A Study of the Profiling of the Screws in Conical Screw Compressors Using the Virtual Contact Point Method

Conical screw compressors are equipment used to compress air or other gases, using a mechanism consisting of two conically shaped rotors (screws), which rotate one inside the other. This specific design offers advantages in terms of its efficiency, durability and compactness. These compressors are characterized by high efficiency, efficient compression, low air loss, durability, compact dimensions and silent operation. In conical screw compressors, the screw axes are arranged at an angle, due to the conical shape of the screws. This arrangement allows for the progressive compression of the gas as it advances along the screws. On the one hand, the arrangement of the axes and the conical shape of the screws contribute significantly to the high performance of this type of compressor, but on the other hand, this shape makes it difficult to profile these active elements. The screw profiles of conical screw compressors are mutually enveloping, and this aspect is essential for the correct operation of the compressor. In this paper, a new algorithm for profiling the compressor’s external rotor starting from a known internal rotor shape is proposed. The proposed algorithm was developed at “Dunarea de Jos” University of Galati and was based on the observation that the compression chambers in conical screw compressors are sealed according to a curve that follows the axial section of the two screws, in a plane determined by their axes. Practically, the two screws admit a common contour of the axial section in the plane determined by their axes. Taking this aspect into account, the transverse profile of the outer screw can be determined by identifying the positions where contact will take place with the points belonging to the transverse profile of the inner screw. In order to verify the viability of this method, the volume occupied by the inner screw during its relative movement with respect to the outer screw was determined. This volume was compared with the volume of the outer rotor cavity, with the result demonstrating the identity of the two volumes.