Repairing the piston-cylinder group in a gas motorized compressor

Abstract

A technology has been developed for repairing the worn cast-iron cylinder and piston in a motorized gas compressor: if the surface wear is more than 1.5 mm, sleeving is used, while with wear not more than 1.5 mm, gas-thermal coating is employed. Tests have been performed on a proposed material for plasma coating. There is a considerable increase in the working life of the repaired cylinders.Research has been done on the viability of the cylinder and piston group in an internal combustion engine (ICE), which has shown that the friction conditions in ICE cylinders are the most unfavorable when the friction surface temperature attains its maximum, i.e., about 350°C, when the thickness of the oil film becomes minimal and the oil is dispersed, where it burns up in a period of ignition and is blown out from the upper rings during compression. This leads in fact to elimination of the oil film * . One then has essentially dry friction between the cylinder, the piston rings, and the piston.More favorable lubrication conditions for the friction surfaces are required to increase the working life. To a certain extent, this can be attained by adjusting the porosity of the cylinder and piston walls, improving their wear resistance, and increasing the antifriction properties.This company has handled these tasks in the repair of worn cast-iron cylinders and pistons. The company has collaborated with organizations in the petroleum industry and has found that there is a considerable demand from the latter for repairing worn parts of compressors, in particular cylinder-piston groups. This can be handled not only by sleeving but also by using the latest technologies for reconstructing worn surfaces, including gas-thermal spraying methods.Developments in the technology for repairing worn cylinders have taken two lines: with surface wear more than 1.5 mm, by sleeving; and with surface wear not more than 1.5 mm, by gas-thermal coating.The sleeving uses cylinders cast from SCh-20 cast iron of hardness 160-180 HB. The working life of the sleeved cylinders was less than that of new ones, so it was proposed to alloy the sleeves during casting.We added 0.2-0.5% of nickel and chromium to the cast iron. This greatly improved the quality of the castings and increased the wear resistance. As a cylinder is a large component of height about 900 mm and internal diameter 355 mm, special equipment was needed to press the sleeves into place (Fig. 1).After sleeving, the cylinder was turned on a lathe and honed. The working life was much increased for cylinders installed by pressing alloy sleeves.The most complicated tasks were handled in devising the plasma coating technology. The mass of a cylinder exceeds 700 kg, and its shape is not convenient for mounting on the chuck of a lathe in the horizontal position, so a special equipment was developed for plasma coating (patent 2279904 RF). The working principle is that the cylinder is set up vertical on