Dynamic NDT sorting of ferromagnetic components

Dynamic NDT sorting of ferromagnetic components based on fast magnetic signature measurement Piotr Gazda1, Marcin Czuwara1, Michał Nowicki1, Roman Szewczyk2 1Institute

of Metrology and Biomedical Engineering, Warsaw University of Technology, sw. Andrzeja Boboli 8, 02-525 Warsaw, Poland [email protected] 2 Industrial Research Institute for Automation and Measurements, al. Jerozolimskie 202, 02-486 Warsaw, Poland [email protected]

Abstract. The following paper presents the idea of distinguishing ferromagnetic objects based on their magnetic signature. This method is based on the measurement of the magnetic moment of the samples. The developed method could be attractive to the industry due to its simplicity, scalability and low implementation costs. The paper presents detailed description of the measuring station and measurement procedure. Tests of the proposed solution confirmed the correctness of the operation and indicated further directions of the method development. Keywords: NDT, component sorting, magnetic moment measurements, magnetic signature

1

Introduction

Currently, in the industry related to new technologies, namely the aerospace, energy, defense and aviation industries, the requirements for operating elements are becoming more demanding. The use of techniques leading to the destruction of the material is undesirable due to the fact that we want to check out these specific parts that work later in the system. For this reason, non-destructive testing methods are becoming increasingly important. For ferromagnetic objects possible application have eddy current, magnetovision and magnetic induction tomography method[1,2]. The above mentioned methods are hard for universal use in industry due to the cost, or difficulty to use the method on the large scale production line. Therefore, it is necessary to develop a simple, flexible and low cost method. The designed system should be able to distinguish the elements and control their condition on the basis of the dynamic measurement of the magnetic signature. The paper presents the results of working prototype of such system, based on fast measurement of samples magnetic moment. Sorting by magnetic moment is usually used in distinguishing molecules or cells [3]. There are solutions to differentiate permanent magnets based on the moment [4], but the authors could not find a description

of the industrial use of the method for the case of ferromagnetic materials. The most popular industrial magnetic sorting method is the use of permanent magnets [5].

2

General idea and Test stand

The magnetic moment is the characteristic quantity of magnetic objects [6].This quantity is used to for example determine the interaction of an object with an external magnetic field. Determining the magnetic moment usually involves dipole magnetic moment, but sometimes the nondipole component of the magnetic moment has a significant effect on its magnitude [7]. When we apply the same external magnetic field to samples made of the same ferromagnetic material of different volumes, the magnetic moment of the samples will be different [8]. This is due to the significantly different number of atoms in the sample. Introduction of stresses to the sample by mechanical damage leads to changes in magnetic permeability of the material due to the magnetoelastic effect [9,10]. This is also reflected in the change of the magnetic moment of the sample.

Fig. 1. The scheme of measurement system: 1. Demagnetizing coil, 2. Guiding pipe, 3. Test item, 4. Magnetizing coil, 5. Measurment coil, 6. AC Power Generator, 7. Laboratory power supply, 8. Fluxmeter

Fig. 1. presents schematic diagram of the measuring station of developed method. At the beginning of the measurement line, a coil is used to pre-demagnetizes the sample. This is to equalize the initial state of the samples. Otherwise the samples were

previously in contact with the magnetic field, this could have an impact on the results. Then the magnetizing coil is used. At the very end of the measuring line there is measuring coil which measure the induced voltage, integral of which is proportional to the magnetic moment of the sample. The guide tube was at the same time a base for winding the coils. The coil (1) consists of 1000 turns made of wire with a 3 mm diameter of. In order to pre-demagnetize the samples, a 50 Hz sinusoidal signal is used. Parameters of magnetizing coil (2): the number of turns of the magnetizing winding n2=500 and the length of the coil l = 0.06m, and the current flowing through it equal to 5.83 A allows the production of a field of intensity: 𝑁 ∗ 𝐼 500 ∗ 5,83 𝑘𝐴 𝑘𝐴 𝐻= = = 48,583 ≈ 50 (1) 𝑙 0,06 𝑚 𝑚

3

Measurement procedure and results

The first step of experiments was to investigate the usefulness of the method for detection of damaged elements. In this part of the test samples were steel screws with a diameter of ɸ = 8 mm and length of l=75 mm. In order to ensure proper results of measurements it is essential to choose samples with similar properties, in this case with a similar magnetic moment generated after magnetization. In this case pre-tests were carried out to reject outgoing samples. Such samples, though at a glance are ideal, can be made in other series, so they cannot be compared. After performing 10 measurement series and averaging results, the outgoing samples were discarded and the histogram of the remaining samples is presented in Figure 2.

Fig. 2. Histogram showing the results of the measurements for the 31 selected screws

As shown in Fig. 2. value of the Shapiro-Wilk test is 0.99208 and P-value = 0.12437. Therefore is no reason to reject the hypothesis of normal distribution for the 31 selected samples, which should be provided for further measurements. After selecting the samples, they were prepared by intentionally damaging 9 of the screws. Damage types were: hammering of screw thread (Fig3 a), or 4 mm diameter hole made of different lengths (Fig3 b). The results of the utility measurements for the selection of damaged elements are shown in Table 1. a) b)

Fig. 3. Photos of damaged parts: a) hammered object, b) object with axial hole of 4 mm diameter Table 1.Summary of metal screw measurements Number Number of of samples samples in % Total number of samples 31 100 Damaged samples 9 29 Undamaged samples 22 71 Damaged samples Damaged samples detected as damaged Damaged samples not detected as damaged

9 7 2

100 77,8 22,2

Undamaged samples Samples undamaged detected as undamaged Undamaged samples detected as damaged

22 19 3

100 86,4 13,6

The second phase of the test was to investigate the possibility of using a developed method for recognizing objects made from the same material. The test pieces were 12 drills for metal with a diameter of 3.5 to 10 mm and a diameter step of 0.5 mm. A series of 10 measurements was made using each of the samples, and the mean of these measurements was used for further calculations. For such averages, the t test for dependent variables was performed to verify that the measurements of drill bits with adjacent

diameters differ substantially. The results of all comparisons are summarized in Table 2. For each test, the P-value was less than 5%, which means that there is no dependents between the measurements. Table 2. Summary of magnetic signature measurements of metal drills Compare samples P-value of test t ϕ=10; ϕ=9,5 1,623E-13 ϕ=9,5; ϕ=9 9,041E-14 ϕ=9; ϕ=8,5 1,190E-16 ϕ=8,5; ϕ=8 3,233E-10 ϕ=8; ϕ=7,5 1,186E-11 ϕ=7,5 ϕ=7 0,013 ϕ=7; ϕ=6,5 2,449E-14 ϕ=6,5; ϕ=6 4,466E-16 ϕ=6; ϕ=5,5 1,527E-9 ϕ=5,5; ϕ=4,5 5,048E-15 ϕ=4,5; ϕ=3,5 9,599E-14

4

Analysis of uncertainty

The uncertainty of the magnetic torque measurement consisted of the standard uncertainty of type A and the uncertainty associated with the measurement with the magnetic flux meter. The standard uncertainty of type A is given by the formula: 𝑛

𝑢(𝑥) =

√𝑠𝑥̅2

1 =√ ∑(𝑥𝑖 − 𝑥̅ )2 𝑛(𝑛 − 1)

(2)

𝑖=1

The uncertainty of the fluxmeter is determined by the following formula: ∆𝑥 = 0,01% ∙ measuring range + 5% ∙ measured value Total uncertainty is expressed by: 𝑢(𝑥) = √𝑠𝑥̅2 +

(∆𝑥)2 3

Extension uncertainty U(x) with expansion factor k = 2 is: 𝑈(𝑥) = 𝑘 ∙ 𝑢(𝑥)

(3)

(4)

(5)

Using the formulas (2) to (5), we can calculate that the magnetic moment measurement used in the developed method is with an uncertainty of 5.8 to 8.0% for screw measurements and 5.8 to 6.5% for discriminating drills.

5

Conclusions

This work confirms the operation of the ferromagnetic components control method based on dynamic measurements of their magnetic signature. Based on the results of the first test, it can be said that the method is effective, but before implementing this method in industry, its performance to minimize misinterpreted results should be improved. To increase the sensitivity, increase of the number of turns on the measurement winding is needed. The test screws were quite large, but if smaller screws were tested, the number of turns of measurement coil used in the test (1000) might be insufficient. In the case of the second test, it confirmed the possibility of distinguishing ferromagnetic elements of the same shape and similar, but slightly different geometrical dimensions. The system can be thus implemented for rapid ndt sorting of ferromagnetic objects. Acknowledgements. This work was partially supported by the statutory founds of Institute of Metrology and Biomedical Engineering, Warsaw University of Technology (Poland). References 1. Tumański, S.: Handbook of Magnetic Measurements, CRC Press, Boca Raton (2011) 2. Nowicki, M., Szewczyk, R.: Ferromagnetic objects magnetovision detection system, Materials,6(12), 5593-5601 (2013) 3. Zborowski, M., Sun, L., Moore, L. R., Williams, P. S., & Chalmers, J. J.: Continuous cell separation using novel magnetic quadrupole flow sorter, Journal of Magnetism and Magnetic Materials, 194(1), pp. 224-230. (1999) 4. Nelson, D., H., Barale, P., J., Green, M., I., VanDyke, D. A.: The Lawrence Berkeley Laboratory magnetic-moment sorting system, In Proceedings of the 9 International Conference on Magnet Technology, pp. 735-738 (1985) 5. Svoboda, J., & Fujita, T.: Recent developments in magnetic methods of material separation, Minerals Engineering, 16(9), 785-792. (2003) 6. Jiles, D.: Introduction to Magnetism and Magnetic Materials. 3rd edn., CRC Press, Boca Raton (2016) 7. Gerginov, V., Derevianko, A., Tanner, C. E.: Observation of the Nuclear Magnetic Octupole Moment of 133Cs. Physical Review Letters 91(7), s. 072501, (2003). DOI:10.1103/PhysRevLett.91.072501 8. Serway, R., Jewett, J.: Physics for Scientists and Engineers, Volume 2, Chapters 23-46, 7th edn., Brocks Cole, Belmont (2008) 9. Jackiewicz, D., Szewczyk, R., Salach, J., Bieńkowski, A., Kachniarz, M.: Influence of Stresses on Magnetic B-H Characteristics of X30Cr13 Corrosion Resisting Martensitic Steel. In: Szewczyk R., Zieliński C., Kaliczyńska M. (eds) Recent Advances in Automation, Robotics and Measuring Techniques. Advances in Intelligent Systems and Computing, vol 267, pp. 607-614, Springer, Cham (2014) 10. Kachniarz, M., Jackiewicz, D., Nowicki, M., Bieńkowski, A., Szewczyk, R., Winiarski, W.: Magnetoelastic Characteristics of Constructional Steel Materials. In: Awrejcewicz J., Szewczyk R., Trojnacki M., Kaliczyńska M. (eds) Mechatronics - Ideas for Industrial Application. Advances in Intelligent Systems and Computing, vol 317, pp. 307-315, Springer, Cham (2015)