Protect the bottom of your foundry

[Florida Man Metals]

It is important to protect your foundry from metal spills and flux. Putting a 3/8 inch or so layer on the bottom makes for easier clean up of any spilt materials and prolongs the life of your foundry.

I used to use a layer of fine silica on top of my fire brick to protect them from spills. I recently switched to bone ash. It is much finer than silica and works better. More of a powder than a grain consistency.

Technically the books calls for calcined bone ash. I used bone meal from Lowe's garden department. Initially it turned black upon the first firing, then turned into the desired white ash.

[Frosty]

When you say foundry it sounds like you're talking about the melter rather than the shop. No?

Frosty The Lucky.

[Florida Man Metals]

Yes, the bottom of the furnace/melter. I hope your shop doesn't get hot enought to burn bone to ash. You would definitely need some crazy PPE.

[Florida Man Metals]

You can also place it in the area where you are casting as well instead of a sand box. I guess this would technically be considered the foundry?

[Frosty]

I believe the foundry is the facility rather than a single piece of equipment though I'll be happy to learn differently. English is such a slippery thing you just never know for sure. 

One of our club members is a professional bronze caster and pours over a sand box or outdoors on dry dirt. He conducts the yearly iron pour at Art on Fire event and that's all on the ground. Until a couple years ago I demoed blacksmithing about 50' from the cupola and iron pour. 

Frosty The Lucky.

[Florida Man Metals]

Since we're on the subject of proper terminology the only melter I have is a wax melter. Have you ever seen a tilt melter or assay melter? They are referred to as furnaces. 

[Scott NC]

  I have always called them melters.  Don't forget, a drain hole to protect the bottom of your "unit" for those inevitable spills....

[Frosty]

A melter is a type of furnace though probably not a wax melter but a tar pot on the roof with the roofers is fired by propane or fuel oil would be a furnace. We heat our house with an fired oil boiler, the firebox section is called the furnace. Furnaces burn things whether as the process or the end result. 

Frosty The Lucky.

[Phil K.]

I call mine a Foundry Furnace. My small one I turn on the side and use it as a forge. In steel mills there are Electric Arc Furnaces, Basic Oxygen Furnaces, and reheat Furnaces.

[Nobody Special]

I would tend to think it would depend on the design a bit. Been a long time since I had a crucible fail inside, and since I switched to using charcoal the bottom is usually covered in regular ash. My furnace has a drain hole that I place a ceramic plinth over to set the crucible on. It's got two channels built into the bottom that run down to the hole so if something happens to the crucible it will go out the hole, plinth or not. Last time I had a problem was a long time ago, but the aluminum just ran out the bottom onto the sand.

I use a variation on the backyard metalcasting refractory recipe in my furnace, in a metal shell, over reinforcing bolts and wire, with fibreglass insulation up against the shell. Portland cement, sand, perlite, and fireclay and secret ingredient X. It's maybe not the way I would go now, but it keeps working, so why not? Worst complaint is that it's heavy.

Built my first forge out of the stuff, wouldn't recommend it for that; it chipped out a bit and widened the firepot. But I only ever had a problem using it in a furnace once; when I was ramming the refractory I left an air pocket in one wall and it blew a hole out on the inside. Patched it and it's been fine since - the one I use now. I would have thought the portland cement would fail and start to slag but it just keeps going without any apparent damage. If I was on firebrick though...