Contribution to determination of the life time of chemically self-hardening mould sand

The article presents the problem of quality of casting moulds made of self-hardening sand, especially for manufacturing moulds for large-sized iron alloy castings. In such cases, unequivocal determination of so-called time of life of moulding sand is one of the most important issues, since it affects usability of a self-hardening sand for making subsequent layers of the mould prepared in time above one hour. Life time, measured in minutes, is dependent on the type of used sand grains, resins and their hardeners (catalysts) and also on the temperature and air humidity. Companies which manufacture and sell binding materials estimate the time of life according to their own criteria, which do not always correspond with real conditions. This article shows the experiences of the author, who has been working as an expert in European foundries for many years. New proposed parameter named FIP characterizing a life time of tested sands is also presented.