Monday, December 19, 2016

Bearing Design Guide: Chapter Twenty-Two: Soldering, Brazing and Welding of Bronze Alloys

          Copper-based alloys, like other metals, occasionally require joining by soldering, brazing and welding. The following is intended to assist in those procedures.
          In soft soldering, the low melting solders of tin and lead, in varying proportions, are used to join bronzes at relatively low temperatures well below the melting point of the bronze alloy or its lead content (if the lead content is 3% or less). The solders most generally used are the 60 tin and 40 lead solder which melts at 374 degrees F and the 50 tin and 50 lead solder which melts at 477 degrees F.  You can see a great detailed example of this here.

          Soldering is used to provide a convenient joint that does not require any great mechanical strength. It is used in combination with mechanical staking, crimping or folding and used to seal against leakage or to assure electrical contact.

          Fluxes for soldering: Soldering requires the metals being joined to be clean and fluxes clean the surface by removing the oxide coating present, keep the area clean by preventing formation of oxide films and lower the surface tension of the solder by increasing its wetting properties.

          Rosin, tallow and stearic acid are mild fluxes but are not too effective in removing oxides present. Zinc chloride and ammonium chloride used separately or in combination will remove oxide films readily, however, this flux residue must be removed or neutralized to prevent their corrosive effects. Washing with water or with commercial water soluble detergents will neutralize any further corrosive effects.

          Methods of application: Soldering can be done with a soldering iron, a torch, electric induction or resistance heating. There are no special techniques used to solder except the usual precautions of cleanliness and fit of mating surfaces. The advantage of soldering is a low-temperature process, good manual application, no fusion of parent metals, and, therefore, no warpage. It is applicable to most copper-based alloys (with less than 3% lead) with minimum finishing requirements being necessary.

          Brazing is a method of joining two metals through the use of heat and a filler metal below the melting point of the metals being joined. Brazing creates a metallurgical bond between the filler metal and the surfaces of the two metals being joined.

          Again, here in order to obtain a sound joint, the surfaces in the join and around it must be free from oil, dirt and oxides. Cleaning can be achieved by chemical means such as using trisodium phosphate, carbon tetrachloride and trichlorethlene for chemical method and the use of filing, grinding, machining or sand-blasting for mechanical means of cleaning.

          Fluxes are used mainly to prevent formation of oxides and to remove oxides from the base and filter metals and to promote free flow of the filler metal.

          We're in the home stretch.  Only ONE more chapter to go!  Be sure to check out the Blog on Thursday the 22nd for a special Christmas edition of Metalchic.

That is all for today...Until next time, my metal loving friends!

Next Up: Chapter 23: CBBI Manual Bearing Procedure and Notes


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