The paper presents results of preliminary examinations of possibility to measure binder content in traditional moulding sands using a new method employing electromagnetic waves. The presented examinations were carried-out with use of an innovative test station, the so-called microwave slot line. The measurements of binder content in moulding sand were based on the results of power balance investigation of microwaves affecting the specimen. An advantage of the suggested, new method of binder content measurement is short measuring time

D. Nowak

K. Granat

M. Stachowicz

English

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207METALURGIJA 52 (2013) 2, 207-210D. NOWAK, M. STACHOWICZ, K. GRANATDETERMINATION OF THE BINDER IN SAND MOLDS WITH THE USE OF MICROWAVESReceived – Prispjelo: 2012-07-04Accepted – Prihvaćeno: 2012-10-30Preliminary Note – Prethodno priopćenje ISSN 0543-5846METABK 52(2) 207-210 (2013)UDC – UDK 621.74:537.86=111D. Novak, M. Stachowicz, K. Granat. Wroclaw University of Technol-ogy, Wroclaw, PolandThe paper pr esents r esults of pr eliminary examinations of possibilit y t o measur e binder c ontent in traditional moulding sands using a new method employing electromagnetic waves. The presented examinations were carried-out with use of an innovative test station, the so-called microwave slot line. The measurements of binder content in moulding sand were based on the results of power balance investigation of microwaves aff ecting the specimen. An advantage of the suggested, new method of binder content measurement is short measuring time.Key words: foundry, moulding sand, binder, microwavesINTRODUCTIONIn foundry practice, the most commonly applied among traditional moulding sands are those with syn-thetic binders. This is fi rst of all related to the possibil-ity of controlling composition and thus also technologi-cal properties of these sandmixes. The main components of a synthetic sandmix are sand base and a binder. The sand base of synthetic sandmixes most often consists of high-silica sands and less often of other sands, e.g. zir-con, chromite or magnesite sand. From among the bind-ers used in foundry practice, the most important with respect to binding capacity are bentonites [1].Technological properties of a sandmix are fi rst of all decided by its kind and composition. In the case of a specifi c sandmix grade, its technological properties are decided by quantity and quality of the binder (bentonite) and humidity. Knowledge of the binder content, espe-cially of an active one and especially in the case of re-bonding the circulating sandmix, is an important infor-mation about technological properties of this sandmix.Analysis of the results of preliminary laboratory ex-aminations carried-out using a microwave slot line in the Foundry and Automation Team of Wroclaw Univer-sity of Technology proved that it is possible to develop a new method of qualitative identifi cation of a binder in the traditional moulding sand [2,3].TEST STANDThe phenomenon of a standing wave present in a wave-guide, resulting from superposition of the wave refl ected from the given medium and the wave incident on this medium, is often used in microwave metrology. With its aid, it is possible to determine the standing-wave ratio (SWR) that plays an important role in heat-ing processes, and the absorption loss. Microwave slot lines [4-7] are used in these measurements. Investiga-tion of SWR of selected moulding materials was car-ried-out using a test stand composed of an electromag-netic wave source, rectangular wave-guide with mova-ble probes and a SWR meter.The wave-guide was so made that a measuring probe connected to the detector could be introduced inside through a specially made slot. The movable probe per-mits measuring distribution of the electromagnetic fi eld Figure 1  Layout of the test stand: 1 - load chamber with exchangeable substrates, 2 - wave-guide measuring line, 3 - probe with detector, 4 - transition of the wave-guide to the coaxial system in the WR340 standard, 5 - microwave generator208  METALURGIJA 52 (2013) 2, 207-210D. NOWAK et al.: DETERMINATION OF THE BINDER IN SAND MOLDS WITH THE USE OF MICROWAVESinside the waveguide. On the ground of this distribu-tion, the wave refl ection coeffi cient can be determined as a function of the load impedance (of substrate).Figure 1 shows layout of the test stand. A device made by Marconic Company, equipped with a frequen-cy synthetizer, was used as the electromagnetic wave source. The signal generated by this device has constant power of 3,98 mW during the entire measuring cycle.Modulus of the measured standing-wave ratio was read-off on the meter. Before the measurement, calculat-ed was wavelength λf in the wave-guide for the measure-ment frequency 2,45 GHz. To this end, the equation (1) was applied, in that λo is wavelength in vacuum [5-7]:  (1)The wavelength λgr of 188 mm for the limit frequen-cy was calculated on the ground of the wave-guide di-mensions and the accepted kind of fi eld TE10. The wavelength λf in the wave-guide was determined from the equation (1) as 174 mm. Places of the measured sig-nal minimum and maximum values are repeated every 0,5 wavelength in the wave-guide, i.e. exactly every 87 mm. In addition, in order to allow reading-off the posi-tion of at least one minimum and one maximum, the condition of minimum wave-guide length should be met: L >> 0,5 λf [1].MEASUREMENT OF MICROWAVE ABSORPTIONThe performed research was aimed at determining precisely the part of microwave power input Pin that is absorbed by the examined material. Knowledge of this parameter permits, in the considered case, determining quantity of a binder in the sandmix.Figure 2 shows balance of microwave power affect-ing the examined specimen.The parameter directly related to the losses resulting from power absorption in the examined material is ab-sorption damping Ad [6]:  (3)where:s11, s21 – coeffi cients of the scattering matrix.To determine the scattering parameters s11 and s21 properly, it is necessary to measure the refl ection coef-fi cient for the examined specimen with matched load and with shorting at the end of the slot line.The input refl ection coeffi cient for a symmetrical two-port loaded by impedance ZL is described by the relationship:  (4)The parameter s11 id determined directly from a measurement of the refl ection coeffi cient for the exam-ined specimen at matched load, for that ΓL = 0,and thus: Γin = s11, (5)where Γin is a complex quantity that can be written as:  (6)where:  (7)  (8)and  (9)where: Umax – maximum voltage, Umin – standing wave minimum voltage, dL – standing wave minimum dis-placement , λ – wavelength.The quantities Umax, Umin and dL are determined dur-ing measurements on the test stand, see Fig. 1.For the examined specimen and the line shorted at the end, the following expression for the parameter s21 is obtained from (4):  (10)where Γin2 is the measured refl ection coeffi cient and s11 is determined from (5):  (11)  (12)Therefore, determining absorption damping Ad re-quires obtaining measurements of maximum and mini-mum standing wave voltage (see formula 9 and 12), wavelength and wave displacement (see formula 7) for the specimen with matched load and with shorted slot line.Figure 2 Balance of microwave power aff ecting the specimenThe respective equation is as follows:  (2)where:Pin = power input,Pref = refl ected power,Pabs = absorbed power,Pout= power output.209METALURGIJA 52 (2013) 2, 207-210D. NOWAK et al.: DETERMINATION OF THE BINDER IN SAND MOLDS WITH THE USE OF MICROWAVESPREPARATION OF TEST SPECIMENSThe examined specimens were introduced to the constant-volume chamber installed at the end of the wave-guide. The chamber was made of a material with very low microwave damping coeffi cient, so that the wave freely penetrated through the chamber walls and then deep into the moulding sand present inside. The specimens were preliminarily compacted with a labora-tory rammer LU-type to guarantee a constant thicken-ing degree of the sandmix.DETERMINATION OF ABSORBED POWER AND OUTPUT POWER OF MOULDING SANDSBefore the main research, preliminary measurements were taken to determine correlation between bentonite content, Pabs absorbed power and output power Pout of microwave energy. These measurements consisted in determining the Pabs and Pout values for dried moulding sand with various content of bentonites Specjal and GecoFigures 3 to 6 show dependences of Pabs absorbed power and output power Pout on contents of bentonite Specjal and bentonite Geco in a traditional moulding sand.Analysis of the preliminary results presented in Figs. 3 to 6 indicates that the changes of Pabs absorbed power and output power Pout are linear. So, it can be found that it is suffi cient to measure a single parameter only, namely Pabs absorbed power or output power Pout, to be able to determine concentration of bentonite contained in a sandmix.FINAL CONCLUSIONSAnalysis of the obtained examination results leads to the following conclusions:It is possible to measure binder content in a mould-• ing sand using a new microwave-based measure-ment method consisting in determining, be means of a slot line, values of one of the two parameters: Pabs absorbed power or output power Pout,An advantage of the new method of measuring bind-• er content in moulding sand is short measurement time related to specifi city of microwave radiation.The presented results of preliminary measurements • with use of a microwave slot line, consisting in measuring parameters absorbed power Pabs and out-put power Pout, make an introduction to developing a method of measuring active binder content in circu-lating sandmixes, identifying binder grade and, at a further stage, determining humidity of a moulding sand.REFERENCES[1] J. L. Lewandowski, Materials for casting moulds, Akapit, Cracow, 1991, pp. 40-85.Figure 6  Eff ect of bentonite Geco content in traditional moulding sand on power output PoutFigure 3  Eff ect of bentonite Specjal content in traditional moulding sand on absorbed power PabsFigure 4  Eff ect of bentonite Specjal content in traditional moulding sand on power output PoutFigure 5  Eff ect of bentonite Geco content in traditional moulding sand on absorbed power Pabs210  METALURGIJA 52 (2013) 2, 207-210D. NOWAK et al.: DETERMINATION OF THE BINDER IN SAND MOLDS WITH THE USE OF MICROWAVES[2] M. Pigiel, K. Granat, D. Nowak, W. Florczak, Wykorzysta-nie energii mikrofalowej w procesach odlewniczych, Ar-chiwum Odlewnictwa. 6 (2006) 21, 443-452.[3] K. Granat, D. Nowak, M. Pigiel, M. Stachowicz, R. Wikie-ra, Measurement of standing-wave ratio for effectiveness assessment of microwave absorption by moulding mate-rials, Archives of Foundry Engineering, 8 (2008), Special Issue 3,31-34.[4] H.E. Thomas, Microwave technologies and microwave equipment, Handbook, Wydawnictwa Naukowo-Techni-czne, Warsaw 1978, pp.157-186.[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, Poland

Determination of the binder in sand molds with the use of microwaves

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