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Ch4iS
3rd Aug 2009, 07:38 PM
Hi, I was looking to get a bed made out of aluminium, I would expect ~ 50kg of aluminium there.

Where would I go to find a foundry who will melt my scrap aluminium I have about 15KG now (offcuts from some little projects I have been doing) but I will go hunting for more soon (buying billets would be a huge waste of money)

Also how does aluminium machine if I wanted to face the bed?

Its a new thought on how to make a small cnc router as the chinese seem to do this alot but with steel.


Or does anyone in NSW have a big furnace :D


I have found a few companies I will call tommorow but just wondering if someone can recomend a smaller business who will not charge through the roof to melt the alu.

What price should I expect from the larger companies? $500, $1000?

.RC.
3rd Aug 2009, 09:18 PM
Foundries do not melt metal you supply (AFAIK)...You give them the pattern and you tell them what you want and they supply you with the finished article..

With foundry work you need special fluxes and other stuff to get good clean metal...

ian
3rd Aug 2009, 11:43 PM
my take is that supplying and melting the Al is a small cost compared to the cost of preparing the pattern and then the mold

You might be able to get a partial credit for your scrap Al if you toss it into foundary's scrap bin

Lastly, others will know more, but compared to steel does Al have the properties — stiffness, heat capacity, etc — needed in a lathe bed?

Woodlee
4th Aug 2009, 12:52 AM
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 :doh:

Kev.

Ch4iS
4th Aug 2009, 02:14 AM
my take is that supplying and melting the Al is a small cost compared to the cost of preparing the pattern and then the mold

You might be able to get a partial credit for your scrap Al if you toss it into foundary's scrap bin

Lastly, others will know more, but compared to steel does Al have the properties — stiffness, heat capacity, etc — needed in a lathe bed?


na router bed, I will design a example and post some pictures.

added pics of a quick mockup.


Now that I think about it I think it would be closer to 100KG

Mockup is max 1050x850x120 so its massive.

bollie7
4th Aug 2009, 08:44 AM
Mate
For that size I reckon you would be better off watching the auctions and /or scrap yards for a 2nd hand cast iron marking out table or even an old worn out radial arm drill. strip the drill down and salvage the base. I know you are probably looking for lightness but I reckon a one off in that size would cost a bit to get cast and then you would have the cost to machine it as well. Something that size is not what your average home shop machinist has the machine capacity to handle.
Something else might be worth thinking about, though it would be pricey as well, is trying to buy part of a billet of alloy. There is a smelter near where I live and I quite often see billets on trucks. they look about 200mm thick X about 1000mm wide X 2 or 3 metres long. If you could find out who buys them maybe you could buy part of one and machine it. Either way its going to be an expensive exersize.

bollie7

gmack
4th Aug 2009, 10:12 AM
Ch4iS,

Based on my experience in the Aluminium industry......
It is most unlikely that anyone will cast the bed you designed up.:?
For the likes of Alcoa and Alcan, when these smelters do their casting of ingots, they normally cast 10 tonne ingots at a time.:((
However, Alcoa (Victoria) do cast small (approx. 250kg) sough ingots.
Alcoa has a plant at Yennora (they recycle aluminium there), that would be your best bet in NSW.:D
You may be able to find some smaller companies that do their own in-house castings, but majority still source their aluminium from either Alcoa or Alcan.
You would be better maching one of those, not casting.:)

For a casting, you will need to consider the following options.......
The casting would be a typical "sand box" casting.
(Don't go for "lost foam" casting, costs more than sand box)
You will need a professional designer to desin the cast model....$1k (min. thats what I do):oo:
Pattern made for the casting....$1k (min):oo:
No engineering business will be able to use your 3d model either, CAD software is far more complex than Google SketchUp.
You are looking at quite a expensive and complex process, thats why eveyone gets thsi done in China.:(
Hope this helps
Glenn

19brendan81
4th Aug 2009, 12:32 PM
Try google, there are a number of small companies that cast small run specialist parts out of aluminium in Australia. I have no idea what they charge or whether they will do your job, but when I was researching my DIY home foundry I stumbled accross a number of these sites. One of them had pics up of some castings they did and they were magnificent.

joe greiner
4th Aug 2009, 10:38 PM
na router bed, I will design a example and post some pictures.

added pics of a quick mockup.


Now that I think about it I think it would be closer to 100KG

Mockup is max 1050x850x120 so its massive.

Rule of thumb: For equivalent stiffness of flat bars, aluminium should be about 1.5 times the thickness of steel, width held constant. Slightly more complicated for other shapes.

The shape depicted can have stiffer torsional resistance, with the ribs oriented diagonally each way, instead of rectangular. Refer to Blodgett's book on welded structures.

Cheers,
Joe

soundman
4th Aug 2009, 10:45 PM
A mate of mine used to cast ram tubes and manafolds in his back yard, and thera re plenty like him... BUT.... a 50Kg lump... thats a bit of an ask for most back yard set ups......you need a lot of heat to deal with that amount of ally..........


cheers

gmack
5th Aug 2009, 11:41 AM
Ideal pouring temp for aluminum is 750-800 degrees.
Also, aluminium does not change colour at any temp either.
You must also remember, get any water trapped by pouring and you create a hydrogen bomb....
ie; sand must be dry.

19brendan81
5th Aug 2009, 11:46 AM
Hydrogen Bomb? Not really. All green sand mixtures used for casting contain a certain amount of water in them, the sand will have no strength if it doesnt. If you have too much water, you get excess steam which can bubble through the molten aluminium, potentially spitting it around the place, but you will never get a hydrogen explosion.

Of course if you use oil bonded sands like petro bond you dont have to worry about this.

gmack
5th Aug 2009, 12:26 PM
19brendan81,

I have seen this first hand, the water is trapped in the casting and cannot escape.
In the dropcast method, water does not "bubble" and does not escape.
The water content becomes steam before the molten metal even touches the water.
The water becomes superheated steam, and it then expands immensly.
A small explosion occurs, which is exactly the same principle of a hydrogen bomb.
This is why casting aluminium is very dangerous process.

19brendan81
5th Aug 2009, 12:35 PM
800 degrees in nowhere near hot enough to make water seperate into hydrogen and cause an explosion. What you are describing is the result of poor venting in a mold that has been too tightly packed causing steam to blow through the molten aluminium, as I described earlier.

All metalworking processes have their own risks, most of which can be mitigated. In this instance, if people are worried about foundry explosions, use $90 a bucket petrobond sand instead of green sand...no water, hence no steam or explosions of any kind.

P.S for the record, a hydrogen bomb uses a regular nuclear bomb to compress and initiate fusion in a secondary nuclear bomb, releasing prodigal amounts of energy in the process. This has not, and never will occur in any foundry work of any kind.

RayG
5th Aug 2009, 09:20 PM
Interesting project, it might be overreaching a bit for a backyard furnace, but lets crunch the numbers and see what would be needed...

1. 1050 x 850 x 50 would be 44.6 liters volume of Aluminium.
2. The density of Aluminium is 2700 Kg per m3. (2.7 kg per liter)
3. So a guess at the weight would be 44.6 * 2.7 = 120 Kg
4. Allowing for slag and degassing etc, you would want at least 50-60 liter capacity crucible, a little bigger is always better.

5. The weight of the crucible plus the 120Kg of aluminium is going to be of the order of 200Kg (just a guess)

6. 200 Kg will need some mechanical lifting and pouring mechanism, remembering that this is stuff at 700 degrees plus.
This is going to require OH&S considerations to be taken seriously :D

7. The amount of heating required, is doable with an air forced propane burner and good insulation.

Ok, suppose, we now have 50 liters of molten aluminium and the means to safely handle and pour it.

8. We need to prepare and pack a sand mold that is bigger than 1m x 1m, and make sure we can pour it without too many defects.
This is going to depend on the design of the pattern and making sure we have correct venting, gating and so on..

9. The chances of success in getting a good casting is dependant on how much experience you have in the design and implementation of the casting process.

Conclusions.
This is not a job for the backyard. The amount of material is beyond what is reasonable for a backyard caster could handle safely.
The design of the pattern and casting strategy requires someone with experience to provide input to the design.

I would try to find a smallish firm that will do it on the basis that you make the pattern, to their design parameters.

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

pjt
6th Aug 2009, 02:17 AM
I have worked at the smelter down the road a bit from here and during inductions they talked about the possibility of explosions... cue video of said explosions... filmed under controlled conditions, two possible types of explosion, one steam and one hydrogen, from what I remember what they worry about is a sealed can/container of something ending up in a molten bath of Alu in a furnace. the sealed container can be anything that has moisture in it... baked beans, vegemite, soup, etc etc, rust is another thing they dont like.
If the can of stuff gets chucked in and stays on the surface of the molten metal no real drama, just melts and gets burnt up steam given off, however if the can of stuff sinks it becomes a bomb due to xpansion of steam, 1700 times seems to ring a bell, it remains a steam explosion if all the steam can get away to the atmosphere, it does this by emptying a furnace of the metal, 1 to 2 tonne of molten alu, woulndt want to be standing at an open furnace door when that happens, if all the steam can't get away then u have a hydrogen explosion and thats a whole lot more serious.

I dont know the chemistry or the physics of this reaction but based on the demo in the vid and the small amount of molten metal required, the second explosion was far more violent and I wouldnt want to be anywhere near if a can of stuff got chucked in to a furnace.

Peter

Ch4iS
6th Aug 2009, 03:17 AM
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.

new_guy90
6th Aug 2009, 11:04 PM
Lathe bed ? I though he was talking about a bed to sleep on .
Kev.

i second that :p

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

pjt
7th Aug 2009, 12:25 AM
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.

ian
7th Aug 2009, 01:00 AM
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/hydrogenandfuelcells/pdfs/aluminium_water_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

19brendan81
7th Aug 2009, 11:30 AM
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.

soundman
7th Aug 2009, 12:21 PM
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

Fossil
7th Aug 2009, 02:11 PM
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.

gmack
7th Aug 2009, 05:11 PM
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.:o:oo::oo::doh:
I hope this helps.

Fossil
7th Aug 2009, 05:50 PM
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??

joe greiner
7th Aug 2009, 08:53 PM
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.:wink:

Cheers,
Joe

pjt
8th Aug 2009, 01:08 AM
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

ian
9th Aug 2009, 11:57 PM
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

bobsreturn2003
10th Aug 2009, 12:16 AM
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

Retromilling
11th Aug 2009, 08:45 PM
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 :doh:

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 .

Woodlee
11th Aug 2009, 09:50 PM
Kero makes a good coolant for ally of most grades .Ive machined ally sheet with my woodwork router and some cheap Bunnies carbide bits .I usually mark it out first and then use a paint brush and paint a bit of kero along the cut line.
Candle wax works too or even the lard from the Sunday roast( smells better ) .
We have some big sheets of 50mm 6061 at work for machining aircraft parts from .
Lucky for me I get the off cuts that are too small for anything they want to make.
Machines nice with tungsten carbide tipped tools on the mill.

I would look at getting a sheet or a cut sheet of 16mm or 20mm ally plate maybe 6061 for the table top .
Or Go to a foundry and ask if you can scavenge though thier scrap pile look for a cast iron machine table.
I use to work for a company that had a cast iron foundry , there was all sorts of good stuff in the scrap pile.


Kev.

4-6-4
14th Aug 2009, 11:54 PM
I can't resist this thread. I had a small non ferousios foundry that was geared to The Model Engineering game. Speaking as one that knows any molten metal and water do not mix. I had two explosions with ally once when there was water in the ingot mould and I was pouring the remnants of a melt into the mould. this was only a small amount of metal but gee it was spectacular I still have a mottly cap from this adventure. The secon time I was melting scrap (not cans) to make Number Plates. No need for quality. The last pieces ito the 15 Kilo crucible were some radiator fittings. I pushed them down and there must a been the tinest amount of water only dampness and the result was even more spectaculat.
The only problem I found with melting from Ingots was the size of the beasts. I bought ingots that you broke in half with a sledge hammer and these went into the 15 kilo crucible. This was of a maximum size I could handle by myself. Even when I used ingots I used a cleaning agent to bring a the gunk to the surface of the melt. These tablets were pushed to the bottom of the melt and bubbled away furisly. Most were pretty toxit not recomended for enclosed spaces. But they did work. Ally cans have an ally in them to make the metal extrude around a former so are not very good for quality work.
Finally a word on furnaces for those fool hardy adventures. The stuff to use for the lining of the furnace is Kaowoll. I am not sure if this is the correct spelling but it is the way it is spoken. This stuff reflects the heat and thus reduces the melt time. it comes in a blanket up to an inch thick. Wraped around a drum 1 layer is enough. You have to be gentle with it when removing a crucible but with a normaly asperated blow torch you are in busines. My furnce looked terrible but it did the job.
If any one is interested I will talk about moulding sand and other foundry bits later on.
Yoursn 4-6-4

pjt
15th Aug 2009, 12:17 AM
yep Kaowool, it is used a far bit at the smelter