Effect of Sand Wetting on Physically Hardened Moulding Sands Containing a Selected Inorganic Binder. Part 2

Abstract

In the paper, an attempt is made to explain the previously observed increased effectiveness of utilising hydrated sodium water-glass grade 137 after hardening moulding sands with selected physical methods. In the modified process of preparing sandmixes, during stirring components, water as a wetting additive was introduced to the sand-binder system. Presented are examination results of influence of faster microwave heating and slower traditional drying of the so-prepared moulding sands on their tensile and bending strength, calculated per weight fraction of the binder. The measurement results were confronted with SEM observations of linking bridges and with chemical analyses of grain surfaces of high-silica base. On the grounds of comprehensive evaluation of hardened moulding sands, positive effects were found of the applied physical process of binder dehydration and presence of the wetting additive. It was observed that introduction of this additive during stirring, before adding the binder, improves flowing the binder to the places where durable linking bridges are created. It was also found that the applied methods of hardening by dehydration enable creation of very durable linking bridges, strongly connected with the sand base, which results in damages of high-silica grain surfaces, when the bridges are destroyed.

Long-term Effects of Relative Humidity on Properties of Microwave Hardened Moulding Sand with Sodium Silicate

“…Moreover, high chemical activity of the binder hardened by microwaves was found. In the areas of its concentration, the binder participates in creation of many new structures with texture [17] (Figs. 10a, b, 11a), fibrous (Fig.…”

Effect of Sand Base Grade and Density of Moulding Sands with Sodium Silicate on Effectiveness of Absorbing Microwaves

“…Measurements of iron content, carried-out with an EDS analyser, clearly indicate that the sands originate from the same deposit. Selected inorganic binder (Table 1) thanks to physical methods of hardening can be classified to the highest 1st quality class binders [10,11], determined by bending R g U and tensile R m U strength calculated per 1 wt% of the binder. 6-kg portions of moulding sands for the examinations were prepared in a laboratory ribbon mixer in the following proportions (by mass, per 100 parts of moulding sand): 0.5 part of water were dosed to the base [10,11], then 1.5 parts of binder 137 were dosed in 60 s after starting the mixer and stirring was continued for 4 min.…”