AU2006337950B2

AU2006337950B2 - Method for monitoring and/or testing without destruction a transmission element, and measuring arrangement for carrying out the method

Info

Publication number: AU2006337950B2
Application number: AU2006337950A
Authority: AU
Inventors: Manfred Baumler; Uwe Boker; Manfred Ziegler
Original assignee: RWE Power AG
Current assignee: RWE Power AG
Priority date: 2006-02-10
Filing date: 2006-12-02
Publication date: 2012-04-12
Anticipated expiration: 2026-12-02
Also published as: DE502006004765D1; DE102006006468A1; PL1981788T3; WO2007090449A1; ZA200806395B; EP1981788A1; ES2331631T3; CN101365637B; EP1981788B1; ATE441608T1; AU2006337950A1; CN101365637A

Abstract

The invention relates to a method for monitoring and/or testing without destruction a transmission element having at least one magnetizable tie beam, and to a measuring arrangement for carrying out the method. The method is distinguished by the fact that a single-axis or multiple-axis measurement of the magnetic field which is disrupted by the tie beam is carried out, by at least one magnetic field sensor or an arrangement of a plurality of magnetic field sensors being guided relative to the transmission element or by the transmission element being guided relative to the measuring arrangement, and by the detected measured signals being evaluated by way of a data acquisition and evaluation device, preferably with regard to an anomaly of the detected magnetic field.

Description

1 Method of monitoring and/or non-destructive testing of a transmission element and a measuring arrangement for carrying out the method The invention concerns a method of monitoring and/or non 5 destructive testing of a transmission element comprising at least one magnetisable tensile carrier. DE 199 21 224 Al discloses a method of monitoring an endlessly circulating conveyor belt having steel cord tensile carriers. The method includes using at least one metal detector for sensing the belt movement, 10 with which a measurement signal produced by the belt is continuously detected over the entire belt length. In a first belt revolution or a first belt sensing operation over the entire length thereof, a reference signal is acquired, which is stored in the form of a belt-specific signal. Monitoring of the belt member is effected by continuously comparing the reference signal 15 to the measurement signal, in the sense of a reference/actual comparison. With that method recording and storing a reference signal over the entire length of the conveyor belt provides for the production and storage of a belt-specific induction pattern (fingerprint), from which the positional location, the signal level and the signal shape of the load-carrying elements 20 disposed in the conveyor belt, that is to say the steel cord tensile carriers, can be determined. Damage to the steel cord tensile carriers can be comparatively effectively detected on the basis of a reference/actual comparison between the reference signal stored in that fashion, and the continuously acquired measurement signal. Suitable measures can then be 25 initiated to take the belt conveyor installation out of operation and to perform maintenance operations. That method is carried out with a metal-seeking coil arrangement, wherein the magnetic field of the coil through which current flows is altered when the metallic cross-section of the enclosed conveyor belt changes. 30 In practice it has been found that such a metal-seeking coil can be used only in the lower run of the belt conveyor as the material being conveyed has an interfering influence on the measurement result. In 2 addition only a limited level of resolution is to be achieved with such a measuring arrangement as the measurement signals are integrated over the belt width. Furthermore the sensitivity of the metal-seeking coils is not homogenous in regard to the location of the damage. Thus for example damage in the edge region of the belt is not recognised or s is recognised too late. By virtue of the required arrangement of the metal-seeking coil in the lower run of the belt conveyor, damage caused by violent force to the belt is detected comparatively late. It would be important in that respect to detect for example holes through the belt at the locations in the upper run at which material delivery thereonto is effected. 10 Finally the measuring arrangement itself is comparatively expensive and complicated in terms of assembly, the latter for the reason that the metal-seeking coil must completely enclose the belt. Therefore, to detect individual cable cord tears, the procedure has hitherto been such that a prestressed cable is passed below the belt transversely with respect to the 15 direction of belt movement at a small spacing relative to the belt and connected to limit switches. A cable or a tongue portion which is hanging down is caught in the prestressed cable and actuates the limit switches, thereby causing the belt to be switched off. The cables are stretched across the belt immediately downstream of the material delivery location in the upper run (transfer) or downstream of the discharge drum. 20 Response on the part of that system requires that the damage has already assumed a certain level so that the prestressed cable is engaged thereby. A hanging cable or a tongue portion is further stressed at each support roller station or other elements of the structure, that can result in an extended longitudinal tear, in spite of the monitoring device. 25 DE 28 54 562 Al discloses an apparatus for the contact-less monitoring of conveyor belts, in particular for detecting longitudinal slits, which includes transmitter coils and receiver coils. The transmitter coils are in the form of coils with an iron core that is not closed, producing a magnetic leakage field extending far into space. The force lines of that force field cause magnetisation in the longitudinally extending steel cables 30 disposed within the belt. Arranged downstream of the transmitters in the direction of travel of the conveyor belt are receiver coils, by means of which the remanence of the magnetisation produced in that way can be measured. Evaluation of the measured magnetic field makes it possible to detect a change in position of the conveyor belt. AU 75 689 81 A discloses a method of monitoring a magnetisable conveyor belt 35 which includes tensile carriers, the method being carried out using sensors for detecting 3 the position and arrangement of the steel cable tensile carriers of the conveyor belt. The method is also carried out using an induced magnetic field. For that purpose the sensors are each provided with a respective coil arrangement, wherein the measurement method makes use in known manner of the phenomenon that the magnetic field of the coil 5 through which current is flowing changes if the spacing between the tensile carriers and the coil or the sensor changes. In that respect AU 75 689 81 A is based on the realisation that in the event of longitudinal tears in the conveyor belt it is displaced by the sensor in question to such an extent that the magnetic field of the coil in the measurement head in question changes significantly. 10 That method suffers from the above-described disadvantages of known metal search coil arrangements. Therefore, in spite of the monitoring devices already described above, there is still the aim of reliably detecting belt damage when already at an early time, that is to say in the damage-originating phase in order to be able to switch off the installation in good is time. Hitherto there is to date no system which sufficiently satisfactorily automatically detects the state of the belt in order to be able to repair or replace the belt at the optimum moment. Object of the Invention 20 It is the object of the present invention to substantially overcome or ameliorate one or more of the disadvantages of the prior art. Summary of the Invention The present invention provides a method of monitoring and/or non-destructive 25 testing of a transmission element having at least one magnetisable tensile carrier, wherein a single-axis or multi-axis measurement of the magnetic field of the earth which is disturbed by the tensile carrier is carried out by a procedure wherein at least one magnetic field sensor or an arrangement of a plurality of magnetic field sensors is guided relative to the transmission element or the transmission element is guided relative to the measuring 30 arrangement and the detected measurement signals are evaluated with a data acquisition device in regard to anomalies in the detected magnetic field, wherein the measurement operation is carried out without magnetisation (separate external magnetisation) of the tensile carrier. As the method according to the invention manages without a coil arrangement 35 but only provides for the use of magnetic field sensors, it is possible to carry out a 4 measurement operation at any location on the belt circulation, for example when monitoring a circulating belt of a bulk material conveyor. There is no need for the conveyor belt to be embraced with the measuring arrangement. The measurement signal is not disturbed by the material being conveyed as long as no ferromagnetic material is s being conveyed. The measurement signal is independent of the direction of travel and speed. The measurement operation is carried out without magnetisation of the tensile carrier, that is to say without separate external magnetisation. The magnetic field sensors register disturbances in the natural magnetic field of the earth by virtue of the presence of 10 ferromagnetic substances. Such sensors are extremely compact and can be arranged in mutually juxtaposed relationship in virtually any number. Preferably the measurement operation is carried out in a measurement range (sensitivity range) of up to 200 pT, preferably up to 100 pT. The signal strength of the signals to be measured is about +/- 50 pT. Is In a preferred variant of the method according to the invention the measurement operation is carried out on a belt of a belt conveyor of rubber-elastic material with steel cables embedded therein as the tensile carrier. The method according to the invention however is to be interpreted in such a way that monitoring and/or testing of any circulating or oscillating transmission elements with or comprising magnetisable tensile 20 carriers is possible. By way of example it is possible to implement non-destructive cable testing of a steel cable by means of magnetic field detection instead of the previously known radiological inspection or inductive detection of damage. Any damage to individual cable strands causes a change in the magnetic field lines which are detected by magnetic field sensors. The measurement operation is preferably effected in a three-axis 25 mode and can be carried out for example by means of one or more F6rster probes. Detection of the magnetic field produced by the article to be measured can be effected both dynamically and also statically. It will be appreciated that it is possible for the signal which is to be measured to be boosted by separate external magnetisation. Such separate external magnetisation 30 however is not absolutely necessary. In accordance with the invention it is provided that the reference position of the tensile carriers in the belt is tested by way of the magnetic field measurement operation. In that way it is possible to implement quality testing of the belt used, possibly already at a time prior to installation thereof in the belt conveyor apparatus. By virtue of the signal 5 produced by each tensile carrier it is possible to detect the position of the tensile carriers of a belt relative to each other comparatively precisely. In that way it is possible not only to identify the reference position of the tensile carriers relative to each other, but rather it is also possible to detect any skewed running 5 of the belt, whereby it is possible in good time to prevent the belt running into the structural components of the belt conveyor as a consequence of skewed running. Calibration of the measuring arrangement can be effected by detecting a reference signal of the transmission element in question or another transmission element in a defined condition. 10 Alternatively or additionally to material testing with the above-described method it is provided that the measurement operation is effected during operation of the belt conveyor for the purposes of monitoring thereof. In addition the measurement operation can be used for ascertaining the speed of the belt. The step of ascertaining the speed of the belt can be effected for example by is continuous comparison of one or more reference signals detected in a first belt circulation with one or more measurement signals. Desirably the width of the belt is sensed in a plurality of belt circulations. That means that the measuring arrangement can be of a comparatively simple configuration. The present invention further provides a measuring arrangement for carrying out 20 the above-described method with at least one magnetisable tensile carrier, wherein the measuring arrangement includes one or more, preferably multi-axis magnetic field sensors which are arranged at a spacing relative to the transmission element in such a way that the magnetic field of the earth which is disturbed by the tensile carrier can be detected as a measurement signal. A preferred embodiment of the measuring 25 arrangement can further include at least one data acquisition and evaluation device. The measuring arrangement can be stationarily provided on a belt conveyor. Preferably provided over the width of the belt is a number of n-sensors at a spacing from each other which approximately corresponds to 6 the spacing of the tensile carriers of the belt from each other. In that way a measurement operation affords information about the condition of each tensile carrier in the belt. In a variant of the measuring arrangement according to the 5 invention it is provided that the sensors are arranged beneath the belt in the upper run of the belt conveyor. They can and should all be arranged at the same spacing relative to the belt. It is particularly desirable if the sensors are arranged to follow the 10 contour (trough configuration) of the belt. They can be disposed for example in the form of a per se known garland at the underside of the belt. As already mentioned hereinbefore the overall width of the belt does not have to be covered by sensors, rather it may be desirable if a number 15 of n-sensors is arranged on a support structure displaceable over the width of the belt. The support structure can then be respectively displaced for one or more belt revolutions over the width of the belt so that the overall cross-section of the belt can be detected for a measuring process in a plurality of revolutions of the belt. That arrangement also has the 20 advantage that it is possible to set any desired tracking position for the sensors. For carrying out material testing operations prior to installation or prior to vulcanisation of belts it may be desirable to mount the measuring arrangement on a hand truck with which then a stationarily arranged or 25 spread-out belt can be movably negotiated and sensed. For punctiform inspection of a belt it may be desirable for the measuring arrangement to be in the form of a portable measuring and detection device (hand scanner). The invention is described hereinafter by means of an embodiment 30 by way of example as illustrated in the drawings, more specifically using the example of monitoring a belt conveyor. In the drawings: 7 Figure 1 shows a diagrammatic, greatly simplified view of a belt conveyor with a measuring arrangement according to the invention, Figure 2 shows a part of the measuring arrangement mounted in the top run of the belt conveyor, 5 Figure 3 shows a view of a measuring arrangement provided for stationary mounting to a belt conveyor, Figure 4 shows a view from below of the top run of the belt conveyor with a measuring arrangement according to the invention, Figure 5 shows a perspective view of the Figure 4 measuring 10 arrangement on a belt conveyor, and Figure 6 shows a diagrammatic measurement record of a measurement operation on a belt in accordance with the method of the invention. As already mentioned hereinbefore the method and the measuring 15 arrangement according to the invention are described hereinafter only by way of example for monitoring a belt conveyor for the transport of bulk material. Such a belt conveyor 1 includes a circulating belt 2 of rubber-elastic material with steel cables embedded therein as a tensile carrier. The belts 20 2 which are frequently used in belt installations in brown coal open-cast mines comprise rubber and are approximately of a width of 2800 mm. Steel cables of a diameter of 9.2 mm are vulcanised into the rubber, at a pitch of 15 mm. A belt of the width of 2800 mm contains 165 steel cables. Such a steel cable conveyor belt has a nominal strength St 4500. The 25 service life of the belt is on average between about 6 and 7 years. Service life-determining factors are damage to the belt due to material impinging thereon at the transfer location, the belt running into structural components as a consequence of skewed running thereof, overstretching of the steel cables by virtue of material being caked on the drums as well as 30 frictional wear at the longitudinal seals. A belt conveyor 1 is shown in greatly simplified diagrammatic form in Figure 1. It includes the endlessly circulating belt 2 of rubber with steel cables which are vulcanised thereinto, a drive drum 3 and one or more 8 guide drums 4, between which the belt 2 is tensioned. The belt 2 forms a top run 5 (load run) and a lower run 6 (idle run), wherein the belt 2 is held by support rollers 7 both in the top run and also in the lower run. The support rollers 7 are suspended on a support frame structure (not shown). 5 Reference 8 denotes a delivery chute, by way of which the bulk material is delivered onto the belt 2. It will be appreciated that the trough configuration of the belt 2 is greater in the top run than in the lower run 6. In addition the spacing of the support rollers 7 relative to each other is shorter at least in the region of the chute 8 than in the lower run 6. 10 In the embodiment shown in Figure 1 the circulatory belt travel is in the clockwise direction. A measuring arrangement 9 according to the invention is arranged in the top run 5 beneath the belt 2 immediately downstream of the chute 8 in the direction of circulatory movement of the belt. The measuring arrangement 9 includes a number of magnetic field 15 sensors 10 which are positioned in mutually juxtaposed relationship and which are fixed relative to each other and which in the described arrangement are in the form of F6rster probes. As can be seen in particular from Figure 2, the embodiment illustrated therein provides that the magnetic field sensors 10 are combined 20 to form a sensor packet. The sensor packet 11 includes a predetermined number of magnetic field sensors arranged in mutually juxtaposed relationship at equal spacings. The sensor packet can be arranged for example in the tubular guide passage 12 shown in Figure 2 beneath the belt, protected from dirt and weather influences. The length of the sensor 25 packet 11 is different from the belt width, the sensor packet is displaced for a respective one or more belt circulations in the guide passage 12 so that the width of the belt 2 is sensed in a plurality of measurement cycles. In the illustrated embodiment 6 magnetic field sensors 10 are combined to form a sensor packet 11, the spacing of the magnetic field sensors 10 from 30 each other being about 70 mm, which is wider than the spacing of the steel cables in the belt 2 from each other. By virtue of displacement of the sensor packet 11 in the guide passage 12 however it will be noted that it is possible to achieve any desired resolution in the measurement operation for 9 it is desirable to acquire a measurement signal for each steel cable in the belt 2. The sensor packet 11 can be arranged on a carriage which is displaceable with a linear drive. Alternatively it is possible, at a location beneath the belt, to arrange a plurality of sensor packets in mutually 5 juxtaposed relationship in order to be able to arrange the sensors at a spacing which is as uniform as possible relative to the belt even when the belt is of a severely trough-shaped configuration. The sensor packet 11 and each individual magnetic field sensor 10 within the sensor packet 11 are connected to a data acquisition and 10 evaluation device 13 only diagrammatically shown in the Figures. In the simplest case this can be a PC with a corresponding number of analog signal inputs. In the embodiment shown in Figures 4 and 5 a total of three sensor packets 11 of different sizes are suspended in the manner of a garland 15 beneath the belt 2 in the top run 5 of the belt conveyor 1, wherein the sensor packet 11 is held by means of guide rollers 14 against the belt 2 to achieve a uniform spacing of the magnetic field sensors 10 relative to the belt 2. That permits precise sensing of the belt 2 over the entire width thereof, up to the edges. A uniform spacing in relation to the belt 2 can be 20 maintained, even when the belt 2 is of a severely trough-shaped configuration, by virtue of the particular arrangement of the sensor packets. Figure 6 shows a measurement of a belt portion, in which the belt width is plotted on the ordinate and the belt length on the abscissa. The 25 individual signals are approximately straight when undisturbed, deflections are to be seen where the tensile carriers of the belt 2 are damaged. The measuring method according to the invention is highly sensitive so that tensile carriers suffering from incipient corrosion already produce a comparatively marked change in the measurement signal.

10 List of references 1 belt conveyor 2 belt 3 drive drum 5 4 guide drum 5 top run 6 lower run 7 support rollers 8 chute 10 9 measuring arrangement 10 magnetic field sensors 11 sensor packet 12 guide passage 13 data acquisition and evaluation device 15 14 guide rollers

Claims

1. A method of monitoring and/or non-destructive testing of a transmission element having at least one magnetisable tensile carrier, wherein a single-axis or multi s axis measurement of the magnetic field of the earth which is disturbed by the tensile carrier is carried out by a procedure wherein at least one magnetic field sensor or an arrangement of a plurality of magnetic field sensors is guided relative to the transmission element or the transmission element is guided relative to the measuring arrangement and the detected measurement signals are evaluated with a data acquisition device in regard to io anomalies in the detected magnetic field, wherein the measurement operation is carried out without magnetisation (separate external magnetisation) of the tensile carrier.

2. A method according to claim 1, wherein the measurement operation is carried out in a measurement range of up to 200 pT, preferably up to 100 T.

3. A method according to claim 1 or 2, wherein the measurement operation 15 is carried out on a belt of a belt conveyor of rubber-elastic material with steel cables embedded therein as the tensile carrier.

4. A method according to claim 3, wherein the reference position of the tensile carriers in the belt is tested by way of the magnetic field measurement operation.

5. A method according to any one of claims 1 to 4, wherein calibration of 20 the measuring arrangement is effected by detecting a reference measurement signal of the transmission element in question or another transmission element in a defined condition.

6. A method according to claim 4, wherein the measurement operation is effected during operation of the belt conveyor.

7. A method according to claim 4 or 6, wherein the measurement operation 25 is used for ascertaining the speed of the belt.

8. A method according to claim 1, wherein the speed is ascertained by continuous comparison of one or more reference signals detected in a first belt circulation with one or more measurement signals.

9. A method according to any one of claims 4 to 8, wherein the width of 30 the belt is sensed in a plurality of belt circulations.

10. A measuring arrangement for carrying out the method according to any one of claims I to 9 wherein the measuring arrangement includes one or more, preferably multi-axis magnetic field sensors with a measuring sensitivity of < 200,T, which are arranged at a spacing relative to the transmission element in such a way that the magnetic 12 field of the earth which is disturbed by the tensile carrier can be detected as a measurement signal.

11. A measuring arrangement according to claim 10, wherein it further includes at least one data acquisition and evaluation device. 5

12. A measuring arrangement according to claim 10 or 11, wherein it is stationarily provided on a belt conveyor.

13. A measuring arrangement according to claim 12, wherein over the width of the belt it has a number of n-sensors at a spacing from each other which preferably approximately corresponds to the spacing of the tensile carriers of the belt 1o from each other.

14. A measuring arrangement according to any one of claims 10 to 13, wherein the sensors are arranged beneath the belt in the upper run of the belt conveyor.

15. A measuring arrangement according to any one of claims 12 to 14, wherein the sensors are arranged at an equal spacing relative to the belt. is

16. A measuring arrangement according to claim 14 or 15, wherein the sensors are arranged to follow the contour or trough configuration of the belt.

17. A measuring arrangement according to any one of claims 10 to 16, wherein a number of n-sensors is arranged on a support structure or a carriage displaceable over the width of the belt. 20

18. A measuring arrangement according to claim 10 or 11, wherein it is arranged on a hand truck.

19. A measuring arrangement according to claim 10, wherein it is in the form of a portable measuring and detection device or a hand scanner.

20. A method of monitoring and/or non-destructive testing of a transmission 25 element having at least one magnetisable tensile carrier substantially as hereinbefore described with reference to the accompanying drawings. Dated 6 March 2012 RWE Power Aktiengesellschaft 30 Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON