6 replies to this topic

[Pretty green flames]

As stated in the title how would one build some sort of container to ensure maximum safety during ball milling proces.

I have recently read on rec.pyro that there was an accident during WET milling
Ball mill accident

This has sparked something off in my head and made me want to build a blast box.

I figured i'd use wood but that's not good becouse in case of explosion there would be splinters besides of lead media.

Please post your bright ideas on this subject.

As a side note this thread is dedicated to ball mill safety so you can post your questions regarding ball mill safety here.

[Andrew]

Good materials for blast walls are thick heavy rubber (the sort at the end of firing ranges), lead, mild steel, anything that is not brittle really.

The best and cheapest one I can think of is mud, dig a hole and put your ball mill in it, put a ridged lid/cover on it and place a 1 ton aggregate bag on top and fill with mud, preferably damp (that doesn't mean fill and then piss in the bag ). Not only have you removed 99% of the sound, you have a blast proof box ranging in thickness from 1 metre to 12,750 km.

There are many methods used but mud, being mud, is cheap and easy to use. The covering on the top is debatable, there are many designs that allow the gas to pass unhindered yet catch most of the non gaseous action. Some argue that having a massive lid is dangerous, but 400g of bp (content of a 3 litre milling jar) going up under 1 ton of earth will cause a very small thud, an even smaller rise in the ground and then white smoke will billow out of the sides. Having a fragile roof in the case of the small ball mill in relatively confined spaces, is more likely to cause damage and injury.

[Pretty green flames]

Thnx, that pretty much solves my problem.

[Arthur Brown]

For reasonable "home" mills operation in a pit is a major help but you should analyse the mill load risk and NOT mill things that cannot happen safely in your location. It will help if you let the blast dissipate while restraining the shrapnel (balls etc) definitely use sparkfree motors and tools.

The gas that collects in central heating radiators is hydrogen and burns, its the same reaction as proposed for the incident you quote Fe + H2O > H2 + Fe oxide in certain conditions.

[1145climber]

but still, out of curiosity, what can one do if the mixture inside has become pyrophoric, kind of like what happened in the article? slowly open it like a little bit of a turn at a time over a few hours? or maybe the only way is the just avoid compounds that might become pyrophoric in the first place? any tips/advice?

[Andrew]

We have a 15 Litre mill which we keep in a hole in the ground. The primary reason for putting it there in the first place was because a 15 Litre mill is very loud. It actually hurt your ears if you were next to it. Just by having it in a hole, the noise envelope was shaped into a better but still unacceptable form. We put a 1 ton sack with about 200kg of earth in it on top of the hole, smothering the gap. Now you can not actually hear it unless you stand a couple feet away.

On a pyrophoric point, you can?t really avoid it as such, unless you stop milling well before it is down to a useful size. You can take steps to turn a pyrophoric material into one that is not though. You can add a coating to the milling jar contents part way through the batch. If you don?t do this and you suspect that the contents are pyrophoric, you should at least take the following steps.

Take the jar and shake it while upright.

Wait about half an hour.

Shake upright again, but considerably less vigorously this time.

Leave to settle for at least a few hours, over night is probably a good idea.

Open the jar very very slightly. Leave for an hour or so.

Repeat until the lid is off. You?re not out of the woods yet!

Leave for at least 24 hours as it is, without disturbing.

Put the lid back on and roll the jar a few times, until free flowing.

Leave to settle.

Open again, with caution!

You should be ok-ish by now.

If at any point the jar feels warmer than ambient, stop what you are doing, tighten the lid and place in a container filled with water, and then place all of this well out of the way, maybe in a hole if you have one!

There are tell tail signs that you can look out for. Like if the jar is warm, or the walls have collapsed inwards. The warmth is from the material reacting with the oxygen in the milling jar. If the jar is airtight, this will cause a lower pressure inside the jar, if your jar is not airtight the oxygen concentration will become slightly depleted but will replenish itself. For this reason, if your jar is not airtight, you will not really have to worry about pyrophoric material as much. If your jar is airtight, you will have a negative pressure on the inside, which makes the opening it in a controlled manor difficult.

On our 15L jars we are going to add an air tap, to allow us to raise the oxygen concentration at a controlled rate. Remember if it is pyrophoric, any oxygen will have already been consumed, assuming the jar is airtight, and the pressure inside will only be about 790mBar.

[1145climber]

thank you very much for the instructions, thats exactly what i was looking for and was a very interesting read. im not sure how often accidents happen with unsuspecting victims of mixtures that have become pyrophoric, but i think this everyone should read about this.