Mechanical seal arrangement with torque measuring device and method therefor

Description

[0001] The present invention relates to a mechanical seal arrangement with a torque measuring device and a method for checking wear of sliding surfaces of a mechanical seal arrangement.

[0002] Mechanical seal assemblies are known from the prior art in various designs. One problem area with mechanical seal assemblies is the determination of the wear condition of the sliding surfaces of the seal rings. Although the mechanical seal is usually a non-contact seal during normal operation, with a gas cushion or a liquid cushion present between the sliding surfaces of the stationary and rotating seal rings, situations also arise during operation in which contact occurs between the seal rings, for example when starting up or shutting down the machine or from the time the machine starts up until the seal surfaces lift off. Pressure surges acting in the axial direction of the mechanical seal can also occur during operation, creating contact between the seal surfaces. However, such contact can damage the seal surfaces and make it necessary to replace the seal rings.It is known, for example, that wear of the sliding surfaces is determined based on leakage across the sealing gap. However, it would be desirable to have alternative options for determining the condition of sliding surfaces. US 2005 / 0 016 303 A1 discloses a mechanical seal assembly according to the preamble of claim 1. Furthermore, DE 10 2018 206 219 B3, JP H02 199374 A, and CN 102 183 327 A disclose mechanical seal assemblies with sensor devices for measuring various parameters of a mechanical seal assembly.

[0003] It is therefore an object of the present invention to provide a mechanical seal arrangement and a method for checking the wear condition of sliding surfaces, which enable a quick and reliable wear determination of the sliding surfaces with a simple structure and simple, cost-effective manufacture.

[0004] This object is achieved by a mechanical seal arrangement having the features of claim 1 and a method having the features of claim 11. The subclaims each show preferred developments of the invention.

[0005] The mechanical seal assembly according to the invention with the features of claim 1 has the advantage that an alternative and simple method of detecting wear on the sliding surfaces of a rotating and / or stationary seal ring of a mechanical seal is possible. In particular, a direct torque measurement of a torque applied to the stationary seal ring is possible both during test operation on a test bench and when the mechanical seal is installed for sealing on a shaft or the like. This is achieved according to the invention in that the mechanical seal assembly has a mechanical seal with a rotating and stationary seal ring, which define a sealing gap between their sliding surfaces. Furthermore, a torque measuring device is provided, which is configured to detect a torque applied to the stationary seal ring. The torque measuring device comprises a measuring unit and a sensor.The measuring unit is fixed to a housing of the mechanical seal by a base and arranged with a free end in a groove formed in the outer circumference of the stationary seal ring. The sensor is designed to detect a change in the position of the measuring unit in the groove. The change in position of the measuring unit is a measure of the torque exerted on the stationary seal ring. The detected torque value on the stationary seal ring provides information about the wear condition of the sliding surfaces of the rotating and stationary seal rings. This enables simple and reliable detection of the condition of the sliding surfaces and, if necessary, rapid replacement of the seal rings.

[0006] In particular, the torque measuring device according to the invention enables reliable torque measurement even during axial movements of the stationary sliding ring, which can occur during operation due to pressure surges or the like.

[0007] The mechanical seal assembly further comprises a control device configured to determine wear on the sliding surfaces of the mechanical seal based on the detected torque on the stationary sliding ring. The control device is particularly preferably configured to determine the wear on the sliding surfaces of the sliding rings as a function of the torque level. For example, a threshold value for a torque can be stored in a database, and the threshold value can be compared with the detected torque value. If the threshold value is exceeded, this indicates excessive wear on the sliding surfaces, and the control unit can, for example, output a replacement signal or a replacement message or the like.

[0008] Furthermore, the control device is configured to operate the mechanical seal assembly such that contact occurs between the sliding surfaces of the rotating and stationary seal rings. The torque measuring device detects a contact torque occurring upon contact between the sliding surfaces and, based on the contact torque, determines wear on the sliding surfaces. Determining the torque upon contact between the sliding surfaces is particularly informative with regard to wear on the sliding surfaces. This can occur, for example, at a low speed of a shaft to be sealed when there is no or insufficient medium in the sealing gap for the sliding surfaces of the seal rings to lift off.

[0009] This enables reliable torque measurement even with axially movable stationary sliding rings.

[0010] The measuring unit is preferably designed as a flat bar. The measuring unit thus comprises a flat, rod-shaped beam fixed on one side, the length of which is greater than its cross-sectional dimensions. The cross-section of the flat bar is preferably rectangular. Since the free end of the flat bar is arranged in the groove in the stationary slide ring and the foot of the flat bar is fixed in place to the housing, when a torque is introduced onto the stationary slide ring, the stationary slide ring is moved in the circumferential direction, so that the free end of the flat bar experiences a change in position upon contact with a groove wall. This change in position is a measure of the torque introduced into the stationary slide ring, on the basis of which wear of the sliding surfaces of the slide rings can be determined.

[0011] Preferably, a protruding region, in particular a cam-shaped region, is formed at the free end of each flat side of the flat bar. Preferably, the flat bar then has a width in the groove that is only minimally smaller than the groove width, so that when a torque is introduced into the stationary sliding ring, the free end of the flat bar immediately changes position. This allows even small torques to be reliably detected.

[0012] Further preferably, the base of the measuring unit has a greater thickness than the free end. Preferably, the thickness at the base of the measuring unit is twice as large as the thickness at the free end.

[0013] The sensor of the torque measuring device is particularly preferably an optical sensor. The optical sensor detects position changes of the free end of the measuring unit due to the torque introduced into the stationary slide ring. The optical sensor is preferably of the reflection type, which detects a light beam, for example a laser beam, reflected from the free end of the measuring unit. Alternatively, the optical sensor is an optical FBG sensor (Fiber Bragg Grating). The optical sensors have the particular advantage that no electrical current is required for measurement at the measuring unit, so they are preferably used for sealing tasks with an explosion hazard or similar. If the measuring unit is designed as a flat bar, a special reflection surface for the optical sensor is preferably formed on at least one flat side of the flat bar. This can, in particular, increase measurement accuracy.

[0014] Alternatively, the torque measuring device's sensor is a strain gauge (SG). Strain gauge sensors are very cost-effective and have a very robust design. Strain gauge sensors can be used, for example, in sealing applications where a large number of dust particles or similar substances are present, where optical measurement methods produce poor results.

[0015] Another alternative is a piezo element, the sensor for the torque measuring device. Piezo elements are also very robust and relatively inexpensive to produce. Since electrical current also flows through piezo sensors, their application is usually limited to gaseous media where electrical short circuits do not occur.

[0016] A particularly simple and cost-effective design is possible if the groove in the stationary seal ring runs in the axial direction of the mechanical seal arrangement. The groove is thus parallel to the center axis of the shaft to be sealed.

[0017] Further preferably, the stationary seal ring is preloaded in the axial direction by means of a preloading device. Preferably, a pressure ring is provided between the preloading device and the stationary seal ring. The preloading device is particularly preferably a plurality of individual spring elements arranged along the circumference of the mechanical seal.

[0018] The control unit is further preferably configured to detect a breakaway torque of the mechanical seal when the mechanical seal is at a standstill. When the mechanical seal is at a standstill, the sliding surfaces of the rotating and stationary seal rings touch each other. The breakaway torque is reached when the rotating seal ring begins to rotate relative to the stationary seal ring. This can be determined reliably and easily using the torque measuring device according to the invention. Here, too, the greater the breakaway torque of the mechanical seal arrangement, the more wear there is on the sliding surfaces of the seal rings. If a threshold value for the breakaway torque is exceeded, it can then again be concluded that excessive wear has occurred and that the seal rings need to be replaced.

[0019] Furthermore, the present invention relates to a method for checking wear of sliding surfaces of a mechanical seal assembly according to the invention as described above. The method comprises the steps of detecting a torque acting on the stationary seal ring and comparing the detected torque with a stored torque threshold. If the torque is greater than the torque threshold, it is determined that excessive wear of the sliding surfaces is present. The method according to the invention enables the advantages described above.

[0020] The method further comprises the steps of operating the mechanical seal assembly at a speed such that the sliding surfaces of the rotating and stationary seal rings are in contact. A contact torque acting on the stationary seal ring upon contact of the sliding surfaces is detected, and the detected contact torque is compared with a stored threshold value for the contact torque. If the contact torque is greater than the threshold value, it is determined that excessive wear of the sliding surfaces is present. A signal or message can then preferably be output, and the seal rings can be replaced.

[0021] Particularly preferably, the method according to the invention detects a breakaway torque from a standstill of the mechanical seal as a contact torque. As described above, the breakaway torque is the torque value at which a relative rotation of the rotating seal ring to the stationary seal ring begins.

[0022] Preferably, the torque on the stationary seal ring is also continuously recorded during operation of the mechanical seal. Although there is no direct contact between the sliding surfaces of the seal rings during normal operation of the mechanical seal, a certain torque is always exerted on the stationary seal ring during operation, which also increases with increasing wear of the sliding surfaces. Therefore, the recorded torque during operation is also an indicator of the wear of the sliding surfaces of the seal rings, and a comparison with a stored threshold value can then indicate the need to replace the seal rings if the threshold is exceeded.

[0023] Embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawing: Fig. 1 is a schematic sectional view of a mechanical seal arrangement according to a first embodiment of the invention, Fig. 2 is a schematic partial plan view of the mechanical seal arrangement of Fig. 1 , Fig. 3 a perspective partial view of the mechanical seal arrangement of Fig. 1 , Fig. 4 a partial side view of the mechanical seal arrangement of Fig. 1 , Fig. 5 is a schematic sectional view of a mechanical seal arrangement according to a second embodiment of the invention, and Fig. 6 is a schematic sectional view of a mechanical seal arrangement according to a third embodiment of the invention.

[0024] The following is based on the Fig. 1 to 4 a mechanical seal arrangement 1 and a method for checking wear of sliding surfaces of the mechanical seal arrangement are described in detail.

[0025] The mechanical seal arrangement 1 comprises, as shown in Fig. 1shown, a mechanical seal 2 with a rotating seal ring 3 and a stationary seal ring 4. A sealing gap 5 is defined between a sliding surface 3a of the rotating seal ring 3 and a sliding surface 4a of the stationary seal ring 4. During operation, there is usually no contact between the sliding surfaces 3a, 4a of the seal rings.

[0026] The mechanical seal arrangement 1 seals a product area 13 from an atmospheric area 14 on a shaft 17.

[0027] The rotating slide ring 3 is connected to the shaft 17 by means of a slide ring carrier 30, so that a rotation of the shaft is transmitted to the rotating slide ring 3 via the slide ring carrier 30.

[0028] The stationary seal ring 4 is arranged on a housing 8 in a non-rotatable manner. As can be seen from Fig. 1As can be seen, the housing 8 has a sleeve region 80 extending in the axial direction XX of the mechanical seal arrangement 1. The stationary slide ring 4 is movable in the axial direction XX on the sleeve region 80. On a rear side 4b of the stationary slide ring 4, a pressure ring 11 is provided, which is preloaded in the axial direction XX against the rotating slide ring 3 by means of preloading elements 10, in particular a plurality of spring elements.

[0029] Furthermore, the mechanical seal arrangement 1 comprises a torque measuring device 6. The torque measuring device 6 is shown in detail in the Fig. 1 to 4The torque measuring device 6 comprises a measuring unit 7 and a sensor 9, which in this embodiment is an optical sensor. The sensor 9 comprises a light guide 90 and a light source / receiver arrangement 91. The light source / receiver arrangement 91 emits a light into the light guide 90 and receives a corresponding reflection.

[0030] The measuring unit 7 is shown in detail in summary from the Fig. 1 and 3 The measuring unit 7 comprises a flat bar 70, which is fastened on one side to the housing 8. The flat bar 70 is fastened on one side by means of a base plate 73, which is fixed to the housing 8 with screw bolts 15, 16. A free end 71 of the flat bar 70 projects into a groove 40 formed on an outer circumference of the stationary slide ring 4. A foot 72 connected to the base plate has a greater thickness than the free end 71 (cf. Fig. 3 ).

[0031] As is particularly evident from Fig. 1 As can be seen, the groove 40 runs in the axial direction XX of the mechanical seal arrangement 1. As further Fig. 1 As can be seen, the free end 71 extends in the axial direction XX from the base plate 73 through the entire groove 40 and has a small overhang in the axial direction over the groove 40.

[0032] As in Fig. 1 shown in dashed lines, the light guide 90 is also guided to the groove 40, whereby the light guide 90 has a 90° bend (cf. Fig. 2 ). Here, a reflection surface 75 is provided on a flat side 71a at the free end 71 of the flat bar 70 (cf. Fig. 2 ). As a result, a light beam (arrow A) emitted by the light source / receiver arrangement 91 is reflected and sent back to it.

[0033] Furthermore, protruding areas 74 are provided on both sides of the flat bar 70 (see in particular Fig. 2 and 3), which are also arranged in the groove 40. The projecting areas 74 are designed such that a small gap 18 is present on both sides to the walls of the groove 40 ( Fig. 2 ).

[0034] Since the groove 40 is formed in a straight line and parallel to the axial direction XX in the stationary seal ring 4, the stationary seal ring 4 can perform axial movements. For example, when the shaft 17 moves in Fig. 1 to the left, which also causes a movement of the rotating sliding ring 3 in the axial direction, a readjustment is made possible by the preload force F applied by the preload element 10 via the pressure ring 11. As can be seen from Fig. 3 As can be seen, the torque measuring device 6, which is fixed to the housing 8, remains stationary, but the measuring recording areas of the torque measuring device 6 are still arranged in the groove 40 of the stationary slide ring 4.

[0035] The function and measuring method of the torque detection device 6 is as follows: During normal operation of the mechanical seal assembly 1, when a medium is present in the sealing gap 5 and there is no contact between the sliding surfaces 3a, 4a of the seal rings 3, 4, a torque is exerted on the stationary seal ring 4, which is shown schematically in Figure 4As indicated by arrow B, a groove wall 40a of the groove 40 comes into contact with the measuring unit 7, in particular one of the protruding areas 74. As a result, there is no longer a gap 18 between the groove wall 40a and the protruding area 74. This causes a deformation of the flat bar 70 with a corresponding change in the position of the measuring unit 7, in particular at the free end 71, so that the sensor 9, which emits a light beam A continuously or at intervals, can detect a change in a reflection of the light beam. The change in reflection can then be detected by the sensor 9. The sensor 9 is connected to a control device 12, which evaluates the sensor signal. The torque exerted on the stationary slide ring 4 can be determined from the change in the sensor signal.

[0036] The control device 12 is further configured to compare the torque value thus determined with a torque threshold value. If the determined torque value is above the threshold value, this is a clear indication of wear on the sliding surfaces 3a, 4a, since with unworn sliding surfaces 3a, 4a, the torque transmission from the rotating sliding ring 3 to the stationary sliding ring 4 is much lower than with sliding surfaces that exhibit wear, for example, scoring or waviness or the like.

[0037] A torque measurement can also be carried out when there is contact between the rotating seal ring and the stationary seal ring at the sliding surfaces 3a, 4a, for example when the shaft 17 is at a standstill or at a very low speed at which contact is still present at the sliding surfaces 3a, 4a. With worn seal rings, the contact between the sliding surfaces lasts longer than with new seal surfaces. Thus, the torque transmitted from the rotating seal ring 3 to the stationary seal ring 4 is significantly greater than with new seal rings, which exhibit no wear and no waviness. In particular, a breakaway torque can also be measured when the shaft 17 is at a standstill, which is also significantly greater with worn sliding surfaces than with a sliding surface with no or only slight wear.

[0038] As is particularly evident from Fig. 1 and 4As can be seen further, the stationary sliding ring 4 has a radially outwardly directed, circumferential flange area 41 in which the groove 40 is formed. The flange area 41 has no sliding surface (see also Fig. 4 ).

[0039] The circumferential force thus generated during torque transmission from the rotating seal ring 3 to the stationary seal ring 4 acts on the flat bar 70, causing it to bend and deform. This deformation can be detected by optical displacement measurement. The control device 12 is configured, for example, to determine a force on the measuring unit 7 based on the known material parameters of the measuring unit 7 and then to calculate the torque applied to the stationary seal ring 4 based on the known seal ring geometry.

[0040] Due to the axial arrangement of the groove 40, the torque applied to the stationary slide ring 4 can always be measured, regardless of the axial position of the stationary slide ring 4. The measuring unit 7 is preferably made of stainless steel.

[0041] Fig. 5 shows a mechanical seal assembly 1 according to a second embodiment of the invention. Identical or functionally identical parts are designated by the same reference numerals as in the first embodiment. The second embodiment essentially corresponds to the first embodiment, with a strain gauge 92 being used as sensor 9 instead of an optical sensor in the second embodiment. As shown in Fig. 5As shown, the strain gauge 92 is arranged in the area of ​​the base 72 of the flat bar 70. When a torque is transmitted to the stationary sliding ring 4, a force is introduced onto the free end 71 of the flat bar 70 of the measuring unit 7, as in the first exemplary embodiment, so that an electrical resistance of the strain gauge 92 changes depending on the magnitude of the bend in the flat bar 70. This change can be detected by the control device 12, and from this, the force acting on the measuring unit 7 due to the torque introduced into the stationary sliding ring 4 can be determined. Otherwise, this exemplary embodiment corresponds to the previous exemplary embodiment, so that reference can be made to the description given there. Alternatively, an optical FBG sensor can also be used at the position of the strain gauge 92.

[0042] Fig. 6shows a mechanical seal arrangement 1 according to a third exemplary embodiment of the invention. Identical or functionally identical parts are designated by the same reference numerals as in the previous exemplary embodiments. In the third exemplary embodiment, a piezo sensor 93 is arranged as sensor 9 on a groove wall 40a of the groove 40. When a torque is transmitted from the rotating slide ring 3 to the stationary slide ring 4, a force is transmitted to the measuring unit 7, which bends particularly in the region of the free end 71. As a result, a force can be exerted on the piezo sensor 93, whereby its electrical resistance changes, which can be detected by the control device 12. The control device 12 can then determine the force exerted on the piezo sensor 93 and thus the torque based on the changed electrical resistance of the piezo sensor 93.To enable torque detection independent of the direction of rotation, piezo sensors 93 are preferably arranged on both groove walls of the groove 40. Otherwise, this embodiment corresponds to the previous embodiments, so that reference can be made to the description given there.

[0043] The method according to the invention for checking the wear condition of sliding surfaces 3a, 4a is carried out in all of the described embodiments, in particular, upon contact between the sliding surfaces of the sliding rings. The various sensors 9 of the torque detection device 6 described in the embodiments can thus detect a contact torque upon contact between the sliding surfaces. This contact torque is then compared with a threshold value stored in the control device 12. As soon as the contact torque is greater than the threshold value, the control device 12 determines that excessive wear of the sliding surfaces 3a, 4a of the sliding rings is present. A signal or message can then be output, for example, indicating the excessive wear and recommending replacement of the sliding rings.

[0044] Furthermore, the method according to the invention can be used, in particular, to detect a breakaway torque of the sliding surfaces when the shaft 17 is at a standstill. If the breakaway torque is also greater than a predetermined threshold value for the breakaway torque, excessive wear of the sliding surfaces can also be concluded, and corresponding indications can be issued by the control device 12. List of reference symbols

[0045] 1 Mechanical seal assembly 2 Mechanical seal 3 Rotating seal ring 3a Sliding surface of the rotating seal ring 4 Stationary seal ring 4a Sliding surface of the rotating seal ring 4b Back of the stationary seal ring 5 Sealing gap 6 Torque measuring device 7 Measuring unit 8 Housing 9 Sensor 10 Preload element 11 Pressure ring 12 Control device 13 Product area 14 Atmosphere area 15, 16 Screw bolt 17 Shaft 18 Gap between groove wall and measuring unit 30 Seal ring support 40 Groove 40a Groove wall 41 Flange area 70 Flat bar 71 Free end 71a Flat side 72 Foot of the flat bar 73 Base plate 74 Projecting area 75 Reflecting surface 80 Sleeve area 90 Light guide 91 Light source / receiver assembly 92Strain gauge 93Piezo sensor ALight beam BForce applied to the stationary sliding ring FPreload force X-XAxial direction

Claims

1. Mechanical seal assembly, comprising: - a mechanical seal (2) comprising a rotating slide ring (3) and a stationary slide ring (4) which define a sealing gap (5) between their sliding surfaces (3a, 4a), and - a torque meter (6) which is configured to detect a torque acting on the stationary slide ring (4), - characterized in that the torque meter (6) comprises a measuring unit (7) and a sensor (9), wherein the measuring unit (7) is fixed by a foot (72) to a housing (8) and comprises a free end (71) which protrudes in a groove (40) formed in an outer periphery of the stationary slide ring (4), and - wherein the sensor (9) is configured to detect a position change of the measuring unit (7) in the groove (40) - a controller (12) which is configured to conclude a wear of the sliding surfaces (3a, 4a) of the mechanical seal (2) based on the detected torque on the stationary slide ring (4), and - wherein the controller (12) is furthermore configured to operate the mechanical seal assembly (1) in such a way that contact between the rotating slide ring (3) and the stationary slide ring (4) occurs at the sliding surfaces (3a, 4a), and is further configured to detect a contact torque arising upon contact of the sliding surfaces (3a, 4a), and to conclude a wear of the sliding surfaces based on the contact torque.

2. Mechanical seal assembly according to claim 1, wherein the measuring unit (7) comprises a flat rod (70) that is fixed at one end.

3. Mechanical seal assembly according to any of the preceding claims, wherein a protruding region (74) is formed on the free end (71) of the measuring unit (7), on each side facing towards a groove wall (40a) of the groove (40).

4. Mechanical seal assembly according to any of the preceding claims, wherein the foot (72) of the measuring unit (7) is of a greater thickness than the free end (71).

5. Mechanical seal assembly according to any of the preceding claims, wherein the sensor (9) is an optical sensor.

6. Mechanical seal assembly according to claim 5, wherein a reflective surface (75) for the optical sensor is formed on the measuring unit (7).

7. Mechanical seal assembly according to any of claims 1 to 4, wherein the sensor (9) comprises a strain gauge (92) which is arranged on the measuring unit (7).

8. Mechanical seal assembly according to any of claims 1 to 4, wherein the sensor (9) comprises a piezo sensor (93) which is arranged in the groove (40), on the groove wall (40a).

9. Mechanical seal assembly according to any of the preceding claims, - wherein the groove (40) extends in the axial direction (X-X) of the mechanical seal assembly (1), and / or - wherein the stationary slide ring (4) is preloaded in the axial direction (X-X) by means of a preload element (10).

10. Mechanical seal assembly according to claim 1, wherein the controller (12) is furthermore configured to determine the wear of the sliding surfaces (3a, 4a) based on a comparison of the detected torque value with a threshold value, if the detected torque value is greater than the threshold value.

11. Method for examining wear of sliding surfaces (3a, 4a) of a mechanical seal assembly, comprising: - a mechanical seal (2) comprising a rotating slide ring (3) and a stationary slide ring (4) which define a sealing gap (5) between their sliding surfaces (3a, 4a), and - a torque meter (6) which is configured to detect a torque acting on the stationary slide ring (4), - wherein the torque meter (6) comprises a measuring unit (7) and a sensor (9), wherein the measuring unit (7) is fixed by a foot (72) to a housing (8) and comprises a free end (71) which protrudes in a groove (40) formed in an outer periphery of the stationary slide ring (4), and - wherein the sensor (9) is configured to detect a position change of the measuring unit (7) in the groove (40), comprising the steps of: - operating the mechanical seal assembly, - detecting a torque acting on the stationary slide ring (4), and - comparing the detected torque with a stored threshold value for the torque, - wherein, if the torque is greater than the threshold value for the torque, it is determined that there is excessive wear of the sliding surfaces (3a, 4a), - operating the mechanical seal assembly at a rotating speed such that the sliding surfaces (3a, 4a) of the rotating slide ring (3) and of the stationary slide ring (4) are in contact, - detecting a contact torque occurring on the stationary slide ring (4) upon contact of the sliding surfaces, and - comparing the contact torque with a stored threshold value for the contact torque, - wherein, if the contact torque is greater than the threshold value for the contact torque, it is determined that there is excessive wear of the sliding surfaces (3a, 4a).

12. Method according to claim 11, wherein a breakaway torque of the sliding surfaces is detected proceeding from a standstill of the mechanical seal (2) and is compared with a threshold value for the breakaway torque and, if the breakaway torque is greater than the threshold value for the breakaway torque, it is determined that there is excessive wear of the sliding surfaces (3a, 4a).