The paper presents a semi-industrial reactor designed for microwave utilization of waste moulds and cores made of moulding sands prepared in furane resin technology. It was found that a possibility exists of effective incinerating this way prepared residues of cores separated from moulding sands or waste moulds left after casting. The preliminary tests evidenced that microwave heating is an effective way of disposing waste moulding sands and the applied apparatus permits effective control of the microwave heating process

D. Nowak

K. Granat

M. Pigiel

M. Stachowicz

English

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211METALURGIJA 52 (2013) 2, 211-214D. NOWAK, M. STACHOWICZ, K. GRANAT, M. PIGIELPOSSIBILITIES OF USING MICROWAVE HEATING IN DISPOSAL PROCESS OF THERMO AND SELFSETTING SANDMIXESReceived – Prispjelo: 2012-07-04Accepted – Prihvaćeno: 2012-10-25Preliminary Note – Prethodno priopćenje ISSN 0543-5846METABK 52(2) 211-214 (2013)UDC – UDK 621.74:628.4.038:537.86=111D. Nowak, M. Stachowicz, K. Granat, M. Pigiel. Wroclaw University of Technology, Wroclaw, PolandThe paper presents a semi-industrial reactor designed for microwave utilization of waste moulds and cores made of moulding sands prepared in furane resin technology. It was found that a possibility exists of eff ective incinerating this way prepared residues of cores separated from moulding sands or waste moulds left after casting. The prelimi-nary tests evidenced that microwave heating is an eff ective way of disposing waste moulding sands and the applied apparatus permits eff ective control of the microwave heating process.Key words: foundry, innovative technologies, moulding sand, microwaves, utilizationINTRODUCTIONProblems related to utilization of foundry wastes, consisting mostly of various grades of used moulding and core sands, combine numerous fi elds of science and advanced technology [1]. Neutralization of used mould-ing sand presents the main economical problem of each commercial foundry plant. Due to restrictive environ-ment protection law, implemented are various technolo-gies consisting in cleaning used moulding sands from residues of binding materials.The experiences gained from the tests of utilizing noxious industrial wastes containing, among others, as-bestos [2] contributed to the attempt of applying the electrothermal process [3], i.e. transforming electrical energy into thermal energy of the heated materials by means of microwave-frequency electromagnetic fi elds. In [4], presented are results of microwave utilization of used moulds and cores made of sandmixes containing thermohardening resins. Residues of shell cores sepa-rated from moulding sand after casting were neutralised in a short time. In the examinations applied were addi-tives intensifying the heating process and thus shorten-ing the time to reach the required incineration tempera-ture. Moreover, it was found that in the microwave uti-lization process important is proper preparation of the used moulding sand by its mechanical disintegration. The materials suggested for microwave utilization are these with suitable dielectric properties guaranteeing ef-fi cient and suffi ciently deep penetration of microwave radiation to transfer the energy emitted by the micro-wave generator to the substrate [5-7].It should be emphasised that microwave radiation has found wide application also in other foundry proc-esses, e.g. for drying traditional moulding sands or hardening sandmixes containing water-glass or thermo-hardening resins.MEASURING STANDThe microwave reactor used in the preliminary re-search to determine possibilities of microwave utiliza-tion of noxious substances was adapted to the needs of testing loose materials with low bulk density. In the pre-vious design of the combustion chamber, an obstacle limiting application of the reactor to microwave utiliza-tion of moulding sands was granulation of the used ma-terials. In order to restrict infl uence of refi nement de-gree and to ensure uniform absorption of microwave energy in the whole volume of charge material in the Figure 1 Design of the microwave reactor212  METALURGIJA 52 (2013) 2, 211-214D. NOWAK et al.: POSSIBILITIES OF USING MICROWAVE HEATING IN DISPOSAL PROCESS…chamber, design of the reactor was complemented with additional components permitting its rotations.The reactor shown in Figure 1 is equipped with four microwave generators with total power output of 6,5 kW. The closures (upper and lower covers) are equipped with reactance chokes preventing microwaves from „leaking“ outside. Moreover, the reactor was furnished with safety systems preventing the generators from be-ing turned-on with the combustion chamber opened.Radiators of the reactor are arranged on its circum-stance to make possible simultaneous, failure-free op-eration of all the installed generators, see Figure 2.A condition of correct operation is also homogeneity of electromagnetic fi eld in the entire reactor chamber.The four microwave generators with maximum mi-crowave power up to 1,6 kW each are connected with the reactor‘s chamber by means of wave-guide fl anges. The microwave generating lamps (magnetrons) are equipped with a water cooling system, so each of the generators is connected to the water collecting tube. The generators system is supplied from a specially de-signed set of microwave power packs (installed in a separate housing) and connected with the generators by means of cables.The charge material is loaded through the upper metal cover. The space between the metal chamber wall and the ceramic tube, visible in Figure 3, is fi lled with insulating material, so that thermal energy of combus-tion can not be conveyed to the metal housing. The ap-plied insulating material is characterised by low micro-wave attenuation coeffi cient, thanks to that practically the whole electromagnetic fi eld energy is focused on the charge to be utilised. These requirements are fulfi lled by insulating wool named SIBRAL.The chamber is equipped with microwave chokes eliminating risk of leaking microwaves outside the re-actor during its operation.The set of microwave generators is placed in a mo-bile metal control cabinet. In addition, the power packs permit independent switching the generators on and off, as well as reducing power of each generator down to half the maximum power.PREPARATION OF TEST MATERIALThe material used in the preliminary research con-sisted of non-burnt waste casting moulds and cores made in technologies applied in foundry plants.Four grades of moulding sands, M1, M2, M3 and M4, were used in the tests. The following used mould-ing and core sands were examined:–  core sand with phenolic resin and protective coat-ing novanol 165, M1, (Figure 4),–  sandmix with water-glass R-145 hardened with Flour, M2, (Figure 5),–  sandmix with urea-furfuryl resin Kalahari U404, M3, (Figure 6)–  sandmix with phenolic resin Fenotec P439, M4, (Figure 7).Residues of protective coating were left on the sur-face. The charge chamber was fi lled with ca. 700 g of the mentioned sandmixes.Analysis of the preliminary results and their com-parison with those for other materials tested [4] for pos-sibility of using microwave utilization shows that ef-Figure 3  View of reactor chamber lined with thermo-insulating wool SIBRALFigure 2  Layout of microwave generator chamber with arrangement of microwave coupling systemsFigure 4  View of waste moulds and cores before utilization in the microwave chamber; moulding sand M1213METALURGIJA 52 (2013) 2, 211-214D. NOWAK et al.: POSSIBILITIES OF USING MICROWAVE HEATING IN DISPOSAL PROCESS…fectiveness of heating the wastes depends on their re-fi nement degree. Therefore, the material to be tested was subject to preliminary mechanical refi nement in a laboratory roll mixer.Microwave heating was performed after closing the chamber and starting the drive ensuring a determined rotational speed. Operation of the generators was con-trolled in two working stages, see Table 1. In the fi rst stage, all the four generators were successively switched-on to a half of their rated power. In the second stage, the generators’ power was increased to the maximum value of ca. 6,6 kW. During that time recorded were changes in the substrate temperature. The incineration process was fi nished when stabilisation of the charge material temperature was observed.UTILISATION PROCESSBasic process parameters for the moulding sands M1-M4, measured during the tests, are settled in Table 1. The given heating temperatures are those recorded after the process became stabilised.Figure 5  View of waste moulds and cores before utilization in the microwave chamber; moulding sand M2Figure 6  View of waste moulds and cores before utilization in the microwave chamber; moulding sand M3Figure 7  View of waste moulds and cores before utilization in the microwave chamber; moulding sand M4Table 1 Parameters of microwave heatingStage 13,2 / kWStage 26,5 / kWMass 1 Temp. 420 °C 670 °CHeating time: 10 min. + 5 min.(stabiliza-tion)10 min. + 5 min.(stabiliz-ation)Mass 2 Temp. 470 °C 665 °CHeating time: 10 min. + 5 min.(stabiliz-ation)10 min. + 5 min.(stabiliz-ation)Mass 3 Temp. 380 °C 450 °CHeating time: 10 min. + 5 min.(stabiliz-ation)10 min. + 5 min.(stabiliz-ation)Mass 4 Temp. 370 °C 780 °CHeating time: 10 min. + 5 min.(stabiliz-ation)10 min. + 5 min.(stabiliz-ation)In the case of the moulding sand M1 in the stage 1, the stabilisation temperature of 420 °C was reached af-ter 10 minutes. Further microwave heating for 5 min did not result in any measurable temperature rise. Switch-ing to the stage 2 permitted heating-up the charge to 670 °C after 5 minutes. Monitoring the temperature changes for further 5 min did not reveal any temperature rise. As a fi nal result, obtained was a very powdery mixture with lumps, with visible residues of protective coating, see Figure 8.Course of incineration process of the moulding sand M2 was similar to that of M1. The highest temperature Figure 8  View of mass M1 treated with microwave heating proces214  METALURGIJA 52 (2013) 2, 211-214D. NOWAK et al.: POSSIBILITIES OF USING MICROWAVE HEATING IN DISPOSAL PROCESS…was reached only when using the working stage 2. Pow-er of 6,5 kW allowed incinerating the moulding sand M2 at the maximum measured temperature of 665 °C.The obtained material was very powdery with its grains very easily separating from each other. The proc-ess resulted in practically complete disintegration of the moulding sand (Figure 9), which could facilitate further transportation of these wastes to a location of further processing, utilizing or storing.The combustion process mass M3 (Figure 10) and M4 (Figure 11) had a similar course in the fi rst mode Both weight within the temperature reached 370 °C. The highest temperature was reached by using the other mode, but only in the case of mass M4. For a mass M3 to raise the temperature of the process, it is recommend-ed to use the materials to intensify the process of micro-wave heating.CONCLUSIONSAnalysis of the results of the preliminary research on possibilities of thermal utilization of waste moulds and cores containing a furane-resin binder in the proc-ess of microwave heating leads to the following conclu-sions:–  Waste moulding sand moulds and cores can be ef-fectively and effi ciently utilized in microwave ov-ens.–  The incineration process using high-power heating facilities is mostly infl uenced by homogeneity de-gree of the used electromagnetic fi eld.–  Time and temperature of microwave thermal utili-zation of waste moulding sands depend on power of microwave heating.–  Microwave heating of waste moulding sands guar-antees measurable economical benefi ts resulting from signifi cant reduction of thermal utilization time.AcknowledgementsThe scientifi c work was fi nanced from the budgetary means for science in the years 2010 to 2012 as a re-search project.REFERENCES[1] J. L. Lewandowski, Materials for casting moulds, Akapit, Cracow, 1991, pp. 541-546.[2] M. Pigiel, K. Granat, D. Nowak, W. Florczak, Microwave reactor for utilizing waste materials, 10 (2010) spec. iss. 1, pp. 251-254.[3] M. Hering; Basic electrothermics, part II, WNT, Warsaw 1998, pp. 206-224.[4] K. Granat, M. Pigiel, W. Florczak, Application of micro-waves for incinerating waste shell moulds and cores, Ar-chives of Foundry Engineering. 8 (2008), spec. iss. 3, 167-170.[5] B. Galwas, Microwave metrology, Wydawnictwa Komu-nikacji i Łączności, Warsaw 1985, pp. 162-175.[6] R. Litwin, M. Suski, Microwave technology, Wydawnic-twa Naukowo-Techniczne, Warsaw 1972, pp. 597-630.[7] W. Czarczyński, Basics of microwave technology, Edito-rial Offi ce of Wroclaw University of Technology, Wrocław 2003 pp.123-145.Note:  The responsible translator for English language: INTER-TK, Translation Offi ce, Wrocław, PolandFigure 9  View of mass M2 treated with microwave heating procesFigure 11  View of mass M4 treated with microwave heating processFigure 10  View of mass M3 treated with microwave heating proces

Possibilities of using microwave heating in disposal process of thermo and selfsetting sandmixes

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