GB1598305A - Apparatus for magnetic testing - Google Patents

Description

(54) IMPROVEMENTS IN APPARATUS FOR MAGNETIC TESTING (71) We, BRITISH STEEL CORPOR ATION, a Corporation incorporated and existing under the Iron and Steel Act 1967 whose principal office is at 33 Grosvenor Place, London, S.W.1 do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to testing of ferromagnetic material for a magnetic characteristic and is particularly concerned with apparatus for continuous testing of electrical steel sheet, that is to say sheet intended to form a part of the magnetic circuit of electric machines such as transformers, motors and generators.

The production of ferromagnetic sheet or strip, particularly magnetically soft sheet and strip such as low carbon mild steel or electrical steels containing silicon at concentrations of up to 6% by weight, involves a number of annealing treatments to achieve the required mechanical and magnetic characteristics. The various annealing treatments to which the sheet is subject, particularly the final anneal, have been found to significantly affect magnetic properties, and some control of annealing conditions must occur to maintain magnetic properties within acceptable limits. One magnetic parameter of importance which must be controlled within specified limits is the total power loss which occurs in the sheet when this is excited by an alternating field; since this parameter is an accepted criterion of quality, accurate measurement of such power loss is important.

Conventionally, power loss is assessed by testing small strip samples which are cut from production material and which are arranged to form a magnetic circuit. One known method for testing power loss is known as the Epstein frame method; this is a static method and is characterised in enabling only relatively infrequent testing of strip produced on a continuous line.

When strip is produced on a continuous line, the accurate measurement of power loss must be relatively rapid if the quantity of strip produced with uncorrected magnetic properties is to be reduced to a minimum or if the rate of production is not to be slowed down while strip samples for Epstein testing are cut and measured.

In our co-pending United Kingdom Patent Application No. 55052/71, S.N.

1427703 there is disclosed and claimed apparatus for the continuous on-line testing of electrical steel strip by a method which comprises magnetising the strip at a selected region as it approaches the end of the line and measuring the induced magnetic field by way of suitable sensors. The core loss can be translated for display by measuring the ratio of the applied to the induced magnetic field and may be suitably corrected before translation or display for variation in strip thickness.

In order to produce both a high level of accuracy and high level of consistency in the measurement of core loss, a uniform level of magnetisation must be achieved over at least that area of the strip to which the sensors are sensitive. In the apparatus disclosed in our co-pending application the strip is uniformly magnetised by a solenoid wound on a suitable former surrounding that region of the strip under test. Such a solenoid configuration however limits the testing procedure to that involving magnetic fields having lines of force substantially aligned with the direction of strip feed and provides no opportunity for testing by strip magnetisation transversely of this direction.

It also poses problems in threading strip through the solenoid, particularly when this is associated with yokes effective to compensate for solenoid edge effects and other field perturbations.

Since the magnetic testing of both isotropic and anisotropic electrical steel sheet or strip with various field orientations is becoming progressively more important, it is one obJect of the present invention to provide means for continuously magnetising an area of strip in any selected field direction.

According to one aspect of the present invention, apparatus for testing of sheet or strip for a magnetic characteristic includes an array of substantially parallel rectilinear conductors supported adjacent the plane of the sheet or strip to be tested, the conductors being incorporated into at least one electric circuit arranged to feed current through the array in one direction so as to induce in use a magnetic field in the adjacent region of the sheet or strip, the remainder of each circuit being completed such that any magnetic field generated thereby does not substantially modify the field induced by the conductor array within the region under a test together with means for detecting magnetic induction in the sheet or strip.

In one embodiment of the invention the remainder of each circuit is spatially removed from the region of the sheet or strip under test.

In a preferred embodiment of the invention, however, the remainder of each circuit is aligned normally of the line of the conductors in the array so that any magnetic field generated by current flow in the remainder has substantially no component in that field direction induced by current flow in the array and so that the combined effect of distance and direction ensure minimal perturbation of field at the region of the sheet or strip under test.

In the case where the material under test is continuously moving strip, the remainder of each circuit conveniently is disposed clear of the strip edge.

Suitably the conductors in the array are arranged in a single plane parallel to the plane of the sheet or strip under test. One array only adjacent one face of the strip may be employed.

In a more suitable arrangement, however, an array of conductors is disposed adjacent each of the opposite faces of the sheet or strip to produce more uniform magnetisation.

The circuit or circuits incorporating the array of conductors suitably are supported upon a non-magnetic base which ideally can be rotated within its own plane, preferably through at least 180 , to enable the orientation in which sheet or strip under test is magnetised to be varied.

Embodiments of the invention will now be particularly described by way of example with reference to the accompanying drawings in which: Figure 1 represents schematically an array of conductors disposed adjacent one face of a moving strip of an electromagnetic steel, to produce magnetisation according to the present invention.

Figure 2 illustrates a different configuration of conductors arranged to produce the magnetisation of Figure 1.

Referring to Figure 1 of the drawings, this shows a continuous strip 2 of electrical steel moving in the direction indicated by arrow A and at a station towards the end of the line in which it is being processed. In general, the station at which the strip is tested for magnetic properties will be after final anneal and finishing and when the strip is in condition for final coiling. At this station, and for testing in the manner substantially described in our co-pending Application No. 55052/71 SN 1427703 the strip is uniformly magnetised in a selected orientation which is indicated by arrow B and is in this embodiment transversely of the direction of strip feed. The magnetic field is induced by current flow through the array of spaced parallel and rectilinear conductors indicated generally at 4.

The array 4 comprises two separate groups of conductors 6 and 8. Each group is connected in parallel relation and to a suitable current source S or to source terminals by way of single or grouped leads 10 which complete the magnetising circuit.

With current flowing in the circuit, the magnetic field generated by leads 10 will have substantially no component in the direction of the field induced within the strip by current flow through the array 4 and will accordingly produce minimum perturbation of the induced field.

In the case where S represents only source terminals, the leads to the source are conveniently arranged in similar manner to leads 10 so as to produce a minimal component along the magnetising field direction. The leads to conductors 10 together with the source terminals are preferably as far removed as possible from that region of the strip which is magnetised by the array.

As shown in Figure 1, array of conductors 8 terminates at the centre line of the strip 2 and covers only half of the strip width; the remaining half is covered by the mirror image array of conductors 6 similarly connected to a or the current source. While in Figure 1 conductors are shown adjacent one face only of the strip 2, a similar array may be provided adjacent the other opposite face.

Figure 2 illustrates an alternative magnetising circuit configuration. In this configuration one circuit is used to produce current through a conductor array adjacent each of the opposite faces of the strip under test.

The array comprises conductors 12, 14 respectively adjacent opposite faces and effective to induce in the strip a magnetic field aligned with the direction shown by the arrow A. The conductors are connected together and to the current source by leads aligned with the induced field direction so that any field generated by the leads again has substantially no component in the direction of the induced field and combined with the distance from the region T of sheet or strip under test leaves this induced field at T substantially unperturbed.

To enable power loss to be measured, the induction developed in the steel must be measured separately. There are many means available to those skilled in the art to measure magnetic induction and a suitable embodiment of induction measurement coupled with the magnetisation system herein described enables power loss to be determined.

It will be appreciated that while the magnetising circuits have been described with reference to measurement of core loss, they are equally applicable to the measurement of other magnetic characteristics.

WHAT WE CLAIM IS: 1. Apparatus for testing of sheet or strip for a magnetic characteristic including an array of substantially parallel rectilinear conductors supported adjacent the plane of the sheet or strip to be tested, the conductors being incorporated into at least one electric circuit arranged to feed current through the array in one direction so as to induce in use a magnetic field in the adjacent region of the sheet or strip, the remainder of each circuit being completed such that any magnetic field generated thereby does not substantially modify the field induced by the conductor array within the region under test together with means for detecting the magnetic induction in the sheet or strip.

2. Apparatus as claimed in Claim 1 wherein the conductors in substantially the remainder of each circuit lie normal to the line of conductors in the array producing magnetisation.

3. Apparatus as claimed in Claim 1 wherein the conductors in substantially the remainder of each circuit are distanced from the area of the sheet or strip to be tested.

4. Apparatus as claimed in Claim 3 wherein the remainder of the circuit is disposed clear of the edge of sheet or strip under test.

5. Apparatus as claimed in any preceding claim wherein the conductors in the array lie in a single plane parallel to that of sheet or strip under test.

6. Apparatus as claimed in any preceding claim wherein the array of conductors is disposed adjacent each side of the plane of sheet or strip under test.

7. Apparatus as claimed in any preceding claim wherein the or each array of conductors is supported on a non-magnetic base.

8. Apparatus as claimed in any preceding claim wherein the array or each of conductors is/are rotatable about an axis normal to their plane so that the direction of the magnetic field generated can be varied.

9. Apparatus for magnetic testing of sheet or strip substantially as herein described with reference to the accompanying drawings.

10. Apparatus for magnetic testing of sheet or strip substantially as shown in, and adapted to operate substantially as herein described with reference to, the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. the opposite faces of the strip under test. The array comprises conductors 12, 14 respectively adjacent opposite faces and effective to induce in the strip a magnetic field aligned with the direction shown by the arrow A. The conductors are connected together and to the current source by leads aligned with the induced field direction so that any field generated by the leads again has substantially no component in the direction of the induced field and combined with the distance from the region T of sheet or strip under test leaves this induced field at T substantially unperturbed. To enable power loss to be measured, the induction developed in the steel must be measured separately. There are many means available to those skilled in the art to measure magnetic induction and a suitable embodiment of induction measurement coupled with the magnetisation system herein described enables power loss to be determined. It will be appreciated that while the magnetising circuits have been described with reference to measurement of core loss, they are equally applicable to the measurement of other magnetic characteristics. WHAT WE CLAIM IS:

1. Apparatus for testing of sheet or strip for a magnetic characteristic including an array of substantially parallel rectilinear conductors supported adjacent the plane of the sheet or strip to be tested, the conductors being incorporated into at least one electric circuit arranged to feed current through the array in one direction so as to induce in use a magnetic field in the adjacent region of the sheet or strip, the remainder of each circuit being completed such that any magnetic field generated thereby does not substantially modify the field induced by the conductor array within the region under test together with means for detecting the magnetic induction in the sheet or strip.

2. Apparatus as claimed in Claim 1 wherein the conductors in substantially the remainder of each circuit lie normal to the line of conductors in the array producing magnetisation.

3. Apparatus as claimed in Claim 1 wherein the conductors in substantially the remainder of each circuit are distanced from the area of the sheet or strip to be tested.

4. Apparatus as claimed in Claim 3 wherein the remainder of the circuit is disposed clear of the edge of sheet or strip under test.

5. Apparatus as claimed in any preceding claim wherein the conductors in the array lie in a single plane parallel to that of sheet or strip under test.

6. Apparatus as claimed in any preceding claim wherein the array of conductors is disposed adjacent each side of the plane of sheet or strip under test.

7. Apparatus as claimed in any preceding claim wherein the or each array of conductors is supported on a non-magnetic base.

8. Apparatus as claimed in any preceding claim wherein the array or each of conductors is/are rotatable about an axis normal to their plane so that the direction of the magnetic field generated can be varied.

9. Apparatus for magnetic testing of sheet or strip substantially as herein described with reference to the accompanying drawings.

10. Apparatus for magnetic testing of sheet or strip substantially as shown in, and adapted to operate substantially as herein described with reference to, the accompanying drawings.