RU2778414C1 - Bearing support of a sealed centrifugal pump with a magnetic coupling - Google Patents

Abstract

FIELD: mechanical engineering.

SUBSTANCE: 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. The bearing support of a centrifugal pump with a magnetic coupling consists of a separating cup, a rotor with an impeller, and an external half coupling. The support contains fully ceramic ball bearings, which are produced as standard with a normal radial clearance group, which have reliable fastening and retention from turning the inner rings by means of an elastic bellow spacer coupling with spring-like properties, the required thermal clearance between the bearing rings and the shaft; moreover, the support contains a separate, independent filter for separating abrasive particles from the working fluid, the forced supply of working fluid through ceramic bearings is provided due to the pressure difference between the pressure and suction lines of the pump, the liquid flow out of ceramic rolling bearings is carried out through a slit labyrinth seal into a low pressure zone.

EFFECT: creating a reliable and easy-to-manufacture design of bearing supports with a wet rotor, increasing the efficiency of a pump with a magnetic coupling, increasing the chemical resistance of the supports and their protection from abrasive inclusions using commercially available bearings.

1 cl, 1 dwg

Description

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

Magnetic coupling pumps are a centrifugal pump with torque transmission from the electric motor to the pump unit by means of a magnetic coupling having a dividing screen called a dividing cup. The dividing cup is used for hermetic separation of the pumped working medium (liquid) from the external atmosphere. Pumps of this type are characterized by zero leakage, therefore they belong to the class of hermetically sealed pumps. The rotor with magnets and bearing supports of this type of pumps are located directly in the working pumped medium, lubrication and cooling of such supports is also carried out by the pumped medium. Due to the highly corrosive nature of the pumped medium, the use of metal plain and rolling bearings in these pumps is not recommended. Metal rolling bearings are mainly used in pumps with mechanical, stuffing box and other metal seals, where the bearing chamber is separated from the chamber with the working solution and has its own lubricant.

Plain bearings, in turn, have an almost an order of magnitude higher coefficient of friction compared to rolling bearings, as a result of increased heat generation (cooling problems), a decrease in pump efficiency, and a shorter service life.

And most importantly, the main criterion for pump manufacturers is the possibility of long-term operation of the bearing assembly without destruction under conditions of limited or complete cessation of the supply of the working fluid, the so-called "dry running" mode. Sliding sleeves do not solve this problem, because they can work in this mode for no more than 1.5 minutes, and during this time it is impossible to quickly detect and respond to an unusual situation that has arisen.

It should be further clarified that the subclass "pumps with a magnetic coupling" refers to the general class of hermetically sealed pumps, which includes the subclass "pumps with a" wet rotor "and which have almost the same main components - a separating long nozzle and bearings operating in the pumped medium, but there are no magnets. Therefore, since the rotors of pumps with both a magnetic coupling and a “wet rotor” are equally located in the pumped medium, the problems of these subclasses are the same, which means that the level of the invention under consideration can be extended to the general class - i.e. for all sealed pumps, except for the cryogenic subclass, which have a temperature operating range of pumped liquids from -100 ° C and below and which have their own specific problems different from those considered. Thus the invention extends to pumps with an operating temperature range from -40°C to +250°C.

In addition, the second most important criterion for pump manufacturers is a significant increase in the threshold values for the service life of pumping units. On sleeve bushings, average service lives are up to 8 years, while pumps with a service life of 24 years and more are now required. 24 years can now provide only pumps with insulated bearing chambers and their own lubricating medium with mechanical seals (for example, mechanical seals), with periodic replacement of mechanical seals over the entire service life. In all hermetic pumps, in particular those with a magnetic coupling, the bearing arrangements are not only exposed to aggressive media, but most importantly to abrasive media.

Thus, the following issues need to be addressed:

1. Significantly reduce friction and heat generation in bearings;

2. provide the possibility of long-term operation of the pump in the "dry running" mode;

3. ensure good resistance of bearing supports to aggressive media;

4. ensure good resistance of bearings to abrasive media;

5. to ensure reliable, long-term operation with service life of pumping units up to 24 years.

Known "Centrifugal pump with a magnetic coupling" EP 1329638 A1 from 23.07-2003, which, according to the Claims, has a vertical arrangement of both the housing and the axis with the impeller. Here, the axle, with two rolling bearings fixed on it through the spacer sleeve 15, already has a fixed fastening on the tide in the inlet pipe, and the outer rings of the bearings pressed into the outer sleeve 16, and that, in turn, into the rotor housing, having one piece with the impeller and magnets spaced as diametrically as possible on the periphery of the impeller. The separating sleeve here is almost flat, it has a small cylindrical section separating the inner magnetic half-coupling and the outer half-coupling. The bearings here are rolling, ball ceramic (the type of ceramic is not specified), at least 1 piece, having a slotted closure of the internal inter-bearing cavity, then two ball or one ball, and the other roller ceramic bearings are mentioned, pulled together by a spacer sleeve 15 along the inner rings, as option is allowed instead of bearings - outer sleeve 16 with sprayed ceramic raceways and filling with ceramic balls, and more options for fixing the outer sleeve 16 are indicated, the maximum unity of the coefficients of linear expansion of the sleeve 15 and sleeve 16 is also indicated.

The proposed design also improves the operation of the bearing assembly in comparison with the plain bearings and reduces friction in comparison with them and can already work longer in dry running mode, but still not as long as it is necessary due to the unfavorable operation of ball bearings in vertical shaft arrangement when the main load is axial (for ball bearings, radial load is much more preferable than axial).

In addition, the slotted closure on one side and fully open on the other does not protect the bearings from abrasive media and, as a result, does not reduce friction and heat generation in the bearings. Does not provide resistance of bearing supports to abrasive media.

Additionally, there is still the same design flaw - the fixing of ceramic bearing rings through rigid spacers 15 and 16, where the difference in linear expansions of ceramics and metal increases the stresses in the ceramics and thereby further reduces the reliability of the support.

Known "Magnetic pump" CN 103470514 B dated 02.03-2016, which, according to the claims, has a horizontal arrangement of the Rotor, has an outer casing with a separating cylindrical cup 2 separating the inner and outer magnetic coupling halves, also has a fixed axis 5, which has a two-bearing fastening in the pump casing through intermediate bushings 11 and 12, the rotor is a single housing with an impeller and an inner half-coupling, with two rolling bearings installed in it with rotating outer rings, which have sealing covers between the inner and outer rings to protect the rolling elements. As an option, the console location of the Rotor is also shown, i.e. already with a rotating shaft and inner races of bearings pressed on it that do not have a spacer and other bushings, with the impeller and the body of the internal magnetic coupling half fixed separately. Bearings here can be ball, roller or needle bearings, with rolling elements, outer and inner rings made of silicon carbide ceramics baked without pressure, sealing covers made of polytetrafluoroethylene.

The proposed design also improves the operation of the bearing assembly in comparison with sliding bearings and reduces friction compared to them and can already work longer in the “dry friction” mode, but does not solve the resistance of bearing bearings to abrasive media.

Sintered Silicon Carbide has unsatisfactory impact characteristics in relation to, for example, Silicon Nitride or Zirconium Oxide, which reduces the reliability of the bearing support and the main disadvantage is the lack of protection of the bearings from the abrasive medium in the pumped liquid.

Closing the bearing cavities with polytetrafluoroethylene caps does not solve the problem of abrasive getting into the bearings, but it sharply worsens the pumping, lubrication and cooling of the bearings by the pumped liquid.

In addition, in the version with the cantilever arrangement of the impeller, the inner bearing rings are kept from turning only by a certain fit of the inner ceramic ring on the steel shaft, which, during thermal expansion in the operating range from -40°С to +250°С, unambiguously leads to an unacceptable increase in stresses in ceramics and bearing failure.

Known "Self-lubricating bearing for use in cryogenic liquids" (Patent US 6558139 B2 06.05.2003 Application US 2002/0094286 A1 18.07.2002 items 12-17), taken as a prototype, which can only be installed according to the Claims of the invention, item 12 in centrifugal cryogenic pumps with a magnetic coupling at a very low temperature below -100 ° C and consists of ball bearings, in which, according to paragraphs 12-17, the balls are made of both ceramic (from a special type of ceramic resistant to very low temperatures) - and steel, hardened, and the surface of the balls must be specially prepared - have microporosity to hold microparticles of solid lubricant, the outer and inner rings of the bearing are made only of hardened stainless steel 440, the race to hold the balls is made of a polymer material with a self-lubricating effect, in particular from polyetherketone (PEEK) in order to get PEEK microparticles as a solid type of lubricant to the surface balls, at low temperatures, in addition, the pump housing 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 shirt for circulation or blowing with special liquids or hot air to eliminate condensation and freezing of the separating cup of the housing and the housing of the external magnetic coupling. In addition, there is a liquid supply in two ways from the high-pressure zone (through special "choke plugs") to the impeller suction zone - one part of the flow goes through the bearings, the other through the hollow shaft. In addition, the magnets have a way of fixing by the method of additional crimping with a steel casing when the temperature drops, and there is a frequency drive for speed control. The impeller is mounted on a rotating shaft, and at the opposite end of the shaft there is a magnetic half-coupling, at the bearing supports, the outer rings are fixedly fixed in the housing, and the inner rings are compressed through a spacer sleeve, which has the same linear expansion coefficient as that of the housing and bearing rings. The number of bearings is not specified here (there is only the phrase "multiple rolling elements").

The proposed design, although it improves the operation of the bearing assembly in comparison with sliding bearings and reduces friction compared to them, it still cannot work in dry running mode for a long time due to the limited resource of ceramic rolling elements (balls) on steel rings, since lubricating properties for The count of microparticles with a PEEK cage is clearly insufficient due to the limited volume of these microparticles and the porosity of the balls, and as a result of increased friction and, accordingly, heat release, which is compensated while there is cryogenic liquid and increases sharply in the absence of it in non-standard modes. It is only ceramic balls on ceramic running rings with a minimum porosity of ceramic balls that can work for a long time in dry running mode, as they have the lowest coefficient of friction and maximum resistance to abrasion against steel ball bearings.

In addition, the problem of good resistance to aggressive media has not been solved due to media to which there is poor resistance of bearing rings made of steel 440 and if the pump housing can be varied according to the materials made, then the specific design of the rings limits the scope of this pump. Well, the main drawback is the absence of any protection against exposure to abrasive media - the bearings are completely open to the pumped liquid and, as a result, the resistance of the bearing supports to the effects of abrasive media and, accordingly, long-term and reliable operation of pumping units are not ensured. There is a design flaw in fixing the inner bearing rings - through a rigid separating sleeve, where it is necessary to strictly observe the equality of the coefficients of linear expansion of materials, which further limits the use of the pump in terms of resistance to aggressive media, complicates and increases the cost of the design, and still does not guarantee excessive wedging in case of non-compliance with dimensional tolerances. force on ceramic rolling elements, which reduces the reliability of the assembly as a whole.

The special design of the bearings increases the cost of the overall design.

This design of the pump is partially justified only for cryogenic pumps for application temperatures below -100°C, where there is a distinctive application specificity, in contrast to sealed pumps with a magnetic coupling operating in the temperature range from -40°C to +250°C.

Therefore, it became necessary not only to replace plain bearings with another type of bearings that can operate for hours in dry friction mode without repair, but most importantly, not to be afraid of solid abrasive inclusions in the working fluid and have very low friction losses.

Such supports with the above set of properties can only be ceramic rolling bearings. It should be further clarified that under the Ceramic bearing in the invention under consideration is understood, firstly, completely ceramic (rings and balls and a separator - firstly from the same, and secondly from solid ceramics, for example, Silicon Nitride, Zirconium Oxide), and secondly, and more importantly, the use of standard, commercially available ceramic bearings, which greatly simplifies and reduces the cost of implementing this invention. Silicon carbide Silicon ceramics are inferior to the two ceramics mentioned above in terms of impact strength and corrosion resistance and linear expansion coefficients.

A ceramic rolling bearing can operate without lubrication for a long time, has a lower coefficient of friction compared to a ceramic plain bearing, has better resistance to small abrasive impurities in the working fluid due to the greater hardness of ceramics compared to hardened bearing steel in metal rolling bearings and, as a result, greater resource and lower noise level during operation. But as a rule, abrasive impurities are present in working fluids in a very significant amount, but even if there is a minimum amount of them, in order to achieve a bearing service life of 24 and 32 years, it is necessary to supply a well-cleaned liquid to the bearing.

The technical problem to be solved by the proposed solution is to create a reliable and easy-to-manufacture design of bearing supports with a wet rotor, increase the efficiency of a pump with a magnetic coupling, increase the chemical resistance of the supports and protect them from abrasive inclusions using commercially available bearings.

The task is achieved in that the bearing support of a centrifugal pump with a magnetic coupling, consisting of a separating cup, a rotor with an impeller, an outer half-coupling, is characterized in that the support contains all-ceramic ball bearings, standardly produced with a normal radial clearance group, having reliable fastening and keeping the internal rings from turning by means of an elastic bellows-type spacer sleeve with springy properties, the required thermal gap between the rings and the shaft; moreover, the support contains a separate, independent filter for separating abrasive particles from the working fluid, the forced supply of the working fluid through the ceramic bearings is provided due to the pressure difference between the pressure and suction lines of the pump, the fluid flow exits from the ceramic rolling bearings through a slotted labyrinth seal into the low pressure zone .

Figure 1 is a diagram of the bearing support of a sealed centrifugal pump with a magnetic coupling and a filtration system.

Bearing support of a sealed centrifugal pump with a magnetic coupling, consisting of an inlet flange 1, an outer casing 2 with an outlet flange 3; a rotor consisting of an impeller 4 fixed on a movable shaft 5 and coupled to the shaft with profile projections for the impeller and secured with a nut 6, an internal magnetic half-coupling body 7 having a permanent connection with the shaft and with internal magnets 8 placed in it in a sealed way, bearing supports placed motionlessly in the housing 2 in the form of two or more Ceramic ball bearings 9, having between them an elastic spacer sleeve 10 along the shaft; an outer magnetic coupling half 11 fixed on the motor shaft 12 and separated from the inner cavity of the pump and the inner half-coupling by a non-metallic cup 13, and consisting of a hub 14 with magnets 15 placed in it; adapter-case 16 connecting the pump unit and the electric motor 17; bearing support filter 18, consisting of a housing 19, which can be separated from the pump housing 2 for the purpose of inspection or replacement, with a replaceable or reusable filter element 20 installed in it, made of corrosion-resistant meshes or pressed from porous metal or ceramic powders, a removable cover 21 with seal 22, pressure sensor 23, signaling a decrease in pressure below the threshold value when the filter element 20 is clogged and turning off the pump, located in the filter chamber for supplying a clean solution, channels made in the pump housing 2: supplying d1 from the high pressure zone Pin untreated working fluid to the inlet to the filter element, outgoing d2, supplying the purified working fluid to the bearings 9 by pumping through the bearings and exiting the fluid through the labyrinth-slot seal 24 and then through the holes d3 into the low pressure zone of the suction of the pump Pvs at the impeller inlet, with the flow rate through the supports, depending from pressure drop ny Rvh and Rvs and hydraulic resistance of the entire line.

Due to the constant unidirectional flow of the cleaned working fluid through the filter and further along a certain path through the bearings, the ingress of abrasive into the supports, incl. and in pump stop mode - due to the special design of the hydraulic path.

The design of the unit is simple, lubrication is carried out by the pumped medium. Due to the high hardness of the rings and rolling elements, the bearing itself is resistant to small abrasive inclusions of the pumped medium, but this undoubtedly affects the reduction of its service life. The system: Bearing Support + Filter allows the bearing to operate under ideal conditions with clean coolant and a real possibility of reaching a service life of 24 years or more. Due to the lower heat emissions, even in relation to a metal rolling bearing in dry running mode, the bearing unit can operate for a long time without noticeable overheating or wear. But in the case of the 3 patents considered, due to the lack of protection against abrasive, after the absence of liquid, abrasive particles remain in the rings, which drastically reduce the operation of the bearing in the “dry running” mode. The design under consideration is free from this disadvantage and in the dry running mode of the rolling element it works on clean treadmills.

In the course of experimental work, the applicant obtained a positive result both from the introduction of ceramic rolling bearings in chemical pumps with an increase in efficiency by 11% and operation in the dry friction mode for an unlimited time, and due to the introduction of a filtration system and repeated periodic increase in the time for reliability.

This type of “bearing support with filter element” system can also be used for pumps with a “wet rotor-stator” (the rotor and stator of the electric motor are separated by a separating screen).

Claims (1)

Bearing support of a sealed centrifugal pump with a magnetic coupling, consisting of a separating cup, a rotor with an impeller, an outer half-coupling, characterized in that the support contains all-ceramic ball bearings that are securely fastened and kept from turning the inner rings by means of an elastic bellows-type spacer sleeve, the necessary thermal gap between the rings and the shaft, and the support contains a separate, independent filter for separating abrasive particles from the working fluid, the forced supply of the working fluid through the ceramic bearings is provided due to the pressure difference between the pressure and suction lines of the pump, the fluid flow exits from the ceramic rolling bearings is carried out through a slotted labyrinth seal into the zone of low pressure.

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