Coal Forge Design Question

[Avadon]

I've already built a really good coal forge and it drafts quite well. It actually has a hood that overarches the firepot perhaps 2' above it and reaching over about 50% of the firepots diameter.

Here is a rough view

So I am wondering if coal forges that actually encase the entire fire pot, and mimic the design of gassers, heat hotter or are more efficient? Seems lke an ecased coal forge would work like an oven and reach higher temperatures quicker then the average firepot design where most of the heat is instantly lost into the non-enclosed atmosphere or right up the flu. Can someone tell me if I am correct in these assumptions?

[ChrisDial]

I would think that it would. I mean coal (or at least the coal I get) works as an oven because the coke and the coal sticks together and makes some what of an oven already. :confused: This is just a guess so dont take me seriously.

[David Einhorn]

Form follows function. It depends on what you are heating. If you are heating rivets, horseshoes, small knives, then an enclosed mini blast furnace may work for you.

At the other extreme, if you are heating large objects such as iron wagon tires, then any obstruction in front of the chimney prevents heating the large iron project.

The local historic shop at the local museum has the firepot within the brick chimney structure. This prevents heating projects much larger than a horseshoe, and drives me nuts.

[HWooldridge]

The ambient flames that come off the coke pile do nothing to heat the work (although they might do nicely to warm the smith on a cold winter day...). On the other hand, heating the steel is done entirely down in the fuel mass - so it's already acting like a miniature oven. IMHO, it's better to move the fumes and smoke away as efficiently as possible while retaining full access to the firepot for odd shaped work.

[Avadon]

The ambient flames that come off the coke pile do nothing to heat the work (although they might do nicely to warm the smith on a cold winter day...). On the other hand, heating the steel is done entirely down in the fuel mass - so it's already acting like a miniature oven. IMHO, it's better to move the fumes and smoke away as efficiently as possible while retaining full access to the firepot for odd shaped work.

ahhh okay I get it.

So Gassers have a different ideology for forges though right? They are basically like a large convection oven bringing a small space up to the desire heat, correct? In this case wouldn't the entire inside of a Gas forge be considered the fuel mass?

[HWooldridge]

ahhh okay I get it.

So Gassers have a different ideology for forges though right? They are basically like a large convection oven bringing a small space up to the desire heat, correct? In this case wouldn't the entire inside of a Gas forge be considered the fuel mass?

Correct. A gas forge is a "hot box" or high temp oven; a loose definition is a container with some level of insulation and/or refractory that can be heated to a useful temperature by a variety of means. There will be places within the gas forge that are relatively hot or cold depending on where the flames are - but that can also happen to a coal/coke fire.

BTU's are everything in either design. Substandard solid fuel or poor blast will not generate enough heat to be useful in a coal/coke forge; the same goes for a poorly conceived gasser. For example, a #3 oxacetylene tip will get very hot in a small area - hot enough to weld - but it's not really efficient at generating a forging temp, except maybe on one or two pieces of small stock. Better to use a propane/air mix and pour the BTU's to it, but that won't help either if the heat is not contained effectively to raise the temp to a useful range.

[Avadon]

Correct. A gas forge is a "hot box" or high temp oven; a loose definition is a container with some level of insulation and/or refractory that can be heated to a useful temperature by a variety of means. There will be places within the gas forge that are relatively hot or cold depending on where the flames are - but that can also happen to a coal/coke fire.

BTU's are everything in either design. Substandard solid fuel or poor blast will not generate enough heat to be useful in a coal/coke forge; the same goes for a poorly conceived gasser. For example, a #3 oxacetylene tip will get very hot in a small area - hot enough to weld - but it's not really efficient at generating a forging temp, except maybe on one or two pieces of small stock. Better to use a propane/air mix and pour the BTU's to it, but that won't help either if the heat is not contained effectively to raise the temp to a useful range.

Sounds like your describing my exact circumstance. I dont' have a forge inside and it's to darn cold to work outside lol so i've been heating things up with oxy/acet which is really expensive since my torch is basically just sitting there always on, albeit a low flame. I know people have talked about gas savers, but I think that's a bandaid when my real problem is I just need a gas forge.

Everything you said makes total sense. Is there a chart somewhere that gives relative heat for using wood, coal, coke, in coal forges? Or could even a chart like this be made?

On Gasers how do people vent them? From the pics i've seen in catalogs they look like they just expell the heat into the room? Am I missing the attachment where they hook up to some kinda ventilation.

I noticed that when forging with my torch on for a few hours I get kinda a dry/sore throat. I'm getting it's something with the burning of the oxy/acet and probably not 'enough' ventilation. Although I do have storm windows in my basement and fan creating draft. Of course in cold N.E. weather it's almost unbearable to get a significant draft going; i might as well work outside then.

[HWooldridge]

There are charts about BTU output - IIRC, Centaur Forge used to have one in their catalog but I do not know if it is on their website. If not, you should be able to google some type of comparative data as all solid fuels have BTU ratings.

Most gassers dump into the room since they typically don't produce smoke but that can be deadly since they still generate CO and other noxious byproducts. If I lived in a really cold area, I would simply pipe it into the coal stack (assuming I had both available) or build a dedicated exhaust. Obviously, it's very important that you do not starve yourself for oxygen while in the shop. I work in an old pole barn with holes everywhere so I never have circulation issues but I can easily see that an enclosed garage or basement could be a problem. Your sore throat could well be a friendly warning sign that you need better ventilation and I'd say a carbon monoxide detector is pretty cheap insurance against the potential for serious health issues or even death.