COMPRESSION LOAD TRANSMISSION IN SCREW COMPRESSORS

Abstract

In the current investigations of the bearing forces in screw compressors, the supports at the bearings are basically treated as ideal, simply supported boundary conditions. By using statics theory, the loads on the rotors are converted to the bearings at the suction and discharge ends. Some studies on rotor dynamics have shown that the behaviors of a rotor bearing system are, to some extent, controlled by the bearings that support the rotor. Therefore, it is important to study the dynamic performance of the rotor bearing system in screw compressors so that the bearing forces can be more accurately described. In this paper, a numerical method is presented for computing the compression loads by integrating the pressure over the rotor surface. Vector calculus and numerical integration methods are implemented to calculate the compression loads in order to obtain a robust procedure that can be applied to arbitrary rotor profiles. In addition, a dynamic model of a rigid compressor rotor supported by two cylindrical roller bearings and a four point contact ball bearing is developed from basic principles. This model simulates the dynamic responses of a typical screw compressor configuration. It includes five degrees of freedom of rotor motion interacting with the bearings of non-linear characteristics. Under the compression loads, the resulting bearing forces in the screw compressor are compared with those obtained by assuming ideal, simply supported boundary conditions at the bearings. It is shown that the interactions between the rotor and bearings are quite different by coupling the global rotor motion with the local dynamics of the bearings.