Jim:One thing to consider is the final inside diameter. It is important to build the furnace to fit the crucible. A #8 crucible is 1/2" to 3/4" smaller than 6" pipe. If you sized it to fit the pipe and then make it 1/2" larger with less refractory it may become a little large for the crucible. It shouldn't make a huge difference. If you plan to use the crucible 95% of the time build it so that will have the fastest melting time and efficiency. The furnace might be a little tight for the 6" pipe but again it should not make a huge difference. Carl
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From: Jim Ash <ashcan@earthlink.net>
To: gingery_machines@yahoogroups.com
Sent: Thursday, August 4, 2011 10:57 AM
Subject: [gingery_machines] Foundry dimensions
Gents -
I've been taking my time and putting together a nice foundry furnace that I hope will last me a long time when I'm done. I've got some good commercial castable refractory, some ITC-100 magically showed up in the mail yesterday and some kaowool is due in the next day or so. I put together a spreadsheet (which I'll probably clean up and download to the files section for list consumption at some point) which takes in some basic dimensions and outputs volumes of refractory and dimensions for sheet metal.
Although I've taken information from a number of different sources, the basic design is from 'Building a Gas-fired Crucible Furnace' (I like the ability to grab a hot charge from the side at arm's length instead of having to hover over it). I've sized it to accommodate a #8 Silicon-carbide crucible, but I've also been known to use 5- or 6-inch schedule 80 pipe in a pinch. I plan to cast the basic furnace parts, wrap the outsides of it with a couple inches of kaowool, then strap some sheet steel around it to clamp the kaowool in place.
The question I've got for the group here is: How thick have you guys made your furnace walls, bottom and lid? I was planning on 2 1/2" for the side and bottom, and 3" for the lid. I may be a little tight on refractory mix, so I was wondering if I could make the side thickness 2". The question is probably more related to mechanical and thermal stresses; I figure the kaowool wrapped around the outside will significantly supplement the insulating ability of the furnace, and I'm planning on brushing it down on the inside with the ITC-100. I don't have a permanent place to keep and operate this furnace, so it will be wheeled out from a storage shed for use, which is certainly going to contribute to the mechanical stress on it.
So how thick are your furnaces and would you make them that thick (or thin) again?
Jim Ash
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