Effect of Temperature on Chromite-Based Moulding Sands Bonded with Sodium Silicate

Abstract

In the paper, a research on effects of baking temperature on chromite sand base of moulding sands bonded with sodium silicate is presented. Pure chromite sand and its chromite-based moulding sand prepared with use of sodium silicate were subjected to heating within 100 to 1200 °C. After cooling-down, changes of base grains under thermal action were determined. Chromite moulding sand was prepared with use of 0.5 wt% of domestic made, unmodified sodium silicate (water-glass) grade 145. After baking at elevated temperatures, creation of rough layer was observed on grain surfaces, of both pure chromite sand and that used as base of a moulding sand. Changes of sand grains were evaluated by scanning microscopy and EDS analyses. It was found that changes on grain surfaces are of laminar nature. The observed layer is composed of iron oxide (II) that is one of main structural components of chromite sand. In order to identify changes in internal structure of chromite sand grains, polished sections were prepared of moulding sand hardened with microwaves and baked at elevated temperatures. Microscopic observations revealed changes in grains structure in form of characteristically crystallised acicular particles with limited magnesium content, intersecting at various angles. EDS analysis showed that these particles are composed mostly of chromium oxide (III) and iron oxide (II). The temperature above that the a.m. changes are observed in both chromite-based moulding sand and in pure chromite sand. The observed phenomena were linked with hardness values and mass of this sand.

Influence of sand base preparation on properties of chromite moulding sands with sodium silicate hardened with selected methods

“…Visible is segregation of elements and local loss of Mg in form of brighter areas (Figs. 1b-d) and characteristic needle-shaped grains [16] similar to Widmanstätten structure, see (Figs. 1c,d).…”

“…1b,c). Observed are also the changes caused by baking in internal structure of base grains, described in [16]. Visible is segregation of elements and local loss of Mg in form of brighter areas (Figs.…”

“…It can be seen in the photographs that a superficial rough layer grows with extension of baking time from 10 to 24 h. The about 1 to 2 μm thick layer (Fig. 1b) created after 10 h is overgrown by a layer of iron oxides [16] even to 3-3.5 μm (Fig. 1d), causing also sintering of grains (Figs.…”

“…Results of own research works [15][16][17] have inspired us to continue evaluation of chromite sand as prospective base of moulding sands that could be used as eco-friendly and economical moulding sands, possibly also as circulating foundry materials.…”

3D Printed (Binder Jetting) Furan Molding and Core Sands—Thermal Deformation, Mechanical and Technological Properties

“…In this regard, molding and core sand systems based on organic binders should not be considered the most environmentally friendly due to the emission of BTEX group compounds, which is an indicator of the environmental harm of the molding sands. Therefore, in recent years, much attention has been paid to inorganic molding and core sand systems [7][8][9][10][11][12]. Their significant advantage is their low emissivity, but they are not without disadvantages, including poor knockout properties [13,14], a limited reclamation ability, and unfavorable effects on bentonite (deactivation).…”