Can you braze an object made of brass?

Discussion in 'Fettling Forum' started by JonD, Jan 31, 2019.

  1. JonD

    JonD Subscriber

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    I hope the title is self explanatory.
    It has been kicked off by the lovely little blowlamp which @Thomas soldered recently.

    I was looking at that and thinking could it be brazed? Sadly my experience falls short.

    If it was an object made of moderately thin mild steel (like a car for example) I would know the answer.
    With the right gas nozzle and filler rod (no 'leccy welding here) I could fix it - might be ugly - but functional.

    I realise I have no idea if that could work with brass. Soft solder - yes. Silver solder -yes, I can see how.

    But could it be brazed? Which when the object is brass is the analogy to welding mild steel with a steel filler rod.

    I have some feeling it might collapse in a heap. What do others reckon?
     
  2. Tony Press

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    @JonD

    I always use hard “silver solder” and a MAPP torch or “oxy-MAPP” to repair brass.

    Brass can be brazed. Here’s a guide to the fundamentals:

    Brazing Fundamentals

    Tony
     
  3. Thomas

    Thomas Subscriber

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    Brazing brass would actually be fusion welding, I had been considering using brass snare wire as filler but silver solder is much easier to work with. While filling a crack in thin brass the edges will ball up you need to then have the filler rod ready and near melting to bridge the gap. It is possible to accomplish a welded seam with a torch but much easier using the TIG process.

    The stresses that caused the cracking in the torch font from a lack of annealing will also cause the crack to open and push outward, I preheat the crack and tap it down with a small hammer before I start any repair.
     
  4. MYN

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    Of course the answer is a 'yes, you can'.
    Its more like hard soldering, with or without silver. You don't use a brass filler rod to braze brass. Brass filler rods are meant for brazing metals which have significantly higher melting points than brass, such as iron and steels.
    You would need a brazing alloy filler rod with a somewhat lower melting point than brass for the job. Normally, a MAPP torch would suffice but it takes longer to heat up the piece compared to an oxy-fuel torch.
    I normally use an oxy-acetylene welding torch for this. And, most critical, would be cleanliness on the piece as well as some practice. Brazing fluxes are available for the job too. Sometimes they are not necessary but normally they are.
    I have attempted to braze brass using brass filler rods, but its a tough one as one could easily melt through the brass piece and ruin everything. This is more like fusion-welding. Not recommended.
    Copper-Silver brazing alloy rods are better suited for this as it could work by capillary action. Fluxes could be used to ensure a clean, oxide-free surface for better wetting and capillary action during brazing. Some skills are necessary and only a fair amount of practice could enable you to do it properly.
     
  5. paparazi

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    Difficult but not impossible, I've done a fare amount of 'gas welding' steel rods on steel plate and brazing. A workmate of mine was pure genius at welding Aluminium (crankcases and housings) what a skill. Knowing the point of 'flow' with the sacrifice (rod) needing to be kept marginally hotter (through technique) compared to the receiving plate accepting that each needs to flow to blend. Other techniques are preferable.
     
  6. JonD

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    Thanks for all the replies. It sounds like it is difficult to gas weld brass then - but maybe not quite as hard as aluminium.
    I have tried doing that and it was a complete failure. Anyone who can do it deserves full respect.

    It was just something that I had bever seen discussed before. I am sure silver soldering and such techniques are perfectly adequate in most cases.
    I was just curious to know if brazing brass with itself was possible :)
     
  7. MYN

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    @JonD ,
    Its still possible to 'braze' brass with a brass filler rod but its difficult and the results are not as good as using an alloy specific for the purpose. I've done it on a preston loop generator before with a fair amount of flux and an oxy-acetylene torch. The molten brass filler does not wet the brass piece very well unless its red hot and just beginning to melt on its surface. The oxygen needs to be adjusted to just the right ratio with acetylene so that the flame is somewhat oxidizing, preventing the lower melting zinc content from vaporizing and bubbling into fumes. Do not heat too long or you'll end up with a blackened porous mess of melted filler on the piece, despite flux being used.
    Its tough to get consistent results. I'd say its more like a partial fusion-weld rather than just a regular braze. Its ok for the jointing of larger pieces of brass with a higher mechanical strength requirement but not ideal for sealing pinholes or leaks as new pinholes tend to develop from this technique due to the vaporizing zinc in the brass.(its working at the melting temperature of the brass piece itself).
     
  8. JonD

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    You stir up some memories.

    And they are nagging me that for brass it could be that a reducing, not an oxidising, flame is needed?

    I don't know why that old thought has come back to me but it came from fixing a Mini (a proper one - not a BMW one) Somebody had fitted some over sills by brazing them. I think that is against the law today - so please understand this was very long ago.

    Anyway trying to take those sills off and and weld back proper steel ones using steel rod was a complete nightmare.

    Great Green Balls of Fire! When you hit a fillet of brass you had to burn it away or cut around it and let it drop to the ground. It was like the Martians coming in War of the Worlds.

    Then you had to make the best of what was left of the steel / rust /fresh air hole...:roll:
    Straying well off topic now. If the mods think Open Forum - that is OK!!
     
    Last edited: Feb 25, 2019
  9. MYN

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    Normally an reducing flame is preferred for most metal welds. That'll prevent, for example steel, from oxidizing into inert black iron oxide that'll prevent a good joint.
    If you're weld brass with oxy-gas, I think an oxidizing flame would work better. I can't remember the exact reasoning but it has to do with brass being an alloy of predominantly copper and zinc. Their melting temperatures differ by a considerable margin and the zinc would melt first, and then starts to bubble as the brass starts to melt. And so on...
    All in all, it makes gas welding of brass rather difficult with a brass filler rod.
     
  10. JonD

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    This is getting deeper than I ever meant it to be - but it is fun!

    Good points about Oxy/Reducing flames.

    A reducing one is very useful for converting the rust around holes in steel back to something that can be welded.
    Particularly as steel often rusts in layers - because it was rolled that way in production.

    When melting a proper alloy I'm not convinced any component melts first. One component could be attacked before another by chemical reactions but
    surely thermally it should be quite homogenous.

    In soldering we don't find lead and tin melting at different temperatures. The Sn/Pb composition and any trace metals present fix the temperature at which it melts.

    Soldering seems to be joining with alloys at temperatures well below the melting point of the metals of the work.
    Silver Soldering - uses metals that have melting point closer to those of the metals of the work.
    Welding uses practically the same metals as the work as a filler.

    Then the term Brazing just depends what you are joining and with what.
     
  11. MYN

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    Hard(silver included) soldering is what most would regard as brazing. Its basically still a form of soldering but at higher temperatures than soft soldering. Does not involve fusion of the base metal. Capillary action, wetting and 'overcoating' the base metal piece with the brazing alloys. Less locallized heat required compared to a fusion weld.
    Nice discussion. As you've already known, the process appears easy in words on paper but some practice and skills are required to make that work.
     

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