The leakage magnetic flux inspection method is effective for detecting minute inclusions in light gauge steel sheets. However it has been not put to practical use at on-line manufacturing processes, because the sensitivity of conventional magnetic sensors was not enough to detect such minute inclusions.
Then we have developed a new high sensitivity magnetic sensor which has higher sensitivity by 100 times in comparison with conventional ones, and have realized an on-line inspection system for detecting minute inclusions in light gauge steel sheets.
For higher detectability and higher speed inspection, we had to make clear the influence of stray magnetic field and the change of magnetic field generated by the travelling of light gauge steel sheets.
We have analyzed changes of magnetic field at the on-line inspection of light gauge steel sheets running at very high speed by computer calculation programs. On these results, we have developed a shield technique from stray magnetic disturbance and on-line high speed inspection technique.
