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  • sbmathias
    replied
    Mag Fire

    Many, many years ago I set a lathe on fire machining magnesium. Had a VW transmission housing up in a good-sized lathe. To convert old 6volt engines to 12volt (including starter), you had to move to a barely larger diameter flywheel. As such, you had to open up the bell housing in the transmission case.

    So, with the bell housing just barely clearing the ways, around and around it went. As slow as we could go, as it was quite unbalanced. Had to feed the tool using only the compound, but that worked OK.

    UNTIL

    I let the tool pause at the deepest part of the cut. With all those nice magnesium shavings right there, and a little extra friction heat from the stationary cutter, it all went up in a spectacular fire.

    Fortunately, it didn't last long, nor was there any damage done to people or equipment. Obviously, it was memorable.

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  • Evan
    replied
    Good plan Mike. 2000 series is most commonly used in aircraft and is alloyed with copper which does raise the solution temperature. It also machines very nicely and without burrs.

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  • madman
    replied
    Billet?? Magnesiumn

    I have a nice sized chunk of it, might just leave it sit and use some 20 series aluminumn, its said to be the most heat resistant and suitable for caliper hangers.

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  • Evan
    replied
    Ferric chloride eats SS just fine as well as brass, copper and aluminum.

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  • darryl
    replied
    I've wondered about that ever since I first heard of chlorine on stainless problems. Here we have stainless steel sinks and bleach, ammonia- whatever all chemical products that we routinely put in sinks. Ferric chloride is another-

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  • Evan
    replied
    You can get metal to corrode internally quite well, its called intercrystalline corrosion,. . .
    Or, in the case of stainless steel, chloride induced stress corrosion cracking.

    This looked fine on the outside until I hit it with a hammer.



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  • Guest's Avatar
    Guest replied
    Originally posted by boslab
    You can get metal to corrode internally quite well, its called intercrystalline corrosion, it occurs between the grains of metal which was probably what your friend was thinking of, mostly the result of poor degassing during manufacture.
    As has been pointed out watch the swarf! no water! and are you quite sure its the right material for the job, i would have thought an ali alloy would be ok but i'm certainly no brake expert!
    mark

    Aluminum alloy is just fine for brake calipers on most any car or motorcycle except the most exotic racing vehicles. If one were to machine one's own calipers, the small advantage in reduced weight with the use of magnesium would be more than outstripped by the extra cost and the potential dangers.

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  • boslab
    replied
    You can get metal to corrode internally quite well, its called intercrystalline corrosion, it occurs between the grains of metal which was probably what your friend was thinking of, mostly the result of poor degassing during manufacture.
    As has been pointed out watch the swarf! no water! and are you quite sure its the right material for the job, i would have thought an ali alloy would be ok but i'm certainly no brake expert!
    mark

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  • Evan
    replied
    It isn't a component according to the link you posted which agrees with what I said. When an element is list as a "max" value like it is there as ".3% max" that means that is the most that will be tolerated, not desired. In other words the alloy is just fine if it contains none at all. It is very difficult to separate all traces of magnesium from aluminum so the specification allows a trace amount.
    wait...

    Strike the above. I read one line down at Matweb and took the value for manganese as the value for magnesium. My mistake. Still, the primary alloying element is zinc for 7075 and copper for 2024. What I said about separation is also correct.
    Last edited by Evan; 05-01-2010, 09:19 PM.

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  • topct
    replied
    Magnesium is a component of 7075.

    http://www.suppliersonline.com/prope....asp#chemistry

    I got real curious when someone said they made lug nuts for race cars out of magnesium.

    Looked up "magnesium lug nuts".

    http://specs.jazzproparts.com/wiki/Lug_nuts

    It looks to have become one of those trick words.

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  • Guest's Avatar
    Guest replied
    Originally posted by Evan
    Do you have a Class D fire extinguisher? Magnesium burns really well, especially when you put water on it. I won't machine magnesium even though I have some. The last thing I want is a metal fire.

    All too true. I saw a magnesium fire in a rocket engine turbo pump many years ago at Rocketdyne. It was completely gone in ten minutes.

    Magnesium is nasty to work with. You never know what's going to happen.

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  • Evan
    replied
    Magnesium isn't the least bit difficult to light in swarf form. It is so easy that all you need is a stick of lighter flint and a pocket knife. You can buy a fire starter stick anywhere that camping supplies are sold. It is magnesium with a large stick of Misch metal embedded on one edge. To use you shave off some magnesium with your knife and then strike some sparks on the shavings with the knife scraping the Misch metal.

    BTW, magnesium is NOT a component of 7075 or other 7000 series alloys. They are alloyed with zinc. Any magnesium in the alloy is restricted to less than .3% to zero. 2024 contains a small amount of magnesium, less than 2%. The regular aluminum alloy series are not alloyed with any significant amount of magnesium. There are aluminum/magnesium alloys but they are identified differently.
    Last edited by Evan; 05-01-2010, 06:07 PM.

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  • Thruthefence
    replied
    Many wheels, and indeed brake housings on commercial aircraft are magnesium. And yeah, they will catch fire & burn.

    "In fact I think I have heard somewhere where it is illegal for use in certain applications, in and or around brakes for one"

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  • JoeLee
    replied
    When I was in high school we had magnesium tape in the science lab. It came in short pieces about the size of a twist tie that you would put on your garbage bag. You could lite it with a match.
    One day while in the dark auditorium I lit up a piece, you would think someone was welding in there. Got my ass booted out for that stunt.

    JL..............

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  • drof34
    replied
    I once did some machine work on a pair of valve covers off a double A dragster that were made of magnesium. I had no trouble machining them and tried to burn the shavings but couldn't. Magnesium only burns when you don't want it to.

    Some time later was doing some welding on steel some 5 or 6 feet away and it (mag) caught fire in the middle of my shop. I scooped it up on a piece of plywood to take outside and when I did it exploded. It exploded because it had burned a hydraulic hose causing oil to get on it.

    I'm 76 yrs old but nearly half the skin on my left arm is only 2 yrs old. Once is one too many.

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