Ball Mill Explosion!

[dagabu]

Everyone, I am submitting this telling of Gary Smith accident yesterday with his ball mill. I am posting this with his direct consent.

 

I can’t believe I’m having to type this, but unfortunately I am.

 

I had a ball mill explode this afternoon, no one was hurt, but my favorite mill was destroyed, and it was in my greenhouse, which I had recently replace the plastic film on, and it was damaged pretty good as well, as you might imagine,,, although not as bad as it could have been.

 

Also my nerves are quite jangled too.

 

Here is what I know:

 

I had just completed a new mill jar, 8” pvc, 12”long, with one lift bar, wooden end caps that were taped on with masking tape.

 

The jar was identical to my 6” jars, except for the end caps on the 6” jars are hdpe [bottom of Clorox bottles] taped on.

 

The reason I built this jar was to accommodate some new ceramic grinding media that I bought at 4F this fall, these are the ceramic “mentos” looking media that is being used by several FPAG members, and they are too large for a 6” jar so I built a bigger 8” jar for them.

 

I finished the jar and loaded it with a 1000 gram 75/15/10 charge and put it on the mill last night for about 30 min. just to see how it was working then I removed it and checked to see how it was progressing inside and all seemed well.

 

Today it went back on the mill, and after about 2 hours… bang!

 

First run with ceramic media…. I can not see any obvious reason for this to happen other than a spark from within, however [thankfully] I was not there when it went off.

 

And there are other possibilities, like contamination with a stray piece of metal in the charcoal or maybe it was leaking powder, but I don’t have any evidence of that.

 

My other mill jars use lead, and have spent many hours on the now destroyed mill, in the same spot, in the same greenhouse.

 

I was about 250’ from the mill when it blew, with a building between myself and it, and let me tell you it was a lot like a sizable salute going off!

 

You could feel it in the ground like a tremor.

 

Although it would seem no one noticed or cared but me, which is good, but somewhat surprising, others shoot/make noise around me but,,, not quite like this!

 

I’d thought in the past if something like this where to happen, the greenhouse would be a place that would limit the possible damage, while keeping things dry and at a source of electric power.

 

And now seeing what it did, I can tell you, if this were in a garage or shed and near living quarters it would have razed the building.

 

This greenhouse is open on both ends [screened] and it still built enough pressure, [or shock wave] to rip the fastening device screws out of the 2x6 boundary boards on both sides for at least 20’. the mill was at one end of the 56’long x 28’ wide structure.

 

Now that I have to fix it, I’m not sure if it was a good idea to put it in there, and it won’t be in there in the future.

 

It was a cool [45-50] very dry day.

 

I am bummed about this incident for two reasons,

 

One is pretty obvious.

 

Two is the fact that I was looking forward to not using lead media, and after this, all but lead will be suspect, we don’t even seem to be sure of SS at times and I think I would rather die slow of lead poisoning at the moment.

 

I’ll keep everyone updated on anything I find out, if I do.

 

On a positive note,,, all my tomatoes ripened instantly….. Just kidding, but they are still there,, here I’ve been desperately trying to keep them from freezing, and then I go and try to blow them up!

 

Interesting day,,,

 

G.

 

http://www.pyrobin.com/files/img_4006.jpg

 

In this next picture, those plywood frames were squarely on the mat they are near, and notice bottom one’s ½ ply broken and knocked apart and the wooden mill end cap lying there.

 

http://www.pyrobin.com/files/img_4007.jpg

 

http://www.pyrobin.com/files/img_4008.jpg

 

http://www.pyrobin.com/files/img_4012.jpg

 

Last picture of shaken but living eye witness.

[Richtee]

Holy crap. Who ever said "Get the lead out!"?

 

Glad only the tomatoes suffered from the blast... yeesh.

[Swede]

I think I'll stick with brass for BP... Yow.

 

Edit: Actually, I changed my mind after reading the replies on Passfire to this accident. I think it was a leak.

First off, I am VERY glad there were no injuries and no issues other than some damage to your greenhouse.

 

After looking at the pictures, I place myself in the "leak" category, especially given the DC motor, if I have read that correctly. If you run a brushed DC motor in a dark room, the interior of the motor is lit up with a shower of sparks at the brush to rotor interface, or whatever the spinning part of the motor is. Given the ultra-fine dust, and the air currents in the immediate vicinity generated by the moving parts, I don't think it is impossible for some of the dust to reach an ignition source.

 

I think we pay excess attention to media, and perhaps not enough to jar, mill, and motor type.

 

Again, I'm glad you're OK.

 

I just don't think taping cut sections of thin HDPE plastic to the barrel is going to make a safe mill jar. A mill setup MUST be taken seriously, and use only high-quality components.

Edited January 13, 2010 by Swede

[Kweltan]

So i take it no one would recommend Alumina Media? Because i recently got my ball mill from pyrocreations with some Alumina Media; though not enough to half-fill my ball bill. And i was going to buy some more Alumina Media but now im not so sure if i want to, and risk a ball mill explosion. Should i stick with Alumina, or go with Brass or Lead?

 

 

As for Gary Smith, at least he and the tomatoes are safe, a ball mill and greenhouse can always be replaced! Imagine what could've happened if he'd been inside the greenhouse at the time; i could be replying to a thread with a completely different title right now.

 

 

Thanks,

Kweltan

[KruseMissile]

im glad i have lead now! As for Gary, I'm glad he and his tomatoes weren't injured.

[dagabu]

So i take it no one would recommend Alumina Media? Because i recently got my ball mill from pyrocreations with some Alumina Media; though not enough to half-fill my ball bill. And i was going to buy some more Alumina Media but now im not so sure if i want to, and risk a ball mill explosion. Should i stick with Alumina, or go with Brass or Lead?

 

The jury is still out on the cause but I can assure you and will look for the link but there is no way the alumina caused a pyrotechnic spark. When struck, it creates a photonic spark, meaning that it creates light, not heat.

 

Use your ceramics, use the proper load, charge the jar with the right amount of material, dont use lifter bars and dont run it to fast. Make sure it doesn't leak and run it remotely.

 

There are risks to using lead as well, be careful and barricade your mill, now go light something!

[NightHawkInLight]

It's hard to see an accident like this as a bad thing with how much worse it could have been. What a thing.

 

I for one don't know that I would jump to conclusions that the explosion was caused by a brushed motor and a barrel leak. Sure both of those things are hazards to be avoided, but in reality I think it would be quite difficult for dust from the mill to ignite and lead back to the drum, then there happen to be enough buildup to burn its way past the threads of the lid into the barrel. I understand that it's possible, but it seems like a chain of events needs to line up pretty well. In other words, I would expect there to be more close calls with powder igniting outside the barrel were it really likely to occur, and not a blown barrel the first time. A visible burn mark upon return to a mill left running or something from a few people before one blew. Just seems accidents typically half happen before they go all out.

 

I still suspect the media.

[mike_au]

The jar wouldn't necessarily need to be too sealed to produce good confinement. If it was just a small leak then the odds of a flame getting back inside the jar might be fairly small, but if the entire end cap came off and some of the powder got into the motor then there is a good chance that any powder still in the jar (which could be a significant portion, for example if it was caked to the sides) would go up as well.

 

Having blown up a mortar (completely destroying a fairly solid rack in the process) by putting too much C#6 into a starmine I can confirm that an open ended tube can still give a decent amount of confinement.

 

Personally I have ceramic media for individual chems, brass and lead (which needs replacing, probably with more brass) for BP.

[Kweltan]

The jury is still out on the cause but I can assure you and will look for the link but there is no way the alumina caused a pyrotechnic spark. When struck, it creates a photonic spark, meaning that it creates light, not heat.

 

Use your ceramics, use the proper load, charge the jar with the right amount of material, dont use lifter bars and dont run it to fast. Make sure it doesn't leak and run it remotely.

 

There are risks to using lead as well, be careful and barricade your mill, now go light something!

 

 

I definitely wont be using lifter bars or anything like that; for now im going to keep it as simple as possible. As ive read somewhere on this forum, im going to tape the lid of my jar to prevent it from coming undone and leaking. Hopefully i'll light something real soon

 

 

Regards,

Kweltan

[FREAKYDUTCHMEN]

These kinds of topics, is why misunderstandings arise.

Just follow the topic on passfire, g smiths replies over there.

It's good to learn from others mistakes, not from rumors.

[pyrogeorge]

so,the problem was the ceramic media?

[optimus]

Anyone fancy posting the relavant reply from Passfire on here?

[pyrogeorge]

There are risks to using lead as well, be careful and barricade your mill, now go light something!

 

There are risks using lead media?I think that the lead is safer than other media..or i make wrong?

[dagabu]

Anyone fancy posting the relavant reply from Passfire on here?

 

Yup, I will do so. Again, the jury is still out but it now appears that the old snorts are leaning towards a detonation from within the jar due to the jar being under charged with BP, too much media and a big lifting bar that dropped the media from a height on to the sparse BP in the bottom.

 

I have to disagree with Dutchman, i think it is important that we keep dialog like this open for all to comment on. We learn the best when we don't have artificial limits imposed upon us. These are not rumors.

 

Remember, alumina media does not spark pyrotechnically, it is photonic in nature but a single grain of BP will detonate under certain conditions as listed in BAFN (I know, more searching) as will all compositions.

 

"In this case, we're talking about microscopic effects like crystal fracture, friction heating, and compression to such an extent that chemical reactions begin spontaneously. It's called "impact sensitivity", and is a well-documented effect. Shimizu rates a number of compositions for sensitivities including that of impact."

-Lloyd Spoenburgh-

 

Stay tuned...

Edited January 14, 2010 by dagabu

[dagabu]

There are risks using lead media?I think that the lead is safer than other media..or i make wrong?

 

Yes, lead sloughs of into the composition and it burns to make it a gas which is very bad for you. The risks are not pyrotechnic but an exposure hazard.

[Swede]

Nighthawk, I had a MASSIVE leak of a benzoate from a normally well-behaved lortone-style rubber jar. It produced a pile of white powder about 3 cm tall right next to the motor. I don't think it's a stretch to see an ignition source from the motor touch off that pile (if it was BP and not benzoate) and the resulting WHOOMPF is definitely going to find the leak that caused that pile in the first place and make it into the jar. It sounded like he was cutting the bottoms off of HDPE containers and taping those to the drum to form lids. That does not sound safe to me. If the drum drifts against the edge, which it often does, the caps can be cut open in minutes from friction, which is why I added a ball bearing attachment to my own mill:

 

http://www.5bears.com/firew/bp018.jpg

 

I was under the impression that he was using a brushed DC motor. If I'm misreading it, I'll happily be corrected. But take a dremel tool, for example, and look at the sparks it generates in a dark room. These are real sparks capable of ignition.

 

The other possibility is even a small pebble in the mix. or a piece of steel. Steel + ceramic media = flint and steel, and again you're going to get a healthy spark.

 

I think true alumina media is safe for BP. But I think a better choice is brass or stainless. Or hardened lead.

 

I don't know that we'll ever find out the "why" of this. But my point is this: a ball mill setup goes beyond media choice. It is a combination of factors, and all must be taken seriously with the thought that avoiding ignition is critical. I'm very glad he was milling remotely. That is safety rule #1.

[NightHawkInLight]

Thanks for the clarification Swede.

 

@ mike au, what you said is true about confinement, however, in such a case the lid to the drum would be left intact after the explosion. If that were the case the cause would be fairly simple to diagnose as a faulty lid.

 

Honestly I have no idea why this happened, it could have been anything mentioned. None of the reasons particularly concern me in my own case fortunately.

[50AE]

Photos of the end lids:

 

http://www.pyrobin.com/files/img_4014.jpg

http://www.pyrobin.com/files/img_4015.jpg

http://www.pyrobin.com/files/img_4016.jpg

http://www.pyrobin.com/files/img_4017.jpg

http://www.pyrobin.com/files/img_4018.jpg

http://www.pyrobin.com/files/img_4021.jpg

[Swede]

I must have misread the whole episode, then. Those caps are not what I pictured. They look like fiberboard cut into circles and glued. Normally they'd be pretty darned secure. The ideal attachment would be about 6 stainless studs affixed to the barrel, with the lids then secured in place with nuts. You can buy neoprene rubber sheet pretty cheaply, and you could cut a gasket for the lid, which should eliminate leakage and avoid any need for tape.

 

So now I'm leaning back towards a contaminated load. I have no idea, and I don't think we'll ever know. This is a bit like the BP rocket ramming accident(s) we've had in the past year. Extremely rare, but possible.

[pyrogeorge]

Yes, lead sloughs of into the composition and it burns to make it a gas which is very bad for you. The risks are not pyrotechnic but an exposure hazard.

 

i think that in open area it's not a problem..

[Miech]

That fully depends on the scale you're working on . When shooting a little it isn't much of a problem, but when numerous people are shooting a little or more you get quite a lot of lead in the air.

[Bonny]

These kinds of topics, is why misunderstandings arise.

Just follow the topic on passfire, g smiths replies over there.

It's good to learn from others mistakes, not from rumors.

 

 

I have to disagree with Dutchman, i think it is important that we keep dialog like this open for all to comment on. We learn the best when we don't have artificial limits imposed upon us. These are not rumors.

 

I agree with dagabu here as this not being rumors.

Also, FREAKYDUTCHMEN, what about all the members here that are not Passfire Members?? they should learn from this too.

[FREAKYDUTCHMEN]

Well tell me what your conclusion is, so far.

 

 

I think people shouldn't get too scared because of this story.

There were quite a lot of factors that could have caused the explosion, new barrel, new endcaps, new media, big liftbar (which is rediculous) a motor that could have give sparks, a under charged ballmill. etc etc.

 

I see many people asking if it was the media that caused the explosion, well I can say NOT IMO. I've milled quite a lot of BP batches with it, and so were many people from what I've read in that topic. Even with exact the same mentos shaped media. I wonder why they don't use round media, but thats another question.

 

But this is just my opinion, not scientific proven facts.

[dagabu]

i think that in open area it's not a problem..

 

I agree but most don't wear respirators when handling BP.

[Bonny]

Well tell me what your conclusion is, so far.

 

 

I think people shouldn't get too scared because of this story.

There were quite a lot of factors that could have caused the explosion, new barrel, new endcaps, new media, big liftbar (which is rediculous) a motor that could have give sparks, a under charged ballmill. etc etc.

 

I see many people asking if it was the media that caused the explosion, well I can say NOT IMO. I've milled quite a lot of BP batches with it, and so were many people from what I've read in that topic. Even with exact the same mentos shaped media. I wonder why they don't use round media, but thats another question.

 

But this is just my opinion, not scientific proven facts.

 

I'm not making, not did I ever claim to be making a conclusion as to the cause. They are not rumors, but specualtion as to potential causes... the actual cause will never be known for certain. However, you obviously either don't understand or simply don't care why the info should be made available to other people involved in pyro and those NOT on Passfire. The reason is SAFETY. These "rumors" identify possible dangers that many could learn from and might even prevent someone else from having an accident (that could easily be fatal) like that one.

And yes, people shouldn't get scared, but they should be reminded and always be aware of the danger.