The experimental stand for investigation of induction surface hardening of gear wheels was described in the paper. In order to control parameters of the process a specialized equipment for identification of all important process parameters including registration of temperature changes in time and measurements of current intensity was installed. Exemplary results are presented. It is planned that the stand will be used as a demonstrator for a presentation of advantages of modern induction hardening technologies

A. Smagor

A. Smalcerz

G. Kopec

J. Barglik

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341METALURGIJA 57 (2018) 4, 341-344J. BARGLIK, A. SMALCERZ, A. SMAGOR, G. KOPEC EXPERIMENTAL STAND FOR INVESTIGATION OF INDUCTION HARDENING OF STEEL ELEMENTS Received – Primljeno: 2017-12-20Accepted – Prihvaćeno: 2018-06-01Preliminary Note – Prethodno priopćenjeJ. Barglik: jerzy.barglik@polsl.pl, A. Smalcerz, A. Smagor, G. Kopec – Silesian University of Technology, Katowice, PolandThe experimental stand for investigation of induction surface hardening of gear wheels was described in the paper. In order to control parameters of the process a specialized equipment for identification of all important process parameters including registration of temperature changes in time and measurements of current intensity was in-stalled. Exemplary results are presented. It is planned that the stand will be used as a demonstrator for a presenta-tion of advantages of modern induction hardening technologies. Key words: steel, gear wheel, induction heating, surface hardening, microstructure.INTRODUCTIONInduction hardening (IH) consists of three consecu-tive stages: induction heating, austenitisation and cool-ing [1]. It causes expected changes in the crystalline microstructure resulting in higher hardness. In case of the induction surface hardening (ISH) the second stage - austenitisation could be neglected or its time is very short. As a result we have local changes in the crystal-line microstructure of surface layers only.Microstructure of internal zones of the treated body does not change at all. In order to investigate the ISH pro-cess a specialized laboratory stand was designed and built. It was done within the framework of the research project realized by the consortium of three Polish Universities [2]. The laboratory stand makes possible to investigate various kinds of ISH processes including Continual In-duction Surface Hardening (CISH) and Spin Induction Surface Hardening (SISH) [3]. Investigations were con-centrated on steel elements with different shapes in-cluding gear wheels and cylinders. The stand was equipped with two separate transistor generators mak-ing possible to provide contour induction hardening of gear wheels. Universal character of the stand makes possible to use it as the demonstrator presented advan-tages of IH technologies. EXPERIMENTAL STANDA general view of the experimental stand is present-ed in Figure 1. The process was provided in the cham-ber 1. Two separate generators selected accordingly to process requirements were located in power cabinet 2 (Figure 2). Automatic steering system placed in the con-ISSN 0543-5846METABK 57(4) 341-344 (2018)UDC – UDK 669.15:621.833:621.365.5.783:620.178.1/621.9.015:620.18=111trol cabinet 3 makes possible to establish requested pa-rameters of the process and their registration. Closed cooling system (column 4) making possible to use as a quenchant both water, mixture of water and air as well as or any polymer solutions. Figure 1  Experimental stand 1 – hardening chamber, 2 – power cabinet, 3 – control cabinet, 4 – cooling columnFigure 2  Transistor generators in the power cabinet. 1 – medium frequency (MF),  2 – high frequency (HF)342J. BARGLIK et al.: EXPERIMENTAL STAND FOR INVESTIGATION OF INDUCTION HARDENING OF STEEL ELEMENTS METALURGIJA 57 (2018) 4, 341-344MEASUREMENT SYSTEMSCorrect identification of time evolution and spatial distribution of temperature in a hardened element seems to be crucial aspect influencing on control systems of the process. Such kind of measurement was complicat-ed because of big heating rates (1 000 K/s or even more) characteristic especially in case of high frequency in-duction heating. The equipment for temperature meas-urement applied in the stand was shown in Figure 3.The measurement of temperature during the process was provided simultaneously by three different methods.The first of them means use of the pyrometer 2 mak-ing possible to provide continual measurement and tem-perature registration in a point at the working surface of the gear wheel and identification of maximal tempera-ture reached there. The second method means use of the measurement system with two infrared cameras making possible to identify temperature distribution at working surface of gear wheel during the first step of the induc-tion heating typically to a temperature which exceeds the Curie point (camera 3) and then in the second step to the hardening temperature (camera 4). The third method makes possible to identify time when the color of se-lected drops (points) painted on the working surface changes or disappears when the point reaches the as-sumed temperature [4]. All methods were compared and finally the combination of pyrometer and two cam-eras system was used for temperature measurement. The laboratory stand was applied mostly, but not only, for investigation of two kinds of the SSIH pro-cesses: the Single Frequency Induction Hardening (SFIH) and Consecutive Dual Frequency Induction Hardening (CDFIH). The steering system could register basic parameters of the hardening process including time, current, power and frequency of MF (HF) heating, time of austenitisa-tion, velocity of rotation, kind of quenchant, its flow-rate and pressure, time and temperature of tempering in order to repeat the cycle of process in the same condi-tions. A front cover of the control cabinet is presented in Figure 4.In order to measure correctly current and power the stand is equipped with three Rogowski coils installed in the primary winding of the MF matching transformer (1 in Figure 5) and directly at the MF inductor (2 in Figure 5) and directly at the HF inductor (Figure 6). Figure 3  Temperature measurement arrangement. 1 – gear wheel, 2 – bio-color pyrometer, 3, 4 – infrared camerasFigure 4 Control panelFigure 5  Location of MF Rogowski coils 1 , 2.   1 – placed at the primary winding of MF matching transformer, 2 – placed directly at MF inductorFigure 6  Location of HF Rogowski coil 1, 2 – HF matching transformer343J. BARGLIK et al.: EXPERIMENTAL STAND FOR INVESTIGATION OF INDUCTION HARDENING OF STEEL ELEMENTSMETALURGIJA 57 (2018) 4, 341-344Current intensity are measured by means of Ro-gowski coils are presented and registered by oscillo-scope (exemplary oscillograms for the CDFIH process are presented in Figure 7).The stand was equipped in the specialized computer system for registration of all measurement data. Gear wheel immediately after the hardening process was tempered in the resistance chamber furnace. The first approximate measurement of hardness was realized at the experimental stand [5]. As a quenchant the polymer solution Aqua Quench 140 was mostly applied. The stand was equipped with converters and meters making possible to identify cooling parameters: concentration of a quenchant (Figure 8) and its flow-rate and pressure (Figure 9).ILLUSTRATIVE EXAMPLEAs an illustrative example the CDFIH process of gear wheel made of steel 300 M was described. The hardening system is presented in Figure 10. The gear wheel 3 was heated first by the MF induc-tor 1, then by the HF inductor 2 with flux concentrator and finally cooled by the sprayer 4. In order to obtain similar hardness distribution for all teeth the cylinder 5 rotates with a velocity of about 3 – 5 r/s. In order to minimize electrical losses in the bus-bars 6 and 7 their lengths and distance between conductors were as small as possible. The process was provided for following pa-rameters and dimensions of the CDFIH system: Material: steel 300M Gear wheel: teeth number – 40, width of the tooth ring – 0,007 m, external diameter 0,087 m, internal di-ameter – 0,079 m, MF inductor: height – 0,008 m, external diameter – 0,109 m, internal diameter – 0,9 m, length of bus-bars – 0,363 m,HF inductor: height – 0,0205 m, external diameter – 0,121 m, internal diameter – 0,89 m, length of bus-bars – 0,127 m, flux concentrator made of Fluxtrol 50, Sprayer: distance between MF inductor and sprayer – 0,01 m, external diameter – 0,135 m, internal diameter – 0,1235 m, MF heating: power – 60 kW, time – 4,5 s, frequency – 35,6 kHz, intermediate temperature – 720 0C, HF heating: power – 20 kW, time – 1,3 s, frequency – 276 kHz, hardening temperature – 990 0C,Other parameters: time between MF/HF heating – 0,1 s, time between heating and cooling – 0,1 s, rotation velocity – 3 r/s,Cooling: Quenchant: Aqua Quench 140, concentra-tion – 12 %, flow-rate – 2,5.10-4 m3/s, pressure – 0,11 MPa. Tempering: temperature – 160 0C, time – 7 200 s. Figure 7 Oscillograms of MF current (1) and HF current (2)Figure 8 The meter for the concentration of the quenchantFigure 9  Location of converters  for  measurements of flow-rate 1 and pressure 2 Figure 10  CDFIH system. 1 – MF inductor, 2 – HF inductor 3 –  gear wheel, 4 – sprayer, 5 – cylinder, 6 – MF bus-bars, 7 – HF bus-bars Figure 11  Dependence of hardness on distance from the surface at symmetry line perpendicular to the top of the tooth 344J. BARGLIK et al.: EXPERIMENTAL STAND FOR INVESTIGATION OF INDUCTION HARDENING OF STEEL ELEMENTS METALURGIJA 57 (2018) 4, 341-344The hardening depth was equal to 3 mm (Figure 11). In order to obtain an uniform contour hardness distribu-tion it is necessary to optimize parameters of the CD-FIH process. Microstructure of hardened zone of the gear wheel was shown in Figure 12. Microstructure of internal zone has not changed at all (tempered martensite). SUMMARYThe laboratory stand for different kinds of ISH pro-cesses was presented in the paper. The stand was equipped with specialized measurement systems mak-ing possible to determine and register the most impor-tant parameters of the process like: dependence of tem-perature on time and modified critical temperatures for investigated steel. As the example the CDFIH process for gear wheels made of steel 300M was presented. Ex-pected hardness and microstructure distributions were observed, however in order to obtain uniform contour hardness distribution it is necessary to optimize param-eters of the CDFIH process by means of advanced mathematical modelling validated by experiments. The stand will be used as a demonstrator of modern IHS technologies. AcknowledgmentThe paper was prepared within the NCBiR project PBS2/41/A5/2014 REFERENCES[1] V. Rudnev, G. Totten, Induction Heating and Heat Tre-atment, Materials Park, ASM International, 2014. [2] J. Barglik, K. Ducki, D. Kukla, J. Mizera, G. Mrówka-Nowotnik, J, Sieniawski, A. Smalcerz, Comparison of single and consecutive dual frequency induction surface hardening of gear wheels. Proceedings of the VIII Interna-tional Colloquium on Modeling of Material Processing, Riga, 2017, pp. 185 – 190.[3] S. Lupi, Fundamentals of Electroheat. Electrical Technolo-gies for Process Heating, Springer, 2016. [4] M. Spezzaria, M. Forzan, F. Dughiero, Multiphysical-mul-tiscale FEM simulation of contour induction hardening of aeronautical gears. Proceedings of the EPM conference, Cannes, 2015.[5] T. Wróbel, The influence of inoculation type on structure of pure aluminium”, Proceedings of 21st International Con-ference on Metallurgy and Materials, Brno, 2012, pp. 1114-1120.Note:  Krajewska T. is responsible for English language, Katowice, PolandFigure 12  Martensitic microstructure in the hardened surface layer (x 500)

Experimental stand for investigation of induction hardening of steel elements

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