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The paper presents results of a research on identifying opportunities for effective reclamation of waste molding sand with water-glass, hardened by microwave heating. The molding sand applied in the tests was prepared with use of selected type 145 of sodium water-glass. The sand was sequentially processed by microwave hardening, cooling, thermal loading to 800• C, cooling to ambient temperature, crushing and mechanical reclamation. These stages create a closed processing loop. After each cycle, changes of tensile strength and bending strength were determined. Results of the study show that it is possible to activate surface of high-silica grains of waste foundry sand hardened with microwaves, provided that applied are appropriate processing parameters in successive operation cycles.Keywords: molding sand, water-glass, reclamation, microwave heating, hardening W pracy przedstawiono wyniki badań nad określeniem możliwości prowadzenia skutecznej regeneracji zużytych mas formierskich ze szkłem wodnym utwardzanych w procesie nagrzewania mikrofalowego. Przeznaczoną do badań masę, sporządzoną z wybranym szkłem wodnym sodowym gatunku 145, poddawano kolejno procesom: utwardzania mikrofalowego, studzenia, obciążaniu termicznemu do temperatury 800• C, studzenia do temperatury otoczenia, rozkruszania i regeneracji mechanicznej. Opisane procesy tworzyły jeden zamknięty cykl przerobu zużytej masy. Po każdym kolejnym cyklu przerobu masy określano zmianę wytrzymałości na rozciąganie i zginanie. Analizując wyniki przeprowadzonych badań stwierdzono, że istnieje możliwość aktywacji regeneratu zużytej masy formierskiej ze szkłem wodnym, utwardzanej w procesie nagrzewania mikrofalowego, pod warunkiem zastosowania odpowiednich parametrów jej przygotowania, odbywającego się w kolejnych cyklach eksploatacji.

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Influence of wet activation of used inorganic binder on cyclically refreshed water glass moulding sands hardened by microwaves * M a t eu s z S t a c h ow i c z Sodi um si l i c at e ( i . e. w at er-g l ass) , an i norg ani c b i nder ap p l i ed i n f oundry i ndust ry, i s c h arac t eri sed b y l ow c ost and l ow h arm f ul ness. H ow ever, i t h as c onsi derab l e di sadvant ag es suc h as p oor k noc k i ng -out p rop ert i es [ 1 ] , t oug h c ast i ng c l eani ng w i t h used m oul di ng sand and difficult waste sand reclamation. It is hard to find examples in literature concerning the ef f ec t i ve rec l am at i on of w at er-g l ass m oul di ng sands, w h i c h c an ac t i vat e t h e w ast e b i nder and rest ore t h ei r Abstract: The paper presents the research results of using an innovative method to reclaim the waste moulding sands containing water glass. Two of the examined processes are connected with "dry" or "wet" activation of inorganic binder in waste moulding sand mixtures physically hardened by microwave radiation. The sand mixtures consisting of high-silica sand and water-glass with average molar module 2.5, were subjected to the following cyclical process: mixing the components, compacting, microwave heating, cooling-down, thermally loading the mould to 800 °C, cooling-down to ambient temperature, and knocking-out. After being knocked-out, the waste moulding sands were subjected to either dry or wet activation of the binder. To activate thermally treated inorganic binder, each of the examined processes employed the surface phenomenon usually associated to mechanical reclamation. The study also covered possible use of some elements of wet reclamation to rehydrate waste binder. To evaluate the effectiveness of the two proposed methods of waste binder activation, selected strength and technological parameters were measured. After each subsequent processing cycle, the permeability, tensile strength and bending strength were determined. In addition, the surface of activated sand grains was examined with a scanning electron microscope. Analysis of the results indicates that it is possible to re-activate the used binder such as sodium silicate, and to stabilize the strength parameters in both activation processes. Permeability of the refreshed moulding sands strongly depends on the surface condition of high-silica grains. The wet activation process by wetting and buffering knocked-out moulding sands in closed humid environment makes it possible to reduce the content of refreshing additive in water-glass. The moulding sands cyclically prepared in both processes do not require the addition of fresh high-silica sand. The relatively high quality achieved in the refreshed moulding sands allows them to be reused for manufacture of next moulds. Thus, the two proposed methods for cyclically processing used moulding sands containing sodium silicate, subject to microwave hardening, are suitable for economic and ecological circulation moulding mixtures.

Presented are results of a research on usability of an innovative reclamation process of microwave-hardened moulding sands containing water-glass, combined with activation of binder. After each subsequent stage of reclamation, quality of the reclaimed material was determined on the grounds of measurements of permeability and results of screen analysis. The reclaimed material was next used again to prepare new moulding sand. The sandmix based on high-silica sand prepared with water-glass grade 145, was subject to the following cyclical treatment operations: mixing components, consolidation, microwave hardening, cooling, heating the mould up to 800 °C, cooling to ambient temperature, mechanical reclamation dry and wet. It was found that the used-up and reclaimed sandmix containing water-glass is susceptible to the applied activation process of thermally reacted film of binder and, in addition, it maintains good quality and technological properties of high-silica base. Observations of surfaces of reclaimed high-silica grains with activated film of reacted inorganic binder were carried-out using a scanning microscope. Thanks to properly selected reclamation parameters, the high-silica base can be reused even five times, thus reducing demand for fresh aggregate and inorganic binder.

The paper describes preliminary examinations on establishing usefulness criteria of foundry tooling materials in the microwave heating technology. Presented are measurement results of permittivity and loss tangent that determine behaviour of the materials in electromagnetic field. The measurements were carried-out in a waveguide resonant cavity that permits precise determination the above-mentioned parameters by perturbation technique. Examined were five different materials designed for use in foundry tooling. Determined was the loss factor that permits evaluating usefulness of materials in microwave heating technology. It was demonstrated that the selected plastics meet the basic criterion that is transparency for electromagnetic radiation.Keywords: microwaves, permittivity, loss tangent, loss factor, foundry tooling W pracy podjęto wstępne badania nad ustaleniem kryteriów oceny przydatności materiałów do budowy oprzyrządowania odlewniczego, przewidzianego do zastosowania w technologii nagrzewania mikrofalowego. Przedstawiono wyniki pomiarów przenikalności elektrycznej oraz tangensa kąta stratności, które określają zachowanie materiałów w polu elektromagnetycznym. Pomiary przeprowadzono na stanowisku falowodowej wnęki rezonansowej, która umożliwia precyzyjne wyznaczenie metodą perturbacyjną wymienionych parametrów. Badaniom poddano pięć różnych materiałów przewidzianych do zastosowania w budowie oprzyrządowania odlewniczego. Określono współczynnik stratności, który pozwala, na ocenę przydatności materiałów w technologii nagrzewania mikrofalowego. Wykazano, że wybrane tworzywa sztuczne spełniają podstawowe kryterium, jakim jest transparentność dla promieniowania elektromagnetycznego.