Rotary screw-type machine

摘要

A compressor or a vacuum pump has male and female rotors 1', 2' which rotate within a casing 3', with or without mutual contact. The male and female rotors include a non-electrolytic Ni plating layer 4' and at least one of the rotors may have at least one covering layer of organic resin. Examples of resins are given in the specification. Solid lubricants may be dispersed in the Ni layer. The plated rotors may be heat treated to produce cracks in the Ni layer and the plastics layer may be formed by injection into a mould (11, Fig. 9). The Ni layer may include P or B.