The Effects Of High-Temperature Baking On Technological Properties Of Foundry Quartz Sand

Sand castings account for 80%-90% of the total casting production in foundry industry. Although sand casting production may decrease with new casting technologies emerging, it is asserted that the vast majority of castings would have to be produced by sand casting technology. In developed countries, reclamation of moulding materials has been studied for almost a century and the reclamation technology of the used sand has been developed and popularized, which has led to higher casting quality, lower consumption of the natural resources and less environmental pollution. The annual 12 million tons of sand casting production has ranked China the first in the world, with about 120 million tons of sand needed. If, say, 1/10 of the sand is discarded, 12 million tons of used sand would be wasted. It is well-known that the temperature-resistant and high-quality quartz sand is needed for most casting production. China, however, lacks the reserve of it as comparedwith the consumption, so it is of great significance to study and popularize the reclamation technology of the used sand in China.Reclamation of used sand is a technology to recover its technological properties mechanically, physically or chemically so as to reuse the claimed sand. In the past several decades, foundry scientists in China have focused their study on reclamation equipment and technology, with lack of overall research of used sand quality.In view of the above situation, the following study is conducted. With foundry quartz sand samples from four sources of Dalin of Inner Mongolia, Pingtan of Fujian, Weichang of Hebei and Muping of Shandong, their technological properties of new and baked sand have been examined and studied. The effects of high-temperature baking on technological properties have been analyzed.The sand has been baked one to six times in a high-temperature oven to simulate casting and reclamation process. After that, their technological properties of new and baked sand have been examined. It is shown that evaporation capacity, proportion of gravity to volume, loss of ignition, grain size, tensile strength and thermal expansion of new sand vary with sand from different sources. The above properties of sand after different times of baking change in the direction favourable for improving the casting quality, with less evaporation capacity for quartz sand, evidently higher tensile strength for resin sand, and basically constant grain distribution.A device for the detection of the thermal expansion has been developed, and the experimental method and procedure have been designed Comparison of expansions between slow heating and abrupt heating proves the usefulness of the device. It is found that volume thermal expansion ofthe sand from the various sources is less than 5% within 1000C. Furthermore, it is indicated that their volume expansion is becoming smaller and smaller with the baking times, which shows that the expansion is incompletely reversible. The thermal expansion rate in quasi-equilibrium is obviously different from that under abrupt heating near casting condition, with the former bigger than the latter generally.To sum up, high temperature has obvious effects on the technological properties of quartz sand, which, however, are favourable for casting production. The result indicates that the properties of reclaimed quartz sand can totally assure the quality of casting production and can even be better than those of new sand. Therefore, this study may provide scientific evidence for application and popularization of reclamation of used sand.