Using a Heat Sink to Your Advantage

[JHCC]

We've spoken many times about how using hard refractory brick to line a forge is a problem, as it acts as a heat sink without providing any insulative value. In other words, you're wasting gas heating it up and keeping it hot. However, it occurs to me to ask, what if you have a well-insulated forge (the usual 2" of kaowool etc) and add some bricks (or a shaped lump of kastolite) to reduce the volume of the forge? Yes, it could take a bit more time to get it up to forging heat. However, once the forge reaches its target temperature, it seems to me that the added mass inside the insulated space would help keep the temperature steady, and the smaller volume would be easier to bring to higher heats (especially if you're otherwise having difficulty reaching forge welding temps). Thoughts?

[ThomasPowers]

Contact heating is a big plus for production work.  It does help to have a well insulated forge around the contact heat sinks to reduce wasted heat.  Decreasing the size of the area to be heated can help too; but the thermal mass does h=introduce a bit more lag in temp stabilization.

[Frazer]

I'm glad you posted this. Although I don't have a gas forge at the moment, I was thinking that when I do eventually decide to build one I might insulate using the tried and true method, but sacrifice a bit of the overall efficiency by using a firebrick or kast-o-lite brick as the floor. Not only might having a floor that holds the heat longer after the burners are turned down/off have some use for normalizing, heat treatment, etc, but it would be easier to maintain by replacing the brick every so often with a new one as the old one erodes due to flux overflow or other conditions that, while generally affecting the liner as a whole, have the worst effects on the floor.

I'm not saying that the whole floor needs to be lined with firebrick or anything like that. All I'm thinking is for a smaller forge where coming up to temperature could be done relatively quickly and if it were if it were done properly, there might be some balance between long term cost of fuel and long term cost of relining the forge. Plus while having a cylindrical wall, in my mind, seems to be better to induce that swirling effect for increased convective heating, having a flat floor will be better for increased conductive, contact, heating.

Of course, having only used a gas forge during classes a while back (where they use firebricks as the floor, yes plural, and yes they took somewhat of a long time to come up to temperature) and never having made one myself and really tinkered around with them, maybe my thinking is wrong.

Anyway, you will have to excuse my poor artistic prowess, but here is a quick sketch on how I picture this could be implemented pretty easily.

*doodle not drawn to scale*

Edit: In my case I am actually using Kaowool to reduce volume. Not the firebrick.

Edited October 20, 2020 by Frazer
Added afterthought.

[Mikey98118]

Hard insulating refractory does make a better, that is more usable, heat sink.

[swedefiddle]

Good Morning Frazer and JH,

The only/best way to find out, is to try it. I used a stack of hard bricks for a Forge, for years. I was not interested in welding heat, just hot Forging Heat. I learned that it takes about 20 minutes for the Hard bricks to come up to temperature. Refractory is better, it bounces the flame back into the Forge and/or the heat of the refractory creates another ignition source and consumes more propane for a hotter firebox. Better volumetric efficiency. You have to keep your own note book for what works and what doesn't. I know, I will remember that!!!! NOT!!!

CRS Disease = Can't Remember Squat or Can't Remember what the "S" stands for!!

Neil