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→Silver–Graphite (GRAPHOR)-Materials
manufacturing process of single pressed tips by pressing - sintering - repressing (PSR) has been replaced in Europe for quite some time by extrusion. In North America and some other regions however the PSR process is still used to some extend mainly for cost reasons.
The extrusion of sintered billets is now the dominant manufacturing method for semi-finished AgC materials [[#figures3|(Figs. 43 82 – 7585)]](Figs. 2.126 – 2.129). The hot extrusion process results in a high density material with graphite particles stretched and oriented in the extrusion direction [[#figures4|(Figs. 82 – 85)]](Figs. 2.130 – 2.133)''. Depending on the extrusion method in either rod or strip form the graphite particles can be oriented in the finished contact tips perpendicular (GRAPHOR) or parallel (GRAPHOR D) to the switching contact surface <xr id="fig:fig2.131"/> (Fig. 2.131) and <xr id="fig:fig2.132"/> (Fig. 2.132).
Since the graphite particles in the Ag matrix of Ag/C materials prevent contact tips from directly being welded or brazed, a graphite free bottom layer is required. This is achieved by either burning out (de-graphitizing) the graphite selectively on one side of the tips or by compound extrusion of a Ag/C billet covered with a fine silver shell.
