Study On The Influence Of Raw Material Particle Gradation And Mineralizer On The Properities Of Magnesium-based Ceramic Core

In this paper,refractory magnesium oxide is used as the matrix,CaCO₃ and Al₂O₃ as mineralizers,and wood powder as pore-forming agent.The magnesium-based ceramic core is prepared by the compression molding method,and the effects of mineralizer,pore former,preparation process and sintering process on the bending strength,sintering shrinkage,porosity,fracture morphology and phase composition of the core were tested.The collapsibility of the core in acetic acid solution was tested,too.With magnesium oxide of 400 mesh as the matrix and Al₂O₃ with different particle sizes as the mineralizer,the cores were prepared.As the Al₂O₃ particle size decreases,the bending strength of the ceramic core increases,but the collapsibility becomes worse.The effect of different particle gradations of magnesium oxide on the core performance was studied with magnesium oxide of 150 mesh,200 mesh and 400mesh as the matrix and Al₂O₃ as the mineralizer.When the mass ratio of the different particle sizes of magnesium oxide powder is M₁₅₀:M₂₀₀:M₄₀₀=60:35:5,and the mineralizer Al₂O₃ particle size is 25?m,the overall performance of the core is the best.At this time,the bending strength of the ceramic core is 12.02 MPa,the porosity is25.93%,the sintering shrinkage rate is 0.53%.The mass loss rate of the ceramic core is 37.59%when soaked in acetic acid solution for 10h and its collapsibility is good.The ceramic core is prepared with magnesium oxide powder of 400 mesh as the matrix and CaCO₃ as the mineralizer.With the increase of CaCO₃ addition,the bending strength of the core decreases;extending the holding time at sintering temperature reduces the collapsibility of the core.When the addition of CaCO₃ is 5%,the sintering temperature is 1340?,the molding pressure is 6MPa,and the holding time at sintering temperature is 0.5h,the overall performance of the core is the best.At this time,the bending strength is 24.03MPa,the sintering shrinkage rate is 0.97%,the porosity is 28.12%,and the core loss ratio is 55.80%soaked in acetic acid solution for 10h,which is better than that of Al₂O₃ Mineralizer.It was found that the properties of the ceramic core with 5wt.%CaCO₃ addition changes slowly with the variation of sintering temperature and has better stability.In order to further improve the collapsibility of the ceramic core,the ceramic core is prepared with magnesium oxide of 400 mesh as the matrix,CaCO₃ as the mineralizer,and 200 mesh wood powder as the pore former.The addition of the pore former effectively improves the collapsibility of the core,but also reduces the bending strength of the core.When the addition amount of CaCO₃ is 5%and the addition amount of wood flour is 1%,the overall performance of the ceramic core is the best.At this time,the bending strength is 10.56 MPa,the sintering shrinkage rate is 0.46%,the porosity is 31.31%,and the collapsibility is good.The core is strengthened with epoxy resin as the strengthening agent.The strengthening effect is significant and the bending strength of the ceramic core increases from 23.28 MPa by 86%to 43.39Mpa.Ceramic cores are use d in preparing stainless steel castings and their shake out property was tested.Three kinds of ceramic cores were fabricated with the addition of wood powder of 1wt.%,3wt.%and 5wt.%,respectively.The dissolution rate of ceramic cores with 5wt.%wood powder is the fastest,which is 0.78mm/h;the dissolution rate of ceramic cores with 3wt.%wood powder is the slowest,which is 0.49mm/h.