Molten metal impeller with rock guard

Abstract

An impeller for use in a molten metal pump is provided. The impeller comprises (a) a body including a plurality of blades or passages and (b) a top portion having an inverted cup-shape. A top wall of the cup includes a bore configured to receive a shaft. A sidewall includes a plurality of openings. A rim of the cup is mated to the body.

1 . An impeller for use in a molten metal pump, the impeller comprising:
 (a) a body including a plurality of blades or passages and (b) a top portion having an inverted cup-shape wherein a top wall includes a bore configured to receive a shaft, a sidewall includes a plurality of openings, and a rim mated to the body.   
     
     
         2 . The impeller of  claim 1  wherein the top portion is comprised of material harder than the body. 
     
     
         3 . The impeller of  claim 1  wherein the top portion is comprised of a ceramic and the body is comprised of graphite. 
     
     
         4 . The impeller of  claim 1  wherein the sidewall of the top portion has a height at least 50% of a height of the body. 
     
     
         5 . The impeller of  claim 1  wherein the rim is cemented to a peripheral edge of the body. 
     
     
         6 . (canceled) 
     
     
         7 . The impeller of  claim 1  wherein the at least part of the top portion is configured to extend above a pumping chamber of the molten metal pump. 
     
     
         8 . The impeller of  claim 1  wherein the sidewall is inwardly inclined between the rim and the top wall. 
     
     
         9 . The impeller of  claim 8  wherein the incline is between about 20 and 50 degrees relative to a plane in which the rim resides. 
     
     
         10 . The impeller of  claim 1  wherein the body includes a bearing ring. 
     
     
         11 . The impeller of  claim 1  wherein the openings are oval. 
     
     
         12 . The impeller of  claim 1  wherein the passages have at least one dimension that is smaller than an inlet to a space between adjacent blades or an inlet to the passages. 
     
     
         13 . The impeller of  claim 1  wherein the bore includes at least one key-way configured to receive a key to secure the top portion to the shaft. 
     
     
         14 . The impeller of  claim 1  wherein the body includes an aperture receiving the shaft. 
     
     
         15 . The impeller of  claim 1  wherein a circumference of the top wall is less than a circumference of the rim. 
     
     
         16 . The impeller of  claim 1  wherein an interface between the top wall and the sidewall is rounded or beveled. 
     
     
         17 . A molten metal pump including the impeller of  claim 1 . 
     
     
         18 . The molten metal pump of  claim 17  that includes a superstructure on which a motor is supported, a pump base including a pump chamber in which the impeller is received, and a plurality of support posts connecting the superstructure to the pump base. 
     
     
         19 . The molten metal pump of  claim 18  wherein the plurality of openings reside above a top surface of the pump base. 
     
     
         20 . A molten metal pump comprising a base defining a pumping chamber, said base including an upper surface and a lower surface, at least one post engaging the base, and a shaft configured to drive an impeller, said impeller being disposed in the pumping chamber, the impeller comprising a body including a plurality of blades or passages and a top portion, the top portion including a top wall including a bore configured to receive the shaft and a sidewall including a plurality of openings, the sidewall being inwardly inclined between the body and the top wall, and wherein at least a portion of the sidewall extends above the upper surface of the base. 
     
     
         21 . The molten metal pump of  claim 20  wherein the openings are elongated in a direction parallel to an axis of the shaft and wherein the openings include forward and trailing walls canted in a direction of impeller rotation.