Detection and Location Estimate of External Surface Defects Using Velocity Effects From Double-Sided Quadrupole Permanent Magnets

The round bar steel made of C45 steel material is widely used as a general machine part material, such as springs for automobiles. This round steel bar requires high-speed surface defect inspection during the manufacturing process. In this research, an inspection method is proposed in which a round steel bar is moved at a high speed of 1 m/s in a ring-shaped permanent magnet with a single differential detection coil to detect surface defects in the round steel bar. In addition, the possibility of estimating the location of a circumferential defect on the round steel bar is demonstrated by using two double-sided quadrupole permanent magnets with only one differential detection coil.