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Help, My Carbide is Solderophobic!

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  • Help, My Carbide is Solderophobic!

    I got a surface plate for christmas, so It;s time to try scraping. A while ago I broke a brazed carbide parting blade giving me a piece about 3/4 by 3/32 by 1/8. So I heated it up and pulled off the carbide piece. Then I tried to silver solder it onto a shank made from an old file. No success. The solder just balls up off of the carbide, using an HCL and zinc flux that came with a solder. I heated, cooled, and polished the carbide before soldering. Any idea how to solve this problem?

    Also, the torch gave up the ghost in a rather scary way with fire coming out of places it shouldn't. Opinions on various bernzomatic style small torches?

  • #2
    Carbide likes to form an oxide that's a pain to solder. Lightly hone the edge you're going to solder with a diamond hone so it's shiny and bright, and it will solder/braze just fine.

    It also helps if you use black (carbide) flux, instead of the usual blue brazing flux.
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


    • #3
      Hmm, OK. I was using soft sandpaper..

      Flux is neither blue nor black, its a clear, runny liquid stuff that contains zinc dichromate and hydrochloric acid.


      • #4
        Here's a link to an excellent thread about carbide brazing that explains some of the pitfalls you may encounter while brazing carbide.
        Home, down in the valley behind the Red Angus
        Bad Decisions Make Good Stories​

        Location: British Columbia


        • #5
          if you don't have diamond, sandpaper or rather emery will work, if its fine....the abrasive isn't going to cut through the carbide but the oxide is a lot softer


          • #6
            Originally posted by Teenage_Machinist
            Then I tried to silver solder it onto a shank made from an old file. No success. The solder just balls up off of the carbide, using an HCL and zinc flux that came with a solder. I heated, cooled, and polished the carbide before soldering. Any idea how to solve this problem?
            What is the silver content? I use stuff up in the 44 - 56% range and black flux.



            • #7
              Re: Brazing carbide

              A couple of things to consider with this. Aircosil brazing flux seems to work the best of any fluxes I have tried, a white and chalky paste, it adheres well to the parts where you want the silver solder to flow.

              Heating the substrate is a little tricky. You want to heat it to about dark cherry red but not to bright orange. You have to adjust the torch so that it comes up to temp in a controlable manner, rather than overshooting the mark. If you overheat the flux it will not work and the silver solder will ball up and fall off.

              I have always said that getting silver solder to flow correctly is "magic and JuJu." Some days you can do it and some days it just won't cooperate.
              Jim (KB4IVH)

              Only fools abuse their tools.


              • #8
                Get your self to the welding store and buy some black are real dark brown silver solder flux. That will take care of the problem . The white and blue stuff is no good for this application.
                Every Mans Work Is A Portrait of Him Self


                • #9
                  Brazing Carbide

                  I have brazed carbide using the powder borax based flux with no problem. You first need to polish the carbide and you want to get you heat just right so as to not overheat the carbide. The only place I have used a liquid flux was for soldering sheet metal...


                  • #10
                    Hmmm// I do not know the silver content, but will check. I think it came with this old Weller propane-canister torch that just blew up (almost singed my eyebrows there) and a tube (who puts liquid in a tube?) of clear flux. Torch does not really have much in the way of adjustments...

                    EDIT, no actualy I cannot find out the silver content, but it is a fairly soft solder, and it melts LONG before anything glows red hot. This is definitely soldering, not brazing, done with soft propane torch. The substrate is not a problem, the solder sticks to it fine. it balls up on carbide or if it does not, the carbide easily pops off with not a speck left on. Hopefully I can find this stuff...
                    Last edited by Teenage_Machinist; 12-28-2008, 11:29 PM.


                    • #11
                      Deleted-accidental double post.


                      • #12
                        Are you sure you have silver solder ?????

                        Is it pretty stiff to bend ?


                        • #13
                          One reason why I like the Sandvik Coromant scraper with the replacable tips. Each blade has four cutting edges so you can sharpen all four and almost always have a spare edge on hand. It is also possible to have special blades for doing small areas and such. They also work well in the Biax power scapers
                          Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.


                          • #14
                            Sounds like you have "Silver bearing solder", 1% or less, the rest likely Tin.

                            e-mail me an address and I will send you a bit of EZ Flow and some black flux, enough to do a few joints. You'll know what you need to buy. Someone just mentioned, elsewhere, that they were quoted 32 USD per ounce for true silver solder. Surely, that is not what you are using.

                            Also, when you have abraded the pieces to be soldered, blow them clean, do not rub the dust off. The oil from your skin will keep a bond from forming.



                            A Bernz-O-Matic SHOULD give you enough heat, though not ideal.


                            • #15
                              Let me suggest to you the stuff I use. I use Harris Safety Silv 56 silver solder and Harris Stay Silv white flux. These are excellent products available from most welding supply shops. There are other good products on the matket. With the Harris stuff and most others there are clear instruction for its use. Needless to say you don't get much silver solde for $16; about 1 troy ounce. That's enough for me to make 60 scrapers. It goes quite a long way.

                              Joint cleanliness is vital in silver brazing. It's not enough to wire brush off the crud and go to town. Both sides of the joint has to be abrasive scoured to clean bright grease free metal. A clean piece of enery cloth or a clean unused ScothcBrite pad works well.

                              Since carbide is so hard only diamond will abrade it. I suggest a diamond hand stone like a knife sharpener from a sporting good store. A couple of swipes from the stone will take off the oxide to clean carbide.

                              A good barrier to keep excess silver from drooling over the work is welder's soapstone. Mark the work with ruled soabstone lines. 1/16" away from the joint. The flux attacks the soapstone to a certain extent so this trick isn't fool proof.

                              Finally, use no lead or tin base solder products in connection with silver soldering. Silver soldering isn't really soldering anyway. It's more like low temperature brazing. The silver adds aggressive fluidity, as I understand. As soon as the joint is heated to the silver alloy's melting point it almost instantly slurps into the the crevices wetting the base metal and forming a surprizingly high strength bond.
                              Last edited by Forrest Addy; 12-29-2008, 04:19 AM.