EP4709998A1

EP4709998A1 - Pump with bearing assembly

Info

Publication number: EP4709998A1
Application number: EP24728169.4A
Authority: EP
Inventors: Per Hovmand; Kim PEKRUHN HEDEGAARD
Original assignee: Grundfos Holdings AS
Current assignee: Grundfos Holdings AS
Priority date: 2023-07-05
Filing date: 2024-05-17
Publication date: 2026-03-18
Also published as: WO2025008105A1; CN121358957A

Abstract

The invention relates to a pump (20) having a bearing assembly (10). The bearing assembly (1) comprises a core ring structure (11); and an outer ring structure (12) which at least partially surrounds the core ring structure (11) on all sides; wherein the core ring structure (11) has a higher mechanical stiffness than the outer ring structure (12).

Description

Pump with bearing assembly

TECHNICAL FIELD OF THE INVENTION

The invention relates to a pump with a bearing assembly. The invention further relates to a method for processing a bearing assembly .

BACKGROUND OF THE INVENTION

Many pumps, such as submersible pumps or other centrifugal pumps, comprise an impeller which is mounted on a rotary shaft. The shaft is thereby held by one or more bearings.

The bearings that hold the shaft are typically plain bearings made of a rubber material. When running the pump in clean water, such full rubber bearings can control the shaft at lower speeds of, e.g., 2,900 RPM (50Hz) . Furthermore, the combination of the rubber material of the bearing and the steel in the shaft leads to good sand handling properties.

However, when running the pump at higher speeds, e.g., up to 4,500 RPM (75Hz) the rubber bearings can become too soft to handle the rotational instability forces. Consequently, the impeller can come in contact with a seal in the pump housing causing an increase in frictional losses, which results in a loss of pump efficiency. At the same time, contact between an impeller suction piece and the seal can speed up sand wear on the impeller if particulates are present in the fluid. This can eventually lead to a pump failure due to a loss of efficiency.

Thus, it is an objective to provide a pump with an improved bearing assembly, which avoids the above-mentioned disadvantages . In particular, it is an obj ective to provide a bearing assembly which can maintain its functionality at high speeds .

SUMMARY OF THE INVENTION

The obj ect of the present invention is achieved by the solution provided in the enclosed independent claims . Advantageous implementations of the present invention are further defined in the dependent claims .

According to a first aspect , the invention relates to a pump with a bearing assembly comprising : a core ring structure ; and an outer ring structure which at least partially surrounds the core ring structure on all sides ; wherein the core ring structure has a higher mechanical sti f fness than the outer ring structure .

This achieves the advantage that a bearing assembly is provided which combines the advantages of soft and hard bearings . In particular, due to its sti f fer core ring, the bearing assembly can maintain its functionality at higher speeds compared to a conventional full rubber bearing, while maintaining the advantageous interface properties of a softer bearing .

The bearing assembly can be a rotary bearing, in particular a slide bearing or plain bearing . The bearing assembly can be used in a pump, for instance a submersible and/or a centri fugal pump, to hold a rotary shaft .

In particular, the fact that the core ring structure has a higher mechanical sti f fness than the outer ring structure means that a material of the core ring structure has a higher mechanical sti f fness than a material of the outer ring structure . The outer ring structure can partially or completely surround the core ring structure on all sides. For example, only small and localized portions of the core ring structure are not covered by the outer ring structure, for instance due to restrictions of the manufacturing process (e.g., fixation points during an overmolding process) .

In an embodiment, the core ring structure and the outer ring structure are each formed in one piece from a single material.

In an embodiment, the core ring structure comprises a plastic material, in particular a stiff plastic material.

This achieves the advantage that the overall stiffness (or hardness) of the bearing assembly is enhanced.

For example, the plastic material is polyethylene terephthalate (PET) .

For instance, the overall stiffness of the bearing assembly can be controlled by adjusting the stiffness of the core ring and/or outer ring structure, and/or by adjusting the dimensions of the core ring and/or outer ring structure (e.g., their respective thicknesses) .

In an embodiment, the outer ring structure comprises a rubber material, in particular a soft rubber material.

This achieves the advantage that a good contact to a rotary shaft, which is hold by the bearing assembly, can be established. This can improve sand handling properties when the bearing assembly is used in a submersible pump. In particular, the rubber material is softer than the plastic material of the core ring structure .

For example , the rubber material is a liquid silicone rubber ( LSR) or a nitrile butadiene rubber (NBR) .

In an embodiment , the outer ring structure is overmolded over the core ring structure .

In an embodiment , the outer ring structure encapsulates the core ring structure .

In an embodiment , the core ring structure comprises several protrusions which are arranged axially on each end of the core ring structure .

For example , when forming the outer ring structure in a overmolding process , these protrusions allow to fixate the core ring structure in the mold while allowing the rubber to bond around the plastic of the core ring structure .

The protrusions can be pins or other type of raises which protrude from a surface of the core ring structure in axial direction .

In an embodiment , the bearing assembly is a slide bearing assembly .

The pump may be a submersible pump, comprising : a rotary shaft ; wherein the bearing assembly is arranged around a rotary shaft of the pump . In particular, the bearing assembly is arranged to hold the rotary shaft .

The pump can be a centri fugal pump . A centri fugal pump is a type of dynamic pump that uses a rotating impeller to increase the pressure of a fluid and move it through a piping system . The pump can comprise such impeller which is mounted on the rotary shaft . For instance , the shaft is made of steel .

For example , the pump comprises several pump stages which are arranged axially along the shaft . For instance , each pump stage comprises at least one bearing assembly of the invention .

According to a third aspect , the invention relates to a method for processing a bearing assembly, comprising the steps of : providing or forming a core ring structure ; and forming an outer ring structure around the core ring structure , wherein the outer ring structure at least partially surrounds the core ring structure on all sides ; and wherein the core ring structure has a higher mechanical sti f fness than the outer ring structure .

In an embodiment , the outer ring structure i s formed by overmolding the core ring structure with a material of the outer ring structure .

For instance , the outer ring structure is formed around the core ring structure by means of an inj ection molding process .

In an embodiment , the core ring structure is fixated by several pins which engage the core ring structure on an outer surface during the overmolding .

For example , the fixation of the core ring structure via the pins causes the formation of several holes in the outer ring structure , in particular on a section of the outer ring structure which covers the outer surface of the core ring structure .

The above description regarding the bearing assembly according to the first aspect of the invention is correspondingly valid for the method for processing the bearing assembly according to the third aspect of the invention .

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in the following together with the figures .

Fig . 1 shows di f ferent views of a bearing assembly according to an embodiment ;

Fig . 2 shows components of a bearing assembly according to an embodiment ;

Fig . 3 shows a cross-sectional view of a pump according to an embodiment ;

Fig . 4 shows force-displacements for di f ferent bearing embodiments ;

Figs . 5A-B show results of pump ef ficiency measurements performed with di f ferent bearings according to an embodiment ;

Fig . 6 shows results of sand wear measurements performed with di f ferent bearings according to an embodiment ; and

Fig . 7 shows steps of a method for processing a bearing assembly according to an embodiment .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig . 1 shows di f ferent views of a bearing assembly 10 according to an embodiment . Such a bearing assembly 10 is used in a pump, e . g . , for holding a rotary shaft of the pump, such as e . g . , a centri fugal pump .

One example of a pump according to the invention, having such bearing assembly, is an immersible pump with a shaft and impeller Such type of pump is designed to be submerged in a fluid it is pumping, such as water or other liquids . Such pump comprises several components including the rotary shaft and an impeller :

1 . Shaft : The shaft is a long, cylindrical rod that connects an electric motor of the pump to the impeller . The shaft transmits power from the motor to the impeller, allowing the impeller to rotate and move the fluid . The shaft is may be made of durable materials such as stainless steel or other corrosion-resistant alloys to withstand the conditions of being submerged in liquids .

2 . Impeller : The impeller is a rotating component of the pump that is responsible for creating the flow of the fluid . It may comprise blades or vanes that spin when the pump is in operation, drawing in the fluid and then expelling it through an outlet of the pump .

When the immersible pump is submerged in the fluid, the electric motor, controlled by a pump control unit , powers the shaft , which in turn rotates the impeller . As the impeller spins , it creates a low-pressure area at the center, drawing fluid into the pump through one or more inlets . The fluid is then propelled outwards by the spinning impeller and forced out through the pump outlet.

Such immersible pumps may be used in applications such as wastewater treatment, drainage systems, fountains, and other situations where the pump needs to be submerged in the fluid it is pumping.

The bearing assembly 10 comprises a core ring structure 11, and an outer ring structure 12 which at least partially surrounds the core ring structure on all sides. The core ring structure 11 has a higher mechanical stiffness than the outer ring structure 12.

In particular, the bearing assembly 10 forms a slide bearing or a plain bearing. This means that the bearing assembly 10 may comprise no rolling elements and a part of a rotary shaft which is in contact with the bearing assembly 10 slides over the bearing surface (i.e., the inner surface) of the bearing assembly 10.

Preferably, the bearing assembly is a two-component bearing assembly, i.e., it only comprises the core ring structure 11 and the outer ring structure 12.

The core ring structure 11 can be formed from a stiff plastic material, such as polyethylene terephthalate (PET) .

The outer ring structure 12 can be formed from a soft rubber material, such as liquid silicone rubber (LSR) or nitrile butadiene rubber (NBR) . Preferably, this rubber material is softer than the relatively stiff material of the core ring structure 11. In particular, the soft outer ring structure 12 fully covers the bearing assembly 10 on an inner surface towards the bore, i.e., the bearing surface that is in contact with a rotating object, e.g., a rotary shaft of a pump. In this way, only the soft outer ring structure 12 forms an interface with the rotary shaft which allows for a compensation of slight misalignments without harmful bearing contact and for a prolonged sand wear lifetime compared to standard hard bearings. At the same time, the stiff core ring structure enhances the overall stiffness of the bearing assembly 10, which allows for higher rotating speeds of the shaft without strong deformation of the bearing.

The outer ring structure 12 can be overmolded over the core ring structure 11. As such, the core ring structure 11 can be an inner ring structure that is partially or fully surrounded by the material of the outer ring structure.

As it can be seen in Fig. 1, especially in the cross-sectional view and the isometric view, the core ring structure 11 may comprise several protrusions 13 which are arranged on each axial end of the core ring structure.

These protrusions can facilitate a bonding of the outer ring material around the plastic of the core ring structure 11 during an overmolding process, while the core ring structure 11 is fixated in a mold.

For example, the core ring structure 11 can have a wall thickness between 0.5 and 2 mm. The wall thickness of an inner section of the outer ring structure 12, which ranges from the inner surface (bearing surface) to the core ring structure 11, can be between 0.5 and 2 mm. The overall wall thickness of the outer ring structure 12 (from inner surface to outer surface) can be at least two , at least three or at least four times the wall thickness of the core ring structure 11 . However, di f ferent geometries are possible , depending on the requirements .

Fig . 2 shows isometric views of the isolated outer ring structure 12 ( left ) and core ring structure 11 (middle ) , as well as the bearing assembly 10 ( right ) in an assembled state according to an embodiment .

Both the core ring structure 11 and the outer ring structure can be one-piece components which are each formed from a single material .

The core ring structure 11 can be fully surrounded by the outer ring structure 12 except for small and separate areas , such as the protrusions 13 on the core ring structure 13 . These protrusions 13 can be formed as towers ( or pins ) on each axial side of the core ring structure 11 . Depending on the processing parameters , these protrusions 13 may not be fully covered by the outer ring structure 12 which can have gaps 14 at the respective position of the protrusions 13 .

In addition, or alternatively, small gaps in the outer ring structure 12 may exist on an outer radial surface 15 of the bearing assembly ( opposite to the slide surface ) . This can also be a consequence of the manufacturing process which is , e . g . , an inj ection molding process . For example , the core ring structure is fixated by pins while overmolding it with the material of the outer ring structure . The areas where the pins engage the core ring structure 11 during this process might not be covered by the material of the outer ring structure 12 .

The outer ring structure 12 can encapsulate or enclose the core ring structure 11.

Fig. 3 shows a cross-sectional view of a pump 20 according to an embodiment. The pump 20 can be a centrifugal pump and/or a submersible pump.

The pump 20 comprises a rotary shaft 21 and one or more bearing assemblies 10 as, e.g., shown in Fig. 1 and 2, wherein the bearing assemblies 10 are arranged around the rotary shaft 21.

For instance, the pump 20 comprises several stages, wherein each stage comprises a bearing assembly 10 (in Fig. 3, two pump stages are shown) .

The pump may further comprise at least one impeller 23 which is mounted on the shaft 21. Both the shaft 21 and the impeller 23 can be arranged in a pump housing 24.

The pump 20 can further comprise several seals 22 which are arranged in an area between the impeller 23 and the housing 24.

Using the bearing assembly 10 with the stiff core ring structure 11 and the softer outer ring structure 12 in such a pump 20 overcomes several disadvantages that occur with conventional full soft rubber bearings or hard bearings. For instance, a conventional soft rubber bearing typically has a lower stiffness than the seal 22 between impeller 23 and housing 24 due to the selection of materials. This is typically not an issue when running the pump in clean water at lower speeds of e.g., 2,900 RPM (50Hz) . However, when running the pump at higher speeds, e.g., up to 4,500 RPM (75Hz) , a conventional soft rubber bearing can become too soft to handle the rotational instability forces and the bearing functionality shifts from the bearing to the stiffer seal (s) 22. This can, in turn, increase frictional losses and enhance sand wear on the impeller 23 due to particles in the fluid. A conventional hard bearing could solve the shifting bearing functionality. However, a hard bearing has inferior interface properties with the steel shaft 21.

The two-component bearing assembly 10 combines the advantages of conventional soft and hard bearings. In particular, the soft outer ring structure 12, which forms the interface with the pump shaft 21, has good sand handling properties and at the same time allows handling the long and complex tolerance chain that exists in pumps with a plurality of stages. At the same time, the overall stiffness of the bearing assembly 10 is increased significantly (compared to a pure rubber bearing) due to its stiff core ring structure, which keeps the bearing functionality on the bearing-shaft contact interface and prevents impellerseal contact.

The fact that the bearing assembly 10 is more robust could further allow to split the bearing and seal directions in the pump 20 such that they are not both radial, e.g., using an axial seal or a floating seal design.

Furthermore, the enhanced bearing functionality allows driving pumps at higher speeds to increase the flow rate or to use smaller sized pumps for the same flow rate.

Fig. 4 shows resulting force-displacements for different bearing embodiments determined by simulations.

The curve 41 with the lowest stiffness (i.e., strongest displacement at low forces) represents a conventional full LSR bearing. The remaining curves 42 which show much higher stiffnesses represent different two component bearing assemblies

10 as shown in Fig. 1 and 2.

These simulations show that the two component bearing assemblies 10 can be much stiffer than conventional soft rubber bearings. Furthermore, the exact stiffness of the bearing assemblies 10 can be tailored by adjusting their exact geometries (e.g., wall thickness of core ring structure and/or outer ring structure) and/or their exact material compositions.

For instance, the tailoring of stiffness properties means that the bearing stiffness can be conformed to fit the installation in which it is to be used, e.g., to a specific pump or environment. Tailoring the stiffness of the bearing assemblies 10 allows for increasing the stiffness enough to ensure full bearing functionality, whilst still having the benefits of a soft rubber on steel contact interface to a shaft, which is beneficial in terms of sand wear and tolerance handling. This would not be possible with a full rubber molding with similar stiffness characteristics, since the sand handling ability of the material would change.

The bearing assembly 10 can further be scalable to different pump sizes and types, as well as to different demands on tolerances or required stiffnesses.

Figs. 5A-B show results of pump efficiency measurements performed with different bearings according to an embodiment. The measurements shown in the diagram of Fig. 5A were performed at a pump speed of 2,900 RPM and the measurements shown in the diagram of Fig. 5B were performed at a pump speed of 4,500 RPM. Each diagram shows two pump efficiency curves 51, 52 as a function of flow rate. Curve 53 shows the absolute difference between curves 51 and 52 (right y-axis) .

These tests were performed on a submersible pump with the two- component bearing assembly 10 (as shown in Figs. 1 and 2) mounted (curve 52) , and with a conventional soft rubber bearing mounted (curve 51) . The measurements show that the two-component bearing assembly 10 introduces an efficiency increase as compared to a pump with the conventional bearing, in particular at higher pump speeds and flow rates. At 2900 RPM (50Hz) the efficiency gain is not as consistent as it is at 4500 RPM, as shown in Fig. 5A and 5B . At 4500 RPM (75Hz, overspeed) , efficiency gains of upwards of 0.25-0.5% are achieved, as shown in Fig. 5B . This points towards the bearing assembly 10 having a better functionality and hence limiting the contact between the impeller 23 and the seal 22 at higher speed.

Fig. 6 shows results of sand wear measurements performed with different bearings according to an embodiment. The plot shows an efficiency drop over time of the pump running a standard internal sand wear test.

The two curves 61, 62 with slightly higher values were recorded with the two-component bearing assembly 10 mounted, and the two curves 63, 64 with slightly lower values were recorded with a conventional bearing mounted.

These sand wear tests show that the two-component bearing assembly 10 can at least provide the same or even a slightly better sand wear performance as conventional bearings.

Fig. 7 shows steps of a method 70 for processing the bearing assembly 10 according to an embodiment. The method 70 comprises the steps of: providing or forming 71 a core ring structure 11; and forming 72 an outer ring structure 12 around the core ring structure, wherein the outer ring structure at least partially surrounds the core ring structure on all sides; and wherein the core ring structure 11 has a higher mechanical stiffness than the outer ring structure 12.

The method 70 can be used to process any one of the bearing assemblies 10 as shown in Figs. 1 and 2.

The outer ring structure 12 can be formed by overmolding the core ring structure 11 with the material of the outer ring structure 12, e.g., in a two-component molding process. However, alternative processing techniques other than overmolding could be used if they allow for combining different materials for the core ring structure 11 and the outer ring structure 12.

For example, the core ring structure 11 can be first formed in the mold and subsequently overmolded, e.g., by changing the geometry of the form and injecting another material.

The core ring structure 11 can be fixated by several pins which engage the core ring structure 11 on a radial outer surface (i.e., a surface opposite of the slide surface) during the overmolding. For example, this causes the formation of several holes in the outer surface 15 of the outer ring structure 12.

Claims

1. A pump (20) , preferably a submersible pump, comprising: a rotary shaft (21) ; and a bearing assembly (10) arranged around a rotary shaft (21) of the pump (20) , preferably a rotary shaft holding an impeller, the bearing assembly (10) comprising: a core ring structure (11) ; and an outer ring structure (12) which at least partially surrounds the core ring structure (11) on all sides, wherein the core ring structure (11) has a higher mechanical stiffness than the outer ring structure (12) .

2. The pump of claim 1, wherein the core ring structure (11) and the outer ring structure (12) are each formed in one piece from a single material .

3. The pump of claim 1 or 2, wherein the core ring structure (11) comprises a plastic material, in particular a stiff plastic material.

4. The pump of any one of the preceding claims, wherein the outer ring structure (12) comprises a rubber material, in particular a soft rubber material.

5. The pump of any one of the preceding claims, wherein the outer ring structure (12) is overmolded over the core ring structure (11) .

6. The pump of any one of the preceding claims, wherein the outer ring structure (12) encapsulates the core ring structure (11) .

7. The pump of any one of the preceding claims, wherein the core ring structure (11) comprises several protrusions (13) which are arranged axially on each end of the core ring structure (11) .

8. The pump of any one of the preceding claims, wherein the bearing assembly (10) is a slide bearing assembly .

9. A method (70) for processing a bearing assembly (10) , comprising the steps of: providing or forming (71) a core ring structure (11) ; and forming (72) an outer ring structure (12) around the core ring structure (11) , wherein the outer ring structure at least partially surrounds the core ring structure on all sides; and wherein the core ring structure (11) has a higher mechanical stiffness than the outer ring structure (12) .

10. The method (70) of claim 9, wherein the outer ring structure (12) is formed by overmolding the core ring structure (11) with a material of the outer ring structure (12) .

11. The method (70) of claim 10, wherein the core ring structure (11) is fixated by several pins which engage the core ring structure (11) on an outer surface during the overmolding.