I’m keeping track of flux recipes used by blacksmiths for forge-welding as I run across them. The flux reduces oxidation and lowers the melting point of any slag or scale and helps to carry it away. There are two schools of thought: borax and no borax. Fortunately, the MSDS for commercial fluxes is available.
- Borax, Sodium tetraborate decahydrate (Na2[B4O5(OH)4]·8H2O), sold as Dial Corp 20-Mule Team Borax. Some report better results after baking it to remove the water, producing Anhydrous Borax.
- Iron Mountain Forge Welding Flux. Reportedly anhydrous borax and iron powder. No MSDS, no proportions. The third party videos of its use are convincing.
- Folk recipe #1: 3 parts Borax, 1 parts Sal Ammoniac (NH4Cl) available from hardware stores and ground.
- Folk recipe #2: 2 parts Borax, 1/4 to 1 part Boric Acid. Some include 1 part Black Iron Oxide (Fe3O4) or chips from a bandsaw or lathe. This sounds like a homemade version of the Iron Mountain product.
- Folk recipe #3: 3 parts Borax, 1 part Sal Ammoniac, 1 part metallurgical grade calcium fluoride powder (CaF2, aka Fluorite or Fluorspar). Used for Damascus steel. (Looks like reagent quality in small quantities sells for $2.00/g so I’m not going to try this one soon…)
- James Hrisoulas uses: 5 parts anhydrous borax, 2 parts powdered boric acid, 1 part powdered iron oxide, 1/2 part fluorspar, 1/4 part sal ammoniac.
- Boric Acid-based
- Boric acid, sold as Copper Brite Roach Prufe (98%), Pic Boric Acid Roach Killer (99%)
- Superior Flux & Mfg. products, aka Anti-Borax, Cherry Weld, EZ-Weld, etc. Composition varies but the MSDS reads:
- Boric Acid 8-13%
- Iron Oxides (FeO, Fe2O3, Fe3O4) 45-55%
- Steel Chips 35-45%
Interestingly, there are remarks on forums about using clean, white sand and ordinary table salt in lieu of flux. This makes me think they rely on a mechanical action instead of a chemical one.
I built a forge out of a scavenged refrigerant canister. It works! Here’s my first effort, a 1/2” steel bar drawn, scrolled, and twisted.
The construction of the shell was simple. First, I holed the empty canister with a large punch and filled it with water (the MSDS read that the old contents were non-flammable, but better safe than sorry), then cut the opening with an angle grinder fitted with a cutting wheel and trimmed the cut with aviation shears and snips. Next, I brazed on two pieces of bed frame angle iron and two flat sections to make legs. The burner support is a hand drilled and tapped 4” x 2 1/2” threaded pipe nipple held to the forge body with a pair of thin collar nuts. If I do this again, I’ll need a better method as the grinder is sloppy on curves and the shears barely make it through the steel. A drill press would also have made for easier going on the burner support, I improvised a U-shaped wooden jig and clamped the whole thing in the vise.
The lining was applied in layers. I lined the shell with 1” 8# Inswool 2400dF refractory blanket. I wanted it to fill in so I used the exterior circumference (c=Π*d, see how that middle school geometry is useful?) plus a half inch over and the full, untapered length of the cylinder for my measurements. The ceramic blanket was easy to cut and I misted it with water to keep the dust down but I misjudged how hard it was to work with it in a tight space. I had planned to roll it up, slip it in, and let it unroll and expand but I had to cut it into three pieces to get it to fit without crushing. I cut a tapered hole for the burner flare and later I stuffed some scrap into the collar around the mounted burner to seal it. The second layer is roughly 1 1/2” of Kast-o-lite 3000dF castable refractory applied in two layers. I mixed up six pounds of it a little thinner than indicated and applied it by hand to the wetted ceramic blanket, let it dry a few days, fired the forge for a few minutes then followed the next day with another six pounds. I paid attention to making a cone for the burner. After letting the refractory cure for a few days, I fired the forge to full heat and let it cool overnight. The last layer is a thin coat of Plistix 900F, a refractory service coating that is good to 3400dF and supposedly improves the efficiency of the forge due to reflecting IR. I mixed roughly a pound of it to a thin consistency and dabbed it on with an old paint brush. It went on like a chalky, slightly gritty, thin white paint.
The insulation works fairly well. After forty-five minutes the exterior of the forge is uncomfortably warm but not painfully hot. The burner holder gets just less than searing hot where it enters the shell and the pipe collar does not show discoloring yet.
Forge in operation and tuned. Nice blue flame.
The dragon’s breath and a look into the hot forge
I assembled an atmospheric injector burner loosely based on Michael Porter’s design using plumbing parts and a .035” MIG tip. When you figure my time, buying miscellaneous hardware like small taps and drill bits, multiple trips to several area hardware stores and ordering the schedule-80 1/8” pipe nipple, I’m not sure it’s more economical than buying a precision-made burner like those from Rex Price or Steve Gensheimer but it works (and I learned a bit). The flame is very stable and it easily brings a 1/2” square bar to a light-red heat. I can’t wait to build the forge.
In my copious free time, I like to work with metal so I started setting up a hobby smithy to do some ironwork. I’ve read that about the only thing you can’t make is the anvil and that hammering on a shop vise will quickly ruin it. Last week, I scored a nice 138# Peter Wright anvil and a 5”-jaw leg vise from a local seller on Craigslist. I doused the anvil with Liquid Wrench, let it sit overnight and brushed off the rust:
Sunday afternoon I cobbled together a stand based on Jack Dempsey’s box idea. It’s a frame of 4“x4” posts, 2“x12” lumber on the top and ends, two scrap 19/32” T1-11 panels for the faces, and all held together with 3 1/2” structural screws. It’s sturdy enough:
Next I need to come up with a forge, mount the leg vise, and clear some space. Then I need to practice.