CA2889593A1 - Composite impeller for a centrifugal slurry pump - Google Patents

Abstract

An impeller for use in a centrifugal slurry pump having vanes including a core structural member; an elastomer layer bonded onto the core structural member; at least one hard material nose segment; and at least one exposed hard material vane segment embedded in and backed by the elastomer layer.

Description

DOCKET NO.: NS-486 COMPOSITE IMPELLER FOR A CENTRIFUGAL SLURRY PUMP
Inventors: Soon Won Moon Assignee: Syncrude Canada Ltd. In Trust for the Owners of the Syncrude Project Field of the Invention [0001] The present invention relates to a composite impeller having a vane comprising hard material segments and an elastomer.
Background

[0002] A conventional centrifugal slurry pump generally includes an impeller having multiple vanes and which is mounted for rotation within a volute casing. The slurry pump imparts energy to the slurry through the centrifugal force produced by rotation of the impeller. The slurry enters into the impeller through an intake conduit positioned in line with the rotating axis and is accelerated by the impeller, flowing radially outward into the volute casing and subsequently exiting through a discharge conduit. A suction sideliner is positioned a predetermined short distance away from the impeller suction side, the distance being so small as to substantially preclude slurry flow between the impeller and the suction sideliner.

[0003] Slurries are two-phase mixtures of solid particles and fluids in which the two phases do not chemically react with each other and can be separated by mechanical means. Slurries are typically characterized as either non-settling or settling in accordance with the size of the solid particles suspended within the fluid. Non-settling slurries include fine particles (less than about 50 m) which form stable homogeneous mixtures. Settling slurries include coarse particles (greater than 50 p.m) which form an unstable heterogeneous mixture.
Examples of slurries include sand/oil/water; tailings/water; and coke/water slurries.
Slurries can cause abrasion, erosion, and corrosion, resulting in significant wear to pump parts.

[0004] Attempts have been made to reduce wear of the pump parts, particularly the impeller, volute casing, and suction sideliner. The use of bigger slurry pumps operating at low speeds may mitigate wear issues by decreasing the slurry speed. Various modifications related to the configuration, thickness, number, and arrangement of impeller vanes can also affect the degree of wear on the pump components. For example, thicker impeller vanes are capable of handling an abrasive slurry and surviving longer, but necessitate a reduction in vane number to avoid narrowing the passageways through which the slurry flows.

[0005] Impellers have been formed of various metals and metal impellers are suitable for pumping abrasives. Chrome white iron has been the most common construction material, with stainless steel being used for corrosive slurries. The performance of a chrome white iron impeller may be enhanced by laser cladding which deposits a wear-resistant alloy coating to the surfaces of the impeller.

[0006] Elastomer-lined impellers have been used as well. Due to the capability of elastomers to dampen impact energy from the solid particles, elastomer-lined impellers demonstrated successful wear performance in many slurry applications. However when the energy input exceeds the elastic deformation limit of the elastomer, the liner may experience tear or gouge damage. It has been known that elastomer-lined impellers are susceptible to large particles with high impact speed and/or sharp edges.

[0007] Despite these innovations, the impeller is still one of the most short-lived components of a slurry pump.
Summary Of The Invention

[0008] In one aspect, the invention may comprise an impeller for use in a centrifugal slurry pump comprising a plurality of vanes, the vanes each comprising:
a. a core structural member;
b. an elastomer layer bonded onto the core structural member; and c. at least one hard material nose segment.

[0009] In one embodiment, the at least one hard material nose segment is attached to the core structural member and/or is bonded to the elastomer layer. The vane may comprise a plurality of hard material nose segments separated by elastomer filled gaps.

[0010] In one embodiment, the impeller may further comprise at least one exposed hard material vane segment embedded in and backed by the elastomer layer. Each vane comprises a front side and a back side, and may comprise a plurality of hard material vane segments, placed on either or both of the front side and back side of each vane.

[0011] The hard material elements may protect the elastomeric liner from excessive energy input, which may improve the service life of the impeller when used in high velocity slurry pumping applications.

Brief Description of the Drawings

[0012] The following drawings form part of the specification and are included to further demonstrate certain embodiments or various aspects of the invention. In some instances, embodiments of the invention can be best understood by referring to the accompanying drawings in combination with the detailed description presented herein. The description and accompanying drawings may highlight a certain specific example, or a certain aspect of the invention. However, one skilled in the art will understand that portions of the example or aspect may be used in combination with other examples or aspects of the invention.

[0013] Figure 1 is a cross-sectional view of one embodiment of a centrifugal pump comprising an impeller of the present invention.

[0014] Figure 2 is a cross-sectional view of a prior art impeller having an elastomer lining, taken along line II in Figure 1.

[0015] Figure 3 is a cross-sectional view of one embodiment of an impeller along line III in Figure 1.

[0016] Figure 4A is a cross-sectional view of one embodiment of an impeller of the present invention, and Figure 4B is a view of the impeller vane of Figure 4A.

[0017] Figure 5A is a cross-sectional view of one embodiment of an impeller of the present invention, and Figure 5B is a view of the impeller vane of Figure 5A.

[0018] Figure 6A is a cross-sectional view of one embodiment of an impeller of the present invention, and Figure 6B is a view of the impeller vane of Figure 6A.

[0019] Figure 7A is a cross-sectional view of one embodiment of an impeller of the present invention, and Figure 7B is a view of the impeller vane of Figure 7A.

[0020] Figure 8A is a cross-sectional view of one embodiment of an impeller of the present =
invention, and Figure 8B is a view of the impeller vane of Figure 8A.
Figure 9A is a cross-sectional view of one embodiment of an impeller of the present invention, and Figure 9B is a view of the impeller vane of Figure 9A.
Detailed Description

[0021] As used herein, the recited terms have the following meanings. All other terms and phrases used in this specification have their ordinary meanings as one of skill in the art would understand.

[0022] To the extent that the following description is of a specific embodiment or a particular use of the invention, it is intended to be illustrative only, and not limiting of the claimed invention. The following description is intended to cover all alternatives, modifications and equivalents that are included in the spirit and scope of the invention, as defined in the appended claims. References in the specification to one embodiment", "an embodiment", etc., indicate that the embodiment described may include a particular aspect, feature, structure, or characteristic, but not every embodiment necessarily includes that aspect, feature, structure, or characteristic. Moreover, such phrases may, but do not necessarily, refer to the same embodiment referred to in other portions of the specification. Further, when a particular aspect, feature, structure, or characteristic is described or claimed in connection with an embodiment, it is within the knowledge of one skilled in the art to affect or connect such aspect, feature, structure, or characteristic with other embodiments, whether or not explicitly described.

[0023] The present invention relates generally to an impeller for use in a centrifugal slurry pump. An embodiment of a centrifugal slurry pump (5) wherein an impeller of the present invention can be used is shown in cross-section in FIG. 1. The centrifugal pump (5) is driven by a motor (not shown), such as electric motor, turbine, etc., that is connected to an impeller (10) of the present invention by a shaft (12). The impeller (10) is provided in a volute casing (14). An intake conduit (16) is provided in the volute casing (14) to route liquid into the pump (5), where the liquid will be subsequently discharged from the pump (5) through a discharge conduit (18) provided in the volute casing (14). A suction sideliner (20) is provided to allow access to the inside of the volute casing (14). Rotation of the impeller (10) causes slurry within the volute casing (14) to be accelerated radially from the intake conduit (16) and discharged circumferentially at increased pressure at pump outlet, discharge conduit (18), in a manner well understood by those skilled in the art.

[0024] The present invention comprises a composite impeller (10) having at least one hard material segment (50) backed by an elastomeric layer (60), and a core structural member (70).
The core structural member is to provide mechanical strength required to operate the impeller.
The core structural member may be any material of suitable strength or rigidity, and will typically be steel.

[0025] The hard material segments (50) provide additional wear resistance, however, the primary role of the segments is to protect the elastomer layer (60) underneath from excessive energy input. The leading edge of the impeller vane is one of the frequent damage areas in elastomer-lined impeller, mainly due to direct impact from solid particles. At least one hard material segment (50) is positioned over the elastomer layer (60) on the vane nose (140), which is the leading edge of the impeller as it rotates. The hard material nose segment (50) may be attached to the elastomer layer, or may be attached directly to the core structural member (70), or both the elastomer layer (60) and the core structural member (70). The hard material nose segment can be attached to the core structural member through mechanisms including but not limited to, mechanical interlocking, welding, and bonding.
The hard material nose segment can also be attached to the elastomer layer, thereby the elastomer layer being sandwiched between the hard material segment and the core structural member.

[0026] The front and back sides of the vane can also experience wear due to slurry turbulence and cavitation, requiring additional protection. Preferably, additional hard material segments (52) are embedded in the elastomer on one or both of the front and back sides of the vane.

[0027] The elastomer (60) backing the hard material segments (50, 52) may provide an energy dampening function, thereby reducing the net impact energy directly imparted to the hard material segments. In this sense, embodiments of the present invention are distinct from overlay coatings of a wear-resistant material. The elastomer layer (60) may entirely encapsulate the core structural member (70), or it may be placed only on the wet side of the core structural member. Preferably, the hard material is segmented into a plurality of segments, so that impact energy can be effectively transfeffed to the elastomer behind the segment.

[0028] As used herein, a "hard material" is any material known to have greater mechanical strength than the underlying elastomer and good abrasion resistance. Such material may include, without limitation, metallic materials, ceramic or non-ceramic carbides such as chromium carbide, tungsten carbide, or a cermet such as sintered tungsten carbide. Sintered tungsten carbide, also known as cemented carbide, is a composite material comprising tungsten carbide powder mixed with a binder metal such as cobalt or nickel, compacted in a die and then sintered at a very high temperature. Wear-resistant hard materials may also include various ceramic materials such as alumina or a nitride such as silicon nitride. As used herein, a ceramic material is an inorganic, non-metallic, oxide, nitride or carbide material, which may or may not be crystalline. Suitable hard materials are well known in the art and are readily commercially available.

[0029] As used herein, an elastomer is a polymer having the property of elasticity, whereby the polymer deforms in response to the application of stress, and substantially recovers its original form when the stress is removed. Elastomers typically have a low Young's modulus and a high yield strain, as is well known in the art. Suitable elastomers include, without limitation, natural or synthetic rubbers, polyurethanes, thermoplastic polymers, and other thermoset polymers. Elastomers can have fillers such as Kevlar fibers or nano-fillers for higher tear and wear resistance, as is well known in the art.

[0030] In one embodiment, as shown in Figure 4A and 4B, 6A and 6B and 8A and 8B, a single hard material segment (50) is attached to the vane to form the vane nose (140). In alternative embodiment, the hard material portion (50) may be segmented, with elastomer filling the gaps (62) between the hard material segments (50), as is shown in Figures 5A and 5B, 7A and 7B, or 9A and 9B.

[0031] The vane nose hard material segment (50) or segments may be supplemented with several tile-like hard material segments (52) on both the front side and back side of the vane.
Typically, these locations suffer from wear due to cavitation and recirculation of the slurry as the impeller is rotated. The tiled segments (52) are embedded in and backed by the elastomer, as is shown in Figures 6B or 7B. Alternatively, the additional hard material segments (52) may be spheres or cylinders, exposing a circular surface on both the front and the back sides of the impeller vane, as is shown in Figures 8B or 9B.

[0032] As may be apparent, there are numerous options as to the shape and configuration of the segments (50, 52), and the above exemplary description of alternatives should not be considered limiting of the claimed invention.

[0033] The segments (50, 52) present a wear-resistant hard face to the slurry which impacts the vane nose as the impeller is in motion. The elastomer gaps (62) between segments provide some energy dampening capacity laterally (ie. between hard material segments). The elastomer layer (60) behind the hard material segments absorbs a significant amount of impact energy from larger slurry particles, thereby reducing the risk of fracture damage of the hard material segments (50, 52).

[0034] Accordingly, the size and thickness of the wear-resistant segments and the elastomeric layer may be configured to minimize the propensity of the segments to crack in response to particle impact. The shape and size of the hard material segment; the degree of energy absorbing capability of the elastomer; and the environmental conditions such as solid particle size, impact velocity, temperature, etc. may also be factors to consider.

[0035] The elastomer backing must be thick enough, having regard to its energy dampening capacity, to adequately cushion impacts to the hard material segments.

[0036] The interface adhesion strength between the hard material segments and the elastomer layer must be greater than the forces which would tend to separate the two. In a preferred embodiment, the interface adhesion between the two includes chemical bonding.
Without chemical bonding, cured elastomer adheres to the metal surface by means of physical interlock at the microscopic level. It is common practice when using adhesives to bond polymers and metal to deliberately increase the surface roughness of the metal component to promote this microscopic interlock. Chemical bonding provides adhesion at the molecular bond level, and may work well even with polished surfaces. Instead of microscopic material shear provided by the mechanical interlock of surface roughness, adhesion is created via atomic forces. For this reason, such bonds can exceed the shear resistance of the elastomer itself If one were to forcibly separate the bonded components so described, the bond surface would be covered with a thin layer of the elastomer. Such destructive testing is commonly employed in the manufacture of elastomeric-metal composites. Examples of such are well described in the American Society for Testing and Materials (ASTM) publication: ASTM D429 ¨ 14, Standard Test Methods for Rubber Property¨Adhesion to Rigid Substrates.

[0037] Chemical bonding may be exemplified by, but is not limited to, the type of vulcanized bond commonly used in vibration isolation components, automotive tires, conveyor belts, and other rubber-metal composites known in other arts.

[0038] In one embodiment, a bonding agent is used, and may comprise a single coat material placed between the hard material and the elastomer. The bonding mechanisms of the multiphase systems involved in making elastomer to hard material bonds are complex and the chemistry of the reactions involved may not be totally disclosed or understood in the art.
Descriptions of such bonds may be found in the prior art, such as US Patent 6,632,319 assigned to Bridgestone Corporation, and US Patent 5,268,404 assigned to Lord Corporation, the entire contents of which are incorporated herein by reference, where permitted.

[0039] Therefore, in one embodiment, and depending on the specific elastomer and hard material, an additional primer coat may be applied to the hard material, and a cover coat is applied thereon which adheres between the elastomer and the primer.

[0040] A primer layer and an adhesive layer may be provided between the hard material and the elastomer. Prior to curing, chemical agents in the primer layer diffuse into the substrate material by chemisorption. Chemical agents in the adhesive layer diffuse into the elastomer layer. In addition, chemical agents inter-diffuse between the primer and adhesive layers.

[0041] Upon curing, crosslinks form between the polymer chains in the elastomer. Internal crosslinks are formed between the polymer chains of the adhesive layer. And similarly, internal crosslinks are formed between the polymer chains of the primer layer.
Crossbridging reactions then form chemical bonds or linkages between the respective layers which have been assisted by the chemisorption, and inter-diffusion as described above.

[0042] Those skilled in the art are aware that creating an effective chemical bond between an elastomer and a hard material requires suitable surface preparation. Any contamination of the surfaces at any interface will reduce the bond strength. For example, to prepare a metal surface, all traces of oil, grease or solid lubricant must be completely removed from the metal surface. Degreasing and shot blast, and wet blast followed by a phosphate conversion methods are suitable.

[0043] The composite impellers of the present invention may be manufactured using casting or molding techniques well known to those skilled in the art.
Definitions and Interpretation

[0044] The singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for the use of exclusive terminology, such as "solely," "only," and the like, in connection with the recitation of claim elements or use of a "negative" limitation. The terms "preferably,"
"preferred," "prefer," "optionally," "may," and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.

[0045] The term "and/or" means any one of the items, any combination of the items, or all of the items with which this term is associated. The phrase "one or more" is readily understood by one of skill in the art, particularly when read in context of its usage.

[0046] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges recited herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof, as well as the individual values making up the range, particularly integer values. A recited range of values includes each specific value, integer, decimal, or identity within the range. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc.

[0047] As will also be understood by one skilled in the art, all language such as "up to", "at least", "greater than", "less than", "more than", "or more", and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into sub-ranges as discussed above. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio.

[0048] One skilled in the art will also readily recognize that where members are grouped together in a common manner, such as in a Markush group, the invention encompasses not only the entire group listed as a whole, but each member of the group individually and all possible subgroups of the main group. Additionally, for all purposes, the invention encompasses not only the main group, but also the main group absent one or more of the group members. The invention therefore envisages the explicit exclusion of any one or more of members of a recited group. Accordingly, provisos may apply to any of the disclosed categories or embodiments whereby any one or more of the recited elements, species, or embodiments, may be excluded from such categories or embodiments, for example, as used in an explicit negative limitation.

[0049] As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the scope of the invention claimed herein. The various features and elements of the invention described herein may be combined in a manner different than the specific examples described or claimed herein without departing from the scope of the invention. In other words, any element or feature may be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility between the two, or it is specifically excluded.

Claims (8)

WHAT IS CLAIMED IS:

1. An impeller for use in a centrifugal slurry pump comprising a plurality of vanes, the vanes each comprising:
a. a core structural member;
b. an elastomer layer bonded onto the core structural member; and c. at least one hard material nose segment is attached to the elastomer layer such that the elastomer layer is disposed between the nose segment and the core structural member.

2. The impeller of claim 1 further comprising at least one exposed hard material vane segment embedded in and backed by the elastomer layer.

3. The impeller of claim 2 comprising a plurality of hard material nose segments separated by elastomer filled gaps.

4. The impeller of claim 2 wherein each vane comprises a front side and a back side, further comprising a plurality of hard material vane segments, placed on either or both of the front side and back side of each vane.

5. The impeller of one of claims 1 to 4 wherein either or both the at least one hard material nose segment and each at least one hard material vane segment comprises tungsten carbide, or sintered tungsten carbide, a cermet, or a ceramic material.

6. The impeller of claim 5 wherein the at least one hard material vane segment comprises a tile, a block, a cylinder, or a sphere.

7. The impeller of any one of claims 1 to 4 wherein the elastomer layer comprises a rubber or a polyurethane.

8. The impeller of claim 1 wherein the core structural member comprises steel.