Effects Of Refractory Aggregates And Binders On The Properties Of Water-soluble Ceramic Cores

Water-soluble ceramic core is indispensable in the production of complex hollow thin-walled investment castings in light alloys.In this paper,ceramic cores were prepared based on the material of fused corundum powder and mullite powder as refractory aggregate using the method of compression molding,respectively.The effect of the contents of two water-soluble salt potassium sulfate and sodium chloride and preparation process conditions on the properties of ceramic cores was systematically evaluated.The ceramic core composition and forming process with superior comprehensive properties were determined.The core was prepared by hot die casting and the pouring experiment of aluminum alloy was carried out and the casting simulation software Pro CAST was used to simulate and analyze the forming process in the hot die casting and the temperature variation in the pouring process of the core,which initially accumulated relevant data for the core preparation and the process design of the casting in practical applications.The ceramic core was prepared with fused corundum powder and mullite powder as refractory aggregate and potassium sulfate as binder,and the properties of ceramic cores at sintering temperature of1000 ℃,1050 ℃ and 1100 ℃were studied,respectively.With fused corundum powder as refractory aggregate,when the additive amount of potassium sulfate is less than 20 wt.%,the strength of the core is high,but a small amount of fused corundum powder fell off on the surface of the core after the core was bathed in water at 80 ℃ for 6 h.When the sintering temperature is 1050 ℃ and the additive amount of potassium sulfate is 25 wt.%,the core has the best comprehensive properties,the bending strength of 5.53 MPa,the porosity of 30.68 % and the shrinkage of-0.50 %,and the core almost completely collapses in80 ℃ water for 6 h.With mullite powder as refractory aggregate,the strength of the core is high and the addition of binder has little effect on the strength of the core,but the dissolution collapsibility of the core is poor.After being immersed in water at 80 ℃ for 6 h,the surface of the core has no obvious change.With the increase of the sintering temperature,the dissolution collapsibility of the cores becomes poor within the temperature range studied.At the same sintering temperature,when the holding time is 60 min,the comprehensive performance of the core is optimal.Adding wood powder in the core that is composed of fused corundum and potassium sulfate can improve the porosity of the core and accelerate the watersoluble collapse speed,but significantly reduce the bending strength of the core.The ceramic core was prepared with fused corundum powder and mullite as refractory aggregate and potassium sulfate as binder,and the properties of ceramic cores at sintering temperatures of 775 ℃,800 ℃and 825 ℃were studied,respectively.The influence trends on the mechanical properties and dissolution collapsibility of the core with two refractory materials are similar.When the sintering temperature is lower than 775 ℃,the strength of the core continues to increase with the increase of the amount of sodium chloride and the core has superior collapsibility and completely collapsed in 80 ℃ water within 1 min.When the sintering temperatures are 800 ℃ and 825 ℃,and the additive amount of sodium chloride is 20 wt.%,the strength of the core is the highest.Continue to increase the content of sodium chloride,the strength of the core tends to be stable.Meanwhile,the dissolution collapsibility of the core is poor and there is no obvious change on the surface of the core after immersing in water at 80 ℃ for 3 h.When the additive amount of sodium chloride is less than 15 wt.%,the sintering temperature has little effect on the strength of the core and the dissolution collapsibility is worse.The core was prepared by hot die casting and the pouring experiment of aluminum alloy was carried out.Pro CAST software was used to simulate the thermoforming process and the optimal forming parameters of the core were decoded as follows: the die preheating temperature is 40 ℃,the injection pressure is 0.4 MPa,and the pouring temperature is 65 ℃.The ceramic core was prepared with fused corundum powder as refractory aggregate,30 wt.% potassium sulfate as binder and sintered at 1000 ℃.The bending strength of the core is 4.23 MPa,the porosity is 38.56 %,and the shrinkage is 0.95 %.The casting was poured with EN AC43000 aluminum alloy and the sample with diameter 14 mm and length50 mm can successfully dissolve and collapse after bathing in water at 80 ℃ for 10 h,and the forming quality of the inner cavity is terrific.The heating process of the core during the pouring process was simulated,and the accuracy of the simulation is analyzed in combination with the measured results.To improve the accuracy of the simulation,it is necessary to reasonably select the thermophysical parameters in the filling process.