Study On Water Soluble Sodium Carbonate Core Formed By Hot Pressing Sintering

With the rapid development of domestic automobile industry and the structural trend of automotive lightweight,the application demand of aluminum alloy castings has been greatly increased.In the production of Aluminum Alloy castings with complex cavity or curved pipe structure,being scattered by water,small pollution and low energy consumption of the water soluble core technology have broad application prospects.At present,the limitation of water soluble core lies in its relatively low strength,poor moisture absorption performance and high equipment requirements.In this paper,the water-soluble sand cores are taken as the research object.After the advantages and disadvantages of various kinds of water soluble sand core making process are summarized,the hot pressing sintering core is put forward on the basis of hot pressing and pressing sintering.Making ten water sodium carbonate as the binder and siliceous sand as collective materials,this thesis researches hot pressing technology in formulation process and molding process,the sintering process of core strength and collapsibility of water soluble effect.The main content in this paper is following:(1)The influence of the amount of sodium carbonate added in the hot pressing sintering process,the amount of bentonite,the heating temperature,the heating time,the sintering temperature and the sintering time on the tensile strength of the core were studied.The results show that the strength of the core increases first and then decreases with the change of the parameters.When the amount of sodium carbonate was 40%,the amount of bentonite was 7%,the heating temperature was 150 ?,and the heating time was 10 min,the initial tensile strength of the core was 1.1MPa.When the sintering temperature was 850 ?,sintering time is 30 min,the core sintered strength is the highest,6.4MPa.(2)The bonding mechanism of the hot press process was analyzed.The influence of heating time and heating temperature on core water content and core strength was studied by thermogravimetric analysis.Reasonable heating system to fully crystallize the inorganic salt at the same time,the bentonite retention of trace moisture and thus provide the core enhancement effect.The effects of the amount of sodium carbonate added and the amount of bentonite on the morphology of the inorganic salt on the surface of the sand were analyzed by electron microscopy.(3)The strengthening mechanism of the sintering process was analyzed.Combined with core strength analysis,electron microscopy scanning analysis,water solubility test,the sintering reaction can be divided into three stages over time: the first stage,the core due to dehydration and lower than the initial strength;the second stage,From the adhesion of sodium carbonate on the surface of the sand into the cohesion of sodium carbonate,the core at this time to obtain a higher sintering strength;the third stage,the basic conversion of sodium carbonate into a new phase,a significant reduction in water-soluble properties,Mainly provided by the new phase,core strength reduction or even bending deformation can not be used.