GB2100440A

GB2100440A - Magnetic flaw detector for steel wire ropes

Info

Publication number: GB2100440A
Application number: GB8117937A
Authority: GB
Original assignee: G MAKEEVSKY NI; INST BEZOPASNOSTI RABOT V GORN
Current assignee: G MAKEEVSKY NI; INST BEZOPASNOSTI RABOT V GORN
Priority date: 1981-06-11
Filing date: 1981-06-11
Publication date: 1982-12-22
Also published as: GB2100440B

Abstract

A magnetic flaw detector for steel wire ropes comprises magnetic cores (1) mounted on a steel wire rope by means of clamping devices (5). The magnetic cores (1) are connected therebetween by means of ferromagnetic plates (4). The magnetic cores (1) and the ferromagnetic plates (4) form a closed magnetic circuit encircling the steel wire rope. On the magnetic cores (1) are mounted inductor coils (2) and pole pieces (3) to contact with the steel wire rope. The pole pieces (3) are constructed from a nonferromagnetic conductive material. The invention can be also utilized for inspection of losses in the cross- section of metal of zinc coated steel wire ropes. <IMAGE>

Description

SPECIFICATION Magnetic flaw detector for steel wire ropes The invention relates to measuring devices intended for inspecting losses in the cross-section of metal of steel wire ropes in the process of operation thereof by means of magnetic flaw detection.

The invention may be utilized for flaw detection in zinc coated wire ropes as well.

Prior art magnetic flaw detectors for steel wire ropes provide only an approximated quantitative evaluation of losses in the cross-section of metal of steel wire ropes.

Thus, known in the art is a magnetic flaw detector for steel wire ropes (US. Patent No. 3,242,425), comprising an inductor coil having 50 turns and cut into two halves, and measuring devices. The halves of the inductor coil are mounted by means of clamping devices directly on the wire rope, which serves as a magnetic core thereof.

The inductor coil is moved along the wire rope being inspected, and the value of coil inductance and that of active resistance are recorded by corresponding measuring devices, and the losses in the cross-section of the wire rope metal is determined.

Since the halves of the inductor coil are mounted on the wire rope and coupled therebetween by means of one hundred contact pairs, which are to be connected in series, the value of MTBF counts to tens of hours.

Unstable total resistance of a large number of contact pairs results in a decrease in active resistance of the inductor coil and is recorded by the measuring devices as a flaw of the wire rope.

In the use of such a flaw detector for inspection of a zinc coated wire rope, a change in the coil inductivity caused by destruction of the zinc coating of the rope wires is taken as a loss in the cross-section of the wire rope.

The above device allows only an approximated quantiative evaluation of losses in the crosssection in the wire rope metal to be obtained.

An accurate quantitative evaluation of losses in the cross-section of the wire rope metal can be obtained by this device in the case of elimination of the influence of active resistance of the inductor coil on the value of readings of said device.

Known in the art is a magnetic flaw detector for steel wire ropes (USSR Author's Certificate No. 231,876), eliminating the utilization of a split inductor coil and allowing the device to be easily and rapidly assembled on the wire rope.

The above device comprises U-shaped magnetic cores each having an inductor coil disposed thereon, and connected to a measuring device. The U-shaped magnetic cores comprise pole pieces constructed from a ferromagnetic material. The U-shaped magnetic cores are mounted and fixed by means of clamping devices on the wire rope to obtain a complete contact between the pole pieces and the wire rope, thereby eliminating a non-magnetic gap between the wire rope and the U-shaped magnetic cores.

The magnetic circuit is formed in the device by the U-shaped magnetic cores and a wire rope under inspection through the contact between the pole pieces of the U-shaped magnetic cores and the wire rope.

To accomplish magnetic flaw detection of steel wire ropes, the device is first mounted onto a reference length of a wire rope under inspection whose metal cross-section is assumed to be 100%, and the value of a magnetic flux is measured by the measuring device. Then the device is removed from the reference length of the wire rope under inspection, mounted onto the rope under inspection, the rope is drawn through the device and the value of the magnetic flux is measured.

From the difference between the value of the magnetic flux in the wire rope under inspection and that in the reference length thereof, losses in the cross-section of metal of the wire rope under inspection are determined.

The above device permits obtaining a precise quantitative evaluation of losses in the crosssection of metal of a rope which is not contaminated with grease, dirt, ice and similar coatings. The above coatings form nonmagnetic gaps between the rope and the pole pieces of the magnetic cores. The nonmagnetic gaps cause asymmetry and changes in a magnetic field generated by the U-shaped magnetic cores within the rope under inspection. The change in the magnetic flux, recorded by the measurement device, is not related with losses in the crosssection of the wire rope metal.

In the magnetic flaw detection of wire ropes contaminated with grease, dirt, ice and similar coatings the device provides only for an approximated quantitative evaluation of losses in the cross-section of metal of the wire rope under inspection.

In carrying out the magnetic flaw detection of zinc coated wire rope by means of said device, a secondary loop is formed, said loop being inductively connected with the magnetic core coils of the device.

The secondary loop is annihilated in the damage of the zinc coating of rope wires thereby resulting in changes in the magnetic flux generated by the device in the flaw detection of the wire rope.

The obtained change in the magnetic flux is practically of the same magnitude as that in the magnetic flux of the device in the case where losses in the cross-section of wire rope steel are of 5 to 1 0%, thereby resulting in rejection of the wire rope having slight damage of the zinc coating of rope wires without any losses in the cross-section of steel of rope wires.

Changes in the magnetic flux of the device, which are also recorded as losses in the crosssection of metal of the wire rope under inspection, are caused by the rotation of the device about the wire rope in the process of drawing the wire rope through the device.

The main object of the invention is the provision of a magnetic flaw detector for steel wire ropes, wherein a magnetic core is constructed to ensure inspection of losses in the cross-section of steel of zinc coated wire ropes.

Another object of the invention is the provision of a magnetic flaw detector for steel wire ropes, wherein a magnetic core is constructed to upgrade accuracy of inspection of losses in the cross-section of metal of steel wire ropes whose surface is contaminated with solidified grease, dirt, ice and similar coatings.

The invention consists in that a magnetic flaw detector for steel wire ropes comprises at least two magnetic cores; inductor coils mounted on said magnetic cores; pole pieces mounted on said magnetic cores, contacting with the steel wire rope and made from a non-ferromagnetic conductive material; ferromagnetic plates connecting the magnetic cores to create a closed magnetic circuit encircling a steel wire rope.

The above detector provides for locating a wire rope under inspection, which is contaminated with grease, dirt, ice and similar coatings, at equal distances from the surfaces of the magnetic cores, and ensures a symmetric magnetic field relative to the wire rope axis.

The movements of said detector along and about a contaminated wire rope in the course of flaw detection cause far less changes in the magnetic flux as compared to the changes in magnetic flux in the prior art device, wherein the magnetic circuit is formed by the magnetic cores and the rope under inspection through the pole pieces of the magnetic cores and the rope.

In the flaw detection of zinc coated wire ropes with the use of the above device, the nonferromagnetic conductive material of the pole pieces permits,the influence of the secondary loop on the magnitude of the magnetic flux generated by the detector to be reduced to a practically acceptable value.

The invention is further explained in terms of embodiment thereof and reference to the accompanying drawings, in which: Fig. 1 is an axial sectional view of a magnetic flow detector for steel wire ropes; Fig. 2 is a sectional view taken along the line Il-Il in Fig. 1.

Referring to Fig. 1 , the magnetic flaw detector for steel wire ropes comprises two U-shaped magnetic cores 1 each having an inductor coil 2 disposed thereon and connected to a measuring device (not shown). On the magnetic cores 1 are mounted semicylindrical pole pieces 3 so constructed that in the installation of the magnetic cores 1 on a steel wire rope the pole pieces 3 encircle the latter and contact therewith.

According to the invention, the pole pieces 3 are constructed from a nonferromagnetic conductive material, namely brass.

Ferromagnetic plates 4 (Fig. 2) are mounted on side surfaces of the magnetic cores 1, connect the latter therebetween and provide a closed magnetic circuit in the shift of the magnetic cores 1 as a result of the slide of the device along a wire rope contaminated with grease, dirt, ice and similar coatings.

To mount the magnetic cores 1 on the wire rope, the device comprises clamping devices 5.

The inventive magnetic flaw detector for steel wire ropes operates as follows.

To accomplish magnetic flaw detection of steel wire ropes, the U-shaped magnetic cores 1 are mounted on a reference length of a wire rope under inspection so that the pole pieces 3 encircle the rope and contact therewith. Using the clamping devices 5, the U-shaped magnetic cores are fixed on the wire rope, the U-shaped magnetic cores 1 being connected therebetween by means of the ferromagnetic plates 4. Following this, the inductor coils 2 are connected to a measuring device (not shown), the wire rope is drawn through the magnetic flaw detector for ropes, and the magnitude of a magnetic flux generated in the rope by means of the magnetic flaw detector for ropes is measured by the measuring device.

Then the magnetic flaw detector for wire ropes is removed from the reference length of the rope under inspection and is mounted on the rope under inspection in the same manner. Next, the wire rope under inspection is drawn through said detector and a value of the magnetic flux generated by said detector in the rope under inspection is measured.

A non-magnetic gap formed by the pole pieces 3 between the rope and the magnetic cores 1 reduces the changes in the magnetic flux generated by the detector in the rope and caused by rotation of the detector about the rope and by the shift of the magnetic cores 1 in their slide along the rope contaminated with grease, dirt, ice and similar coatings.

The difference between the magnitudes of magnetic fluxes generated by the detector in the reference length of the rope and the rope under inspection provides a precise quantitative evaluation of losses in the cross-section of metal of the rope under inspection.

In the flaw detection of zinc coated wire ropes the nonferromagnetic conductive material of the pole pieces 3 of this detector generates an opposite magnetic flux in the magnetic cores 1, said flux coinciding with the direction of a magnetic flux generated by a zinc coating of the rope wires, though essentially exceeding the latter in the magnitude, thereby allowing the change in the magnetic flux of the detector to be reduced in case of the damage of the zinc coating of the rope wires, and the accuracy of measurement of losses in the cross-section of metal of the zinc coated ropes to be upgraded.

It will be appreciated that various changes can be made in the invention without departing from the scope thereof described in terms of a specific example.

Claims

1. A magnetic flaw detector for steel wire ropes, comprising at least two magnetic cores; inductor coils mounted on the magnetic cores; pole pieces mounted on the magnetic cores contacting with a steel wire rope and constructed from a non-ferromagnetic conductive material; ferromagnetic plates connecting the magnetic cores to create a closed magnetic circuit encircling the steel wire rope.

2. A magnetic flaw detector for steel wire ropes substantially as herein described with reference to the accompanying drawings.