Low-speed combined turbomolecular vacuum pump

Abstract

This utility model relates to turbomolecular vacuum pumps. The proposed low-speed combined turbomolecular vacuum pump can be used in various process installations for creating and maintaining vacuum, such as in the aerospace, petrochemical, food, optical, and electronics industries, as well as in various scientific, research, and laboratory installations that operate under vacuum conditions. Low-speed pumps are used in helium leak detectors. The technical result of the utility model is to improve the pumping characteristics of the pump while maintaining the same level as existing analogs or reducing its weight and dimensions. The low-speed combined turbomolecular vacuum pump is oil-free and is used in helium leak detectors. 1 fig.

Description

[0001] Technical field

[0002] This utility model relates to vacuum technology, vacuum-generating equipment, and turbomolecular vacuum pumps. The proposed low-speed, combined turbomolecular vacuum pump can be used in various process installations to create and maintain a vacuum.

[0003] Technology Level

[0004] A prior art analogue of the combined turbomolecular vacuum pump is a high-vacuum hybrid pump (RU 2561514, August 27, 2015). It is a combined high-speed axial turbine with an active viscous stage, implemented in the form of a four-start rectangular threaded groove with a variable cross-section, located on the inner surface of the rotor. The pump has a cylindrical body consisting of three parts, inside which the flow path is located. The flow path consists of a turbomolecular stage and a viscous stage, implemented in the form of a four-start rectangular threaded groove with a variable cross-section.

[0005] The closest analogue of a combined turbomolecular vacuum pump is known from the prior art - a single-flow four-stage turbomolecular pump (RU 2560133, 20.08.2015). The flow path of the turbomolecular vacuum pump includes four sequentially following stages: one turbomolecular, one transitional end molecular and two, the first and second, concentrically located opposite each other cylindrical molecular stages. The flat end surface of the stator is made with grooves formed by arcs of circles with centers uniformly spaced on the central circumference and with an angle of inclination counter to the rotation of the rotor and facing with an axial working gap towards the end surface of the last rotor disk of the turbomolecular stage with blades located on the periphery at an angle of inclination in the direction of rotation of the shaft. The inter-blade channels of the blades are optically closed and form a transitional end molecular step.Concentrically located opposite each other, equidistant cylindrical sections between the inner surface with multi-start helical grooves of the stator and the outer surface of the hollow cylinder of the rotor, as well as between the inner surface of the hollow cylinder of the rotor and the outer surface of the multi-start grooves of the cylindrical protrusion of the middle housing form the first and second cylindrical molecular stages of the flow part of the pump, respectively.

[0006] Unlike the above analogs, whose designs use cylindrical molecular stages, the flow section of the low-speed combined turbomolecular vacuum pump uses only disc molecular stages with alternating smooth rotating discs and stationary discs on which spiral channels are cut.

[0007] The main disadvantages of the closest analogues considered are the high ultimate residual pressure (about 10 -6Pa) and low pump compression ratio.

[0008] Disclosure of Utility Model

[0009] The technical result of the utility model is to increase the compression ratio of the pump and reduce the maximum residual pressure by selecting the optimal composition of the flow part of the pump and each of its stages.

[0010] The above technical result is achieved by a low-speed combined turbomolecular vacuum pump, including a shaft mounted in bearing assemblies and located in a composite casing consisting of an upper casing and a lower casing on which a rotor is fixed, the shaft is driven by an electric motor, the flow part of the pump includes molecular stages, characterized in that the turbomolecular stage consists of alternating nine rotor working blade wheels and eight stator working blade wheels, on the first two blade wheels the angle of inclination of the blades to the plane of the wheel is 35 °, on the next three - 30 °, on the next three - 25 °, on the next three - 20 ° and on the last six wheels 15 °; the rotor of the pump is made monolithic and includes nine working blade wheels of the turbomolecular stage and three smooth disks of the molecular stage;The stator working blade wheels of the turbomolecular stage are made split, between them there are spacer rings, the stator working blade wheels and spacer rings are pressed from below by an adjusting ring; the flow part contains six molecular stages, consisting of three alternating stationary stator and three rotating rotor disks, wherein the movable rotor disks are made smooth, on the stationary stator disks on both sides there are cut spiral channels; the value of all axial clearances in the molecular stage is constant no more than 0.5 mm; the first molecular stage consists of the last working blade wheel of the turbomolecular stage and the first stator disk of the molecular stage; on each stator disk of the molecular stage there are 5 channels on each side.

[0011] Implementation of a utility model

[0012] The essence of the utility model is explained in Fig. 1, which shows a longitudinal section of a combined turbomolecular vacuum pump.

[0013] The flow part of the low-speed turbomolecular vacuum pump includes a turbomolecular stage and six molecular stages arranged in series.

[0014] The low-speed combined turbomolecular vacuum pump consists of a shaft 1 mounted in bearing assemblies 2 and 3, located in housings 4 and 5, on which a rotor 6 is fixed. The shaft is driven by an electric motor 7. The rotor of the pump 6 with working blade wheels 25-32.15 of the turbomolecular stage 35 and smooth disks of the molecular stage 8, 9, 10 is made monolithic.

[0015] Turbomolecular stage 35 consists of 17 working blade wheels with a diameter of 66 mm, including 9 rotor 25-32.15 and 8 stator 17-24; on the first two wheels, the angle of inclination of the blades to the plane of the wheel is 35 °, on the next three - 30 °, on the next three - 25 °, on the next three - 20 ° and on the last six wheels 15 °. This composition of the turbomolecular stage 35 allows to reduce the ultimate residual pressure and increase the compression ratio accordingly.

[0016] Stator impellers 17-24 are split. Spacer rings 33 are positioned between them. The stator impeller and spacer ring assembly is pressed from below by adjusting ring 34, which ensures the axial clearance between the rotor and stator impellers.

[0017] The flow path contains six molecular stages consisting of alternating fixed disks (12, 13, 14) and rotating disks (8, 9, 10). The rotating disks are smooth, and the stator portions of the fixed disks have spiral channels cut into them on both sides. On one side of the stator wheel, the pumped gas moves along the spiral channel from the center to the periphery, while on the other side, it moves from the periphery to the center.

[0018] All seven stages of the pump operate sequentially. The first molecular stage consists of the final impeller 15 of the turbomolecular stage 35 and the fixed disk 12 with five spiral channels. The size of all axial clearances in the molecular stage is constant. Preferably, the axial clearance of the molecular stage is 0.5 mm or less.

[0019] The outer surface of the housings is equipped with air cooling fins.

[0020] The operating principle of the low-speed combined turbomolecular vacuum pump is that gas molecules enter the suction pipe of the pump and then into the inter-blade channels of the turbomolecular stage 35. Upon collision with the moving surface of the channels, the gas molecules are given an additional impulse of momentum in the pumping direction and are involved in movement along the inter-blade channels of the turbomolecular stage and the spiral channels of the molecular stages, after which they are removed from the discharge cavity by the forevacuum pump through the discharge pipe 16.

[0021] The use of disk molecular stages in the flow path of a turbomolecular pump allows the pump's compression ratio to be increased by several orders of magnitude, subject to high requirements for manufacturing and assembly accuracy.

[0022] The pumping parameters of the molecular stage depend on the geometric parameters of the channels, including the axial size of the channel, the working length of the channel, the size of the axial gap between the rotor and the stator, as well as the rotation speed of the disks, and the inlet surface area.

[0023] As the speed of rotation of the wheels increases, the probability of gas molecules passing through the channels in the pumping direction increases, which leads to an increase in the speed of the pump, however, the speed of rotation of the wheels is limited by the strength properties of the material used for manufacturing, taking into account its geometric shape.

[0024] The compression ratio and operating speed of the molecular section of the pump depend on the number of molecular stages. Designing flow sections for different operating speeds and compression ratios is achieved by selecting the required number of disks to achieve a given compression ratio and pump operating speed.

[0025] Increasing the compression ratio is achieved by increasing the molecular stage's compression ratio by changing its type and installing a disk-type molecular stage. Calculation results show that the disk-type molecular stage has a compression ratio hundreds of times higher than other molecular stage types.

[0026] In addition, an increase in the compression ratio is achieved by reducing the gap sizes (down to 0.5 mm) in the axial and molecular stages of the pump.

[0027] The reduction of the ultimate residual pressure and the increase in the compression ratio are achieved by the composition of the flow path. The flow path, consisting of a given number of impellers, with a given distribution of the blade angle and the gap size between them, made it possible to reduce the ultimate residual pressure by 2-10 times, depending on the pumping conditions (from approximately 10 -6 … 10 -7 up to 10 -8), increase the speed of action (from 50-60 l / s to 70-80 l / s) and increase the compression ratio by 10 times or more depending on the type of gas (for nitrogen from 10 8 … 10 10 up to 10 11 ). A further reduction in the clearance size will lead to an even greater increase in the compression ratio, however, this is technologically difficult to implement and requires very high precision in the manufacture and assembly of the pump, which in turn leads to an increase in the cost of manufacture by 30-50 times and is economically unfeasible.

Claims

A low-speed combined turbomolecular vacuum pump comprising a shaft mounted in bearing assemblies and located in a composite casing consisting of an upper casing and a lower casing on which a rotor is secured, the shaft is driven by an electric motor, the flow path of the pump includes molecular stages, characterized in that the turbomolecular stage consists of alternating nine rotor working blade wheels and eight stator working blade wheels, on the first two blade wheels the angle of inclination of the blades to the plane of the wheel is 35°, on the next three - 30°, on the next three - 25°, on the next three - 20° and on the last six wheels - 15°; the rotor of the pump is made monolithic and includes nine working blade wheels of the turbomolecular stage and three smooth disks of the molecular stage;The stator working blade wheels of the turbomolecular stage are made split, between them there are spacer rings, the stator working blade wheels and spacer rings are pressed from below by an adjusting ring; the flow part contains six molecular stages, consisting of three alternating stationary stator and three rotating rotor disks, wherein the movable rotor disks are made smooth, on the stationary stator disks on both sides there are cut spiral channels; the value of all axial clearances in the molecular stage is constant no more than 0.5 mm; the first molecular stage consists of the last working blade wheel of the turbomolecular stage and the first stator disk of the molecular stage; on each stator disk of the molecular stage there are 5 channels on each side.

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