Study On Strength Properties Of Phosphate Bonded Core Used In Investment Cast And Formed By Pouring

Based on the phosphate bonded cores used in investment cast formed by pouring (made of JXR, JXR-2 and JX-2 series core material), which were developed recently, the wet strength, dry strength, pre-fired strength, dip-strengthened strength, strength after stimulating shell firing, and residual strength after stimulating pouring casting were tested and studied. The result indicates the wet strength is very large, it is very easy to extract the cores from the wax by steam; furthermore, the wet strength will increase in the hardening and drying process of the cores; When the cores were fired under low temperature, the cores can not be strengthened fully by dipping silica sol because the wax has not been wiped off completely in cores; But after the cores adopting above the work procedure, firing the cores for 2 hours in 600℃, the cores can be strengthened fully by dipping silica sol because the wax has been wiped off completely in cores, but the strength of cores increase little with the increase of fired time and temperature; The strength of cores strengthened 2 times are larger greatly than the strength of cores strengthened 1 times; Among the cores, the strengthened strength of the cores (made of JXR core material) is largest, the strengthened strength of the cores (made of JXR-2 core material) is the second, the strengthened strength of the cores (made of JX-2 core material) is smallest.The cores after stimulating shell firing (firing thecores for 1.5 hours in 1000°C), the strength of the cores is enough to fulfill the requirement to the strength of cores in investment cast, and the strength is larger than the strength of the cores strengthened 2 times, hereinto, the strength of the cores (made of JXR core material) enhances most, the strength of the cores (made of JXR-2 core material) enhances secondly , the strength of the cores(made of JX-2 core material) enhances least .The cores after stimulating pouring casting (firing the cores for 2 minutes in 1550°C), the residual strength of the cores is smaller than the strength of the cores after stimulating shell firing, the average residual strength of the cores (made of JXR core material) is still highest, only 4.39MPa, but the average residual strength of the cores (made of JX-2 core material) is smallest, only 3.23MPa.After comparing with silica sol bonded core formed by pouring, it is found that phosphate bonded core formed by pouring, which possesses large wet strength, it is not easy to craze and get easily when manufacturing the cores, the residual strength of the cores is very small and the cores in castings is easy to be eliminated after pouring casting.