Research on Reclamation and Activation of Moulding Sands Containing Water-Glass Hardened with Microwaves

Abstract

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.

Influence of wet activation of used inorganic binder on cyclically refreshed water glass moulding sands hardened by microwaves

“…B ased on t h e p revi ous researc h [4,5] , t h e c ont ent of t h e w at erglass grade 145 (average molar module = 2.5) in fresh moulding sands was set at 1.5wt.%. Moreover, to improve spreading ab i l i t y of t h e b i nder on surf ac es of t h e h i g h -si l i c a sand, 0.5wt.% of water was added to the ribbon laboratory mixer duri ng t h e p rep arat i on of t h e m oul di ng sands ( S t ag e 0 ) .…”

“…The first process, described in details in Ref. [4,5] referred as "dry activation", consisted of dry mechanical activation of g l assy sodi um si l i c at e usi ng a di si nt eg rat i ng and g ri ndi ng devi c e, ac c om p ani ed b y c ont rol l ed c ont i nuous rem ovi ng of t h e c reat ed dust y f rac t i ons ( S t ag e I ) . T h e sec ond m et h od so called "wet activation" began from wetting (with addition of water at 2.3wt.%) the knocked-out waste moulding sand and buffering it at ambient temperature in a closed chamber for 240 m i nut es ( S t ag e I ) .…”

“…5), which is followed by intensive mixing and stirring at "Stage II". As the previous st udi es sh ow ed [4,5,6] , it is important to keep the film of binder remained after effective disintegration of waste moulding sand, w h i c h i s susc ep t i b l e t o reh ydrat i ng . T h e ob servat i ons of t h e reclamation after the second, third, fourth and fifth processing c yc l es reveal ed l arg er num b ers of c ong l om erat es of si l i c a grains.…”

“…L i t erat ure dat a ab out rec l am at i on of b ondi ng m at eri al s l i k e sodi um si l i c at e are h ardl y avai l ab l e. A n exception is the Ref. [4,5], where preliminary research resul t s w ere p resent ed on t h e p ossi b i l i t y t o rec l ai m i norg ani c b i nder i n w ast e m oul di ng sands c ont ai ni ng sodi um si l i c at e, m i c row ave h ardened or t radi t i onal l y dri ed [ 6 ] . T h e ref resh i ng p roc ess w as c arri ed out i n t h e chamber of a laboratory roll mixer.…”

Effect of Electrical Properties of Materials on Effectiveness of Heating Their Systems in Microwave Field

“…A properly adapted stand of microwave slot line, described in [8], permits measuring collective percentage indices of power absorbed, reflected and transmitted through multimaterial systems like a batch of moulding sand in foundry instrumentation and also multicomponent systems like e.g. moulding sands.…”