Application of Manufacturing Simulation for Screw Compressor Rotors

This paper shows how simulation of screw rotor profile manufacturing can be used in the design phase to assess profile alternatives. To do this, variations in manufacturing parameters are studied to illustrate how these deviations affect different rotor profile shapes and the resulting rotor pair clearances. INTRODUCTION Clearances between rotors in a twin screw compressor play a key role in determining the compressor's performance and reliability. A balancing act is played between clearances small enough for good performance yet large enough for high reliability. To achieve the proper balance requires knowledge of all of the factors that affect rotor-to-rotor clearance and the ability to control these factors during design and production. The two significant issues facing the designer are the effects of operating load induced deformations of the rotors and manufactured rotor variability; this paper addresses the latter. A computer simulation allowing investigation into the effects of variability that might occur during the manufacturing process has been developed. Using this simulation, we first consider how selected variations in the profile manufacturing process affect the profiles of two different rotor designs. Then the effect of these profile variations on clearances of a rotor pair is examined. Rotors considered were designed for different models of screw compressors used in air-cooled refrigeration systems. The profiles are designated E and J. TheE profile is an older design used in larger capacity compressors; the J is a second generation design for smaller compressors. Both profiles are designed by specifying a generating rack /1/. TheE profile uses a simple rack with four circular arcs and two straight lines. The J rack is more complex, with 12 rack segments, including three generated curves. Rotors with both the E and J profiles have five male and seven female lobes and are designed with a 300° male wrap angle and 1.5 LID. Production profiles are applied to rotors with displacements of34 mminat 3600 rpm. Rotor pairs and their generating racks are compared in the transverse plane in Figure 1.