CN103062057B

CN103062057B - A kind of screw-type vacuum pump

Info

Publication number: CN103062057B
Application number: CN201310002156.9A
Authority: CN
Inventors: 朱志松; 郭东军; 严晓照; 朱龙彪; 陈阳阳; 徐海黎; 王恒
Original assignee: Nantong University
Current assignee: Guangdong Gaohang Intellectual Property Operation Co ltd; Nanjing Vacuum Pump Factory Co ltd
Priority date: 2013-01-06
Filing date: 2013-01-06
Publication date: 2015-11-25
Anticipated expiration: 2033-01-06
Also published as: CN103062057A

Abstract

The present invention discloses a kind of screw-type vacuum pump.A kind of screw-type vacuum pump, described screw-type vacuum pump comprises two rotors that shape is identical, rotation direction is contrary, and described rotor center is symmetrical; Described rotor is made up of two centrosymmetric blades, and the profile of each blade comprises the first molded line, the second molded line, the 3rd molded line, the 4th molded line and the 5th molded line that connect successively, and described 5th molded line connects with the first molded line of another blade.The present invention, by the workload decreasing the aspects such as many designs, processing, decreases the process-cycle of rotor, is conducive to the raising with service behaviour of applying of screw-type vacuum pump.In addition, rotor of the present invention only has two symmetrical blades, and each blade only has five molded line, and rotor structure is also relatively simple, further reduces the workload of design and processing.

Description

Screw type vacuum pump

Technical Field

The invention relates to the field of pump body manufacturing, in particular to a screw type vacuum pump.

Background

The screw type vacuum pump is an ideal dry pump appearing in 90 years of the 20 th century, has a wide application prospect and a great development potential, and plays an important role in the vacuum pump market. The dry screw vacuum pump generates suction and exhaust actions by a pair of screws rotating in a pump housing in a synchronous high-speed reverse direction. Its advantages are compact structure, long service life, high dynamic balance, no need of lubrication and high pumping speed. The vacuum pump is mainly applied to a high-purity vacuum process, has extremely high vacuum degree, can adapt to severe working conditions, has the capability of pumping coagulation and particulate matter-containing gas, and is particularly suitable for the fields of electronics, chemical engineering, medicines and the like.

The claw type dry vacuum pump is a non-contact type dry vacuum pump, has a large compression ratio, can be directly discharged into the atmosphere, and can also treat solid particles. The pump belongs to a positive displacement vacuum pump, and the working cycle of the pump can be divided into three processes of air suction, compression and exhaust. The core element is a pair of intermeshing rotors for pumping, and the design of the rotor profile is a key technology. Different tooth-shaped molded lines directly determine the technical performance of parameters such as ultimate vacuum degree, pumping speed, volumetric efficiency, vibration and the like of the vacuum pump.

As shown in fig. 1, a conventional claw-type dry vacuum pump has a rotor end face profile which is a cross-sectional line of a rotor tooth face and a rotor axis vertical plane. If the end face molded line rotates around the Z axis at a constant speed and moves along the Z axis at a constant speed, the curved surface formed by the end face molded line on the space is the tooth surface of the screw rotor.

The shapes of a pair of rotors of the special claw type vacuum pump are different, wherein the first rotor consists of an arc, a straight line and a cycloid, and the profile line of the second rotor is the conjugate line of the first rotor. The composition of the first rotor profile is: the section AB is a cycloid and is conjugated with a sharp point on the right side of the second rotor; the BC section is a circular arc, the radius is R1, and the center of the circle is at O1; the CD section is a straight line, is parallel to the X axis, has a distance R1 from the X axis, and is tangent to the BC arc; the DE section is a circular arc with the radius of R2 and the center of a circle of O2; the EF section is a straight line which is parallel to the y axis and tangent to the circular arc DE; the FG segment is also a cycloid, conjugate to point F on the rotor 2, and centrosymmetric to the AB segment.

The special claw-shaped molded line has higher volume utilization coefficient and pumping speed and better comprehensive performance, but the design of the rotor is complex, the processing process is troublesome, the processing period of the rotor is prolonged, and the popularization and the application of the rotor and the improvement of the working performance are influenced.

Disclosure of Invention

The invention aims to provide a screw type vacuum pump which can be simplified in design and convenient to process.

The purpose of the invention is realized by the following technical scheme:

a screw vacuum pump comprises two rotors with the same shape and opposite rotation directions, and the rotors are centrosymmetric; the rotor is composed of two centrosymmetric blades, the end face molded line of each blade comprises a first molded line, a second molded line, a third molded line, a fourth molded line and a fifth molded line which are sequentially connected, and the fifth molded line is connected with the first molded line of the other blade.

Furthermore, the intersection line of two blades of the rotor is set as an X axis, and the symmetric center of the rotor is a first intersection point; the fifth molded line and the X axis are intersected to form a second intersection point; the first intersection point is on the X axis; the first profile is a dedendum arc having an included angle α around a first intersection₁(ii) a The second profile is an envelope curve generated by a third profile of the other rotor, which encloses an angle α around the first intersection point₂(ii) a The third molded line is an equal angle-changing spiral line or an arc, and the included angle formed by the third molded line around the first intersection point is alpha₃(ii) a The fourth molded line is a tooth top circular arc, and the included angle formed by the fourth molded line around the first intersection point is alpha₄(ii) a The fifth molded line is a cycloid line, one end of the fifth molded line is connected with the end point of the fourth molded line, and the other end of the fifth molded line is connected to the second intersection point; a is said₁+α₂+α₃+α₄180 deg.. The end face molded line of the rotor in the technical scheme is formed by continuously and smoothly connecting cycloid curves, contour lines, inner circles, outer circles and the like of the rotor, the molded line cannot interfere with a meshing line of the molded line, the molded line can be completely sealed, and a sealing line is short. Although the molded line also has a leakage triangle, the interstage leakage is small, the area utilization coefficient is high, and the air extraction efficiency is high.

The position of the whole rotor tooth surface which is difficult to process is a concave tooth surface part, and the concave tooth surface part requires higher shape precision and position precision, so that the air suction performance of the pump can be ensured. The tooth profile structure of the rotor in the technical scheme is simple, except that the profile corresponding to the fifth profile is a concave profile (the profile of the end face is concave, and the profile of the tooth is formed by scanning), other tooth surfaces are straight tooth surfaces, and the rotor is convenient to process and manufacture.

Further, the equation of the first profile is:

π-α₁≤ζ≤π

zeta is the included angle between the connecting line of any point of the first profile and the first intersection point and the X axis; r_rAnd the radius of the tooth root circular arc taking the first intersection point as the circle center.

Further, the second profile is an envelope generated by a third profile of another rotor, the curvature radius ρ > 0, and the parameter equation is as follows:

wherein ζ is any one of the second type lineThe included angle between the connecting line of the point and the first intersection point and the X axis;is rotor angle, a is rotor center distance;O₁is the first intersection point, O₁₁Is a second intersection; i O₁O₁₁I is the distance between the first intersection point and the second intersection point; rt is the radius of the tip circle, r₁Is the engagement circle radius.

Further, the third profile is an arc with the second intersection point as a circle center, and a parametric equation of the arc is as follows:

α₄≤ζ≤π/2

zeta is the included angle between the connecting line of any point of the third profile and the second intersection point and the X axis; and R' the arc radius of the third profile.

Further, the fourth profile is a segment of arc on the addendum circle with the first intersection point as the center of circle, and the parametric equation is as follows:

0≤ζ≤α₄

zeta is the included angle between the connecting line of any point of the fourth molded line and the first intersection point and the X axis; rt is the addendum radius.

Further, the fifth profile is a cycloid generated by using the meshing circle as a base circle and the meshing circle of the other rotor, and the parametric equation is as follows:

zeta is an included angle between a connecting line of any point of the fifth molded line and the first intersection point and the X axis; rt is the addendum radius.

Further, the equation of the first profile is:

π-α₁≤ζ≤π

the second profile is an envelope generated by a third profile of another rotor, the curvature radius rho of the envelope is greater than 0, and a parameter equation is as follows:

the third molded line is an arc with the second intersection point as the center of a circle, and the parameter equation is as follows:

α₄≤ζ≤π/2

the fourth molded line is a section of circular arc on the addendum circle with the first intersection point as the center of a circle, and the parameter equation is as follows:

0≤ζ≤α₄

the fifth molded line is a cycloid generated by using the meshing circle as a base circle and the meshing circle of the other rotor, and the parameter equation is as follows:

the parameter zeta of the third molded line is an included angle between a connecting line of any point of the third molded line and the second intersection point and the X axis, and the parameter zeta of the other molded lines is an included angle between a connecting line of any point of the corresponding molded line and the first intersection point and the X axis; r_rThe radius of the tooth root circular arc with the first intersection point as the circle center;is rotor angle, a is rotor center distance;O₁is the first intersection point, O₁₁Is a second intersection; i O₁O₁₁I is the distance between the first intersection point and the second intersection point; rt is the radius of the tip circle, r₁Is the radius of the meshing circle; and R' the arc radius of the third profile.

Further, the screw Rt is 60mm, Rr is 20mm, r1 is 40mm, a is Rt + Rr is 2r1 is 80mm, Po is 60mm, the pumping speed n is 3000r/min, and Po is the thread pitch.

The inventor researches and discovers that the existing rotor molded lines have diversity, the calculation and solving of conjugate curves are complex, great inconvenience is brought to design work, the molded lines of two conjugate rotors are different, the processing of the rotors is troublesome, the processing period of the rotors is prolonged, and the popularization and application of the rotors and the improvement of the working performance are influenced. Because the two rotors with the same shape are adopted and the centers of the rotors are symmetrical, the molded lines of the other part can be obtained only by designing the molded lines of one part of the symmetrical rotors, so that the molded lines of the whole rotors are obtained, the workload in the aspects of design, processing and the like is greatly reduced, the processing period of the rotors is shortened, and the popularization and the application of the screw vacuum pump and the improvement of the working performance are facilitated; in addition, the rotor of the invention only has two symmetrical blades, each blade only has five molded lines, the rotor structure is relatively simple, and the workload of design and processing is further reduced.

Drawings

FIG. 1 is a schematic view of a rotor of a prior art screw vacuum pump;

FIG. 2 is a schematic view of a profile of a rotor according to an embodiment of the present invention;

FIG. 4 is a schematic view of a rotor tooth surface of a rotor according to an embodiment of the present invention;

fig. 3 is a schematic view showing the area utilization of a rotor according to an embodiment of the present invention.

Detailed Description

A screw vacuum pump comprises two rotors with the same shape and opposite rotation directions, and the rotors are centrosymmetric.

The inventor researches and discovers that the existing rotor molded lines have diversity, the calculation and solving of conjugate curves are complex, great inconvenience is brought to design work, the molded lines of two conjugate rotors are different, the processing of the rotors is troublesome, the processing period of the rotors is prolonged, and the popularization and application of the rotors and the improvement of the working performance are influenced. Because the two rotors with the same shape are adopted and the centers of the rotors are symmetrical, the molded lines of the other part can be obtained only by designing the molded lines of one part of the rotors which are symmetrical, so that the molded lines of the whole rotors are obtained, the workload in the aspects of design, processing and the like is greatly reduced, the processing period of the rotors is shortened, and the popularization and the application of the screw vacuum pump and the improvement of the working performance are facilitated.

The invention is further described with reference to the drawings and the preferred embodiments.

Rotor end face profile: the rotor tooth surface and the rotor axis vertical plane.

Rotor tooth surface: if the end face molded line rotates around the Z axis at a constant speed and moves along the Z axis at a constant speed, the curved surface formed by the end face molded line on the space is the tooth surface of the screw rotor.

Conjugate curve: the conjugate curve ensures that the two curves are continuously tangent and envelope each other in the meshing process.

Envelope curve: in geometry, the Envelope (Envelope) of a family of curves is a curve that is tangent to at least one point on each line of the family. (the family of curves, i.e., an infinite set of curves that have specific relationships; the stress-strain relationship of the soil in soil mechanics, as determined by a plurality of extreme Moire stress circles, is a straight line.)

Area utilization coefficient: the area utilization factor or the area utilization ratio is a ratio of a sectional area included between a surface curve of the rotor and a surface of the pump chamber to a sectional area of the pump chamber, as viewed from a section of the pump chamber.

As shown in fig. 2, the screw vacuum pump includes two rotors with the same shape and opposite rotation directions, and the rotors are centrosymmetric. The rotor consists of two centrosymmetric blades, the end surface molded line of each blade comprises a first molded line, a second molded line, a third molded line, a fourth molded line and a fifth molded line which are sequentially connected, and the fifth molded line is connected with the first molded line of the other blade;

setting the boundary line of two blades of the rotor as an X axis, and setting the symmetric center of the rotor as a first intersection point; the fifth molded line and the X axis are intersected to form a second intersection point; the first intersection point is on the X axis; the first profile is a root arc having an included angle α around the first intersection₁(ii) a The second profile is an envelope curve generated by a third profile of the other rotor, which encloses an angle α around the first intersection point₂(ii) a The third molded line is an equal angle-changing spiral line or an arc, and the included angle formed by the third molded line around the first intersection point is alpha₃(ii) a The fourth molded line is a tooth top circular arc, and the included angle formed by the fourth molded line around the first intersection point is alpha₄(ii) a The fifth line is a cycloid curve, one end of whichConnecting the end point of the fourth profile, and connecting the other end of the fourth profile to the second intersection point; alpha is alpha₁+α₂+α₃+α₄＝180°。

The equation for the first profile segment a1-b1 is:

π-α₁≤ζ≤π(1)

the second profile b1-c1 is the envelope generated by the third curve of the other rotor, and is obtained according to the meshing principle with the c2d2 segment of the rotor 2. In order to ensure that the section b1c1 has a smooth envelope curve, the curve conjugated to the section c2d2 of the rotor 2 should be convex, i.e. have a radius of curvature p > 0. The parameter equation of the section of the profile c2d2 of the rotor 2 is

α₄≤ζ≤π/2(2)

Wherein R' ═ O₁₁c₁L is the arc radius of the c2d2 segment,

coordinate transformation of formula (2) to obtain

In the formula, the first step is that,is the rotor angle, and a is the rotor center distance. Formula (3) is a curve cluster equation and envelope supplement conditions

Is obtained by the arrangement of formulas (3) and (4)

Equations (3) and (5) are combined to form the line segment b1c 1.

The third line c1-d1 is an arc with the second intersection point as the center, and the parameter equation is as follows:

α₄≤ζ≤π/2(6)

the fourth line d1-e1 is a circular arc on the addendum circle with the first intersection point as the center, and the parameter equation is as follows:

0≤ζ≤α₄(7)

the fifth section of the profile e1-f1 is a cycloid generated by taking the meshing circle as a base circle and the meshing circle of the other rotor, and the parameter equation is as follows:

the parameter zeta of the third molded line is an included angle between a connecting line of any point of the third molded line and the second intersection point and the X axis, and the parameter zeta of the other molded lines is an included angle between a connecting line of any point of the corresponding molded line and the first intersection point and the X axis; r_rThe radius of the tooth root circular arc taking the first intersection point as the circle center;is rotor angle, a is rotor center distance;O₁is the first intersection point, O₁₁Is a second intersection; i O₁O₁₁I is the distance between the first intersection point and the second intersection point; rt is the radius of the tip circle, r₁Is the radius of the meshing circle; and R' the arc radius of the third profile.

The molded line of the end face of the rotor in the embodiment is formed by continuously and smoothly connecting cycloid, contour line, inner circle and outer circle of the rotor and the like, the molded line cannot interfere with a meshing line of the molded line, the molded line can realize complete sealing, and the sealing line is short. Although the molded line also has a leakage triangle, the interstage leakage is small, the area utilization coefficient is high, and the air extraction efficiency is high.

As shown in fig. 3, the position where the entire rotor tooth surface is difficult to be processed is the concave tooth surface portion, which requires high shape accuracy and position accuracy so as to ensure the pumping performance of the pump. The tooth profile structure of the rotor in the technical scheme is simple, except that the profile corresponding to the fifth profile is a concave profile (the profile of the end face is concave, and the profile of the tooth is formed by scanning), other tooth surfaces are straight tooth surfaces, and the rotor is convenient to process and manufacture.

The performance of a screw vacuum pump employing the present invention is illustrated by analytical demonstration.

First, area utilization factor and pumping speed

As shown in fig. 4, the hatched portion represents the cross-sectional area of the cavity of the screw vacuum pump, the remaining non-hatched portion is the cross-sectional area included between the surface curve of the rotor and the surface of the cavity of the pump, and the area ratio between the non-hatched portion and the hatched portion is the area utilization coefficient, which is represented by the letter K, and it represents the utilization degree of the total area within the range of the diameter of the rotor, that is, the larger the area utilization rate, the higher the effective utilization degree of the cavity of the pump.

Referring to fig. 4, it can be seen that:

a2, A3 and A5 are all fan-shaped, and the areas are respectively

A₃＝γ₃R′²/2

Wherein gamma is₂，γ₃And gamma₅Respectively, the radians corresponding to the sectors.

The corresponding area can be obtained by integrating the equation of the section of the end face profile e1f1

<math> <mrow> <msub> <mi>A</mi> <mn>1</mn> </msub> <mo>=</mo> <mo>&Integral;</mo> <mi>ydx</mi> <mo>=</mo> <mrow> <mo>(</mo> <mn>2</mn> <msup> <msub> <mi>r</mi> <mn>1</mn> </msub> <mn>2</mn> </msup> <mo>+</mo> <msubsup> <mi>R</mi> <mi>t</mi> <mn>2</mn> </msubsup> <mo>)</mo> </mrow> <mi>φ</mi> <mo>-</mo> <mn>3</mn> <msub> <mi>r</mi> <mn>1</mn> </msub> <msub> <mi>R</mi> <mi>t</mi> </msub> <mi>sin</mi> <mi>φ</mi> <mo>+</mo> <msup> <msub> <mi>r</mi> <mn>1</mn> </msub> <mn>2</mn> </msup> <mi>sin</mi> <mn>2</mn> <mi>φ</mi> </mrow> </math>

Wherein

<math> <mrow> <mi>φ</mi> <mo>=</mo> <mi>arccos</mi> <mfrac> <msub> <mi>r</mi> <mn>1</mn> </msub> <msub> <mi>R</mi> <mi>t</mi> </msub> </mfrac> </mrow> </math>

The corresponding area can be obtained by integrating equation (3)

Wherein,

theoretical pumping speed S: the volume of gas discharged by the pump in unit time is the volume of gas discharged by one tooth space when the screw rotor rotates once. Since two screws are engaged to rotate, the rotation is multiplied by a factor of 2, so that the theoretical pumping speed is

S＝2nπPKR_t ²(10)

In the formula, n is the rotation speed of the screw rotor, and P is the screw lead.

First, quantitative example of rotor end face profile parameters

The advantages of the rotor end face profile of the invention are illustrated quantitatively by way of example: screw Rt 60mm, Rr 20mm, r1 40mm, a Rt + Rr 2r 180 mm, Po 60mm, and pump speed n 3000r/min, screw lead P360 mm, a1 345.4mm, a2 mm, A3 mm 1204.9mm, a 4mm 381.5mm, a 5mm 104mm, and area coefficient using formula (9)

= 0.6

Since the ratio of the diameter of the root circle to the diameter of the tip circle of the rotor, i.e., the inner-outer diameter ratio ρ of the rotor, is an important influence factor of the theoretical pumping speed, it should be in the range of 0.30 to 0.65. The smaller ρ is, the larger the theoretical pumping speed S is, and the higher the efficiency is. In this example, ρ is 0.33. The area utilization coefficient of the molded line is greatly improved to 60 percent, and the theoretical pumping speed is synchronously improved.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims

1. A screw vacuum pump is characterized by comprising two rotors with the same shape and opposite rotation directions, wherein the rotors are centrosymmetric; the rotor consists of two centrosymmetric blades, the end surface molded line of each blade comprises a first molded line, a second molded line, a third molded line, a fourth molded line and a fifth molded line which are sequentially connected, and the fifth molded line is connected with the first molded line of the other blade;

setting the boundary line of two blades of the rotor as an X axis, and setting the symmetric center of the rotor as a first intersection point; the fifth profile intersects the X-axis to form a second intersection(ii) a The first intersection point is on the X axis; the first profile is a dedendum arc having an included angle α around a first intersection₁(ii) a The second profile is an envelope curve generated by a third profile of the other rotor, which encloses an angle α around the first intersection point₂(ii) a The third molded line is an equal angle-changing spiral line or an arc, and the included angle formed by the third molded line around the first intersection point is alpha₃(ii) a The fourth molded line is a tooth top circular arc, and the included angle formed by the fourth molded line around the first intersection point is alpha₄(ii) a The fifth molded line is a cycloid line, one end of the fifth molded line is connected with the end point of the fourth molded line, and the other end of the fifth molded line is connected to the second intersection point; a is said₁+α₂+α₃+α₄＝180°；

The equation of the first profile is:

wherein zeta is any one point of the first profileThe connecting line of the first intersection point forms an included angle with the X axis; r_rThe radius of the tooth root circular arc with the first intersection point as the circle center;

zeta is the angle between the X axis and the connecting line of any point of the second section line and the first intersection point;is rotor angle, a is rotor center distance;O₁is the first intersection point, O₁₁Is a second intersection; i O₁O₁₁I is the distance between the first intersection point and the second intersection point; rt is the radius of the tip circle, r₁Is the radius of the meshing circle;

zeta is the included angle between the connecting line of any point of the third profile and the second intersection point and the X axis; r' arc radius of the third profile;

zeta is the included angle between the connecting line of any point of the fourth molded line and the first intersection point and the X axis; rt is the addendum radius;

2. A screw vacuum pump as claimed in claim 1, wherein the equation for the first profile is:

wherein the parameter zeta of the third profile is the connection between any point of the third profile and the second intersection pointThe included angle between the line and the X axis, and the parameter zeta of the other molded lines is the included angle between the connecting line of any point of the corresponding molded line and the first intersection point and the X axis; r_rThe radius of the tooth root circular arc with the first intersection point as the circle center;is rotor angle, a is rotor center distance;O₁is the first intersection point, O₁₁Is a second intersection; i O₁O₁₁I is the distance between the first intersection point and the second intersection point; rt is the radius of the tip circle, r₁Is the radius of the meshing circle; and R' the arc radius of the third profile.

3. A screw vacuum pump according to claim 2, wherein the screw Rt is 60mm, Rr is 20mm, r1 is 40mm, a Rt + Rr is 2r1 is 80mm, Po is 60mm, the pumping speed n is 3000r/min, and Po is the pitch of the thread.