Inspection Method of Outer Side Defect in Ferromagnetic Steel Tube by Insertion Type Electromagnetic Sensor Using Square Wave Alternating Magnetic Field with DC Bias

2021 ◽  
pp. 1-1
Author(s):  
Makoto Tohara ◽  
Yuji Gotoh
Machines ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 75
Author(s):  
Huijun Xie ◽  
Yanhua Zou

The magnetic abrasive finishing (MAF) process is an ultra-precision surface finishing process. In order to further improve the finishing efficiency and surface quality, the MAF process using an alternating magnetic field was proposed in the previous research, and it was proven that the alternating magnetic field has advantages compared with the static magnetic field. In order to further develop the process, this study investigated the effect on finishing characteristics when the alternating current waveform is a square wave. The difference between the fluctuation behavior of the magnetic cluster in two alternating magnetic fields (sine wave and square wave) is observed and analyzed. Through analysis, it can be concluded that the use of a square wave can make the magnetic cluster fluctuate faster, and as the size of the magnetic particles decreases, the difference between the magnetic cluster fluctuation speed of the two waveforms is greater. The experimental results show that the surface roughness of SUS304 stainless steel plate improves from 328 nm Ra to 14 nm Ra within 40 min.


2020 ◽  
Vol 64 (1-4) ◽  
pp. 281-288
Author(s):  
Makoto Tohara ◽  
Yuji Gotoh

The ferromagnetic steel tubes are used as heat exchangers in power plants or oil plants. When the usual eddy current testing (ECT) of inner type is used for the defect inspection of these steel tubes, it is difficult to detect defects on the opposite side due to the influence of skin effects. In this research, the non-destructive inspection method using rectangular wave excitation current with DC bias is proposed for detecting of the opposite side defect. It is shown that the detecting of the opposite side defect in the steel tube is possible, and the detection sensitivity using the alternating magnetic field of rectangular wave is higher than that with sine wave. The detailed phenomenon of the inspection method is examined using the 3-D nonlinear FEM (finite element method) taking account of minor loop magnetizing properties using the play model method.


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