The nitric acid corrosion method that is currently in use in the production field to inspect for grinding burns on workpieces has some disadvantages: its detection levels depend on people and equipment, and is a destructive inspection method that does not allow for a total inspection. This study therefore aims to develop a non-destructive technology for detecting grinding burns, one that will allow for quantitative total inspections on a production line. An eddy current sensor seems very promising as a means of performing non-destructive inspections because of its short measuring time and low costs. In this paper, we propose a method of simultaneously measuring the eddy current sensor’s output at two different frequencies (the multi-frequency measuring method), as this method is not affected by any variations in the basic material of the inspection object, and we then verify its effectiveness. In addition, we prototype a grinding burn detection system using the proposed measuring method, and we evaluate the determinations it makes on grinding burns on workpieces. As a result, the proposed multi-frequency measuring method is found capable of determining grinding burns on workpieces more quantitatively and with higher sensitivity than the nitric acid corrosion method.
Calculation of HNO2 Concentration from Redox Potential in HNO3-H2O System as an Aid to Understanding the Cathodic Reaction of Nitric Acid Corrosion