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

Abstract

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.

Evaluation of the Possibilities of Sodium Silicate Sands Application in Automated Hot-Box Process of Cores Shooting

“…Sand made on a fine matrix, due to a larger proper surface area and reduced binder viscosity by addition to the matrix of 1% wt. of water proved to be a much more demanding core mixture in the shooting process than a traditional: manual or vibratory compaction [19]. As a result of linking the settings of the core shooter with moulding sand parameters there was small, as not exceeding 33%, "efficiency" in some series.…”

“…With the use of physical methods of drying, i.e. microwave heating [18], the binder content can be substantially reduced while preserving hydrophilic properties [19][20][21][22] of sodium silicate film. This advantages can be successfully used in reclaim methods [19] reducing the costs of casting.…”

“…Will similar phenomena be accompanied by hydrated sodium silicate sands, at the stage of hardening in hot core-box, should be further explained in the presented paper. In used sands with hydrated sodium silicate subjected to elevated temperatures it can be also noted that there is tendency for secondary hydration [19,20] of the binder in humid environment.…”

Recycling water glass from wet reclamation sewage of waste sodium silicate-bonded sand

“…S odium silicate-bonded sand casting is popular due to its advantages including good casting quality, low cost, and non-toxicity [1][2] . Currently, millions of tons of waste sodium silicate-bonded sand are produced in China every year, and cause serious environmental problems if not properly treated [3] .…”

“…Reclaiming the waste sodium silicatebonded sand refers to removing the impurities such as residual binder on the surfaces of the waste sand grains to regain a state close to that of new sand. Currently, the main methods for reclaiming the waste sodium silicate-bonded sand are wet reclamation and dry reclamation [1][2][3][7][8][9] . The reclaimed sand obtained by wet reclamation is better than that obtained by dry reclamation in quality, and can directly replace the new sand [10] .…”