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→Resistance Brazing
==== Resistance Brazing====
In this process the resistive heating under electric currents is the source of thermal energy. For contact applications two methods are used for resistance brazing <xr id="fig:Resistance brazing (schematic)"/> <!--(Fig. 3.8)-->.
<figure id="fig:Resistance brazing (schematic)">
[[File:Resistance brazing (schematic).jpg|right|thumb|Resistance brazing (schematic)]]
In Indirect Resistance Brazing the current flows only through one of the components to be joined (usually the non-precious contact carrier). This
process allows to move the contact tip (“puddeling”"puddeling") when the brazing alloy is in its liquid stage and this way remove residue bubbles from the heated and boiling flux and increase the percentage of the bonded area. Two different kinds of electrodes are used for resistance brazing:
*Electrodes from poorly conducting carbon containing materials (graphite)<br />The heat is created in the electrodes and thermally conducted into the joint area<br />
*Electrodes from higher conductive and thermally stable metallic materials<br />The heat is created by the higher resistance in the joint area which, through selected designs, creates a constriction area for the electrical current in addition to the resistance of the components to be joined.<br />
Graphite electrodes are mainly used for indirect resistance brazing and for joint area > 100 mm<sup>2</sup>. For contacts tips with a bottom area < 100 mm<sup>2</sup> which are already coated with a phosphorous containing brazing alloy the heating time can be reduced to a degree that the softening of the contact carrier occurs only very closely to the joint area. For this “short"short-time brazing” brazing" specially designed metal electrodes with compositions selected for the specific assembly component pairings are used.
The bond quality for normal resistance brazing with the application of flux ranges from 70 to 90% of contact size, for short-time welding these values can be exceeded significantly.