A novel tilt form grinding method for the rotor of dry vacuum pump

• Form grinding method with tilt spindle is proposed for the grinding of rotor.
• The minimum tilt angle is derived in terms of swivel angle to avoid undercutting.
• The D.O.F. of the tilt angle is perpendicular to the machine base.
• The mechanism of tilt angle can use an incremental indexing mechanism.

The twin-screw dry vacuum pump is widely used in low and medium-low vacuum applications. Its core element consists of a pair of rotors rotating in opposite direction on parallel axes. Usually one side of the rotor profile is a concave cycloid curve to prevent the inter-lobe leakage. Screw rotors are typically finished by the form grinding method. However, such concave rotor profile is almost impossible to grind on a conventional thread grinder due to severe undercutting and secondary enveloping problems. In this paper we propose a novel tilt form grinding (TFG) method to overcome the problem of concave profile grinding. The conventional thread grinder is modified by tilting the grinding wheel about an axis normal to the rotor and swivel axes. By using this proposed machine arrangement, the concave rotor profile can be ground without undercutting and secondary enveloping. Numerical examples are presented to validate the proposed TFG method.

The figure shows the proposed novel form grinding machine with TFG method. This machine is modified from the conventional thread grinder by introducing an additional rotation DOF (tilt angle ψ) between machine base and grinding head module. The TFG method can overcome the undercut problem of concave profile grinding. The rotation mechanism of tilt angle ψ can use a less-expensive incremental indexing mechanism such as a curvic coupling.Figure optionsDownload as PowerPoint slide