Shaft sealing module for sealing vacuum chambers

A shaft sealing module is proposed for sealing a shaft which extends driving rotationally from a normal pressure chamber into a high vacuum chamber. It is essential for the shaft sealing module according to the invention that the dynamic seal of the shaft takes place not on the shaft itself but on a bushing mounted rotatably in a housing through which is guided a shaft and which is held on the shaft in friction connection, statically sealed, by elastic rings so that the bushing rotates with the shaft. The dynamic seal between the bushing and the housing is achieved by several radial shaft sealing rings which are preferably arranged so that between them is provided a prevacuum chamber with intermediate evacuation so that a two-stage dynamic seal is provided, where the prevacuum acts on the static seal between the bushing and the shaft in the sense of a gas penetration barrier towards the high vacuum chamber.

RELATED APPLICATIONS

BACKGROUND OF THE INVENTION

The present invention relates generally to a shaft sealing module for sealing a shaft which extends, driving rotationally, from a normal pressure chamber into a high vacuum chamber. As an example, manufacturing processes in the semi-conductor field largely take place under vacuum, in particular coating processes. During these processes the substrates to be coated must be moved. As the drive elements for these are usually mounted on the atmospheric or normal pressure side of these machines or devices, the substrates can only be moved if rotational movements are transmitted into the evacuated system via a sealed shaft.

These processes often take place at very high vacuum pressures, often of the order of 10−8mbar. In order, however, to be able to work with small vacuum pumps and avoid the penetration of gases (O2, N2, CO2) harmful to these processes into the high vacuum chamber from the normal pressure chamber via the shaft arrangement, very high requirements are imposed on the shaft seal.

In such shaft seals it is known to use a “magnetic fluid” comprising a suspension of ferritic nanoparticles in an oil with high vapor pressure which is maintained in a gap about the rotating shaft via a particular arrangement of magnets and pole shoes. However, many coating processes involve the use of high frequency electric field. In such instances, the use of “magnetic fluids” is not possible because the magnets of the shaft seals makes it difficult or impossible to control the high frequency currents flowing on the surfaces. Additionally, the magnetic fluid shaft seals can be damaged by the flowing currents and hence become ineffective.

BRIEF SUMMARY OF THE INVENTION

Certain aspects of embodiments of the present invention relate to a shaft sealing module which operates without “magnetic fluids”, ensures a reliable seal over long periods at the shaft transition between the normal pressure chamber and the high vacuum chamber, and has a comparatively simple construction.

According to certain aspects of the present invention, a shaft sealing module is provided for sealing a shaft which extends driving rotationally from a normal pressure chamber into a high vacuum chamber. A bushing is rotatably mounted within a housing through which bushing the shaft can be passed concentrically. The bushing is held in friction connection statically sealed on the shaft by a multiplicity of elastic rings and is dynamically sealed against the housing by radial shaft sealing rings with elastomer sealing lips pressed by coil tension springs on the bushing.

Certain aspects of the invention relate to a shaft sealing module which can be handled and produced separately from the shaft and the shaft passage through the container wall or similar separating the normal pressure chamber from the high vacuum chamber. The module can be pushed onto the corresponding shaft and attached tightly sealing to a container wall or similar feature.

According to certain aspects of the present invention, a bushing is rotatably mounted within a housing. A shaft can be passed concentrically through the bushing. The bushing is held in friction connection statically sealed on the shaft via a multiplicity of elastic rings and is sealed dynamically against the housing by radial shaft sealing rings with elastomer sealing lips pressed by coil tension springs against the bushing. This arrangement advantageously allows a prevacuum chamber to be created for intermediate evacuation if the shaft sealing module has several radial shaft sealing rings. This results in a two-stage dynamic seal and also allows the prevacuum chamber to be connected with the chambers formed between the elastic rings, the shaft and the bushing. As a result, a single intermediate evacuation can be used to increase the sealing effect of both the dynamic and the static seal.

The elastic rings, which may be formed as O-rings, are suitably held in ring grooves of the bushing. The contact pressure with which the shaft is held in friction connection with the bushing can be determined via the choice of groove depth, groove width, and/or O-ring dimensions. The necessary amount of contact force depends on the friction moment exerted by the radial shaft sealing rings under the contact pressure of the sealing lips on the bushing and operating conditions, plus the rolling friction of the roller bearings via which the bushing is rotatably mounted in the housing. The roller bearings, which may for example be two deep groove roller bearings separated by an intermediate ring, are arranged adjacent to the normal pressure chamber and not therefore exposed to vacuum pressure.

To prevent HF arcing between the fixed part and the moving parts of the shaft sealing module, the bushing and shaft may be electrically isolated from the housing. For example, the outer roller bearing rings can sit in an insulating bushing supported on the housing. This excludes HF transitions to the roller bearing bodies, where applicable the balls, and destruction of the bearings from HF arcing, The bushing may be connected electrically conductively with the shaft via a metal spring washer sitting in the receiving groove of the bushing. These measures ensure that the bushing has the same electrical potential as the shaft.

According to certain aspects of one embodiment, three radial shaft sealing rings are provided. One of the radial shaft sealing rings is adjacent to the roller bearings and has a sealing lip which faces the normal pressure chamber and has a rear face which rests on a spacer ring forming the prevacuum chamber. The other two radial sealing rings are adjacent to the high vacuum chamber, have rear faces and lie against each other with their rear faces and rest firstly on the spacer ring and secondly on a ring step of a stepped bore of the housing holding the radial shaft sealing rings and the roller bearings. The spacer ring can include radial bores in order to connect the prevacuum chamber with a vacuum pump.

The shaft sealing module may include several sealing rings, so as to provide a two-step dynamic seal by means of a prevacuum chamber with an intermediate evacuation arranged therebetween. The prevacuum chamber may be connected with the cavities between the elastic rings by channels in the bushing. In this regard, the bushing can include a wall in which is provided a collection channel, axially parallel and closed on both sides. The collection channel extends over all of the elastic rings and is connected via radial channels with the cavities between the elastic rings and via a further channel with the prevacuum cluster.

According to certain aspects of one embodiment, the inner roller bearing rings rest firstly on a ring shoulder of the bushing and secondly on a ring nut which can be screwed onto an external thread of the bushing. According to certain other aspects of one embodiment, outer roller bearing rings, with their insulating bushing, rest firstly on a further ring step of the stepped bore of the housing and secondly on a threaded ring of electrically insulating material which can be screwed into an internal thread of the stepped bore. According to certain other aspects of one embodiment, the side of the housing facing the high vacuum chamber has a cylindrical mounting collar concentric with the stepped bore and terminating in a flat face in which is located a receiving groove for a sealing ring to ensure a static seal against a wall delimiting the high vacuum chamber. This results in a centered attachment of the shaft sealing module on a wall limiting the high vacuum chamber and its seal to this wall.

According to another aspect of one embodiment, the housing includes a first atmosphere bore which connects the normal pressure chamber with the stepped bore of the housing in front of the radial shaft sealing ring adjacent to the roller bearings via a degasification groove in the insulating bushing. The first atmosphere bore ensures that atmospheric pressure is present in front of the first radial shaft sealing ring adjacent to the roller bearings. According to another aspect of one embodiment, a second atmosphere bore is provided in the housing to ensure that normal pressure is present in front of the outer elastic ring between the bushing and the shaft. The first and second atmosphere bores also serve as channels for the supply of helium for a leakage test of the shaft sealing module by measurement of the leakage rate.

According to another aspect of one embodiment, the housing includes a plurality of disassembly bores which are axially parallel to the stepped bore and evenly distributed over the periphery, through which the radial shaft sealing rings can be pushed out from the stepped bore. The provision of several dismantling bores allows removal of the radial shaft sealing rings from the housing, for example for maintenance work.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

Further details of the invention are described below with reference to a preferred embodiment example of the shaft sealing module shown in the drawings.

FIG. 1shows an axial view of the shaft sealing module from the high vacuum side and without the shaft.

FIG. 2shows a section through the shaft sealing module along the section line II—II inFIG. 1with shaft.

FIG. 3shows the section broken away in enlarged scale through the shaft sealing module according the section line III—III inFIG. 1without shaft.

DETAILED DESCRIPTION OF THE INVENTION

As shown inFIGS. 2 and 3, the shaft sealing module has a housing1, the outer periphery of which is formed essentially cylindrical. In the housing1and throughout its entire axial length is provided a stepped bore2concentric with the cylindrical outer periphery, which bore holds the remaining the parts of the shaft sealing module in a manner to be described. The housing1, on its side facing the high vacuum chamber3, has a cylindrical mounting collar4which is concentric with the stepped bore2and held suitably in a corresponding hollow cylindrical recess5in the wall6enclosing or delimiting the high vacuum chamber3. The mounting collar4terminates in a flat face7in which is formed a receiving groove8for a sealing ring9which ensures a static seal against the wall6when the shaft sealing module is mounted on the wall6. The shaft sealing module is mounted by several screws10which extend through the wall6and are screwed into corresponding threaded bores11of the housing1.

Within the housing1is rotatably mounted an essentially hollow cylindrical bushing12, For this are provided two roller bearings14arranged adjacent to the normal pressure chamber13, in the example shown deep groove ball bearings. Firstly the one inner roller bearing ring15of the roller bearing14rests on a ring shoulder16of the bushing12while secondly the other outermost inner roller bearing ring15lies on a ring nut17screwed onto an external thread18of the bushing12.

The outer roller bearing rings19sit in an insulating bushing20of electrically non-conductive material of sufficient strength. The insulating bushing20has an inwardly directed ring flange21on which rest the two outer roller bearing rings19. Between the two outer roller bearing rings19is an intermediate ring55, as is shown most clearly inFIG. 3. The insulating bushing20for its part rests axially on a ring step22of the stepped bore2. Radially the insulating bushing20rests on a medium diameter section23of the stepped bore2. Screwed onto an internal thread24of the stepped bore2is a threaded ring25of electrically insulating material of adequate strength, which lies on the outermost outer roller bearing ring19. In this way the bushing12and the shaft26, passed through the bushing12in a manner to be described, are electrically isolated from the housing1. The bushing12is connected electrically conductively with the shaft26via a metal spring washer27which sits in a receiving groove28of the bushing12.

The bushing12is held in friction connection statically sealed on the shaft26by a multiplicity of elastic rings29, in the embodiment example shown eight O-rings. The elastic rings29are laid in ring grooves30in the inner wall surface31of the bushing12.

The bushing12is sealed against the housing1by several radial shaft sealing rings32,33and34. These radial shaft sealing rings are of known design and have sealing lips35or36or37which are pressed by coil tension springs38against the bushing12. The embodiment example has three radial sealing rings32,33and34, where between them in a manner to be described in more detail below is provided a prevacuum chamber39with intermediate evacuation for a two-stage dynamic seal between the bushing12and the housing1.

As is shown most clearly fromFIG. 3, the radial shaft sealing rings32,33and34are arranged so that the radial shaft sealing ring32adjacent to the roller bearings14faces the normal pressure chamber13with its sealing lip39and with its rear surface40rests on a spacer ring41. This spacer ring41inserted between the radial shaft sealing rings32and33forms the prevacuum chamber39. The two other radial shaft sealing rings33and34are adjacent to the high vacuum chamber3and lie with their rear faces on each other. Thus they rest firstly, namely with the radial shaft sealing ring33, on the spacer ring41and secondly, namely with the radial shaft sealing ring34, on a ring step42of the stepped bore2. With their outer peripheral surfaces the radial shaft sealing rings32,33and34rest on a section47of the stepped bore2of which the diameter is smaller than that of the medium diameter section23.

In the spacer ring41are provided radial bores43which starting from a peripheral groove44of the spacer ring41connect the prevacuum chamber39with a vacuum connector46inserted sealed in a housing bore45. The prevacuum chamber39is limited by the spacer ring41and the two adjacent radial shaft seals32and33and is connected via a channel48in the wall of the bushing12with a collection channel49which is also located in the wall of the bushing12. The collection channel49is formed by a blind bore which runs parallel to the bushing axis and is closed tightly after its creation in the bushing wall e.g. by a spot weld or by a sealing stopper56.

The collection channel49is connected via radial channels50with the chambers between the elastic rings29so that a prevacuum applied via the vacuum connectors46is effective up to the cavities between the elastic rings29. These cavities are narrow gaps which are each limited laterally by two elastic rings29and by axial peripheral sections of the inner wall surface31of the bushing12and the outer periphery of the shaft26.

The operating manner of the shaft sealing module tightly mounted on the wall6is described in more detail below.

The shaft26which in most applications is driven at low rotation speed, for example 20 rpm, carries the bushing12rotationally and slip-free via the friction connection described. Via the vacuum connectors46is applied a prevacuum, usually generated by a split ring pump, the quality of which is lower than the vacuum generated by the turbomolecular pump in the high vacuum chamber3. Under the effect of the prevacuum the sealing lip35of the first radial shaft sealing ring32, which is exposed to atmospheric pressure, lies tightly on the bushing rotating with the shaft. At the same time the prevacuum acts on the cavities between the elastic rings29and forms a gas barrier for gases penetrating from the outside from the normal pressure chamber13via the static seal.

The two other radial shaft sealing rings33and34act in two ways. On operation with prevacuum, the sealing lip36of the second radial shaft sealing ring33lies tightly on the bushing12because of the pressure difference between the prevacuum in the prevacuum chamber39and the high vacuum predominating behind the radial shaft sealing ring33. The sealing lip37of the third shaft sealing ring34, exposed to the high vacuum on both sides, is pressed by the allocated coil tension spring38against the bushing12. If the prevacuum is broken, atmospheric pressure is present in front of the second radial shaft sealing ring33and its sealing lip36presses tightly on the bushing12under the effect of the great pressure difference between atmospheric pressure and high vacuum, thus blocking with the same intensity as in operation with prevacuum. Here too the sealing lip37of the last radial shaft sealing ring34is pressed against the bushing12by the associated coil tension spring38. In this way the shaft sealing module according to the invention has a safety reserve.

Further module units, e.g. for targeted introduction of process gases or cooling fluids, can be mounted with the same function principle on the shaft26and connected in succession, statically sealed, with the shaft sealing module.

AsFIG. 2shows, in the housing1close to the vacuum connector46is arranged a first radially directed atmosphere bore51which, via a radially arranged degasification groove54in the insulation bushing20, connects the normal pressure chamber13surrounding the shaft sealing module with the stepped bore2of the housing1in front of the first radial shaft sealing ring34adjacent to the roller bearings14, as shown inFIG. 2.FIG. 3shows a second atmosphere bore52which is also arranged radially directed in housing1. The atmosphere bore52is provided on the outside in front of the roller bearings14and ensures that normal pressure is also present in front of the outer elastic ring29between the bushing12and the shaft26, in particular if a further module unit (not shown) is connected statically sealed on the shaft sealing module.

For a leakage seal test of the shaft sealing module, helium can be supplied through the atmosphere bores51and52. The leakage rate, i.e. the quantity of helium emerging through the shaft sealing module, can be revealed by means of a helium detector (not shown) which is or can be connected with the high vacuum chamber3. The leakage rates achievable with the shaft sealing module according to the invention are extremely low. Leakage rates have been found of just

As is clear fromFIGS. 1 and 3, in the housing1can be provided several dismantling bores53axially parallel to the stepped bore2. For example four dismantling bores may be evenly distributed around the periphery with the same angular intervals, of which only one is shown inFIG. 3. The radial shaft sealing rings32to34can be removed from the stepped bore2through the assembly bores53using suitable tools (not shown).

A shaft sealing module is proposed for sealing a shaft which extends, driving rotationally, from a normal pressure chamber into a high vacuum chamber. It is essential for the shaft sealing module according to the invention that the dynamic shaft seal takes place not on the shaft itself but on a bushing mounted rotatably in a housing, through which bushing the shaft is guided and which is held on the shaft in friction connection, statically sealed, by elastic rings so that the bushing rotates with the shaft. The dynamic seal between the bushing and housing is achieved by several radial shaft sealing rings which are preferably arranged so that between them is provided a prevacuum chamber with intermediate evacuation so that a two-stage dynamic seal is present, where the prevacuum also acts on the static seal between the bushing and shaft in the sense of a gas penetration barrier towards the high vacuum chamber.