Long-life bearing support for sealed centrifugal pump with magnetic coupling

Abstract

FIELD: mechanical engineering.SUBSTANCE: invention concerns the design of bearing supports for a class of sealed pumps, in particular for a subclass of pumps with a magnetic coupling and more specifically for pumps with fully ceramic rolling bearings having a built-in filter for cleaning the working fluid entering the supports. For this purpose, the bearing support of a sealed centrifugal cantilever pump with a magnetic coupling consists of a separating cup, a rotor with an impeller mounted on fully ceramic ball bearings, an outer half coupling, a built-in filter for lubricating the bearings with purified working fluid; according to the invention, the front bearing is moved beyond the plane of the impeller in such a way that the center of gravity of the impeller lies between the supports and condition A≥2B is maintained, where A is the distance between the impeller's centre of gravity and the centre of the front bearing, B is the bearing width; on the rear plane of the impeller there are special oblique blades, the contour of which coincides with the main working blades and creates additional vacuum behind the rear plane of the impeller and prevents the flow of impurified working fluid to the front bearing.EFFECT: while maintaining the reliable and simple design of the above-mentioned bearing supports and while maintaining the advantages of the cantilever impeller fastening scheme, the durability of the bearing supports is increased by using the advantages of the double-bearing arrangement of bearings in the cantilever scheme and additional conditions are created that guarantee that contaminated working fluid does not enter the front bearing during transient operating modes of the pump, through which the purified liquid is discharged into the contaminated zone.1 cl, 3 dwg

Description

[0001] The invention relates to mechanical engineering and concerns the design of bearing supports for a class of sealed pumps, in particular for a subclass of pumps with a magnetic coupling.

[0002] Magnetic coupling pumps are centrifugal pumps that transmit torque from the electric motor to the pumping unit via a magnetic coupling with a separating screen called a canister. The canister serves to hermetically separate the pumped working fluid (liquid) from the outside atmosphere. Pumps of this type are characterized by zero leakage, therefore they are classified as hermetically sealed pumps. The rotor with magnets and bearing supports of this type of pump are located directly in the pumped working fluid; lubrication and cooling of these supports are also provided by the pumped fluid. Due to the highly corrosive nature of the pumped fluid, the use of metal plain and rolling bearings in these pumps is not recommended.Metal rolling bearings are used mainly in pumps with mechanical, gland and other metal seals, where the bearing chamber is separated from the chamber with the working solution and has its own lubricant.

[0003] Plain bearings, in turn, have an almost order of magnitude higher coefficient of friction compared to rolling bearings, which results in increased heat generation (cooling problems), reduced pump efficiency, and a shorter service life.

[0004] And most importantly, the main criterion for pump manufacturers is the ability of the bearing assembly to operate for extended periods without failure under conditions of limited or complete interruption of the working fluid supply, the so-called "dry-running" mode. Sliding bushings do not solve this problem because they can only operate for 1.5 minutes in this mode, making it impossible to promptly detect and respond to any abnormal situation.

[0005] Therefore, pumps with ceramic rolling bearings have recently appeared, which can already operate in the pumped medium and at the same time retain all the advantages compared to plain bearings (see Patent RU 2 778 114 C1 08 / 18 / 2022 Application RU 2021129791 , 12.10.2021).

[0006] Therefore, further consideration of the problems will be carried out only among sealed pumps with a magnetic coupling and only on ceramic rolling bearings.

[0007] But despite all this, hermetically sealed magnetic coupling pumps still have one problem. Based on the rotor support design, magnetic coupling pumps are divided into two-bearing designs (see Fig. 1) and single-cantilever designs (see Fig. 2). These designs comprise: pump casing 1, pump flange 9, separating canister 2, rotor shaft 3, internal magnetic coupling half 4, external magnetic coupling half 5, and ceramic rolling bearing assemblies 6 and 7, operating in the pumped medium.

[0008] In the two-support design (see Fig. 1), the rotor shaft 3 passes through the impeller and rests with its front end on the bearing support 7, fixed in the input flange 9. For this, the flange has a rather complex design with a partition for the bearing 7 and milled special channels E for the passage of the working fluid.

[0009] Thus, the two-support design has the peculiarity of bearing supports 6 and 7 located on different sides of the impeller 8, which allows for minimal radial vibration F of the impeller 8 due to the location of the impeller’s center of gravity between the supports.

[0010] The advantage of this design is reduced radial vibration F of the impeller due to the increased rigidity of the overall support system, as the impeller's center of gravity is located between the bearings. This positively impacts the longevity of the bearing assemblies.

[0011] The serious disadvantages of this scheme are:

[0012] -increased misalignment or increased tilt of rotor shaft 3 due to a large chain of errors (a longer path of the dimensional chain) negatively affecting the service life of bearing supports due to incorrect rotation of the balls along the rolling raceways;

[0013] - a more complex design of the input flange 9 and shaft 3 and the entire pump in general, which negatively affects its cost;

[0014] -increased hydraulic losses of the suction tract G due to the limited permissible flow areas of the windows E with an unchanged outer diameter of the impeller, which negatively affects the pressure-flow characteristics of the pump;

[0015] - the need to make the front bearing 7 extremely small in size compared to the rear bearing 6, which also negatively affects the durability of the front bearing support;

[0016] -less protection of the front bearing 7 from the negative influence of abrasive and dirt particles in the pumped liquid, in contrast to the rear, which also negatively affects the durability of the front bearing support;

[0017] -disassembling the pump unit is more difficult due to the presence of a front bearing in the input flange, and a greater likelihood of damage, which negatively affects performance.

[0018] In the classic cantilever (mono-cantilever) design (see Fig. 2), both bearings 6 and 7 are located behind the impeller. This results in shaft 3 being shorter and simpler, and the bearings can now be made the same size. This design is considered preferable by pump manufacturers and pump operators because it eliminates all the disadvantages inherent in the two-bearing design, and these disadvantages are actually its advantages. It is especially worth noting that pumps with a cantilever impeller, compared to two-bearing designs, have better pressure-flow characteristics, are easy to disassemble and assemble, are simpler to operate, have longer bearing life, and are less expensive to manufacture. However, they also have their drawbacks, specifically one drawback: lower rigidity of the support system and, as a result, increased radial vibration F of the impeller, becauseThe wheel's center of gravity is located cantilevered relative to the supports, which negatively affects the durability of the front bearing 7 in particular and leads to an increase in the vibration level in the pump unit, which in turn reduces the performance of the pump unit.

[0019] Now, looking at the situation as a whole, the following conclusions can be drawn. While the two-bearing design has more disadvantages than the cantilever design, the lower radial vibration of the impeller still cannot outweigh the more serious drawbacks that negatively impact the service life of the bearings, especially the front bearing 7.

[0020] In turn, the factor of increased radial vibration F of the cantilever design also cannot outweigh the presence of more positive and more significant advantages in terms of the durability of the supports, and as a result, it turns out that the cantilever design has a higher resulting service life of the bearing supports compared to the two-support design.

[0021] Therefore, the use of a cantilever design in sealed pumps with magnetic couplings is preferable. However, due to the aforementioned negative factor, the cantilever design does not fully utilize all the potential for further increasing the durability of bearing supports and reducing vibration of the entire pump unit. Therefore, it is necessary to implement a cantilever design that not only retains its advantages but also incorporates the advantages ("pluses") of a double-bearing design.

[0022] Therefore, the following problems need to be solved:

[0023] 1. Significantly reduce the radial vibration of the impeller

[0024] 2. significantly increase the durability of bearing supports by increasing the rigidity of the rotor support system;

[0025] 3. Prevent as much as possible the ingress of uncleaned working fluid into ceramic rolling bearing supports.

[0026] A "Magnetic Pump" CN 103470514 B from 02.03.2016 is known, which, according to the claims, has a horizontal rotor arrangement, has an outer casing with a separating cylindrical cup 2 separating the inner and outer magnetic half couplings, and also has a fixed axis 5 having a double-support fastening in the pump casing through intermediate bushings 11 and 12. The rotor is a single casing with an impeller and an inner half coupling, with two rolling bearings installed therein with rotating outer rings, which have sealing covers between the inner and outer rings to protect the rolling elements. A cantilever rotor arrangement is also shown as an option, i.e. already with a rotating shaft and inner bearing rings pressed onto it, without spacer or other bushings, with separately secured impeller and housing of the internal magnetic half coupling.The bearings here can be ball, roller or needle, with rolling elements, outer and inner rings made of pressure-free sintered silicon carbide ceramics, and sealing covers made of polytetrafluoroethylene.

[0027] The proposed design in the cantilever version, although free from all the disadvantages of the two-support design and has ceramic rolling bearings, still has insufficient reliability of the bearing unit (namely the front bearing) due to the insufficient rigidity of the entire support unit and due to the lubrication of the bearings with uncleaned working fluid.

[0028] A “Self-lubricating bearing for use in cryogenic liquids” is known (Patent US 6558139 B2 06.05.2003 Application US 2002 / 0094286 A1 18.07.2002 pp. 12-17), which can, according to the Claim of the Invention, p. 12, be installed only in centrifugal cryogenic pumps with a magnetic coupling at very low temperatures below -100 ° C, and consists of ball bearing supports which, according to p.12 - 17 balls are made of both ceramic (a special type of ceramic resistant to very low temperatures) and hardened steel, and the surface of the balls must be specially prepared - have micro porosity to retain microparticles of solid lubricant, the outer and inner rings of the bearing are made only of hardened stainless steel 440, the cage for holding the balls is made of a polymer material with a self-lubricating effect, in particular, polyester ketone (PEEK) in order to get microparticles of PEEK as a solid type of lubricant on the surface of the balls, at low temperatures, in addition, the pump body contains a material with a coefficient of linear expansion as close as possible to the rings of the balls, the pump additionally has an additional jacket for circulation or purging with special liquids or hot air to eliminate condensation and freezing of the separating cup of the body and the body of the outer magnetic clutch.Additionally, there are two paths for fluid supply from the high-pressure zone (via special "throttle plugs") to the impeller's suction zone: one part of the flow goes through the bearings, the other through the hollow shaft. Additionally, the magnets are secured by additional compression with a steel casing when the temperature drops, and a frequency drive is used to regulate the speed. The impeller is mounted on a rotating shaft, and at the opposite end of the shaft is a magnetic coupling. The outer rings of the bearing assemblies are fixed in the housing, while the inner rings are compressed through a spacer sleeve, which has a coefficient of linear expansion identical to that of the housing and bearing rings. The number of bearings is not specified here (only the phrase "multiple rolling elements").

[0029] The proposed design, although it uses ceramic rolling elements and is designed using a cantilevered design, suffers from the same drawbacks noted in the previously reviewed patent. Another drawback remains: the bearing assemblies operate in untreated liquid.

[0030] In addition, the problem of good resistance to aggressive environments has not been solved due to the environments to which bearing rings made of 440 steel have poor resistance.

[0031] There is a design flaw in the fastening of the inner bearing rings - through a rigid spacer sleeve, where it is necessary to strictly maintain the equality of the coefficients of linear expansion of the materials, which further limits the use of the pump in terms of resistance to aggressive environments, complicates and increases the cost of the design and still does not guarantee excessive wedging force on the ceramic rolling elements in the event of non-compliance with dimensional tolerances, which reduces the reliability of the entire unit.

[0032] Special design of bearings increases the cost of the overall design.

[0033] This pump design is partially justified only for cryogenic pumps for operating temperatures below -100°C, where there are specific application specifics, unlike sealed pumps with a magnetic coupling operating in the temperature range from -40°C to + 250°C.

[0034] Known "Bearing support of a sealed centrifugal pump with a magnetic clutch" (Patent RU 2 778 114 C1 08 / 18 / 2022 Application RU 2021129791, October 12, 2021), adopted as a prototype, which also implements a cantilever horizontal arrangement of the impeller 4 relative to the bearing supports 9 in the pump casing 2. There is also a separate suction flange 1, free of any partitions (unlike the two-support design), an internal 7 and external 14 coupling halves, and a separating cup 13. This patented solution already has an independent system for pumping purified working fluid through the bearing supports due to the use of a built-in (modular) filter 18, where the fluid is pumped through the bearing supports in only one specific direction - from the high-pressure zone Pвх to the low-pressure zone Рвс. It also has a labyrinth seal 24, which prevents unpurified working fluid from entering the bearings when the pump starts or during various hydraulic pulsations.

[0035] This solution already eliminates one of the two drawbacks mentioned above for the cantilever system: the bearings are flushed with purified fluid, which undoubtedly has a positive effect on increasing the service life of the bearing supports. Another solution—the inner bearing rings are secured to shaft 5 by a bellows-type bushing 10—also has a positive effect on bearing service life.

[0036] However, the main drawback of this patent remains unresolved: increased load on the front bearing, insufficient rotor support rigidity, and increased radial vibration of the impeller. An additional drawback of this solution is the insufficient protection of the front bearing 9 from the ingress (or backwash) of untreated working fluid during transient pump operation.

[0037] The technical objective of the proposed solution is to eliminate the main drawback of sealed magnetic coupling pumps with ceramic bearings, designed using a cantilever design, and, as a result, to further increase the durability of the bearing supports. An additional objective is to further increase the protection of the front bearing from the ingress of untreated hydraulic fluid during transient pump operating conditions.

[0038] The stated objective is achieved by the following:

[0039] 1. The only advantage of the two-support design, i.e. the location of the impeller's center of gravity between the supports, must be implemented (applied) in the cantilever design, thus eliminating its only drawback.

[0040] 2. Additionally, it is necessary to ensure that contaminants are removed from the rear surface of the impeller to ensure that they do not even enter the bearing labyrinths during pump transients, which will also positively impact the bearing life.

[0041] To do this:

[0042] 1. A ceramic rolling bearing support of a sealed centrifugal pump with a magnetic coupling (see Fig. 3), consisting of a separating cup, a rotor with an impeller mounted cantilevered on fully ceramic ball bearings, an outer half coupling, a built-in filter for lubricating the bearings with purified working fluid, is distinguished in that the front bearing 21 is moved beyond the plane of the impeller in such a way that the center of gravity of the impeller lies between the supports and the condition A≥2B is maintained, where A is the distance between the center of gravity of the impeller and the center of the front bearing, B is the width of the bearing. Thus, the rigidity of the rotor support system now corresponds to the rigidity of a two-support system;

[0043] 2. An additional difference is the presence of special oblique blades 22 on the rear plane of the impeller, whose contour matches the main working blades and creates additional vacuum behind the rear plane of the impeller and prevents the flow of unpurified working fluid to the front bearing 21.

[0044] Fig. 3 shows a diagram of a ceramic rolling bearing support of a sealed centrifugal pump with a magnetic clutch and a filtration system with an increased bearing service life.

[0045] A bearing support for a sealed centrifugal pump with a magnetic coupling, consisting of an input flange 1, an outer casing 2 with an output flange 3; a rotor consisting of an impeller 4, fixed in a cantilever manner on a movable shaft 5 and mated with the shaft by profile projections under the impeller and secured with a nut 6, a casing of an internal magnetic half coupling 7, having an inseparable connection with the shaft and with internal magnets 8 placed in it in a sealed manner, bearing supports placed motionlessly in the casing 2 in the form of two or more ceramic ball bearings 9 and 21, having an elastic spacer sleeve 10 between them along the shaft; an external magnetic half coupling 11 secured to the shaft of an electric motor 12 and separated from the internal cavity of the pump and the internal half coupling by a non-metallic cup 13, and consisting of a hub 14 with magnets 15 placed in it; an adapter-housing 16 connecting the pump unit and the electric motor 17;a bearing support filter 19, with a replaceable or reusable filter element 20 installed in it, a pressure sensor 23, signaling a drop in pressure below a threshold value when the filter element 20 is clogged and turning off the pump, channels made in the pump body 2: supplying untreated working fluid from the high-pressure zone Pвх to the inlet of the filter element, and then after the filter element supplying purified working fluid to bearings 9 and 21, pumping through the bearings and the liquid exiting through the labyrinth-slot seal 24 and then through openings 25 into the low-pressure zone of the pump suction Pвс at the inlet of the impeller, with the flow rate through the supports depending on the pressure difference Pвых and Pвс and the hydraulic resistance of the entire line.

[0046] Due to the constant unidirectional flow of the cleaned working fluid through the filter and then along a specific path through the bearings, the ingress of abrasive into the bearings is excluded, including in the pump stop mode, thanks to the special design of the hydraulic tract.

[0047] The design of the unit is simple, lubrication is carried out by the pumped medium.

[0048] In the proposed design, the front bearing support 21, compared to the prototype, is extended as far forward as possible (as far as the suction flange design allows) into the impeller hub, ensuring that the impeller's center of gravity (C.G.) lies between the supports and that the condition A≥2B is met, where B is the bearing ring width. The condition A≥2B was determined experimentally and confirmed by pump test results, resulting in a 42% increase in bearing support service life compared to the prototype.

[0049] Furthermore, this design includes special low-height oblique vanes 22 located on the rear plane of the impeller. This solution creates a low-pressure zone behind the impeller, significantly relieving the rotor of the axial force caused by the suction force at the impeller inlet, thereby further relieving the ball bearings of axial force (the axial force on the rotor in pumps due to the suction force is always quite significant). Additionally, the impeller guarantees protection of the front bearing 21 from the ingress of untreated liquid during transient pump conditions, further increasing the service life of the rotor bearing assemblies.

[0050] As a result, the combined solution (support offset 21 + oblique blades on the rear plane of the impeller) is capable of increasing the service life of bearing supports by over 42% compared to the prototype.

Claims

A bearing support for a sealed centrifugal pump with a magnetic coupling, consisting of a separating cup, a rotor with an impeller mounted in a cantilever manner on fully ceramic ball bearings, an outer half coupling, a built-in filter for lubricating the bearings with purified working fluid, characterized in that the front bearing is located beyond the plane of the impeller in such a way that the center of gravity of the impeller lies between the supports and the condition A≥2B is maintained, where A is the distance between the center of gravity of the impeller and the center of the front bearing, B is the width of the bearing, on the rear plane of the impeller there are special oblique blades, the contour of which coincides with the main working blades and creates an additional vacuum behind the rear plane of the impeller and prevents the flow of unpurified working fluid to the front bearing.

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