[kram]

Ive built a small 250ml furnace. Im using propane/mapp to heat it.


My crucibles are 100ml, but my project needs around 150ml.


Im wondering if I can put some alu sheet in the bottom of my mould, to reduce the amount to be melted.

I would clean the sheet, preheat with the mould (to 200-250c?), and super heat the melt to ~800c (dull red) to make sure its got a good joint.

thanks

[metalworkz]

Ive built a small 250ml furnace. Im using propane/mapp to heat it.


My crucibles are 100ml, but my project needs around 150ml.


Im wondering if I can put some alu sheet in the bottom of my mould, to reduce the amount to be melted.

I would clean the sheet, preheat with the mould (to 200-250c?), and super heat the melt to ~800c (dull red) to make sure its got a good joint.

thanks

Hello,
I think you will be better off to use a larger crucible. You might be able to do what you suggest if the casting does not need to meet any special requirements like water tight etc., but I would think you might want to create some grooves or other feature for the poured metal to grab onto and hold it secure. I assume you are melting aluminum to go on top of the alu sheet? Will a crucible large enough fit in your furnace?

[paprjam]

If this is for a one time pour. Since Aluminum is one of the easiest metals to melt, you could just set up some charcoal with a small blower and put the Aluminum in a stainless steel pot.

[kram]

100ml is the biggest porcelain type I can get. Stainless might be better for aluminuim anyway? but not sure where I might find one.

Even if I had a bigger pot, id like to know if this is possible, as it would allow even bigger parts. I think it should work as long as its preheated and fluxed so that the sheet is partially melted.

Heres the result of the first pour a few days ago. The mould split, and it flowed perfectly, but mostly onto the floor. It got a couple of woodlouse too...





Since my scrap is mostly cast, theres a lot of silicon in it. 3 shades of grey, possibly salt crystals also. Its slightly porous. Biggest holes are 0.2mm. Im not sure if the way Im fluxing is ideal, but my parts came out shiny with no oxides.


Id like to try the above anyway. Making moulds in plaster is a PITA. I need to find some cheap wax or foam :/

[DMF_TomB]

in aluminum metal porosity increases with over heating and metal absorbing hydrogen from fuel combustion and water from surface of added metal. nitrogen bubbles and or chlorine tablets are sometimes used for degassing. melting a large amount of thin scrap increases porosity usually.
.
another option is to weld 2 smaller casting together. you can spend a lot of time and energy have larger foundry capacity but if for only occasional jobs it is usually better to invest in welding equipment.

[jc56au]

100ml is the biggest porcelain type I can get. Stainless might be better for aluminuim anyway? but not sure where I might find one. :/

Try Legend no stainless but porcelain/graphite/silica/zirconium in a wide range of sizes. Or other suppliers of mining/geological gear

Legend Inc. Sparks, Nevada USA:

[paprjam]

I've bought several things from Legend, no complaints. Their clay crucibles are inexpensive and work great for Aluminum. I got a six pack the last order.

[jimmy111]

If you are doing aluminum you can use any small cast iron or stainless steel ladle or small cup to melt in.

You can also take a piece of plumbing pipe and weld a bottom on it. Weld a couple of lugs onto the side to grasp it with and melt away.

If you need bigger you can make yourself. Ive made thousands of them. All you need is some fire clay and some silica sand. Both pretty easy to find anywhere.
Here is a book on how to make them.

Lindsay: Gingery's Making Crucibles

They have many other foundry and machining books too.