DE102009052180A1 - High vacuum pump - Google Patents

Abstract

The invention relates to a high vacuum pump (100) with a stator (120), a rapidly rotating rotor (110), a roller bearing (130; 230; 330) and a means (144; 268; 368) for lubricating the roller bearing. The invention proposes that the means be adapted to prevent flashovers between stator (120) and rotor (110) by discharging the rotor.

Description

The invention relates to a high vacuum pump according to the preamble of the first claim.

Vacuum pumps of molecular and turbomolecular design have proven to produce high vacuum. A generic vacuum pump has a fast rotating rotor that rotates at tens of thousands of revolutions per minute. Various types of storage are known, including non-contact magnetic bearings and bearings, such as ball bearings with oil or grease lubrication and ceramic balls. These known bearings lead to an electrically insulated suspension of the rotor, so that it can come to a charging of the rotor with appropriate fluids to be pumped. As a result, uncontrolled electrical discharge, so-called flashovers, between rotor and stator, which lead to mechanical damage to these components and are therefore undesirable.

The EP-A 1915512 Suggests two solutions to this problem. The first solution provides a filamentous and conductive body contacting the rotor. The second solution is to generate by geometric design at a specific location flashovers between the rotor and stator.

Both solutions have disadvantages. The first solution is disadvantageous in that the body and its contacting point on the rotor are subject to wear due to the contact which occurs even at a low relative speed. The abrasion generated by this wear accumulates in the ball bearing and destroys it.

The second solution has the disadvantage that the component to which the flashovers take place, erosion damage occur. This erosion means wear, so that the arrangement lacks long-term stability. After some time, the arrangement does not work anymore and uncontrolled flashovers occur again.

It is therefore an object of the invention to provide a high vacuum pump, are avoided in the flashovers between the rotor and stator.

This object is achieved by a high vacuum pump having the features of the first claim. The dependent claims indicate advantageous developments.

The means for lubricating the rolling bearing are adapted such that such a discharge of the rotor is caused to prevent flashovers between the rotor and the stator. Damage to the rotor and stator is thus prevented. Since the already existing means for lubricating the bearing are adjusted and used, this is done advantageously without the use of other components. This is inexpensive and avoids mistakes. In addition, this solution is very low wear compared to the prior art and allows long service life.

A further embodiment provides that a conductive feed wick is used. In addition to the advantages mentioned above, this is advantageous because a lasting good discharge due to the constant contact is effected.

Another embodiment provides to use a conductive lubricant. This is a virtually completely wear-free solution.

In one embodiment, the conductive lubricant comprises carbon nanotubes. The addition of these carbon nanotubes causes a well-defined in the sense of the claim formulated to claim 1 sufficiently good conductivity, without a deterioration of the essential properties for use in a high vacuum pump properties of the lubricant occurs.

According to another embodiment, it is proposed that the means is designed as a lubricant circuit. This improves the discharge of the rotor, since an additional transport takes place. This solution is also advantageous in a vibration-decoupled mounting of the rolling bearing in elastomeric bodies, since the discharge via the lubricant circuit and not interrupted by the elastomer body contact from outer ring to housing of the high vacuum pump of the bearing.

With reference to embodiments and their developments, the invention will be explained in more detail and the representation of its benefits to be deepened. Show it:

1 : Section through a high vacuum pump with grease-lubricated bearings,

2 : Section through the bearing arrangement of a high vacuum pump with wick lubrication,

3 : Section through the bearing assembly of a high vacuum pump with oil circulation lubrication.

A section through a high vacuum pump 100 is in 1 shown. The high vacuum pump has a housing 102 which has a flange 104 and allows the releasable attachment to a container to be evacuated. The flange limits the gas inlet 106 ,

The housing surrounds the components of the stator 120 , the one bladed stator disk 122 and a spacer 124 includes. Depending on requirements such as pumping speed and compression, the number of stator disks is dimensioned. In addition to or as a substitute for the turbomolecular pumping stages shown here, other molecular pumping principles can be used, for example, according to the Holweck, Siegbahn and Seitenkanal principle.

The stator interacts with the rotor 110 together, which is a bladed rotor disk 114 and a wave 112 includes. The number of rotor disks mounted on the shaft corresponds to the number of stator disks. The rotor may also include other pump-active elements that interact with stator elements, such as a Holweck cylinder.

A motor coil 128 is located in the housing and puts the shaft and thus the rotor in rapid rotation.

At the gas inlet end, the shaft is through a permanent magnetic bearing 126 rotatably supported. The end of the shaft remote from the gas inlet is from a bearing assembly 170 carried.

The bearing assembly comprises a rolling bearing 130 , which is designed in this example as a grease-lubricated ball bearing. The inner ring sits on the shaft 134 of the ball bearing, the outer ring 132 is by means of a Axialschwingringes 140 and a radial swing ring 142 supported in the housing in the axial and radial directions so that they can vibrate. Axialschwingring and Radialschwingring are designed as electrically non-conductive elastomer rings. Between inner ring and outer ring are balls 136 arranged as rolling elements. A cover disk 144 closes the space between inner ring and outer ring and holds the lubricant supply 144 in the rolling bearing.

The lubricant supply contains the grease as a lubricant and is designed as a lifetime lubrication.

The described type of bearing with contact-free permanent magnet bearing and roller bearings causes, especially when ceramic balls are used in the rolling bearing, a good electrical insulation of the rotor relative to the stator.

The insulation is removed, in which a conductive grease is used in the lubricant supply. The electrical charging of the rotor is prevented because it is earthed via the rolling bearing and the grease.

To improve grounding, either axial or radial ring or both may be made of electrically conductive material, such as an embedded conductive material elastomer. Alternatively, an electrical conductor may be provided between the outer ring and the housing.

Both fat and axial and radial resonant rings can be loaded with carbon nanotubes for improved electrical conductivity. The achieved conductivity must only be so dimensioned that the charging of the rotor is so low that the field strengths between rotor and stator reach no value that allows discharge by flashover or sparks.

The 2 shows a section through the bearing assembly of the high vacuum pump in an alternative embodiment.

This alternative bearing arrangement 270 includes a ball bearing 230 , whose inner ring 234 on the wave 212 is fixed. The outer ring 232 is by means of a Axialschwingrings 240 and a radial swing ring 242 oscillatable in the housing 202 supported. Between inner ring and outer ring are the balls 236 , Lubrication takes place through a lubricant circuit 268 , This one is in 2 illustrated by arrows. Part of this lubricant circuit is the lubricant reservoir 252 , He has at least one feed wick 250 in sliding contact with a conically shaped and arranged on the shaft of the spray nut 256 stands. About this feed wick is the lubricant shown by dots 250 transferred from the lubricant reservoir to the spray nut. About the centrifugal force, the lubricant is conveyed along the cone in the space between the bearing inner ring and bearing outer ring and there causes the lubrication. The lubricant falls from the intermediate space back into the lubricant reservoir and can be re-supplied to the ball bearing there by capillary action via the feed wick in the next circulation of the lubricant circuit.

The grounding of the rotor via the means for lubricating the ball bearing can be done via two alternative ways, whereby both ways can be realized simultaneously.

On the one hand, the lubricant itself can be made conductive. This is achieved by the addition of conductive substances to lubricants, such as graphite. Carbon nanotubes prove to be particularly advantageous. Lubricant circulation and filling of the lubricant reservoir then cause a conductive connection from shaft to housing. The charging of the rotor is thereby kept so low that there is no electrical Discharges or sparks between rotor and stator comes.

On the other hand, the feed wick can be made of conductive material. Feed wick and lubricant reservoir comprise a felt-like material which stores the lubricant in its pores and promotes it via capillary action.

Electrical conductivity is sufficiently effected by admixture of metallic fibers or conductive carbon fiber.

The 3 shows a section through the bearing assembly of the high vacuum pump in a third embodiment.

The bearing arrangement 370 has a ball bearing 330 on. Its inner ring 334 is on the wave 312 fixed. His outer ring 332 is by means of a Axialschwingrings 340 and a radial swing ring 342 in the axial and radial directions oscillatable in the housing 302 supported. As a means for lubricating the ball bearing is a lubricant-containing lubricant circuit 368 provided in 3 is illustrated by arrows. The lubricant circuit includes a lubricant pump 352 which is the lubricant 350 which is in 3 is illustrated by dots, through the feed channel 360 in a feed nozzle 362 promotes. From the feed nozzle, the lubricant on the conically shaped spray nut 356 promoted. The lubricant is conveyed by the centrifugal force along the cone in the ball bearing. From there it enters the drainage channel 364 and through this back into the lubricant pump.

The adaptation of the means for lubricating the ball bearing in this example is to carry out the lubricant itself conductive. This is achieved in an advantageous variant via the addition of carbon nanotubes. The lubricant circuit then causes a conductive connection from shaft to housing. As a result, the charging of the rotor is kept so low that none of the electrical discharges occurring between the rotor and the stator occur in the prior art.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1915512 A [0003]

Claims (5)

High vacuum pump ( 100 ) with a stator ( 120 ), a fast rotating rotor ( 110 ), a rolling bearing ( 130 ; 230 ; 330 ) and a means ( 144 ; 268 ; 368 ) for lubricating the rolling bearing, characterized in that the means is adapted, by discharging the rotor flashovers between stator ( 120 ) and rotor ( 110 ) to prevent. High vacuum pump according to claim 1, characterized in that the means ( 268 ) a conductive feed wick ( 254 ). High vacuum pump according to claim 1 or 2, characterized in that the means ( 144 ; 268 ; 368 ) a conductive lubricant ( 144 ; 250 ; 350 ). High vacuum pump according to claim 3, characterized in that the conductive lubricant ( 144 ; 250 ; 350 ) Contains carbon nanotubes. High-vacuum pump according to one of the preceding claims, characterized in that the means as a lubricant circuit ( 268 ; 368 ) is designed.

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