Variable-pitch screw vacuum pump

Abstract

The invention provides a variable-pitch screw vacuum pump, and belongs to the technical field of pump bodies. The variable-pitch screw vacuum pump solves the problem that in an existing variable-pitch screw vacuum pump, the length of a screw needs to be increased in order to achieve high air exhaust efficiency. The variable-pitch screw vacuum pump comprises a pump body, two rotors are arranged in the pump body, each rotor is provided with K spiral turns, the total length of the rotors is L, the pitches of the rotors from the air inlet end to the air outlet end are P1-Pi in sequence, the two rotors are respectively a left-handed rotor and a right-handed rotor, and the two rotors are meshed with each other, wherein the rotating angle of one rotor end face molded line around the rotating center is a central angle theta, the rotor has a spiral line coordinate equation, the spiral line coordinate equation comprises an X axis, a Y axis and a Z axis, and the peripheral surface of the rotor is formed by rotating each section of curve on the end face molded line along a spiral line. According to the rotor of the variable-pitch screw vacuum pump, the optimal pitch can be adjusted according to different requirements, and therefore the length of the rotor can be reduced while high air exhaust efficiency is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of pump bodies and relates to a variable pitch screw vacuum pump. Background Art

[0002] The screw vacuum pump is a vacuum device that uses a pair of screws to rotate synchronously at high speed in opposite directions in the pump housing to produce suction and exhaust effects.

[0003] There are two types of screw rotors in current screw vacuum pumps:

[0004] One is the equal pitch screw, which is easy to process and is more similar to the rotors of screw gas compressors and screw liquid delivery pumps. On the other hand, because the equal pitch screw vacuum pump has no internal compression and exhaust method, it is more suitable for dry vacuum pumps because it can remove impure gases containing solid particle impurities or condensable vapors.

[0005] The other is a variable pitch screw, usually a sudden variable pitch screw. The simplest variable pitch method with the simplest geometric structure is to directly connect in series two sections of equal pitch screws with the same end profile but different leads, so that the intake and exhaust compression ratio of the pump is equal to the lead ratio of the two-section screw. During the pumping process, the pumped gas is sucked in from the long lead end, and after being transported for a distance without compression, it is rapidly compressed at the interface of the two-section screw as the screw rotates one circle. The volume reduction ratio is equal to the compression ratio of the pump, and then it is transported for a distance without compression again and connected to the exhaust port. The pressure rises to the exhaust pressure, and finally it is discharged from the pump body together with the recoil gas.

[0006] The above two types of screws are composed of one or more sections of equal pitch screws. In actual production, the gas can only be compressed in one section. During the production process, the working vacuum degree at the inlet end of the pump body is high. When approaching the outlet, the pressure difference increases, resulting in a decrease in the pumping speed. If the above structure is to achieve a higher pumping efficiency, the length of the screw needs to be designed to be longer, resulting in a larger overall axial length and volume of the pump body. Summary of the invention

[0007] The purpose of the present invention is to address the above-mentioned problems in the existing technology and to propose a variable pitch screw vacuum pump. The technical problem to be solved by the present invention is: how to solve the problem that the existing variable pitch screw vacuum pump needs to increase the length of the screw in order to achieve higher suction efficiency.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] A variable pitch screw vacuum pump comprises a pump body, wherein two rotors are arranged in the pump body, wherein the rotor has K spiral turns, the total length of the rotor is L, the pitch of the rotor from the air inlet end to the exhaust end is P1 to Pi, one of the two rotors is left-handed and the other is right-handed, and the two rotors are meshed with each other, and the angle of rotation of one rotor end face profile around the rotation center is the central angle θ,

[0010] The calculation equation of the central angle θ is:

[0011] θ=2Ωkt;

[0012] Where, t∈【0~1】;

[0013] The coordinate equation of the helix of the rotor is:

[0014] X(θ) = R sinθ;

[0015] Y(θ)=R cosθ;

[0016] Z(θ)=P(θ)=LA(1-t)-B(sin(90(1-t))) n ;

[0017] In the formula, R is the distance from any point on the end face profile to the rotation center, L=A+B, A=KPi, where Pi is the minimum pitch of the exhaust end of the rotor, the range of A is 0.5L~0.7L, and a smaller value is taken when the rotor compression ratio needs to be increased, and a larger value is taken when the rotor compression ratio needs to be reduced; the range of n is 10~40, and a larger value is taken when the rotor compression ratio is increased, and a smaller value is taken when the rotor compression ratio is reduced. The outer peripheral surface of the rotor is formed by rotating the various curves on the end face profile along the spiral line.

[0018] This center angle is formed when one of the points on the rotor end profile rotates around its own axis Z axis. Before the rotor is formed, it is necessary to first determine the rotor end profile and the rotor helix, and then form the outer circumference of the rotor by rotating along the helix through each curve on the rotor end profile. In order to minimize the length of the screw while ensuring a high suction efficiency, a variable pitch rotor is used. Each pitch of the variable pitch rotor is different, and the pitch needs to be designed according to the air pressure at the intake end of the pump body. In the above helix coordinate equation, the center angle θ is obtained by the value of the ratio variable t and the change in the number of spiral turns k on the rotor, and the spiral is determined from the X-axis, Y-axis and Z-axis. The entire shape and direction of the spiral line, where the direction of the Z axis is required for the different pitches of the rotor. Therefore, in the spiral line algorithm of the Z axis, it is necessary to adopt the selection of multiple fixed values ​​A, B, and n. The multiple fixed values ​​are determined by the size of the air pressure at the inlet end of the pump body. The specific change of the spiral line Z axis, this formula is by changing the parameters of A and n, and can flexibly obtain different gradual compression ratios from large to small, thereby ensuring that the formula can realize the adjustment of the rotor's spiral line, that is, the various pitches of the rotor according to the size of the air pressure at the inlet end of the specific pump body. The rotor can adjust the optimal pitch according to different needs, thereby achieving a higher exhaust efficiency while reducing the length of the rotor.

[0019] In the variable pitch screw vacuum pump, when the central angle θ rotates in the opposite direction, opposite helical lines of the rotor are obtained, and the rotors formed by the rotation of the two helical lines mesh with each other.

[0020] By rotating in the opposite direction of the angle θ, an opposite helix can be obtained, so that the rotors obtained by the two mutually opposite helical lines in the variable pitch screw vacuum pump can mesh with each other.

[0021] In the above-mentioned variable pitch screw vacuum pump, the n value is larger when the air pressure at the air inlet end of the pump body is low, and the n value is smaller when the air pressure at the air inlet end of the pump body is high.

[0022] The n value is adjusted according to the air pressure at the inlet end of the pump body. For example, when the air pressure at the inlet end is 3Kpa during operation, the n value is 50, which makes the compression ratio of the screw rotor large and obtains a lower shaft power. For example, when the air pressure at the inlet end is 30Kpa during operation, the n value is 30, which makes the compression ratio of the screw rotor smaller to obtain a lower shaft power. Therefore, by adjusting the n value, the pitch can be adjusted for different inlet end pressures to achieve the purpose of obtaining a lower shaft power, reduce the driving power required for the pump body, and further improve the performance and exhaust efficiency of the variable pitch screw vacuum pump.

[0023] In the above variable pitch screw vacuum pump, the compression power calculation equation of the variable pitch screw vacuum pump is: P w =S1ΔP1+……+S iΔP i ,

[0024] Where i = K-1,

[0025] S1……S i is the geometric pumping speed of each rotor stage, ΔP1…ΔP i is the pressure difference between the rotor stages.

[0026] According to different inlet pressures, appropriate A and n values ​​are selected to obtain a smaller variable pitch screw vacuum pump compression power.

[0027] By calculating the compression power of the vacuum pump, when the pressure difference is small, the pumping rate is reduced to 2.46 times. When the pressure difference increases near the outlet, the pumping speed has been reduced, so that the variable pitch screw vacuum pump can achieve high energy-saving efficiency.

[0028] In the above variable pitch screw vacuum pump, the volume of each sealed cavity formed by the rotor of the vacuum pump and the pump body when the vacuum pump rotates is:

[0029]

[0030] Where S(θ) is the area of ​​the exhaust space formed by the mutual meshing of the two rotors at different central angles, dθ is a variable, θ∈[a~a+4π].

[0031] The above equation is the volume of each sealed cavity formed by integrating the area of ​​the exhaust space formed by the meshing of the two existing rotors at different central angles through the change of the central angle, the derivative of the helix coordinate function and the variable dθ. When the central angle changes continuously, the volume of the sealed cavity formed by the rotor and the pump body can be quickly measured.

[0032] In the above-mentioned variable pitch screw vacuum pump, the end profiles and outer peripheral surfaces of the two rotors are the same, and the rotating helical lines are divided into left-handed and right-handed.

[0033] The design can make the processing of the variable pitch screw vacuum pump more convenient and reduce the manufacturing cost.

[0034] Compared with the existing technology, this variable pitch screw vacuum pump has the following advantages:

[0035] 1. This formula can flexibly obtain different gradual compression ratios, which are first large and then small, by changing the parameters of A and n, so as to ensure that the formula can adjust the helix of the rotor, that is, the pitch of each rotor, according to the value of the air pressure at the inlet end of the specific pump body. The rotor can adjust the optimal pitch according to different needs, so as to achieve a higher exhaust efficiency while reducing the length of the rotor, effectively utilize space, and save the overall volume of the variable pitch screw vacuum pump.

[0036] 2. When selecting fixed value parameters, the pitch of the screw rotor can be adjusted by the air pressure at the air inlet end of the pump body, thereby improving the pumping efficiency of the variable pitch screw vacuum pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a structural schematic diagram showing a spiral line on the rotor in the present invention.

[0038] Figure 2 It is a front view of the rotor in the present invention.

[0039] Figure 3 It is a schematic diagram of the rotor pitch changing with the central angle and taking multiple n values ​​in the present invention.

[0040] Figure 4 It is a schematic diagram of the rotor pitch changing with the central angle in the present invention, with A being 0.6L and n being 25.

[0041] Figure 5 It is a schematic diagram of different meshing states of the two rotors rotating from 0° to 330° in the present invention.

[0042] Figure 6 It is a schematic diagram of different meshing states of the two rotors rotating from 360° to 720° in the present invention.

[0043] In the figure, 1, rotor; 2, end face profile; 3, helix. DETAILED DESCRIPTION

[0044] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0045] like Figure 1 As shown, the variable pitch screw vacuum pump includes a pump body, and two rotors 1 are arranged in the pump body. The pump body structure and how to connect the pump body can adopt the existing technology, so it will not be described in detail in this article, and the drawings are not shown.

[0046] Specifically, if Figure 1-6 As shown, the rotor 1 has K spiral turns, the total length of the rotor 1 is L, the pitch of the rotor 1 from the intake end to the exhaust end is P1 to Pi, the two rotors 1 are respectively left-handed and right-handed, and the two rotors are meshed with each other, and the angle of rotation of the end face profile of one of the rotors 1 around the rotation center is the central angle θ,

[0047] The calculation formula for the central angle θ is:

[0048] θ=2Ωkt;

[0049] Where, t∈【0~1】;

[0050] The coordinate equation of the helix 3 of the rotor 1 is:

[0051] X(θ) = R sinθ;

[0052] Y(θ)=R cosθ;

[0053] Z(θ)=P(θ)=LA(1-t)-B(sin(90(1-t))) n ;

[0054] Wherein, R is the distance from any point on the end profile 2 to the rotation center, L=A+B, A=KPi, wherein Pi is the minimum pitch of the exhaust end of the rotor 1, the range of A is 0.5L~0.7L, and a smaller value is taken when the compression ratio of the rotor 1 needs to be increased, and a larger value is taken when the compression ratio of the rotor 1 needs to be reduced; the range of n is 10~40, and a larger value is taken when the compression ratio of the rotor 1 is increased, and a smaller value is taken when the compression ratio of the rotor 1 is reduced. The outer peripheral surface of the rotor 1 is formed by rotating the various curves on the end profile 2 along the helix 3. When the central angle θ rotates in the opposite direction, the opposite helix 3 of the rotor 1 is obtained. The rotor 1 formed by the rotation of the two helices 3 is meshed with each other. When the air pressure at the inlet end of the pump body is low, the larger the n value is, and when the air pressure at the inlet end of the pump body is high, the smaller the n value is.

[0055] This center angle is formed when one of the points on the end profile 2 of the rotor 1 rotates around its own axis Z axis. Before the rotor 1 is formed, it is necessary to first determine the end profile 2 of the rotor 1 and the helix 3 of the rotor 1, and then form the outer circumference of the rotor 1 by rotating along the helix 3 through each curve on the end profile 2 of the rotor 1. In order to minimize the length of the screw while ensuring a high suction efficiency, a variable pitch rotor 1 is used. Each pitch of the variable pitch rotor 1 is different, and the pitch needs to be designed according to the air pressure at the intake end of the pump body. In the above-mentioned helix 3 coordinate equation, the center angle θ is obtained by the value of the ratio variable t and the change of the number of spiral turns k on the rotor 1, and is obtained by changing the value of the ratio variable t and ... Determine the entire shape and direction of the helix 3, wherein the direction of the Z axis is required for the different pitches of the rotor 1. Therefore, in the algorithm of the helix 3 of the Z axis, it is necessary to adopt the selection of multiple fixed values ​​A, B, and n. The multiple fixed values ​​are determined by the size of the air pressure at the intake end of the pump body. For the specific change of the helix 3 Z axis, this formula can flexibly obtain different gradual compression ratios from large to small by changing the parameters of A and n, thereby ensuring that the formula can realize the adjustment of the helix 3 of the rotor 1, that is, the various pitches of the rotor 1, according to the size of the air pressure at the intake end of the specific pump body. The rotor 1 can adjust the optimal pitch according to different needs, thereby achieving a higher exhaust efficiency while reducing the length of the rotor 1.

[0056] The compression power calculation equation of the variable pitch screw vacuum pump is: Pw =S1ΔP1+……+S i ΔP i ,

[0057] Where i = K-1,

[0058] S1……S i is the geometric pumping speed of each stage of rotor 1, ΔP1…ΔP i is the pressure difference of each stage of rotor 1. According to different inlet pressures, appropriate A and n values ​​are selected to obtain a smaller compression power of the variable pitch screw vacuum pump.

[0059] When the rotor 1 of the variable pitch screw vacuum pump rotates, each seal formed by the pump body

[0060] The cavity volume is:

[0061] V(θ)=∫ a a+4π S(θ)P(θ)′dθ

[0062] Where S(θ) is the area of ​​the exhaust space formed by the mutual meshing of the two rotors 1 at different central angles, dθ is a variable, θ∈[0~4π].

[0063] The end profiles 2 and outer circumferences of the two rotors 1 are the same, and the rotating helical lines 3 are divided into left-handed and right-handed.

[0064] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A variable pitch screw vacuum pump, comprising a pump body, wherein two rotors (1) are arranged in the pump body, characterized in that: The rotor (1) has K spiral turns, the total length of the rotor (1) is L, the pitches of the rotor (1) from the air inlet end to the air outlet end are P1 to Pi, one of the two rotors (1) is left-handed and the other is right-handed, and the two rotors (1) are meshed with each other, the angle of rotation of the end surface profile (2) of one of the rotors (1) around the rotation center is the central angle θ, The calculation equation of the central angle θ is: θ=2Ωkt; Where, t∈【0~1】; The coordinate equation of the helix (3) of the rotor (1) is: X(θ) = R sinθ; Y(θ)=R cosθ; Z(θ)=P(θ)=LA(1-t)-B(sin(90(1-t))) n ; In the formula, R is the distance from any point on the end profile (2) to the rotation center, L=A+B, A=KPi, wherein Pi is the minimum pitch of the exhaust end of the rotor (1), the range of A is 0.5L-0.7L, and a smaller value is taken when the compression ratio of the rotor (1) needs to be increased, and a larger value is taken when the compression ratio of the rotor (1) needs to be reduced; the range of n is 10-40, and a larger value is taken when the compression ratio of the rotor (1) needs to be increased, and a smaller value is taken when the compression ratio of the rotor (1) needs to be reduced. The outer peripheral surface of the rotor (1) is formed by rotating each segment of the curve on the end profile (2) along the spiral line (3).

2. The variable pitch screw vacuum pump according to claim 1, characterized in that: When the center angle θ rotates in the opposite direction, opposite helical lines (3) of the rotor (1) are obtained, and the rotors (1) formed by the rotation of the two helical lines (3) mesh with each other.

3. The variable pitch screw vacuum pump according to claim 1 or 2, characterized in that: The greater the n value is when the air pressure at the air inlet end of the pump body is low, and the smaller the n value is when the air pressure at the air inlet end of the pump body is high.

4. The variable pitch screw vacuum pump according to claim 1 or 2, characterized in that: The compression power calculation equation of the variable pitch screw vacuum pump is: w =S1ΔP1+……+S i ΔP i , Wherein, i=K-1, K is the number of spiral turns mentioned above; S1……S i is the geometric pumping speed of each stage of the rotor (1), ΔP1…ΔP i is the pressure difference between the various stages of the rotor (1).

5. The variable pitch screw vacuum pump according to claim 1 or 2, characterized in that: When the rotor (1) of the variable pitch screw vacuum pump rotates, the volume of each sealed cavity formed by the rotor (1) and the pump body is: Where S(θ) is the area of ​​the exhaust space formed by the meshing of the two rotors (1) at different central angles, dθ is a variable, θ∈[0~4π].

6. The variable pitch screw vacuum pump according to claim 1 or 2, characterized in that: The end profiles (2) and outer peripheral surfaces of the two rotors (1) are the same, and the rotating helical lines (3) are divided into left-handed and right-handed.

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