Technical Field

This disclosure relates to impellers for use with pumps and particularly relates to an improved ceramic-based impeller design for use in centrifugal slurry pumps used in mineral processing applications.

Background

Centrifugal pumps are used in mineral processing applications to handle various liquids and slurries. Components of these pumps, such as the impellers, experience very arduous working conditions which lead to wear due to abrasion by the material being pumped. In some applications, ceramic type impellers are desirable due to their wear resistant properties.

Traditional steel impellers are mounted to the driveshaft of a centrifugal pump by way of providing an internal screw thread at the centre of the impeller which engages with a corresponding external screw thread provided about the driveshaft. However, due to the brittle nature or ceramic materials, it is not feasible to provide an internal screw thread at the centre of a ceramic impeller.

To overcome this problem, some have tried to embed a small steel boss at the centre of a ceramic impeller for the purpose of mounting the impeller to a driveshaft. However, such arrangements have been found to be suitable only for pumps of relatively small sizes.

Some have tried using a metal hub in the form of a large circular steel plate with a steel boss located at its centre, the steel plate having a similar diameter to the impeller, and ceramic impeller parts being affixed by a series of fasteners to the front and back of the steel plate. However, such arrangements have involved use of a large number of fasteners, with a consequent provision of a large number of holes in the ceramic parts which have undesirably weakened the ceramic parts.

There remains a need for improved impeller arrangements.

Summary

In a first aspect there is provided an impeller for a pump, the impeller including: an impeller body formed from a ceramic material and including pumping vanes; an impeller hub formed from a metallic material; the impeller hub includes a central boss arranged to engage with a pump driveshaft wherein the hub further includes a series of projections which are spaced away from the axis of rotation of the hub and the projections engage with apertures in the impeller body; and wherein the projections and corresponding apertures are spaced away from the axis of rotation by a distance of no more than 70% of the radius of the impeller.

In certain embodiments, the hub is located within the impeller body.

In certain embodiments, the impeller body includes an impelling portion and a back vane portion, and the hub is located between the impelling portion and the back vane portion.

In certain embodiments, the projections and apertures are substantially cylindrical.

In certain embodiments, the projections are spaced away from the axis of rotation of the hub by a distance of at least 40% of the radius of the impeller.

In certain embodiments, the projections are spaced away from the axis of rotation of the hub by a distance of about 50% of the radius of the impeller.

In certain embodiments, the apertures in the impeller body are located within the pumping vanes of the impeller.

In certain embodiments, each pumping vane includes no more than one aperture.

In certain embodiments, a region of polyurethane bonds the impeller hub to the impeller body.

Some embodiments further include an arrangement of back vanes, and the number of back vanes provided is at least double the number of pumping vanes.

In certain embodiments the number of back vanes is between three to four times greater than the number of pumping vanes.

Some embodiments further include an arrangement of front vanes, and the number of front vanes provided is at least double the number of pumping vanes.

In certain embodiments the number of front vanes is between three to four times greater than the number of pumping vanes.

In a second aspect there is provided a method of producing an impeller including the steps of: providing an impeller body formed from a ceramic material and including pumping vanes; providing an impeller hub formed from a metallic material; the impeller hub includes a central boss arranged to engage with a pump driveshaft wherein the hub further includes a series of projections which are spaced away from the axis of rotation of the hub and the projections engage with apertures in the impeller body; and pouring liquid polyurethane in between the impeller hub and the impeller body which flows into the apertures to surround the projections in the apertures.

In a third aspect there is provided a method of retrofitting a centrifugal pump including the steps of replacing the impeller of the pump with an impeller according to the first aspect.

Brief Description of the Drawings

Notwithstanding any other forms which may fall within the scope of the methods and apparatus as set forth in the Summary, specific embodiments will now be described, by way of example, and with reference to the accompanying drawings in which:

Figure 1 is an exploded view of an impeller for use in a centrifugal pump;

Figure 2 is a rear view of the impeller of Figure 1 ;

Figure 3 is a cross section along the line C-C of Figure 2; and

Figure 4 is a front view of the impeller of Figure 1.

Detailed Description of Embodiments

Referring to Figure 1, an impeller 10 is shown including a body comprised of an impelling portion 12, an inner back vane portion 14 and an outer back vane portion 15, all of which are formed from a ceramic material, such as silicon carbide. The impelling portion 12 includes major pumping vanes 13 which in use act to pump the medium that is being handled by the pump. The outer back vane portion 15 includes outer back vane portions 19. The back vane portion 14 includes inner back vane portions 17. When the parts shown are assembled together, the inner back vane portions 17 align with the outer back vane portions 19 to form back vanes which, in use, operate to assist in expelling pumping medium away from the driveshaft of the pump to improve sealing of the pump.

A hub 16 formed from mild steel is located between the impelling portion 12 and the back vane portion 14 of the impeller 10. The hub 16 includes a central boss 18 for engaging with the metal driveshaft of the pump. The boss 18 includes means for engaging with the driveshaft in the form of an internal screw thread (not visible) which fits to an external screw thread provided on the driveshaft of the pump. The hub 16 further includes a circular plate portion 21 which bears five cylindrical projections 20 which engage with corresponding cylindrical recesses 22 formed in the impelling portion 12. The hub 16 is formed in one piece in a casting process.

The projections 20 have threaded ends and are secured with nuts fitted from the front side of the impeller (see Figure 4). The recesses 22 are formed to coincide with the vanes 13 of the impeller portion 12. The recesses 22 are located a distance of approximately 50% of the radius of the impeller away from the central axis of rotation of the impeller in use.

During assembly of hub 16 with the impelling portion 12, liquid polyurethane resin is poured between the hub 16 and the impelling portion 12 which flows into apertures 22 to surround the projections when located in their respective apertures. When cured, the polyurethane acts to provide a bond between the hub 16 and the impelling portion 12 and also acts to absorb shock loads which might be experienced, for example during start up and shut down of the impeller 10 in use.

The inner back vane portion 14 is affixed to hub 16 by inserting screw fasteners through six apertures 24 provided about the periphery of in inner back vane portion 14, which are received in threaded apertures 23 provided in the hub 16.

The screw fasteners used in assembling the impeller are protected by filling the remainder of apertures 22, 24 with polyurethane, as has been described hereinabove.

The outer back vane portion 15 is affixed to the impelling portion 12 by way of a suitable ceramic adhesive.

In use, the hub portion 16 transmits torque from the driveshaft to the impeller 10. The projections 20 spread the applied load away from the region nearest the central, axis of the impeller, to reduce the forces applied to the impeller 10. This enables fabrication of one-piece impeller portions, and larger impellers than would otherwise be the case if the projections were not provided.

Each pumping vane 13 has only one aperture associated with it, which minimises any weakening effect of forming apertures in these vanes.

By forming the impeller hub so that the projections and corresponding apertures are spaced away from the axis of rotation by a distance of no more than 70% of the radius of the impeller, allows a greater fill of ceramic material in the peripheral region of the impeller providing additional strength to that ceramic portion of the impeller.

The impeller 10 includes a total of eighteen (18) back vanes 19, and five (5) major pumping vanes 13. It has been found that the operational efficiency of the back vanes 19 is improved if the number of back vanes provided is greater than the number of pumping vanes. In some embodiments, the number of back vanes is at least double the number of major pumping vanes. In some embodiments, the number of back vanes is between three to four times the number of major pumping vanes. Similarly, in some embodiments, front vanes are provided in a similar distribution to the back vanes. At least as twice as many front vanes as major pumping vanes 13 may be provided, and in some embodiments the number of front vanes provided is between three and four times the number of major pumping vanes.

In further embodiments it may be possible to retrofit various ceramic impellers which feature different combinations of pumping vanes, back and front vanes, at different times into a pump during a maintenance cycle, depending on the duty or application for the impeller, and with projections and corresponding apertures which are spaced away from the axis of rotation by a distance of between 40% and 70% of the radius of the impeller, depending on the end use application.

It can be seen that embodiments of the invention have at least one of the following advantages:

• Torque from the driveshaft is distributed away from the axis of rotation of the impeller to reduce internal stresses.

· The metal hub is located within the body of the impeller and so the metal hub is protected from wear.

• The number of apertures in the impeller vanes is kept to a minimum.

• Fill of ceramic material in the peripheral region of impeller is maximised

• There is a flexibility to be able to modify the ratio of the number of front or back vanes provided in relation to the number of major pumping vanes

In the foregoing description of preferred embodiments, specific terminology has been resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "front" and "rear", "inner" and "outer", "above", "below", "upper" and "lower", "horizontal" and "vertical" and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

In this specification, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear.

The preceding description is provided in relation to several embodiments which may share common characteristics and features. It is to be understood that one or more features of any one embodiment may be combinable with one or more features of the other embodiments. In addition, any single feature or combination of features in any of the embodiments may constitute additional embodiments.

Any. inventions which have described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the inventions. Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.