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Machining magnesium

It machines beautifully but it will burn. Don't let the chips accumulate. Keep them cleaned out of the chip pan. Thin flaky chips will of course burn more readily. I have both machined and welded it and it really isn't bad material to work with.
 
I do know this much, when we took on a job machining it out on our machining center, we had to buy the special fire extinguisher to have right at the machine because we were using water-soluble coolant. If you do not know, DO NOT THROW WATER ON BURNING MAGNESIUM, it only intesifies it. I can't remember right off hand what exactly type of exstinguisher it is, but we still have it and it was an OSSHA requirement.

[This message has been edited by toolmaker (edited 06-28-2004).]
 
Type D fire extinguisher is for flammable metals. (Mg, Ti, Na, K, etc)

I have not machined Mg, but looked into it to try to convince my university shop to let me, (need a light broom handle).

Anywho, it machines alot like Al I hear. But something Id like to add is to NOT let it sit in water. Mg will reduce the water to MgO and free H. So dry your chips or use oil based coolant.

Hope this helps some
Nick

[This message has been edited by SLOEIT (edited 06-28-2004).]
 
A bucket of dry sand will work to smother smaller class D fires.
Class D extinguishers are available with different chemicals. The extinguishing agent used depends on the metal the extinguisher was designed for. It will specify what metals it is effective for on the label. Water reacts relatively violently with mg due to the rapid expansion of water into steam (1:1,700). The fire department will likely use a large volume of water to smother the fire. In case you didn’t know, aluminum poses many similar problems. BTW, I am a firefighter.
 
IBM had a machine to trim (cut off tool) magnesium type cylinders. the chip pan had a trap door. When you got done cutting off one cylinder you opened the trap and brushed the chips down into a steel box.

You then closed the trap and trimmed the next cylinder.

The idea was that if things got hot, the whole bunch of chips wouldn't go up at once.

I have seen magnesium burn and frankly I don't think there is any way to put it out.

By the way, some years back, the metalworking gurus developed a machinabiity index. Magnesium was chesen as 100, the most machinable of metals, every other metal has an index of less han 100.

Don't let that fool you, high spped means high heat, things coud get real dicey!
 
The class D extinguisher contains a powder know as METAL-X. When it is used it comes out in a slow soft stream so as not to send the burning metal flying all over the place. You wave it back and forth to cover the metal and it puts out the fire by melting and coating the chips. Actually it isolates the burning metal from the rest of it before it gets going. Mag has to burn its self out. While we carry it on our trucks for use on aircraft, in the shops they just use straight talc as METAL-X is a very corrosive substance and can do a number on your machinery. The maint. guys said that you have to practicaly dis-assembly the machine to get it all out of the nooks and crannies after you use it, or you end up with rust where your can not see it until it is too late. The talc basicly does the same thing as the METAL-X by isolating the burning metal but it does not melt and stick to the Mag. It is cheaper and you can tell right away, before starting the job if there is any moisture in it as it clumps. Sand that feels dry may have enough water trapped in it to cause small steam explosions or generate hydrogen gas and have it flare or burp, throwing the metal around. Mag burns bright white and it is like looking at a welding arc trying to get it covered so be careful.

Mag chips need to be kept to a minimum on and around the machines cutting it and the tools need to be kept sharp at keep the heat down. We make the shops use heavy steel bins or 55 gallon drums with secure fitting lids to hold the chips and they must be emptied every night or when full, just like a rag can. No major fires yet, so the system must be working.

About 20 years ago a local shop that did work for Boeing, Lockheed, GE and Thiokol had a major mag fire. As they were not carefull with the chips they lost the shop in about 40 minutes. It was around a 15,000 Square foot building too. As with any shop good housekeeping helps to minimize problems when they do occur, and they always do when you least expect it.

If you cut any of the combustable metals or grind a lot of Aluminum take care with the chips and the grinding swarf and you should not have any problems.
 
Back in the late '60s or early '70s Piers Courage was racing a F1 race in a March chasis IIRC powered by a Magesium engine. Saddly he crashed and was killed in the resulting fire. Magnesium was also used in some parts of the Pratt & Whitney R2800. The old timers used to tell me stories about the fires on the Bullard Multimatics. Often the safety blocks for presses are made from Magnesium exrusions. Every time we had to shorten one up for a different application some idiot always had to play around with the chips.
 
Anyone who was in the Coast Guard or Navy has probably had to watch the training films showing the USS Forrestal's tragic fire. The planes on deck had plenty of magnesium in them.

Policy on burning magnesium is to jettison it overboard if at all possible.

Here's a link to a site about the tragedy:

http://www.forrestal.org/fidfacts/page13.htm

My Chief Petty Officer's uncle was aboard that ship at the time. I understand he died in the accident. Fire at sea is about the biggest fear a sailor can have.

Not only is the heat intense, the fire is extremely bright. I have heard it compared to a welding arc, but have not seen it myself, nor do I ever want to.

Richard



[This message has been edited by Richard Rogers (edited 06-29-2004).]
 
Magnesium is what the decoy flares used by military aircraft are made from. Magnesium flares are also used by spelunkers in caves and are what the old style flash bulbs were made from.
 
I am quite familiar with magnesium's potential for igniting, but aluminum is a new one for me.

Can anyone go into some detail as to what to watch for? I saw grinding dust mentioned, don't do much of that but would like to find out any potential problems.
 
Aluminum burns quite well when heated enough. That was clearly shown when the destroyer HMS Sheffield was hit by an Exocet missle during the Falklands war. Aluminum powder is the fuel component of the Space Shuttle boosters with potassium perchlorate the oxidizer. Very finely divided aluminum dust made by spraying molten aluminum into a vacuum will spontaneously explode if tossed into the air. Aluminum powder as used for paint pigment is coated with oil for this reason.

See here for more:

http://www.g2mil.com/aluminum.htm

[This message has been edited by Evan (edited 06-30-2004).]
 
Back in my younger days when no firecracker was big enough, I would order aluminum powder and potassium chlorate from a company that was in the business of selling do it yourself fireworks. The biggest ones I made were approximately equivalent to 1/4 stick of dynamite. Made some serious noise!

Dale
 
FQA would eat you alive if you said that Richard Rogers...

the line is, use water fog around the area to reduce the heat and let the guys with deck pay do whatever it is they do.

I have seen magnesium burn but I haven't had a chance to throw water on it yet.
 








 
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