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Nekateri dejavniki, ki vplivajo na utrjevanje peščenih mešanic za ester-silikatni postopek = Some factors that control the hardening of soda-water glass ester bonded sands
Uršič, Vito ; Mlakar, Franc ; Slabanja, Branka
Influence of different parameters upon hardening of soda - water glass - ester bonded sand mixtures was investigated. Instead of ▫$CO_{2}$▫-gas a liquid hardening substance - ester - was used since ...its distribution is more even than that of the gas. This process is especially suitable for manufacturing massive moulds and cores. Beside several advantages there is one great disadvantage - the hardening intensity is much lower at lower temperatures (Table 1). In the near past it was possible to buy suitable soda-water glasses and esters in other parts of Yugoslavia, now they must be imported or should be developed in our factories. In one of our foundries a soda-water glass ester bonded sand for moulding was used but in manufacturing heavy moulds several problems appeared because of slow hardening, especially during the wintertime. In the laboratory tests silica sand (medium grain size - 0.16 mm) and soda-water glass (M = 2.79) which had been used in the foundry, both from Termit Domžale, were used. Two applied esters - M1 and S1 - were imported from Austria and the third one - D 10 - from Teslić in Bosnia. The results of hardening the sand mixtures with different additions of the binder and of the ester are presented in Figs. 1 and 2. At lower temperatures a mixture of esters (85% M1/15% S1) was used (Fig. 3). Furthermore an influence of mixing time and of the sequence of soda-water glass and ester additions were to be determined. It was found that much better results were obtained with the ester M1 if it was admixed to dry silica sand the first, and after 3 minutes of mixing soda-water glass was added, and all was mixed for further 2 minutes (Fig. 4). In Termit Domžale two samples of soda-water glasses with M = 2.40 and 2.72 and two esters - T1 and T2 - were prepared. The later ones were compared to the esters M1 and D 10 (Figs. 5, 6) but till now results were not yet encouraging. According to the results it was proposed to use in future silica sand with greater grain size and soda-water glass with a lower modulus M. Furthermore the temperature in workshops should be rised during cold periods. The preparation of sand mixtures should be under supervision and their properties tested. It has to be taken into account specificities of this process and the producing technology should be adapted.
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