Variable-pitch double-screw rotor for screw vacuum pump

Abstract

The utility model relates to a variable-pitch double-screw rotor for a screw vacuum pump, which comprises a driving screw and a driven screw which are parallelly mounted in a pump cavity of the screw vacuum pump, rotate reversely at a constant speed and are meshed in pairs, and the rotating directions of the driving screw and the driven screw are opposite. The end face molded lines of the driving screw rod and the driven screw rod are meshed with each other at a phase difference of 180 degrees; the curved surfaces of the driving screw rod and the driven screw rod are completely meshed, the end surface molded line of the driving screw rod is composed of four sections of conjugate curves, and the end surface molded line of the driven screw rod is composed of four sections of conjugate curves which are completely the same as those of the driving screw rod. According to the screw vacuum pump, the machining cost is reduced, the precision of the screw rotor is higher, and the screw curved surface meshing clearance is smaller and more uniform, so that the air exhaust efficiency of the screw vacuum pump can be improved, the air exhaust temperature rise of the screw vacuum pump is effectively reduced, and the air suction amount of the screw vacuum pump is increased.

Description

Technical Field

[0001] The utility model relates to the technical field of screw vacuum pumps, in particular to a variable pitch twin-screw rotor for a screw vacuum pump. Background Art

[0002] A screw vacuum pump is a high-vacuum pump with a maximum operating vacuum of approximately 1 Pa (1.000 psi) and an exhaust pressure exceeding 101,325 Pa (101,325 pa). This high compression ratio causes the exhaust temperature of traditional screw vacuum pumps to rise by over 250°C. This high temperature rise significantly impacts the proper operation of the screw vacuum pump, particularly its seals and wearing parts. The larger the screw vacuum pump, the greater its heat generation. Due to this high temperature rise, the current maximum screw vacuum pump capacity is limited to 1,300 m³ / h. To increase the suction capacity of a screw vacuum pump, its temperature rise must be addressed. The temperature rise of a screw vacuum pump is primarily due to the meshing properties of the screw end faces and the volume ratio between the threads of each segment.

[0003] At present, the rotor end face meshing profile of a twin-screw rotor dry vacuum pump usually adopts a combination of multiple cycloids and circular arcs, or a combination of cycloids, involutes, and circular arcs, etc. The end face curve of the rotor with a cycloid structure has certain inflection points, which not only increases the processing difficulty but also reduces the processing efficiency; in particular, the multi-segment cycloid profile structure has many transition connections between the curves, which makes it difficult to control the meshing clearance when the two rotors mesh with each other, resulting in incomplete meshing between the two screw rotors, thereby affecting the pumping performance of the screw vacuum pump; it also causes the dynamic balance of the screw rotor to deteriorate, which easily causes noise and vibration of the pump.

[0004] Therefore, the applicant proposes a variable pitch twin-screw rotor for a screw vacuum pump. Summary of the Invention

[0005] The purpose of the utility model is to overcome the above-mentioned shortcomings and provide a variable pitch twin-screw rotor for a screw vacuum pump, which has good rotor meshing, more uniform rotor gap, simpler processing, less gas reflux, higher pumping efficiency, lower temperature rise and energy consumption, and a wider range of use.

[0006] The purpose of this utility model is achieved in this way:

[0007] A variable pitch twin-screw rotor for a screw vacuum pump comprises a driving screw and a driven screw mounted in parallel within a pump chamber of the screw vacuum pump, rotating in opposite directions at constant speeds and meshing in pairs. The driving and driven screws rotate in opposite directions, and their end profiles are meshed with a 180° phase difference. The curved surfaces of the driving and driven screws are fully meshed, the end profile of the driving screw is composed of four conjugate curves, and the end profile of the driven screw is composed of four conjugate curves identical to those of the driving screw.

[0008] The rotor linear profile of the active screw from the highest point of the peak to the lowest point of the valley is composed of a tooth root arc line AB, an involute BC, a tooth top arc line CD and an involute DA connected in sequence; the centers of the tooth root arc line AB and the tooth top arc line CD are located on the same pitch circle, and the tooth root arc line AB and the tooth top arc line CD are smoothly transitioned and connected by the involute BC and the involute DA;

[0009] The active screw is provided with a first screw thread, a second screw thread, a third screw thread, a fourth screw thread, a fifth screw thread, a sixth screw thread and a seventh screw thread in sequence from the suction end to the exhaust end, the pitch lead between the first screw thread and the second screw thread is P1, the pitch lead between the second screw thread and the third screw thread is P2, the pitch lead between the third screw thread and the fourth screw thread is P3, the pitch lead between the fourth screw thread and the fifth screw thread is P4, the pitch lead between the fifth screw thread and the sixth screw thread is P5, and the pitch lead between the sixth screw thread and the seventh screw thread is P6;

[0010] The space between the first and third threads is the intake section, and the pitches of adjacent threads in the intake section are equidistant; the space between the third and fifth threads is the compression section, and the pitches of adjacent threads in the compression section gradually decrease; the space between the fifth and seventh threads is the exhaust section, and the pitches of adjacent threads in the exhaust section are equidistant; the lead at the starting point of the intake end is P1, and the lead at the ending point of the exhaust end is P2;

[0011] The tooth top circle radius of the active screw 1 is R, the tooth root circle radius is r, the pitch circle radius is r1, and the base circle radius is r0; the lead at the starting point of the suction end is P1, and the lead at the ending point of the exhaust end is P2;

[0012] r=2 / 5×R, r1=(R+r) / 2, r0=2 / 5×r.

[0013] Furthermore, the connection between the tooth root arc line AB, the involute line BC, the tooth top arc line CD and the involute line DA is smooth and has no inflection point.

[0014] Furthermore, the centers of the tooth root arc line AB and the tooth top arc line CD are both located on the main shaft center line.

[0015] Furthermore, the ratio of the radius of the tooth root arc line AB to the radius of the tooth top arc line CD is 2:5.

[0016] Furthermore, the tooth pitch P1 of the suction section is three times the tooth pitch P2 of the exhaust section.

[0017] Furthermore, the coordinate equation of the tooth root arc line segment AB is:

[0018] X = r × SINα;

[0019] Y = r × COSα;

[0020] α∈[0°,78°].

[0021] Furthermore, the coordinate equation of the involute BC segment between the root circle and the addendum circle is:

[0022] X=R×COS(θ+α)+R×(θ+ tgβ) ×SIN(θ+α);

[0023] Y= R×SIN(θ+α)- r0×(θ+ tgβ) ×COS(θ+α);

[0024] Where: θ is the initial angle of the involute, θ = tg(arccos(R / r)) - arccos(R / r), α is the rotation angle range of the involute, α∈[78°, 206°].

[0025] Furthermore, the coordinate equation of the tooth top circular arc line CD segment is:

[0026] X=R×COSφ;

[0027] Y=R×SINφ;

[0028] φ∈[206°, 270°].

[0029] Furthermore, the equation of the involute DA between the root circle and the addendum circle is:

[0030] X=R×SIN(2φ)-(R+r)×SINφ;

[0031] Y=(R+r)COSφ-R×COS(2φ);

[0032] φ∈[270°,360°] .

[0033] Furthermore, mutually meshing synchronous helical gears are respectively mounted on one side of the shaft ends of the driving screw and the driven screw.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] The utility model provides a variable pitch twin-screw rotor for a screw vacuum pump, wherein the end face profile is formed by a tooth root arc, a lower involute, a tooth top arc and an upper involute connected in sequence to form a meshing profile of the end face that is smooth, continuous and has no inflection point; through this four-section structure, no interference will be generated between the two screw rotors after they are formed, and the active and driven screw rotors always maintain the same meshing gap, ensuring that the screw tooth profile has good dry sealing performance and reducing gas reflux; compared with the previous end face profile structure, the screw rotor of the utility model has lower requirements for processing machine tools and processing tools than the traditional screw rotor processing requirements, thereby reducing processing costs, and the screw rotor has higher precision, and the meshing gap of the screw curved surface is smaller and more uniform, thereby improving the pumping efficiency of the screw vacuum pump.

[0036] Compared with the screw vacuum pump composed of the traditional multi-segment cycloid arc profile rotor, the screw vacuum pump using the screw rotor of the utility model has greatly improved the suction volume, suction efficiency and vacuum degree; and the rotor profile of the four-segment curve structure is more convenient to process than the conventional six-segment curve structure, and no trimming of the rotor is required during the later assembly process, and has a wide range of applications.

[0037] The screw threads of the suction section of the screw of the utility model are equidistantly distributed, the pitch of the screw threads of the compression section gradually decreases, the screw threads of the exhaust section are equidistantly distributed, the pitch P1 of the suction section is a multiple of the pitch P2 of the exhaust section, and the pitch ratio between the screw threads of each section from the suction port to the exhaust port is reasonably distributed, thereby reducing the compression ratio of the exhaust end of the screw vacuum pump close to the atmospheric pressure side, effectively reducing the exhaust temperature rise of the screw vacuum pump, and thus increasing the suction volume of the screw vacuum pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a structural diagram of the present utility model.

[0039] Figure 2 This is the end face matching diagram of the double rotors of the present utility model.

[0040] Figure 3 This is the end face meshing profile diagram of the present utility model.

[0041] Figure 4 This is the end profile diagram of the active screw rotor of the utility model.

[0042] in:

[0043] Active screw 1, first thread 1.1, second thread 1.2, third thread 1.3, fourth thread 1.4, fifth thread 1.5, sixth thread 1.6, seventh thread 1.7, driven screw 2. DETAILED DESCRIPTION

[0044] To better understand the technical solution of the present invention, the following detailed description is provided with reference to the relevant illustrations. It should be understood that the following specific embodiments are not intended to limit the specific implementation of the technical solution of the present invention; they are merely examples of possible implementations of the technical solution of the present invention. It should be noted that the description herein of the positional relationships of the various components, such as component A being located above component B, is based on the relative positions of the components in the illustrations and is not intended to limit the actual positional relationships of the components. Example 1

[0045] See also Figures 1-4 , Figure 1 A schematic structural diagram of the present invention is provided. As shown in the figure, a variable-pitch twin-screw rotor for a screw vacuum pump comprises a driving screw 1 and a driven screw 2 mounted in parallel within the pump chamber of the screw vacuum pump, rotating in opposite directions at constant speeds and meshing in pairs. The driving screw 1 and the driven screw 2 rotate in opposite directions, one to the left and the other to the right, and the end profiles of the driving screw 1 and the driven screw 2 are arranged in a meshing arrangement with a 180° phase difference.

[0046] The curved surfaces of the driving screw 1 and the driven screw 2 are fully meshed, the end profile of the driving screw 1 is composed of four conjugate curves, and the end profile of the driven screw 2 is composed of four conjugate curves identical to those of the driving screw 1; the end profile of the driving screw 1 is composed of four curves: the root arc line AB, the involute BC, the tooth top arc line CD, and the involute DA, and the end profile of the driven screw 2 is composed of four curves: the root arc line A'B', the involute B'C', the tooth top arc line C'D', and the involute D'A'; the connection between each of the above curves has a smooth transition without inflection points, ensuring that the two screw rotors of the driving screw 1 and the driven screw 2 are fully meshed in the pump body.

[0047] Since the end profile of the driven screw 2 is identical to that of the active screw 1, the rotor end profile of the active screw 1 is used as an example in this embodiment:

[0048] The rotor line of the active screw 1 from the highest point of the peak to the lowest point of the valley is composed of the tooth root arc line AB, the involute BC, the tooth top arc line CD and the involute DA connected in sequence;

[0049] The centers of the tooth root arc line AB and the tooth top arc line CD are located on the same pitch circle, that is, the centers of the tooth root arc line AB and the tooth top arc line CD are both located on the center line of the main shaft, and the tooth root arc line AB and the tooth top arc line CD are smoothly transitioned and connected by the involute BC and the involute DA.

[0050] In this embodiment, the ratio of the radius of the tooth root arc line AB to the radius of the tooth top arc line CD is 2:5, so that the screw dry vacuum pump can achieve the best volumetric efficiency and ensure that the screw rotor has sufficient mechanical strength.

[0051] The active screw 1 is provided with a first screw thread 1.1, a second screw thread 1.2, a third screw thread 1.3, a fourth screw thread 1.4, a fifth screw thread 1.5, a sixth screw thread 1.6 and a seventh screw thread 1.7 in sequence from the suction end to the exhaust end. The pitch lead between the first screw thread 1.1 and the second screw thread 1.2 is P1, the pitch lead between the second screw thread 1.2 and the third screw thread 1.3 is P2, the pitch lead between the third screw thread 1.3 and the fourth screw thread 1.4 is P3, the pitch lead between the fourth screw thread 1.4 and the fifth screw thread 1.5 is P4, the pitch lead between the fifth screw thread 1.5 and the sixth screw thread 1.6 is P5, and the pitch lead between the sixth screw thread 1.6 and the seventh screw thread 1.7 is P6;

[0052] The area between the first screw thread 1.1 and the third screw thread 1.3 is the intake section, and the pitches of adjacent screw threads in the intake section are equidistant; the area between the third screw thread 1.3 and the fifth screw thread 1.5 is the compression section, and the pitches of adjacent screw threads in the compression section gradually decrease; the area between the fifth screw thread 1.5 and the seventh screw thread 1.7 is the exhaust section, and the pitches of adjacent screw threads in the exhaust section are equidistant; the lead of the starting point of the intake end is P1, and the lead of the ending point of the exhaust end is P2, and the pitch P1 of the intake section is 3 times the pitch P2 of the exhaust section.

[0053] The tooth top circle radius of the active screw 1 is R, the tooth root circle radius is r, the pitch circle radius is r1, and the base circle radius is r0; the lead at the starting point of the suction end is P1, and the lead at the ending point of the exhaust end is P2;

[0054] r=2 / 5×R,

[0055] r1=(R+r) / 2,

[0056] r0=2 / 5×r,

[0057] P1=3×P2.

[0058] The rotor end profile equation of the active screw 1 is as follows:

[0059] (1) The coordinate equation of the tooth root arc line segment AB is:

[0060] X = r × SINα;

[0061] Y = r × COSα;

[0062] α∈[0°,78°].

[0063] (2) The coordinate equation of the involute segment BC between the root circle and the top circle is:

[0064] X=R×COS(θ+α)+R×(θ+ tgβ) ×SIN(θ+α);

[0065] Y= R×SIN(θ+α)- r0×(θ+ tgβ) ×COS(θ+α);

[0066] In the above formula: θ is the initial angle of the involute, θ = tg(arccos(R / r)) - arccos(R / r), α is the rotation angle range of the involute, α∈[78°, 206°].

[0067] (3) The coordinate equation of the CD segment of the tooth top arc is:

[0068] X=R×COSφ;

[0069] Y=R×SINφ;

[0070] φ∈[206°, 270°].

[0071] (4) The equation of the involute DA from the root circle to the top circle is:

[0072] X=R×SIN(2φ)-(R+r)×SINφ;

[0073] Y=(R+r)COSφ-R×COS(2φ);

[0074] φ∈[270°,360°] .

[0075] One side shaft end of the active screw 1 and the driven screw 2 is respectively provided with synchronous helical gears that mesh with each other.

[0076] Working principle:

[0077] This utility model provides a variable-pitch twin-screw rotor. The two screw rotors rotate synchronously in opposite directions within the pump chamber of a screw vacuum pump, forming a periodically changing working chamber volume and achieving the three working processes from suction to compression to exhaust. There is no contact between the two screw curved surfaces, between the two screw end faces and the pump chamber end face, or between the screw outer circle and the pump chamber inner hole. This type of screw vacuum pump has many advantages, including dry and oil-free operation, compact structure, smooth operation, no wearing parts, and high reliability. Therefore, the screw vacuum pump is suitable for extracting general gases, condensable gases, corrosive gases, and process gases containing certain dust particles. It can be widely used in the fields of solar energy, lithium batteries, aerospace, chemical and pharmaceutical industries, microelectronic integrated circuits, metallurgy, etc.

[0078] The better the meshing of the screw end profile, the less gas recirculation, the smaller the gas turbulence, and the lower the temperature rise. Properly distributing the pitch ratio between the threads of each section from the suction port to the exhaust port, especially reducing the compression ratio on the exhaust side of the screw vacuum pump close to atmospheric pressure, can effectively reduce the exhaust temperature rise of the screw vacuum pump, thereby increasing the suction capacity of the screw vacuum pump. In this utility model, the threads of the suction section are evenly spaced, the pitch of the threads of the compression section gradually decreases, and the threads of the exhaust section are evenly spaced. The pitch P1 of the suction section is three times the pitch P2 of the exhaust section.

[0079] The screw rotor profile of this utility model is composed of four sequentially connected peak-valley curves. The profile, from the highest point of the peak to the lowest point of the valley, is formed by the root circle AB, the involute BC, the tip circle CD, and the involute DA, which are connected in sequence. The radii of the root circle (AB) and the tip circle (CD) are set at a predetermined ratio, and the centers of the root circle (AB) and the tip circle (CD) lie on the same axis. The root circle (AB) and the tip circle (CD) are transitionally connected by the involute (BC) and the involute (DA). This four-segment structure prevents interference between the two screw rotors after molding, and the meshing clearance between the driving and driven screw rotors is always the same. A vacuum pump manufactured using this screw profile is simple to manufacture, has good rotor meshing clearance, good sealing between the screw teeth, good rotor coordination, low energy consumption, and a wide range of applications.

[0080] The above are only specific application examples of the present invention and do not constitute any limitation on the scope of protection of the present invention. Any technical solution formed by equivalent transformation or equivalent replacement shall fall within the scope of protection of the present invention.

Claims

1. A variable pitch twin screw rotor for a screw vacuum pump, characterized in that: The invention comprises a driving screw (1) and a driven screw (2) which are installed in parallel in a pump chamber of a screw vacuum pump and rotate at a constant speed in opposite directions and meshed in pairs, wherein the driving screw (1) and the driven screw (2) rotate in opposite directions, and the end surface profiles of the driving screw (1) and the driven screw (2) are arranged in a meshing manner with a 180° phase difference; the curved surfaces of the driving screw (1) and the driven screw (2) are completely meshed, the end surface profile of the driving screw (1) is composed of four conjugate curves, and the end surface profile of the driven screw (2) is composed of four conjugate curves which are completely identical to those of the driving screw (1); The rotor linear profile of the active screw (1) is formed by connecting the tooth root arc line AB, the involute BC, the tooth top arc line CD and the involute DA in sequence; the centers of the tooth root arc line AB and the tooth top arc line CD are located on the same pitch circle, and the tooth root arc line AB and the tooth top arc line CD are smoothly transitioned and connected by the involute BC and the involute DA; The active screw (1) is provided with a first screw thread (1.1), a second screw thread (1.2), a third screw thread (1.3), a fourth screw thread (1.4), a fifth screw thread (1.5), a sixth screw thread (1.6) and a seventh screw thread (1.7) in sequence from the air intake end to the air discharge end; the pitch lead between the first screw thread (1.1) and the second screw thread (1.2) is P1, the pitch lead between the second screw thread (1.2) and the third screw thread (1.3) is P2, the pitch lead between the third screw thread (1.3) and the fourth screw thread (1.4) is P3, the pitch lead between the fourth screw thread (1.4) and the fifth screw thread (1.5) is P4, the pitch lead between the fifth screw thread (1.5) and the sixth screw thread (1.6) is P5, and the pitch lead between the sixth screw thread (1.6) and the seventh screw thread (1.7) is P6; The space between the first thread (1.1) and the third thread (1.3) is an intake section, and the pitches of adjacent threads in the intake section are equidistant; the space between the third thread (1.3) and the fifth thread (1.5) is a compression section, and the pitches of adjacent threads in the compression section gradually decrease; the space between the fifth thread (1.5) and the seventh thread (1.7) is an exhaust section, and the pitches of adjacent threads in the exhaust section are equidistant; the lead at the starting point of the intake end is P1, and the lead at the ending point of the exhaust end is P2; The active screw (1) has a tooth top circle radius of R, a tooth root circle radius of r, a pitch circle radius of r1, and a base circle radius of r0; a lead at the starting point of the suction end is P1, and a lead at the ending point of the exhaust end is P2; r=2 / 5×R, r1=(R+r) / 2, r0=2 / 5×r.

2. The variable pitch twin-screw rotor for a screw vacuum pump according to claim 1, characterized in that: The connection points of the tooth root circular arc line AB, the involute line BC, the tooth top circular arc line CD and the involute line DA are smoothly transitioned without an inflection point.

3. The variable pitch twin-screw rotor for a screw vacuum pump according to claim 1, characterized in that: The centers of the tooth root arc line AB and the tooth top arc line CD are both located on the main shaft center line.

4. The variable pitch twin-screw rotor for a screw vacuum pump according to claim 1, characterized in that: The ratio of the radius of the tooth root arc line AB to the radius of the tooth top arc line CD is 2:

5.

5. The variable pitch twin-screw rotor for a screw vacuum pump according to claim 1, characterized in that: The tooth pitch P1 of the suction section is three times the tooth pitch P2 of the exhaust section.

6. The variable pitch twin-screw rotor for a screw vacuum pump according to claim 1, characterized in that: The coordinate equation of the tooth root arc line AB segment is: X = r × SINα; Y = r × COSα; α∈[0°，78°]。 7. The variable pitch twin-screw rotor for a screw vacuum pump according to claim 1, characterized in that: The coordinate equation of the involute BC segment between the root circle and the addendum circle is: X=R×COS(θ+α)+R×(θ+ tgβ) ×SIN(θ+α); Y= R×SIN(θ+α)- r0×(θ+ tgβ) ×COS(θ+α); Where: θ is the initial angle of the involute, θ = tg(arccos(R / r)) - arccos(R / r), α is the rotation angle range of the involute, α∈[78°, 206°].

8. The variable pitch twin-screw rotor for a screw vacuum pump according to claim 1, characterized in that: The coordinate equation of the tooth top circular arc line CD segment is: X=R×COSφ; Y=R×SINφ; φ∈[206°, 270°].

9. The variable pitch twin-screw rotor for a screw vacuum pump according to claim 1, characterized in that: The equation of the involute DA between the root circle and the addendum circle is: X=R×SIN(2φ)-(R+r)×SINφ; Y=(R+r)COSφ-R×COS(2φ); φ∈[270°,360°] .

10. The variable pitch twin-screw rotor for a screw vacuum pump according to claim 1, characterized in that: The driving screw (1) and the driven screw (2) are respectively provided with mutually meshing synchronous helical gears on their shaft ends.

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