GB2152088A

GB2152088A - Detection of deterioration in rope

Info

Publication number: GB2152088A
Application number: GB08333918A
Authority: GB
Inventors: John Mawson Walton; Andrew Gordon Stacey
Original assignee: Bridon PLC
Current assignee: Bridon PLC
Priority date: 1983-12-20
Filing date: 1983-12-20
Publication date: 1985-07-31
Also published as: GB8333918D0; GB2152088B

Abstract

The rope comprises bundles of fibres 2, each bundle 1 incorporating at least one electrical, optical, or fluid transmission element 3 (e.g. a carbon fibre yarn or two) whose mechanical properties approximate to those of the bundle. Failure of a fibre bundle can be detected by testing whether the transmission element transmits a signal or matter. <IMAGE>

Description

SPECIFICATION Detection of deterioration This invention relates to ropes comprising high strength fibres. In the context of the present specification the term "rope" is used to include strand and cable.

The introduction of high strength fibres such as Du Pont's aramid "KEVLAR" (trade mark) has led to an increasing demand for high stength ropes of synthetic material as replacements for conventional steel wire ropes, especially in those areas where the significant weight savings of synthetic materials can be advantageous. A major problem with these materials, however, is the difficulty of assessing rope deterioration in service.

With conventional wire ropes there are well established methods of monitoring rope condition (e.g. visual or magnetic inspection) and the mode of failure is very gradual and predictable. These methods cannot be used with synthetic materials and several instances of unexpected catastrophic failure have been recorded.

Typically, ropes of high strength synthetic fibre are constructed of bundles or tows of yarn, each containing perhaps 1000 or more separate fibres. This is because the fibres themselves are too small (diameter of the order of 10 pm) and fragile to be conveniently handled individually. For greater ease of handling and improved mechanical performance the fibres or yarns may be twisted, impregnated, and bonded together using a wax, resin, or plastics material to form an integral or composite wire-like member.

The present invention provides a rope comprising at least one bundle of fibres, the bundle incorporating at least one transmission element whose mechanical properties approximate to those of the fibre bundle.

Such a rope can be tested by attempting to transmit a signal along a given length of the bundle by way of the or each transmission element. The element may, for example, transmit electricity, light or fluids.

For example, if the transmission element is electrically conductive (e.g. comprising carbon fibres or a wire) one may apply a potential difference across the ends of a given length of the element and detect the presence or absence of an electric current in the given length. Faiiure of the fibre bundle will be indicated by an open circuit along the given length. In this way it is possible to monitor rope deterioration.

The bundle may comprise more than one electrically conductive transmission element.

Most often, the rope will comprise a plurality of fibre bundles, in which case it is preferable for the electrically conductive elements of adjacent bundles to be insulated from one another, e.g. by being surrounded by the fibres.

If the transmission element includes an optical waveguide, one may detect whether a light pulse is transmitted by the element or whether it is reflected from a break in the element. By measuring the interval between emission of the pulse and reception of the reflected pulse (if any) it is possible to locate the break (if any).

If the transmission element includes a fine tube capable of conducting a fluid, it may be practicable to supply helium, for example, to one end of the element and to detect whether the helium reaches the other end without leakage. It may also be possible to locate the leak (and therefore the region where the rope has deteriorated) by means of a gas detector, known as a sniffer, moved along the outside of the rope.

The fibre bundle may comprise synthetic fibres or glass fibres, for example, preferably bonded together to form an integral or composite wire-like member.

It is important for the transmission element to have approximately the same mechanical properties as the fibre bundle, in order that both should fail substantially simultaneously.

Premature failure of the transmission element would falsely indicate rope deterioration, whereas the converse would allow rope deterioration to proceed undetected.

Given the fact that the transmission elements and the fibres may be of different material, there is a limit to the degree to which their mechanical properties can be approximated. The most significant property will in general be the module of elasticity, since the rope will normally be used well within the elastic limit of the synthetic fibres. For a rope of high modulus synthetic fibre such as "KEVLAR" the preferred electrically conductive transmission elements are carbon fibre yarns or tows, which have a low resistivity.

Carbon fibre yarns and tows are available with a range of moduli, depending on the raw material source and the method of manufacture. They can, therefore be selected to suit the modulus of the synthetic fibres. For materials of dissimilar modulus, it is important that the elongation to fracture is similar for both materials, having regard to the disposition (e.g. level of twist) and stressing of the respective fibres.

Preferably, the transmission element is bonded to the fibres or at least the adjacent fibres, in order to increase the probability thay they will fail simulataneously.

The invention will be described further, by way of example with reference to the accompanying drawings, in which: Figure 1 is a cross-section through a fibre rope consisting of a single strand made up of 37 bundles of synthetic fibres, each bundle incorporating one electrically conductive transmission element; Figure 2 is a cross-section through a fibre rope consisting of seven strands, each made up of seven bundles of synthetic fibres; Figure 3 is an elongated fragmentary perspective view of one of the fibre bundles of Fig. 1 or 2; Figure 4 is a similar view of an alternative form of fibre bundle; Figure 5 illustrates the testing of the fibre bundles of Fig. 3; and Figure 6 illustrates one method of testing the fibre bundle of Fig. 4.

The ropes illustrated in Figs. 1 and 2 each consist of fibre bundles 1 comprising a multiplicity of "KEVLAR" fibres or yarns 2 bonded together in a cohesive matrix. The bundle shown in Fig. 3 incorporates a single transmission element consisting of a carbon fibre yarn or tow 3 whereas that shown in Fig.

4 incorporates two such electrically conductive elements 3a, 3b insulated from each other.

In order to test whether a bundle as shown in Fig. 3 has failed, it is possible to apply a voltage to the two ends of the transmission element 3 by a source V such as a battery or generator, as shown in Fig. 5, and to detect whether or not a current flows along the element 3, by means of an ammeter A.

With the bundle as shown in Fig. 4 it is possible to connect the elements 3a, 3b together (permanently or temporarily) at one end of the rope and to apply a voltage across them at the other end by the source V, the presence or absence of a current flowing along the carbon fibres again being detected by means of an ammeter A, as shown in Fig.

6. This method is useful if access to one end of the rope is difficult or impracticable. Similarly, the transmission elements 3 of two bundles 1 can be connected in series for the same purpose.

Alternatively, it is possible to connect a transmitter to the transmission elements at one end of the rope and to monitor the transmitted or reflected signal.

Claims

CLAIMS 1. A rope comprising at least one bundle of fibres, the bundle incorporating at least one transmission element whose mechanical properties approximate to those of the fibre bundle. 2. A rope as claimed in claim 1, in which the fibres are aramid fibres. 3. A rope as claimed in claim 1, in which the fibres are glass fibres. 4. A rope as claimed in any of claims 1 to 3, in which the transmission element is electrically conductive. 5. A rope as claimed in any preceeding claim, in which the transmission element is bonded to at least the adjacent fibres. 6. A rope as claimed in claim 4 or 5, in which the conductive element is surrounded by the fibres of the bundle. 7. A rope as claimed in claim 6, comprising a plurality of said bundle, the conductive elements of adjacent bundles being insulated from one another. 8. A rope as claimed in any of claims 1 to 3, in which the transmission element comprises an optical waveguide. 9. A rope as claimed in any of claims 1 to 3, in which the transmission element is capable of conducting a fluid. 10. A rope as claimed in any preceding claim, in which the transmission element is bonded to at least the adjacent fibres. 11. A method of testing a rope according to any preceding claim, comprising attempting to transmit a signal or medium along a given length of the bundle by way of the transmission element. 1 2. A method as claimed in claim 11, in which the transmission element is electrically conductive comprising applying a potential difference across a given length of the transmission element and detecting the presence or absence of an electric current in the given length. 1 3. A method as claimed in claim 11, comprising detecting reflection of the signal. 14. A method as claimed in claim 11, in which the transmission element is capable of conducting a gas, comprising supplying a gas to one end of the element and detecting leakage of the gas.

1. A rope comprising at least one bundle of fibres, the bundle incorporating at least one transmission element whose mechanical properties approximate to those of the fibre bundle to such an extent that the bundle and the transmission element will fail substantially simultaneously.

1

2. A method as claimed in claim 11, in which the transmission element is electrically conductive, comprising applying a potential difference across a given length of the transmission element and detecting the presence or absence of an electric current in the given length.

1 5. A rope substantially as described with reference to, and as shown in, Fig. 1 or 2 and Fig. 3 or 4 of the accompanying drawings.

CLAIMS (21 Nov 1984) Amendments to the claims have been filed, and have the following effect: New or textually amended claims have been filed as follows:-