Study On Modification Of Sodium Silicate Binder For Sand Mould 3D Printing

The moldless casting technology based on sand-based additive manufacturing provides a technical basis for the foundry industry to shift to intelligent production.Three-dimensional printing（3DP）technology has many advantages.As more and more stringent national environmental protection policies and regulations are introduced,and new green binders are developed,inorganic water glass is expected to replace resins as a new generation of 3DP binders.However,the performance of the common casting water glass binder is still a certain distance away from the sand mold 3DP production requirements.Carrying out research on modification of water glass to make it suitable for sand mold 3DP technology has become a very important subject in the field of sand mold additive manufacturing.In this paper,modifier1 with molecular weight of D230（R_nO_nNH₂）,modifier2 with molecular weight of 200（HOR`_n）and modifier3（R``OH）are used as modifiers for casting water glass（Na₂O?mSiO₂）,and sand samples were prepared with 70/140 mesh silica sand as raw sand,and the effects of modifiers and their additions on the fluidity of water glass and the strength,hygroscopicity,and disintegration of water glass sand were studied.The mechanism of modification is analyzed.The research results show that the three modifiers modifier1,modifier2 andmodifier3 can improve the fluidity of the water glass solution to different degrees,and can increase the strength and collapsibility of the water glass sand.Modifier2 andmodifier3reduce the hygroscopicity of water glass sand.There is no chemical reaction between modifier1 and water glass solution,but not simple mechanical mixing between the two,the intermolecular hydrogen bond is formed between modifier1 and water glass,and it is adsorbed on the surface of polysilicic acid colloidal particles.Add 0.8wt%modifier1 to the water glass solution,the fluidity of the water glass solution is increased by 9.2%,the binder is added 4wt%to 6wt%,the tensile strength is 0.905MPa to1.678MPa,about 13%to 45%increase,the residual strength is 0.026 MPa to 0.157 MPa,which is reduced by about 60%to 91%.It has little effect on the bending strength of water glass sand,but the hygroscopicity of water glass sand is increased by about 78%.Modifier2 reacts with the water glass solution to form a high molecular organic silicon compound,which changes the network structure of the colloidal silica particles.Add 1.2wt%modifier2,the fluidity of the water glass solution is increased by 15%;the binder is added 4wt%～6wt%,the tensile strength is 0.915MPa to 1.768MPa,an increase of about 8%to 47%,the bending strength is 3.882MPa to 4.941MPa,it can be increased by about 4%to 14%;the residual strength is between 0.047MPa and 0.089MPa,which is reduced by about 48%to 85%,which improves the collapsibility of water glass sand;the hygroscopicity is reduced by about45%.Mannitol reacts with water glass solution to produce organosilicon compound and sodium hydroxide.Adding 0.3wt%modifier3 to the water glass solution improves the fluidity by 22.8%.Adding 4wt%to 6wt%of the binder,the tensile strength at room temperature is as high as1.712MPa to 2.140MPa,an increase of about 35%to 175%,the bending strength is 4.305MPa to 5.359MPa,an increase of about 3%to 42%;the residual strength is 0.011MPa～0.041MPa,a decrease of about 86%to 95%,hygroscopicity is reduced by about 46.3%.