Breviary Technical Ceramics


      Joining and Bonding Techniques

 Hard Soldering

According to DIN 8505 hard solders melt at temperatures above 450 °C; typical hard solders melt at between 600 and 800 °C, and are processed typically at temperatures of between 600 and 900 °C. Typical representatives of this class include hard silver solders based on silver, copper and zinc. Flux-free vacuum soldering and soldering under a protective atmosphere in soldering ovens is used for high temperature soldering at temperatures > 900 °C.
The metallisation requires metals with high melting points (refractory metallisation) such as molybdenum or tungsten. Metallised ceramic suitable for hard soldering can be supplied in this form by ceramic manufacturers.
The most frequent applications are found in machine construction.

The soldering temperatures involved are not usually critical for the ceramic material. It must, however, be borne in mind that the materials that are to be soldered have different coefficients of thermal expansion. Mechanical stresses will develop in the solder and in the materials that have been soldered together as the item cools. The stresses must be held down to acceptable levels through matching temperature coefficients and through appropriate construction.


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