Study On Ultrathin Shell Of Shell Casting With Vacuum And Negative Pressure

In this paper, the high-strength shell specimens of vacuum shell casting was obtained by bauxite coatings added with modified binder α-starch or aluminum dihydrogen phosphate, respectively, with based binder silica or white latex and CMC.The dry strength and sintered strength of shell specimens influenced by the amount of two modified adhesive were researched. The microstructural changes of the specimens section, before and after adding adhesive as well as before and after heating, was analyzed by SEM. Meanwhile, the changes of adhesive effect of the specimens were discussed and analyzed. The changes of the chemical bond and chemical composition under different heating temperatures was analyzed by XRD and TG-DSC, combined with the change of microstructure to analyze the strength under the condition of adding aluminum phosphate monobasic.By analyzing the bending strength of specimens before and after adding α-starch,the average drying rate and dry strength as well as sintered strength of silica sol shell were improved by adding α-starch. The amount of 2% is the most appropriate,dry strength and high temperature sintered strength were twice and 4.67 times before adding α-starch respectively.By analyzing the bending strength of specimens before and after adding aluminum dihydrogen phosphate, when adding 5% to 9% aluminum dihydrogen phosphate, dry strength and sintered strength of specimens have been greatly improved, the maximum intensity can be improved 4.1 times and 1.8 times before adding aluminum dihydrogen phosphate respectively. At the same time, the specimens by adding aluminum phosphate monobasic were heated at 100℃~500℃temperature points, found that the specimen has the highest sintered strength when it was heated at 300℃ and kept 1h.By SEM analysis, specimen cross section α-starch added after the formation of a layer of film, film forming silica particles promotes the contraction of the skeleton and the refractory aggregate and silica particles which cover tightly wrapped. Shrink film coating of aluminum phosphate monobasic condensed molecules are also formed such that the cross-sectional structure of the specimen shows a dense,non-state micro-cracks, so add these two samples after final binder with a high dry strength. After the addition of the sample cross section at the 1400℃ high temperature sintering shows that the gap between the particles well block, smaller pores and the pore reduces.By XRD and TG-DSC curve analysis, specimen shows changes in the internal composition of a sample of aluminum phosphate monobasic modified mainly through three stages: the first stage at 100℃~140℃, volatile adsorbed water on the specimen and other impurities; the second stage at 150℃~180℃, as the temperature rising, TG curve shows the weight loss is still large at this stage, while distinct endothermic peak appears on the DSC curve, which is due to volatilization of the adsorbed water and Al(H2PO4)3 begins to dehydration condensation due into Al H2P3O10?H2O; the third stage at 220℃~300℃, since Al(H2PO4)3 dehydration condensation continued in this temperature range, TG curves of weight loss continues to occur in staircase while Al H2P3O10?H2O as the temperature rising, the bound water steadily lost, and further converted to Al PO4 and Al(PO3)3 phase, so a DSC curve appears a distinct endothermic peak again.When the temperature to300℃~500℃, stabilize the quality of the sample, don’t change weightlessness, and DSC curve no obvious, the emergence of the endothermic peak, show that the binder has been to stabilize the temperature stage of phase is present in the sample.