Rotors and manufacturing methods for rotors

Abstract

A rotor for driving, or being driven by, a fluid has rotor blades that follow a screw thread shape, all portions of all blades having the same screw pitch. This enables the rotor, or a molding pattern for use in making a mold, to be withdrawn from a mold part by a screw motion without damage to the mold part. This helps to make it economically viable to manufacture the rotor by a molding or casting process in which the mold parts are not destroyed to release the rotor, such as injection molding, for example with reinforced plastics. Additionally, in the case of manufacturing methods in which the mold is destroyed to release the rotor, the process of making or assembling the mold may be improved. In some molding processes, the ability to remove the rotor or the pattern by screw motion improves the economic viability of the process by reducing the number of mold parts required.

1 . A rotor, for driving a fluid by rotation of the rotor about an axis of rotation or for being driven by a fluid so as to rotate about an axis of rotation, or a pattern for making a mold part for making the rotor, wherein the rotor or pattern comprises (i) a hub having a blade-bearing surface and (ii) a plurality of rotor blades extending from the blade-bearing surface of the hub,
 the blade bearing surface of the hub having a first surface portion at a first radial distance from said axis of rotation and a second surface portion at a second radial distance, greater than said first distance, from said axis of rotation, the second surface portion being spaced from the axis of rotation in the same angular direction from said axis of rotation as the first surface portion and being spaced from the first surface portion in a direction parallel to the axis of rotation, both the first and second surface portions bearing at least a part of a rotor blade,   at least some of the rotor blades having a respective portion that is spaced from a respective portion of another rotor blade in a direction parallel to the axis of rotation but is at the same radial distance from the axis of rotation and is spaced from the axis of rotation in the same angular direction,   wherein the value of dθ/dx is constant and the same for the whole of all blades of the rotor or pattern (where x represents distance in a direction parallel to the axis of rotation, and θ represents angular direction perpendicular to the axis of rotation taking the axis of rotation as the origin) except for differences in the slopes of the blade surfaces arising solely from variation in the thickness of the rotor blades.   
     
     
         2 . The rotor or pattern according to  claim 1 , wherein the blade-bearing surface of the hub has a third surface portion at a third radial distance from the axis of rotation, the third surface portion being spaced from the axis of rotation in the same angular direction from said axis of rotation as the first and second surface portions and being midway between the first and second surface portion in a direction parallel to the axis of rotation, and wherein the third radial distance is less than the average of the first and second radial distances. 
     
     
         3 . The rotor or pattern according to  claim 2 , wherein the blade-bearing surface of the hub is substantially parallel to the axis of rotation at the first surface portion and the blade-bearing surface of the hub is substantially perpendicular to the axis of rotation at the second surface portion. 
     
     
         4 . The rotor or pattern according to  claim 1 , wherein said respective portions of at least one pair of rotor blades extend circumferentially with respect to the axis of rotation over an angle of at least 5° subtended at the axis of rotation. 
     
     
         5 . The rotor or pattern according to  claim 1 , wherein said respective portions of at least one pair of rotor blades extend circumferentially with respect to the axis of rotation over an angle of at least 10° subtended at the axis of rotation. 
     
     
         6 . The rotor pattern according to  claim 1 , wherein said respective portions of at least one pair of rotor blades extend circumferentially with respect to the axis of rotation over an angle of at least 15° subtended at the axis of rotation. 
     
     
         7 . A rotor, or a pattern for making a mold part for making a rotor, having a hub and a plurality of rotor blades extending from the hub, wherein,
 for each rotor blade, all portions of the rotor blade at the same radial distance from the axis of rotation of the rotor form part of the same screw thread spiral, and the screw pitch of the screw thread spiral is the same at all radial distances of the blade and is the same for all of the rotor blades,   at least some of the rotor blades overlap axially at least partially in the sense that a part of one rotor blade at the same polar co-ordinates from the axis of rotation as a part of another rotor blade but is spaced axially therefrom, and   at least a part of the hub has a diameter which varies with distance along the axis of rotation.   
     
     
         8 . Apparatus for driving a gas, the apparatus comprising an impeller that is a rotor according to  claim 1 . 
     
     
         9 . A turbocharger or supercharger for an internal combustion engine, comprising a rotor according to  claim 1 . 
     
     
         10 . Apparatus for driving a gas, the apparatus comprising an impeller that is a rotor according to  claim 7 . 
     
     
         11 . A turbocharger or supercharger for an internal combustion engine, comprising a rotor according to  claim 7 . 
     
     
         12 . A mold part for use in making a rotor, the mold part having a recess for receiving molding material in use, said recess having recess portions that define both faces of each blade of the rotor, all parts of each said recess portion having a common value of dθ/dx, where x represents distance in a direction parallel to the axis of rotation, and θ represents angular direction perpendicular to the axis of rotation taking the axis of rotation as the origin, except for differences in the slopes of the surfaces of the recess portions arising solely from variation in the width of the recess portions in the direction of the thickness of the rotor blades, and at least some of said recess portions overlapping another said recess portion in the axial direction of the rotor 
     
     
         13 . The mold part according to  claim 12 , wherein part of the surface of said recess defines a blade-bearing surface of a hub of the rotor, and said part of the surface of said recess has respective portions axially spaced from each other, with reference to the axis of rotation of the rotor, which portions are at different radial distances from said axis of rotation. 
     
     
         14 . The mold part according to  claim 13 , wherein said part of the recess surface defining a blade-bearing surface is convex so that said part of the recess surface is less parallel to the axis of rotation of the rotor where it is further from said axis of rotation 
     
     
         15 . A method of making a rotor comprising filling the recess of a mold part according to  claim 12  with a flowable material, causing or allowing the flowable material to solidify, and removing the solidified material from the mold part by moving it relative to the mold part with a screw motion. 
     
     
         16 . The method according to  claim 15 , wherein the step of filling a mold part with a flowable material comprises injecting the flowable material under pressure. 
     
     
         17 . The method according to  claim 15 , wherein said flowable material is a settable plastics resin. 
     
     
         18 . The method according to  claim 17 , wherein the plastics resin contains re-inforcing material. 
     
     
         19 . A method of making a mold part according to  claim 12  comprising immersing or embedding a rotor pattern in a mold-forming material, allowing or causing the mold-forming material to solidify, and withdrawing the pattern from the solidified material by movement with a relative screw motion to leave the recess in the solidified material. 
     
     
         20 . The method according to  claim 19 , wherein the mold-forming material is or mostly comprises sand. 
     
     
         21 . A method of making a rotor comprising making a mold part by a method according to  claim 19 , filling the recess left by the pattern with a molding material, allowing or causing the molding material to solidify, and releasing the solidified molding material by destroying the mold part. 
     
     
         22 . The method according to  claim 21 , wherein the molding material is molten metal, and the step of allowing or causing the molding material to solidify comprises allowing or causing the molten metal to cool. 
     
     
         23 . An inter-blade mold part for a mold for use in making a rotor by molding or casting, the inter-blade mold part having a first surface that defines a surface on one side of a blade of a rotor and a second surface that defines a surface on the other side of another blade of the rotor,
 wherein for both of the first and second surfaces of the inter-blade part, all parts of the surface that define a blade surface of a rotor slope at a common screw pitch, with reference to an axis of rotation of the rotor, except for differences in the slopes of the first and second surfaces arising solely from variation in the thickness of said blades.   
     
     
         24 . The inter-blade mold part according to  claim 23  which is or mostly comprises sand. 
     
     
         25 . A sand mold forming pattern for defining an inter-blade sand mold part according to  claim 24 .