Studies of hardening kinetics of selected self-hardening masses at low temperatures

The article presents an analysis of the kinetics of the hardening process of self-hardening masses. In this study, moulding sand with a quartz sand grain matrix by Sibelco, main fraction F_m 0.40; 0.32; 0.20 mm, was used. Two resins were used as binders. The first tests were performed on a mass with phenol-formaldehyde-phurphuril resin (FF/AF), hardened with methylbenzenesulfonic acid. The hardener was added to the mass in two variants: with a low concentration - the so-called "slow" hardener - and a high concentration - the "fast" hardener. The second examined mass was a mass with urea-formaldehyde-phurphuril (MF/AF), which was, in turn, hardened with p-toluenesulfonic acid. Similarly to the case of the first resin, the hardener was applied in two concentrations - low and high. The measurements were made on a bench for ultrasound tests on moulding sands. During the examinations, the course of the hardening process was determined, and more precisely, the change in the time of the longitudinal ultrasound wave’s passing through the newly-prepared moulding sand sample was recorded. On this basis, the velocity of the ultrasound waves passing through the mass in time C_L = f(t) was determined, which was, in turn, the basis for the determination of both the change in the hardening degree of the mass in time, that is S_x = f(t), and the kinetics of the hardening process dS_x/dt. The tests of the mass binding process were performed at 10°C.

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