't actually fly very far in the event of a catastrophic failure, so the main concern is any other shrapnel - correct?

 

Theatrical pyros sometimes use a 'b0mb tank' to collect flying bits - look at the bottom of this page:

 

http://www.hfmgroup.com/professionalsupplies/fx_tpl.html

 

Mabye this kind of mesh system would suffice?

[Swede]

It just so happens that I am working on my lawn irrigation system this morning also.

Has anyone thought about using the large valve box for sprinklers as there ball mill containment system?

 

All you do is dig a whole and set the box in. Then you put the remaining dirt back around the box and tamp it down.

The cover fits tight enough to keep out the critters but loose enough that you can remove it by hand.

 

I have the 6lb mill from Harbor Freight and it would easily fit in this box.

 

What do you think?

 

I know what you are talking about, and I think that would be a slick way to do it... stealthy, too, especially if you used UF cable and buried the power to the "pit" with a remote on/off switch. Maybe when it is in use, you could lay a bag of play sand over the lid, or even just ignore it - I doubt anything dangerous would happen with just the lid in place.

 

Drainage might be a problem. Bury the box on a layer of gravel, and be sure drain holes are in place. Otherwise, it sounds good to me.

[FrankRizzo]

Ventilation may become an issue with larger motors if the lid is secured. I've got a 1/2HP TEFC motor on mine that gets quite toasty even running out in the free-air.

[NightHawkInLight]

Ventilation may become an issue with larger motors if the lid is secured. I've got a 1/2HP TEFC motor on mine that gets quite toasty even running out in the free-air.

Good point, mine does as well, even in wintertime at 0 fahrenheit it's warm if the air is still.

[RUUUUUN]

How many pounds of BP do you mill in one batch?

 

How heavy is the iron dome?

 

The whole shooting anvils bit is extreme... You have to use granulated BP for shooting anvils, you aren't going to be able to achieve even slightly similar results from mill dust! The best I have been able to get mill dust to do is foosh with a giant flame, even with 200g of it in a pile. So, unless you have a pretty thick HEDP barrel with some very very secure end caps, I am very sure that it wouldn't do anything except make a small pop as the lip popped off, destroy/melt everything around the ball mill, and then leak smoke.

 

If you are really worried about it lifting; gap it and inch or two so you still have the benefit of protection and the gap would be large enough to vent any gasses that would be produced

[Mumbles]

You might want to try some burn rates under pressure tests before making assumptions like that. It will explode. With careful confinement, even a polumna of mill powder can be made to explode. BP has a high DDT volume/mass as it were. More of a self confinement mass, but same general concept. It is somewhere around 500lbs, or so I've heard. Obviously shells lift and break with more than a poof.

 

I believe there is something along the lines of this somewhere on passfire, where a jar was intentionally set off to see what kind of damage it would do. I can't seem to find it right now though.

[poisonkiller]

How many pounds of BP do you mill in one batch?

 

How heavy is the iron dome?

I can't be exactly sure, but I think one batch is about 0.5 pounds. The iron dome is about 20 pounds.

 

I'm currently thinking, that maybe I can dig a hole for the ball mill, make it waterproof with a plastic sheet and then cover it with the iron dome (leaving a small gap between the ground and the dome as RUUUUUN suggested). That way nothing can go flying around, gasses would have more room to expand, heat would build up more slowly and most of the noise would be blocked. Can someone find a flaw in my logic?

[TheSidewinder]

Can someone find a flaw in my logic?

 

Yes. The dome.

 

If you want to cover it, use a piece of tarp. Prop it off the ground a foot or so to allow air circulation. If you have an accident, all that will happen is....... you'll need a new piece of tarp.

 

Well, that and another ball mill.

[Swede]

I'm picturing one of those homemade PVC jars. Schedule 80, heavy stuff, with a thick rubber end cap, secured very tightly with a hose clamp. If a kilogram of BP went off in there, the first thing to go is the end cap, but I think it will provide enough containment, and the pressure will build rapidly enough, to cause a significant explosion. It's not FP, but a kilo of good BP has a lot of energy. I wouldn't underestimate the damage.

 

The last thing you want, besides injury, are pieces of the jar, the media, maybe even the ball mill, landing in a neighbor's yard, or breaking a window, or banging into his Mercedes. The wrath of the neighbor and the po-po will be terrible to behold.