Study On Preparation Technology Of High Strength Water Soluble Salt Core For Casting

With the development of lightweight technology,more and more castings are made of cavity structure.It is difficult to form the complex inner cavity structure under the production of high pressure casting.The water-soluble salt core can be dissolved in water because of it has low gas evolution,if we want to use it in the production of die casting,it need to have high strength to resist the high-speed impact of liquid high pressure metal.Bending strength and water solubility were considered as the main indicators,the preparation technology of multi-component composite salt cores was studied.Firstly,salt core bending sample of the cold-setting furan resin sand mold was prepared by melting pouring method.Several kinds of salt were combined because of the strength of monocomponent salt core was low.Sodium chloride and sodium sulfate were determined as basic materials by experiments.The ratio of compound salt component was optimized by orthogonal test: sodium chloride: sodium sulfate: barium chloride =6:4:1,the bending strength of the salt core can reach 27.9MPa,the water soluble time is 15 min at room temperature.When the water temperature is 85?,the water-soluble time is 2min.Secondly,the ceramic powder were added to the matrix material to enhance the salt core.It was found that the ceramic powder have the best addition that the bending strength of the salt core can reach 32.3MPa,the water soluble time is 13 min at room temperature,the water temperature is 85?,the water-soluble time is 3min when the 20wt% alumina ceramic powder is added to the matrix material(sodium chloride: sodium sulfate=7:3).Thirdly,the formability of the salt core was studied,in which the shrinkage rate of the ternary salt core of barium chloride compound is 3.04%;The shrinkage rate of salt core at this time is 3.35% when the amount of alumina ceramic powder is 20wt%.The excess of the ceramic particles could lead to the poor fluidity of the molten salt and the difficult filling of the molten salt.In addition,the slow cooling process after pouring was adopted in order to prevent the cracking of salt core.Next,two kinds of strengthening mechanisms to improve the strength of salt cores were theoretically studied.The grain size of the ternary composite salt core is finer and denser,and there is a large number of composite phases between the grains.In the ternarycomposite salt core with barium chloride,the main component of the composite phase is barium sulfate.The dense and uniform distribution at the composite phase at the grain boundary of the matrix phase can effectively consume the energy of crack propagation,and the existence of ceramic reinforcements can reduce the columnar grain region of the salt core.In addition,ceramic powder and the distribution of miscible phase in salt cores increases the bending strength of salt cores.Finally,the field experiment was carried out,cylindrical salt cores were prepared and tested on the die casting site.The results show that the strength of the salt core is high enough,and the inner cavity surface is bright and clean,the size is precise,and the water soluble time is short.The expected technological effect is achieved.