Patent GB-1358505-A (GB)
Title: Rotors for helical screw rotor machines
IPC: F01C1/08
Filed: 1972-09-21
Abstract: 1358505 Rotary positive-displacement machines GARDNER-DENVER CO 21 Sept 1972 [24 May 1972] 43811/72 Heading F1F Main and gate rotors 28, 30 of a helical screw rotor machine have profiles formed such that, in a plane transverse to the rotation axes 46, 48, each gate rotor groove 38 has a concave curved portion forming at least a part of a first groove flank 47 and defined by a circular arc having its centre of curvature 50 outside the gate rotor pitch circle 44, the arc extending from the line joining axes 46, 48 to a point 54, a convex curved portion on the limit flank 47 extending outwardly from point 54 to the pitch circle 44, a concave curved portion forming part of a second groove flank 58 and being travelling generated by a portion of the main rotor lobe tip, this tip portion being defined by a circular arc with centre of curvature 70 located on a line which passes through the point of intersection 72 of the two pitch circles 44, 74 and makes an angle As with the line joining axes 46, 48, and the concave portion of the second flank 58 extending from a point 62 where the line with centre 70 intersects the groove surface to a point 66, and a convex curved portion on the second flank 58 which extends from point 66 to the gate rotor pitch circle 44, and each main rotor lobe 28 has flanks 78, 80 which are formed by travelling generation by the concave curved portion of the first flank and the convex curved portions on the gate rotor groove flanks 47, 58. The convex portion on the first flank 47 is tangential to the concave portion at the point 54 and is a circular arc of radius R 2  having its centre of curvature at a point 56 located on a line through points 50, 54 outside pitch circle 44. the other extemity of theconcave portion on first flank 47 is tangential to a portion extending from the line joining axes 46, 48 to a point 60 and formed by a circular arc centred on the gate rotor axis 46. This last mentioned portion merges tangentially with a concave portion extending between points 60 and 62 and is generated by a point 64 on the main rotor lobe tip, from which point 64 to a point 68 extends the rotor lobe tip portion centred on point 70. The convex portion on the second flank 58 is tangential to the concave portion at 66 and is formed by a circular arc of radius R 4  centred at a point 76 located outside pitch circle 44 on a line through point 74 and making an angle A 4  with the line joining axes 46, 48. The flank 78 of the main rotor lobe from point 68 to its pitch circle 74 is travelling generated by the outer convex portion of second gate rotor flank 58. The other main rotor lobe flank 80 has a portion from pitch circle 74 to a point 82 travelling generated by the outer convex portion of the first rotor flank 47, a further portion generated by the main concave portion of flank 47 extending from point 82 to a point 118, Fig. 4. A straight line joins points 116, 118 and points 116 and 64 are joined by a convex portion centred on main rotor axis 48. The various portions merge tangentially at points 118, 116 and 64. As shown by the dashed line in Fig. 4 the main rotor lobe is cut away slightly from the theoretical shape to permit some clearance between the co-operating rotors. The tips of the gate rotor lobes 36, Fig. 6, each are formed by a central portion forming part of the pitch circle 44 and extending between points 86 and 88 and by side parts 90, 92 of the same curvature as the central part but with their centres of curvature 98, 100 offset from axis 46. The edge portions 101 of the tip are equivalent to a circular arc portion formed on a milling cutter which is used to cut the gate rotor flanks and tip portions. The corresponding main rotor groove 34 is travelling generated by the gate rotor tip. The groove portion between points 106, 108 is on pitch circle 74, the portion from point 108 to point 110 is travelling generated by tip portion 90 and the curved corner portion between points 110, 112 is travelling generated by curved tip portion 101. A modified groove profile is also described Fig. 5, (not shown).