METHOD AND DEVICE FOR MEASURING THE THICKNESS OF A COATING LAYER ON A RUNNING STRIP

• US 20130133575A1
• Filed: 05/30/2011
• Published: 05/30/2013
• Est. Priority Date: 05/31/2010
• Status: Active Grant

• Current Assignee: Arcelormittal Investigacion Y Desarrollo, S.l. (ArcelorMittal SA)
• Original Assignee: Arcelormittal Investigacion Y Desarrollo, S.l. (ArcelorMittal SA)
• Inventors: Gauje, Pierre
• Granted Patent: US 10,203,194 B2
• Time in Patent Office: Days
• US Class Current: 118/712
• CPC Class Codes: G01B 15/02 for measuring thickness
• CPC Class Codes: G01B 7/105 for measuring thickness of coating
• CPC Class Codes: G01B 7/107 for measuring objects while moving G01B7/105 takes precedence

Abstract

A method and device for measuring the thickness of a coating material layer of a running strip according to which, by means of an eddy current sensor for at least one area of the strip, a quantity is measured, representative of the thickness of the coating layer and the thickness of the coating layer is determined from the measured quantity and from at least one calibration value. The measurement made with an eddy current sensor comprises the measurement of the complex impedance of a coil facing the running strip for a low excitation frequency and a high excitation frequency and the elaboration of a quantity representative of the thickness of the coating layer from said complex impedance measurements. A device for applying the method and a coating installation equipped with the device.

Claims

1. A method measuring a thickness of a coating material layer of a running strip using a sensor with eddy currents, for at least one area of the strip, comprising the steps of:

measuring a quantity representative of the thickness of the coating layer; and

determining the thickness of the coating layer for the area from the quantity measured and from at least one calibration value,

wherein the measuring step is conducted with an eddy current sensor and comprises the steps of;

measuring a complex impedance of a coil facing the running strip for a low excitation frequency and a high excitation frequency; and

elaborating a quantity representative of the thickness of the coating layer from said complex impedance measurements.

2. The method according to claim 1, wherein the low excitation frequency is comprised between 40 kHz and 150 kHz and in that the high excitation frequency is comprised between 400 kHz and 1000 kHz.

3. The method according to claim 1, wherein at least one calibration value is determined by the step of carrying out a measurement of the thickness of said layer in at least one point of the area in which a measurement with an eddy current sensor is carried out.

4. The method according to claim 3, wherein said thickness measurement is conducted with an X fluorescence thickness gauge.

5. The method according to claim 1, wherein the measuring step made with the eddy current sensor further comprises measuring the complex impedance, for a low excitation frequency and a high excitation frequency, of a coil facing a reference sample and in that the quantity representative of the thickness of the coating layer, is determined from differences between the complex impedances of the coil facing the strip and of the coil facing the reference sample.

6. The method according to claim 1, wherein the strip is a metal strip.

7. The method according to claim 6, wherein the metal strip is in steel and the coating comprising of zinc or zinc alloy.

8. The method according to claim 6, further comprising the step of demagnetizing the strip before carrying out measurements with eddy current sensors.

9. The method according to claim 1, further comprising the steps of:

arranging a plurality of eddy current sensors along at least one line substantially parallel to the surface of the strip is used, extending transversely relatively to the running direction of the strip; and

sequentially exciting the sensors so as to obtain a series of measurements distributed over the width of the strip.

10. The method according to claim 9, further comprising the step of distributing a plurality of said series of measurements over the width of the strip by timing the triggering of each of said series of measurements from a longitudinal displacement signal of the strip such as a signal generated by a pulse generator driven by a roll in contact with the strip.

11. The method according to claim 9, further comprising the steps of:

detecting the lateral position of the strip relatively to said at least one line of eddy current sensors, and

determining the position of each measurement area relative to the thickness of the strip by the lateral position of the strip relatively to said at least one line of eddy current sensors and of the position of each sensor in the line of probes.

12. The method according to claim 11, wherein a strip beginning is detected such as the weld between two successive strips, and then the displacement of the strip is continuously detected and for each measurement the length of strip separating the measurement point and the strip beginning is determined, in order to determine the position of the measurement areas relatively to the length of the strip.

13. The method according to claim 12, further comprising the step of recording the position of the measurement areas relative to the length and to the width of the strip, elaborating a mapping of the coating thickness over the strip.

14. The method according to claim 13, wherein the strip runs in a continuous coating installation, such as hot-dip galvanization installation and further comprising at least one of the steps of:

displaying at least one portion of the mapping in real time in a control cabin of the coating installation with a viewing means

transmitting at least one portion of the mapping real time to an automatic control device of the coating installation so that the control device elaborates a set regulation value for the coating installation;

recording the mapping in a computer for quality control purposes.

18. An installation continuously coating a running strip of the type comprising a coating device and a line for discharging and treating the strip after coating, comprising a device according to claim 15 arranged in the discharging and treatment line for the strip in order to apply the method according to claim 1.

19. The installation for continuously coating a strip according to claim 18, wherein the installation is an installation for hot-dip coating of a metal strip with a metal or metal alloy such as a continuous hot-dip galvanization installation.

15. A device continuously measuring the thickness of a coating layer on a running strip, comprising:

a plurality of eddy current sensors arranged in at least one line on a supporting beam (150),

a device controlling the eddy current sensors connected to at least one following device following the progression of the strip,

an automatic controller comprising;

detector detecting the lateral position of the strip relatively to the plurality of eddy current sensors, and

an X fluorescence thickness gauge, and

a computer controlling and managing the measurements connected to the device controlling the sensors and to the automatic controller.

16. The device according to claim 15, wherein the eddy current sensors are of the differential and two-frequency type.

17. The device according to claim 15, further comprising:

a supporting beam supporting the eddy current sensors is movably mounted between a service position and a retracted position, and

a displacing unit displacing the beam between the service position and the retracted position by said automatic controller, and

a detector, connected to said automatic controller, detecting a geometrical defect of the strip,

wherein the automatic controller and the displacing unit are adapted so as to rapidly displace the eddy current sensors towards the retracted position in the case of detection of a geometrical defect of the strip.