WO2021023660A1

WO2021023660A1 - Closed centrifugal pump channel impeller for fluids which have abrasive or erosive admixtures

Info

Publication number: WO2021023660A1
Application number: PCT/EP2020/071669
Authority: WO
Inventors: Fritz JOCHEN; Christoph Jäger; Wolfgang Metzinger; Steffen Schmidt; Rolf Witzel
Original assignee: KSB SE & Co. KGaA
Priority date: 2019-08-05
Filing date: 2020-07-31
Publication date: 2021-02-11
Also published as: CN114423951A; EP4010598A1; DE102019005469A1

Abstract

The invention relates to a closed centrifugal pump channel impeller for fluids which have abrasive or erosive admixtures, consisting of a support disc and a cover disc and one or more blades arranged therebetween, characterised in that, in the interface region to the support disc and/or cover disc, at least one blade comprises a blade profile shape which is asymmetrical with respect to the camber line.

Description

Closed centrifugal pump channel impeller for liquids with abrasive or erosive additions

The invention relates to a closed centrifugal pump channel impeller for liquids with abrasive or erosive admixtures, consisting of a support and a cover disk and one or more blades arranged in between ...

Depending on the conveying parameters, centrifugal pumps are often used for pumping media with components that promote wear. Wear occurs primarily on the components of the pump that come into contact with the flow. These include in particular the impeller, any stator, the pump housing with attachments and housing covers, but also the shaft seal.

The wear or the material removal rate depends strongly on the local flow velocity. The pump impeller is particularly badly affected by this, because particularly high speeds occur when the air flows around the impeller blades. In order to achieve an economical service life for the affected parts, there are several catfish approaches. One possibility is to coat the affected surfaces with elastomers such as rubber or polyurethane of low hardness. The elastomer coating absorbs the impact energy of the solid particles contained in the conveying medium, which means that they do not damage the components or damage them less. Another possibility is the use of component materials whose hardness is greater than the hardness of the solids contained in the conveying medium. Both metallic and non-metallic materials can be considered as materials with great hardness. The pump components, in particular the impeller, are essentially manufactured using primary molding processes. For this purpose, components made of alloyed steels are created using conventional foundry processes and then mechanically reworked. The above-described process for component production is comparatively expensive, the additional costs result mainly from the energy-intensive casting process, but also from the metallic alloy components.

One approach to cost optimization with the same properties is the use of polymers with wear-resistant embedded particles. Fine-grain silicon carbides (SiC), which are stored in a polymer matrix, are usually used for this. Although the embedded silicon carbide particles are harder than the particles contained in the conveying medium, wear occurs due to the washing out of the polymer matrix between the embedded particles. The stored silicon carbide components are removed over a longer period of time.

A particularly wear-critical location is the leading edge of the impeller. During the running time, wear can progress to such an extent that the impeller blades are largely worn away. In the case of impellers without a cover plate on the suction side, this can lead to a collapse in the delivery rate. In the case of impellers with a cover plate on the suction side, the cover plate can become detached, which leads to a complete destruction of at least the impeller.

Impellers made of polymer with silicon carbide inclusions are particularly affected by this type of destruction, since both the tensile strength and the breaking strength of plastics with silicon carbide inclusions are significantly lower than those of a steel alloy. Even comparatively little wear can lead to total failure of the impeller. The application deals with the above problem and tries to show possible solutions that can reduce material wear through an optimized design of the impeller. This object is achieved by an impeller according to the features of claim 1. Advantageous embodiments of the impeller are the subject of the dependent claims.

The aim of the invention is to minimize and delay the wear and tear of the leading edge of the impeller, so that the service life of the impeller is increased. According to the invention, this is achieved by a special profiling of at least one of the impeller inlet edges. The main aim is to reduce the sensitivity of the leading edge to incorrect flow and to reduce the velocity gradient when the flow around the leading edge from the pressure side to the suction side at partial-load operating points.

The suction and pressure side of the vane is created by placing the vane profile with a vane thickness s _d on the pressure side and with the vane thickness s _s on the suction side on an existing skeleton surface, resulting in a total vane thickness. The starting point for this are sketches for the profiling on the support disk (hub, pressure-side cover disk) and on the cover disk (suction-side cover disk). According to the invention, it is specifically proposed that at least one blade in the interface area to the support and / or cover disk has a blade profile shape that is asymmetrical with respect to the skeleton line. The asymmetry is achieved by placing a different blade thickness / profile thickness on the pressure and suction side, in other words the thickness of the blade profile from the camber line to the suction-side or pressure-side edge of the blade is different, so that with respect to the camber line an asymmetry is present as a line of symmetry at least for partial areas over the blade length, ie in the direction from the inlet to the outlet edge. The channel wheel is made of a cast or otherwise molded material, for example steel or mineral casting. The impeller can also be made of polymers wear-resistant embedded particles, e.g. fine-grain silicon carbides (SiC).

It is particularly preferred if the suction-side blade Z-profile thickness is greater than the pressure-side blade Z-profile thickness. The asymmetrical blade thickness of the suction and pressure side preferably extends only over a limited area of the blade length; there is quasi a regional thickening of the blade profile on its suction side. Such a thickening is preferably provided with a relative blade length of 10% -50% starting from the leading edge. The greatest difference in thickness is particularly preferably provided in the range of 5% -15% of the relative blade length, ideally around 10% of the relative blade length.

It is also conceivable that the profile thickness in the area of the suction-side thickening at the interface with the support disk is 20% to 40% higher than the profile thickness in the area of the outlet edge of the suction side.

According to an advantageous embodiment of the invention, the aforementioned asymmetry or thickening comprises a size ratio of the suction-side to the pressure-side profile thickness of at least 1.3-1.8. If there is a thickening on the suction side of the blade, the size ratio increases, for example, starting from the leading edge until a maximum value in the aforementioned range between 1.3-1.8 is reached. The size ratio then decreases again in the direction of the trailing edge. It can be sensible for a relative blade length of approximately 20% -30%, in particular approximately 25%, to have a size ratio of at least 1.3, preferably at least 1.4.

According to a further advantageous embodiment of the invention, the shape of the impeller leading edge is elliptically profiled, in particular the profile shape of the leading edge is formed by two partial ellipses merging tangentially into one another at the leading edge point with an elliptical angle of at least 90 ° to a maximum of 180 °. For example, the leading edge shows a quarter-ellipse shape in the transition to the pressure side, which is then divided by a constant profile width up to the trailing edge. The transition from the inlet edge point to the suction side is formed by an ellipse with an ellipse angle greater than 90 ° so that the ellipse shape forms the section-wise thickening and then drops to a constant profile thickness up to the exit edge. This has the advantage that the transition from the largest suction-side profile thickness to a profile thickness that remains almost constant in the direction of the impeller outlet edge is formed by a kink-free curve (ellipse angle> 90 °).

In a further embodiment, the leading edge point can be shifted from the skeleton line or skeleton surface of the blade in the direction of the pressure side or in the direction of the suction side.

The asymmetrical blade profile shape, in particular the aforementioned thickening on the suction side, can extend from the support disk to the cover disk. However, a profile shape that changes between the support disk and cover disk is also conceivable. For example, there is the possibility that an asymmetrical blade profile shape is only provided in the interface area with the support disk. Instead, there is a profile shape symmetrical to the skeleton line in the interface area to the cover plate. Regardless of whether the profile shape is symmetrical or asymmetrical, the leading edge profile can be formed by two quarter ellipses which merge tangentially into one another at the entry edge point there.

If the profile shape between the carrier and cover disk changes, it is advantageous if the ratio of the total profile thickness of the blade in the area of the carrier and cover disk with a common radial beam from a relative blade length of 8% - 12% has a ratio of 1, 08 to 1.12.

In addition to the impeller according to the invention, the invention also relates to a centrifugal pump with an impeller according to the invention. The same advantages and details result for the pump as have already been explained above with reference to the impeller. A repetitive description is therefore dispensed with and reference is made instead to the above statements. Further advantages and details are to be explained below using the exemplary embodiments shown in the figures. They show: FIG. 1: a perspective view of the suction side of the invention

Sewer wheel,

FIG. 2: a detailed representation of the blade shape according to the invention

FIG. 3: a profile representation of the impeller blade according to FIG. 2 in the area of its transition to the support disk,

Figures 4a, b: a modified embodiment according to Figure 3 and

Figures 5a, b: Profile representation of the blade in the area of the cover disk.

FIG. 1 shows a perspective view of the centrifugal pump channel impeller according to the invention. The impeller is designed as a closed channel impeller with a cover plate 1 and a support plate 2. Several blades 3 extend between the support and cover disks. The blades 3 are delimited in the direction of flow by their leading edge (suction edge) 3a and their trailing edge (pressure edge) 3b. Transverse to the direction of flow, they are delimited by the cover and support disks 1, 2. The channel wheel is made of a cast or otherwise formable material, such as steel or mineral casting. The impeller can also consist of polymers with wear-resistant embedded particles, for example fine-grain silicon carbides (SiC). The impeller is primarily used for pumping liquids with abrasive or erosive additions.

According to the invention, the wear resistance of the impeller and thus its achievable runtime performance is optimized by a special profiling of the impeller leading edges 3a. Due to the new profiling, the sensitivity of the leading edges to incorrect flow can be reduced by reducing the speed gradient of the The resulting fluid flow around the inlet edges 3a from the pressure side B to the suction side A is reduced at partial-load operating points. The suction and pressure side of the blade 3 is created by placing the blade profile on an existing skeleton surface 5 with the blade thickness s _d on the pressure side B and the blade thickness s _s on the suction side A. The result is a total blade thickness of s, which is in blade lengths - direction varies. This can be seen in FIGS. 2, 3, FIG. 3 here showing the profile shape of the blade 3 in the area of the support disk 2.

Specifically, the leading edge 3a of the blade 3 on the pressure side B is designed as a quarter ellipse, ie with an ellipse angle a _B = 90 °. The length of the profiling on the pressure side is referred to here as X _ed . In addition, the blade profile on the suction side A is thickened over a length of X to a dimension Y in relation to the blade thickness of the leading edge 3a. In this case, the thickening on the suction side reaches its greatest profile thickness at a length of X _{es as seen} from the leading edge 3a. From point X _es , the profile thickness s _s decreases in the direction of the trailing edge 3b in the form of a kink-free curve until the profile thickness s _s , which remains constant up to the trailing edge, is reached. The profile shape from the leading edge point 3c to the greatest thickness at point X _es and to the point where the profile thickness remains constant can also be described as a partial ellipse with an ellipse angle of a _A.

The two ellipses of the pressure side B and the suction side A merge tangentially into one another at the leading edge 3a at the leading edge point 3c.

A slightly modified version is shown in FIG. 4 a, which also shows the blade profile in the area of the support disk 2. Here the leading edge point 3c on the suction side A is shifted by the amount y _es from the skeleton surface 5 in the direction of the suction side A. A displacement of the leading edge point 3c by the amount y _ed in the direction of the pressure side B is also possible, as shown in FIG. 4b. Said thickening according to the above exemplary embodiments can extend from the support disk 2 to the cover disk 1. In another embodiment, this thickening is only arranged on the support disk 2. The profile on the cover disk 1 also consists of two quarter ellipses which merge tangentially into one another at the entry edge. The transition point 3c at the leading edge 3a can lie above (see FIG. 5b) or below (see FIG. 5a) the center 10 of the blade profile, which results in an asymmetrical profile of the leading edge 3a.

The material thickness ratio between the carrier disk and the cover disk 2, 1 can have a ratio of 1.08-1.12 from a relative blade length of 10%, the maximum blade thickness on the carrier disk 2 at a relative blade length of 0.25 has at least a ratio of 1.425. The maximum blade thickness on the support disk 2 is reached at 10% of the length of the skeleton line 10 on the suction side. The vane thickness of the suction-side thickening is 20% - 45% higher than the vane thickness in the exit area of this flow filament.

It is also conceivable that the profile thickening, as described above for the support disk 2, is arranged only on the profile of the cover disk 1, while the profile on the support disk 2 is designed as described above for the cover disk 1.

The profiles on the support and cover plate 2, 1 can have the same geometric parameters. However, if the profiles on the support and cover plate 2, 1 are designed differently - as described above - then the profiles should merge evenly into one another above the blade height.

The spatial profiling of the impeller blades according to the invention minimizes cavitation by minimizing shear stress on the blade surface, which in impellers made of polymer cast with silicon carbide significantly reduces surface wear. Also, detachments in the design area that negatively affect energy conversion are avoided. The special profiling reduces the wear caused by abrasion and cavitation erosion and at the same time increases the energy conversion and thus the efficiency of such an impeller.

Claims

Claims Closed centrifugal pump channel impeller for liquids with abrasive or erosive additions

1. Closed centrifugal pump channel impeller for liquids with abrasive or erosive additions consisting of a support and a cover disk and one or more blades arranged in between, characterized in that at least one blade in the interface area to the support and / or cover disk is one with reference to the skeleton line has asymmetrical blade profile shape.

2. Impeller according to claim 1, characterized in that the suction-side profile thickness is greater than the pressure-side profile thickness, in particular a thickening of the profile thickness difference, which is in sections in a range of the relative blade length of 5% -40% The suction side of the blade is formed, the greatest difference in thickness preferably being in the range of 5% -15%, ideally around 10% of the relative blade length.

3. Impeller according to claim 2, characterized in that there is a size ratio of the suction-side to the pressure-side profile thickness of at least 1.3-1, 8, preferably with a relative blade length of 20% -30% a size ratio of at least 1.3, especially preferably at least 1.4 is present.

4. Impeller according to one of the preceding claims, characterized in that the shape of the impeller leading edge is profiled elliptically, in particular is Profile shape of the leading edge formed by two hm leading edge point tangentially merging partial ellipses with an ellipse angle of at least 90 ° to a maximum of 180 °.

5. Impeller according to one of the preceding claims, characterized in that the transition from the largest suction-side profile thickness to a profile thickness that remains almost constant in the direction of the impeller outlet edge is formed by a kink-free curve, in particular the suction-side profile shape corresponds to from the inlet edge to to the area with an almost constant profile thickness of an ellipse with an ellipse angle between at least 91 ° and a maximum of 180 °.

6. Impeller according to one of the preceding claims, characterized in that the leading edge point is shifted from the skeleton line or skeleton surface of the blade in the direction of the pressure side or in the direction of the suction side.

7. Impeller according to one of the preceding claims, characterized in that the asymmetrical blade profile shape extends from the support disk to the cover disk.

8. Impeller according to one of claims 1 to 6, characterized in that an asymmetrical blade profile shape is only provided in the interface area to the support disk and a profile shape symmetrical to the skeleton line is present in the interface area to the cover disk, the leading edge profile being formed by two quarter ellipses, which on the the leading edge point there merge tangentially into one another.

9. Impeller according to claim 8, characterized in that the ratio of the total profile thickness of the blade in the area of the support and cover disk with a common radial jet from a relative blade length of 8% -12% a ratio of 1.08 to 1.12.

10. Impeller according to one of the preceding claims, characterized in that the profile thickness in the area of the suction-side thickening at the interface with the support disc is 20% to 40% higher than the profile thickness in the area of the exit edge of the suction side.

11. Centrifugal pump with an impeller according to one of the preceding claims.