Hi all, I wanted to put a post together for other newbies out there that are trying to figure out how to improve a commercial propane forge. Thanks to everyone here to helped answer my questions over the past couple of months. There is so much useful information in this forum and there are several posts or answers from the experts here that come really close to being the perfect guide for what I wanted to do. However, for a newbie it can be a lot to digest and make sense of, so I tried to summarize what I learned and also include pictures in the step-by-step guide, since some of us are more visual learners the first time.
Also, I’m not trying to open a debate about buying vs building a forge. I hope to one day build my own, and I think I probably have the information I need now to build one, but given that I am just getting into this as a weekend hobby since I still have a 60hr/week job and two school-age kids, I felt that buying a cheap eBay forge and modifying it to improve its capability, durability and safety was the better way for me to go at this point. So if you are in the same boat, or came across a forge already built that needs improvement, then maybe this is for you.
I bought a single burner oval forge from Hell’s Forge on eBay for $190. It included:
1) 1/8” steel shell (approx 9” wide by 7” tall by 10” long)
2) 1” ceramic wool pre-rigidized blanket
3) hard fire brick floor
4) 180k BTU (@ 20psi) burner
5) 0-20psi regulator, hose, propane tank connector
The cost of the other supplies I bought to modify it totaled $110 and included:
1) 1” Kaowool blanket (1”x12”x24”) from eBay - $20
2) Simwool rigidizer from eBay - $30
3) 10 lbs Kast-O-Lite 30 castable refractory from Wayne Coe - $30
4) 1 pint Plistix IR refractory from Wayne Coe - $15
5) 8”x9”x1/2” alumina kiln shelf from local pottery supply - $15
The total build was $300, but the extra $110 I would have needed for a home build anyway, so really I paid $190 for the shell, burner and connections, and the 1” ceramic blanket liner.
Though the stock forge comes with a rigidized blanket, it is not really safe or durable to run a forge for a long time with just this setup. Plus the propane consumption would be very high and I’m not even sure if this forge could have gotten to welding temps. I would have liked to have run a set of control runs with the stock forge to see how well it worked, but I had no interest in running it like this after doing all of the research here.
Below are pictures of the stock forge, small and simple with questionable burner positioning.
My final liner design is shown in the cartoons below. The left picture is a cross-section of the top of the forge and the right picture is the floor. I added a total of 1.5-2” of additional liner to each side, cutting the volume down from 265in3 to 70in3 … so very tiny. I designed the floor so that the distance from the burner to the floor face is identical to the stock forge (whether that was a good distance or not).
The first thing I did was add the second layer of Kaowool. I cut it slightly larger than the inner diameter so that it fit in tight. I cut the burner port hold 1” diameter larger than the port so that I could get ½” of the Kast-O-Lite refractory into the hole. I also chamfered the edge to make easier to coat (see cartoons above). The Koawool cuts easily, and I used regular scissors for the edges and an exacto knife for the hole. I then sprayed on the rigidizer with a standard home spray bottle, with a little bit of blue food coloring added so that I could see the coverage. This was allowed to dry for a few days until I got to the next step. It was very hard and crispy at this point.
Next I wanted to set the correct height of my floor as mentioned above, so I cut out up to 1/2” of the Kaowool at the very bottom of the forge so that I could fill it with a thicker layer of the Kast-O-Lite and screed a flat(ish) floor. The rigidized wool is much easier to cut and shape than unrigidized wool, which is why I did it in this order. I simply used a metal hack saw blade, which was longer than the forge, to cut out the shape. I then reapplied the rigidizer to the newly exposed wool and let it harden overnight again. If you have sufficient volume in your forge, this step isn't really necessary.
Next was the Kast-O-Lite 30 liner. I calculated that I needed 4 lbs to coat the inside of the forge and so I prepared a full 5 lb bag so that I would have enough extra for the thicker floor and the outer edges. I underestimated how much I would use for the outer edges, so I ended up mixing a total of about 6 lbs. I used the exact amount of water as advised by the manufacture (2.8oz per 1 lb, for a total of 14 oz). This created a very dry and “crumbly” consistency that ended up being a bit harder to spread and shape than I had anticipated. The extra pound I mixed up I made with more like 3-4 oz, and it turned out runnier and more spreadable, so if I had it to do over I’d probably use a bit more than 3 oz per pound of mix, but making sure that I dried it out appropriately.
I applied the upper half of the forge first, let it dry for 1 hour and then turned it over and applied the lower half. This almost didn’t work as I had some sections fall off after only 1 hour of drying, but I had mixed up the entire 5 lbs and didn’t want to waste it. In hindsight and based on other advice obtained in this forum, I would mix up only half of the mix and then let the top half dry overnight before mixing and applying the bottom half the next day.
It dried in my garage for two full days, and it was rock hard at this point. Summer hit early this year in Austin, and we already had 100F days and very hot garages, so I had no qualms with only letting it cure for two days. In colder climates or with more water in the mixture, you could go for up to a week of curing. Next I proceeded to do a controlled drying sequence. According to the manufacturer, you are supposed to bake it at the rate of 100F/hour from 100F to the use temp to dry it out. After some research and determining that there was no safety issue, I decided to do the initial bake in my kitchen oven from 100F to 500F at 100F/hr. There were no noxious fumes or any issues with this method. After that I had no way to control or measure the temperature, so I decided to use the burner to complete the baking. I ran the burner for a total of ~ 2 hours from low flow to high flow with some cool-downs in between and got a good portion of the interior glowing red on the final heatup. The final look was a sandy gray finish.
After this final bake and letting it cool down overnight, I sanded the Kast-O-Lite to smooth it out a bit, especially on the flat(ish) floor. I used both 60 grit sandpaper and drywall sanding sheets with equal effectiveness. Next I applied the Plistix refractory as the final coating to create as thermally efficient forge as possible. Because of my very small final interior, I mixed only half of the pint bag that I bought. This will leave leftovers for future repairs. I mixed it to a pretty thin consistency so that I could paint it on with a paint brush and it went on very easily. After drying for 1 day it resulted in a bright white finish.
I decided to make the floor out of alumina kiln shelf to protect the refractory from forge welding flux because apparently the flux will degrade even these refractories over time. The smallest I could get at the local pottery supply was 8”x9”x1/2”, but I wanted the thinnest one possible so that the floor was at the right final height. I cut a 3”x9” strip with a concrete carbide saw blade and then shaped the bottom with an 80 grit belt on my belt grinder to fit nicely on the floor. It cut and sanded very easily, so you can create any size and shape you need. Below is the side-by-side of original out-of-the-box to final modified version. I think (hope) the modified one is going to work much better and save a lot of fuel!
I fired it up slowly to not thermally shock the new Plistix coating, and then easily heated up an old file in minutes. I banged out a crude knife (that I still need to harden and finish) with ~ 60 sec to get to orange with each heating since the file was only 1/8” thick to start. Next up is a 3/8” thick leaf spring experiment to see how efficient this thing is.
Hopefully some people find this useful. It certainly gave me practice with the steps I'll need to make my own forge when I need to upgrade. Experts, feel free to add to or offer improvements or alternatives to this recipe.