Muffle furnace

[Sonic EscapeParticipant @sonicescape38234]

I recently read some books about heat treatment and thought it would be interesting to try it myself. I’m thinking of making a small electric furnace with a usable volume of about 150x150x250mm that can heat up to about 900-1000°C.

I’ve seen that many types are made of refractory bricks. I’m thinking of making it from vermiculite plates. These are easy to cut and insulate better than refractory concrete. The only disadvantage is that vermiculite is more expensive. But for a small furnace it’s ok.

I haven’t decided what kind of heating element to use. Probably some khantal wire wrapped on a support. I could size it for a 3kW power, to be on the safe side since I don’t want to dive into heath losses calculations.

Anybody tried to build an electric furnace or have any suggestions?

 

[bernard towersParticipant @bernardtowers37738]

buy your vermiculite blocks from a fireplace supplier they are much cheaper!!!

[BazyleParticipant @bazyle]

remember there are two types of brick shaped furnace blocks out there (not talking vermiculite). One type is heavy and meant for pottery kilns so has low insulation but very high thermal mass. The type you might use are very lightweight and used in enamelling and similar hobby furnaces. You can aso use loose vermiculite if you can invent some containment.

[not done it yetParticipant @notdoneityet]

Dunno the cost of things these days, but it may be more economic (unless you are bent on a self-build) to look for a second hand kiln?

I have a Paragon (Sc2, I think), which has been fine for most odd bits I’ve wanted to heat treat.  There are several other makes and different types out there.

Hardening is the easy part for many jobs – heat to red with a gas flame and quench.  Tempering is easy enough, too – up to the maximum temperature of a domestic oven, or colour if you can see it (I cam’t).

Check out lampworking, metal clay, enamelling and other glass hobby sites (such as slumping) for inspiration, maybe?

My kiln has a ‘bead door’ (for lampworking) which has, on occasions, been useful for heating the end of longer items without opening the main door.

[noel shelleyParticipant @noelshelley55608]

Whilst the lightweight furnace bricks used in pottery kilns are excellent and made for this job. Get the right type and they will have grooves for the elements built in. I used them for a smelting furnace where the wall temp was about 1500c, the outside wall was hot but painted, and 25 years old. Plan B is ceramic fibre, this comes in many forms, tube, blanket Etc. This material is very effective in keeping heat in and will easily take the temperatures you mention. DO NOT consider any type of heavy brick, eg those used in night store heaters ! Noel.

[not done it yetParticipant @notdoneityet]

DO NOT consider any type of heavy brick, eg those used in night store heaters ! Noel.

I’ll second that!  Ages to heat up – and likely too slow to cool down on a ramped cooling program.  Little or no thermal insulation, either.

I’m not sure, but think the paragon (etc) kilns use both bricks and ceramic fibre/wool for insulation.

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