Abstract: A method is provided for making a surface-hardened sinter-iron part by impregnating the sinter-iron part with an alkali silicate solution, hardening the iron part by heat treatment to harden the surface of the part, the sinter iron part having closed pores on the upper surface.

Abstract: An impregnated carbon brush for electrical machinery with improved running properties and increased wear-resistance, in which the carbon brush has an impregnating medium containing non-melting grease, and/or a non-melting wax, and/or a non-flowing oil. The impregnating medium in the carbon brush is on a synthetic, mineral, animal or vegetable base which is thoroughly mixed with a gelatinizing agent on an inorganic and/or organic base and thereby transformed to a non-melting or non-flowing harder and more wear-resistant condition. The gelatinizing agent contained in the carbon brush as a component of the impregnating medium comprises montmorillonite flakes with surfaces coated with long-chain hydrocarbons. The carbon brush includes additives for improving the sliding properties in the form of inorganic and/or organic additives such as metal sulfides, metal oxides and PTFE powder. The carbon brush contains 0.1 to 25% by weight of impregnation medium relative to the weight of the impregnated carbon brush.