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Induction Brazing -
Induction brazing is used where
(i) Very rapid heating is desired.
(ii) Production rate is high.
(iii) Parts are self jigging.
The components to be brazed are fluxed, filler metal is preplaced (in the form of a ring, washer etc.) in proper position and this assembly is placed within (or near) an induction coil. When high frequency electric current is passed through the induction coil, the energy is transmitted to the assembly/workpiece by induction, rather than by electric connection.
Heating of the workpiece surface takes place as a result of eddy currents or PR losses in the work metal which, by virtue of its electrical resistively and the flow of induced alternating current through it, generates heat. In addition, on ferromagnetic materials, a further increase in heating results from hysteresis. |
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The interior of the workpiece is heated by thermal conduction from the hot surface.
The depth into the workpiece to which it is heated depends upon the frequency of the alternating current employed. As a rule, the higher the frequency, the shallower the heating.
High frequency current is obtained with the help of
(i) The motor generator set (3,600 to 10,000 Hz).
(ii) The tube-operated oscillator (450 kHz and higher).
For steel and ferrous alloys, the generator type is quite adequate.
A flux or a special gaseous atmosphere is necessary to prevent oxidation during brazing. |
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Advantages
(i) Induction brazing associates high-speed localized heating that minimizes oxidation and thus reduces cleaning requirements.
(ii) Because the heating is localized, warpage is often less than when the entire assembly is heated. The nature and extent of metallurgical changes, such as the softening of cold worked or heat treated metal, are also minimized.
(iii) Since power output and time at heat can both be precisely controlled in induction heating, the process can be carried out by less skilled operators.
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Limitations
Brazing large assemblies entails major problems in the construction of induction coil, coupling and circuit balancing etc.
Applications
With the exception of Al and Mg, most of the common metals and alloys brazed by other methods can be satisfactorily joined by induction brazing.
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