Warning to all: Coffeegrinding MgAl

[Stinger]

Hi

 

First of:

 

I am glad that I am still alive.

Everything is ok, excet my heart which is beating terribly because of the shock.

 

I made some MgAl yesterday and then I smacked it don with a hammer to coffeegrind it.

 

I dumped it in a coffeegrinder and grind it for 30 seconds.

Suddenly, there was a pretty big spark in the grinding room followed by a pretty big

electric spark, then an explosion of the MgAl-dust occured.

Now, all the lights in the basement are dark (caused?) by a shortcirciut.

 

NEVER GRIND MgAl IN A COFFEEGRINDER, NEVER DO IT!!!

 

I still can´t believe what happened, and I was dumb and felt pretty save.

I could be dead, but I thank god that I am not.

 

Stinger

[WarezWally]

Will the person who told me that metal powders wont explode in a coffee grinder please step forward, you need to eat some words

[justanotherpyro]

I'm surprised that when you broke it down with a hammer that you didn't notice that putting in a coffee grinder might not be such a great idea. Whenever I break down larger chunks with a hammer I put the chunks between a few layers of paper bags but eventually I end up igniting a small piece which burns. Usually only when I give it a good smack, so I try and keep them as soft as possible.

 

You already know that it was stupid so instead of ragging on you It's a good thing that you decided to post it so that people, especially beginners, can read a first hand experience at how reactive MgAl is.

[jacob]

Hey I've had that happen to JAP, I couldn't figure out what was going on, I didn't know it would burn like that in open air.

Thanks for clearing that up for me.

[justanotherpyro]

No problem. It usually happens on pieces that have sharp edges or points. If you are hitting the pieces directly without any thing in between the MgAl and the hammer then the chances of a piece igniting are higher. Also covering the chunks helps keep dust down and flying particles to a minimum. When I ball mill MgAl some of the bigger chunks don't get broken up and become rounded out an smooth. These are easier and safer to break up( relatively). I use a brass hammer to break them up, so the problem can't be fixed by using a non sparking hammer because friction is energy and if you can break the activation energy then a piece can ignite. As stinger learned first hand and demonstrated MgAl is a very reactive metal and dangerous to work with, so take any precautions you can.

[tentacles]

Interesting. I coffee milled a bunch of MgAl a while back, no problems. Maybe it has something to do with particular coffee grinders? I didn't know it'd ignite when hammered - we used a meat grinder to grind up chunks, the big blocks pretty much fall apart when you rapid cool them.

 

FrankRizzo and I definitely saw sparks when we coffee milled some of Bob's Ti turnings.

 

Glad you're okay!

[FrankRizzo]

Yeah, I've milled quite a bit myself with no problem. Is it possible that you stalled the motor or had some of the magnalium migrate down in the motor housing next to the sparking brushes? If you tripped the circuit breaker, there's more to the story.

 

Tenacles is right, we did see a few sparks when grinding down those titanium turnings with the coffee grinder, but had no ignition.

[Bonny]

I've also ground MgAl a few times with a coffee grinder and have not (seen) any sparks. I break up the MgAl witha hammer first, then into the coffee grinder.

My last few batches however have been ball milled and I open the mill jar about every 1/2hr (after taking the jar off and allowing the dust to settle for a few minutes).

 

As for Ti shavings from Bob, I grind mine up in a blender with water. Works quite well and it also cleans most of the cutting fluid off.

[Stinger]

Hi

 

Interesting with the ball milling.

Whats the particle size in general you get from ball milling MgAl?

I was planning to get some steel media.

 

But please, even if your coffeegrinder is clean ( mine was),

never attempt to grind MgAl.

Some people maybe say " yea, nothing happened, just the motor burned or so".

But I could also got an electric shock and I nearly killed myself.

 

I think i had pretty damn luck that nothing happened, only an explosion.

So stay safe and ball mill it!

 

Stinger

[Bonny]

Hi

 

Interesting with the ball milling.

Whats the particle size in general you get from ball milling MgAl?

I was planning to get some steel media.

 

But please, even if your coffeegrinder is clean ( mine was),

never attempt to grind MgAl.

Some people maybe say " yea, nothing happened, just the motor burned or so".

But I could also got an electric shock and I nearly killed myself.

 

I think i had pretty damn luck that nothing happened, only an explosion.

So stay safe and ball mill it!

 

Stinger

I ball mill using 1/2" to 3/4" steel bearing balls. I think the chrome has long been worn away, but they have a permenant MgAl coating now anyway. The finest size screen I use is 200mesh and most passes this. I also try and retain as much -100+200 as I can so I frequently open and screen the material, I have a shaker machine for this so it is really easy. In the past I also screened -250 no problem and that is the finest screen I have. As for the coarser stuff I save whetever is left for fountains etc...