General methodological principles for improving the reliability of threaded connections of agricultural machines and implements

Abstract

From 50 to 70% of failures of working organs and support frames of agricultural machines and implements are accounted for the connections with threaded fasteners. The paper deals with the basic general methodological principles for ensuring the reliability of threaded connections of agricultural machines and implements. The structural scheme of general problem of improving the reliability of threaded connections is proposed. The main ways of improving their reliability are: the development of new designs of threaded connections that meet the above-noticed basic principles; the improvement of the method of calculation of group threaded connections that operate under partial joint opening and contact vibration displacement; the improvement of the method of calculation of group threaded connections that operate under complex loading taking into account the radial and angular contact compliances; the use of numerical methods for calculating of group threaded connections; the improvement of methods of screw retention; the improvement of methods of corrosion protection. The classification of the main factors of fatigue wear failure of threaded connections that operate under complex loading is proposed. The elaboration of fatigue safety factor of connections of agricultural machines is given, depending on the operating conditions, with the use of additional factor which depends on the rate of wear and corrosion. For the expression to determine the degree of fatigue strength on the shear stresses, the uniformity factor of distribution of lateral load between the fasteners is introduced; it depends on the type of connections, constructive gap in the connection and quantity of fasteners. The specified method of calculating the fatigue strength and the proposed basic principles of improving the reliability may be used in the practice of design and repair of agricultural machines.