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I Forge Iron

moya034 is attemtping to engineer a forge


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Greetings all! I'm new to this site.

I'm into hobby metalcasting, but am getting the blacksmith/bladesmith disease as well. I realized the only cure known to mankind is to actually go out and do it!

In my garage I got a 25' roll of 1" thick 8# density INSWOOL, and a 55# bag of VERSAFLOW 60 PLUS. I got the materials for the construction of a new crucible furnace, however, I will have plenty of materials left over for making a forge.

I'm mostly interested in bladesmithing, however I'd like to be able to do some more general blacksmithing work too. I'm planning on making a typical horizontal forge, fired with either propane, natural gas, or used motor oil.

I've looked at a variety of forges online, but I still have some questions, I'm sure there will be more to come:

1. If I were to make my forge 1 foot long on the inside, about how wide should I make it?

2. Where is the best place to install the burner on the forge to promote the best heating efficiency?

3. Instead of a firebrick floor, I'm thinking of just using the VERSAFLOW 60 castable and a kiln shelf, how's that sound?

4. How important is it to have a door on the forge, or can I leave the working end wide open? Do I need a vent on the other end?

Thanks in advance for any help :D

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Assuming you are talking round, I can pass on what I have been taught and read myself. Size- 1 foot length= 4" working inside diameter. Many believe that the burner should be at middle of the length. And, for a round forge, tangent to the interior circle so it picks up a rotational swirl. Many use a pourable refractory cement to make the floor and some will then also lay a high temp firebrick silica-alumina on top of the cast portion to better survive flux. A door at the rear is useful for longer pieces and to control dragon's breath- a simple hinged flap will do well but it shouldn't truly seal because that means all of the DB is aiming out the front at you... Finally, I think there is near universal agreement that coating the blanket with ITC-100 will increase efficiency and give longer service for the liner. The seasoned veterans will be here to correct me if I am passing on questionable info. I hope I have helped your planning.mike

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Yes, I'm talking round.

I was actually planning on lining the entire forge with the VERSAFLOW 60 castable refractory over the INSWOOL. That particular refractory is good up to 3100F. I'll then put a coating of ITC100 over that.

Speaking of ITC100, I've spoken to the owner of the company who happens to be a ceramic engineer. Long story short, he told me his industrial customers report a fuel savings of 30-50%. ITC products are used by the US military, just about every car manufacturer, and most of the steel producers.

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Just a quick note on used motor oil forges. Make sure you have a good source of the oil before you decide to build it. I built mine and then found it was not legal for oil change places to sell/give away the used motor oil to an unlicensed recyclers. There is also a very competitive market for used motor oil which is converted to home heating oil by the recycling companies.

No idea on used vegetable oil, I haven't gotten that far yet.

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The forge itself will be made so I can put in a variety of burners and use nat gas, propane, or oil, whatever I feel like at the time.

I already use used motor oil for my crucible furnace. If you are curious, here is my burner design. The one I use for a forge would be smaller and made of 3/4" pipe probably. My burner will burn veggie oil too, or any non-volatile liquid fuel for that matter.

click here for moya034's waste oil burner

As far as the forge itself goes, I'm thinking of making it with 2 doors now for added flexibility.

Question: Assuming a forge with an inside of 12"x4", how big would the vents on each door need to be?

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  • 2 weeks later...

4" - 5" dia is about right for that size forge. Chamber length should be about 9". Many people prefer to close up the back and leave a 2" hole for long work to poke thru. Work that doesnt fit in the chamber can be layed across the mouth of the forge with fire brick on the other side. I prefer the burner at the back giving the hot gas more time to swirl and more dwell time to transfer heat. Many people place it in the center. IMO tangential is best.

Its important to realize that to get the forge hot you have to minimize heat loss. Like trying to fill a leaky bucket. A lot of heat is lost by the exhaust and there is not a lot you can do about that. However a very significant factor is radiant heat loss. Radiant heat transfer rate increases very rapidly with temperature and at temps above orange it becomes a major player. So while you dont try to seal up the forge gas tight, its important to block up the forge so that there is no direct, line of sight exit. Firebrick or a refractory wall in front of the mouth of the forge with a 1"-2" gap will reflect back most of the heat.

If you are just bending stuff at orange heat then this is not really an issue but if you need high forging heat or welding heat then you have to capture as much of the radiant heat as possible.

Edited by maddog
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I recently made a great gas forge for knife making based upon the designs by Larry Zoeller. His web site includes all the necessary information for constructing a few forges from coffee can size and up along with all the specs and measurements you'll need and its all free on the internet. He also supplies pre made burners (in whole or part) that work on a venturi principal requiring no added air supply along with all the other components short of the metal forge body. For mine I used a piece of twelve inch diameter half inch pipe which I believe was a well casing and about eighteen inches long and welded up the door,hinges, back and base from some scrap plate steel that I had lying around. I purchased the complete burner kit and tank hook up kit from Larrys web site all the rest cost me was time and welding rods. Google 'zoeller gas forges' and good luck. Tom Coles

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