Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Reexamination Certificate
1999-07-26
2002-04-23
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
C324S242000
Reexamination Certificate
active
06377040
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an eddy current test probe for testing metal articles.
2. Description of Related Art
Test instruments of the type to which the invention is directed have been known for some time and are used especially to test tubular articles from their inside or outside. Other important applications of these devices relate to checking of rolled sheets, rods or wires in the metalworking industry. Diverse efforts have been made, especially, to inspect the periphery of rods, tubes or wires on all sides. To do this, test probes are used which are guided around these articles with a mechanically driven device and with high speed in order to continually carry out eddy current tests. At the same time, and with a stipulated linear speed, the workpiece to be examined is moved through this test means. The material faults to be detected are of a varied nature. They can either be extremely visible, or can be located within the material. They can be punctuate or can have an extended, especially oblong shape. Depending on which of these prerequisites are present, an eddy current test probe can have a more or less high detection efficiency. But again, it has been established that detection of defects on the edges of metal rods with a roughly rectangular cross section (billets, slabs) is extremely difficult and usually imperfect. This relates especially to the problem formulation when defects can occur, at the same time, in the longitudinal direction and the transverse direction of these rods and are to be detected with high reliability. Conventionally, the problem is additionally exacerbated by the fact that the cross sectional dimension of these products can be subject to slight variations without edge defects actually being present.
An attempt to solve the above problem is described in U.S. Pat. No. 5,130,652; compare FIGS.
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there. The field coils there are not only large, unwieldy and expensive, but due to their volume can only be operated with direct or low frequency alternating current. The known advantages of high frequency testing based on eddy currents thus cannot be observed there. A similar approach is followed in the invention described in U.S. Pat. No. 5,648,721. As in the approach in U.S. Pat. No. 5,130,652, due to the circling motion of the probe in edge testing, however, the disadvantage arises that material areas of interest, then adjacent material areas are alternately checked. Accordingly, the invention according to U.S. Pat. No. 5,648,721 is mainly intended also for checking of rivets and screws on aircraft.
In U.S. Pat. No. 5,617,024, derived from the same invention as U.S. Pat. No. 5,648,721, test probes are presented which are only of a rather general nature and are not suited for simultaneously discovering transverse and longitudinal faults on the edges of rod-shaped articles of metal or an electrical conductor. Another probe guided on an arc for checking flat metal pieces is described in U.S. Pat. No. 4,274,054. As is described there, the proposed rotating coil arrangement is, however, unsuited for checking edges of the test specimens to be examined since another approach with nonrotating probes is presented for checking of edges.
SUMMARY OF THE INVENTION
The primary object of the invention is in making available an economical, very reliable test instrument which is easy to operate and which is especially suited to the detecting of defects on or near the edges of polygonal metal rods, and at the same time, is able to detect defects in at least the longitudinal and transverse direction of these rods. In addition, as much as possible, defects should also be detectable which have an angular position between these directions. Moreover, the test instrument or a corresponding probe (without modifications) should also be usable for material tests on flat metal articles.
This object is achieved by a test probe for nondestructive material testing and for detecting inhomogeneities or defects of an article of conductive material which has a instrument transformer, optionally one or more measurement oscillators, with an impedance or reactance which changes when these material defects are present, at least changes differentially. Especially in an embodiment with a instrument transformer, it is provided that one or more transmitting (primary) and receiving (secondary) coils, connected as instrument transformers and supplied with a high frequency voltage, are used to acquire magnetic fluxes or partial fluxes produced as eddy current, the instrument transformer being able to detect differences of partial magnetic fluxes which are generated by the instrument transformer in a metal test specimen and are emitted by it, and the instrument transformer having at least one axis of symmetry. In accordance with the invention, the transformer is continuously turned around a preferred axis of the axes of symmetry, especially the vertical axis. In doing so, the instrument transformer executes rotary motion relative to the test specimen (or vice versa). This axis of symmetry, in accordance with the invention, is thus oriented essentially perpendicular to the surface of a metal test specimen or points at its longitudinal axis. The rotary motion of the instrument transformer is best effected mechanically, i.e., preferably by means of an electric motor drive.
In the embodiment according to the invention with an instrument transformer, this object is therefore achieved in a special way by a test probe for nondestructive material testing and detecting inhomogeneities or defects of an article of a conductive material being prepared which can produced eddy currents in the material to be tested and which can detect them (by the correspondingly emitted eddy magnetic fields) and has the following features:
The test probe is equipped with one or more transmitting coils with longitudinal axes oriented essentially perpendicularly to the surface of the article to be tested or at least aligned such that a surface normal of the article on an area to be tested points in the parallel direction to the longitudinal axis of one such transmitting coil.
The transmitting coil is supplied with a high frequency AC voltage from roughly 1 to 5000 kHz.
A receiving coil which is located preferably within the transmitting coil is assigned to the latter. The receiving coil has a ratio of the lengthwise dimension to the width dimension (i.e., coil height to coil width) of less than 1 and is preferably less than 0.3, typically even less than 0.2. In particular, the receiving coil can be wound with a not overly large number of turns around a ferromagnetic core with higher relative magnetic permeability, for example, from 10to 10000.
The longitudinal axis of the receiving coil is especially perpendicular to the longitudinal axis of the transmitting coil, the two longitudinal axes having at least roughly one common point or intersection point.
Transmitting and receiving coils form a transformer system with a primary coil and secondary coil which are connected as a (magnetic) flux difference detection arrangement. The transformer interaction between the primary coil and secondary coil is equivalent, i.e., the primary side and secondary side of the transformer system can be interchanged without loss of system function (with consideration of the ratio of number of turns). This arrangement of the transmitting and receiving coils is located within a shielding cup or hollow cylinder with a preferably unilateral opening on its face. The cup is used as the conductor for a magnetic flux and is made of a ferromagnetic material with a relative magnetic permeability greater than 10. The test probe is pivotally mounted relative to an article to be tested and can be turned by a motorized drive with roughly uniform speed around an axis which agrees with an axis of symmetry (especially the longitudinal axis) of the transmitting and receiving coil.
It is advantageous according to the invention if the magnetic shielding cup, at the same time, has electrical shieldin
Patidar Jay
Pruftechnik Dieter Busch AG
Safran David S.
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