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Silver Solder & Braze

Thursday, 19th March 2020
Graham (Tech Advisor)
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Silver Solder & Braze are both products used with either an Oxy Acetylene Torch or Oxy Propane Torch.

Silver Solder & Braze, what’s the difference?

For me, the key difference is how they work on the joint.

Silver Solder

Silver Solder is more fluid than Braze and works by being drawn into the joint by a capillary action.  So if, for example, you want to join two pieces of thin sheet metal together, you would need to overlap them.  The Silver Solder will be drawn through the joint, filling the minute crack between the two pieces of metal, bonding with the surfaces to join them.  If you tried to butt the two pieces of metal together, there simply wouldn’t be enough surface area touching to achieve a strong joint.

Silver Solder is used with a Flux, which chemically cleans the metal and keeps it clean during the Silver Soldering process.  Silver Solder is also know as Silver Brazing.

Braze

Braze on the other hand, does not get drawn into the joint, but is built up on the surface of the metal being joined, so it looks more like a weld.  Like Silver Solder, the Braze material bonds with the surface of the metal being joined.

Braze is used with a Flux, which chemically cleans the metal and keeps it clean during the Brazing process.  Brazing is also known as Bronze Welding.

What Silver Solder & Braze have in common is that neither involve melting the metal that’s being joined, that would be welding!

In the joint examples shown, I would use Silver Solder on the Edge & Lap Joint and Braze for the Butt, Corner & Tee Joint.

Types of Silver Solder & Braze

Whilst there are a number of Brazing Alloys on the market, for this article we’ll keep it simple and just cover the most common, C2.

C2 is a multi purpose, Silicon Bronze brazing rod that’s suited to most general purpose brazing on metals including Steel, Copper, Cast Iron and dissimilar metals.

C2 Braze is Brass Coloured and typically melts at around 875⁰C.

Most Silver Solders can be categorised by their Silver content.  The Silver content will determine the fluidity and melting temperature, the more Silver, the more fluid and the lower the melting temperature.

Most common are 33% Silver (around 720⁰C), 40% Silver (around 675⁰C) and 55% Silver (around 650⁰C).

Also available are Silver bearing Copper Phosphorus Alloys (CoPhos).  These are available with either 2% or 5% Silver and are used primarily for joining Copper to Copper, where, if the metal is clean, no Flux need be used.

Silver Solder can be used to join most common metals, including Mild Steel, Stainless Steel, Copper, Brass, Cast Iron and Dissimilar Metals.

Fluxed or Bare Wire?

Silver Solder & Braze is usually available in 2 or 3 forms:

  1. Bare Wire – (Silver Solder & Braze). This is my preferred type.  With this wire you use a powder flux.  This can be coated onto the wire as necessary by gently warming the end of the wire in your flame, then dipping in the powder.  This can be repeated as necessary.
  2. Flux Coated – (Silver Solder & Braze). This may seem like a good idea, but there are, for me, three flaws.  Flux coated wires are more expensive than bare wire.  If you need additional flux, you’ll still need a pot of powder. If the wires are bent, the flux tends to fall off!
  3. Flux Impregnated – (Braze Only). Here the flux is in little nicks on the wire.  This works very well and the wires can be bent.  The downside is that flux impregnated wires are the most expensive.

I hope you found this blog article useful, if things work out well for you, please feel free to post some pictures of your achievements on our Facebook Page

Please let me know what you thought of this article by leaving a comment.  Don’t worry, your email address won’t be added to a database or shared and you won’t receive any unsolicited email.

Cheers

Graham

The Welders Warehouse

23 responses to “Silver Solder & Braze”

  1. ADRIAN HAYWARD says:

    Hi Graham, I am in the startup phase of sourcing materials for an aircraft project. The fuselage around 2 metres long will be made using a variety of stainless steel tubes of 0.5mm wall and 6mm to 8mm O/D butt joined using a small torch and mappgas. I hope to be able to form a small flange to assist in strengthening the joints, but will be small. Would you suggest braze or silver solder? a 4 stroke engine will be mounted to the front end on A/V mounts so vibes will be minimised as much as possible

    • Graham says:

      Hi Adrian
      You will need to Silver Solder Stainless because Braze will be too hot. Overlapping type joints will be necessary as you cannot build up Silver Solder to create a weld looking joint.
      You will need a deft hand because the melting point of Silver Solder is close to the temperature at which the Chrome in Stainless will burn/oxidise (presents as Blueing). Once this happens you will not be able to get Silver Solder to bond, the only course of action is to remove the bluing and start again.
      I would strongly suggest practice!!!
      Hope that helps.
      Good luck with what sounds like an interesting project.
      Graham

  2. Jerry says:

    I want to silver-solder a folding handle onto a stainless steel thin-wall vessel weighing about 15kg. I wonder how the pull-strength of the silver-solder joint varies with the alloy?
    Where can I look up the tensile strength of the silver-solder alloys? Then it should be easy for me to calculate the pull strength of the joints.

  3. David Tweddle says:

    I hand a bent clock hand so without annealing… I now have two bent clock hand parts the clock hand is two hundred or so years old difficult to find the correct type so do I silver solder or braze, the hands are latticed so looking at 1x1mm square x2 joints
    same clock bell gear stripped three teeth so looking at insert and then hand profile teeth. Insert i would be happy to just silver solder in a new section but the hand I do not think silver solder is the way to go as it is the minute hand and my only way to correct the time 12 or more times a year.
    The hand in question 162.5mm x .98mm the first 100mm is left on the clock, so with care I could adjust the hand by the first 80-90mm or better still adjust clock to gain time over a month. then I could just stop and restart, not ideal or the most accurate way to do it but hey. if this blog is to old I will try to converse another way.

    • Graham says:

      Hi David
      Difficult to offer specific suggestions without being able to see the job. But things to consider in the process of deciding whether to Braze or Silver Solder are:

      1) Silver Solder requires a significant surface area of joint as it use’s capillary action, so an overlapping type joint is likely to be needed.
      2)Braze can be used for Butt joints etc as it does not rely on capillary action.
      3) Braze needs a higher temperature, so more care may be needed to avoid damaging any metallurgical properties of parts.

      Adjusting the clock via the first 80-90mm would seem a sensible way to go, but it all depends on the strength of joint that can be achieved and how much effort is needed to move the Hand to adjust the clock.

      Sorry I can’t be more specific, but I hope that helps.
      Kind Regards
      Graham

  4. John Kerr says:

    Thx for that.
    I’ll try something else.
    Tig would be too “industrial”,brazing would leave a brassy edge, I suppose if it was polished long enough…back to the drawing board.
    Thank you.

  5. sinnytim says:

    I am trying to join thin stainless sheets for decorative purposes merely to “stick” them together. Would silver solder be strong enough?

    • Graham says:

      Hi John
      Silver Solder relies on surface area and a tight joint for strength.
      You would not use Silver Solder for an edge to edge joint.
      An overlapping joint is ideal.
      So the short answer is YES, it would be strong enough, but only if the right type of joint is used.
      Silver Soldering Stainless is tricky, DO NOT let the Stainless Steel discolour in the heat! Once discoloured you will never get the Silver Solder to bond with it. Heat the Stainless carefully!
      Hope I’ve helped.
      Cheers
      Graham

  6. Michael R Norris says:

    *typo- should not be engulfed in roaring flame… although lower half would be exposed… ty for your time and the wealth of knowledge.

  7. Michael R Norris says:

    hi graham i know this article seems a little old maybe your still responding? im trying to make a small tank using very thin (22 gauge or smaller)sheet metal, steel probably with a galvanized coat that will be removed further reducing the size, that will be used as a boiler/ water heater. it will used directly over open flame. do you think something like 33% solder would be sufficient to withstand temperature like that, is something like c2 the only way to go, or is there something in the category of not most common therefore not covered here that will flow a little better but hold up over open wood fire? It just occured to me reading this article it should be engulfed in roaring flame but it will be over a hot fire with the bottom half likely in the flame. thank you for the article and allthe information you share, its been invaluable over the past year venturing into fabrication i havent had the ability to pursue until recently.

    • Graham says:

      Hi Michael
      A 33% Silver Solder melts at around 700ºC, I would have thought it unlikely the part is going to get that hot in use.
      C2 Braze Brazing Alloy melts at around 860ºC.
      I would suggest that choice of joining material will depend on joint configuration. Silver Solder will need an overlapping type of joint, brazing will not.
      Hope this helps
      Cheers
      Graham

  8. Ray Farrell says:

    Really enjoyed the column Graham.
    I’m putting a bush fire sprinkler system around the house under the gutter.
    I’m using copper but soft solder melts at too low a temperature and has been known to fail in fires.
    A solder rod manufacturer recommends 2% silver solder rod (which I assume is a phos Copper rod). I’ve never silver soldered 50mm Cu before. I’m going to use Oxy Mapp gas.
    What should I look out for compared to soft soldering 19mm tube.

  9. Andrew Michael says:

    Great colunm, I have a question, I’m trying to put a mast mount which is 6″*6″ carbon steel about 1/2″ thick, on a cast iron counterweight that is on a excavator. I was wanting to ask you for any ideas or suggestions for this application and would silver soldering be a feasible application. This counterweight is huge and there is no way I could heat the whole thing.

    • Graham says:

      Hi Andrew
      Thanks for the positive comment, much appreciated.
      Re your Cast Iron Counterweight on to ½” thick box steel. I don’t think Silver Solder would work as you will need to gat the parts VERY Hot. I would warm up the Cast Iron so that it’s not cold (doesn’t need to be hot), so warm to touch, at least around the area to be welded. Then use Ferro Nickel Cast Iron Arc Rods to Weld them. Alternatively, could you use a non heat method? Tapping the Cast Iron and bolting for example?
      Hope I’ve helped, at least a bit 🙂
      Cheers Graham

  10. davidokkefe says:

    Brazing and soldering are classed as semi permanent opposed to welding which is permanent brazing would be achieved by capillary action as well excellent technical information graham enjoy reading comments

  11. Michael Poore says:

    In the motor trade we found that repairing exhaust brackets & similar items [a lot of vibration] the repaired item was stronger than the original item!

    • Graham says:

      Thanks for the comment Michael
      Braze is soft and ductile, so is particularly good at resisting vibration.
      Keep up the good work
      Graham

  12. Adrian says:

    Very helpful and succinct! I presume the silver solder and braze wire mentiond is available on the website, along with the fluxs?

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