Casting aluminum

[leftiye]

Does anyone know what material is used for molds to cast aluminum? I'm trying to make my own frame wrench for removing revolver barrels, and the shape would be a mess to machine. Doing it by hand (filing) would be worse, and wouldn't turn out well either. :killingpc

[andrew375]

For one off's we use sand. This is a sand combined with a binder, either clay or oil based.

Casting temp for aluminium is a bit over 700 degrees C. and you will need a specific flux to keep the metal clean and prevent excessive drossing.

My suggestion is to look up foundries in your yellow pages and take your pattern along and get them to cast it for you. Also some schools and colleges have small aluminium casting set ups, like mine, you might be able to tap in to.

Do a search on sand casting and all will be revealed.

For mass production die casting they use steel alloy dies that are water cooled in automated machinery.

[Bret4207]

www.lindsaybooks.com has several titles on casting. Google home casting or home foundry and you'll find LOTS of info.

[DeanoBeanCounter]

:roll: If it helps, try this web sight.
www.backyardmetalcasting.com/index.html
Deano :coffee:

[grumpy one]

For what it's worth, I suggest you listen carefully to the recommendation of going to a small commercial sand foundry or perhaps your local trades school. Aluminium is very prone to oxidation, and melts at a temperature high enough to make lead alloys look safe and easy by comparison. Home-cast aluminium is prone to both oxide inclusions, and extremely coarse grain structure due to overheating and slow cooling. This can be acceptable for ornaments and large, lightly stressed objects but is quite unhelpful in wrenches.

I'm not saying you can't do it yourself with enough learning-time, but unless you want to make it your new hobby, it doesn't seem worthwhile.

Long ago as part of engineering undergrad training I took an aluminium casting unit, and the guys involved would have been happy to help in a project like yours so long as you made a decent pattern and took it to them.

Incidentally the only time I needed a large, weird and complicated wrench I made it out of a piece of half inch aluminium plate by using a filing machine first as a jigsaw, then for filing. Shaped internal holes are no problem that way - I think it took me two or three hours. The wrench was for the very large, strangely-fluted nut that locked a quick-release aircraft hydraulic coupling, used on my detachable back hoe. It worked for years, until somebody stole the entire front-loader/backhoe.

[dnepr]

As someone who does his own home aluminum casting I have to agree with andrew 375 and grumpyone My home castings work for some stuff but have tomany inclusions and are to porous for anything like a wrench. It can work for bigger stuff under less stress. The bellhousing on the bike in my aavatar is my own casting , it has held so far but I wouldn't rev it to redline and dump the clutch and the bellhousing is one of the reasons for that. If you happen to be looking for a new hobby go for it it is great fun.

[leftiye]

Thanks for all of the help guys . So the afore mentioned specialty flux (BTW what is the brand name?) doesn't stop the oxide problem? I kinda figured that I could put some aluminum in a large Ladle with some of that flux, heat the ladle with an oxy/ acteylene torch (cherry), or over my turkey cooker, and immediately pour it into the mold. This is only an insert that fits the area of the frame around the barrel, and is not very large (maybe1X2X3 inches). You could say that it makes the frame fit the wrench. So, it might work still even if porous maybe? I just remembered that guy's name, David Gingery had a whole slew of stuff about casting Aluminum. Will molten aluminum stick to steel?

[grumpy one]

First, the flux will work under the correct conditions, but it might take a few tries to get right. Things that are easy in a thermostatically controlled open-topped electric furnace heated from inside a heat shield aren't so easy with a torch in one hand. Properly used, the flux can remove inclusions, and in a proper furnace it would probably work that way, but in a pot with a torch waved around, probably not.

The main rule with aluminium sticking to steel is that it will do whichever you don't want it to do. If you cast it around steel, it will most likely stick enough so that you can't get it off, but not enough so you could rely on it staying together. There is a special salt-bath bonding technique for getting a good join between aluminium and steel - in the 1950s when it was still under patent it was called Al-Fin Bonding.

[andrew375]

The flux I use for aluminium is called Coverall which we get in a school size casting support package given away to educational institutions by a company called Forseco. The Coverall not only prevents oxidation but also controls the loss of Silicon from the melt. You have to match the type of coverall to the alloy. The grade of aluminium used in extruded bar is not the same as we use for casting, so you cannot simply take some scrap and melt it as you would a lead alloy and expect good results.

DNEPR - I knew someone who did aluminium casting at home as he was a model engineer. He too complained of the problems you report with inclusions and blow holes. I gave him some coverall and off cuts from our castings and the problems went away.

BTW: A student here took a job to a local foundry, he is building what appears to be a small spiral staircase and he wanted the steps casting, they did him 15 steps for £110. At that price it is not worth even considering casting anything myself.

:drinks:

[holycross]

leftiye,

Instead of Aluminum use lead to fill in the gaps. 3 cardboard strips, one either side of the frame and seperating the 2 forms. The third piece acts as the base.
Probably not the best description of the job. I'll try and do a quick drawing tomorro.
This was the way colorado school of trades teaches there students to make a barrel holding setup. easy, quick and can fit any job.

Mark

[leftiye]

Holy cross, thanks for the idea. Made me think of using Cerro Safe alloy.

[scrapcan]

You can also make inserts using epoxy, glass bedding (or the bedding with steel fiber), or high density fiberboard. with the epoxy you need someway to make sure you do not bond to the metal and a way to hold until set. Same goes for bedding material. The HDFB can be shaped with wood working or carving tools.

If you are going to use the wrench many times it may just be easier to order the proper insert and make a handle/block.

Another option is to see if you have a ceramic shop and see what they can due to make you a mould. The pottery wiz at the shop may find it to be a challenge. Or go to the art department at a local college or university, they generally have some methods of bronze sculpting and bronze mould making.

[holycross]

leftiye,

Glad for once I had something useful to contribute.

Mark Holycross

[dnepr]

I should try some flux . Another problem with my method and using a ladle as mentioned by leftiye is iron pickup, molten aluminum is very corrosive and the iron it picks up as an impurity weakens it . I really need to get some proper clay carbide crucibles but I haven't found a local supplier and I have my doubts about a crucible surviving shipping.

[leftiye]

So, what do y'all thimk? Would a ceramic crucible -maybe not clay carbide, just a good quality high temp clay- work okay. We're only talking less than 800 degrees here. I have an electric heat treating furnace that could easily melt the aluminum.

Andrew375 What is the alloy you were mentioning for casting, and do you know where to get it?

[andrew375]

The alloy I use is LM4. availble from metal factors. Also try looking under "foundry supplies". The latter will also be a source for your crucible, ladles and refactory coatings that are used to protect your tools.

As well as the flux, I use Coverall 11, you should also use a degasser which cleans the molten alloy before pouring.

The molten aluminium isn't corroding your steel tools at all, they are actually being dissolved in the same way that sugar is dissolved in water. To be honest on the small scale we are talking about and using a ceramic pot this isn't an issue. But not using a clean casting alloy, correct flux and not degassing are resulting in serious casting flaws.


I should try some flux . Another problem with my method and using a ladle as mentioned by leftiye is iron pickup, molten aluminum is very corrosive and the iron it picks up as an impurity weakens it . I really need to get some proper clay carbide crucibles but I haven't found a local supplier and I have my doubts about a crucible surviving shipping.

Whist the crucibles are fragile they will be well packed for shipment and will withstand shipping in the same way as china or glassware.

You might also try model engineering suppliers as one of the problems we have is getting supplies in the small quantities we use, everything is a minimum order of a tonne!

[leftiye]

Great info guys! It doesn't take much to see how valuable casting things from aluminum could be. I think the model (railroad, or?) supplies thing might be the place to look. There are magazines, and sites that I've seen (Home Shop machinist) that themselves list suppliers, and also have advertising for these types of suppliers. I think I'll revisit these. I once found a place that would supply grey iron, and meehanite (bullet molds?) for making (in my case machine tools) whatever in whatever size desired. I remember that they had crucibles. Just an aside.

[dnepr]

I can see Iam going to get back into the aluminum casting again this summer.[smilie=1: