DE3533311A1 - DIFFERENTIAL PROBE WITH A SINGLE COIL FOR NON-DESTRUCTION-FREE TESTING OF IRON AND STEEL PRODUCTS - Google Patents

Description

description

The invention relates to a measuring arrangement for the non-destructive testing of steel mill products. In particular, the invention is concerned with an arrangement for the hot and cold determination of defects in slabs,
pre-rolled blocks and billets.

The device of the invention is intended to be an alternative to and an improvement over that commonly used Bring differential measuring probe arrangement based on the Foucault current or eddy current principle and to other measuring systems of the electromagnetic type can be applied, for example, to the electromagnetic Based on the principle of resonance.

To understand the method to be used according to the invention, the eddy current measuring principle is first described below
explained.

An eddy current probe consists of a coil in which Primary winding generated by an oscillator currents circulate

3Q culture. These currents generate an alternating magnetic field, which eddy currents in the investigated
Material. In turn, these currents generate an electromagnetic field which induces voltage in the secondary winding of the coil. The voltage

g ₅ varies depending on the distance of the material being examined from the probe and on the type of material in question
standing material.

Embodiments known to those skilled in the art The above principle is generally based on two identical coils placed side by side are applied, spaced apart from each other at an appropriate and adjustable distance and are switched against each other.

It follows from this, since the coils 1 and 2 are identical and are connected against one another, that the voltages are different cancel if the part of the material in front of each spool is identical in both cases. In other words, the the following relationship applies:

a + AV b + AV c) - (AV a + AV b ■> - AV c) = O (1)

whereby:

a = stress due to the distance from the one to be examined Material,

AV = voltage due to the faultless material, b

in particular due only to the surface roughness of the material, which is regarded as a constant,

AV

^c = stress due to errors.

Since the two coils are arranged side by side, it is assumed that the distance between them and des material being tested is the same in both cases. So it follows that

AV a = AV ₂ a ( ² ^

In addition, since it is believed that the surface roughness is constant, the following applies:

AV b = AV b (3)

If the coil 1 is facing a defect-free material, while the coil 2 faces a material with a defect, which is a condition which is obtained by appropriately determining the distance between the center lines of the turns and then taking equations (1), (2) and (3) into account, the following applies:

AV c = 0

The value A V ^ c is the voltage that indicates the presence and size of the fault.

The differential probe according to the invention requires only one coil; the differential process is done by computer is made because the voltage data is stored according to a predetermined program.

The measured voltage values are, taking into account the relationship:

AV = AVa + AVb + AVc. .

The mean values of the stresses due to the distance of the winding from the surface (ÄVa_) are calculated using statistical methods based on the stored, previously taken measurement data, as well as the mean values of the stresses due to the faultless material (AVb _m ).

For each measuring point the values Λ Va and Λ Vb from

"m * ■ · m

Total voltage value Λ V subtracted, so that it follows:

AV - AVa - AVb = AVc. m m

The A Vc values in the output are the values due to the errors.

Based on this principle, only one coil as specified is made is used, eliminating the problem that two exactly identical coils are used need while the mechanical work of arranging the distance is simplified as it is quite a complicated maneuver in an arrangement is to work at high temperature for example and is critical if the mechanical adjustment, however perfect it may be, is always fraught with fundamental errors, which lead to a decrease in the sensitivity and accuracy of the measurements.

15th

With the differential probe for non-destructive testing of iron and steel products, based on the eddy current or electromagnetic resonance principle only a single turn is required for implementation. The function of the second turn is from Computer made.

25th

30th

35

Claims (1)

European patent attorneys Dr. Mailer-Bore and Partners ■> POB 260247> D-8000 Munich 26 German patent attorneys Dr. W. Müller-ΒθΓέ t Dr. Paul Deufel Dipl.-Chem., Dipl.-Wirtsch.-Ing. Dr. Alfred Schön Dipl.-Chem. Werner Hertel Dipl.-Phys. Dietrich Lewald Dipl.-Ing. Dr. Ing.Dieter Otto Dip! .-Ing. Brit. Chartered Patent Agent B. David P. Wetters M.A. (Oxon) Ch. Chem. M. R. S. C. CENTRO SPERIMENTALE METALLURGICO S.P.A. Rome / Italy C 3564 Lw / nc Case C 156 Single coil differential probe for non-destructive testing of iron and steel products Claim Differential probe with a single coil, characterized in that the second coil is replaced by a computer which determines, from the voltage values at the output of the coil, those due to the distance of the winding from the surface of the material a _m and also those due to the faultless material D-8000 Mündien 2 FOB 26 02 47 Cable: phone Telecopier Infotec 6400 B telex subtracts in such a way that the result of the subtraction operation is a voltage value AVc attributable to the presence of a flaw in the material inspected by the coil, the values A Va and Λ Vb being calculated by software programs which process the stored measurement data.