Rotor for pump

Abstract

The present invention relates to a rotor for a vacuum pump having a roots pumping mechanism, the rotor comprising at least two hollow lobes, each lobe having an outer wall which defines a lobe profile, a hollow cavity generally inward of the outer wall, and at least one strengthening rib located in the cavity to resist stress on the lobes generated during rotation.

1 . A vacuum pump rotor for use in a vacuum pump having a roots pumping mechanism, the rotor comprising at least two hollow lobes, each respective hollow lobe comprising:
 a respective outer wall which defines a lobe profile,   a respective hollow cavity generally inward of the respective outer wall, and   at least one respective strengthening rib located in the respective hollow cavity to resist stress on the respective hollow lobe generated during rotation.   
     
     
         2 . The rotor of  claim 1 , wherein the at least one respective strengthening rib extends around an interior wall of the respective hollow lobe. 
     
     
         3 . The rotor of  claim 1 , wherein the at least one respective strengthening rib has a varying extent and is distributed within the respective hollow cavity dependent on the varying stresses applied to the respective hollow lobe in use. 
     
     
         4 . The rotor of  claim 1 , wherein the respective outer wall has a varying thickness and is thicker at a radially inner portion than at a lobe tip. 
     
     
         5 . The rotor of  claim 1 , wherein the respective outer wall defines a thickness such that the respective hollow lobe deforms under centrifugal loading when the rotor is rotated in use and the deformation is greater than manufacturing tolerances. 
     
     
         6 . The rotor of  claim 5 , wherein the respective hollow lobe defines a first configuration in a first condition in which the rotor is rotated in use and a second condition when the rotor is not rotated and the respective hollow lobe is not in the first configuration, and wherein the respective hollow lobe deforms from the second condition to the first condition when tip speed of the respective hollow lobe is greater than 100 m/s. 
     
     
         7 . The rotor of  claim 1 , wherein a ratio of the thickness of the respective outer wall to a radius at the a lobe tip of the respective hollow lobe is less than 1:20. 
     
     
         8 . The rotor of  claim 1 , wherein the thickness of the respective outer wall is less than 5 mm and the radius of the a lobe tip of the respective lobe is at least 100 mm. 
     
     
         9 . The rotor of  claim 1 , wherein each respective hollow lobe comprises a respective plurality of hollow lobe sections joined in axial succession along the rotor which together form the respective hollow lobe. 
     
     
         10 . The rotor of  claim 9 , wherein each respective hollow lobe section of the respective plurality of hollow lobe sections has a respective flange extending circumferentially and radially inwardly around at least one axial end of the respective hollow lobe section for joining together adjacent hollow lobe sections. 
     
     
         11 . The rotor of  claim 10 , wherein one or more holes are provided in each of the respective flange for allowing the respective plurality of hollow lobe sections to be fastened together by fixing members. 
     
     
         12 . The rotor of  claim 1 , wherein each respective hollow lobe further comprises two end faces for closing the respective hollow cavity at each axial end of the respective hollow lobe. 
     
     
         13 . The rotor of  claim 1 , wherein the rotor further comprises a shaft and each respective hollow lobe comprises respective means for fixing the respective hollow lobe to the shaft, the at least two hollow lobes and the shaft being shaped to provide a generally continuous profile of the at least two hollow lobes and the shaft. 
     
     
         14 . The rotor of  claim 13 , wherein the at least two hollow lobes and the shaft of the rotor are adapted to fit together by means of a dovetail or similar joint, such that the radial movement of each respective hollow lobe with respect to the shaft of the rotor is reduced. 
     
     
         15 . The rotor of  claim 1 , wherein each respective hollow lobe further comprises means for allowing the pressure within the respective hollow cavity to substantially equalize with the pressure outside of the respective hollow lobe. 
     
     
         16 . The rotor of  claim 15 , wherein the means for venting comprise a filter for filtering deposits from gas conveyed through the means for venting into the respective hollow cavity. 
     
     
         17 . A vacuum pump comprising a rotor comprising at least two hollow lobes, each respective hollow lobe comprising:
 a respective outer wall which defines a lobe profile,   a respective hollow cavity generally inward of the respective outer wall, and   at least one respective strengthening rib located in the respective hollow cavity to resist stress on the respective hollow lobe generated during rotation.   
     
     
         18 . The vacuum pump of  claim 17 , further comprising a plurality of pumping stages, wherein each of the plurality of pumping stages comprises a respective pumping chamber and at least two of the hollow lobes. 
     
     
         19 . The vacuum pump of  claim 17 , wherein at least one of the plurality of pumping stages comprises a hollow lobe having a plurality of lobe sections joined together in axial succession. 
     
     
         20 . The vacuum pump of  claim 17 , wherein the at least one respective strengthening rib of the respective hollow lobe extends in a respective radial plane relative to an axis of a rotor shaft to which the respective hollow lobe is attached, and the radial plane of the respective hollow lobe of a first rotor is misaligned with a respective radial plane of a second rotor. 
     
     
         21 . The pump of  claim 20 , wherein portions of the respective hollow lobe between the respective radial planes are arranged to deform when impacted by portions of hollow lobes in line with the respective radial planes to absorb energy of the first and second rotors in the event of a rotor clash. 
     
     
         22 . A method of making a rotor for a vacuum pump, the method comprising:
 providing the rotor with at least two hollow lobes, each respective hollow lobe having a respective outer wall which defines a lobe profile and a respective hollow cavity generally inward of the respective outer wall; and   locating within the respective hollow cavity at least one respective strengthening rib to resist stress on the respective hollow lobe generated during rotation of the rotor.