Rozwój badań nad materiałami na styki elektryczne

Rozwój materiałów stykowych został omówiony w następujących grupach tematycznych: 1 — nowe dodatki do podstawowych ich składników — srebra i miedzi, a mianowicie a— Cr2N do Ag; b — In do Ag-SnO2 ; c — Fe do Ag; d — Cr do Cu, 2 — chemiczne powlekanie srebrem cząstek SnO2, 3 — wysokoenergetyczne mielenie srebra i dodatków, będących nośnikami niemetalicznych składników materiałów stykowych (układy Ag-SnO2, Ag2O-Ag3Sn, Ag-C), 4 — wytwarzanie nakładek stykowych zespolonych z warstwą lutowia.

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Not long ago the composite Ag-CdO was the most widely used material for electrical contacts. But it turned out that at people employed at manufacturing and exploitation of the contacts are exposed to inhalation of harmful, toxic cadmium. This is the reason of introducing in Europe other nonmetallic additivies replacing CdO. In accordance with Japanese experience the greatest interest is paid to SnO2 as the substitute. Unfortunately the Ag-SnO2 material requires further investigation with regard to improvement of the plastic and switching properties (endurance behaviour). One way of attaining these aims is using In2O3 as an additional admixture, the second one relies upon chemical coating of tiny SnO2 particles with silver, the third — is mechanical alloying of silver with SnO2 by high-energy ball milling in attritors and disc mills at high rotary speeds. Such kind milling of Ag-C materials gives entirely different results in comparison to Ag-oxide composites leading to lower welding forces but greater erosion rates, due to very fine grained graphite particles (approximately 1 µ). Replacement of nickel by iron in Ag-Ni and tungsten by chromium in the copper-based material is another trend in the electrical contact materials. In the last case together with the economic bonus (cheaper admixture) the killing of the electric arc in vacuum breakers, due to Cr easy volatility, is of significance. As the next topic development of contact tips with permanently connected brazing layers has been discussed.