Screw vacuum pump

Abstract

The invention provides a screw vacuum pump, and belongs to the technical field of pump bodies. The screw vacuum pump solves the problem that in an existing screw vacuum pump, the length of a screw needs to be increased in order to achieve high air exhaust efficiency. The screw vacuum pump comprises a pump body, two rotors are arranged in the pump body, and the screw vacuum pump is characterized in that each rotor is provided with K spiral turns, the total length of each rotor is L, the screw 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, 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 screw vacuum pump, the screw pitch of the rotor is adjusted according to specific requirements, the optimal screw pitch is achieved, and therefore the length of the rotor can be reduced while high air exhaust efficiency can be guaranteed.

Description

Technical Field

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

[0002] A 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. Currently, there are mostly two types of screw rotors in screw vacuum pumps: one is a constant pitch screw and the other is a variable pitch screw.

[0003] For equal-pitch screws, processing is more convenient, but when compressing gas, the compression ratio between each pitch can only be the same. The closer the gas is to the outlet, the smaller the volume is, and the greater the compression ratio is required. Therefore, the setting of the same compression ratio requires the screw to be set longer to achieve gas compression. The variable-pitch screw achieves rapid compression through a sudden screw method. It is formed by splicing multiple sections of equal pitch. While facilitating processing, the pitch of the screw near the outlet can also be reduced to obtain a larger compression ratio, thereby achieving rapid compression of the gas near the outlet.

[0004] 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 compression. During the production process, the vacuum degree at the inlet end of the pump body is high, and a large suction volume is required at the inlet end to accommodate enough gas for rapid compression. The pressure difference increases near the outlet end, so that during the compression process, the compression ratio required by the gas is continuously increased rather than increasing linearly and suddenly. Therefore, the use of a screw with a sudden pitch results in the compression ratio not being able to change continuously with the demand for gas. If the above structure is to achieve a higher suction efficiency, the length of the screw still needs to be designed to be longer, resulting in a larger overall axial length and volume of the pump body. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems in the existing technology and propose a screw vacuum pump. The technical problem to be solved by the present invention is: how to solve the problem that the existing screw vacuum pump needs to increase the length of the screw in order to achieve higher suction efficiency.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A 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,

[0008] The calculation equation of the central angle θ is:

[0009] θ=2Ωkt;

[0010] Where, t∈【0~1】;

[0011] The coordinate equation of the helix of the rotor is:

[0012] X(θ) = R sin θ;

[0013] Y(θ)=Rcosθ;

[0014] Z(θ)=P(θ)=LA(1-t)-B(sin(90(1-t) m )) n ;

[0015] Wherein, R is the distance from any point on the end face profile to the rotation center, L=A+B, A=KPi, wherein 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 20~80, 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 range of m is 0.3~0.9, and generally 0.5 is taken. When the compression ratio needs to be further adjusted, the compression ratio increases when m takes a larger value, and decreases when m takes a smaller value. The outer peripheral surface of the rotor is formed by rotating the curves on the end face profile along the spiral line.

[0016] 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 rotate along the helix through the curves on the rotor end profile to form the outer circumference of the rotor. In order to achieve a larger suction volume at the air inlet end of the screw, the Z-axis formula of the above helix can take the center angle θ within 180 degrees. The rotor pitch will be shorter, and the rotor is always connected to the air inlet in the first half of the circle. The first half of the rotor plays a closing role to ensure that the rotor pitch can obtain a larger suction volume at the air inlet end as much as possible, effectively increasing the suction space, so that the screw rotor can be closed as soon as possible to enter the compression exhaust, so that the screw rotor of the same length can obtain a larger suction speed, effectively improving the suction efficiency. In the spiral 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, and the entire shape and direction of the spiral line are determined from the X-axis, Y-axis and Z-axis, where the direction of the Z-axis needs to be targeted at different pitches of the rotor. Therefore, in the spiral line algorithm of the Z-axis, it is necessary to adopt multiple fixed values ​​A, B, and n. In the Z-axis equation of this spiral line, the larger the value of n, the greater the compression ratio, and the smaller the value of n, the smaller the compression ratio. When the value of n changes, the pitches of several screws near the inlet end will change, while the pitches of several screws near the outlet end basically remain unchanged, so that the suction volume can be increased as much as possible while ensuring that the subsequent screw can quickly compress the gas. The rotor pitch is adjusted according to specific needs to achieve the optimal pitch, so that both a high suction efficiency and a reduced rotor length can be ensured.

[0017] The value of m is generally 0.5. The value of m needs to be adjusted only when the compression ratio of the screw rotor needs to be further adjusted. Specifically, the compression ratio of the screw rotor increases with the increase of the value of m, and decreases with the decrease of the value of m.

[0018] The above-mentioned rotor outer peripheral surface can have the following advantages: 1. Reduce the energy consumption of the screw pump, specifically reduce the energy consumption per liter of air pumping; 2. The temperature rise is uniform and stable, ensuring the thermal stability of the whole machine and improving the working reliability of the whole machine; 3. Reduce noise, gradually increase the exhaust pressure, reduce the pressure difference between the screw outlet and the exhaust port, and reduce the airflow pulse noise; 4. The same exhaust speed can be achieved with a shorter rotor length, saving materials and space.

[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 screw vacuum pump, the compression ratio of the screw rotor (1) gradually decreases. For example, when the spiral turn K of the rotor is 5, the sealed cavity formed by the two rotors and the pump body is isolated and closed from the air inlet, and the compression ratio of each stage is: V1:V2:V3:V4.

[0022] In the above-mentioned screw vacuum pump, the compression power calculation equation of the screw vacuum pump is: P w =S1ΔP1+……+S i ΔP i ,

[0023] Wherein, i=K-1, K is the number of spiral turns mentioned above;

[0024] S1……S i is the geometric pumping speed of each rotor stage, ΔP1…ΔP i is the pressure difference between the rotor stages.

[0025] ΔP is the pressure difference within a certain period of time. By calculating the power of the vacuum pump, when the pressure difference is small, the pumping rate decreases. When the pressure difference increases near the outlet, the pumping speed has decreased, so that the screw vacuum pump can achieve high energy-saving efficiency.

[0026] In the above-mentioned screw vacuum pump, the volume of each sealed cavity formed by the rotor of the screw vacuum pump and the pump body when the rotor rotates is:

[0027]

[0028] 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].

[0029] 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.

[0030] In the above-mentioned screw vacuum pump, the end profiles and outer circumferences of the two rotors are the same, and the rotating helical lines are divided into left-handed and right-handed.

[0031] This design can make the processing of the screw vacuum pump more convenient and reduce the manufacturing cost.

[0032] Compared with the existing technology, this screw vacuum pump has the following advantages:

[0033] 1. When the Z-axis formula of the spiral line can take the central angle θ within 180 degrees, the rotor pitch will be shorter, and the rotor is always connected to the air inlet in the first half circle. The first half circle of the rotor plays a closing role to ensure that the rotor pitch can obtain a larger suction volume at the air inlet end as much as possible, effectively increasing the suction space, so that the screw rotor can be closed as soon as possible to enter the compression exhaust, so that the screw rotor of the same length can obtain a greater suction speed and improve the suction efficiency.

[0034] 2. Reduce the energy consumption of the screw pump, specifically reduce the energy consumption per liter of air pumped.

[0035] 3. The temperature rise is uniform and stable, ensuring the thermal stability of the whole machine and improving the working reliability of the whole machine.

[0036] 4. Reduce noise, gradually increase the exhaust pressure on the flat ground, reduce the pressure difference between the screw outlet and the exhaust port, and reduce airflow pulse noise. 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 partial structural schematic diagram of the assembly of two rotors in the present invention.

[0040] Figure 4 It is a schematic diagram of the rotor pitch changing with the central angle and taking multiple n values ​​and m being 0.5 in the present invention.

[0041] Figure 5 It is a schematic diagram of the changes in compression ratio and pitch of each stage along with the central angle when K is 5 in the present invention.

[0042] Figure 6 It is a schematic diagram of different meshing states of the two rotors rotating from 0° to 330° in the present invention.

[0043] Figure 7 It is a schematic diagram of different meshing states of the two rotors rotating from 360° to 720° in the present invention.

[0044] Figure 8 It is a schematic diagram of the rotor pitch changing with the central angle in the present invention, with K being 5, A being 0.6L, n being 30, and m being 0.5.

[0045] Fig. 9 It is a schematic diagram of the rotor pitch changing with the central angle in the present invention, with K being 5, A being 0.6L, n being 40, and m being 0.5.

[0046] Fig.10It is a schematic diagram showing that the rotor pitch varies with the central angle in the present invention, with K being 5, A being 0.6L, n being 50, and m being 0.5.

[0047] Fig.11 It is a schematic diagram of the rotor pitch changing with the central angle in the present invention, with n being 50 and taking multiple m values.

[0048] In the figure, 1. rotor; 2. end face profile; 3. spiral line; 4. air inlet. DETAILED DESCRIPTION

[0049] 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.

[0050] like Figure 1 As shown, the 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.

[0051] Specifically, if Figure 1-11 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 1 are meshed with each other, and 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,

[0052] The calculation formula for the central angle θ is:

[0053] θ=2Ωkt;

[0054] Where, t∈【0~1】;

[0055] The coordinate equation of the helix 3 of the rotor 1 is:

[0056] X(θ)=Rsinθ;

[0057] Y(θ)=Rcosθ;

[0058] Z(θ)=P(θ)=LA(1-t)-B(sin(90(1-t) m )) n ;

[0059] Where R is the distance from any point on the end profile 2 to the rotation center, L = A + B, A = KPi, where Pi is the minimum pitch of the exhaust end of the rotor 1, A ranges from 0.5L to 0.7L, and takes a smaller value when the compression ratio of the rotor 1 needs to be increased, and takes a larger value when the compression ratio of the rotor 1 needs to be reduced; n ranges from 20 to 80, and takes a larger value when the compression ratio of the rotor 1 is increased, and takes a smaller value when the compression ratio of the rotor 1 is reduced; m ranges from 0.3 to 0.9, and is generally taken as 0.5. When the compression ratio needs to be further adjusted, m takes When m is large, the compression ratio increases, and when m is small, the compression ratio decreases. The outer circumference of the rotor 1 is formed by rotating the 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 helical lines 3 and the mutually meshing screw rotor 1 gradually reduce the compression ratio. For example, when the helical circle K of the rotor 1 is 5, the sealed cavity composed of the two helical rotors and the pump body is isolated and closed from the air inlet 4, and the compression ratio of each stage is: V1:V2:V3:V4.

[0060] This center angle is formed when one of the points on the end profile line 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 line 2 of the rotor 1 and the helix line 3 of the rotor 1, and then rotate along the helix line 3 through the various curves on the end profile line 2 of the rotor 1 to form the outer peripheral surface of the rotor 1. In order to achieve a larger suction volume at the air inlet end of the screw, the Z-axis formula of the above helix line 3 can take the center angle θ within 180 degrees. The pitch of the rotor 1 will be shorter, and the rotor 1 is always connected to the air inlet 4 in the first half of the circle. The first half of the circle of the rotor 1 plays a closing role to ensure that the rotor 1 pitch can obtain a larger suction volume at the air inlet end as much as possible, effectively increasing the suction space, so that the screw rotor 1 can be closed as soon as possible to enter the compression exhaust, so that the screw rotor 1 of the same length can obtain a larger suction speed, improve the suction efficiency, and on the helix line 3 In the 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 the entire shape and direction of the spiral line 3 are determined from the X-axis, Y-axis and Z-axis, wherein the direction of the Z-axis needs to be targeted at the different pitches of the rotor 1. Therefore, in the algorithm of the spiral line 3 of the Z-axis, it is necessary to adopt the selection of multiple fixed values ​​A, B, and n. In the Z-axis equation of the spiral line 3, the larger the value of n, the larger the compression ratio, and the smaller the value of n, the smaller the compression ratio. When the value of n changes, the pitches of several screws near the inlet end will change, while the pitches of several screws near the outlet end basically remain unchanged, so that the suction volume can be increased as much as possible while ensuring that the subsequent screw can quickly compress the gas. The pitch of the rotor 1 is adjusted according to specific needs to achieve the optimal pitch, so that both a higher suction efficiency can be guaranteed and the length of the rotor 1 can be reduced.

[0061] The value of m is generally 0.5. The value of m needs to be adjusted only when the compression ratio of the screw rotor 1 needs to be further adjusted. Specifically, the compression ratio of the screw rotor 1 increases with an increase in the value of m, and decreases with a decrease in the value of m.

[0062] The outer peripheral surface of the above-mentioned rotor 1 can have the following advantages: 1. Reduce the energy consumption of the screw pump, specifically reduce the energy consumption per liter of air pumping; 2. The temperature rise is uniform and stable, ensuring the thermal stability of the whole machine and improving the working reliability of the whole machine; 3. Reduce noise, gradually increase the exhaust pressure, reduce the pressure difference between the screw outlet and the exhaust port, and reduce the airflow pulse noise; 4. The same exhaust speed can be achieved with a shorter rotor length, saving materials and space.

[0063] The compression power calculation equation of the screw vacuum pump is: P w =S1ΔP1+……+S i ΔP i ,

[0064] Wherein, i=K-1, K is the number of spiral turns mentioned above;

[0065] 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.

[0066] When the rotor 1 of the vacuum pump rotates, the volume of each sealed cavity formed by the pump body is:

[0067] V(θ)=∫ a a+4π S(θ)P(θ)′dθ

[0068] 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].

[0069] 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.

[0070] like Figure 8-10 As shown, it is the coordinate diagram of the variable pitch rotor designed with P(θ) where K=5, A=0.6L, m=0.5, and n=30, 40, and 50 respectively.

[0071] 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 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) m )) 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 it is necessary to increase the compression ratio of the rotor (1), and a larger value is taken when it is necessary to reduce the compression ratio of the rotor (1); the range of n is 20-80, and a larger value is taken when it is necessary to increase the compression ratio of the rotor (1), and a smaller value is taken when it is necessary to reduce the compression ratio of the rotor (1); the range of m is 0.3-0.9, and is generally taken as 0.

5. When it is necessary to further adjust the compression ratio, the compression ratio increases when m takes a larger value, and decreases when m takes a smaller value. The outer peripheral surface of the rotor (1) is formed by rotating the various curve segments on the end profile (2) along the spiral line (3).

2. The 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 screw vacuum pump according to claim 1 or 2, characterized in that: The compression ratio of the screw rotor (1) gradually decreases. For example, when the number of spiral turns K of the rotor (1) is 5, when the sealed chamber formed by the two rotors (1) and the pump body is isolated and closed from the air inlet (4), the compression ratios of each stage are: V1:V2:V3:V4.

4. The screw vacuum pump according to claim 1 or 2, characterized in that: The compression power calculation equation of the 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 screw vacuum pump according to claim 1 or 2, characterized in that: When the rotor (1) of the screw vacuum pump rotates, the volume of each sealed cavity formed with 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 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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