Novelty: Tunnel brazing

Brazing as in the shielding-gas furnace, but with local heating

W&P Wolf & Partner GmbH has developed a new brazing technology: Tunnel brazing.

The result of the development of tunnel brazing with local heating is a gas-shielded brazing process that combines the advantages of local heating with the advantages of the tunnel furnace. For this purpose, the components are heated inductively or by resistance heating and cycled through a shielding gas tunnel.

The condition for this is that the length of the shielding gas tunnel is chosen in such a way that the component has enough time to cool down under shielding gas in order not to anneal anymore at the air after leaving the tunnel. The joints produced under such conditions are bright, rigid and tight. They comply with the usual quality criteria required from a good brazing seam.

Tunnel brazing is successfully applied in the subcontractor industry of the automotive industry and for heating and sanitary equipment. The advantages as compared with furnace brazing are better automatability of the production process and lower operating costs

Bright surfaces provide the condition for Filler metal flow

The necessary changes as compared with conventional methods can be derived from the physical processes of the brazing process. The bright surfaces being formed during gas-shielded brazing result from the heating process, and they are the condition for Filler metal flowing. If the component cools down under shielding gas for a sufficiently long time (to approx. 200 °C), no visible annealing colours are produced on the component surface and the component remains bright.

In order that the brazed components can cool down without additional expenditure of time, they have to be transported through an oxygen-free shielding-gas atmosphere, just as in the continuous shielding-gas furnace, until no annealing colours can be produced anymore. This means that the component has to be cooled down under shielding gas to approx. 200 °C. This is achieved the easiest by moving the component on a workpiece holder through a fixed shielding-gas tunnel. It can take place in a circuit by using a round cycle table or horizontally by using lifting bars. The brazing components can be charged to the tunnel manually or automatically. Heating is realized locally by means of resistance or induction heating.