Hazards of machining Magnesium

A new customer has a few jobs to quote, machining Magnesium parts.
Several area shops declined the work.
A quick visit to their shop, and there are no heroic fire suppression efforts.
Just a few Drill Tap machines.. They outsource a lot of their production, beyond their in house machining.

Initially, I am wary of magnesium. Is it as bad as some would suggest?
Will there be insurance concerns?

Thanks for any guidance.

We have machined magnesium and it's not as bad some would make it sound. Actually it machines very similar to aluminum. Here is what I would recommend as good housekeeping techniques if you get the job.

Make sure you clean out your chip pans. That way when you machine the magnesium you can keep it completely separate from the other chips.

Don't store the chips inside for long periods of time.

Of course avoid all open flames.

When the job is completed - take the chips outside and light 'em up - very fun!

Back in the 70s there was a fire from the machining of magnesium at Wentworth Institute in Boston. The fire was in a lab doing research for the Air Force and was caused by poor housekeeping. What Joe Miranda advised should prevent any problems as it is the chips that are easy to ignite, not the solid.

^^ Yep, it cuts very similar to 7075 aluminum, maybe a bit easier.
Make sure you have the correct type of fire extinguisher on hand ( I think class D or C, can't remember).
Just use common sense with the chips, so an errant spark doesn't land in them or else you'll have a fire that will burn underwater.
SHARP tooling!! Don't let your cutters rub and create heat.
Other than that, it's not that bad.

have a small foundry and was melting what i thought was aluminum. when i removed furnace lid molten magnesium metal on fire with bright white flame and white ash.
.
i ended up digging a groove in the dirt outside and pouring in groove and covering it up. it was still burning for quite some time. no easy way to put fire out. i hate to think what that would do to a machine. i was told to cover fire with dried sand to smother it as water makes it worse. i did not even have pure magnesium but a mix of magnesium and aluminum. pure magnesium even worse i would think.

And above all, if a fire were to start, NEVER, NEVER, NEVER use water to put it out. NEVER! I remember a fire in Chicago quite a few years back. Some idiot was storing 55 gallon drums of Magnesium, 100's of them, as scrap prices were down. They self ignited (magnesium will do that) and this fire burned for a week because the fire dept. could not get close enough to the epicenter of the fire to adequately contain it. It will also burn through the castings on your machines. Nasty stuff once it is burning.. But it's not likely you could start it with a match. Heavy chips are less likely to ignite than fine, hairy stuff. Class D fire extinguisher next to each machine.

Edit: Titanium will burn the same way, just not as hot. But still hot enough to burn through a machine casting.

yes, class D extinguisher and water based coolant.

I have seen 5 fires on machines running oil and Ti, but never got hot enough to get the Ti going well. (it DID cause the switch to water based tho...)
Keep the tools sharp and chips cleared out, no biggie.
if... IF a fire starts, do NOT hit the E stop! stop the spindle but leave the coolant on! that will usually put out a flare up.
you do NOT want dust!

***EDIT:
The water based coolant comment was from experience with Ti... I'm not sure how Magnesium does with water...

I've done a fair amount of mag machining for satellite use. But, I don't play a doctor on TV, so YMMV:

1) No water-based coolant. Some use mineral oil, I cut dry, conservatively in speed, faster in feed to keep chips a big as possible.

2) Sharp tooling, I like fresh carbide, two or three flute endmills, low helix. Drills are a little trickier without coolant, but bigger drills the same - slower speed, faster feed, and modest pecking to make sure chips can't pack. With small drills careful use of an air blast may help. Watch for dulling!

3) PROVE OUT the program. No crashes or other events that could cause heat or sparks allowed.

4) Frequent cleaning of the machine to limit chip build. No more than 5-gallon steel buckets (metal covers!) for mass storage, keep outside away from anything important and separated from each other. You can make "bunkers" by stacking paving blocks or similar between buckets. Keep water or rain away, so at least a good shed is recommended. Extinguishers of the right type at the machine and near the shed.

5) Mag has a very low modulus of elasticity for a metal, so be careful fixturing parts. Don't over-tighten the vise, but be sure the part can't come loose. Mag can sometimes have the same tendency to "self feed" that brass and acrylic do. If you mod drills don't go for a vertical chisel edge, a slight rake is good. Sharp too!

I made an isolation bucket (5-gallon) so that I could run a Shop-vac but not have the chips build up in the vac itself. I used conductive hoses to minimize risk of static causing a spark, be sure to ground the hose. Empty into long term storage frequently. Change the filters when they get at all clogged, don't try to cheap out here.

Check with the local fire department to see if there's regs for storing mag in your area. At the least, they would want to know what they're dealing with if you ever have to call them. Check with your insurance co, make sure you're covered. If you need a special rider get one, add that to the cost of work.

DMF_TomB said:

have a small foundry and was melting what i thought was aluminum. when i removed furnace lid molten magnesium metal on fire with bright white flame and white ash.
.
i ended up digging a groove in the dirt outside and pouring in groove and covering it up. it was still burning for quite some time. no easy way to put fire out. i hate to think what that would do to a machine. i was told to cover fire with dried sand to smother it as water makes it worse. i did not even have pure magnesium but a mix of magnesium and aluminum. pure magnesium even worse i would think.

Click to expand...

One common way to handle mag in the foundry is add sulfur to the melt. The sulfur fume is heavier than air, displacing oxygen. When poured, the sulfur blankets the molten metal.

Tom

metalmaster10 said:

***EDIT:
The water based coolant comment was from experience with Ti... I'm not sure how Magnesium does with water...

Click to expand...

Bad - no water based coolant, it's seriously dangerous.

I think it also depends on what volume of mag swarf/chips you will end up making? And just out of interest how are various quantities of magnesium "chips" normally disposed of? One would think if they are mixed with chips from other metals then you have the beginnings of an incendiary bomb/thermite type process?

[ A fiend of mine (now passed) working at Curtis Wright (at the time) said that in the 1940's they were working with magnesium for the first time for the B-29 engines/crank cases and did have several shop fires in spite of common sense precautions. Maybe someone in the aviation industry has a set of formal procedures and guidelines. Magnesium is also used a lot in the camera industry too, I don't know how they get away with it also?].

If it were me I'd be tempted to mix the magnesium chips with an inert filler such as dry sand so that each magnesium alloy chip is diluted or separated by its neighbors so it can't burn all together. But not sure how you dispose of a sand and magnesium mix, or whether there is a carefully buffered aqueous solution (like an organic acid that can safely put the magnesium chips in solution (and render them inert) without an extreme exothermic reaction? [MAJOR DISCLAIMER HERE!!!] but there must be someway to render Mag chips as less dangerous?

Otherwise the recyclers might have an answer? Scrap Magnesium Recycling Category -- Non~Ferrous Scrap Metal Recycling



Ta...

It's worth checking the material spec as it may be a magnesium /aluminimum alloy.

I expected to open this thread and see a machine melting to the ground

hello
we would run it dry
and always kept a 5 gallons buckets of sand nearby
no liquid
that would be like dropping water in a deep fryer
this stuff burns way hot
and bright almost welding arc bright
if you want to experiment
try a few chips at first
so you know what to expect
have a good day

Rstewart said:

I expected to open this thread and see a machine melting to the ground

Click to expand...

Hah! The work I mentioned above did lead to two small fires, one in a bandsaw (easy to do because of blade rubbing on the guides), and one in a manual lathe. Again, frequent cleanouts help a bunch.

I've machined a fair amount of mag. I bought a type D fire extinguisher, and I also had a 5 gallon bucket of kiln dried sand to smother with, along with a long pair of pliers to grab pile of chips on fire if needed. Never needed any of it, and I was doing everything wrong... making small chips (engraving and ball nose stuff), water based coolant, running max RPM on all tools, etc.

A mag fire is bad news, no doubt about it. BUT, you have to get it burning first. I tried lighting some very fine chips with a lighter and could NOT get them to catch. Tried burning them on the concrete floor and even in the machine... no dice. I lost a lot of paranoia that day. Still gotta respect the stuff though.

Don't leave parts in a wet fixture over night.

Coat finished parts with WD40 as soon as they are finished.

Be prepared to change your coolant after the job. Mag will fuck your coolant right up unless the coolant is meant for mag.

Magnesium doesn't "burn" underwater, but is reactive enough to oxidize underwater, generating quite a bit of heat. If the magnesium can strip the water of oxygen, the the H (hydrogen) in H2O is left bubbling to the surface. Hydrogen and heat love to be together, or hydrogen and sparks.

Matt@RFR said:

Be prepared to change your coolant after the job. Mag will fuck your coolant right up unless the coolant is meant for mag.

Click to expand...

Yes it does, I've never done a LOT of magnesium, just some castings with a limited amount of metal removal and you end up
with black slime floating all over the place.

As to water... Wrap up some chips in a piece of paper, light the paper, and let it start smoldering... Not all that
exciting... Then give it a squirt from a water bottle.... Then it gets exciting... Keep your distance and make sure you
are outside far away from stuff that can burn.

Thing to remember about magnesium, yes it takes some heat to get it too light, but the secound it has lit, you can only smother it, water both smothers and cools knocking out 2 corners of the so called fire triangle, hence putting it out is the challenge. A fist size ball of lose fine chips burning up won't bother much at all, get a machine half full and its a different story, hence good shop practice - cleanliness and even the odd small fire really won't bother much at all. Key thing is treating it like a hot work - welding type job, keep flammables clear and limit any fuel sources.

Personally i would be more concerned about swaft disposal, i don't know what the price is but its probably worth checking as i seam to remember, it can have a pretty good scrap value. Key thing is storing it safely. Definitely outside and in a place were it won't cause harm if it does go up. The comments about keeping it dry are spot on too, rain on a a large enough amount would undoubtedly self heat to ignition point with ease.

cameraman said:

[ A fiend of mine (now passed) working at Curtis Wright (at the time) said that in the 1940's they were working with magnesium for the first time for the B-29 engines/crank cases and did have several shop fires in spite of common sense precautions. Maybe someone in the aviation industry has a set of formal procedures and guidelines. Magnesium is also used a lot in the camera industry too, I don't know how they get away with it also?].

Ta...

Click to expand...

How many fiends do you have?

In a different life I rebuilt about a jillion VW engines. Never set one on fire. Seen many burn up in vehicles though from leaking fuel lines.