Thread: Melting aluminium

Originally Posted by RayG

Scrap Aluminium, sell it as scrap and buy ingots of a known alloy composition if it's a critical component.
I have been buying 6kg ingots of DA601 for $3.50/Kg.
I'm not adverse to melting down whatever is to hand, but when you want a known alloy it's cheaper and quicker to buy ingots.

Regards
Ray

damn thats cheap, I paid $4kg for some aluminium plate not long ago, 25mm thick. 70 odd kg. from the recycling yard.

I was thinking atleast double that for ingots.

I haven't had time for quotes but ill get some tommorow been flat out with my business.


How does it seperate a liquid into hydrogen, I would think any explosion is a rapid expansion of gases.

Originally Posted by Woodlee

Lathe bed ? I though he was talking about a bed to sleep on .
Kev.

i second that

didnt read all this thread but has anyone pointed out the cost of getting a lump of anything 1000X800mm!!!!!!!!!

you want to pay less than $1000 i would say forget about it and look for an alternative

Originally Posted by Ch4iS

damn thats cheap, I paid $4kg for some aluminium plate not long ago, 25mm thick. 70 odd kg. from the recycling yard.

I was thinking atleast double that for ingots.

I haven't had time for quotes but ill get some tommorow been flat out with my business.


How does it seperate a liquid into hydrogen, I would think any explosion is a rapid expansion of gases.

Like I previously said I'm not sure on the chemistry/physics of it others will know more than me, however from what I think I understand, the liquid (in the can of stuff) first changes to water vapour/steam and yes rapid expansion of gas, if the steam has not reached the air but is still trapped in the molten bath of alu due to the depth of alu, then chemical reaction thingy happens and the hydrogen component of the steam is free to ignite and burn and probably aided by the now free oxygen.
The chemists will be able to explain it
Peter.

Originally Posted by pjt

Like I previously said I'm not sure on the chemistry/physics of it others will know more than me, however from what I think I understand, the liquid (in the can of stuff) first changes to water vapour/steam and yes rapid expansion of gas, if the steam has not reached the air but is still trapped in the molten bath of alu due to the depth of alu, then chemical reaction thingy happens and the hydrogen component of the steam is free to ignite and burn and probably aided by the now free oxygen.
The chemists will be able to explain it
Peter.

Those who want to read up on the chemistry can look at this paper http://www1.eere.energy.gov/hydrogen...r_hydrogen.pdf

briefly, molten aluminium can dissociate water into hydrogen (the oxegen bonds with the Allie to form aluminium oxide) and the process has been seriously examined as a means of generating hydrogen

Cool paper.

Note that the this paper uses an alloy of aluminium and lithium or aluminium and gallium to produce hydrogen, not the aluminium silicon alloys that are being made in smelters. I would say the danger with water in a smelter is that aluminium is smelted by running an electric current thorough it, and this would definately split water into hydrogen and oxygen. This process is easy enough to do at home with a battery charger at room temp. However, at the casting stage there is no longer a current running through the aluminium and the potential for it to disociate water into Hydrogen and Oxygen is nil.

splitting water is easier that many would think.....it is nothing more than school boy science (boy scout science actualy).......if you have a hot enough surface and spray water onto it just right it will bypass or rapidly trasit thru the vapour stage and split into hydrogen and oxygen.......this is one of the problems with oil fires that have a substantial metal mass involved in them.....the steel typicaly will get and retain enough heat to split the water sprayed onto the fire and superfuel it.
I remember the process being detailed in a book on fire I read as a kid....the practical use is high temp incineration.

on a slightly different note
some large aluminium facilities completly ban glass bottles from the sites......what I understand is that the problem is that they can find their way into the recycling bins and then into the furnaces.....and that they may contain water and may cause an explosion in the furnace.


anyway back to the original point.

yep its a bigger casting job than it first seems..........in the past ( in the foundry age)... casting metal was a realy attracive way of doing lits of stuff.....thats why arround a certain time lots of stuff was cast.......these days there are so many other options......casting is only done where there are no more economical and practical methods.

seriouly it would be easier to fabricate it out of rolled products and machine it.

cheers

seriouly it would be easier to fabricate it out of rolled products and machine it.

I agree with that.

1/2" or 5/8" steel plate of that size would probably cost a few hundred, and machining finished fabticated item would surely not cost that much.

Hi Guys,

I did a bit of engineering work at Alcoa for 3 years.
This is the process at Alcoa Point Henry......
Smelting the bauxite into aluminium is done by electrical current.
It is then syphoned from the smelting pot, taken to the pot room furnaces, (they hold 50 tonne molten aluminium), alloys are then added to the molten aluminium. The alloyed aluminium is cast into 8 tonne ingots for rolling or into 250 kg sow's for others to remelt and add further allows as the used in miltary and aircraft industries.
All aluminium cans are banned from Alcoa sites. Plastic bottles are ok.
The aluminium can was the most common type of explosion in furnaces before cans where banned.
That's partly why all of Alcoa's can recycling is done at Yennora in NSW. The have a specific process that can elimate liquid entrapments.
The worst explosion comes from the water being trapped during the casting of the 8 tonne ingots. This is a water cooled "drop cast process".
Water becomes trapped and the steam becomes superheated, temps excede 900 degrees and boom.
I hope this helps.

A few years back I caught a couple of kids stealing lead flashing from one of my sites.

They were cutting it up and inserting it into alluminium cans before crushing the cans to get weighed at the recycler.

Kids will always come up with a scam.
I wonder what the lead does to the whole smelting process??

Originally Posted by Fossil

A few years back I caught a couple of kids stealing lead flashing from one of my sites.

They were cutting it up and inserting it into alluminium cans before crushing the cans to get weighed at the recycler.

Kids will always come up with a scam.
I wonder what the lead does to the whole smelting process??

Probably sinks to the bottom of the crucible. Any last ingots from the pour would likely be rejected by QC.

But I reckon they were too clever by half: The lead is probably worth more than the Al.

Cheers,
Joe

Very interesting, I'm learning something,

The process Boyne Smelter... alumina is loaded into the potline cells and smelted by passing electrical current thru the pot, in goes white powder out comes molten alu, it is then transferred to the casthouse where it is cast into either molds for ingots or billets in a vertical drop casting method, both these casting methods use water for cooling so possibly only a steam explosion could occour here but on the potline a steam and or hydrogen explosion could occour because of the electrical current. Does this sound right?

Was it 1.2volts dc or 12 volts dc anyway low volts but very high current must be a high resistance process. The magnetic field around the busbars would pull your foot towards it because of the steel in your boots, it would drag tools across the tray of the ute as u drove past, it would sound any vehicle dash alrms in the utes, it would stall some vehicles so u needed a run up to get over the busbars in some places.

Peter

Originally Posted by 19brendan81

Cool paper.

Note that the this paper uses an alloy of aluminium and lithium or aluminium and gallium to produce hydrogen, not the aluminium silicon alloys that are being made in smelters. I would say the danger with water in a smelter is that aluminium is smelted by running an electric current thorough it, and this would definately split water into hydrogen and oxygen. This process is easy enough to do at home with a battery charger at room temp. However, at the casting stage there is no longer a current running through the aluminium and the potential for it to disociate water into Hydrogen and Oxygen is nil.

Brendan
this is not the forum to debate the physical chemistry of the reaction of water and molten aluminium.

Surfice it to say the reaction occurs easily with pure aluminium and water, but in the "normal" world the reaction does not occur because the aluminium is covered by a layer of Aluminium Oxide. Molten Al doesn't have this protective layer so can readily split water. From what I remember of my chemestry, the addition of lithium or gallium to Al, as described in the paper, is most probably about preventing the formation of a protective layer of Al oxide.


BTW This is not an experiment to try at home

I bought a flat sheet of alum 1200x1200 x 12mm thick for a base ,just screw some angle to stiffen up and you have it ?? Cheers bob

Originally Posted by Woodlee

Lathe bed ? I though he was talking about a bed to sleep on .
Glad I didn't jump in and make a fool of myself

Kev.

So did I mate ! Machining Al can be a big problem if it is too soft . It gums up your cutters and smears al around stoping the clean cutting action .
Melting scrap could result in an unknown machinability . It could be good or it could be bad.
Grades like 6061 are good to machine with carbide inserts and HSS tooling . Giving nice surface finish .