DE29822073U1 - Bearing arrangement with mechanical seal - Google Patents

Description

Meissner, &Bgr;&ogr;&egr;&idigr;&iacgr;&Ggr;&

Law firm
PO Box*8606*24
81633 Munich

Applicant Munich, 10 December 1998

Pfaudler Werke GmbH M/PFA-034-DE/I

Pfaudlerstrasse MB/PO/AP/jl 68723 Schwetzingen

Bearing arrangement with mechanical seal

Description

The invention relates to a bearing and sealing arrangement according to the preamble of claim 1.

A bearing and sealing arrangement for a rotary-driven shaft of a stirred tank, which extends approximately vertically through a passage formed in a reaction tank, is subject to high requirements in terms of tightness. A mechanical seal is expediently used for this purpose, which is located between the shaft and the tank passage or a bearing housing arranged on the tank passage. The mechanical seal is usually connected to the shaft in a rotationally fixed manner and operates axially between an upper and a lower sealing ring, in particular a ceramic ring. A rotary bearing is arranged further outwards relative to the mechanical seal so that it is protected from the media reacting in the tank. Furthermore, a detection device effective between the shaft and the reaction tank is required in order to record the speed or angular velocity of the shaft. Such a detection device comprises a signal transmitter and a signal receiver. Typically, the signal transmitter is located at the outer end of the shaft, i.e. outside the container and the bearing arrangement, and the signal receiver is located at a suitable distance from the signal transmitter. The signal transmitter and the signal receiver are preferably

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preferably inductively, capacitively or optically coupled with each other.

Such an unprotected external arrangement of the detection device has the disadvantage that the detection of the speed is unreliable. There is a risk that the detection device will be disturbed by environmental influences, such as dust or electromagnetic radiation. The speed of the shaft detected by the detection device is usually used to control other functional elements. For example, the supply of chemicals to the reaction vessel can be controlled by opening and closing valves depending on the speed. An undesirable chemical reaction due to incorrect speed detection can therefore have dangerous consequences.

In addition, holding devices and the like are required for the external arrangement of the detection device, which means a relatively high level of effort. The conventional external detection devices usually also include rotating parts that protrude radially outwards and represent a safety problem.

Furthermore, with a bearing and sealing arrangement according to the state of the art, it is not possible to detect signs of wear on the mechanical seal. Since the mechanical seal represents a weak point with regard to the tightness of the reaction vessel, the tightness cannot be reliably detected. Particularly for reasons of safety, it is desirable to detect signs of wear on the mechanical seal. Only then can it be reliably prevented that ambient air penetrates into the reaction vessel through a seal that is defective due to wear and triggers undesirable chemical reactions. 35

It is the object of the invention to provide a bearing and sealing arrangement of the type mentioned above, in which the reliability of the speed detection for the shaft is improved

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and wear of the mechanical seal can also be detected.

This object is achieved by the features of claim 1. 5

According to the invention, the detection device is arranged within the container passage, in particular the bearing housing.

By arranging the detection device within the container passage or the bearing housing, the detection device is protected from external influences. Within the container passage or the bearing housing, those movements of the shaft that deviate from an exact rotational movement around its longitudinal axis are the smallest. External vibrations have the least effect on the shaft within the container passage. According to the invention, the detection device is arranged in an area in which the shaft carries out the intended rotational movement most precisely.

Preferably, the signal generator and sensor are positioned between the upper and lower sealing rings. In this area, external influences, in particular vibrations of the shaft, are at their lowest. The detection device is therefore in a largely interference-free position.

Furthermore, it can be provided that the mechanical seal comprises two ring seals, which are pre-tensioned in the axial direction by means of compression springs and are each effective against the upper and lower sealing rings 0. This ensures that after the ring seals have worn down, on the one hand the seals are tight between the ring seals and the sealing rings, and on the other hand the ring seals are displaced against the sealing rings. The displacement can be measured so that wear, in particular excessive wear, of the ring seals can be detected.

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In one embodiment, it can be provided that the signal generator is mounted on the shaft in a rotationally fixed manner and the sensor is mounted on the bearing housing. By arranging the signal generator on the shaft, the design effort is minimal. An electrically operated signal generator, for example, requires a maximum of two supply lines. If a permanent magnet is used as the signal generator, no supply line is required at all. The signal generator can be coupled to the sensor optically, capacitively, inductively or mechanically.

For a structurally simple embodiment, it can be provided that the signal transmitter is formed by a marking on the circumference of the mechanical seal or ring seal. If a reflective and/or re-emitting marking is used, both a light source and the sensor can be arranged stationary in the bearing housing.

A prism-shaped circumferential surface of the mechanical seal with reflective flat surfaces enables particularly precise 0 speed detection of the agitator shaft.

The front peripheral edge of the mechanical seal or ring seals can also be used as a marking. Wear of the ring seals causes a shift in the peripheral edge, which can be detected by the sensor.

In an alternative embodiment, the sensor can be mounted on the shaft and the signal generator on the bearing housing. This is advantageous if a relatively complex signal generator is provided and/or a large number of connections are required for the signal generator.

For the design of the detection device, it can be provided that the signal transmitter and the sensor are inductively coupled to one another. For this purpose, one or more coils can be used for the signal transmitter and signal receiver, which are relatively inexpensive.

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Likewise, the design of the detection device can be such that the signal transmitter and the signal receiver are optically coupled to one another. In this case, for example, a light-emitting diode can be used as the signal transmitter and a photocell as the signal receiver. These are insensitive to electromagnetic fields that are generated, for example, by a drive motor for the shaft.

Preferably, both the LED and the photocell are mounted stationary in the bearing housing. A non-rotatably mounted reflector serves as a signal transmitter, which reflects the light from the LED to the photocell when the shaft is in a certain rotational position.

Further features and advantages of the invention are the subject of the subclaims.

The invention is described in more detail below using an embodiment with reference to the attached single figure.

The single figure shows a partial longitudinal sectional view of a bearing arrangement according to the invention. A stirrer shaft 10 extends approximately vertically through a passage 12 which is formed in the upper container wall 14 of a reaction container 16 (not shown in detail). A bearing housing 18 which encloses the stirrer shaft 10 is attached to the outside of the container passage 12. In the area of the bearing housing 18, the stirrer shaft 10 is surrounded by a sleeve 20 which is connected to the stirrer shaft 10 in a rotationally fixed manner. The sleeve 20 is formed in two parts and has a preferably ceramic front sleeve 20'. Between the sleeve 20 and the bearing housing 18 there is a rotary bearing 22. This is designed as a rolling bearing, in particular a ball bearing. The pivot bearing 22 surrounds the sleeve 20 with its rotating inner ring in a form-fitting manner. The stationary ring of the pivot bearing 22 is firmly connected to the bearing housing 18. In the area of the pivot bearing 22,

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the sleeve 20 is clamped onto the shaft 10 preferably with a clamping ring 41. Above the bearing housing 18, the clamping ring 41 encloses the sleeve 20. Between the pivot bearing 22 and the container wall 14, a mechanical seal 24 is connected to the outside of the sleeve 20. The mechanical seal 24 is attached to the sleeve 20 by means of at least one screw 25 and preferably consists of two sleeve-like carbon rings 24' and 24''. In the area in which the mechanical seal 24 encloses the sleeve 20, the inner surface of the sleeve 20 is slightly spaced from the outer surface of the agitator shaft 10. The mechanical seal 24 is axially effective between an upper 26 and a lower 28 sliding seal ring, in particular a ceramic ring, with one carbon ring 24' being assigned to the upper ceramic ring 26 and the other carbon ring 24'' being assigned to the lower ceramic ring 28. The carbon rings 24' and 24'' are pressed against the sliding seal rings 26 and 28 by means of compression springs 40 or similar elastic pre-tensioning elements. The upper 26 and lower 28 ceramic rings are attached to the bearing housing 18 and extend at a radial distance around the stirrer shaft 10 and sleeve 20, respectively. Between the stirrer shaft 10 and the lower end of the sleeve 20 and between the sleeve 20 and the front end sections of the mechanical seal 24 there are sealing rings 34 and 36, respectively, in particular O-rings made of hard rubber or the like, in order to avoid the inclusion of reaction medium between the stirrer shaft 10 and the sleeve 20 or between the sleeve 20 and the mechanical seal 24.

Two signal receivers 32' and 32'' are mounted stationary in the bearing housing between the upper 2 6 and lower 2 8 ceramic rings. Each signal receiver 32' and 32'' is assigned a signal transmitter 30' and 30'', which are designed as a marking next to the upper 2 6 and lower 2 8 ceramic rings on the carbon ring 24' and 24''. The signal transmitter 30' and 30'' and the signal receiver 32' and 32'' can also be coupled to one another inductively or capacitively, for example. With an inductive coupling, a coil or a permanent magnet can be used as the signal transmitter and a coil as the signal receiver.

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Since the detection device consisting of the signal transmitter 30', 30'' and the signal receiver 32', 32'' is located inside the bearing housing 18, malfunctions in the detection device are almost impossible. The preferably metal bearing housing 18 also serves as a shield against electromagnetic interference. The geometrically closed arrangement of the detection device ensures that the signal transmitter and signal receiver, as well as the area between them, are protected against environmental influences such as dust or the like. The detection device is also not exposed to uncontrolled light from outside. The arrangement of the signal transmitter and signal receiver inside the bearing housing 18 eliminates environmental causes for malfunctions in the detection device. The detection device is primarily intended to detect the speed or rotational speed of the stirrer shaft 10. The mechanical seal 24 is ground prismatically in the area of the detection device, for example, so that the circumferential surface of the mechanical seal 24 has flat surfaces. The flat surfaces are provided with a reflective layer. Both a light source for the signal transmitter 30' or 30'' and the signal receiver 32' or 32'' are arranged stationary within the bearing housing 18. The light-emitting area of the signal transmitter 30' or 30'' corresponding to the number of light-emitting diodes and the light-sensitive area of the signal receiver 32' or 32'' are arranged directly next to each other and directed towards the reflective part of the mechanical seal 24, so that they essentially have a common optical axis. As soon as one of the reflective flat layers is perpendicular to the common optical axis, the light emitted by the light source is detected by the signal receiver 32' or 32''. If the mechanical seal 24 rotates, light pulses are detected by the signal receiver 32' or 32''.

Furthermore, the detection device can be provided to detect wear of the mechanical seal 24 or carbon rings 24',

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24''. When the carbon rings 24', 24'' wear, they are pressed against the ceramic rings 2 6 and 2 8 by means of the compression springs 40. This changes the intensity of the light signals detected by the signal receivers 32' and 32''. In this way, the wear of the carbon rings 24', 24'' can be measured. An electrical signal present at the output of the signal receiver 32' or 32'' contains information about both the speed of the stirrer shaft 10 and the wear of the carbon rings 24' and 24'', with the speed corresponding to the frequency and the wear corresponding to the change in intensity of the electrical signal.

Alternatively, light sources, such as light-emitting diodes, can be mounted in a rotationally fixed manner on the stirrer shaft 10 and/or mechanical seal 24 and the signal receiver can be mounted stationary in the bearing housing 18. The reflective prism-shaped area would not be required in this case. With an optical coupling, the photocell acting as a signal receiver delivers electrical pulses corresponding to the number of light-emitting diodes per revolution of the stirrer shaft 10. With a downstream pulse counter, the speed can be determined and the angular velocity calculated from this. The signal generator can also comprise several light-emitting diodes, which are arranged, for example, at equal angular intervals around the stirrer shaft 10. This allows the speed to be recorded precisely even when the stirrer shaft 10 is rotating at a very low speed. Furthermore, the rotational position of the stirrer shaft can also be determined precisely. With an inductive coupling, a coil 0 acting as a signal receiver delivers an induction current that is proportional to the rotational speed of the stirrer shaft 10.

In principle, a line marking is also conceivable instead of the above-mentioned prismatic design of the mechanical seal 24 5.

The reaction vessel 16 is intended for chemicals that can be very aggressive and harmful to health.

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Both the inner wall of the container and the stirrer shaft 10 can be enamelled on the inside of the container. This leads to a high level of resistance to acids and alkalis. The enamel layer is also resistant to rapid temperature changes, so-called heat shocks. These are triggered by exothermic chemical reactions and by extreme heating and cooling conditions in the container 16. The mechanical weak point of this system, namely the mechanical seal 24 and the two ceramic rings 26 and 28, can be reliably monitored by the bearing arrangement according to the invention with the signal transmitter 3 0 and the signal receiver 3 2.

It should also be noted at this point that the mechanical seal 24 is held by means of the screw 25 on the sleeve 20, which is firmly connected to the shaft 10 and is preferably clamped or shrunk onto it, with the interposition of a radially externally located cylinder shell 37, in such a way that the ring seals 24', 24'' can move axially under the influence of the compression springs 40. Furthermore, it should be noted that the mechanical seal 24 in the embodiment shown has axial ring projections 38, 39 at the top and bottom, which correspond to the upper 26 and lower 28 ceramic rings in a fluid-sealing manner.

5 The wear of the mechanical seal 24 can also be indicated by an acoustic signal. For this purpose, the mechanical seal 24 comprises, for example, a metal core, which becomes visible when the carbon layer on the ceramic ring 26 or 28 is rubbed off or worn. The resulting friction between the metal core and the ceramic ring 26 or 28 causes a noise that audibly indicates the wear of the mechanical seal.

Claims (14)

Meissner, BoLTE& Partner #. #··&bgr; .· ,··, ,··. ."pfa-034-de/i Protection claims 1. Bearing and sealing arrangement for a rotary-driven shaft (10), in particular a stirrer shaft, extending approximately vertically through a passage (12) formed in a reaction vessel (16), with a mechanical seal (24) located between the shaft (10) and the vessel passage (12) or a bearing housing (18) arranged on the vessel passage (12) and at least one rotary bearing (22), the mechanical seal (24) acting axially between an upper (26) and a lower (28) sealing ring, in particular a ceramic ring, and the rotary bearing (22) being arranged further outward relative to the mechanical seal (24) so that the rotary bearing (22) is protected from the medium reacting in the reaction vessel (16), and with a detection device acting between the shaft (10) and the reaction vessel (16), which has at least one signal transmitter (30 ¹ ; 30 '') and at least one signal receiver, each associated with a signal transmitter (32';32'') or sensor, characterized in that the detection device is arranged within the container passage (12), in particular the bearing housing (18). 2. Arrangement according to claim 1, characterized in that the signal generator (30'; 30'') and sensor (32'; 32'') are positioned between the upper (26) and lower (28) sealing ring. 3. Arrangement according to claim 1 or 2,
characterized in that the mechanical seal (24) comprises two ring seals (24', 24'') which are prestressed in the axial direction by means of compression springs (40) and are each effective against the upper (26) and lower (28) sealing rings. Meissner, BoLTE& Partner .: .·" 4. Arrangement according to one of claims 1 to 3, characterized in that the signal transmitter (30';30'') is formed by a marking on the circumference of the mechanical seal (24) or the ring seal (24', ²⁴ '). 5 . Arrangement according to claim 4, characterized in that the marking is formed by the front peripheral edge of the mechanical seal (24) or ring seal (24'; 24''). 6. Arrangement according to claim 4, characterized in that the marking is formed by a prism-shaped peripheral surface of the mechanical seal (24) or ring seal (24';24''), the flat surfaces of the prism-shaped peripheral surface at least partially having a reflective layer.
20 7. Arrangement according to one of claims 1 to 4, characterized in that the signal transmitter (30) and the signal receiver (32', 32'') are capacitively coupled to one another. 25 8. Arrangement according to one of claims 1 to 4, characterized in that the signal transmitter (30) and the signal receiver (32) are inductively coupled to one another.
30 9. Arrangement according to one of claims 1 to 8, characterized in that the signal transmitter (30) and the signal receiver (32) are optically coupled to one another.
35 10. Arrangement according to one of claims 1 to 9, characterized in that Meissner, Bolte & Partner .j .···. .: .**. j"§f|£-»034-de/i the mechanical seal (24) is rotationally connected to the shaft (10) and the upper (26) and lower (28) ceramic rings are attached to the bearing housing (18) and tank passage (12) respectively.
5 11. Arrangement according to one of claims 1 to 10, characterized in that the mechanical seal (24) has an axial ring projection (38, 39) on each end face, which correspond in a fluid-sealing manner to the upper (26) and lower (28) ceramic rings. 12. Arrangement according to one of claims 1 to 11, characterized in that the mechanical seal (24) consists of two carbon rings (24', 24·■). 13. Arrangement according to claim 12, characterized in that the mechanical seal (24) or the carbon rings (24'; 24'') comprise a metal core which appears when the carbon layer on the mechanical seal ring (26; 28) is worn and generates an acoustic signal to indicate wear through friction with the mechanical seal ring (26; 28). 14. Arrangement according to one of claims 1 to 13, characterized in that the detection device is provided for detecting the speed of the agitator shaft (10) and wear on the mechanical seal (24).