MEASUREMENT OF ELASTIC MODULUS OF PUNB BONDED SAND AS A FUNCTION OF TEMPERATURE

摘要

The stiffness of molds and cores has a large effect on casting quality in sand foundries. Measurements of the elastic modulus of PUNB bonded silica sand are performed from room temperature to 500℃(932℉). The measurements are taken almost instantaneously during the heating to capture the changes in the elastic modulus throughout the temperature range. The effect of the heating rate is investigated in detail. For an intermediate heating rate of 8℃/min (14.4℉/min), the elastic modulus decreases steeply from a room temperature value of about 3,900 MP a to 600 MP a at 125℃(257℉). Above 250℃(482℉), it increases to 1,200 MP a at 280℃(536℉) and then decreases again to 900 MP a at 325℃(617℉). Above 350℃(662℉), the elastic modulus increases almost linearly with temperature until it reaches 2,400 MP a at 500℃(932℉). At approximately 500℃(932℉), the strength of the bonded sand vanishes. At elevated temperatures, the elastic modulus is found to be a strong function of the heating rate and time. For example, while holding a specimen at a constant temperature of 200℃(392℉)for 30 min, the elastic modulus can increase from 600 MP a to 2,000 MPa. Only the steady-state values of the elastic modulus are in agreement with previous measurements. Upon cooling to room temperature, the bonded sand regains its full stiffness only for holding temperatures below about 275℃(527℉). These variations in the elastic modulus with temperature correlate well with the physical and chemical changes the binder undergoes during heating. Additional experiments are needed to investigate the elastic modulus variation for higher heating rates and other binder systems.