Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1986-10-14
1989-04-04
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
324233, G01N 2772, G01R 3312
Patent
active
048189367
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to methods and apparatus for identifying and classifying steels.
BACKGROUND ART
In a modern steel works producing a wide range of steel products of differing steel grades, it is important to be able to carry out non-destructive testing of steel specimens to establish their correct grades. One current method, known as the "Forster" method, relies on a comparison between the magnetic properties of a steel specimen to be tested and a "standard" sample which has been chemically analysed. The test specimen and the standard sample are inserted into separate coils, each having primary and secondary windings. The primary windings of the two coils are subjected to a common energizing current of fixed frequency and a comparison is made between output signals induced in the secondary windings of the two coils. The output signals may be applied to a comparison circuit which generates a display on a screen.
The Forster method of steel classification has several limitations and problems in practice. These include:
1. A highly trained operator is required to interpret the trace or screen display to enable satisfactory information to be gained.
2. Since the operator must visually access a visual display, estimating the amplitude and shape of a wave form generated by the test sample, only a qualitative idea is obtined of possible differences between successive samples being tested.
3. Since the test method is not quantitative and since there are always some variations in the physical and chemical properties even within a given grade of steel, it is very difficult to be certain whether an observed changed in the display constitutes a real change in grade or only a variation explainable by within grade variations.
4. The method is very sensitive in variations in temperature between the test specimen and the standard sample.
5. Results depend on chemical analysis of the initial standard sample. Once it is considered that a change in grade has occurred the new grade cannot be determined without further recourse to sampling and subsequent chemical analysis.
The present invention has arisen from work aimed at developing an improved magnetic testing method which will enable a more accurate and convenient testing procedure.
DISCLOSURE OF INVENTION
The invention provides a method of classifying a steel specimen comprising:
presenting the specimen to a coil means having a primary winding and a secondary winding such that the specimen contributes to an inductive coupling between the primary winding and the secondary winding;
applying an excitation current to the primary winding at each of a plurality of excitation frequencies whereby to induce in the secondary winding for each excitation frequency a signal indicative of an induction value of the specimen; and
determining a grade classification of the specimen dependent on the induction values obtained at said excitation frequencies.
The primary and secondary windings of the coil means may be generally co-axial and spaced apart in the axial direction and the specimen may be positioned so as to extend into both windings.
Alternatively, the primary and secondary windings may be disposed about a coupling member defining a coupling gap and the specimen may be position so as to provide an inductive coupling across said gap.
Preferably, the critical frequencies at which signals induced in the secondary winding are exactly out of phase with the excitation current are also determined and the determination of the grade classification is also dependent on those critical frequencies.
Preferably further, the grade classification is determined according to the value of a discriminant function of the form a.alpha.+.beta.b+c.gamma.+ . . . where .alpha., .beta., .gamma. . . . are attributes of the specimen comprising said induction values and a, b, c . . . are coefficient reflecting the degree to which the respective attributes are effective to discriminate between steel grades.
Preferably said attributes also comprise said critical frequencies.
The inven
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Tso, "Tower Concentration Meter", Xerox Disclosure Journal, vol. 5, No. 3, May/Jun. 1980, p. 315.
Edmonds Warren S.
Eisenzopf Reinhard J.
The Broken Hill Proprietary Company Limited
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