Grinding of particulate material

Abstract

Apparatus ( 1 ) for grinding a suspension of a particulate solid material. The apparatus ( 1 ) comprises a grinding chamber ( 2 ), means ( 7, 8 ) for introducing a suspension of the particulate solid material into the grinding chamber ( 2 ) and an impeller ( 6 ) which is rotated and thereby agitates the particulate grinding medium and the suspension of particulate solid material in the grinding chamber ( 2 ). The impeller ( 6 ) has at least one blade ( 12 ), the said blade ( 12 ) having a leading face ( 14 ) in the direction of rotation (R) of the impeller ( 6 ), which leading face ( 14 ) is offset relative to a plane of rotation of the impeller ( 6 ). In a preferred embodiment, an upper edge of the said leading face ( 14 ) is the leading edge and a lower edge of the said leading face is the trailing edge of each blade ( 12 ), so that the impeller ( 6 ) acts to drive the material in the grinding chamber ( 2 ) downwards towards a base of the grinding chamber ( 2 ), thereby compresing the material in the grinding chamber ( 2 ). A baffle member ( 16 ) comprising an annular plate may be located in the grinding chamber ( 2 ) above the impeller ( 6 ) at a preset height, so that the material in the grinding chamber ( 2 ) is maintained in a compressed condition.

1 . Apparatus for grinding a suspension of a particulate solid material, which apparatus comprises: 
 a grinding chamber for containing a particulate grinding medium;    means for introducing a suspension of the particulate solid material into the grinding chamber;    a rotatable impeller for agitating the particulate grinding medium and the suspension of particulate solid material in the grinding chamber, the impeller having at least one blade, wherein the or each blade of the impeller is pitched relative to the plane of rotation of the impeller; and    means to drive the impeller, so as to produce a suspension of a ground particulate solid material.    
     
     
         2 . Apparatus as claimed in  claim 1 , in which the said plane of rotation of the impeller is substantially horizontal.  
     
     
         3 . Apparatus as claimed in  claim 1  or  2 , in which the impeller comprises a hub, the or each blade of the impeller projecting from the hub substantially at right angles to the rotational axis of the impeller.  
     
     
         4 . Apparatus as claimed in  claim 3 , in which the hub comprises an annular body having a central opening which receives a rotatable drive shaft.  
     
     
         5 . Apparatus as claimed in  claim 4 , in which the drive shaft is fixed to the impeller at one end and is connected to drive means at its other end.  
     
     
         6 . Apparatus as claimed in any one of  claims 3  to  5 , in which the blades are integrally formed with the hub of the impeller.  
     
     
         7 . Apparatus as claimed in any one of the preceding claims in which the pitch of the or each blade relative to the plane of rotation of the impeller is between 30 and 60°.  
     
     
         8 . Apparatus as claimed in  claim 7 , in which the pitch of the or each blade of the impeller relative to the plane of rotation of the impeller is 45°.  
     
     
         9 . Apparatus as claimed in any one of the preceding claims, in which the impeller has a plurality of blades and each of the blades is pitched at substantially the same angle relative to the plane of rotation of the impeller.  
     
     
         10 . Apparatus as claimed in any one of the preceding claims, in which the impeller comprises a plurality of blades which are arranged in two or more tiers.  
     
     
         11 . Apparatus as claimed in  claim 10 , in which the tiers are located one above the other in a substantially vertically aligned stack.  
     
     
         12 . Apparatus as claimed in  claim 11 , in which each tier of blades is mounted on a respective hub, the hubs being mounted on a common drive shaft.  
     
     
         13 . Apparatus as claimed in any one of  claims 10  to  12 , in which the blades of respective tiers of the impeller are pitched at the same angle relative to the plane of rotation of the impeller.  
     
     
         14 . Apparatus as claimed in any one of the preceding claims, in which a baffle member is located in the grinding chamber above the impeller.  
     
     
         15 . Apparatus as claimed in  claim 14 , in which the baffle member comprises a plate which is disposed in a plane which is substantially parallel to the plane of rotation of the impeller.  
     
     
         16 . Apparatus as claimed in  claim 14  or  15 , in which the baffle member has a central opening which receives a drive shaft of the impeller.  
     
     
         17 . Apparatus as claimed in any one of  claims 14  to  16 , in which the baffle member is of rigid construction and is provided with an anti-wear component.  
     
     
         18 . Apparatus as claimed in  claim 17 , in which the anti-wear component comprises a polyurethane coating lining or element.  
     
     
         19 . Apparatus as claimed in any one of  claims 14  to  18 , in which the baffle member is removably secured to a wall of the grinding chamber.  
     
     
         20 . Apparatus as claimed in any one of  claims 14  to  19 , in which the baffle plate is located at a preset height over the suspension of particulate solid material in the grinding chamber.  
     
     
         21 . Apparatus as claimed in any one of the preceding claims, in which the grinding medium comprises particles having an average diameter in the range of from 0.1 mm to 6 mm.  
     
     
         22 . Apparatus as claimed in  claim 21 , in which the grinding medium has an average diameter in the range of from 0.2 mm to 4 mm.  
     
     
         23 . Apparatus as claimed in  claim 21  or  22 , in which the grinding medium is present in an amount of from 40% to 70% by volume of the material in the grinding chamber.  
     
     
         24 . Apparatus for grinding a suspension of a particulate solid material, which apparatus comprises: 
 a grinding chamber for containing a particulate grinding medium;    means for introducing a suspension of the particulate solid material into the grinding chamber;    a rotatable impeller for agitating the particulate grinding medium and the suspension of particulate solid material in the grinding chamber, means to drive the impeller; and    a baffle member arranged over the particulate grinding medium and the suspension of particulate solid material, so as to produce a suspension of a ground particulate solid material.    
     
     
         25 . Apparatus as claimed in  claim 24 , in which the baffle member comprises a plate which is disposed in a plane which is substantially parallel to a plane of rotation of the impeller.  
     
     
         26 . Apparatus as claimed in  claim 24  or  25 , in which the baffle member has a central opening which receives a drive shaft of the impeller.  
     
     
         27 . Apparatus as claimed in any one of  claims 24  to  26 , in which the baffle member is of rigid construction and is provided with an anti-wear component.  
     
     
         28 . Apparatus as claimed in  claim 27 , in which the anti-wear component comprises a polyurethane coating, lining or element.  
     
     
         29 . Apparatus as claimed in any one of  claims 24  to  28 , in which the baffle member is removably secured to a wall of the grinding chamber.  
     
     
         30 . Apparatus as claimed in any one of  claims 24  to  29 , in which the baffle plate is located at a preset height over the suspension of particulate solid material in the grinding chamber.  
     
     
         31 . A method of grinding a suspension of a particulate solid material, which method comprises: 
 providing apparatus as defined in the first aspect of the invention;    introducing into the grinding chamber the particulate grinding medium and the suspension of particulate solid material; and    agitating the particulate grinding medium and the suspension of particulate solid material by rotation of the impeller, so as to produce a suspension of a ground particulate solid material.    
     
     
         32 . A method of grinding a suspension of a particulate solid material, which method comprises: 
 providing apparatus as defined in the second aspect of the invention;    introducing into the grinding chamber the particulate grinding medium and the suspension of particulate solid material; and    agitating the particulate grinding medium and the suspension of particulate solid material by rotation of the impeller, so as to produce a suspension of a ground particulate solid material.