Foundry hints and tips for a noob on a budget, please!

The Shop > Metal Stuff

<< < (2/3) > >>

vtsteam:
A 50 gallon drum is huge, particularly if you are on a budget. Major expense in making foundries is the refractory. So your aims are seemingly at odds with your wallet.

Since you want to cast 20 lbs of aluminum as a goal, you can do the calculations yourself.

Find the density of aluminum online and determine the volume of 20 lbs of aluminum. Then determine the size of your crucible from that.

When you have the size of your crucible, make the bore of your furnace 2 to 4 inches in diameter larger than that. Give yourself about 6-8 inches taller in height than the crucible is, and that should give you the ballpark for the lining inside dimensions you need. Then add 2 inches minimum for lining thickness. When you've added all the dimensions of bore and lining together, that will yield the outside metal container size you need -- I suspect shorter (and probably narrower) than a 50 gallon drum. But maybe you can cut one down and that might work.

For lowest cost use silica sand and fire clay mix per Gingery charcoal furnace book. It will work fine for an aluminum melter. You don't have to get fancy with additives like sawdust, grog, etc, it works as is. If you want to spend more or experiment with unknown quantities and materials, have at it.

No you don't need insulation, and if you do use it, you will need to support the heavier mass separately from the insulation, and then also encase the fluffy stuff to protect it from moisture. Also you don't need anything thing else, by way of lining additives or coatings unless complexity appeals to you. See my Gingery lathe thread on this forum for what can be done with the simplest 1-1/2" thick clay lined furnace of 8" bore using only charcoal.

For an oil burner, there are millions of examples of every description out there on the net. Pick one, ideally the simplest you can find with high heat output and not necessarily highest temp output and it will most likely melt aluminum in the above. Aluminum wants lots of Btus (calories), but not high temps in a burner.

I've melted and poured aluminum from an open wood fire of pine boughs during a Spring cleanup with no foundry furnace at all. So any foundry with a lining and an adequate burner will do the trick.

None of the above is meant to slight the wonders of modern refractories, high tech insulation, oil burner design advances, hot faces, coatings, etc. It's merely paying attention to your stated needs for low cost and simplicity for a beginner who wants to pour a big mass of AL.

Re crucibles -- I've used cast iron plumbers pots pretty routinely. You will need something bigger. Maybe a piece of 6" pipe with an end welded on -- Better practice than mine would be washing the inside of the crucible with a clay type wash, as iron or steel isn't ideal in contact with aluminum. Or you could spend big bucks on a real crucible -- but again we are supposed to be working within a budget, right? Anything roughly crucible shaped that will hold 20 lbs of aluminum and fit your furnace bore will work, as long as it isn't made out of aluminum or pewter, and if you put a ladle wash in it, should prevent contamination.

My own preferences anyway.....

hopefuldave:
Thanks VT, all useful stuff!

I appreciate that a 50-gallon drum's on the large side, I'm planning to cut it down a bit, maybe 4 - 6" out of the height (the offcuts can go to supports and such) then turn the edges in an inch for a bit more rigidity, so it should end up 22" diameter by 24 - 26" tall, 14" - 16" by 18" tall inside - still; pretty big, I know, but it'll probably have to do double duty as an annealing / heat-treatment furnace (a local garage sends me hardened parts to machine, and I make stuff of my own...)

Re insulation, I was thinking that only the sides would have it, couldn't see a way to support the refractory lining on top of wool, unless I welded supports coming up from the bottom - suspect that would put too much stress on the refractory? They're kinda brittle, I hear!
Does this sound feasible? Use a 2" mineral fibre blanket, weld in brackets and rings every 4 - 6" of height, add temporary inner and outer formers to mould the refractory, so the rings would hold (loosely) it in position within the drum and insulation? The sides would have to sit on the base, and I'd have to allow for shrinkage when firing it, I believe?

Steel pipe sounds my kind of crucible, or just maybe a local recycler will have an old steel extinguisher or gas cylinder I can cut the top off - 1/4" thickness too little, too much, delicious? I'll try the wash, and I see people recommending running an empty crucible to oxidize the inner as an alternative. Both?

I think I have the burner worked out, either a scaled up Kwicky or similar atomising with propane preheat and forced air - a trip to the local plumbers' merchant turned up a.useful selection of parts :)

Thanks again,
Dave H. (the other one)

vtsteam:
Hello David,

I think your inner liner should be permanent solid sheet metal, not rings and not loose fitting to the lining. Your lining will develop cracks, and they are no big deal if supported by a liner, but could be a big problem if it is intermittent support. Simpler this way, anyway. The bottom needs no insulation -- in fact it can be loose sand -- or packed refractory, whichever you want.

I still feel that the insulation is a waste of time in a clay lined furnace -- my melts are usually about 20 minutes, and the furnace shell is barely warm to the touch at the end of the pour with only 1-1/2" furnace lining. Insulation outside of that would only prolong the furnace cool down period, not melting efficiency. This isn't iron pouring, and it isn't long heat treatment furnace running -- those favor different design -- in the first case to get temps up high enough, and the second for reducing heat loss (and fuel expense) over long heating periods for lower temperatures. For aluminum, you're going to want a fast melt, high heat at lower temps for a short period, and then you're done.

So If I were you I'd just go with a nice thick clay/sand lining -- 2 to 4 inches thick inside a simple steel can

You could try adding perlite to the top to increase insulation and reduce weight. I did this on mine. It does erode eventually, but is easy to patch with more perlite mized with furnace cement. And lifting the lid is a lot easier.

re. th 50 gallon job -- I do suggest you do a little calculation of lining volume for your design, and then work out the weight and expense of refractory. I think you'll find that you want to minimize the size of your furnace for that reason. Luckily a sand/clay recipe is considerably less expensive than modern castable refractories. But still, it isn't free.

The sand cost is small, but the fire clay (Hawthorn or Redart or equivalent fire clay) will cost you, particularly if you must ship it rather than purchase locally through a ceramics dealer. In fact shipping can exceed the cost of the clay itself. (The sand I will assume would be purchased locally.)

The other thing to keep in mind is weight for moving your furnace. Unless it's going to be permanently fixed under some form of shelter. Ideally it will be on heavy duty casters on a level concrete floor. Outdoors on dirt, you won't be able to move it easily, if at all. Indoors, you will need a very good ventilation system, which is expensive.

Swarfing:
A lot of so called fire clay is actual just deep dug clay (bentonite). In the main this is denoted by the dark grey colour in it's wet state. I've used both and found no difference in the way it works on my furnaces. I always used a perlite and silica sand mix, perlite from the garden centre, sand from the diy shop (the type used for sweeping into block paving joints. If it was me just do a cheap mix and play, as soon as you understand how the melt works you will want to make a better one anyway :-)

vtsteam:
Forgot that you asked about pipe crucible thickness -- yes 1/4" steel pipe is good and won't burn through for awhile. Steel tends to burn through from the outside more quickly than cast iron. Thin stainless steel seems to burn through rapidly -- I tried some kitchen canisters of SS and they lasted only 5 melts before holes appeared. Holes are no fun. Usually they pour down into the furnace tuyere, etc.

The cast iron plumber's lead pots I use now seem to have an indefinite life. But they are too small for your intended 20 lb pours. It will be tricky handling 20 lbs of molten aluminum -- I'd consider buildng ironman's wheeled pouring trolley if working alone.

Navigation

 Message Index

Go to full version