Burning mag wheels (on purpose)

**pzkpfw** · 2nd November 2007, 11:58

Hi,

I once read in a car magazine about Volkswagen clubs dumping old transmission cases onto their bonfires - apparently there's magnesium in them.

Now, tommorrow night we have a bonfire at a mates farm, and I've seen some really old "mag" wheels in one of his sheds (only three of them, and very old).

So, some questions:

Is there any way to tell what a wheel is made of? (Maybe a destructive test of a small piece?)

Would chucking one of these rims in the fire be a really stupid thing to do? (Any chance of "explosive" reaction?)

Anyone ever done this?

Cheers,

**ManDownUnder** · 2nd November 2007, 12:16

Pure magnesium will burn like there is no tomorrow. It's an optional ingredient in various pyrotechnics and napalm...

Mags (or more accurately Magnesium Alloys) are an alloy of Aluminium and Magnesium (mostly Aluminium). Not sure it'd burn but my money is on it doing nothing. Get a file, take off some fine filings and throw them into a fire. If it sparkles you have some fun on your hands...

Some aircraft parts are pure magnesium and if they ever got lit it could be exciting...!

**Ocean1** · 2nd November 2007, 12:58

Almost all "Mags" contain no magnesium. I know older Alpha's were a high mag alloy and burned very nicely, probably applies to a lot of early european sports car castings. Like the man says, chuck some filings onto a good flame...

Re really silly: magnesium burns rather hot, and most mag aloys need no external source of oxygen. If somat turns to shite run far far away, chucking a bucket of water on it is a seriously bad idea.

Oh, and if you ever need to weld up XL350 cases be very careful or, umm, bad stuff might happen.

**ManDownUnder** · 2nd November 2007, 13:09

Originally Posted by Ocean1

magnesium burns rather hot...

LMAO... ok to define "rather hot". It's like saying the Pope has a passing interest in religion.

And yes -do NOT add water. I don't know the details but it's explosive to the already insane burning process.... Once it's started I advise you stand back. Don't bother trying to do anything about it - you won't.

So don't start it if you have the need to stop it...

Shame really because it's a nice metal to work with (a la the aircraft parts I previously mentioned). Just need to be careful when disposing of swarf etc.

**kiwifruit** · 2nd November 2007, 13:20

give it a go

stand well back

perhaps do it in a hole with the option of pushing a load of dirt over it

video!!

**Ocean1** · 2nd November 2007, 14:04

Originally Posted by ManDownUnder

LMAO... ok to define "rather hot". It's like saying the Pope has a passing interest in religion.

And yes -do NOT add water. I don't know the details but it's explosive to the already insane burning process.... Once it's started I advise you stand back. Don't bother trying to do anything about it - you won't.

So don't start it if you have the need to stop it...

Shame really because it's a nice metal to work with (a la the aircraft parts I previously mentioned). Just need to be careful when disposing of swarf etc.

Err, 'bout 3000 C as I recall. Warm enough to qualify as rather hot.

Not sure of any additional reaction with water, don't think it's hot enough to liberate further oxygen.... (yoo hoo, BASS?) Just dangerous levels of steam and little to zero effect on the combustion process.

**Tank** · 2nd November 2007, 14:09

I recommend doing it in a neighbours back yard rather than your own.

**avgas** · 2nd November 2007, 14:15

If your gonna burn some mags fill up the tyres with oxy/axl.....

**riffer** · 2nd November 2007, 14:28

Hmmm. I'm pretty sure the RF900 Cam chain cover is magnesium...

If I ever blow up the bike this could be fun.

**Bass** · 2nd November 2007, 15:22

Originally Posted by Ocean1

Err, 'bout 3000 C as I recall. Warm enough to qualify as rather hot.

Not sure of any additional reaction with water, don't think it's hot enough to liberate further oxygen.... (yoo hoo, BASS?) Just dangerous levels of steam and little to zero effect on the combustion process.

Sorry to disappoint, but I'm not sure about this one. The 3000 C sounds about right and I know that CO2 extinguishers can make it worse cos Mg burns in CO2, but I don't know if it's hot enough to dissociate water and use the products.
I suspect that small amounts of water would cause molten burning Mg to splatter over a fair area with some pretty nasty consequences though. Thats just extremely rapid steam generation and ensuing violent expansion but.
It would also depend on the proportion of magnesium present. I don't know any specifics, but I thought that Mag's and in fact most mag castings were still mostly ally - but you already know that I see upon reading the whole thread

**The Pastor** · 2nd November 2007, 15:53

its 2000 degs not 3000 afaik

**mitchilin** · 2nd November 2007, 16:17

Aluminium will burn if it gets hot enough.Thermite is a mixture of aluminium and rust so even if its not a "mag" it may catch fire.Got a fireman mate who reckons the vw's that got torched would burn thru the road and there wasn't anything they could do.A toolmaker mate was working a lathe too hard on a piece of aircraft magnesium and fucked the lathe when it caught fire.Give it a go though, it's not going to explode it will just burn really fiercely and you may see spots for days

**wildpudding** · 2nd November 2007, 16:18

I have a good idea....

[YOUTUBE]http://youtube.com/watch?v=rogZBXNqaMo[/YOUTUBE]

**Mikkel** · 2nd November 2007, 16:20

Well, being a firefighter (way back though) I hope I might clear up a few things.

AFAIK both aluminium and magnesium will burn - however, they're both quite hard to set off. As in, you need a FUCKING hot fire to begin with, if you wanna have any hope of igniting it. When they burn, they burn extremely hot with a very characteristic white flame (exact temperature, I do not know and shall therefore not pull any figure out of my ass). The metal does not actually melt in the combustion process (and yes, this is very rare since most solids will have to melt - and THEN evaporate to form combustible components).
As Bass rightly said they can burn hot enough to dissociate the hydrogen and oxygen in water - giving you the perfect 2:1 ratio that'll result in a nice explosion right then and there. However, NOTHING burns in CO2 - all fires need O2 to burn and in most cases CO2 will displace O2 since it's a more dense gas. That being said, I can not exclude the possibility of CO2 dissociating at some temperature, whether it is possible for a magnesium fire to reach this temperature I can not say. Someone with a basic knowledge of chemistry should be able calculate the free energies involved in the dissociation process and figure out the thermal energy necessary.

As for your party. I'd say you'd probably be disappointed unless you got an acetylene blowtorch to set them off with. When they burn they don't burn explosively but steadily. It's not dangerous as such, just don't look at it directly without sunglasses or for long. Oh, pray that some drunken fool does not chuck a beer at it.

Good luck