Re: Burn-out kiln for ceramic shell


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Posted by bpfink on January 15, 1999 at 15:53:28:

In Reply to: Re: Burn-out kiln for ceramic shell posted by Cristin Millett on January 15, 1999 at 14:35:50:

I used a 55 gallon steel drum for years in the 60's to burn out and it was simply wrapped ON THE OUTSIDE with 2 layers of 6 inch glass wool building insulation and chicken wire around that to hold it inplace. Exhaust stack on it was a 4 inch dia. stovepipe coming off the side about 8 inches up from the bottom so it was a downdraft arrangement. Fumes and smell can be reburned on the way out with a mini venturi torch line and then nearly no fumes are left by the time the exhaust leaves the top. Heat source was a round propane burner from an old water heater.

But here is the rub. This was for investments to burn out so the temperature needed was much less than you will want for ceramic shell burnout. The whole unit was hung from a tree branch so it was easily lifted up off the investments when needed, and the insulation was suseptable to rain so it had to be stored indoors and used during the non rainy season or in this case covered with another sheet of corrugated steel so it drained off the side. Temperatures of 900 F were reached but the steel also needed replacing after 6 months or heavy use.

It was built for free plus elbow grease and it worked fine but you can do much better.

These days the very thin (1/4 to 1/2 inch or so) ceramic cloth insulating blankets seem to be the best answer. Cover the inside with several layers so the overlapping seam is covered.

Also you can line the drum on the inside instead and forgo all the other hastles, still lift it from the tree or a simple pipe tripod, and expect the steel drum to hold up for a much longer time.

It does mean that lowering the kiln over the molds needs to be done carefully and the molds should not fall or lean onto the sides or the blankets will scar badly.

The ceramic blankets can be held in place with stainless steel bolts and washers put in stratigic places. The bottom of the drum is left open.

In addition the temperatures reached can be much higher and push the 1500 F areas many prefer, etc.

As for the heat source, a simple propane 'weed burner' or venturi type blow jet (or propane cast iron camping burner if modified for more heat) all from Northern Hydraulics see:

or 1-800 533-5545

(Approx. $35 to $55 depending on models) will give more heat than needed and this can be important since you do not have any mass holding heat source in the kiln to help flash the ceramic shell up quickly.

As a side note, a drain pan of water below will help collect drop out wax and put it out before it also burns up. Just plan for firm and stable holders, lifting systems, and expect 1500 F to radiate heat to your face or hands so still wear protective clothing, etc. Also support the stack well and you may want to locate the outlet to it much higher on the drum body so it draws off closer to the top.

(Yes... you could lift it by hand with handles and 2 people, but I don't like to take chances with any unexpected glitches and would recommend a simple lifting cable to a pulley system instead. Some folks panic at the least sign of unexpected heat, etc. and can get overly excited with an adenaline surge, etc... seen it to often when teaching.)

Play it safe and smartly... don't burn the leaves off any trees and good luck.


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