brazing

Discussion in 'Fettling Forum' started by Javerjayal, Mar 10, 2021.

  1. Javerjayal

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    Dear colleagues I have a question about a burner that is leaking.
    The burner has a leak in a tube and I want to braze.
    what percentage of silver should the welding rod have to make brazing???

    I don't know which flux is better
     
  2. Twoberth

    Twoberth United Kingdom Subscriber

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    Johnson Matthew Silverflo 55 (55% silver) is commonly used for burner repairs with Easyflo flux. It has a melting range of 630-660C. I also use Silverflo 20 (20% silver, and melts between 775-815C) if the area gets really hot in use.

    As a rule-of-thumb I use Silverflo 20 above the nipple and Silverflo 55 at or below it.
     
  3. Murph

    Murph United States Subscriber

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    @Twoberth , the firm is Johnson Matthey, here in the US, I use Lucas-Milhaupt, if for no other reason the company offices are just over 5 miles from home here!

    Harris is another good brand, along with Hobart. Without knowing where on the globe our comrade resides, a recommendation of materials to use could be right difficult!

    Murph
     
  4. Twoberth

    Twoberth United Kingdom Subscriber

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    @Murph I typed ‘Matthey’ but the computer overruled me! :lol:
     
  5. Murph

    Murph United States Subscriber

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    A way to make brazing on stoves MUCH easier is to use copper phosphorus brazing rods. They flow easier, takes a lot of the skill out of doing this sort of work, and best of all - the rod is self-fluxing! No need to thinks about what kind of flux to use, the filler material does it all!

    Murph
     
  6. CW

    CW United States Subscriber

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    Murph Do the brazing rods work in the same temperature range as the silverflow 55? Can i use it to repair a burner?
     
  7. Twoberth

    Twoberth United Kingdom Subscriber

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    I don't think CuP flows better than Silverflo, at least not the S2 composition. In fact, I don't think anything flows better than Silverflo 55 with the right flux

    My views on comparing Copper Phosphorus with Silverflo brazing alloys are below

    Copper Phosphorus.
    Large melting range (650-810C).
    Doesn't flow as well as Silverflo
    Harder deposit (harder to cut and file)
    No flux required
    Much cheaper

    Silverflo 55
    Sharp melting range (630-660C).
    Flows well.
    Cuts and files easily
    Flux needed
    Expensive

    Silverflo 55 (weight for weight) is about 20 times more expensive than S2 copper phosphorus, so that's a big incentive. But the flow characteristics are nowhere near as good (IMHO). Copper phosphorus on the left.

    2021-03-16 001 001.JPG

    Maybe I am doing something wrong, but I couldn't get the pieces much hotter without melting the brass.

    2021-03-16 001 002.JPG s-l1600 (1).jpg
     
  8. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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  9. Twoberth

    Twoberth United Kingdom Subscriber

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  10. Reflector

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    I asked a friend about this out of curiosity and he tells me that this only applies when brazing pure copper to copper. You'll need flux still.
     
  11. Twoberth

    Twoberth United Kingdom Subscriber

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    @Reflector
    Thanks for that. It’s good news and bad news. Good in that it will flow better on brass with flux, and bad as it removes it’s simplicity of use.

    It will be interesting to see if it works with Easyflo flux, as that will save having to buy another flux. Also, copper phos is not recommended for brazing copper/brass to steel (e.g. making lipsticks) as the resulting braze is very brittle.
     
  12. Reflector

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    @Twoberth

    From what I was discussing with my friend, he looked up some specific brand of copper phosphorus brazing rod and mentioned that it called for:
    When he further looked into the MSDS of the flux it mentioned it contained 25-50% potassium tetrafluoroborate. So I assume boric acid/borax based flux is what you'd use since it is already used in silver brazing.

    Caveat: I don't understand much about brazing but out of curiosity on what looked like a really dry solder joint I got curious and asked a friend who knows a bit about brazing.
     
  13. Twoberth

    Twoberth United Kingdom Subscriber

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    Good result with copper phosphorus rod and Easyflo flux.

    Without flux
    2021-03-16 001 001 - Copy.JPG

    Reverse side of same piece with flux
    2021-03-17 001 001.JPG

    At 1/20th of the price, I am a convert to CuP for brass to brass in the mid temp (630-700C) range.
    I will still use Siverflo55 for brass to steel, and Silverflo 20 for higher temperatures.

    Thanks everyone.
     
  14. redspeedster

    redspeedster United Kingdom Subscriber

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  15. Twoberth

    Twoberth United Kingdom Subscriber

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    Thanks Gary.