What do we mean by Brazing & Soldering?
Both brazing and soldering are the metal joining processes in which parent metal does not melt but only filler metal melts filling the joint with capillary action. If the filler metal is having a melting temperature of more than 450°C but lower than the melting temperature of components then it is termed as the process of brazing or hard soldering. However, if the melting temperature of filler metal is lower than 450°C and also lower than the melting point of the material of components then it is known as soldering or soft soldering.
During brazing or soldering flux is also used which performs the following functions:
Dissolve oxides from the surfaces to be joined.
Reduce surface tension of molten filler metal i.e. increasing its wetting action or spreadability.
To protect the surface from oxidation during joining operation.
The strength of the brazed joint is higher than the soldered joint but lower than a welded joint.
Brazing:
The most commonly used filler metal is copper base zinc alloy consisting of normally 50-60% Cu, approximately 40% Zn, 1% Ni, 0.7 % Fe and traces of Si and Mn. This is brass and termed as ‘spelter’. In some cases around 10% Ni may also be added to filler alloys. Copper base alloys may be available in the form of a rod, strip, and wire. Silver brazing alloys are available in form of wire, strip, rods, and powders. Borax and boric acid are commonly used fluxes for brazing with copper base filler metals.
Brazing Methods:
Various commonly used methods of brazing are Torch Brazing, Furnace Brazing, Infra-red Brazing, Resistance Brazing etc.
Soldering:
The soldering filler metal is called solder. The most commonly used solder is lead and tin alloy containing tin ranging from 5 to 70% and lead 95 to 30%. Higher the contents of the tin, lower the melting point of the alloy. Other filler metal are tin-antimony solder (95% tin and 5% antimony), tin-silver solder (tin 96% and silver 4%), lead-silver solder (97% lead, 1.5 tin and 1.5 silver), tin-zinc solder (91 to 30% tin and 9 to 70% zinc), cadmium-silver solder (95% cadmium and 5% silver). These are available in the form of bars, solid and flux-cored wires, sheet, foil, ribbon, and paste or cream.
Fluxes used in soldering are ammonium chloride, zinc chloride, rosin, and rosin dissolved in alcohol.
Soldering Methods:
Various soldering methods are soldering with soldering irons, dip soldering, torch soldering, infra-red and ultrasonic soldering.
