General Coal Forge Notes

[HWooldridge]

Addendum: I posted this note in response to a question about lining a forge sometime in March 2005 but I'm not sure if it still resides in cyberspace. Glenn, you are welcome to post as a sticky or a blueprint, if one does not already exist with this information. I might also add I lined a forge with this clay recipe about three months ago (March 2008) and it is holding up fine with no cracks in the refractory - I hope it helps someone...



Lining a Forge:

I lined a Buffalo forge that has the lips an inch or so above the iron hearth and it turned out well. The process is based on something I learned years ago when I used to help my grandpa build houses. In addition to carpentry, he did some rock work and one thing we would do occasionally is reline fireplaces. On horizontal areas, he would make up a mix, apply it dry and level, then spray water on top. This would rock up in a day or so without cracking. The mix I used (based on his recipe) was 3 parts mortar, 3 parts clean sand, 1 part fireclay and 1 part dry lime. I mixed it, poured in the hearth to a depth that was flush to the top of the firepot and raked it smooth, then sprayed only enough water on it until the surface was wet. I let sit two days before making a fire and it had hardened nicely with no visible cracks anywhere. I think the minimal amount of water helps eliminate the cracking.

Coal Forges:

I have seen more badly constructed coal forges than good ones in my life. A lot of folks make their own (which is perfectly fine) without a basic knowledge of not only how but why it works.

All solid fuels need some amount of air pressure to burn properly. You can have too much velocity with insufficient pressure or too much pressure without enough air movement. The two extremes can be illustrated by a couple of examples. A light wind blowing on a campfire will make it hotter but only the outside of the fuel pile burns because the breeze can't make it to the interior. Conversely, hooking an air compressor to a firepot will make a fire but any amount of pressure much over a few pounds will blow the fuel out of the pot. The reason why bellows and centrifugal fans work so well on a forge is that they generate the right combination of both air supply and pressure. Too big a blower (like a large, electric squirrel cage) will lead to excess fuel consumption, more clinker and an oxidizing fire. In addition, a squirrel cage can be "stalled" because they are designed to move large amounts of air - not push it thru a mass of burning fuel. Conversely, too little air will never allow the fire to reach its proper potential for heating.

The proper size air inlet to the fire is also important. I'm sure a lot of folks have used grates drilled with a bunch of holes but 1-3 larger holes is better. One of the best homemade firepots I ever saw had a 1/2x3" slot cut in the bottom. The pot was entirely made from 1/2 inch steel plate and there was no clinker breaker. This arrangement made a nice hot fire with a center about the size of a grapefruit, which is about like a commercial pot.

I recently exchanged notes with a professional British smith who uses a side blast. It is simply a piece of 1" heavy wall stainless tubing as a tuyere and aimed slightly downward into a molded mortar "duck's nest". The coal is piled up in the hearth and forms it's own bed in the depression. Other fire shapes can be made by employing fire bricks to redirect the blast. This simple arrangement works well and eliminates all the Rube Goldberg creations that get built in back yards. The smith said he can easily weld with this design and some of these forges have lasted over 5 years in daily use.

I use a coal that generates a big clinker in a hurry but it was cheap, gets hot and cokes well so the only disadvantage is the dirt. Therefore, I have learned to build a fire and use it for a half hour or so then let the clinker cool for a couple of minutes. At this point, there is enough to usually pick up in one piece while I try not to disturb the coke around the pot. I can usually clean the fire and get back to work without breaking the whole fire down.

If I have one piece of advice about fire tending, it's that less is usually more. I have seen a lot of people that tear the whole fire down on every heat or spend the entire time digging up the coke ball. A fire has to form a natural bed to work properly and it takes a few minutes for this to occur. A good coal smith will replace the piece for the next heat and rake a little coke on top. As the fire burns hollow, the sides are pushed in a bit. This gentle management is done during every heat - you don't work for an hour and then tend the fire all at once.

[Archie Zietman]

Great post, thanks a lot.

[Thomas Dean]

Excellent post. I have seen much of the "don't" you listed and by "experienced" blacksmiths. Thanks also for the recipe also!

[pete46]

Very Informative Thanks!

[Sabre]

wow thanks alot helped

[CurlyGeorge]

Thanks for the info. That answered a couple of questions that I was pondering about lining my own shop forge.

[GUMLEAFMICK]

Thanks for the info as I am bilding my first forge I have a few questions. The centrifugal fan I am using is an old blower used for oil cooking fires (Japan). My electrican recomended that I dervirt the unwanted air flow with out blocking the fan as in the sliding knife valve at the forge.he was not keen on fitting a speed controler to the motor. I was thinking of making a diverter valve directing the unwanted air flow into the chineny of the forge through a pipe running internaley up the chimeny for about 700mm this will help the draw, without blowing dust of the floor if I was to dump it under the forge

[CurlyGeorge]

I have a hand crank blower on my shop forge, so I don't have to worry about too much air. But I do have a 12 inch fan blowing out of the 12X12 roof vent. That definetly helps the draw. If you run it up the chimney for a ways, I don't see why that wouldn't cause draw. Should work.

[Sabre]

yes that will a saw a guy on here once that diverted his extra air up the chimney

[Rob Browne]

Great and informative post. It just goes to show that you can always learn something new from anyone even if you think you know how to do something.

A few new things to try, thanks :)

[Pat Roy]

I guess I got lucky the first time around. I built a fire pot with steel plate. The bottom has two slots like described in the post by HWoolbridge and no clinker breaker. I reach in periodically and pull out any clinkers. I attached a centrifugal blower(way to much capacity) with a slide gate. I could control the flow with the slide gate but couldn't stand the noise of the blower running full out all the time. So I bought a speed control for the blower and now can tune it down to a quiet level and still get plenty of air. I concocted a tuyere out of scrap pipe & square tube lying around and the whole thing is working out well. I haven'e put any kind of liner in the fire pot and after 4 years of weekend use it shows no sign of burning up.

[devon blacksmith]

We use sand to line the bottom of our forges untill the dust builds up

[yesteryearforge]

I have two buffalo forge with hand crank blowers and some of the air is diverted up the chimney, ( they were designed that way )
there are some photos in the gallery somewhere.

Mike Tanner

[old man merrell]

very informitive the liner mix will be a big help

[loreng59]

Am new to the forum.

I have been coal blacksmithing for a few years, but have been using an original civil war mobile side-draft forge all this time.

Now I am setting up to work at home. A friend gave me a 18" x 20" cast iron pan with 2" tuyere in the bottom stand has 4 metal legs. I have a 3" Buffalo Forge blower.

My question concerns the lining for the opening. I have fire brick for the pan, but do not know if I should line the bottom over the tuyere?

[KenC]

Greetings to all. Just thought I would say hello to everyone. I am new to both this forum and to blacksmithing in general. I currently prefer working with charcoal or coal forges as they are my only experience. I look forward to learning more about blacksmithing by taking clases at the Vista Gas and Steam museum here in sourthern California. I am not yet a member of the California Blacksmith Association but will be by the end of the month. Keep up the good work here and hopefully I will have some articles of my own to publish.

Enjoy.

[Dick L.]

Well I've been practicing Brian's horse heads and just working on hammer control but have been fighting the fire management a bit. Did a search and came up here. Glad I did , I want to say that this design with the 1/2" X3" slot works far better with my firepot the the original multi-hole design. The holes have a tendency to plug and the fire get very uneven in temperature. The slot hasn't plugged yet (only second session tonight) but does require closer watch and less blower. (HOT) HWooldridge Thanks for the info!

Dick