Rotor for a screw rotor machine

Claim 1

A rotor for a screw rotor machine, the rotor having a number of helically extending lands (10) and intermediate grooves forming a working face of the rotor, the rotor comprising: a shaft member (13); a rotor body (1) made of plastics material molded on the shaft member (13) so as to adhere to the surface of the shaft member (13), said rotor body made of plastics material defining said lands such that said lands are substantially made of plastics material; and a plurality of radially directed projections (4) extending from the shaft member (13) with substantially equal distribution around the shaft member (13); said projections (4) being integrally formed as one piece with the shaft member (13) and extending helically around the surface of the shaft member (13) with the same pitch as the lands (10), said projections (4) each being associated with and in registration with a respective corresponding land (10), and said projections also extending into a central part of the corresponding land (10); and said projections (4) further having substantially peripherally directed wings (5) with smoothly rounded edges, said wings (5) being integrally formed as one piece with said projections (4), said wings (5) being located substantially in the central part of the corresponding land (10) and being dimensioned to relieve during rotation of the rotor a large part of tensile stresses acting on the plastics material of said rotor body (1) adhering to the surface of the shaft member (13).