JPH02283898A - Thread groove molecular pump - Google Patents

Abstract

PURPOSE:To reduce air leakage and improve air discharge speed by providing a pair of rotary cylinders meshing to each other with threads of the same direction respectively and arranging thread flanks angles allowing threads to mesh to each other to the threads respectively and rotating each rotary cylinder in the same direction. CONSTITUTION:Two rotary cylinders 4 and 7 are arranged being meshed to each other in a static cylinder 1 comprising two cylinders jointed in such a way that the cross section becomes like figure 8. When the rotary shaft 9 of the rotary cylinder 4 is rotated through the stator 14 engaging to the rotor of a motor, the rotary cylinder 7 is rotated in the same direction as the rotary shaft 9 through the rotary shaft 15 of the rotary cylinder 7 by two gears 18 and 19 which have the same constitution mutually and are meshed to each other. The air sucked from a suction port 20 is introduced in the respective right hand thread grooves 2A and 2B of the two rotary cylinders 4 and 7 and is sent downward by the respective right hand ridges 3A and 3B. At this moment, the moving direction in the vicinity of the radial directional clearance 8 between the bottom section of the right hand thread groove 2A and the right hand ridge 3B is set in the opposite direction to reduce air leakage.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a molecular pump mainly applied to gases in a molecular flow region, and particularly to a threaded groove molecular pump suitable for obtaining a large pumping speed. be.

[Background of the invention]

One of the representative molecular pumps is the screw groove molecular pump, which has a simple structure and is relatively easy to manufacture, but it has a major drawback of low pumping speed. In the conventional threaded groove molecular pump shown in FIG. 5, the one-rotation cylinder A4 and the rotation cylinder B7 are formed with threads in opposite directions, and in the case of FIG. has right-hand thread groove 2
A and right-hand thread 3A, and left-hand thread groove 5 and left-hand thread 6 are formed on rotary cylinder B7, respectively, and as shown in Fig. 6, in the vicinity of radial clearance 8, right-hand thread groove 2A and left-hand thread Since the movement directions of the peaks 6 are in the same direction, gas tends to leak from the radial clearance 8, and there is a disadvantage that the pumping speed cannot be increased. The object of the present invention is to provide a thread groove molecular pump that can obtain a large pumping speed.

[Summary of the invention]

In the present invention, when a pair of threaded rotary tubes are meshed with each other's threads and threads closely with their rotational axes parallel to each other, the direction of movement of the thread grooves and threads near the meshing area is adjusted. This is a pair of rotating cylinders that have the same helical groove and thread so that they run in opposite directions, and the meshing between them has been devised.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. A rotating cylinder A4 having a right-handed thread groove 2A and a right-handed thread 3A on the outer circumferential surface, a right-handed thread groove 2B, and a right-handed thread 3B on the outer circumferential surface are placed in a stationary cylinder 1 whose cross section is a daruma shape made by joining two cylinders. The rotary cylinders B7 are closely engaged with each other so that the radial clearance 8 between the thread grooves and the threads is as small as possible, and their axes are arranged parallel to each other. A rotating shaft A9 of the rotating tube A4 is supported by bearings 10 and 11. Further, a rotor 12 of a motor is provided on the rotating shaft A9, and a stator 1 incorporated in a base 13 is provided on a surface facing the rotor 12.
4 has been installed. The rotating shaft B15 is also supported by a bearing 16 and a bearing 17 (equal) like the rotating shaft A9, but there is no motor on the rotating cylinder B7 side. Rotating axis A9
A gear A18 is attached to the lower end of the rotating shaft B15, and a gear B19 that rotates in the same direction and at the same rotation speed as the gear A18 is attached to the lower end of the rotating shaft B15 via a gear C22. The upper end opening of the stationary cylinder 1 is a suction port 20 to which a device to be exhausted is connected, and the gas is forced downward through the suction port 2o and exhausted through the discharge port 21. In the molecular pump with the above configuration, first,
An auxiliary pump such as an oil rotary pump is connected to the discharge port 21 and opened, and after the pressure inside the screw groove molecular pump body is roughly reduced to a molecular flow region, the body is driven. Due to the relationship between the rotor 14 and the rotor 12, when the rotating shaft A9 rotates, the gear A
18 and gear B19 are in the same direction and have the same rotational speed, the rotating barrel A4 and the rotating barrel B7 rotate in the same direction, and as shown in FIG. Since B7 also rotates to the left, the gas sucked in from the suction port 20 is introduced into the right thread groove 2A and the right thread groove 2B provided in the one-turn cylinder A4 and the rotation cylinder B7, and is compressed downward. At this time, the gas in the right-hand thread groove 2A flows through the right-hand thread 3B, and the gas in the right-hand thread groove 2B flows through the right-hand thread 3A.

As it rotates, it is forced to move downward, and as shown in FIG. 2, the bottom of the right thread groove 2A of the rotating fiA4,
The direction of movement near the radial clearance 8 on the outer periphery of the right-hand thread 3B of the rotating cylinder B7 is the opposite direction, and the circumferential speed is the same as that of the right-hand thread 3B.
Since B is larger, there is less gas leakage from the radial clearance 8, and the exhaust speed can be increased.

In this case, the following first-order conditions are required for the grooves and ridges of the same right-handed thread to closely engage with each other. Fig. 3 is a diagram showing the state in which the thread grooves and threads of the rotating cylinders A4 and B7 are in contact with each other in the radial direction, and Fig. 4 shows the engaged thread grooves and threads seen from the rotating cylinder B7 side. This is a diagram developed linearly. A is the center of the rotating tube A4, B is the center of the rotating tube B7, a
is the radius of the rotating cylinder A4, b is the radius of the rotating cylinder B7, W is the height of the thread, α is the lead angle of the screw, β is the flank angle,
Now, when point P of radius (b-z) located on the flank of the screw thread of rotation wJB7 in Fig. 3 rotates to point Q, the amount of axial movement is as follows: point P moves to point Q in Fig. 4. The amount of axial movement when moving, h = L

cosθ= ((a+b-w) 2+ (b-z)"a
2) / (2x (a+b-w) X (b-z)
) Also, the axial dimension U from the bottom of the screw at point P is U = (w
-z)Xtanβ From Figure 4, if it is 0.5 For 2, tanβ> 2X ((b-z) / (w-z))
X an α Xarccos [((a+
b-w)"+(b-z)"-a2) ) / (2X
(a0b-w)

Note that although FIG. 1 shows a rotary cylinder with a single thread thread for simplicity, the same applies to a case with a multiple thread thread.

〔Effect of the invention〕

As described above, according to the present invention, the gas in the thread groove is moved by the rotation of the rotating station itself, and there is no leakage caused by the rotation of the thread of the mating rotary cylinder, and the gas in the thread groove of the mating rotary cylinder is acts as a moving wall and forcibly moves the gas, making it possible to double the pumping speed.

[Brief explanation of drawings]

4 is a sectional view taken along line nn of FIG. 3, FIG. 5 is a vertical sectional view showing the conventional example, and FIG. 6 is a sectional view of the same related dimensions. 5 is a sectional view taken along the line ■-■ in FIG. 5. FIG. 1 is a stationary cylinder, 2A and 2B are right-hand thread grooves, 3A and 3B are right-hand threads, 4 is a rotating cylinder A, 7 is a rotating cylinder B, 8 is a radial clearance, 20 is a suction port, and 21 is a discharge port. . Name of patent applicant Hitachi Koki Co., Ltd. 3rfiJ 2nd m 5 products OtI! 1

Claims (1)

[Claims] A pair of rotating cylinders are arranged in a stationary cylinder with their rotational axes parallel to each other, their threads and thread grooves closely engaging each other, and each rotating cylinder rotates around its respective rotational axis, and the rotating cylinders In a molecular pump that moves gas molecules in the axial direction by rotation, the threads and threads of a pair of rotating cylinders that have threads and threads in the same twisting direction can approach each other and engage. A threaded groove molecular pump characterized in that it has a threaded flank angle and each rotary cylinder rotates in the same direction.