Is Magnesium ok? [Archive]

Gravity

31-05-2016, 12:52

Magnesium is pretty explosive, so if you have some magnesium chips in your electronics, your robot might catch fire. I'd say it would fall under "hazardous materials", but you should ask a robot inspector :rolleyes:

You also can’t put out a magnesium fire with CO2 or water so be careful.

Ohh, and also don't let it get wet.

anthonyttu

31-05-2016, 13:02

Magnesium is not explosive it is used for wheels on high end cars all day long. The shavings or swarf created when machining do need to be handled properly they can catch fire and burn very well once they catch. The little fire starter kits that you scrap the savings off then spark up is a block of magnesium and flint for the spark.
If you have a mentor or sponsor that has a ton of it and machines it regularly great.
If you just want an exotic metal on your robot to say you used it there are way more exotic materials with very wide range of properties i.e. hastelloy torlon.
Willing to bet 6061 Aluminum will still work

Jon Stratis

31-05-2016, 13:23

Magnesium is not explosive it is used for wheels on high end cars all day long. The shavings or swarf created when machining do need to be handled properly they can catch fire and burn very well once they catch. The little fire starter kits that you scrap the savings off then spark up is a block of magnesium and flint for the spark.

This would have me concerned with respect to machining in the pits... Could I just pick up any old drill and start punching holes in it without any risk of it catching fire? What about cutting a bit off with a hacksaw or saws-all? Do I need to be worried about the little scraps and dust posing a fire risk in the pits?

All of these could be grounds for either not using it or not permitting machining on it at an event - remember, safety is more important!

Munchskull

31-05-2016, 13:29

I am familiar with magnesium's firiery tendencies. That said it is my understanding that magnesium only combusts when it melts. This question is purely academic. Also what is the danger if getting magnesium wet?

techhelpbb

31-05-2016, 13:31

Ignition requires a mixture with adequate oxygen.
I used to make thermite I doubt your drill will do it unless you rub the bit quite a bit.

DO NOT play with thermite it can be very dangerous.
I am familiar with magnesium's firiery tendencies. That said it is my understanding that magnesium only combusts when it melts. This question is purely academic. Also what is the danger if getting magnesium wet?

Magmesium when lit will reach adequate temperature to seperate H2O into hydrogen and oxygen (disassociation). Causing an immediate flare up.

Watched a fire truck full of water try to control a magnesium fire..burnt down 10 trees because they added water. DO NOT mess around: magnesium fuses can be used to ignite charges under water.

ThaddeusMaximus

31-05-2016, 14:05

There's a difference between "ok" and "suitable". You are building an FRC robot; you need it to be cheap, easily made, and have quick turnaround. Lightness is important, but considering the above three, magnesium doesn't seem to be the right material for the task at hand.

Of course there are exceptions (see: carbon fiber can grabbers in 2015).

Gdeaver

31-05-2016, 14:17

If you build with the better AL's you are already using it. It's one of the components of AL alloys.

Alan Anderson

31-05-2016, 14:41

The caution against getting it wet might be confusing magnesium for sodium (or potassium or another alkali metal). While it does burn spectacularly as a powder or shavings (or when molten), there is a significant difference between alkali metals and alkaline earth metals. Sodium reacts with water and is likely to ignite the hydrogen produced by the chemical reaction. Magnesium only has issues with water when it's already burning.

RoboChair

31-05-2016, 14:47

Using magnesium would only pose an issue if you are using open flame in the pits(which you shouldn't as per the rules), or are producing arcs(which you shouldn't). Magnesium is not some super sensitive substance that will spontaneously light on fire, you deliberately have to try and ignite it unless it is a finely divided powder. Aluminum powder is flammable too. As long as you work with it properly and keep chips out of your electronics I see absolutely no problems.

I would bet money that you can't ignite a size-able block(greater than 0.25" minimum dimension) of magnesium with a blowtorch(not a welding torch) in under 15 seconds. Magnesium shavings or ribbon are a different matter but even ribbon still takes effort. Buy a Class-D extinguisher if you are that paranoid.

OccamzRazor

31-05-2016, 14:47

You could also use magnesium alloys that do not have such dangerous properties. You get the weight savings and in general less concerns over volatility.

I believe the .625" dia rod you get every year in the IGUS kit is a magnesium alloy. (correct me if I am wrong?)

Greg Woelki

31-05-2016, 15:42

I believe the .625" dia rod you get every year in the IGUS kit is a magnesium alloy. (correct me if I am wrong?)

Nope, it's a hard-anodized aluminum shaft.

Cory

31-05-2016, 15:56

I see no real safety risk associated with magnesium in the operation of the robot or in the pits at an event.

That being said, you could burn your shop down if you are milling/turning/sawing it and create fine chips that accumulate and aren't cleared out of the machines.

I don't think it really functionally offers any advantage either. there are very few non-power transmission areas on a FRC robot that benefit from more advanced materials than 6061. Those that do you're usually best off with 7075 or 4130/4140/4340.

Mike Schreiber

31-05-2016, 16:07

Wasn't the housing on the NI cRIO magnesium? No one started any fires - although hopefully no one was machining it.

DonRotolo

31-05-2016, 20:44

BBray_T1296

01-06-2016, 00:38

Wasn't the housing on the NI cRIO magnesium? No one started any fires - although hopefully no one was machining it.

No, it was almost certainly certainly steel. Those things were heavy!

InFlight

01-06-2016, 00:50

One of the reasons magnesium (and it's alloys) isn't used much is because it corrodes at a very high rate in comparison to aluminum.

In terms of strength to weight ratio, both Titanium and Alluminum are ahead of Magnesium.

Magnesium prices tend to be volatile, cost is typically quite a bit more than Alluminum but less than Titanium. Magnesium tends to be used for castings and occasionally forgings;, but not normally drawn bar/sheet or extrusion stock.

Nate Laverdure

01-06-2016, 08:09

Wasn't the housing on the NI cRIO magnesium? No one started any fires - although hopefully no one was machining it.
No, it was almost certainly certainly steel. Those things were heavy!
Nope (http://www.chiefdelphi.com/forums/showthread.php?threadid=116253), it's aluminum.

barevalo

02-06-2016, 06:02

Last time I checked, Magnesium is Mg not Ok.

IronicDeadBird

02-06-2016, 09:12

Last time I checked, Magnesium is Mg not Ok.

Beat me to it...

InFlight

02-06-2016, 11:33

Last time I checked, Magnesium is Mg not Ok.

"Magnesium is OK" when it's used in Aluminum Alloys. Both the very common 6061 & 7075 aluminum alloys contain Magnesium.

Magnesium is also used in almost all Steel & Stainless Steel Alloys. MG isn't used in Titanium alloys, as it's not soluble with the any of the TI phases.

RacerX

02-06-2016, 12:54

Our racecar has many magnesium parts, injector, supercharger case, valve covers and manifold. The entire body was made of magnesium sheet.

We have done quite a bit of machining, drilling and tapping of these parts, and never had any issues. But, we did make sure that all shavings were disposed of properly, and were kept from any ignition sources.

It does corrode if left untreated. Most all of our parts were Dow 7 dipped for a coating. They looked nice.... :)

http://www.chiefdelphi.com/forums/attachment.php?attachmentid=20827&stc=1&d=1464886451

Clem1640

02-06-2016, 17:14

I see no real safety risk associated with magnesium in the operation of the robot or in the pits at an event.

That being said, you could burn your shop down if you are milling/turning/sawing it and create fine chips that accumulate and aren't cleared out of the machines.

Cory accurately identifies the hazard of working with magnesium. It's not so much with the robot in competition.

My camera body is cast magnesium, due to the weight benefits provided.

Mark Holschuh

02-06-2016, 19:33

I once proposed to make some small engine parts out of magnesium alloy. Our company's insurance company threatened to cancel our policy immediately if we machined them in house. (They didn't work very well.)

PAR_WIG1350

02-06-2016, 20:54

Mechvet

02-06-2016, 20:58

As many have noted, Magnesium in typical form is no more dangerous than any other metal - even underwater. However, smaller chips or particles are able to be ignited, and then become extremely difficult to extinguish.

Yes a class D extinguisher has a chance, but hav limited effectiveness and are costly.

If you use the metal and don't need to machine it, you'll be fine. But if it needs to be machined, you are better off avoiding it. The risk is small but the consequences very large.

This is a line of reasoning that's excellent. Risk v. reward is always an excellent comparison to run before selecting something outside the "norm."

I once proposed to make some small engine parts out of magnesium alloy. Our company's insurance company threatened to cancel our policy immediately if we machined them in house. (They didn't work very well.)

Seems like a rather uninformed reaction for an insurance company. Magnesium has applications all over, and can be machined and used quite safely.

Just get a Bromotrifluoromethane extinguisher (Halon 1301) for areas where swarf and chips can gather, and all will be well. I've personally used a CBrF3 extinguisher on several fully ignited systems (one jet engine, two transmissions, and one interior cabin fire involving vaporized JP5) with great success.

ctt956

02-06-2016, 21:29

Seems like a rather uninformed reaction for an insurance company. Magnesium has applications all over, and can be machined and used quite safely.

Just get a Bromotrifluoromethane extinguisher (Halon 1301) for areas where swarf and chips can gather, and all will be well. I've personally used a CBrF3 extinguisher on several fully ignited systems (one jet engine, two transmissions, and one interior cabin fire involving vaporized JP5) with great success.

Wow, that's a lot of fires! :eek: Halon hasn't been produced in over 20 years, but it's still legal to use if you can find some; end of first section here (http://www.h3rcleanagents.com/support_faq_2.htm).

techhelpbb

02-06-2016, 21:54

Fine silicon sand works but not instantly and you need enough sand to bury the fire and cut off the oxygen.

The sand will also take heat from the magnesium helping to bring the mass below ignition.

Be very careful: you need to keep adding sand for some time while eliminating other things that can ignite and this means you need to be close to a hot fire. The sand itself can be fuel in small quantites mixed into the magnesium dust. You need to bury and not mix.

There are several YouTube videos that show mixtures of magnesium dust and sand flaring up: in these cases the sand to magnesium ratio is too low and the 2 are mixed.

adciv

02-06-2016, 22:44

Just get a Bromotrifluoromethane extinguisher (Halon 1301) for areas where swarf and chips can gather, and all will be well. I've personally used a CBrF3 extinguisher on several fully ignited systems (one jet engine, two transmissions, and one interior cabin fire involving vaporized JP5) with great success.

USAF?

Dan_Karol

03-06-2016, 00:02

Alloys of various metals can have hugely differing properties in certain areas. throwing blanket statements about classes of materials isn't always appropriate. Please see the link below for some testing performed by the FAA in related to this very topic of conversation.

https://www.fire.tc.faa.gov/pdf/AR11-13.pdf (https://www.fire.tc.faa.gov/pdf/AR11-13.pdf)

Knowing how badly it can go if not handled properly, I highly caution inexperienced users form considering magnesium in FIRST. That said, from experience, I can say that there is at least one Magnesium alloy that can withstand some impressively high temperatures after being machined into fine chips without burning

Dan_Karol

03-06-2016, 12:57

The alloy from my previous post is AZ91D

Mechvet

03-06-2016, 16:14

Wow, that's a lot of fires! :eek: Halon hasn't been produced in over 20 years, but it's still legal to use if you can find some; end of first section here (http://www.h3rcleanagents.com/support_faq_2.htm).

The supply system that I worked inside of had enough Halon to last for quite a long time, so acquisition was never a problem.

Also of note are some of the AFFF agents used in fighting large (and very hot) fires, but these are utterly impractical and too expensive for an FRC team.

The principle of operation is the same: Remove the access to oxygen as rapidly and thoroughly as possible.

USAF?

USMC.