DEVELOPMENT AND INVESTIGATION OF A SYMMETRIC INDUCTION HEATING UNIT FOR SPHERICAL SHAPE METAL WARE

Transcription

1 Journal of Chemial Sergey Tehnology S. Titov, Vitor and Metallurgy, N. Meshheryakov 53, 5, 2018, DEVELOPMENT AND INVESTIGATION OF A SYMMETRIC INDUCTION HEATING UNIT FOR SPHERICAL SHAPE METAL WARE Sergey S. Titov, Vitor N. Meshheryakov Lipetsk State Tehnial University 30 Moskovskaya St Lipetsk, Russian Federation mesherek@yandex.ru Reeived 15 Marh 2018 Aepted 15 June 2018 ABSTRACT The present ommuniation onsiders a symmetri indution heating unit for spherial shape metal ware. It analyzes the orresponding eletromagneti proesses, determines the indutor optimum frequeny and amperage values and provides results of the experimental investigation. Keywords: indution heating, spherial item, temperature, eletromagneti field, frequeny, magneti field strength. INTRODUCTION The reation of energetially effiient ontinuousating equipment for symmetri heating to a given depth of spherial metal produts with no oxidation and dearburization is a hallenging problem for some industries. The latter inlude mass prodution of milling bodies for ore-dressing, balls for rolling bearings and valves in hydrauli systems, and wear-resistant balls in the bakwater gates of deep-well pumps for oil prodution, et. This ombination of heating qualities whih is in demand in industry is most thoroughly met by the indution method with its diret and high-speed (of the order of frations of a seond) onversion of an eletrial energy into a thermal energy. This onversion is haraterized by a simple regulation of the temperature and the heating depth, thus making it possible to obtain, after quenhing and tempering, the optimum ombination of produts high surfae hardness (bak-to-bak endurane) and a relatively elasti ore (antiraking). However, despite all advantages of this method, it is only applied to produe artiles of a ontinuous or near-ontinuous ross setion of ensured heating symmetry of heating. INDUCTOR DESIGN AND MATHEMATICAL MODEL The hoie and alulation of the indutor begins with determining its geometri onfiguration. Copper tubes are the ommon material used in its making. It is worth adding that the indutor must be ooled by running water during its operation. The indutor shape and dimensions depend on the heating onditions, on the size and onfiguration of the heated billet, as well as on the supply power and frequeny. In the ase under onsideration, spherial items are used as billets, inluding grinding balls and rolling elements of ball bearings. Therefore, it is most appropriate to use an indutor of a multi-turn ring onfiguration, i.e. of a round ross setion minimizing the air gap between the indutor turns and the billet. Thus, its effiieny is inreased. Usually, the indutor is made of a round or retangular opper tube. The use of retangular opper tubes gives an effiieny gain of 2-3 perent [1-3], whih is appropriate for high-power plants. However, opper tubes of a round ross-setion are more widespread and less ostly. An indution heating unit (IHU) with a vertial symmetry axis onsists of several indutors (setion- 1009

2 Journal of Chemial Tehnology and Metallurgy, 53, 5, 2018 alization), is with a transporting profile [4] inside it. The setionalization is performed in order to inrease the effiieny of the unit and the ability to operate the heating parameters within wide limits. In order to ensure uniform heating of spherial billets, it is neessary to distribute the eletromagneti field energy transmitted to them uniformly along the transporting profile. Sine the resistivity and permeability of the billets hange in the ourse of heating, the indutor urrent must also vary along the length of the transporting profile. The indutor urrent frequeny must also vary, beause it is neessary to maintain a given heating depth. These requirements the indutor urrent and frequeny varying along the profile length an only be guaranteed by dividing the indutor into setions. In order to arry out the researh, it is neessary to develop one setion of the indutor, as the eletromagneti proesses of heating the moving spherial billets in the different setions is idential. Furthermore, the indutor will be seen as one setion only. At the same time, the hoie of the indutor geometri dimensions, in partiular the length L, depends on the total number of setions, the kinematis of spherial billets moving along the transporting profile (the geometry of the transporting profile, the mass-dimensional parameters of the spherial metalware), the required power and the billet heating depth. Beause at this stage of the researh the whole IHU does not need to be alulated, the indutor length L will be taken as equal to five times the diameters d of the spherial billet. The indutor internal diameter D depends on the billet diameter and the wall thikness of the transporting profile. The wall thikness is determined by the seleted material of the transporting profile. The high melting temperature (beause the temperature of the spherial billets will reah the required quenhing temperature of 700 o C o C), the low thermal expansion oeffiient, the high eletrial resistivity (in order to avoid heating the material by indution eddy-urrents), the relatively high mehanial strength and the non-magnetization of the material refer to the profile material requirements. A high-strength quartz glass tube is used as a spherial billet to move inside the indutor of the experimental unit. The geometri onfiguration of the indutor is shown in Fig. 1. The speifi power P sp at the surfae of the heated artile is usually in the range of 0.5 kw/m kw/m 2, 1010 mainly around 1 kw/m 2 [5] in ase short of indution quenhing of ylindrial bodies geometrially lose to the ball quenhing. The estimated power P of the experimental unit is about 3 kw. Rolling bearing balls made of onstrutional bearing steel 100Cr6 (for European ommunity) are used as billets. The approximate diameter of the ball must not exeed: P 3 d m ðp ð1 (1) sp Aording to ref. [6], the appropriate maximum diameter of the ball is mm. This value will be used for further alulations. Thus, a quartz tube is seleted aording to TU with an external diameter D = 12 mm and wall thikness a = 1 mm. The eletrial parameters of the indutor are further alulated. The required indutor urrent frequeny, f, is determined by the surfae effet and depends on the required ative depth of heating the ball, b, as well as on the properties of the ball material: L a Fig. 1. Geometri onfiguration of the indutor: 1 a billet (ball), 2 a quartz tube, 3 indutor opper turns.

3 Sergey S. Titov, Vitor N. Meshheryakov f = 1 1 πµ 0µ b ρ sr 2 b, (2) 7 where µ = 4π 10 0 H/m (it is the magneti permeability of vauum), µ is the relative magneti permeability b of the billet, while ρsr is the billet speifi resistane (aording to Table 1). The speifi resistane of arbon steels, in this ase of 100Cr6 (for European ommunity), depends on the temperature aording to Table 1. Its relative magneti permeability depends on the temperature, T, as well as on the magneti field strength, H. An approximation of the dependenes is used: µ b = ln( H ) ln( H ) T 1 + Tk T H (3) where T k is the Curie temperature. The required ative depth of heating the ball must be in the range of 1%- 5% of the spherial billet diameter. For the seleted billet it is 0.1mm-0.5 mm. In order to alulate the frequeny aording to Eq. (2), it is neessary to know the value of the magneti field strength, H, determined by Eq. (3). This value an be finally determined by performing the eletri alulation of the indutor. So, first the range of values H = 20 ka/m ka/m is hosen with its subsequent refinement after determining all indutor parameters. The graphs (Fig. 2) demonstrate the dependenes of the required urrent frequeny on the temperature in the form of a range on the basis of the heating depth limitations for two values of the preseleted magneti field strength of 20 ka/m and 100 ka/m. The intersetion area of the two ranges is optimum for frequeny seletion. The latter should be done in view of almost no hanges with temperature variation. This in turn provides unhanged indutor parameters. Fig. 2 shows a line representing the seleted optimum frequeny. The range of the optimum frequeny at temperature hange lies between 75 khz and 132 khz. It will be used in the further alulations. The urrent depth,, of the opper ondutors in the optimum frequeny range an be determined at 100 C aording to the equation: Fig. 2. Temperature dependene of the required urrent frequeny: 1 a range of frequenies at a strength of H = 20 ka/m; 2 a frequeny range at a voltage of H = 100 ka/m; 3 an optimum frequeny. 1011

4 Journal of Chemial Tehnology and Metallurgy, 53, 5, 2018 Table 1. Temperature dependene of steel resistivity. t, ºC ρ sr, 10-6 Ω m ρ = = mm, πµ 0 f (4) whih determines the minimum required thikness of the indutor opper tube. The dependene of the external diameter of the opper tube, d S, on the ative ross-setional area, a, an be estimated aording to the equation: d Sa + π = π 2. (5) The maximum allowable indutor urrent density, J max, under ooling onditions should not normally exeed 150 A/mm 2 [1]. Hene the dependene of the required external diameter of the opper tube on the indutor urrent, I, is: d I J = max + π π 2. (6) The indiated dependene of the previously determined frequeny range is shown in Fig. 3. Diameters above 10 mm are impratial beause it is diffiult to bend the tube to an internal diameter of 12 mm. The values of 6, 8 mm and 10 mm (a wall thikness 1 mm) are seleted among standard opper tube diameters, and a omparative analysis is performed. The value of the heating power released in the spherial billet will serve as the evaluation riterion of the analysis. In order to alulate the heating power, it is neessary to use numerial methods. It is most appropriate to apply the finite element method (FEM) in this ase. Further, an FEMM program pakage will be used providing the given method implementation. FEMM is a free set of programs (freeware) for solving eletromagneti, urrent and thermal problems in two-dimensional flat and axisymmetri areas. The program is used to solve: - linear and non-linear magnetostati problems; - harmoni linear and non-linear quasistati magneti problems; - thermal problems in a steady thermal state. Via FEMM, indutor mathematial models with a billet and with three variants of opper tube diameters are developed: 6 mm, 8 mm and 10 mm (Fig. 4). Next, the values of the heating power are alulated depending on the indutor urrent provided that the optimum frequeny is maintained as shown in Fig. 5. Hene, the value of the indutor opper tube diameter equal to 8 mm is seleted beause the transition to a larger diameter of 10 mm pratially does not yield any power gain. The average power value is 1.6 kw aounting the surfae area of the spherial billet. It yields a speifi power of kw/m 2, whih is in the reommended range of 0.5 kw/m kw/m 2. The final indutor parameters are as follows: (i) the onfiguration of the ondutors of the indutor - a hollow tube, an external diameter - 8 mm, an internal diameter - 6 mm, a number of turns - 5, distane between turns - 2 mm; (ii) the indutor onfiguration an exter- Fig. 3. A dependene of the required external diameter of the opper tube on the indutor urrent within the optimum frequeny range. 1012

5 Sergey S. Titov, Vitor N. Meshheryakov Fig. 4. FEMM program variants of the indutor onfiguration for different diameters of the opper tube used. Fig. 5. Billet heating apaity for indutor tube diameters of: 1) 6 mm. d = 10 d = mm; 2) d = 8 mm: 3) nal diameter - 28 mm, an internal diameter - 12 mm, an indutor length - 48 mm. Fig. 6 shows the pattern of the eletromagneti field for a given onfiguration. The appliation of FEMM provides also the alulation of the parameters of the eletri iruit of the indutor. The main parameters taken down in presene and absene of a spherial billet in the indutor are summarized in Table 2. Further, the magneti field strength, H, is plotted as a funtion of the distane between the surfae and the billet aording to Fig. 7. As seen from the graphs, the values of the intensity are lose to those of the previously aepted interval H = 20 ka/m ka/m. 1013

6 Journal of Chemial Tehnology and Metallurgy, 53, 5, 2018 Table 2. Parameters of the eletri iruit of the indutor. with billet empty 20 0 C C 75 khz 132 khz 75 khz 132 khz 75 khz 132 khz I 2, A U 2, V 20,1 26,3 21,6 28,3 11,1 13,8 P 2, W Q 2, Var S 2, VA r, Ω 0, , , , , , L, H 4,0721E-08 3,934E-08 4,39E-08 4,239E-08 3,0528E-08 2,9118E-08 where Ä is the minimum depth of ball heating, min Ä is the maximum depth of ball heating, ì b is the max relative magneti permeability of the billet material, ñ b is the eletrial resistivity of the billet material, while 7 ì 0 = 4π 10 H/m is the magneti permeability of vauum. EXPERIMENTAL Fig. 6. An eletromagneti field pattern of the indutor size seleted. The metal ball used in the experiments was 10 mm in diameter. The required ative depth of ball heating must was in the range of 1 % - 5 % of the spherial billet diameter [7]. For the seleted billet, the range was 0.1 % mm, whih orresponded to the frequeny range of 75 khz khz. The ball heating time was estimated at three frequenies of 75 khz, 100 khz,and 120 khz. In this ase, for all three measurements, the urrent from the retifiers The optimum indutor frequeny and amperage will be determined aording to the riterion of the maximum possible rate of heating the ball. In this ase, the allowable frequeny range min f f - max must be limited on the basis of the allowable ball heating depth range: 1 f max = ; 2 1 π minµµ 0 b ρ b 1 f min =, 2 1 π maxµµ 0 b ρ b (7) 1014 Fig. 7. Dependene of the magneti field strength of a spherial billet on the distane from the surfae.

7 Sergey S. Titov, Vitor N. Meshheryakov Table 3. Measurement of the ball heating time at different urrent frequenies. Indutor urrent frequeny, khz Retifiersupplied urrent, A Retifier-supplied power, W Indutor urrent, A Bank apaity C, μf Time of heating up to 500 С, s 75 2, , , , , ,75 29,5 Meanwell SE [8], i.e. the onstant ative power was maintained onstant. The retifier amperage was determined aording to the riterion of the indutor urrent reahing the value equal to the apaitor bank allowable urrent of 85A for frequeny 120 khz. It was equal to 2.5 A, whih orresponded to the power onsumed by 500 W retifier. In order to maintain the onstant retifier urrent [9], the indutor urrent was regulated by hanging the value of the effetive output voltage. The ball was heated from 20 C to 500 C [10]. The temperature was measured using the infrared pyrometer CEM DT-8865 with the following harateristis: temperature measurement range from -50 C to C; an auray ± 1% (from +20 to С), ± 1.5% (from +300 to С; a response time of 0.15 s. The results of the measurements arried out are summarized in Table 3. As seen from the table, the heating at a lower frequeny of 75 khz was faster at a onstant power onsumption value. This ould be explained by an inrease of MOSFET heating at a higher frequeny and, hene, by a derease of the unit effiieny. The final hoie was made for the optimum frequeny of 75 khz, the heating time at whih (at the indutor urrent of 130 A) was 25 seonds. CONCLUSIONS As a result of the onduted researh, an optimum indutor design was alulated for heating the seleted billet ball-bearing balls with a maximum diameter of mm. The main elements of the power iruit were alulated and seleted for an indutor supply. They inluded a balaning apaitor, a mathing transformer and a MOSFET inverter. A ontrol system was developed for heating both fixed balls and those moving through the indutor in the eletrial engineering heating omplex [11]. The eletrial engineering omplex performane analysis was desribed in detail in ref. [12]. The experiments were onduted on heating the ball at whih (i) the indutor urrent optimum frequeny and intensity were determined; (ii) the stationary ball heating time was estimated, and (iii) the graphs of the transient proesses when working with a moving ball were obtained. The obtained results provided the advanement of a onept for designing a spiral hute unit with a set of indutors. The onduted researh gave reason to expet a derease in the prodution ost of spherial metal ware due to a signifiant derease in the energy intensity of their heat treatment (diret heating at a set depth) by about 11.2 %. Aording to the results of a series of experiments, there was also a twofold inrease of the lifetime of these items (surfae heating relative to an elasti ore, i.e., the antiraking effet was ahieved along with the symmetry of the impat) ompared to items heat-treated aording to a traditional tehnology. These aspets afford grounds for foreasting a high demand for these items from ore-dressing and proessing enterprises plants (non-ferrous and ferrous metal ore preparation), the onstrution industry (prodution of siliates, ement), the ball-bearing industry (rolling bearing balls), and oil prodution (hek valves of deep-well pumps). REFERENCES 1. А.I. Slukhotsky, V.S. Nemkov, N.A. Pavlov, A.V. Bamuner, Indution heating plants, Leningrad, Energoizdat, 1981, (in Russian). 2. N. Mohan, T.M. Undeland, W.P. Robbins, Power Eletronis. Converters, appliation and design. Seond edition, New Jersey, A John Wiley and Sons, In, B.K. Bose, Modern power eletronis and AC 1015

8 Journal of Chemial Tehnology and Metallurgy, 53, 5, 2018 drives, New Jersey, Prentie Hall PTR, Patent of the Russian Federation , МPК H05B6/36. Titov S.S. Continuous indutor for uniform axisymmetri indution heating of spherial items COMBISPIRAL. Published 12/10/2014, Bulletin 34, 2 pp. (in Russian). 5. G.I. Babat, Indution heating of metals and its industrial appliation, seond edition, Mosow- Leningrad, Energy, 1965, (in Russian). 6. Luo F. L. Digital power eletronis and appliations / F. L. Luo, H. Ye, M. Rashid. San Diego, USA: Elsevier, 2005, 408 pp. 7. GOST Р Rollingbearings. Steel balls. Speifiation, Mosow, Standartinform, 2015, (in Russian). 8. Honeywell Current Sensors. SENSING AND CONTROL. Produt Range Guide. Honeywell International In, V.N. Meshheryakov, S.S. Titov, Indution Heating Plant for Heat Treatment of Spherial Metal Produts, Russian Metallurgy (Metals), 12, 2015, O.V. Fedorov, S.S. Titov, Investigation of the energy distribution of the eletromagneti field in the volume of a metal sphere during heating in the indutor, News of the higher eduational institutions of the Chernozem region, 3, 2015, 7-10, (in Russian). 11. V.N. Meshheryakov, S.S. Titov, An indution heating unit for spherial metalware heat treatment, Eletrometallurgy, 8, 2015, 14-22, (in Russian). 12. V.N. Meshheryakov, S.S.Titov, Energy indiators of the eletrial engineering omplex for the symmetrial indution heating of spherial metalware, Bulletin of South Ural State University. Energy Series, 1, 2015, 54-58, (in Russian). 1016