Welding forge size?

[Nylund knives]

Hi,


I'm about to build a welding forge that will be used for damascus but I was wondering what size I need.

It will be a horizontal design with blown burners. How thick does the layer of wool need to be and how big should the inside of the forge need to be? Should I use two or three burners?

I was thinking something like 3" layer of wool, with an inside diameter of about 8" and 20" long...

I've got a 120lbs airhammer on the way and would like to be able to heat quite big billets to welding temp, but this will also be used for smaller billets.


Best Regards Jakob

 

[EdCaffreyMS]

There may be some who disagree, but the first thing I would say is that if possible, go with a single, blown burner. Multiple burners in a forge, especially the "blown" variety can be very temperamental and difficult to tune. Next, the common though is that the thicker you pile in the insulation (ceramic fiber blanket in this case), the better....no so. It's all about the properties of ceramic fiber blankets....in my tests, I have found that with identical forge body designs/dimensions, 2" of "wool" requires 2-3 more psi of fuel pressure to attain/maintain a given temp than 1" thick wool.

Personally I prefer a single layer of 1", #8 density wool, with a "slurry" of ITC-100 for my welding forges.

Dimensions.....it's going to come down to matching the forge components.....burner size(s) need to have the correct size, for the heat output needed for a given forge body design/size. To give you an idea, my welding forge is a vertical design. I took a 12" diameter X 18" long piece of pipe, and split it down the long axis on each side. I then welded in 6" on each side to create a large oval shape. With the "wool" inside, the interior measures 10" side to side, and 16" from the inside of the front opening, to the inside of the rear opening X 14" top to bottom. (I lined the floor with 3" of castable, and have 1" wool to cover the top). My burner consists of a 164cfm forge blower from The Blacksmith's Depot, attached to a 12" X 2" diameter iron pipe. That is attached to a 2" X 1 1/2" 90 degree elbow, which is attached to a piece of 12"X 1 1/2" pipe, which is what goes into the forge body. The propane/fuel input is a 1/4" pipe nipple, place along the 2" pipe, approx. 3" above where the blower mounts.
This setup my not suit everyone, and I'm by no means saying it's the best, or the only way to go, but time has proven it to be a reliable, trouble free setup, and puts out 2400F+ at 3,300 feet in elevation, at
6 psi of propane.

 

[Wayne Coe]

Ed mentioned it in passing but did not elaborate: Elevation makes a difference, especially if the forge is not blown.
Ed just uses the wool and coats it with ITC 100. That probably works very well with a vertical forge but for a horizontal I suggest the 1" of wool with about a 1/2" cast over it and then coat with the Infrared Reflective product. Ed likes ITC 100 at about $40.00 a pint. I use and sell Plistix at $10.00 a pint. Ed did some tests on these products and the ITC came out ahead. Others have felt that they liked the Plistix. Either is certainly better than neither. Remember, the Inswool (or what ever brand is a Ceramic Insulator. Ceramic, read "glass", and it is fibers, just like fiberglass. You know how you itch when the fiberglass fibers get on your arms. Well, do you want to be breathing that "glass" as it breaks off and is expelled out into the air that you are breathing?? The reason that I prefer the cast interior is that it makes a tuff forge that you are not going to poke holes in.

 

[Nylund knives]

Thank you Ed and Wayne!

I've got an old compressor tank 12" diameter, maybe that would be a good size with 1" or 2" inch "wool".
I can get wool locally, both 2300 degree and 2600 degree, the 2300 degree is twice as cheap though and the 2600 is only available as 2" thick.

Maybe the best would be to use 1" 2300 degree wool that I cover with some casting and either itc-100 or plistix?

Are there any other advantages with a single burner other then it's easier to make and tune, compared to using 2 or 3 burners?



Jakob

 

[EdCaffreyMS]

A couple of things that I think are important..... using the higher temp rated "wool" will generally give you more durability, and the lining will generally last longer....provided it is a #8 density wool.

My input on the single versus multiple burners: With a single burner the initial costs are less, the ability and ease of tuning is much better, and it will be much more efficient. I've had too many bad experiences with trying to help folks figure out problems/issue with multiple burners setups to ever recommend them to anyone.

 

[franklin]

does it hurt to line the bottom with a hard fire brick for the flux to fall on and the sides and top with soft fire bricks of course over the wool? and would a brush torch be hot enough to bring to welding temp in this big of a forge ed ? nylund is this close to the same as yours sorry for hijacking your thread but thought we both might have some of same questions

 

[JMJones]

If the forge will be primarily for welding damascus, I would opt for a vertical forge with one blown burner. The flux dripping off and dropping to the bottom is a great feature of the vertical forge but needing a handle on everything can be a pain for regular forging. If it is your primary forge I would go with a vertical forge with a blown burner.