Over-moisture zone in moulding sands with water glass - ultrasonic investigations of kinetics of its formation

摘要

The changes of the properties of moulding sands in the parts of mould during the solidification and cooling of castings are now not well known. In the study the investigation results of the moulding sand with water glass are presented. In the investigations carried out with the utilization of the new ultrasonic method, elaborated by the author, it was indicated that the quick heating of moulding sand with water glass leads to formation of the over-moisture zone. It means, that in the subsurface layers of the mould the strength of moulding sand in the first period of heating decreases to approx. 10-20 percent of its initial value. Then the moulding sand with water glass also loses its elastic properties. Such changes in the properties of the moulding sand favour the mould deformation under the effect of the metal pressure. The subsequent heating causes an increase of the strength, what results in the worsening of the knockout properties. The over-moisture zone, known hitherto in the classic moulding sands, is the cause of a lot of detects, such as: sand buckle, wavy surface and discrepancy of the shape and dimensions. The existence of the over moisture zone, shown by the author allows to understand better the reasons of some difficulties during the production of castings in moulding sand with water glass, difficulties which are known from industrial practice The author basing on his own solutions, has proved that the ultrasonic method allows to monitor not only the hardening process of moulding sands with binders, but it also allows to investigate the kinetics of the properties changes of these sand mixtures during their heating. It is a new domain of investigations.