JP3979489B2 - Screw rotor and screw machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a screw rotor applied to a screw machine, and a screw machine such as a dry vacuum pump using the screw rotor.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a volume transfer screw machine having a pair of screw rotors in a housing is known as a pump or compressor capable of continuous operation at high speed for a long time.
In this type of screw machine, for example, a screw machine used as a dry vacuum pump, male and female screw rotors having a reverse screw relationship are arranged in parallel and both rotors are engaged with each other with a minute clearance therebetween. A working chamber partitioned by the meshing portions of both rotors is formed between the rotor and the housing surrounding these rotors. In addition, by rotating the male and female screw rotors synchronously, the volume of the working chamber is increased on the intake side and decreased on the exhaust side while the male and female screw rotors are in a substantially non-contact state.
[0004] In general, vacuum pumps generally require two important performances of ultimate pressure and exhaust speed, but in screw machines such as dry vacuum pumps, male and female screw rotors are arranged in parallel. And the clearance between the two rotors and the housing greatly affect the performance. Therefore, in such a screw machine, the performance is improved by minimizing the clearance between the male and female screw rotors and the clearance with the housing as much as possible.
The screw machine includes a re-sholm type, a square screw type (having a Quimby type (square) tooth shape), and a spiral type (a spiral screw synthesized with an epitrochoid and an Archimedes spiral). Some types have a tooth profile).
[0006]
[Problems to be solved by the invention]
However, in the above conventional screw machine, the number of male and female screw rotors is set to one for sealing the exhaust chamber, so that the center of gravity of the rotor is not on the shaft on the shaft cross section and the balance against rotation is poor. For this reason, when the clearance between the male and female screw rotors and the clearance between the housings are very small, vibration occurs when both screw rotors are rotated at high speed with a large load, and the rotors or the rotor and the casing frequently come into contact with each other. . Therefore, seizure occurred between the rotors or between the rotor and the housing. In order to avoid this, there has been a problem that the gap between the male and female screw rotors and the clearance with the housing have to be increased more than necessary, or the rotational speed has to be greatly limited.
In order to avoid this, the center of gravity of the cross section orthogonal to the rotation axis is not greatly displaced from the center of rotation by a cast hole or the like that opens to the end face of the screw rotor so as to balance the couple. There is also a problem that a cavity needs to be formed and the manufacturing process becomes complicated.
Accordingly, the present invention aims to improve the performance by reducing the meshing gap between the screw rotors, and at the same time, a screw machine that can effectively prevent seizure between the rotors even during a long high-speed continuous operation. Is intended to provide.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides screw teeth having a helical tooth tip surface portion and a tooth root surface portion forming a spiral groove between the tooth tip surface portions around the rotation axis, which are opposite to each other. A pitch used as a pair of males and females in a screw relationship, and forming a circular arc in a predetermined angle range having a constant radius on an arbitrary transverse section perpendicular to the rotation axis between the tip surface portion and the tooth surface portion of the screw tooth. In the screw rotor provided with the circumferential portion, each of the screw portions of both the rotors has two or more threads , and at least several pitch circumferential portions are provided on the transverse section, and several pitch circumferential portions. Were arranged symmetrically with respect to the rotation axis.
[0010]
With this configuration, the position of the center of gravity does not greatly deviate from the center of rotation on the cross section orthogonal to the rotation axis, and the center of gravity is near the rotation center axis in any cross section perpendicular to the axis over the entire length of the rotor. Therefore, a very good rotation balance can be obtained. Therefore, it is not necessary to form complicated cavities by casting or the like, and it is possible to reduce the manufacturing cost. Further, since it rotates in a balanced manner around the rotating shaft, the clearance between the male and female screw rotors and the clearance with the housing can be reduced. It can be made extremely narrow, the sealing degree in the pump can be improved, and the backflow of the outside air from the exhaust side is suppressed, and a more efficient vacuum pump can be formed.
In addition, when both rotors come into contact with each other, the number of contact points in the axial direction increases, and the seizure of the rotor that occurs at the time of contact can be distributed throughout the rotor. The expansion contact of the rotor due to the rise can be prevented, and the clearance between the male and female screw rotors and the clearance with the housing can be narrowed.
Further, the pitch circumferential portion having a constant width can exhibit the required sealing performance at the meshing portion of the screw rotor, and the center of gravity can be brought close to the center of rotation, thereby improving the balance.
Further, when the screw rotor is thermally expanded by making the gap between the pitch circumferential portions of the meshing gaps of the male and female screw teeth smaller than the gaps of the other portions, the pitch of the same radius is obtained. The circumferential parts first come into contact with each other and come into rolling contact with each other, and seizure hardly occurs as compared with the conventional machine in which the tooth parts of both rotors are in sliding contact.
[0012]
A screw rotor with a plurality of screw parts having different leads so that the lead is smaller than the intake side, or an uneven lead screw rotor in which the pitch between the screw teeth gradually decreases steplessly as it approaches the exhaust side To do.
With this configuration, when both rotors come into contact, the number of contact points in the axial direction can be increased, and seizure of the rotor that occurs at the time of contact can be distributed throughout the rotor, resulting in a temperature rise only at a specific location. The expansion contact of the rotor can be prevented, and the clearance between the male and female screw rotors and the clearance with the housing can be extremely narrowed.
If the pitch circumferential portion is formed in a band shape at a radial position substantially in the middle between the tooth tip surface portion and the tooth root surface portion, the tooth profile of each rotor is made common to facilitate processing. In addition, the pitch circumferential portion having a constant width can exhibit the required sealing performance at the meshing portion of the screw rotor.
The screw tooth shape is a trocolloid tooth shape or an epitrocolloid tooth shape. With such a configuration, the confidentiality of the transfer chamber can be increased, and the exhaust capacity can be improved.
In the screw machine according to the present invention, the screw rotor is a male and female rotor that mesh with each other, and the rotors are housed in parallel in a non-contact meshing state in a housing formed with an intake port and an exhaust port. A plurality of working chambers are formed between the housing and the two rotors to be transferred in the axial direction of the rotating shaft by the rotation of the screw rotor.
In the present invention, when the screw rotor is thermally expanded, seizure is less likely to occur because the pitch circumferential portions having a constant radius first come into contact with each other and come into rolling contact with each other. In addition, since the meshing gap itself between the rotors can be narrowed between the pitch circumferential portions, the efficiency can be improved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. 1 to 6 are views showing a screw rotor and a screw machine according to an embodiment of the present invention.
The screw machine of this embodiment is an application of the present invention to a dry vacuum pump. FIG. 1 is a front sectional view of a main part of a dry vacuum pump embodying the present invention. A housing 11 having an intake port 11a and an exhaust port 11b; male and female screw rotors 21 and 22 housed in parallel in the housing 11 so as to mesh with each other in a non-contact meshing state with a predetermined clearance (minute gap); Bearings 23a and 23b and seal members 24a and 24b for sealing the shaft holes interposed between the housing 11 and the screw rotors 21 and 22, and the screw rotor 21 so that both the rotors 21 and 22 are synchronously rotated in the opposite directions. And a driving means 27 having a motor 26 connected to one end of the rotor 22.
The female screw rotor 21 and the male screw rotor 22 have a predetermined clearance with respect to the inner wall surface 11i of the housing 11, for example, an outer diameter dimension and an axial length separating a gap of 50 microns. The housing 11 and the screw rotors 21 and 22 are separated from each other by meshing portions of the screw rotors 21 and 22 and are moved in the axial direction of the rotating shaft by the rotation of the screw rotors 21 and 22. A working chamber having a shape is formed.
[0020]
As shown in FIG. 2, the screw rotor 21 is provided with helical screw teeth 211 around the rotation axis C1, and the screw teeth 211 include a helical belt-like tooth tip surface portion 211a and a tooth tip thereof. A tooth root surface portion 211c that forms a spiral groove having a predetermined groove width between the surface portions 211a. Further, between the tooth tip surface portion 211a and the tooth root surface portion 211c of the screw tooth 211, a pitch circumferential portion 211p, a tooth tip side inclined surface closer to the tooth tip surface portion 211a than the pitch circumferential portion 211p, and the pitch circumference A tooth base side inclined surface 211e on the tooth base surface part 211c side of the part 211p is provided.
[0021]
On the other hand, the screw rotor 22 is provided with spiral screw teeth 221 around the rotation axis C2 so as to have a reverse screw relationship with the screw rotor 21, and the screw teeth 221 are formed in a spiral band shape. , And a tooth root surface portion 221c that forms a spiral groove having a predetermined groove width between the tooth tip surface portions 221a. Further, between the tooth tip surface portion 221a and the tooth root surface portion 221c of the screw tooth 221, a pitch circumferential portion 221p, a tooth tip side inclined surface closer to the tooth tip surface portion 221a than the pitch circumferential portion 221p, and a pitch circumference. a tooth root side inclined surface of the tooth root surface portion 221c side of the part 221p, it is provided.
The connecting portions between the tooth tip surface portions 211a and 221a and the pitch circumferential portions 211p and 221p of the screw rotors 21 and 22 are smoothly connected on the transverse section of the rotors 21 and 22, for example, in an arc shape. The connection curve between the pitch circumferential portions 211p and 221p and the tooth root surface portions 211c and 221c of the screw rotors 21 and 22 is smoothly connected on the cross section of the rotors 21 and 22. A connection curve between the tooth tip surface portions 211a and 221a and the tooth root surface portions 211c and 221c of the screw rotors 21 and 22 is formed on the cross section of the rotors 21 and 22 with the mating screw. Each connection shape is set so as to be a trochoidal curve drawn by the tooth tips of the rotors 22 and 21 (one side end portions of the tooth tip surface portions 221a and 211a). To have.
[0023]
FIG. 3 is a right-angle tooth profile curve diagram showing an embodiment of the screw rotor according to the present invention. FIG. 3 shows two rotors meshed with each other, and both rotors are formed in a casing having a rotor chamber having an 8-shaped cross section formed by a rotating cylinder of tooth tips of both rotors shown by outermost dotted lines in the drawing. It is stored. The space 305 formed by the notches 303 and 304 by the rotation of the rotor is transferred from the intake side to the exhaust side to be evacuated. Reference numerals 306, 307, 308, 309, 310, and 311 denote pitch circles. In the case of two strips as shown in FIG. 3, the balance can be improved by arranging pitch circles at 306 and 309 on the diagonal side with respect to the respective rotation axes of the notches 303 and 304. Furthermore, by providing a pitch circle part at a diagonal position with respect to a pair of rotating shafts, such as 308 and 307 and 310 and 311, the center of gravity can be made closer to the center of rotation, and the point where both screw rotors come into contact with each other Can be increased and the force of contact is dispersed.
As shown in FIG. 4, when the screw rotors 21 and 22 are engaged with the mating rotors in which the male and female are opposite to each other, the pitch circumferential portions 211p and 221p of the meshing clearance between the male and female screw teeth 211 and 221 are shown. Pitch circumferential portions 211p and 221p so that the gap g1 between them (gap between opposing surfaces, eg 20 μm) is smaller than the gaps g2, g3, g4 (gap between opposing surfaces, eg 50 μm) etc. And the tooth profile (screw tooth shape in each rotor longitudinal section) are set.
In the screw machine of the present embodiment constructed as described above, the male and female screw rotors 21 and 22 mesh with each other in a non-contact meshing state with a minute clearance at the start or during the normal operation. At this time, the gap g1 between the pitch circumferential portions 211p and 221p among the meshing clearances of the male and female screw teeth 211 and 221 is smaller than the clearances g2, g3, g4, etc. of the other meshing parts. When the screw rotors 21 and 22 are thermally expanded due to high-speed, long-time continuous operation or the like, the pitch circumferential portion 211p having a constant radius is obtained. 221p will contact | abut at first and will be in rolling contact, and it is hard to produce seizing compared with the conventional machine with which the tooth parts 211 and 221 of both the rotors 21 and 22 are slidably contacted. In addition, even in the case of contact, by increasing the number of pitch circles on the axial vertical cross section, the heat generated by the contact of the rotor can be dispersed, and thus the thermal expansion that partially increases the rotor is suppressed. The clearance gap between the male and female screw rotors and the clearance with the housing can be made extremely narrow. Therefore, unlike the conventional case, the clearance is unnecessarily enlarged to prevent seizure, and the pump performance and the compressor performance are not sacrificed. Therefore, a high-performance screw machine can be provided.
Further, since the screw rotors 21 and 22 are configured in two or more lines, the offset of the center of gravity position from the rotation centers C1 and C2 becomes extremely small. Combined with positioning on the central axis, there is no need to form a complex cavity such as casting to balance the couple, and the number of processing steps can be reduced to the extent that a simple shallow recess is formed. .
Further, since the pitch circumferential portions 211p and 221p are formed in a band shape at a radial position substantially in the middle between the tooth tip surface portions 211a and 221a and the tooth root surface portions 211c and 221c, the tooth shapes of the rotors 21 and 22 are formed. The processing can be facilitated by common use, and the required circumferential sealing performance in the meshing portions (between adjacent working chambers) of the screw rotors 21 and 22 is exhibited by the pitch circumferential portions 211p and 221p having a constant width. It will be.
In the above-described embodiment, each screw rotor is described as having the same screw lead from the intake side to the exhaust side. However, for example, the leads are different from each other so that the compression side lead is smaller than the intake side. It may be provided with a plurality of screw parts, or the pitch between the screw teeth gradually decreases steplessly as it approaches the exhaust side. In other words, a screw rotor with unequal leads can be obtained.
[0029]
FIG. 5 is a cross-sectional view perpendicular to the axis when the screw tooth profile of the present invention is made into three strips. In FIG. 5, reference numerals 406 and 407 denote three rotors that mesh with each other, and both rotors are rotor chambers having an eight-shaped cross section formed by rotating cylinders of tooth tips of both rotors indicated by the outermost dotted line in the figure. It is stored in the casing which has. The space 403 formed by the notches 401 and 402 by the rotation of the rotor is evacuated by being transferred from the intake side to the exhaust side. Reference numerals 404, 405, 410 and 411 denote pitch circles. Even in the case of three strips , it is possible to improve the balance by arranging pitch circles at 404 and 405 on each side with respect to the notches 401 and 402 , respectively. Furthermore, by providing another set of pitch circles 410 and 411 , the center of gravity can be made closer to the center of rotation, the number of points where both screw rotors come into contact can be increased, and the force caused by the contact is dispersed. Therefore, the heat generated by the contact of the rotor can be dispersed, so that the thermal expansion that partially increases the rotor can be suppressed, and the clearance between the male and female screw rotors and the clearance with the housing can be extremely narrowed.
Further, the tooth profile of the present embodiment is a trocolloid tooth profile or an epitrocolloid tooth profile, whereby the airtightness of the exhaust phase space formed by both the screw rotor and the housing can be improved.
【The invention's effect】
According to the present invention, by using two or more screws, the balance of the screw rotor is improved during continuous and high speed operation, and when the thermal expansion expands, the pitch circumferential portions having a constant radius are first brought into contact with each other. It is possible to prevent the seizure from occurring due to the rolling contact and the tooth portions of both rotors slidingly contacting each other. Furthermore, by providing a plurality of pitch circumferential portions, it is possible to prevent further seizure from occurring, and even if the exhaust performance is sacrificed, the screw rotor engagement gap must be set large in order to prevent seizure. The conventional problem of not becoming can be solved. Moreover, the airtightness of the phase space formed by both screws can be improved by making the tooth form a trocolloid tooth form or an epitrocolloid tooth form.
[Brief description of the drawings]
FIG. 1 is a front sectional view of an essential part showing a schematic internal structure of a screw machine according to an embodiment of the present invention.
FIG. 2 is a front view showing a meshed state of male and female screw rotors according to an embodiment of the present invention.
3 is a cross-sectional view taken along the line AA in FIG.
FIG. 4 is a schematic cross-sectional view showing a setting state of meshing gaps of male and female screw rotors according to an embodiment of the present invention.
FIG. 5 is a front view showing a meshed state of male and female screw rotors according to another embodiment of the present invention.
[Explanation of symbols]
11 Housing 11a Intake port 11b Exhaust port 21 Female screw rotor 22 Male screw rotor 25a, 25b Synchronous gear 26 Motor 121, 122 Screw rotor 121h1, 121h2, 122h1, 122h2 Recessed portions 211, 221 Screw teeth 211a, 221a Tooth tip surface portion 211c 221c tooth base surface portion 211d, 221d tooth tip side inclined surface 211e, 221e tooth base side inclined surface 211p, 221p pitch circumferential portion

Claims (6)

A screw tooth having a helical tooth tip surface portion and a tooth root surface portion forming a helical groove between the tooth tip surface portions around the rotation axis is used in a pair of males and females having a reverse screw relationship with each other, In a screw rotor provided with a pitch circumferential portion that forms an arc of a predetermined angle range having a constant radius on an arbitrary transverse section orthogonal to the rotation axis, between a tooth tip surface portion and a tooth root surface portion of the screw tooth, Each screw part of both rotors has two or more threads , and at least several pitch circumferential parts are provided on the transverse section, and several pitch circumferential parts are arranged symmetrically with respect to the rotation axis. Screw rotor characterized by   2. The screw rotor according to claim 1, wherein a gap between pitch circumferential portions of the meshing gaps of the male and female screw teeth is equal to or less than a gap of another portion. A screw rotor with a plurality of screw parts having different leads so that the lead is smaller than the intake side, or an uneven lead screw rotor in which the pitch between the screw teeth gradually decreases steplessly as it approaches the exhaust side screw rotor according to claim 1 or 2, characterized in that.   4. The screw rotor according to claim 1, wherein the pitch circumferential portion is formed in a band shape at a substantially intermediate radial position between the tooth tip surface portion and the tooth root surface portion.   The screw rotor according to claim 1, 2, 3, or 4, wherein the screw tooth shape is a trocolloid tooth shape or an epitrocolloid tooth shape. The screw rotor according to claim 1, 2, 3, 4 or 5, wherein both rotors are housed in parallel so as to mesh in a non-contact mesh state in a housing having an intake port and an exhaust port, A screw machine characterized in that a plurality of working chambers are formed between a housing and both rotors to be transferred in the axial direction of the rotary shaft by the rotation of the screw rotor.

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