GB780640A - Improvements in or relating to piston rings - Google Patents

Abstract

A sintered metal piston ring made by a powder metallurgical process includes 0.25 to 20 per cent by weight of hard particles of aluminium oxide. The balance of the powder mixture preferably is iron or steel in the form of 50 to 300 mesh powder, with or without 0.3 to 4 per cent finely divided graphite and 0.3 to 2 per cent of a die lubricant comprising powdered zinc stearate or stearic acid. The aluminium oxide may be in the form of fuzed alumina, "Turkish emery", corundum or tabular corundum, and may be in the form of 100 to 600 mesh powder. The mixture may be briquetted at a pressure of 20,000 to 120,000 pounds per square inch and then sintered in an inert atmosphere for 4 to 90 minutes at a temperature of 1900 to 2300 DEG F. according to the nature of the metal. A two-stage sintering also is described. The inert atmosphere may comprise a mixture of 20 per cent CO, 3 per cent H, and 77 per cent N, or a mixture of 1.5 per cent CO, 1-5 per cent H, and 97 per cent N. After sintering, the metal may be hot or cold worked to improve its tensile strength and reduce its porosity to between 2 and 13 per cent. This may be followed by a tempering treatment for 30 to 60 minutes at a temperature between 800 and 1100 DEG F., and a surface-treatment e.g. with iron-manganese phosphate. Instead of briquetting under high pressure before sintering, the powder may be loosely filled into a mould and may contain a relatively small amount of one ingredient having a lower melting point than the main ingredient.