Magnetic non-destructive method and apparatus for measurement of cross sectional area and detection of local flaws in elongated ferrous objects in response to longitudinally spaced sensors in an inter-pole area

Abstract

A magnetic non-destructive method and an apparatus for measurement of cross sectional area of elongated ferrous objects such as steel wire ropes and for detecting local flaws is disclosed. A section of a wire rope is magnetized by longitudinally spaced magnetic poles. A magnetic field parameter, e.g. magnetic flux density, is measured in, by at least, one pair of points between the poles of magnetizing device (in an inter-pole area) at the object under test surface. The pair of points is formed by two sensors placed in the inter-pole area along a direct line parallel to the rope axis. The rope cross sectional area corresponds to a sum of the sensor pair signals. Local flaws, such as broken wires and pitting corrosion in the rope, is detected by a first differences of signals of the sensor pair. At least one additional magneto-sensitive sensor is located radially inward of the poles and weight coefficient A depending on a nominal value of the rope cross sectional area is subtracted from the sum of signals of the sensor pair thereby providing a second difference of the signals corresponding to the rope cross sectional area. The coefficient A value is chosen to get the minimum value of the second signal difference while the magnetizing device and all the sensors are placed onto the rope having a nominal value of a cross sectional area. A sensor unit in the inter-pole area includes a magnetic core in form of three longitudinally spaced ferrous elements. Pairs of the sensors are located in the gaps along a direct line parallel to the rope. Two embodiments of the magnetic heads are disclosed: the hollow cylinder-shaped one and the U-shaped one.

Description

[0001]The present application claims priority benefits under 35 U.S.C. §119 to Russian Federation application N99126933 / 28 filed Dec. 17, 1999.[0002]1. Field of the Invention[0003]The present invention relates to the non-destructive testing of product quality, and in particular, to magnetic testing of elongated ferromagnetic objects like steel rods, tubes and wires to determine variances in a cross sectional area of object as well as the presence of local flaws.[0004]2. Background of the Invention[0005]A method and apparatus for magnetic non-destructive testing of elongated objects, e.g. steel ropes, by measurement of loss of metallic area (LMA) due to wearing and for local flaw (LF) detecting are described in U.S. Pat. No. 4,659,991, US C1. 324 / 241, Int.C1.G01N27 / 82, issuing in 1987. The method includes the axial magnetizing of the rope part by permanent magnets to a condition close to magnetic saturation and measuring the magnetic flux leakage variation near the rope surface by us...

AI Technical Summary

Benefits of technology

"The present invention solves the problem of improving the accuracy of measuring the cross-sectional area and detecting flaws in steel wire ropes. The invention uses a magnetizing device with poles spaced along the rope's longitudinal axis to magnetize the rope and measure the magnetic flux density. The magnetic flux density is measured by sensors placed in an area between the poles. The rope's cross-sectional area is defined by the magnetic flux density, and changes in the area result in changes in magnetic flux density. The invention also uses an additional sensor placed between the rope and a pole to measure the flux leakage caused by flaws. The invention increases accuracy and reliability in detecting flaws and loss of metallic area (LMA) in steel wire ropes."

Problems solved by technology

In particular, loss of the rope cross section metallic area (LMA) leads to an increase in magnetic flux leakage within the inter-pole space round the rope, which increases magnetic flux density in the inter-pole area.

Thus, an LMA measurement error, from the instability of magnetic flux density round the rope, e.g. from the influence of temperature variation on the magnetizing device, is decreased.

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