非铁磁性金属薄层涡流测厚法

Measurement of the Thickness of Non-ferromagnetic Metal Sheets by Eddy Current Testing

介绍用涡流法弥补超声法检测厚度<1 mm的薄层非铁磁性金属的不足.推导了涡流线圈感抗简化公式,试验测量了厚度为25～250 μm的铝和25～500 μm的不锈钢,得出了其厚度与幅值的关系曲线,理论计算与试验结果吻合较好.最后根据简化公式进行了理论仿真.研究表明,涡流方法适合测量电导率低的薄层金属厚度,选用合适的低频,采用铁心线圈或考虑相位信息与提离的关系后,该方法可有效监控非铁磁性金属薄层的厚度变化.

A simplified formula of eddy current coil inductance was derived for the application of eddy current testing to the thickness measurement of the non ferromagnetic metal sheets of less than lmm in thickness which were not possible to be measured by ultrasonic testing method. The proposed eddy current testing method was used in the testing of the aluminium sheets with thickness from 25-250/tm and the stainless steel sheets with thickness from 25-500μm, and curves showing the relationship between thickness and amplitude were given. Results obtained by this method were found to be in good consistency with the theoratically calculated values, Theoratical simulation was carried out by the simplified formula proposed. It was concluded that eddy current testing was suitable for thickness measurement of the metal sheets with low conductivity, and was also feasible for effective monitor of the variation of the thickness of non-ferromagnetic metal sheets by choosing suitable frequency, using the coil with iron core or considering the relationship of phase and lift-off distance.