Insulation advice.

[Chalky]

Can anyone help me with a rather basic question?

What is the main function of the insulating lining of a gas forge?

Now, before you laugh your socks off, I do know a bit about building propane powered forges and can get them to run reasonably well. The latest has a floor of hard firebrick (for the wear and tear) but does not seem to retain heat as well as soft firebrick. The roof lining is high quality board, seems fine.

Is the idea function of the lining :-
1.to prevent the outer casing getting hot
2.to increase the efficiency of the forge
Does this work by a/ absorbing the heat
b/ reflecting the heat

I know this sounds very basic but my supplier has a vast array of materials available and gives me more tech. info than I need, it's difficult to know what to choose – and expensive to experiment!

Any recommendations? The forges are mostly used for making horse shoes and little jobs not worth lighting the coke forge for. I have a double burner at the moment but have the burners a little too far apart, there is a cool spot in the middle. I think a single burner would work for me if I made it a bit deeper and narrower.

Thanks for any info.

[pkrankow]

Insulation works on 2 principles, preventing heat from escaping, and reflecting heat.

Soft insulations like wool and soft firebrick are effective at preventing heat from escaping because they have a lot of small voids inside them.

Reflective coating such as ITC 100 are helpful for reflecting the heat back, preventing heat from entering the insulation.

Ideally heat is not absorbed by the insulation. At operating temperature radiant heat becomes a significant source of energy loss. This can be combated by having the forge closed down so the openings are limited. Edges between surfaces at right angles will tend to loose less than holes in the center of surfaces, but function is important and cannot be discounted.

Hard firebrick is not an effective insulator, as heat is conducted through the brick readily. The voids in soft brick prevent this. Split hard brick (1 1/4 inch or so) will exceed 1000F and start glowing on the BACK side. Adding soft insulation under the hard brick will help improve the performance of your forge.

Phil