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Forge-welding flux recipes

2012-06-24 , ,

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-based
    • 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%
  • Neither

    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.

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