GB2206969A - Non-destructive magnetic testing device - Google Patents

Description

220CP55 k) A NON DESTRUCTIVE TESTING DEVICE FOR AN ELONGATE MAGNETICALLY

CONDUCTIVE ELEMENT This invention relates to a non destructive testing device for an elongate magnetically conduczive element and is designed for checking in a non-destruczive manner the continuity and the state of an element such as a wire rope, metallic tube pipe or rod which is of a magnetically conductive material.

It is essential for safety reasons to be able to check the stare of ropes and halyards hich are used for load bearing purposes such as supporting cages in mine shafts to ensure that for example in a multiple strand rope no fracture has occurred of any of the wires which would lead to a weakening of the rope at the point of fracture. It is also necessary to ensure that no degradation is taking place within the rope due to corrosion or wear. Normally the rope is oiled or loaded with grease on manufacture but notwithstanding this there can be an ingress of moisture which can cause local rusting inside the rope which can weaken the strands of the rope and eventually lead to failure. This rusting is not normally apparent on a visual inspection and it is necessary to be - 2 able to check the rope by som other method to see whether rusting or degradation is occurring.

There have been prior proposals to check the condition of elongate magnetically conductive elements by using magnetic sensors and, for example, one such system is disclosed in Brizish Patent Specification No 1 539313. This shows a magnet having tubular pole pieces through which the rope is drawn and Hall effect sensors incorporated into the pole pieces to pick up the magnetic flux generated and to detect any modulation of it due to irregularities in the magnetic path constituted by the rope.

Another example is shown in European Specification No 0239537 in which two permanent magnetic stacks produce magnetic fields which are opposed and which magnetise rope pulled through them. Faults in the rope are detected by monitoring changes in magnetic fluxes.

It is an object of the present invention to provide an improved form of testing a rope non-destructively using magnetic devices which does nor use Hall effect devices in association directly with the pole pieces of a magnet but which has them more centrally disposed for more effective operation.

According to the present invention a non-destructive testing device for an elongate magnetically conductive element includes a housing having two hinged parts, in which the housing contains a pair of magnetic poles arranged to be spaced equi-distant around an element to be tested with like poles arranged diametrically opposite to each other and first and second sensor means arranged to be positioned around the element and between the poles of the magnetic devices.

The first sensor means may comprise coils arranged to extend around the element and to detect local flaws in the element. The coil 1-, - 3 may be either of a saddle configuration or conveniently of a kidney configuration and will have a large plurality of turns.The second sensor means conveniently includes a plurality of Hall effect sensors disposed radially around the element for detecting flux changes indicating corrosion or wear within the body of the element. The second sensors means is preferably situated between longitudinally spaced components of the first sensor means and both sensor means are located between the pole pieces of the pair of magnetic devices.

The sensor means may each be connected to respective indicating or recording means such as a cassette tape recorder or a paper chart recorder. Additionally or alternatively a direct display device may have been incorporated so that an indication is visually given as soon as a flaw is deteczed.

The element being tested is designed in operation to be moved relative to the device and it may be necessary to incorporate means to compensate for the speed of movement for example means may be incorporated into appropriate circuitry connected to the sensor means or a mechanical device, such as a roller or wheel driven by the moving element.. may be used to generate a signal to make the indicated output virtually independant of the speed of the element relative to the device.

The pair of magnetic devices may be constituted by permanent magnets or by dc electromagnets.

The magnetic devices may be incorporated with the sensor means in a hinged element adapted to clip over an element to be monitored.

In order that the invention may be readily understood one example of a device in accordance therewith will now be described with reference to the accompanying drawings. In the drawings a device is shown for testing the quality of a steel wire rope used in supporting - 4 winding cages in the shaft of a coal mine.

Figure 1 shows an exterior side view of the device with the position of a rope under test indicated. Figure 2 shows a cross sectional end view of the device of Figure 1 taken on the lines II-II, and Figure 3 shows a plan sectional view taken on the lines III-III of Figure 1. Figure 4 shows in a schematic form only, the outline of the device with the rope in position, while Figures 5 and 6 show two configurations of coils in a schematic form which can comprise the first sensor means. Figure 7 indicates a wave form generated when a break in the wires of the rope occur. Referring now to the drawings and particularly to Figures 1, 2 and 3, the device has a casing (1) which is split into two halves (2),(3) which are hinged together at (4) on one side and joined by releasable quick release latches (6) on the other. The device (1) is secured to a base (7) and a rope (8) is able to be passed through the device.

The top half of the casing (2) has connected to it a biased arm (10) which is pivoted at (11) to a bracket (12). The arm (10) carries a wheel or roller (13) which is profiled to run on the surface of the rope (8) being tested, and to rotate as the rope is passed through the device (1). The wheel is connected to a shaft encoder in the lower part of the arm (10) at (14) and the encoder sends electrical-signals over a flexible cable (15) to an outlet socket (16). Cables. nor- shown, are connected to the socket outlet (16) so that signals indicative of the passage of the cable through the device are able to be taken and recorded.

internally of the housings (2) and (3), there is an array of magnets, basically comprising in the half (2) south poled magnets at the left-hand end, as viewed in Figure 3, and north poled at the right-hand end. This is mirrored by the magnetic arrangement in the top half (3) so t that all the south poles are towards the end of the device on the left, as seen in Figure 3, and all the north poles on the right. The arrangement is better appreciated frcm the schematic view shown in Figure 4. The south poles are indicated by the reference (20) and the north poles are referenced (21).

Between the south and north poles of each of the pole pieces, there are positioned first sensor means (22) which comprise induction coils of many hundred of turns of wire, which fit closely above the rope (8). The confguration of: the coils may be as shown in Figure (5) where it is a saddle coil or as shown in Figure (6) where a kidney shaped coil is shown. The purpose of the coils being the shape they are is so that the two halves (2) and (3) may be separated about the hinges (4), when the device is open to allow a rope to be introduced or taken out.

Second sensor means comprising Hall sensor devices (23) with associated circuitry are positioned in the centre of the device (1) around the rope (8). The output from the sensor devices (22) and (23) are fed to an output terminal unit (24) (Figure 1) for connection to a recording device.

The sensor means measure the magnetic flux which is flowing longitudinally outside the rope and effectively measure also the metallic cross sectional area of the rope. This measurement is used to determine the amount of wear or corrosion in the rope, since variations in the flux are monitored. The flux paths between the magnetic poles (20), (21) are both in the same direction within the rope and these paths are indicated at (26) in Figure 4.

In use the catch (6) is released to allow the rope to be inserted into the device (1) and the two halves (2), (3) are then hinged t)gether and secured. Starting from a zero datum position, the rope is 6 then pulled at a steady and continuous feed through the device and with suitable instruments connected to the outlets (16) and (24), any change in flux path through the rope is noted by a distortion of the magnetic field around the rope, which will be detected by one of the first sensor devices (22). If there is a break in one of the wires, this will give rise to a pulse in the wave form as indicated in Figure 7 to which reference is now made. Here the two ends (30) of a wire in the rope are shown separated by a break area (31). The wave form shown beneath the ends (30) at (32) is shown as being constant at either side of the break, but will appear as a blip (33) as indicated where the break (31) occurs.

The position of any fault is found by recording the length of rope which is passed through the device (1) by the number of rotations which the wheel (13) has made, and which has been picked up by the shaft encoder (14) and sent in electrical signal form to the recording device to determine the exact locarion of the break inside the rope which can then be marked.

Similarly the second sensor means (23) will also monitor the change in the magnetic flux our-side the rope and the metallic cross sectional area signal will be obtained from the Hall sensors. If the metallic cross section of the rope remains constant, and there is no corrosion or rusting thep.,the flux path will give a constant output. if, however, there has been rusting or corrosion internally this flux path will be altered and the change in the external flux which is detected by the Hall sensors will be recorded and monitored. This will then be related to the length of rope passing through-the device and an assessment can be made as to whether the corrosion is sufficiently severe for the rope to be considered unsafe for further use, or whether it can still be used.

-1 l! 1 If necessary the recording device can be arranged to trigger a marking device which will put a mark on the rope at the appropriate area. where a break or corrosion is detected.

Guides (28) are provided in the device to ensure that the rope is positioned accurately between the magnetic poles (20) and (21), and the sensor devices (22), (23). The guides (28) are preferably of a very low friction non-magnetic material and this ensures that the raze of pull of the device is steady.

The magnetic strength of the pole pieces (20), (21) is chosen such that the area of rope within the device is substantially magnetically saturated. The magnetic devices may be either permanent magnets or dc excited magnets. Due to the device (1) being constructed in two halves with the hinge arrangement (4), it will be appreciated that the device is able to be applied quickly to a rope without the end of the rope needing to be threaded through the device. This is particularly useful when certain areas only of a rope are suspected of being corroded or having breakages in its wires is to be tested as the device can easily be applied to the selected area without many metres of rope having to be passed through the device for monitoring unnecessarily.

The device also enables a record to be kept of the state of the rope under test and this ensures that regular tests can be recorded and ccmpared for safety reasons.

Claims (1)

1. CLAIMS:

   1.

   4.

   5.

   7.

   8.

   A non-destructive testing device for an elongate magnetically conductive elementi, ccmprising a housing having two hinged parts in which the housing contains a pair of magnetic poles arranged to be spaced equal distance around an element to be tested, with like poles arranged diametrically opposite to each other and first and second sensor means arranged to be positioned around the element and between the poles of the magnetic devices.

   A device as claimed in Claim 1 in which the first sensor means comprises coils arranged to extend around the element and to detect local flaws in the element.

   A device as claimed in Claim 2 in which each coil is of a saddle configuration.

   A device as claimed in Claim 2, wherein each coil is of a kidney configuration.

   A device as claimed in any Claims 2, 3 or 4, in which the first sensor means =prises coils having a large plurality of turns.

   A device as claimed in any preceding Claim, in which the second sensor means includes a plurality of Hall effecr-sensors disposed radially around the element for detecting flux changes indicating corrosion or wear within the body of the element.

   A device as claimed in any preceding Claim. in which the second sensor means is situated between longitudinally spaced components of the first sensor means.

   A device as claimed in any preceding Claim, in which both sensor means are located longitudinally between the pole pieces of 1 1 1 13.

   the pair of magnetic devices.

   A device as claimed in any preceding Claim and including measuring means for measuring the length of element which has passed through the device.

   10. A device as claimed in Claim 9, in which the measuring means includes a roller engaging the element and being rotated by movement of the element, the roller being connected to a shaft encoder arranged to send an electrical signal to a recording or monitoring device dependant on the amount of rotation of the roller.

   A device as claimed in any preceding Claim and including outlet means for connection to indicating or recording means, or a direct display device.

   A device as claimed in any preceding Claim and including guide means for correctly positioning the element within the body of the device during movement of the element through the device.

   A non-destructive testing device substantially as hereinbefore described with reference to the accompanying drawings.

   Published 1988 at The Patent Office, State House. 66 71 High Holborn. London WC1R 4TP. Further copies may be obtained from The Patent office, Sales Branch, St Mary Gray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Gray, Kent. Con. 1i87.