KR101184716B1 - Screw rotor and vacuum pump - Google Patents

Abstract

The present invention relates to a screw rotor capable of compressing gas, and according to the present invention, an upstream screw portion (43a) formed on the upstream side of the gas conveying direction and formed at equal intervals with an interval of the upstream thread (41a), The downstream screw portion 43b formed continuously on the downstream side in the gas conveying direction of the upstream screw portion 43a, wherein an interval of the downstream screw thread 41b is narrower than an interval of the upstream screw thread 41a and at equal intervals. And a screw rotor 26 having a downstream threaded portion 43b which is formed and is continuously connected to the gas transfer direction upstream end of the downstream thread 41b and the downstream end of the upstream thread 41a by an inflection point 43c. 27) can be provided at low cost.

Description

Screw rotor and vacuum pump

1 is an overall explanatory diagram of a screw type dry vacuum pump according to the first embodiment.

FIG. 2 is an explanatory view of the screw rotor of Embodiment 1, A is a cross-sectional view, FIG. 2 is a side view, FIG. 2 is a view seen from the arrow IIC direction of FIG. 2, FIG. It is the figure seen from the arrow IID direction of B of FIG.

FIG. 3 is an explanatory view of principal parts of the screw rotor of Example 1, FIG. 3A is a cross-sectional view taken along line IIIA-IIIA of FIG. 2B, and FIG. 3B is an enlarged explanatory diagram of part IIIB of FIG. 2A, FIG. 3C is an enlarged explanatory diagram of part IIIC of A in FIG. 2.

4 is an exploded view of the outer side surface of the screw rotor of Example 1. FIG.

FIG. 5 is an overall explanatory diagram of a screw type dry vacuum pump according to the second embodiment, and corresponds to FIG. 1 of the first embodiment.

FIG. 6 is an explanatory view of a screw rotor of Embodiment 2 corresponding to FIG. 2 of Embodiment 1, FIG. 6A is a sectional view, FIG. 6B is a side view, and FIG. 6C is an arrow VIC direction of FIG. 6B. FIG. 6D is a view seen from the arrow VID direction of FIG. 6B, and FIG. 6E is an enlarged explanatory view of the VIE portion of A of FIG.

FIG. 7 is an exploded view of the outer surface of the screw rotor of Example 2, and corresponds to FIG. 4 of Example 1. FIG.

[Description of Symbols]

One… Vacuum pump

21, 22... Axis of rotation

26, 27, 26 ', 27'... Screw rotor

41a... Upstream Thread

41b... Downstream thread

43.. screw

43a, 43a ’... Upstream Thread

43b, 43b ’... Downstream thread

43c... Inflection point

44a... Upstream Interference Prevention Part

44b... Downstream interference prevention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw rotor with a screw formed on its outer circumferential surface and a screw-type vacuum pump having a pair of said screw rotors.

BACKGROUND ART As a vacuum pump for evacuating a vacuum chamber, a screw-type vacuum pump for conveying and evacuating gas by rotating a pair of screw rotors having a screw formed on an outer circumferential surface thereof is known.

As such a screw type dry vacuum pump, for example, conventional techniques such as Japanese Patent Application Laid-Open No. 2000-45976 are known in the art.

The patent document describes a screw-type dry vacuum having a pair of screw rotors formed on the outer circumferential surface of a lead having the same lead (distance advanced when one screw is rotated, and in the case of one screw, a pitch (gap between threads)). Pumps are described.

(Problems with Prior Art)

In the screw type vacuum pump of the prior art, since the screw of the screw rotor is an equal lead, the gas is conveyed without being compressed when the gas is exhausted from the upstream side to the exhaust side.

As a technique for compressing gas during transportation to the screw rotor, a screw rotor in which the screw pitch of the screw rotor is continuously smoothly changed to be the maximum at the intake side and the minimum at the exhaust side is considered. However, when the pitch is continuously changed, the processing is complicated and the cost is high.

In the screw-type vacuum pump, the threads of the pair of screw rotors are arranged to engage with a slight gap, and when the threads are rectangular teeth, they interfere with the mating surface of the threads during rotation (contact). ) Occurs. For this reason, in the conventional screw type vacuum pump, the side surface shape (interference prevention part) of a thread is processed so that the front end side of a thread may become narrow (thinner) in order to prevent interference of a thread. However, since the interference of the teeth increases as the lead increases, it is necessary to continuously change the side shape when the pitch is changed continuously. For this reason, when the pitch is continuously changed, the side shape cannot be processed by one type of end mill, which causes a complicated machining and a cost increase.

In addition, in the screw rotor, a rotor in which a large lead (large pitch) screw is formed and a rotor in which a small lead (small pitch) screw are formed are arranged at axial intervals on the same rotation axis in order to compress the gas transported. It is also practical. However, since the change in the exhaust volume between the large lead rotor and the small lead rotor is not continuous, there is a problem that the exhaust efficiency is lowered. In addition, since the two rotors are arranged at intervals, there is a problem that the length in the axial direction of the rotor (the length of the rotor) tends to be long. When the length of the rotor becomes longer, the apparatus becomes larger and the bearings supporting the rotating shaft must be disposed at both ends, and the bearings must be disposed on the vacuum side. When the bearing is disposed on the vacuum side, it is necessary to supply lubricant to the bearing, to prevent contamination of the vacuum chamber by the lubricant, etc., resulting in a complicated configuration and a cost increase.

It is a first object of the present invention to provide a screw rotor capable of compressing gas at low cost in view of the above problems.

Further, it is a second technical problem to shorten the length of the rotor while increasing the exhaust efficiency of the screw rotor.

(Invention)

(1st invention)

In order to solve the above technical problem, the screw rotor of the first invention,

In the screw rotor is formed on the outer circumferential surface and rotates about the rotation axis to transfer the gas,

An upstream threaded portion formed on the upstream side of the gas conveying direction and formed at equal intervals between the upstream threaded portions;

A downstream screw portion formed continuously to the downstream side of the gas conveying direction of the upstream threaded portion, wherein an interval of the downstream thread is narrower than an interval of the upstream thread and formed at equal intervals, and an upstream of the gas flow direction of the downstream screw thread. A stage and a downstream end in the gas transfer direction of the upstream side thread are provided with the downstream side threaded portion connected continuously by an inflection point.

(Operation of the First Invention)

In the screw rotor according to the first aspect of the invention, the screw is formed on the outer circumferential surface and rotates about the rotation axis to convey the gas. On the upstream side of the screw rotor in the gas conveying direction, an upstream side threaded portion in which an interval of the upstream side threads is formed at equal intervals is formed. The downstream screw portion formed continuously on the downstream side in the gas conveying direction of the upstream screw portion is formed such that the space between the downstream threads is narrower than the space between the upstream threads and at equal intervals. The downstream screw portion is continuously connected to the upstream end of the downstream screw thread in the gas transfer direction and the downstream end of the upstream screw thread by the inflection point.

Therefore, in the screw rotor of the first aspect of the invention, both the upstream screw portion and the downstream screw portion are formed at equal pitches. Therefore, compared with the case where a pitch changes continuously, it can manufacture easily and can suppress a cost.

Further, in the screw rotor of the first aspect of the invention, the pitch of the downstream screw portion is narrower than that of the upstream screw portion, so that the gas is compressed when the gas shifts from the upstream screw portion to the downstream screw portion. At this time, since the downstream end of the upstream screw portion and the upstream end of the downstream screw portion are continuously connected by the inflection point, the exhaust volume is continuously changed near the inflection point. Therefore, compared with the case where rotors with different pitches are arranged at intervals and the exhaust volume is discontinuous, the exhaust efficiency can be increased and the length of the rotor can be shortened. In addition, since the length of the rotor is shortened, it is easy to adopt a one-side supporting structure for arranging the bearing on one side of the rotating shaft.

(Form 1 of 1st invention)

The screw rotor of the form 1 of the first invention is the first invention described above.

The upstream side screw portion having an upstream side interference prevention portion formed on a side of the upstream side threaded portion so as to narrow the tip side of the threaded portion,

And a downstream screw portion formed on a side surface of the downstream screw thread and having a downstream interference preventive portion of a shape different from the upstream interference preventive portion.

(Operation of Form 1 of the First Invention)

In the screw rotor according to the first aspect of the first aspect of the present invention, the upstream side interference prevention part in which the distal end side of the thread is narrow is formed on the side surface of the upstream side thread of the upstream side thread. The downstream side interference prevention part of a shape different from the said upstream side interference prevention part is formed in the side surface of the downstream thread of the said downstream side thread part. Therefore, the interference prevention part corresponding to the interference in the engagement part of screw rotors is formed, and interference can be prevented.

(2nd invention)

In order to solve the above technical problem, the vacuum pump of the second invention,

It is characterized by including the screw rotor of the said 1st invention or the form 1 of 1st invention.

(Operation of the Second Invention)

Since the vacuum pump of the 2nd invention provided with the said structure is equipped with the screw rotor of the 1st invention or the form 1 of 1st invention, it has the same effect | action as the form 1 of 1st invention or 1st invention.

Next, although the specific example (example) of embodiment of this invention is described referring drawings, this invention is not limited to the following example.

In the drawings, the front and rear directions are referred to as the X-axis direction, the left and right directions as the Y-axis direction, and the up and down directions are referred to as the Z-axis direction, and the directions indicated by the arrows X, -X, Y, -Y, Z, and -Z, or the indicated sides, respectively. It is called front, rear, right, left, upward, downward, or front, rear, right, left, top, and bottom.

In addition, in the drawings, '·' in the '○' means an arrow from the back of the ground to the front, and '×' in the '○' means an arrow from the front of the ground to the back.

Example 1

1 is an overall explanatory diagram of a screw type dry vacuum pump according to the first embodiment.

In FIG. 1, the screw type dry vacuum pump 1 of Example 1 as a vacuum pump of this invention has the base 2. As shown in FIG. The base 2 has an upper base 3 and a lower base 4, and a gear chamber 6 is provided inside the upper base 3 and the lower base 4. The motor support part 3a which supports the pump driving motor M is formed in the right part of the base 2, The motor support part 3a has the motor shaft through-hole 3b which the drive shaft M1 penetrates. Formed. A pair of upper bearing supports 3c is formed at the upper left end of the upper base 3. An exhaust duct 7 is fixedly supported on the left side of the upper base 3, and a downstream end of the exhaust passage 3d formed inside the upper base 3 is connected to the exhaust duct 7. An exhaust port 3e is formed at an upstream end of the exhaust passage 3d.

The lower bearing support part 4a is provided in the upper left side of the lower base 4, and the lubricant for bearing lubrication is stored in the bottom of the lower base 4.

A cylindrical casing 11 is supported on the upper left side of the upper base 3, and an upper end of the casing 11 is closed by a cover 12. The cover 12 is provided with an inlet 12a communicating with a vacuum chamber (not shown). Therefore, in the upper end surface of the upper base 3, the casing 11, and the cover 12, the pump chamber 13 which has an exhaust port 3e in the lower end of the inlet 12a is provided in the upper end. On the outer circumferential side of the lower end of the casing 11 and the upper end of the upper base 3, a donut-shaped cooling water passage 14 through which cooling water for cooling the pump chamber 13 flows is formed.

A pair of left and right rotor shafts (rotating shafts) 21 and 22 penetrate the pump chamber 13 and the gear chamber 6 inside the base 2 and the casing 11. The rotor shafts 21 and 22 are rotatably supported by the upper bearing support 3c and the lower bearing support 4a in the gear chamber 6 via bearings 23 and 24. The left screw rotor 26 and the right screw rotor 27 meshing with each other are supported in the pump chamber 13 of the rotor shafts 21 and 22. Seal mechanism accommodating portions 26a and 27a (see FIG. 2 described later) are formed in lower ends of the screw rotors 26 and 27, and a tapered shape penetrating upwards in the upper part of the seal mechanism accommodating portions 26a and 27a. Shaft through holes 26b and 27b are formed. The tapered upper ends of the rotor shafts 21 and 22 penetrate through the shaft through holes 26b and 27b. The upper end of the rotor shaft (21, 22) is formed with a screw portion, the rotor shaft (21, 22) and the screw rotor (26, 27) by a nut (N) screwed to the screw portion via a washer (Ｗ) Is rotatably connected integrally.

The housing 28 for attaching a seal is supported on the upper side of the upper bearing 23. The seal mechanism accommodating portion 26a has an oil seal 29a supported by the seal attaching housing 28 or flingers 29b and 29c rotating together with the rotor shafts 21 and 22, so that gas or lubricant leaks. The seal mechanism 29 for preventing a back flow etc. is arrange | positioned.

The rotor shafts 21 and 22 in the gear chamber 6 are supported with timing gears 31 and 32 which are engaged with each other and transmit a driving force. In the vacuum pump of the first embodiment, a rotation transmission gear portion 32a is formed below the right timing gear 32, and the right timing gear 32 has a key not shown on the right rotor shaft 22. It is integrally rotatably supported by the key groove. In addition, the left timing gear 31 is connected to the left rotor shaft 21 by a joint 33, and the joints 33 engage the gears 31 and 32 and the screw rotors 26 and 27. The engagement can be performed easily.

The drive gear 36 is fixedly supported on the drive shaft M1 of the pump driving motor M through the intermediate gear 37 which meshes with the drive gear 36 and the rotation transmission gear portion 32a. Rotation is transmitted to the timing gears 31 and 32. On the other hand, the lubricant stored in the lower base 4 is supplied to the bearing 38 and the other bearings 23 and 24 which rotatably support the intermediate gear 37 by a lubricant supply device (not shown).

(Explanation of screw rotor)

FIG. 2 is an explanatory view of the screw rotor of Embodiment 1, A is a cross-sectional view, FIG. 2 is a side view, FIG. 2 is a view seen from the arrow IIC direction of FIG. It is the figure seen from the arrow IID direction of B of FIG.

FIG. 3 is an explanatory view of principal parts of the screw rotor of Example 1, FIG. 3A is a cross-sectional view taken along line IIIA-IIIA of FIG. 2B, and FIG. 3B is an enlarged explanatory diagram of part IIIB of FIG. 2A, FIG. 3C is an enlarged explanatory diagram of part IIIC of A in FIG. 2.

4 is an exploded view of the outer side surface of the screw rotor of Example 1. FIG.

2 to 4, one screw (screw) 43 made of a thread 41 and a screw groove 42 is formed on the outer circumferential surfaces of the screw rotors 26 and 27 of the first embodiment. The screw 43 has an upper upstream threaded portion 43a on the upstream side in the gas conveying direction and a lower downstream threaded portion 43b on the downstream side in the gas conveying direction.

In FIG. 3B and FIG. 4, the upstream side threaded part 43a is formed with the space | interval (pitch p1, see FIG. 3B) of adjacent upstream threaded threads 41a at equal intervals, and an upstream side screw The width | variety of the groove | channel 42a is formed in equal width.

In FIGS. 3C and 4, the downstream threaded portion 43b is formed with equal intervals between adjacent downstream threaded portions 42a (pitch p2 and C in FIG. 3) at equal intervals. The width | variety of the groove | channel 42b is formed in equal width. In addition, the pitch p2 (refer to C of FIG. 3) of the downstream thread part 43b is formed narrower than the pitch p1 of the upstream thread part 43a.

In Fig. 4, the downstream end of the upstream threaded portion 43a and the upstream end of the downstream threaded portion 43b are continuously connected by inflection points (bending points) 43c and 43c. Therefore, the exhaust volume continuously changes smoothly in the vicinity of the inflection points 43c and 43c, and continuously changes from the exhaust volume of the upstream screw portion 43a to the exhaust volume of the downstream screw portion 43b.

In Fig. 2C, Fig. 2D, Fig. 3B, and Fig. 3C, the rotors 26 and 27 are rectangular teeth (unchamfered) on the tip end sides of the threads 41a and 42a. Interference prevention parts 44a and 44b cut | disconnected in order to avoid the interference which generate | occur | produces are formed. Meanwhile, as shown in FIG. 3B and FIG. 3C, the interference preventing portions 44a and 44b have different shapes of the upstream interference preventing portion 44a and the downstream interference preventing portion 44b. In response to the increase in the interference on the upstream side, the upstream side interference prevention section 44a has a larger cutting amount than the downstream side interference prevention section 44b.

In addition, a gap filling portion 46a that fills the gap between the interference prevention portions 44a and 44b and the threads 41a and 42a in response to the cutting of the interference prevention portions 44a and 44b on the proximal end sides of the threads 41a and 42a. , 46b) is formed. If there is a gap between the interference prevention portions 44a and 44b and the side surfaces of the threads 41a and 42a in the state where the rotors 26 and 27 are engaged with each other, gas leaks and flows backward to reduce the exhaust efficiency. Therefore, in the first embodiment, in the engaged state, the gap is filled by the gap filling parts 46a and 46b with a slight gap, and when the tooth is out of the interference, the interference is prevented by the interference preventing parts 44a and 44b.

(Operation of Example 1)

In the screw-type vacuum pump 1 of the first embodiment having the above configuration, rotation is transmitted by the gears 31, 32, 36, 37 when the pump driving motor M1 is driven, and the rotor shafts 21, 22. ) Rotates and screw rotors 26 and 27 rotate. As the screw rotors 26 and 27 rotate, the gas is transferred by the screw 43 and the gas sucked from the inlet 12a is exhausted to the exhaust hole 3e.

In the screw rotors 26 and 27 of the first embodiment, an upstream threaded portion 43a of a large lead (large pitch) is disposed on an upstream side, and a downstream threaded portion 43b of a small lead (small pitch) is arranged on a downstream side. Since the gas transported to the upstream threaded portion 43a is transferred to the downstream threaded portion 43b, the exhaust volume becomes smaller, so that it is compressed. Since the upstream screw portion 43a and the downstream screw portion 43b are continuously connected at the inflection point 43c and the exhaust volume is continuously changed, the upstream screw portion and the downstream screw portion are not divided with a gap. The exhaust gas can be exhausted with higher efficiency than when the exhaust volume changes discontinuously.

In addition, since the upstream screw portion and the downstream screw portion are not divided with a gap, the length of the rotor can be shortened. Therefore, as shown in FIG. 1, it can be set as the one-side support structure which does not need to provide a bearing in the vacuum side (intake port 12a side).

In addition, in the screw rotors 26 and 27 of the first embodiment, the interference preventing portions 44a and 44b are formed to correspond to the degree of interference, and the interference when it is out of the engaged state can be prevented. In addition, since the gap is filled in the engaged state by the gap filling portions 46a and 46b, leakage of gas is reduced and the exhaust efficiency can be improved.

Moreover, in the screw rotors 26 and 27 of Example 1, when manufacturing the screw rotors 26 and 27, the upper part of the inflection point 43c is processed with the cutting tool for a large lead, and the lower lead is lower than the inflection point 43c. It can be manufactured by machining with a cutting tool for cutting. Therefore, as compared with the case where the pitch is changed continuously, the processing becomes easier and the manufacture of the screw rotors 26 and 27 becomes easy. Moreover, since the shape of the interference prevention parts 44a and 44b is two types, it can be processed easily compared with the case where shape changes continuously, and cost can be reduced.

[Example 2]

FIG. 5 is an overall explanatory diagram of a screw type dry vacuum pump according to the second embodiment, and corresponds to FIG. 1 of the first embodiment.

FIG. 6 is an explanatory view of a screw rotor of Embodiment 2 corresponding to FIG. 2 of Embodiment 1, FIG. 6A is a sectional view, FIG. 6B is a side view, and FIG. 6C is an arrow VIC direction of FIG. 6B. FIG. 6D is a view seen from the arrow VID direction of FIG. 6B, and FIG. 6E is an enlarged explanatory view of the VIE portion of A of FIG.

FIG. 7 is an exploded view of the outer surface of the screw rotor of Example 2, and corresponds to FIG. 4 of Example 1. FIG.

In addition, in description of this Example 2, the component corresponding to the component of Example 1 is attached | subjected with the same code | symbol, and detailed description is abbreviate | omitted.

The second embodiment is different from the first embodiment in the following points, but the rest is the same as the first embodiment.

5-7, the screw type vacuum pump 1 of Example 2 has the screw rotor 26 ', 27' different from the screw rotor 26, 27 of Example 1. As shown in FIG.

In the screw rotors 26 ′ and 27 of the second embodiment, an endless lead portion 61 having an infinite length corresponding to the lead of the screw on the upstream side (intake port 12a side) in the gas conveying direction of the upstream screw portion 43a. ) Are formed continuously. The infinite lead portion 61 has a wish portion 61a and a large portion 61b, and an arcuate cut portion 61c is formed in the large portion 61b. Moreover, the gas compression part 61d is formed between the element part 61a and the large part 61b. The infinite lead portion 61 is conventionally known as described in Japanese Unexamined Patent Publication No. 2000-45976 (refer to the rotor extensions 7 and 8 of Fig. 1 of the above patent document), Since it exhausts on the principle of exhaust as described in FIG. 3 of the said patent document, detailed description is abbreviate | omitted. On the other hand, in the configuration described in the patent document, the center of the endless rotor portion 61 is biased, so that the balance becomes poor at the time of rotation of the screw rotors 26 'and 27'. The screw rotors 26 'and 27' are balanced by the cutout 61c.

6 and 7, in the screw rotors 26 'and 27 of the second embodiment, the downstream end of the upstream threaded portion 43a' and the upstream end of the downstream threaded portion 43b 'are continuous at the inflection points 43c and 43c. The upstream end of the upstream screw portion 43a 'and the downstream end (lower end) of the endless lead portion 61 are continuously connected at the inflection points 43c' and 43c '.

On the other hand, in the screw rotors 26 'and 27 of Example 2, compared with the case of Example 1, the number of turns of the downstream thread part 43b' is set more (about 7 times).

(Operation of Example 2)

In the screw-type vacuum pump 1 of the second embodiment having the above configuration, when the screw rotors 26 'and 27' are rotated, the gas is transferred from the endless lead portion 61 to the upstream screw portion 43a '. It is also compressed when it is conveyed from the upstream threaded portion 43a 'to the downstream threaded portion 43b'. Therefore, the compression rate can be increased.

Further, in the screw rotors 26 'and 27 of the second embodiment, the infinity lead portion 61 and the upstream screw portion 43a' are continuously connected at the inflection point 43c 'without a gap, and the upstream screw portion 43a is provided. Since the 'downstream threaded portion 43b' is also continuously connected at the inflection point 43c without a gap, the overall length of the screw rotors 26 'and 27' can be shortened. As a result, it becomes easy to set it as a one-side support structure. Moreover, since it is connected continuously, the change of exhaust volume is continuous and exhaust efficiency can be improved.

Moreover, in the screw rotors 26 'and 27 of Example 2, since the number of turns of the downstream screw part 43b' of a small lead is set large, the number of partitions by which the conveyed gas is partitioned increases. Therefore, leakage of gas from the exhaust port 3e side to the intake port 12a side can be reduced.

In addition, the vacuum pump 1 of Example 2 has the same effect as Example 1.

(Change example)

As mentioned above, although the Example of this invention was described above, this invention is not limited to the said Example, A various change can be made within the summary of this invention described in a claim. Modified examples (H01) to (H06) of the present invention are illustrated below.

(H01) In the above embodiment, it is also possible to further provide one or a plurality of threaded portions on the upstream side of the upstream side threaded portions 43a, 43a 'or downstream of the downstream side threaded portions 43b, 43b'. That is, it is also possible to set it as the screw rotor which is not limited to two screw parts but three or more screw parts.

(H02) In the above embodiment, the screw 43 is preferably constituted by one screw, but it is also possible to use two or more screws.

(H03) In the above embodiment, specific values such as the number of turns of the screw, the lengths of the leads p1, p2, p1 ', p2', the total length of the rotor, and the like can be arbitrarily changed depending on the design.

(H04) In the above embodiment, it is also possible to provide a root rotor as described in the patent document instead of the infinite lead portion 61.

(H05) In the above embodiment, the thread is bent at the inflection point (43c, 43c) 'continuously connected, but is not limited to this, for example, by chamfering the bent portion may be smoothly connected in a curve near the inflection point. Do.

(H06) In the above embodiment, the driving force is transmitted from the pump driving motor M supported by the motor support 3a to the rotor shafts 21 and 22 via the driving gear 36 or the intermediate gear 37. However, the present invention is not limited to this configuration, and a so-called built-in motor may be employed in which the motor rotor is supported on one of the rotor shafts 21 and 22 and a motor stator is arranged around the rotor shaft. When the built-in motor is employed, the cost can be reduced and the size can be reduced.

The present invention described above can provide a screw rotor capable of compressing gas at low cost.

In addition, the length of the rotor can be shortened while increasing the exhaust efficiency of the screw rotor.

Claims (3)

In the screw rotor is formed on the outer circumferential surface and rotates about the rotation axis to transfer the gas, An upstream threaded portion formed on the upstream side of the gas conveying direction and formed at equal intervals between the upstream threaded portions; A downstream screw portion which is formed continuously on the downstream side in the gas transfer direction of the upstream screw portion, wherein an interval of the downstream thread is narrower than an interval of the upstream thread and is formed at equal intervals, and in the gas transfer direction of the downstream thread. The upstream end and the downstream end in the gas transfer direction of the upstream side thread are provided with the downstream side threaded portion connected continuously by an inflection point. The method of claim 1, The upstream side screw portion having an upstream side interference prevention portion formed on a side of the upstream side threaded portion so as to narrow the tip side of the threaded portion, And a downstream screw portion formed on a side surface of the downstream screw thread and having a downstream interference prevention portion having a shape different from that of the upstream interference prevention portion. The vacuum pump provided with the screw rotor of Claim 1 or 2.

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