The application of bentonite in classical moulding sands

The article presents results of laboratory tests to develop a new generation of foundry hybrid bentonite. Hybrid bentonite is intended for use as binder for synthetic moulding sands and sandmixes. In the previous practice foundry bentonite was a product of processing of one type of montmorillonite clay coming from one selected deposit with a determined geological origin. Hybrid bentonite is not a homogenous material but a mixture of, most often, two or more materials, which come from several geologically different deposits. This material variety, according to preliminary assessments, gives a chance to obtain hybrid bentonite, which is not used in foundry practice, which has better, in certain scopes, physicochemical and technological properties. From preliminary tests it also results that these bentonites have a number of different parameters which are higher than the properties of previously produced binders for synthetic moulding sands. For tests of hybrid bentonites, which were conducted on a laboratory scale, while preparing batches of test bentonites both montmorillonite clays from several Slovakian deposits and bentonite loam of Polish origin were used. The tests were carried out in two stages, that is, during the first stage hybrid bentonite was obtained on the basis of two bentonites only from Slovakia, and during the second stage on the basis of selected Slovakian bentonite and Polish bentonite loam. In both cases the investigation resulted in achieving hybrid bentonites, which had higher not only physicochemical but also particular technological properties than initial bentonites which were used for the production of hybrid bentonites. These parameters include higher content of montmorillonite, higher wet compressive strength and compressive strength in the over-moisture zone, as well as high thermal durability comparable with the best materials.

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