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Changes
→Silver–Graphite Materials
Ag/C contact materials are usually produced by powder metallurgy with graphite contents of 2 – 6 wt% (<xr id="tab:tab2.32"/>)<!--(Table 2.32)-->. The earlier typical 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. 82 64 – 8571)]]<!--(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. 86 – 89)]]<!--(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 or parallel to the switching contact surface (<xr id="fig:Micro structure of Ag C 95 5"/><!--(Fig. 2.131)--> and <xr id="fig:Micro structure of Ag C 96 4 D"/>)<!--(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 burning out (de-graphitizing) the graphite selectively on one side of the tips.
