JPH0388997A - Primary vacuum pump - Google Patents

Abstract

PURPOSE: To optimize a pressure change by forming a rotor and a stator into a truncated conical or a hemispheric shape to provide variable control of a gap with the relative axial movement of the rotor relative to the stator during exhausting work. CONSTITUTION: A rotor 21 and a stator 22 are formed into a truncated conical or a hemispheric shape and in a symmetrical shape along an axis 23 of rotation. A gap 24 between the rotor 21 and the stator 22 can be modified by the axial movement and a dotted line shows different relative positions of the rotor to cause a smaller gap 24'. The movement is performed by an electromagnet, a fluid pressure or a mechanical device, for example. The gap can be adjusted as a function of the viscosity of a pure gas or the viscosity of a pumped up mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a primary vacuum bomb comprising a rotor stator and at least one rotor rotating inside the stator and maintaining a predetermined leakage gap in relation thereto.

The primary vacuum pump can be used alone or as a set of approximately 10
A total pressure of 'mbtr -10-'mbsr can be generated against atmospheric pressure. Oxygen and nitrogen molecules are drawn into this type of pump in a vortex and/or viscous state. Pumping speed S versus pressure P for this type of pump
The characteristics of are basically a function of the gap j existing between the rotor and stator. This function is shown in the drawing of the accompanying drawings, in which the pressure P is set along the X-axis in units of l1b1f, and the speed S is set along the Y-axis in units of P/h. Each of the five solid curves corresponds to a given gap, the gap increasing from one curve to the next in the direction of arrow j.

When pumping a large capacity relative to the pumping speed, the rotor temperature rises much faster than the stator temperature. To prevent contact, the equipment manufacturer must strive to leave the maximum stator-rotor clearance compatible with the maximum differential expansion. This large gap corresponds to an average characteristic of discharge velocity versus pressure, which in addition changes with rotor and stator temperatures.

Furthermore, gases such as hydrogen, propane, and pentane have absolute viscosities that are ten times lower than that of air. The flow rate of endoleaks is therefore much higher than that of air, and therefore the pumping velocity characteristic for pressure at a constant gap is much lower than for air. It would therefore be advantageous if the gap could be tailored as a function of the viscosity of the pure gas or of the mixture being pumped.

As a result, it is possible to construct a pump with small clearances and thus with excellent properties such as:

At atmospheric pressure, high pumping speeds and very low ds/
dp derivative, and at zero velocity, very low pressure and as large a ds/dp derivative as possible.

In addition, some application examples (semiconductor manufacturing, mass spectrometry measurements,
Leak detection using helium or neon tracer gas,
In space simulations, etc.), it is desirable to be able to control the pumping speed independent of pressure. To do this, two options are available to the person skilled in the art. That is, coupling a variable conductance in series with the pump or reducing the rotational speed of the pump.

The aim of the invention is to achieve very small gaps that change their properties rapidly even during pumping operations and to optimize the pressure change as a function of time in the vessel to which the pump is connected. The goal is to design a pump that makes it possible.

According to the invention, this objective is achieved in that the gap between the stator and rotor can be varied during the evacuation operation.

The invention thus provides a primary vacuum bomb consisting of a stator and a rotor that rotates within the stator and maintains a predetermined leakage gap in relation thereto. The pump may have a rotor and a stator of frustoconical or hemispherical shape, and the gap may be made variable during the evacuation operation by an axial relative movement of the rotor with respect to the stator, and further said movement may be controlled by control means. It is characterized by being obtained by.

This will be explained below.

FIG. 2 shows a pump having a rotor 21 and a stator 22, each of which has a truncated cone shape, and a rotating shaft 23.
It is symmetrical along. Gap between rotor and stator 24
can be modified by moving the rotor axially inside the stator (or vice versa) by a movement that may be purely mechanical. The dotted lines in the figure indicate different relative positions of the rotors resulting in a smaller clearance 24'.

The rotor may be moved within the stator by means of suitable actuating means such as electromagnets, hydraulic pressure, electric motors or purely mechanical devices.

The principle is not limited to a truncated cone shape, but can also be applied to other shapes, such as the one shown in FIG.

The rotor 25 is in this case hemispherical and rotates within the stator 26 about an axis of symmetry 27.

This example shows that it is not absolutely important to uniformly reduce the gap, but that it is sufficient to act on the gap where the gas leakage is particularly large.

[Brief explanation of drawings]

FIG. 1 is a graph representing the pumping speed as a function of pressure for pumps with various clearances; FIG. 2 is a schematic representation of a truncated conical rotor pump according to the invention in which the clearance is varied by moving the rotor or stator. , and FIG. 3 are schematic illustrations of a pump similar to that of FIG. 2, but with a hemispherical rotor. 21.25...Rotor, 22.26...
... Stator, 23 ... Rotating shaft, 27 ...
...Axis of symmetry, 24...Gap. FIG, 1 FIG, 2 FIG, 3

Claims (1)

[Claims] A primary vacuum pump comprising a stator and a rotor rotating within the stator and maintaining a predetermined leakage gap therewith, the pump having a rotor and a stator having a frustoconical or hemispherical shape. A primary vacuum pump, characterized in that it has a gap that is made variable by a relative axial movement of the rotor with respect to the stator during the evacuation operation, and that said movement is obtained by control means.