Abstract
A pair of screw compressor rotors consists of a male and female rotor which have a unique profile each. The rotors mesh with each other and the male rotor drives the female by its leading lobe surface contact like the gears in an oil-injected screw compressor. The pair of rotors has transmission error caused by tolerances and misalignment. The transmission error can increase undesirable noise and vibration. An easy and fast method to calculate and predict the transmission error is proposed to reduce this noise. This method is based on a calculation of clearance distribution along the sealing line between the rotors. The transmission error can be calculated by comparing the male and female rotor rotation angle, when the rotors' leading surfaces contact each other as in virtual meshing. This method was experimentally shown to have enough accuracy for practical use. An oil-free screw compressor needs high accuracy in the setting of its timing gears. Virtual meshing can be applied to the phase adjustment of their settings. This method can predict their margins of backlash on both the leading and trailing sides, including hot condition during the machine operation.
