Increasing wear resistance of the protective bush-ing of the centrifugal pump made of gray cast iron by chemical-thermal treatment

Abstract

Problem. The weak link that reduces the warranty time of centrifugal pumps is a unit that includes protective bushings and seals. The purpose of the bushings is to protect the rotor shaft from erosion, corrosion and wear. The bushing works under conditions of abrasive wear by elements of the seal packing and abrasive particles entering the liquid pumped by the pump. Due to accelerated surface wear, cast iron protective bushings do not satisfy the requirements service life. Goal. The purpose of the work is to increase wear resistance of pump parts made of gray cast iron by chemical and thermal treatment. Method. Metallographic studies of the structure were performed under a UIT MicroMet-D-101 microscope. Wear is studied using the roller-pad method on a friction machine. Sulfocyanation of cast iron samples was carried out in molten salts (K2CO3, CO(NH2)2, Na2S at 560°С at the bottom of the bath. Results. In the cast state, the microstructure of gray cast iron consists of ferrite, pearlite, double phosphide eutectic and lamellar graphite inclusions. The influence of exposure time during sulfocyanation in a bath with molten salts on the structure and properties of the formed surface layer was studied. The exposure was carried out for 2 hours, 3 hours 30 minutes and 6 hours. After exposure in the bath, a thin carbonitride layer is formed on the surface of the cast iron, and a layer consisting of iron sulfide is formed on top. Conducting wear tests showed that sulfocyanation increases the wear resistance of gray cast iron. An increase in the wear resistance of cast iron is provided by a hard carbonitride layer, and good workability – by a layer of iron sulfides, which acts as a lubricant. Scientific novelty. Increasing the exposure time during sulfocyanation in the bath for more than 3 hours 30 minutes does not affect the thickness of the carbonitride layer. Practical significance. As an optimal mode of sulfocyanation, exposure for 3 hours 30 minutes can be recommended, which provides a 4.8-fold increase in wear resistance.