black brazing flux
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  1. #1
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    Default black brazing flux

    Is it possible to make this stuff, what exactly is it made of?

    I tried to buy some stay-silv black flux but it must have a hazardous material classification because no one will ship the stuff. But I tried googling what exactly it contains and came up empty (trade secret?).

    I see guys in China selling the stuff and it looks like they mixed it themselves.

    I want to braze some carbide but the only flux available to me is borax (doesn't work), and white brazing paste (works, not sure of strength). I even tried borax just joining 2 pieces of steel, doesn't work either.

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    It's a boron based flux, but I'm not sure what the difference is between common-or-garden borax and stay-silv, other than there are fluorides in it as well.

    I bought a 1lb pot from Amazon, delivered from the US to the UK after I had difficulty in getting JM tenacity 6A in small quantities. It might be worth trying this route.

  3. #3
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    Quote Originally Posted by taiwanluthiers View Post
    Is it possible to make this stuff, what exactly is it made of?

    I tried to buy some stay-silv black flux but it must have a hazardous material classification because no one will ship the stuff. But I tried googling what exactly it contains and came up empty (trade secret?).

    I see guys in China selling the stuff and it looks like they mixed it themselves.

    I want to braze some carbide but the only flux available to me is borax (doesn't work), and white brazing paste (works, not sure of strength). I even tried borax just joining 2 pieces of steel, doesn't work either.
    if the white flux works, just use it. unless you are doing production, its not going to matter all that much. as long as you get a good flowing joint, the flux has no affect on the joint strength. the black flux is better on steel, and at higher temps, but if you do everything right, clean really well, use plenty of flux, heat quickly to temp, keep the joint in the reducing flame the entire time (easy with a carbide tool of reasonable size), you should be fine.

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    I'm using a propane torch for this, and it takes a good minute or so to get it up to temp... I'm wondering if that caused some difficulties with borax.

    I'm not really wanting to use acetylene torch because oxygen is expensive and doesn't last all that long. I just wonder if acetylene air torch exists...

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    Interesting the the environmental laws are more strict in China

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    It had something to do with the guy wanting to use SF express, and that SF express will NOT accept any powdered substance of any kind. And the guy will only use SF express, not anyone else (not sure why).

    I found a guy selling a pound pot of Stay Silv black flux... 10 dollars and only 31 to ship it to Taiwan through their global shipping program.

    Maybe I should look into an acetylene air torch or something too. Propane takes a good minute or 2 to heat the part to temp.

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    Quote Originally Posted by taiwanluthiers View Post
    I'm using a propane torch for this, and it takes a good minute or so to get it up to temp... I'm wondering if that caused some difficulties with borax.

    I'm not really wanting to use acetylene torch because oxygen is expensive and doesn't last all that long. I just wonder if acetylene air torch exists...
    of course it does, a Smith, prest-o-lite or Lenox plumbers rig is air acetylene. MAPP is good too, hotter than propane. larger, brushier flame is good for brazing, thats what they are made for.

    don't use borax alone, I've done it, but why? use a proper flux made for brazing.

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    I've seen someone sell a gasoline blowtorch... claiming it's a lot cheaper to maintain than acetylene. Any dangers to gasoline torch?

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    Maybe try Peterson hi heat flux, it's really made for cast iron. Might try Sill floss.
    Good luck

  10. #10
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    Quote Originally Posted by taiwanluthiers View Post
    I'm using a propane torch for this, and it takes a good minute or so to get it up to temp... I'm wondering if that caused some difficulties with borax.

    I'm not really wanting to use acetylene torch because oxygen is expensive and doesn't last all that long. I just wonder if acetylene air torch exists...
    Oxygen usually is used up pretty fast if you are cutting thick metal but for just brazing or welding it lasts a very long time unless you have leaks in your system somewhere.. Been using oxy acet torch for over 50 years in USA..Cheers; Ramsay 1


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