Study On Forming Process And Properties Of Lost Foam Sheet For Ductile Iron Casting

By virtue of the excellent properties of nodular cast iron and the advantages of LFC(lost form casting),nodular cast iron is favored in automobile industry.However,in the process of producing nodular cast iron by LFC,some defects such as black slag and wrinkle skin will occur,which will lead to the deterioration of mechanical properties,which greatly limits the application and development of LFC nodular cast iron.Therefore,in order to reduce or even eliminate the defects such as black slag on the surface and internal of the lost form nodular cast iron,and improve the properties of the nodular cast iron.This paper mainly studies the properties of foam pattern material and gropes the forming process of lost foam sheet,and applies it to the lost foam casting of nodular cast iron,so as to reduce the internal black slag defect of nodular cast iron.Firstly,the combustion tests of STMMA and EPS were carried out,and the physical properties such as thermogravimetric analysis,differential thermal analysis,particle size distribution and volatility analysis were analyzed.The results showed that the combustion time or temperature was the same.The residual rate of STMMA is less than that of EPS,and the specific surface area is larger than that of EPS,and the average particle size and volume average particle size of STMMA are smaller than that of EPS.The amount of heat absorbed by STMMA in the process of gasification and decomposition is less than that of EPS.Secondly,STMMA beads were used to prepare STMMA plate,and then SEM and electronic universal testing machine were used to analyze the morphology of the raw material and the mechanical properties of the plate.The effects of prevacuum pressure,penetration I pressure,penetration II pressure and cooling time on tensile strength,elastic modulus,flexural strength and compressive strength were investigated.The results showed that the STMMA beads after prebubble had more honeycomb pores than EPS.Under the conditions of pre-vacuum pressure of 0.15 MPa,penetration I pressure of 0.12 MPa,penetration II pressure of 0.4 MPa,penetration pressure of 0.5 MPa and cooling time of 1600 s,the prepared STMMA sheet has the best mechanical properties.Finally,the application of STMMA sheet in nodular cast iron lost foam casting was tested.The surface morphology was analyzed by means of vhx-5000 superfield depth microscopy system,and the internal black slag was tested and analyzed by turning method.The effects of different plate materials on the surface quality and internal quality defects of large and small ductile iron with less than 4 tons were investigated.The results showed that the surface fluctuation range of ductile iron made by STMMA was within 108.59 ?m,while the surface quality of EPS in 1026 ?m was better than that of EPS.For the large and small nodular cast iron produced by EPS sheet,there is no black slag defect after 17 mm,and the small ductile iron produced by STMMA sheet has no black slag defect after 8mm.However,there are no black slag defects in large ductile iron castings after 13 mm production.It can be seen that the defect of black slag produced by STMMA is obviously lower than those produced by EPS,and the purpose of reducing the internal black slag defects of ductile iron castings is achieved.