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Stumpyjim

Inside of the forge question.

5 posts in this topic

Does the shape of the forge on the inside make a difference in how evenly the heat is dispersed? Is a round inside better than a squared inside or does it not matter?

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That depends (from my experience) on how it is oriented. A round forge is absolutely better for the vertical type, where the burner assembly is on the bottom. The swirling action helps considerably. For horizontal forges, I have heard that round is better, but I am convinced that this is only the case for bringing it up to temperature. Once a piece is inserted into the forge, the vorticity is immediately disrupted and the flow scatters. I have a square forge and it works fine, but then, I do not have much to compare it to. With any forge, there will be hot spots, and the number and angle of the burner(s) will come into play. Hope this helps.

 

John

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There will always be hot spots...unless you take extreme measures such as reverberator boxes where you have a forge that heats a box and you place the steel into that box...such things have great mass to even out heat.

 

The interior shape should allow for the work and room around for the blast to go. Beyond that it comes to burner design and how well it actually burns.

 

For all day forging of large work I like very heavy forges...200 pounds or so of refractory. They heat up slow, but when you throw in 120 pounds of cold steel they keep chugging along. Light fiber blanket forges will cool fast when you place large load into them, but they heat fast as well for smaller work.

 

Look into ribbon burners for even heating. They are more complicated to make, but seem to heat more even.

 

Ric

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I have never really thought about a square forge, however I would have to lean towards the round because of the vortex theory. This is a pic of my propane forge as I was completing I posted a pic on line with a question about something. I will never forget Ed Caffery, ( http://www.caffreyknives.net/ ) looked at it and emailed me that I had a potential problem with the angle of my burner. There was little angle, and they were angled downward. I had copied the design off of a forge I had seen on line. We conversed back and forth and I finally decided on this design. I changed the burner ports and welded shut the originals! If you look closely you can see the patches welded in above the burners. The idea is that the burner is pointed upward, so that the metal is not directly in the path of the flame and the burner creates a swirling motion or vortex inside of the forge. Thus getting a much more even heat and allowing for a quick recovery to that vortex once the metal is removed from the forge!

 

Forge004-1.jpg

 

That original design has morphed over to this. The burners are now controlled with a gas solenoid and a PID controller. I can set it for a temp and once it hits that temp the PID will cycle on and off the propane to maintain a high and low setting.

 

Forge005.jpg

 

I respectfully tend to disagree with some of what John said. The vortex created by angling the burner does let it get too heat quicker and it distributes that heat more evenly! True when you stick a piece of metal in the forge it probably tends to disrupt that vortex, somewhat. However when you pull the metal from the forge, the vortex goes back and the time that you have it out to work it allows for the forge to heat once again more evenly.

 

It is kind of like this if there is no vortex the flame lays directly in one spot much like heating with a torch even though the piece may get red hot it does not heat nearly as evenly.

With most pieces of metal laying in a forge the vortex may get distorted but it still has a better chance of heating that piece evenly, as the heat flows over the metal. IMHO!

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