Modern high-strength steels for heavily loaded gearing (a review of engineering patents)

Abstract

In order to increase the service life of machines the life of their pans should be increased. For example, in machine tool and lifting-and-transport manufacture the maintenance cost of the equipment over the duration of its operation often exceeds the cost of the new equipment by a factor of I0-20. This imposes strict requirements on structural materials for heavily loaded gearings, including the development of high-strength, wear-resistant, manufacture-adaptable, and economically alloyed steels.Heavily loaded gearings are critical parts in the composite structure of gears and transmissions in the automobile and tractor industries, metallurgical and mining equipment, the aircraft industry, and other production [!]. An analysis of failures in the operation of such gearings shows that the steel for these parts should possess a set of properties that provide their reliability and long service life [2,3]. In the process of operation a gearing is subjected to a complex action of forces that cafise elastic and plastic deformations, cold-hardening, embrittlement, low-and high-cyclic fatigue, dynamic aging, self-tempering due to thermal effects, changes in the chemical composition of the surface layer with subsequent oxidation, and other phenomena [4]. It has been shown in [5] that the endurance of the steel used for highly loaded gearings is characterized by a group of factors the most important of which are strength and ductility, which determine the fracture energy capacity. The fracture energy capacity is determined by the simplified criterion K = cy b ~I/, which characterizes the fracture strength of the steel.It should be noted that generalizing and systematizing data on steels for heavily loaded gearings are scarce and exchange of results of relevant investigations is limited. Introduction of new materials of elevated quality and reliability should increase the endurance of gearings, reduce the idle time of equipment due to emergency repairs, decrease the probability of malfunction, and guarantee safe operation of machines. In some cases the structural steels used at present for gearings with a tooth modulus > 8 mm do not provide the requisite level of properties and are poorly adaptable to manufacture [2].Modem materials for heavily loaded gearings should meet strict requirements on such properties as the surface hardness before and after strengthening, hardness of the core, static and dynamic strengths of the surface and the core, bending resistance of the teeth, fracture characteristics, elastic and plastic properties, impact strength of the surface layer and the core, and especially the temperature 7"50, fatigue resistance (at a sufficient isotropy of the properties), wear resistance, adaptability to manufacture, and structural and operational stability.The main cause of failure in gearing of machines that operate in an abrasive medium is abrasive wear. For example, under intense operation the teeth of wheels of crane and exca- . Gearings lose their operating capacity due to damage to the teeth, broken contact...