JPS60153494A - Spiral-grooved molecular pump - Google Patents

Abstract

PURPOSE:To achieve a high evacuation speed with a spiral-grooved molecular pump, by providing the facing surfaces of a static cylinder and a rotary cylinder with screw grooves turning in opposite directions to each other, to increase the cross-sectional area of a gas molecule evacuation passage. CONSTITUTION:A static cylinder 2 having a screw groove 2a on the inside circumferential surface is fitted in the cylindrical casing 1 of a molecular pump. A rotary cylinder 3 is housed in the static cylinder 2 concentrically thereto. The surface of the rotary cylinder 3, which faces the static cylinder 2, is provided with a screw groove which turns in the opposite direction to the screw groove 2a. Gas is evacuated from a suction port A to a discharge port B by rotating a motor 7. Since the mean free path of the gas molecules is much longer than the width of the screw grooves, the gas molecules collide against the surfaces of the screw grooves of the static cylinder 2 and the rotary cylinder 3 alternately and are guided in the direction of the rotation, so that a high evaculation speed is achieved without deteriorating the performance of the pump.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a threaded groove molecular pump suitable for obtaining velocities when the gas is primarily in the molecular flow region.

[Background of the invention]

Thread groove molecular pumps are conventionally representative molecular pumps. This pump has a simple structure (1) and is relatively easy to manufacture, but it has the disadvantage of a low pumping speed.

Conventionally, thread groove molecular pumps generally have a combination of a stationary outer circumference and a rotating inner cylinder, and the thread groove that serves as a flow path for molecular flow is usually provided only on one of the outer cylinder or the inner cylinder. However, the pumping speed was limited by the size of the thread groove, and the pumping speed could not be increased. Therefore, in recent years, axial flow molecular pumps, which can easily achieve high pumping speeds, have been increasingly used.

For this reason, thread groove molecular pumps are rarely used except for special purposes.

[Purpose of the invention]

An object of the present invention is to provide a thread groove molecular pump that can obtain a large pumping speed without causing any problems.

[Summary of the invention]

It is designed to achieve the above purpose.

[Embodiments of the invention]

(2) An embodiment of the present invention will be described below with reference to FIG.

In the figure, a thread groove 2a is formed in a cylindrical molecular pump housing 1.
A stationary cylinder 2 having an inner peripheral surface thereof is attached, and a rotating cylinder 3 is concentrically accommodated within the stationary cylinder 2. A thread groove 3a in the opposite direction to the groove 2a is provided on the surface of the rotating cylinder 3a facing the stationary cylinder 2. The rotating shaft 4 to which this rotating cylinder 3 is fixed is a bearing 5
, 6. Further, a rotor 7a of a motor 7 is provided on the rotating shaft 4, and a stator 7b is provided in the housing 1 on the opposite surface of the rotor 7a. A is the suction port, to which the device to be exhausted is connected, and the gas is passed through the suction port A.
It is exhausted to the discharge port B.

In the molecular pump configured as described above, first, an auxiliary pump such as an oil rotary pump is connected to the discharge port 4 and driven, and after rough evacuation until the pressure inside the thread groove molecular pump body reaches the molecular flow region, the main body is started. do. The gas sucked through the suction port A is compressed while passing through thread grooves 2a and 3a provided in the stationary cylinder 2 and the rotating cylinder 3, and is exhausted from the discharge port B.

(3) In the molecular flow region, the mean free path of gas molecules is sufficiently larger than the thread groove dimensions, so gas molecules move toward the stationary tube 2 in the thread groove.
It alternately collides with the wall and the wall of the rotating cylinder 3, and is guided in the direction of rotation within the groove while bouncing back according to the cosine law. At the point where the thread groove 2a of the stationary cylinder 2 and the thread groove 3a of the rotating cylinder 3 intersect, which are thread grooves in opposite directions, the thread grooves are short-circuited in the pitch direction. If the thread groove shapes are the same, the pressure gradient in the flow direction within the thread groove is approximately equal, so the leakage flow in the pitch direction becomes extremely small. Therefore, the thread grooves provided in the stationary cylinder 2 and the rotating cylinder 3 mutually function as a flow path, and a high exhaust speed can be obtained.

Another embodiment of the invention will be described with reference to FIG.

This shows the case where the present invention is applied to a Siegbahn type molecular pump, and the same parts as in FIG. 1 are given the same reference numerals and will be explained.

The Siegbahn rotor 3 has a spiral groove 3a.

3b, and spiral thread grooves 2a in opposite directions are provided on the surface of the housing 1 facing the grooves 3a and 3b.

(4) 2b is provided.

The thread groove shown in the embodiment of FIG. 1 and the spiral thread groove of this embodiment can provide substantially the same functions and effects. Since the Siegbahn type molecular pump has a short axial dimension, it is advantageous in preventing shaft resonance. Furthermore, it is possible to easily reverse the suction port A and the discharge port B depending on the rotational direction of the rotor 3.

〔Effect of the invention〕

As explained above, according to the present invention, a large exhaust speed can be obtained by providing grooves in opposite directions in the stationary cylinder and the rotating cylinder.

[Brief explanation of the drawing]

1 and 2 are longitudinal sectional views showing an embodiment of the present invention. 1... Molecular pump housing, 2... Stationary cylinder, 2a...
Thread groove, 3... Rotating tube, 3a... Thread groove, A...
Suction port, B mountain discharge (5) Mine 1 figure hand 20

Claims (1)

[Scope of Claims] (1) A molecular pump in which a rotating cylinder is arranged concentrically opposite to a stationary cylinder, and gas molecules are moved in the axial direction by rotation of the rotating cylinder, in which the stationary cylinder and the rotating cylinder are opposed to each other. A thread groove molecular pump characterized by having thread grooves in opposite directions on its surface. 2. The thread groove molecular pump according to claim 1, wherein the rotating cylinder is a Siegbahn rotor.