Analysis of the Noise and Improvement of the Flaw Detecting Ability on the Eddy Current Flaw Detector for Hot Wire Rod

Abstract

Recently, various eddy current flaw detectors have been used in the wire rod mill for the quality control, but, in general, these flaw detectors have been unable to detect the flaw below 0.15mm depth due to the various noises.
In this paper, the analysis of the noise and the improvement of S/N by the phase discrimination are described.
From the result of the frequency analysis of the noise, it was confirmed that the nois was generated mainly due to the vibration of the wire rod in the search coils and such a noise could not be fully decreased by the frequency filter or by the phase discrimination in the case of 40kHz carrier frequency.
Accordingly, the new flaw detector with 160 kHz carrier frequency which enables decrease the noise by the phase discriminator was developed and could detect the small flaw as 0.1mm depth.
This flaw detector has been installed and in operation satisfactorily at the Hoshizaki Plant.