The Influence of Benzoyl Peroxide on Gelation Rate of Silica Binder for Precision Casting

Substituting of ethyl silicate with ecologic sols of colloidal silica in the investment casting technology, resulting from the increased demands concerning environmental protection, caused the prolongation of production cycle for precision castings produced in multi-layer thin-walled ceramic shell moulds. Modification of Sizol 030 binder with benzoyl peroxide, proposed in the paper, was aimed at restriction of time needed for realization of a single layer of the shell mould, and by the same, of such a mould as a whole. Examination of kinetics of the drying process were held for the layers made of prepared moulding material and the influence of binder modification on the mould curing time was determined

Structure and selected properties of high-aluminium Zn alloy with silicon addition

The results of examinations concerning the abrasive wear resistance, hardness, and thermal expansion of high-aluminium zinc alloys are presented. The examinations were carried out for five synthetic ZnAl28 alloys with variable silicon content ranging from 0.5% to 3.5%, and – for the purpose of comparison – for the standardised ZnAl28Cu4 alloy. It was found that silicon efficiently increases the tribological properties and decreases the coefficient of thermal expansion of zinc alloys. The most advantageous set of the examined properties is exhibited by the alloys containing over 2.5% Si. They are characterised by higher parameters as compared with the standardised alloy. Observations of microstructures reveal that silicon precipitates as a separate compact phase, and its morphology depends on t he Si content in the alloy. The performed examinations show that silicon can satisfactorily replace copper in high aluminium Zn alloys, thus eliminating the problem of dimensional instability of castings

The investigation of properties of investment casting moulds reinforced with ceramic fibre

Abstract Increasing of strength and permeability of the thin-walled investment casting ceramic moulds was the main goal of this work. Its essence is a new concept of the mould reinforcement, i.e. the full or the significant replacement of grain silica materials by fibrous aluminosilicate materials. An addition of ceramic fibre increase the permeability and green strength value of the ceramic shell mould material which allows for safe burning out of the pattern set