[PDF] Detection of Grinder Burn Area on Surfaces of Ferromagnetic

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Detection of Grinder Burn Area on Surfaces of Ferromagnetic

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Creative Commons CC-BY-NC licence https://creativecommons.org/licenses/by-nc/4.0/ Detection of Grinder Burn Area on Surfaces of Ferromagnetic

Material by Eddy Current, Barkhausen Noise and

Multi Technical

3MA Methods

Jean-Marc Decitre

1, Benjamin Delabre1, Fan Zhang2, Naim Samet3

1 CEA, LIST, Centre de Saclay, Gif-sur-Yvette cedex, F-91191, France

2 CETIM EPI, 52 avenue Félix Louat, 60300 Senlis, France

3 CETIM CERMAT,

21 Rue de Chemnitz, 68200 Mulhouse, France.

Abstract

One of the issues in Nondestructive Testing by electromagnetic technique concerns its high sensitivity for detecting surface defects, or defects close to the surface in conductive materials, both nonmagnetic and ferromagnetic. These examinations are commonly used in many industrial sectors such as aerospace, energy and metallurgy. A new recurrent request from industry concerns the non-destructive characterization of mechanical properties such as hardness or residual stress, which may occur after bad heat treatment or due to heating during operation. The classical applications are gears in turbine, motors and compressors. Thanks to a link between electromagnetic properties (conductivity, permeability, hysteresis loop of material) and mechanical properties, electromagnetic methods are candidates to this study.

1. Introduction

The application deals with plate mock-ups in ferromagnetic material, representative to material used for gears. These mock-ups include grinder burn area with different intensities obtained by appropriate rectifications. Two principal techniques are used. First, Barkhausen noise is evaluated, thanks to a Microscan device manufactured by the company STRESSTECH, and seems particularly well-suited due to its sensitivity to the microstructure and the stress. Secondly, the Eddy Current (EC) technique is implemented. The EC pattern is optimized thanks to the CIVA platform to obtain, on the one hand a straight response in the complex plane for electrical conductivity variations, and on the other hand a huge sensitivity to the mat

2. Barkhausen noise method

The method of Barkhausen noise (also called ferromagnetic noise) is only applicable to ferromagnetic materials. When a ferromagnetic part is positioned in an excitation magnetic field H, the macroscopic magnetization of the steel (hysteresis loop) is accompanied by movement of Bloch walls (surrounding the WEISS areas). Each

movement produces a small variation of the magnetic flux and the sum of all trips that More info about this article: http://www.ndt.net/?id=22938

2 occur in cooperation, form a significant change in the magnetic flux, easily measurable with a magnetic sensor. This flux variation is called Barkhausen noise. This principle of measurement is illustrated in Figure 1 (left) [1]. Barkhausen noise is usually analyzed by

RMS envelope.

Figure 1. Principle of measurement of Barkhausen noise (left) and amplitude of Barkhausen Noise versus superficial hardness. The evaluation of the Barkhausen noise, led by CETIM using Microscan device, seems particularly well suited by its dual sensitivity: the microstructure and stress. With its increasing monotonic evolution when the compressive stresses decrease and the hardness falls, the Barkhausen noise increases with the severity of the burn income type (figure 1, right). In the case of re-tempered burns, the signal strongly decreases. More, the measurement is sensitive to the early stages of heating, very early before the Nital etching could detect a variation of microstructure. The Barkhausen noise method is often used for the detection of grinding burn, by monitoring the signal during the grinding operation. This allows to work on the machining conditions before a burning deemed dangerous appear.

3. Eddy Current method

We consider now an EC pattern composed of a transmitting coil and a receiving coil. The internal and external diameters (9 and 10mm), the distance between coils (5mm) and the frequency (1MHz) have been optimized to obtain a straight response in the complex plane in case of electrical conductivity or magnetic permeability variations [2,3]. The high frequency is chosen, allowing just the material surface to be sensitive. The experimental data obtained at CEA with EC technique are given on figure 2 on the same mock-ups. 3 hardness HV5

Whitout burning

Burning +

Burning ++

Burning +++

Burning ++++

Whitout burning

Burning +

Burning ++

Burning +++

Burning ++++

18NiCr 5-4

GrinderburnOptimized

Flexible

EC sensor

Figure 2. Complex EC signal in the impedance plane (left) and amplitude of EC signal versus the superficial hardness (right) on mocks-up with different intensities of burnings. Thes axes in the Figure 2 (left) give EC complex signals in the impedance plane for all the available mock-ups with different intensities of burning. We confirm that all the signals are globally on the same straight line, due to the variations of conductivity and/or permeability of material. But, for the two higher levels of burning, we observe a non-monotonic behavior. A modification of metallographic properties of materials (tempered steel) can explain the phenomenon from a certain level of burning. The axes in the Figure 2 (right) give amplitude of EC signal on the same mocks- up versus the hardness HV5 of material. We note it is possible to estimate the hardness of the material by EC technique.

4. Conclusions

The conclusion is that the behavior of the flexible EC pattern in function of the burning intensity is similar to Barkhausen noise obtained with Microscan device. Same result are obtained with 3MA device manufactured by IZFP. It is possible to evaluate the hardness thanks to these two techniques. These results confirm that it is possible to estimate mechanical properties thanks to electromagnetic properties. It is foreseen to evaluate these techniques in the near future on gears for the automotive industry and energy.

References

[1] Zhang F., Walaszek H., Gos C., technique for Non-destructive characterization of mechanical components, ECNDT, 2014. [2] Marchand B., Decitre JM., Casula O., [3] Decitre JM.Optimization of flexible Eddy Current patterns with low sensitivity to lift-off, ENDE 2016.quotesdbs_dbs18.pdfusesText_24