Technical field

[001 ] The present invention relates to a mechanical seal in accordance with the pream- ble of claim 1 and a slide ring in accordance with the preamble of claim 1 1 .

Background art

[002] Mechanical seals are gaining more and more acceptance in various shaft sealing applications. The mechanical seals find use in various pumps, mixers and agitators. Me- chanical seals are of relatively simple construction, they endure high temperatures and their maintenance and service is relatively easy. But, just like all kinds of seals, their lifetime is hard to predict. It is also quite impossible to perform any visual monitoring of the condition of the seal. Therefore, prior art includes numerous documents that discuss the monitoring of the condition of a mechanical seal. [003] US-A-6,065,345 discusses a method of monitoring the condition of a mechanical seal in an apparatus provided with a rotating part, in particular in a pump, which has a rotating shaft for the forwarding of a fluid, the sound emission of the seal is continually measured at discrete times in the operating state of the apparatus and at least one statistical characteristic value is won from the acoustic signals. The goal in the above dis- cussed patent is to monitor the sliding condition of the seal. In other words, if the seal is starting to run dry, i.e. the flushing is, for some reason, not working properly, the acoustic emission from the seal changes with the condition of the lubricating film. The US- patent discusses also the effect of the speed of rotation of the pump, the temperature of the flushing liquid, the pressure of the fluid to be pumped, etc. to the acoustic emission of the seal, whereby the acoustic emission may change even if the sliding conditions were not changed.

[004] US-B1 -6,360,610 discusses a system and a method that are particularly suited for monitoring the interface of two liquid lubricated mechanical seal faces. The system monitors an interface by using a wave source to produce an ultrasonic shear wave, di- recting the wave at the interface, detecting the wave after it interacts with the interface, and comparing the detected wave to predetermined wave characteristics. Based on the comparison, an alarm may be triggered. The alarm may indicate that the mechanical seal is failing. In a preferred example, the approach involves detecting the collapse of the lubricating film between the seal faces and detecting excessive asperity contact. The collapse of the lubricating film and excessive asperity contact are precursors to seal fail- ure. An ultrasonic transducer is placed behind one of the seal faces and used to produce ultrasonic shear waves (at a known frequency and amplitude) which propagate toward the interface between the two seal faces. By monitoring the amplitudes of the waves transmitted through or reflected by the interface, one can detect film collapse and the degree of contact between the faces. [005] Yet another document discussing the condition of the fluid film between the slide surfaces is GB-A-2430034. It discloses a condition monitoring system, using at least one acoustic emission sensory device to indirectly and/or remotely monitor the health status of a piece of rotating equipment, and applications thereof as for example a mechanical seal or a bearing assembly. The acoustic emission sensory device can be placed in direct or indirect contact to counter rotating surfaces. The signal emitted by the acoustic emission sensory device can be amplified, filtered for background noise, computed, compared to reference values and stored on a data storage device.

[006] US-B2-8,527,214 discusses a mechanical device showing the degree of wear of the slide surfaces of the mechanical seal. The discussed mechanical device is, on the one hand, a simple device measuring the physical axial movement of a slide ring due to wear, but, on the other hand, in most applications it is, in practice, quite hard to arrange such in connection with a mechanical seal. Especially, it would also be difficult to arrange a follower to be in mechanical contact with the rotary slide ring carrier the axial movement of which is to be measured, as instructed in the patent. [007] In other words, the above cited prior art discusses either abnormal operating conditions in which the lubrication of the mechanical seal surfaces has failed or is about to fail, or wear in normal operating conditions. However, the monitoring of wear in normal operating conditions, requires, in accordance with prior art such an arrangement that is, though in principle simple, hard to construct and includes a great risk of functional failure, as the follower discussed in the cited patent (US-B2-8, 527,214) is apt to wear, too.

[008] An object of the present invention is, thus, to solve at least one of the above discussed problems. [009] Another object of the present invention is to increase the reliability and predictability of the operation of a mechanical seal.

[0010] Yet another object of the present invention is to introduce a mechanical seal provided with a reliable and simple means for monitoring the wear of the mechanical seal in normal operating conditions.

Disclosure of the Invention

[001 1 ] At least one of the objects of the present invention is met substantially as is disclosed in the independent claims and in the other claims describing more details of dif- ferent embodiments of the invention.

[0012] According to an embodiment of the present invention the mechanical seal having a rotary part and a non-rotary part, the rotary part being formed at least of a rotary slide ring having a second axial end with an area and a rotary slide surface and of a rotary slide ring carrier, and the non-rotary part being formed at least of a non-rotary slide ring having a second axial end with an area and a non-rotary slide surface and of a non-rotary slide ring carrier, comprises an element changing the area of the second axial end of one of the rotary slide ring and the non-rotary slide ring, and a sensor provided in communication with the mechanical seal.

[0013] According to an embodiment of the present invention the slide ring for a mechan- ical seal, the slide ring having an inner circumferential surface, an outer circumferential surface, a first axial end, and a second axial end with a slide surface and an area, comprises an element changing the area of the second axial end of the slide ring.

[0014] This provides a mechanical seal the reliability of which is considerably improved.

[0015] The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also non-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. Brief Description of Drawings

[0016] In the following, the mechanical seal and the slide ring of the present invention will be described in more detail with reference to the accompanying exemplary, sche- matic drawings, in which

Figure 1 is a general representation of a prior art mechanical seal,

Figure 2 illustrates the mechanical seal in accordance with a first preferred embodiment of the present invention,

Figure 3 illustrates an enlarged cross section of a part of the mechanical seal of Figure 2,

Figure 4 illustrates an enlarged cross section of a part of the mechanical seal in accordance with a second preferred embodiment of the present invention,

Figure 5 illustrates an enlarged cross section of a part of the mechanical seal in accordance with a third preferred embodiment of the present invention, Figure 6 illustrates an enlarged cross section of a part of the mechanical seal in accordance with a fourth preferred embodiment of the present invention,

Figure 7 illustrates an enlarged cross section of a part of the mechanical seal in accordance with a fifth preferred embodiment of the present invention,

Figure 8 illustrates an enlarged cross section of a part of the mechanical seal in accord- ance with a sixth preferred embodiment of the present invention, and

Figure 9 illustrates an enlarged cross section of a part of the mechanical seal in accordance with a seventh preferred embodiment of the present invention.

Detailed Description of Drawings

[0017] Figure 1 depicts schematically and exemplarily a single-acting mechanical seal 10 though the present invention is, naturally, applicable to double-acting mechanical seals, too. The mechanical seal 10 is used for sealing the shaft 12 of, for instance, a flow machine such that the interior of the flow machine, at the left hand side of the seal, is kept separate from the atmosphere, at the right hand side of the seal. The mechanical seal 10 is positioned in a seal chamber 14 provided within a specific seal housing 16 or within a casing cover of a flow machine.

[0018] In accordance with Figures 1 and 2 the mechanical seal 10 comprises a rotary part 18 and a non-rotary part 32. The rotary part 18 comprises a retainer ring 20, a rotary slide ring carrier 22, a rotary slide ring 24, at least one set screw 26, one or more springs 28 and an O-ring 30. The non-rotary part 32 comprises a non-rotary slide ring carrier 34, a non-rotary slide ring 36, a body part 38, O-rings 40 and 42, a drive pin 44, a gland ring 46 and bolts 48. The seal is assembled on the shaft 12 such that the retainer ring 20 including the at least one spring 28 is fastened on the shaft 12 at an appropriate position by means of the at least one set screw 26. Next the rotary slide ring carrier 22 with the rotary slide ring 24 is pushed on the shaft such that the rotary slide ring carrier 22 remains floating on the shaft 12 by the support of the O-ring 30. Then the non-rotary slide ring 36 with its carrier 34 and the body part 38 with its O-rings 40 and 42 is installed on the shaft 12 to the support of the seal housing 16, and fastened thereto by means of the gland ring 46 and the bolts 48.

[0019] In accordance with Figure 3, the rotary slide ring 24 has a first axial end 50, which is located in the seat in the rotary slide ring carrier 22 (see Fig. 2) and a second axial end 52 with an area and a slide surface facing a slide surface of the non-rotary slide ring 36, when in use. A circumferential groove 54 is provided in the outer circumferential surface 56 of the rotary slide ring 24 at an axial distance d from the second axial end 52 of the rotary slide ring 24. Figure 3 shows also another, optional circumferential groove 58 provided in the inner circumferential surface 60 of the rotary slide ring 24. The two grooves 54 and 58 are opposite one another, i.e. their axial distances from the second axial end 52 of the rotary slide ring are equal, d. The non-rotary slide ring carrier 34 is provided with a, preferably, but not necessarily a piezoelectric, sensor 62, which is in wired or wireless communication with an external device monitoring, possibly among other things, the life and condition of the mechanical seal. The sensor 62 is one of an acoustic emission sensor, an acceleration sensor and a vibration sensor, just to name a few options without any intention to limit the scope of the patent to only the listed sensors. The sensors and the data processing arrangements discussed in GB-A-2439934 may be applied in putting the present invention to practice.

[0020] In accordance with Figure 4, the non-rotary slide ring 36' has a first axial end 64, which is located in the seat in the non-rotary slide ring carrier 34 and a second axial end 66 with an area and a slide surface facing a slide surface of the rotary slide ring 24', when in use. A circumferential groove 68 is provided in the outer circumferential surface 70 of the non-rotary slide ring 36' at an axial distance d' from the second axial end 66 of the non-rotary slide ring 36'. Figure 4 shows also another, optional circumferential groove 72 provided in the inner circumferential surface 74 of the non-rotary slide ring 36'. The two grooves 68 and 72 are opposite one another, i.e. their axial distances from the second axial end of the rotary slide ring are equal, d'. The non-rotary slide ring carrier 34 is provided with a sensor 62, which is in wired or wireless communication with an external device monitoring the life of the mechanical seal. The sensor 62 is one of an acoustic emission sensor, an acceleration sensor and a vibration sensor, just to name a few options without any intention to limit the scope of the patent to only the listed sensors. The sensors and the data processing arrangements discussed in GB-A-2439934 may be applied in putting the present invention to practice.

[0021 ] In view of the above discussed embodiments it should be understood that, firstly, the circumferential groove in the slide ring may be located in either the inner or outer circumferential surface of the slide ring, or in both, and secondly, that the groove/s may be located either in the rotary or in the non-rotary slide ring. As to the shape of the groove it has a few practical limitations. It is preferable, but not entirely necessary, that the groove is V-shaped or, in any case, such that opens towards the envelope surface of the slide ring, i.e. the angle β between the groove side surface 54' (at a side of the second axial end 52 of the slide ring) and the circumferential surface 56 of the slide ring 24 (see Figure 3) being blunt. The reason for such a design is that, when the above mentioned angle β is blunt, the wear of the slide ring does not result in loosening of any larger particles from the edge of the groove when the wear of the slide ring extends up to the groove. It is easy to imagine that, if the above mentioned angle were sharp, an annular part would be loosened from the edge of the groove, as in such a case the bottom, or in any case a deeper part, of the groove extends closer to the second axial end of the slide ring than the edge of the groove.

[0022] The above described sealing arrangement functions such that when the slide ring having the above discussed groove or grooves is worn up to the edge of the groove, the further wear of the slide ring results in the area (area at right angles to the axis of the slide ring) of the slide surface, i.e. the second axial end, of the slide ring starting to get smaller. As a result, the diminishing area of the second axial end or slide surface (of the slide ring having the groove/s) makes the acoustic emission from between the opposing slide surfaces change its frequency. In a similar fashion the frequency of the vibration of the slide ring changes as a function of the area of the slide surface. The sensor 62 passes the respective information, for instance frequency data, either periodically or continuously to the external device, may be called a control unit, monitoring the life of the mechanical seal that acts in a pre-programmed way. In other words, the external device or control unit has received frequency data since the mechanical seal was installed and, for instance, the flow machine was taken to use. The data, i.e. data from normal operating conditions, has been recorded or manipulated such that the control unit is provided with frequency information on the allowable operating range of the flow machine. Now that the control unit notices that the information, i.e. the frequency data, received from the seal is moved outside the allowable operating range, and possibly continues to change in a direction away from the allowable operating range the control unit may, for instance, perform one or more of the following tasks, light a warning light, give an audible signal, order a new sealing, or send a message to the service personnel.

[0023] The above discussed function may be accomplished with several optional ar- rangement as will be discussed in the following Figures.

[0024] Figure 5 illustrates an enlarged cross section of a part of the mechanical seal in accordance with a third preferred embodiment of the present invention. Here the nonrotary slide ring 76 is provided with an internal ridge 78 on its inner circumferential surface. A feature essential for the working of this embodiment of the present invention is that the inner circumferential surface of the rotary slide ring 80 extends closer to the axis of the seal than the inner circumferential surface of the non-rotary slide ring so that the ridge, when the non-rotary slide ring is worn up to the ridge, starts to wear, too. In this case the enlarging area of the second end of the non-rotary slide ring makes the acoustic emission or vibration from between the opposing slide surfaces change its frequency. Naturally, it is clear that the ridge may be located on the outer circumferential surface of the non-rotary slide ring, too, as long as the outer circumferential surface of the rotary slide ring extends farther away from the axis as that of the non-rotary slide ring. Also, the ridge may be arranged on both sides of the non-rotary slide ring, just like the groove in the earlier embodiments. Also, it is clear that the ridge may as well be arranged on the inner or outer circumferential surface, or on both, of the rotary slide ring, whereby the inner and outer circumferential surface, or both, of the non-rotary slide ring should extend farther away from the axis that those of the rotary slide ring.

[0025] Figure 6 illustrates an enlarged cross section of a part of the mechanical seal in accordance with a fourth preferred embodiment of the present invention. Here, the non- rotary slide ring 82 is provided on its inner circumferential surface with at least one protrusion or bulge 84, which, after the non-rotary slide ring has worn to a certain degree, meets the surface of the rotary slide ring 80, and makes the acoustic emission from between the opposing slide surfaces change its frequency. In case a plurality of bulges is used the array of bulges is preferably arranged on the same circumference, i.e. at an equal distance from the slide surface. Naturally, it is clear that the bulge/s may be located on the outer circumferential surface of the non-rotary slide ring, too, as long as the outer circumferential surface of the rotary slide ring extends farther away from the axis as that of the non-rotary slide ring. Also, the bulge/s may be arranged on both sides of the non- rotary slide ring, just like the grooves in the earlier embodiments. Also, it is clear that the bulge/s may as well be arranged on the inner or outer circumferential surface, or on both, of the rotary slide ring, whereby the inner and outer circumferential surface, or both, of the non-rotary slide ring should extend farther away from the axis that those of the rotary slide ring. [0026] In other words, in the third and fourth embodiments of the present invention the slide surface of the slide ring facing the slide ring having the ridge/s or the bulge/s changing the area of the second end of the slide ring should have a radial extension to the same direction, inwards or outwards, as in which direction the ridge/s or bulge/s extend. The radial extension should be at least equal with the radial height of the ridge/s or bulge/s.

[0027] Figure 7 illustrates an enlarged cross section of a part of the mechanical seal in accordance with a fifth preferred embodiment of the present invention. Here, the nonrotary slide ring 36' having the groove/s 72, though the existence of the groove/s or any other element changing the cross section of the non-rotary slide ring in the non-rotary slide ring 36' is not a necessary feature for the working of the invention, the groove or grooves may be provided in the rotary slide ring, too, is provided with the acoustic emission, the acceleration or the vibration sensor 86 having its wiring 88 passing through a drilled hole in the non-rotary slide ring carrier 34.

[0028] Figure 8 illustrates an enlarged cross section of a part of the mechanical seal in accordance with a sixth preferred embodiment of the present invention. Here, the acoustic emission, the acceleration or the vibration sensor 86 is provided to the axial end of the non-rotary slide ring carrier 34, and not on the outer circumferential surface thereof as shown in Figures 3 - 6. [0029] Figure 9 illustrates an enlarged cross section of a part of the mechanical seal in accordance with a seventh preferred embodiment of the present invention. Here, the nonrotary slide ring carrier and the non-rotary slide ring 90 are made of the same material, whereby there is no separate slide ring carrier but the slide ring is capable of performing the tasks of both the slide ring and its carrier. The acoustic emission, the acceleration or the vibration sensor 86 is attached to the axial end of the slide ring 90, but the sensor could as well be located on the outer circumferential surface of the non-rotary slide ring 90, too.

[0030] As to the material of the rotary and non-rotary slide rings, it is a preferred but not a necessary feature of the present invention that the material of the slide ring having the groove/s, ridge/s or bulge/s is softer than that of the opposing slide surface. Thereby it is the material of the slide ring having the groove/s, ridge/s or bulge/s that wears most and not that of the opposing slide ring.

[0031 ] It should also be understood that the acoustic emission sensor, the acceleration sensor or the vibration sensor may be positioned in any such location or position where it is capable of collecting information from the wear of the slide ring/s. In other words, such a sensor may not only be arranged in direct connection with the slide ring or slide ring carrier but also in the wall of the seal housing, in the cover of the pump or mixer casing or in the flange used for fastening the sealing to the flow machine, just to name a few alternatives without any indication to limit the invention to the listed options. In other words, the phrase "in communication with the mechanical seal" in claim 1 refers to all such positions in the flow machine where the acoustic emission, acceleration or vibration of the seal ring may be recorded by the respective sensor.

[0032] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.