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Thread: Silver Brazing tips???

  1. #1
    Join Date
    Jan 2010
    Posts
    128

    Default Silver Brazing tips???

    Anyone care to offer up some silver brazing tips?

    I need to do some silver brazing, but I've never silver brazed before. . .I did a little brazing while I was in welding school, but not much (only 1 week of one quarter) as the program was primarily focused on welding.

    Is it pretty much the same. . .pre-heat the parts, spoon on some flux, re-heat the metal until the flux starts to melt/boil, then start adding the silver solder?

    I have read quite a few people pre-placing the silver solder as well. . .is pre-placement a better approach for silver brazing?

    Thanks for the help!

  2. #2
    Join Date
    Aug 2006
    Location
    Beaverton, OR
    Posts
    7,104

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    Usually you use the paste flux for silver soldering. No preheat. You apply it before hand and the heat the part. Temperature is pretty critical. Heat the part and touch the joint as it heats up. When it gets to a dull red (Steel) start watching for it wetting the metal and flowing in the gap. Once it does add a little more solder and move the heat around the joint. Capillary effect will pull it though the joint. Be careful with the heat at this point, only enough to keep it molten. Too much and bad stuff happens.

  3. #3
    Join Date
    Dec 2009
    Location
    Calgary
    Posts
    84

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    Wheel Assembly made up of individual components, then silver soldered together with 45% cadium free 1/16 sized SS alloy.

    The integrity of the silver soldered joint depends on successful capillary action, the process by which the silver solder will flow, once the temperature is drawn through the entire joint. The strength of the completed joint is directly related to the space between the two components being assembled. Besides joint clearance, capillary action is also affected by surface finish of the components being bonded. Unlike soft soldering, a mechanical metallurgical action happens between the components being bonded and the silver filler material. The filler at flow temperature actually permeates the surface of the components and creates a very strong joint.

    I always use a aircraft style oxyacetylene torch which is sized especially for silver soldering in my shop. This small Purox torch is especially suited for this type of work, as the temperature that 45% silver solder flows at, is approaching 1200 degrees F. Also critical, is knowing the temperature levels of your soldering process.

    The flux used in silver soldering will tell you when the components being heated, and the joint in particular is ready to flow solder. At 212 degrees F the water in the flux boils off. As the temperature rises to 600 degrees F, the flux becomes puffy and starts a dry bubbling. At 800 degrees F, the flux flattens against the surface of the components with a milky appearance. At 1100 degrees F, the flux liquefies to clear appearance, exposing clean metal underneath. At this point, your almost ready to flow the solder, that requires 1200 degrees F to melt. Once this temperature is reached, the solder melts, flashing through the joint, and your done.

  4. #4
    Join Date
    Sep 2008
    Posts
    305

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    Very nice write up Jerry. Thanks

    bob

  5. #5
    Join Date
    Dec 2009
    Location
    Calgary
    Posts
    84

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    Quote Originally Posted by rowbare
    Very nice write up Jerry. Thanks

    bob
    Thanks Bob,

    I've spent 30 years improving my silver soldering skills in my shop, that include building a number of model steam boilers. I can remember a time when I thought it was a skill that I would never learn.

  6. #6
    Join Date
    Jan 2010
    Posts
    128

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    Thanks for the tips guys. . .

    . . .found out about the paste solder today. The practice piece I did came out looking like a big pile of dog doo-doo, but the two assemblies I silver-brazed together came out looking good. . .I wish I could take pictures at work, but that's a big no-no.

    One assembly was two threaded parts so the threads were the clearance between the parts, that was the easy part. . .I added silver solder until it flowed out between the bottom of the inner and outer parts. . .the other assembly I had a .003" clearance fit with a vent hole in the bottom of the female part. . .I kept adding silver solder until it flowed out the bottom vent hole.

    Really appreciate the help, and Jerry the boiler you posted looks sweet!

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