Papers by Keyword: Eddy Current

Abstract: This paper presents experimental results of eddy current analysis of hydrogen in technically pure titanium alloy. Eddy currents when penetrating various depths change their parameters in relation to material properties. Each layer possesses different degree of hydrogenation and differs in number of defects and their location. The measurement of hydrogenated titanium conductivity in various depths with different angular position of eddy current probe were performed and discussed. Components` surface measurements caused by hydrogenation were registered by currents with the frequency of 10 MHz. The results can be used for the development of new materials with required properties.

Abstract: The article describes the influence the operating frequency of the transducer on the possibility to detect corrosion using the eddy current method. A bearing ring with two artificially made corrosion defects was used as a test object. The authors determined the characteristics of the defect’s signal value in the function of frequency. The results obtained were then compared to the peak-to-peak value of the signal for a model ring. The tests confirmed the possibility of automatic detection of corrosion on the surface of bearing rings using the eddy current method.

Abstract: The study demonstrated that implementation of eddy currents of different frequencies enables identification of altered phase composition, diffusion properties and metal hydrogenation extent. Using the newly developed parameters of eddy current method sensitivity, we have established that the change of a metal structure from one layer to another is identified by the currents of different frequency according to the depth of their penetration into a metal.

Abstract: The article presents the influence of the distance between a measuring head and a tested object on the results of eddy current defectoscopy test. The tests were conducted on the two inner rings of a tapered roller bearing where the test defects were performed. A one-millimetre hole corresponded to the surface defect. Internal blind holes in the shape of a rectangle corresponded to a subsurface defect. The research was performed with the use of a SSEC III PC defectoscope connected to a mobile PC. The measuring device is part of the system for the automatic quality control of bearing rings. The test was conducted for a slit having following dimensions: 0.1, 0.2, 0.3, 0.4, and 0.5 mm. The obtained characteristics are the composition of the pulse caused by the detected defect and the sine wave caused by the axial runout of the tested bearing ring. The correlation between the slit size and the value of the signal of the defect and the sine wave caused by axial runout of the tested ring was observed. The concept of “a coefficient of defect detection” was introduced. The described coefficient is a quotient of the value of the defect signal and the peak-to-peak value of the sine wave caused by axial runout of the tested bearing ring. The increase in the dimensions of the slit from 0.1 to 0.5 mm causes a 35 - 50% decrease in the coefficient of defect detection, depending on the test defect. A handle was designed to ensure a constant pressure of measuring head on the tested surface was proposed.

Abstract: An electromagnetic braking system using eddy current experiment was conducted to study the behaviour of the system in terms of vibration. Brake disc used which is Al6061 has a displacement in z-axis direction which occurred because of the repulsive force generated on both sides of the disc as drag force from electromagnetic braking. This study aims to analyze the vibration behaviour when braking occurred in different initial speeds of DC motor and different air-gap cases. Smaller air-gap will produce high braking torque due to the increasing of magnetic field density. The higher the force generated, the vibration of the disc may illustrates different behaviour of the vibration in the structure. Test rig was developed using sensor of accelerometer and data acquisition of NI-DAQ with the use of Dasylab for the measurement and instrumentation purposes. Findings shows that the electromagnetic braking force generated in smaller air-gap between electromagnetic poles and rotating conductive disc during the braking using eddy current has damped the vibration occur in the structure of bearing cage.

Abstract: This paper presents the statistical analysis that was used to define optimized parameter for the electromagnetic braking using eddy current study. It illustrates parametric study on four different parameters affecting the braking performance using eddy current which are air-gap, number of electromagnet turns, current induced and disc thickness. These four parameters are defined as the factors which contribute to the reduction of RPM speed as the effect. Fully nested ANOVA was used as the first analysis to determine two most significant factors to eddy current braking system. Then, two-way ANOVA was applied to clarify the most significant factors to be used as the controllable parameters in the verification study. Results from both ANOVA test shows that current induced and air-gap are the two most significant factors that affected braking using eddy current.

Abstract: This study was performed to develop a non-destructive inspection system to detect grinding burn, which is capable of quantitative 100% inspection inside a production line. An eddy current sensor, which has advantages of short inspection time and low cost, was used. It was shown that the grinding burn detection technique had been developed and is possible to detect grinding burn by using this technique, in the 1st report¹⁾ and the 2nd report²⁾. In this report, an experiment of in-process detection of grinding burn was conducted, by applying the grinding burn detection technique which we have developed. The eddy current sensor has been combined with an in-process gauge in order to keep the clearance between the sensor probe and the work piece constant. It was shown that grinding burn can be detected successfully during cylindrical machining.

Abstract: Eddy current sensors have various uses. However, there are few studies which show theinfluence of a conductor on the impedance of a detector coil using theoretical formulae. This papershows a simplified calculation method for impedance of a planar coil while considering the influenceof eddy current. An eddy current distribution in a metal plate facing to planar coil was calculatedusing finite element method. It assumed the metal plate to be a one-turn coil that can change shape.Therefore, the impedance of a planar coil considering the influence of the eddy current can beestimated from an equivalent circuit. In addition, calculations were simplified by estimating mutualinductance between the planar coil and the metal plate from an area ratio. This simplified calculationmethod can estimate impedance with the same accuracy as finite element method. The calculatedvalue agrees to within ±2.44 % of the measured value. The computation time was shortened by 1/20.Therefore, it can be immediately estimated how each parameter of a planar coil or a target influencesthe characteristic of the eddy current sensor. This simplified calculation method is useful for anoptimum design of an eddy current sensor.

Abstract: Eddy current testing (ECT) is one of the most representative nondestructive testing methods for metallic materials, parts, structures and so on. Operating principle of ECT is based on two major properties of the magnetic field. One is that alternating magnetic field induces eddy current in conducting materials. Thereby, an input impedance of the magnetic field source, i.e., electric source, depends on the eddy current path. Second is that the magnetic field distribution depends not only on the exciting but also on the reactive magnetic fields caused by the eddy currents in targets. Former and latter are the impedance sensing and magnetic flux sensing types, respectively.This paper concerns with an optimization of a new magnetic flux sensing type sensor named coil. Exciting and sensing coils are composed of shape coil and a finite length solenoid coil wound on ferrite bar, respectively. Development of this coil fully depends on the 2D and 3D finite elements method modeling. According to the simulation results, we have worked out two types of coils. Practical experiments reflect the validity of both simulation and design aims, quite well. Thus, we have succeeded in developing coil having a higher sensibility compared with that of conventional one.

Abstract: In general, the magnetic properties of electrical steel sheets are strongly influenced by mechanical stress. We have reported the measurement results of vector magnetic properties of a non-oriented electrical steel sheet under stress conditions. From these results, it is possible to control the vector magnetic property by applying local mechanical stress. Therefore, we next focus on an induction heating technique that applies mechanical stress in a non-oriented electrical steel sheet. It is very important to control the eddy current distribution inside the non-oriented electrical steel sheet. This paper presents a magnetic flux concentration plate structure to control the eddy current in steel sheets by using an induction heating technique. The magnetic flux concentration plate structure is investigated in a three-dimensional magnetic field analysis by the finite element method.