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Causes of ball mill accidents?

Ball mill black powder safety

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#1 Norwest

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Posted 30 July 2015 - 03:24 PM

Hi,

 

I have been reading many posts and other references in preparation of making my first batch of black powder including accident reports. I have a 15 lb capacity rubber lined rock tumbler (Thumbler's Tumblers) and 200 brass 1/2" beads. If I am making standard black powder with this setup what is the likelihood and possible causes of unintended ignition? Would static be most likely culprit?  Does the biggest risk occur when opening and dumping out BP and beads? Seems like using sparking milling media and milling more reactive mixtures other than BP are the most common causes of accidents. Is this so or have I missed something? I have a back yard but can only get about 50 ft away from house and neighbors. Digging a pit will not be well received by wife but do have some tires I could place around the tumbler. Going to try to convince a friend who has a farm to do it on his property by fear his wife will nix it. Going to try to join local pyro club so perhaps through them I can find a safer place to mill.

 

Thanks,

 

Norwest



#2 fckiamdead

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Posted 30 July 2015 - 04:02 PM

Hi,

 

I have been reading many posts and other references in preparation of making my first batch of black powder including accident reports. I have a 15 lb capacity rubber lined rock tumbler (Thumbler's Tumblers) and 200 brass 1/2" beads. If I am making standard black powder with this setup what is the likelihood and possible causes of unintended ignition? Would static be most likely culprit?  Does the biggest risk occur when opening and dumping out BP and beads? Seems like using sparking milling media and milling more reactive mixtures other than BP are the most common causes of accidents. Is this so or have I missed something? I have a back yard but can only get about 50 ft away from house and neighbors. Digging a pit will not be well received by wife but do have some tires I could place around the tumbler. Going to try to convince a friend who has a farm to do it on his property by fear his wife will nix it. Going to try to join local pyro club so perhaps through them I can find a safer place to mill.

 

Thanks,

 

Norwest

 

I never heard of any accident's during milling, but som few when they opened the drum and pored out the BP. Could have bin static or sparks from metall to metall ect. I think it's rather "safe" to mill.

 

BUT STILL always think "murphy's law" and use ppe and a safe location. Tires and no one else around the place (outside the house) sounds like a good plan.

 

Regards


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#3 SideGlance

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Posted 31 July 2015 - 07:37 PM

Glass marbles was the cause of one explosion that I know of.. You should always baracade the mill with heavy sand bags. If it were to blow you want the stuff to go up not sideways.. But yeah pretty darn safe using proper media and rubber jar

#4 taiwanluthiers

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Posted 31 July 2015 - 11:23 PM

Seems accidents are happening when the person is emptying the jar, so barricading the mill won't solve that. Perhaps some remote way of emptying the mill jar is in order?


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#5 Ubehage

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Posted 01 August 2015 - 03:10 AM

Seems accidents are happening when the person is emptying the jar, so barricading the mill won't solve that. Perhaps some remote way of emptying the mill jar is in order?


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#6 mikeee

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Posted 02 August 2015 - 03:48 PM

Another viable option is to sandwich a stainless steel screen or plastic sorting screen between two mill jars the same size.

Slowly reverse the positions of the mill jars and tap and shake the jars to sift the comp through the screen and contain

the milling media in the other jar. The main issues are heavy hard impact of the media on sparking surfaces and static

discharges to the chemical compound while emptying the mill jar. Minimizing static potential is something everyone talks about 

but very few people do anything to reduce the risk. Dry environments multiply the risk of static sparks higher levels of humidity

and damp surfaces lower the risk. Bonding yourself to a grounded metal surface will discharge static potential of your person,

touching the exterior of the mill jar while grounded will help lower the risk of a static spark reaching the compound when you open and empty the jar. 



#7 dagabu

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Posted 02 August 2015 - 05:46 PM

You can make sure to avoid an electrical spark (non-static) by installing a single pole switch (light switch) on your extension cord that allows the ground to remain in place by disconnecting the hot wire from making a circuit.  DO NOT!  Unplug the ball mill and remove the ground, if by whatever there is an electrical charge built up, the energy will go to ground and not create a spark (hopefully).  

 

One crispy critter is enough around here. 


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#8 mikeee

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Posted 02 August 2015 - 07:58 PM

Maintaining a ground to all of your electrical equipment is necessary to say the least.

An external clip on ground wire is the next level of protection used on process equipment.

ESD (electrostatic discharge) grounding mats and straps are the third level of protection for preventing static spark potential.

The ESD mats and straps normally use a 1 megohm resistor in series to protect the user.

ESD paints can also be used to coat working surfaces and equipment.

There are several resources on the internet that go into detail on ESD grounding protection principals.



#9 taiwanluthiers

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Posted 06 August 2015 - 12:05 AM

I never gotten any static shocks in Taiwan (humidity is way too high for that) but I'm getting a LOT of them in Texas. Doesn't help that I'm wearing a polyester vest at work that is just a magnet for static. This is another reason why you must wear all cotton clothing when working with explosives, because polyester can easily build up a static charge.

 

If you must humidify the heck out of your pyro workspace, will probably make things very uncomfortable if you are in a hot climate though...



#10 SmokinJoe

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Posted 25 May 2016 - 10:47 AM

My background is in semiconductor, where we employ static dissipation (conductive clothing, wrist strapes, conductive tables, mats, etc.) and a continuous path from the device to ground. I find it odd to see suggestions on the use of static charge building materials such as rubber and non-conductive plastics (e.g. plastic paddles in mixers) in making pyro mixtures. I prepare my mixtures on a conductive table which is is connected to ground, and while I don't always where a conductive labcoat and my wriststrap, always touch my hand to the table before contacting the mixture/its holder. My 2 cents.



#11 dagabu

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Posted 25 May 2016 - 11:06 AM

My background is in semiconductor, where we employ static dissipation (conductive clothing, wrist strapes, conductive tables, mats, etc.) and a continuous path from the device to ground. I find it odd to see suggestions on the use of static charge building materials such as rubber and non-conductive plastics (e.g. plastic paddles in mixers) in making pyro mixtures. I prepare my mixtures on a conductive table which is is connected to ground, and while I don't always where a conductive labcoat and my wriststrap, always touch my hand to the table before contacting the mixture/its holder. My 2 cents.

 

And you are probably 100% right in that statement.  The problem for me and others (if they are honest) is that many of the processes we use are out of necessity because we are limited in the materials, components or knowledge. 


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#12 lloyd

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Posted 25 May 2016 - 12:29 PM

Dagabu, no: he's NOT 100% right.  He's on the right track, but it's an "excessive remedy for a mild malady".  Kind of like treating a common cold with thoracic surgery!

 

Mil-spec calls out certain specifications for humidity and conductivity of flooring and footwear.  When the 'general conditions' are inside about 35%-60%R.H. and floor and footing conductivity is around <100Kohms, everything is 'pretty safe', and extreme measures such as working on conductive worktops (which present a WHOLE SET OF THEIR OWN DANGERS) become unnecessary.

 

"Conductive" worktops are not the same as "static dissipative" worktops.  Static-dissipative surfaces are to be desired.  Conductive ones present a whole 'nuther bunch of control issues you don't want to have to deal with!

 

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Edited by lloyd, 25 May 2016 - 12:41 PM.

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#13 Nessalco

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Posted 25 May 2016 - 03:48 PM

Lloyd, a question came up a while back, relating to absolute vs relative humidity and static discharge. I'd be interested in your take on that question, especially since you're involved in the manufacturing end and know how the 'big boys' handle things.

 

http://www.amateurpy...atic-discharge/

 

Kevin


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#14 lloyd

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Posted 25 May 2016 - 05:58 PM

Kevin,

YOUR analysis of it, and the ASHRAE evaluation are more accurate than what is considered "standard practice".  In fact, RH readings have proven sufficient over DECADES of practical use making very-sensitive explosives for military goods.

 

It's completely true that the absolute humidity is a better indicator, but RH has 'worked'.  Oh, well!  What works, works!  What doesn't kills folks.

 

My leaning is to think that the military will be slow to adopt any new standards, given the success of the old ones... no matter HOW valid the new ones might be.

 

Lloyd


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#15 dagabu

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Posted 25 May 2016 - 06:33 PM

Dagabu, no: he's NOT 100% right.  He's on the right track, but it's an "excessive remedy for a mild malady".  Kind of like treating a common cold with thoracic surgery!

 

Mil-spec calls out certain specifications for humidity and conductivity of flooring and footwear.  When the 'general conditions' are inside about 35%-60%R.H. and floor and footing conductivity is around <100Kohms, everything is 'pretty safe', and extreme measures such as working on conductive worktops (which present a WHOLE SET OF THEIR OWN DANGERS) become unnecessary.

 

"Conductive" worktops are not the same as "static dissipative" worktops.  Static-dissipative surfaces are to be desired.  Conductive ones present a whole 'nuther bunch of control issues you don't want to have to deal with!

 

Lloyd

 

Dang, I forgot to use the "smarky" icon when posting again...  :P


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#16 lloyd

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Posted 25 May 2016 - 06:51 PM

<G>

L


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#17 Nessalco

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Posted 26 May 2016 - 01:22 PM

Kevin,

YOUR analysis of it, and the ASHRAE evaluation are more accurate than what is considered "standard practice".  In fact, RH readings have proven sufficient over DECADES of practical use making very-sensitive explosives for military goods.

 

It's completely true that the absolute humidity is a better indicator, but RH has 'worked'.  Oh, well!  What works, works!  What doesn't kills folks.

 

My leaning is to think that the military will be slow to adopt any new standards, given the success of the old ones... no matter HOW valid the new ones might be.

 

Lloyd

 

Thanks, Lloyd. I appreciate the insight.

 

Kevin


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#18 Arthur

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Posted 26 May 2016 - 02:14 PM

The most likely cause of unintended ignition inside a closed drum is included grit especially hard grit -probably especially glass hard grit.this forms pressure concentrations between milling media.

 

Other than that take effective measures to minimise static and wear clothes at all times two layers of full body cover may be "too hot" but the searing flame of burning BP is much hotter. I've seen vids of people making fireworks in T shirt and shorts, that really isnt sensible.

 

Someone from the UKPS once filmed ball mills being ignited. Small mill 100g BP almost no issue, just the end popped off. Big mill 5kilos BP -lead balls over 20m radius and big fireball. Make moderate batches.


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#19 DavidF

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Posted 26 May 2016 - 03:32 PM

One guy had an explosion while milling when he used large ceramic media and large lifter bars in his jar. Another guy used a steel chain (I think) in a steel drum. He was warned of the danger. He pointed it out the barn door in case it blew up while milling, and it did.

Greenhouse grade saltpetre can have hard gritty pieces of stone in it- at least mine does. I screen all my saltpetre through 40 mesh before milling now. I had some old milled stuff around and went to make up some scratch mix. There was a rock the size of a pea in it.
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#20 Ubehage

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Posted 27 May 2016 - 12:05 PM

One guy had an explosion while milling when he used large ceramic media and large lifter bars in his jar. Another guy used a steel chain (I think) in a steel drum. He was warned of the danger. He pointed it out the barn door in case it blew up while milling, and it did.

Greenhouse grade saltpetre can have hard gritty pieces of stone in it- at least mine does. I screen all my saltpetre through 40 mesh before milling now. I had some old milled stuff around and went to make up some scratch mix. There was a rock the size of a pea in it.

Wow, thank you for sharing that information.

 

I have 2 drums: One is with ceramic media, about 8-9mm in diameter. And the other is with different sized lead media.
The ceramic drum is used only for single chemicals, where I used the other for BP (and BP-like compositions, like FairyFountains).


Blowing shit up is not a goal in itself. Seeing your device working the way you intended, is the greatest satisfaction of all.






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