Research On The Expendable Pattern Casting Process And Carbon Defect Of Bridge Bearing

Lost foam casting(LFC)is a near-net forming technology,which has the advantages for the flexible design process,low production cost,less environmental pollution,and higher product quality.Lost foam casting technology is widely used,but there are few researches and applications in the field of low carbon steel.The main limitation of its promotion and application is the carbon defects.With the increasing demand of low carbon steel castings,how to solve the carbon defects of steel castings has become an urgent technical problem.In this thesis,a kind of steel casting for bridge bearing was taken as the research object.Based on ProCast numerical simulation software,the simulation of the mould filling and solidification process of LFC was carried out.Combined with production verification and experimental research on carbon defects,the optimal process was determined.The program aims to improve the quality of products and reduce production costs,and to promote the development of lost foam casting technology in the field of low carbon steel.Based on the structure of the product,two pouring schemes were designed in this thesis: horizontal pouring and vertical pouring.Through numerical simulation analysis and production verification,it was found that the metal liquid filling model was more stable when vertical pouring,the liquid level rise faster,the foam pattern was more fully gasified,and the defects of the test pieces were less after production and processing.The influence of pouring temperature,vacuum degree and pattern density on riser feeding was studied by orthogonal test method.The optimal parameter combination scheme was determined as follows: pouring temperature 1680℃,pattern density 20g/L,vacuum degree 0.05 MPa.In order to reduce the production cost,the process scheme was optimized for the second time,and the product yield rate was increased to 65% by adding external chill,adopting exothermic covering agent,and reducing the size of the riser.By using EPS and STMMA foam materials as sample production and experimental study,the distribution rule of carbon defects and the influence degree on the chemical composition and mechanical properties of steel castings under different foam materials were compared.The results showed that when EPS was used to produce low carbon steel castings,the surface increased carbon content ranged from 0.1% to 0.3%,the volume increased carbon content ranged from 0.01% to 0.04%,and the chemical composition and impact toughness did not meet the quality requirements of bridge bearings.When STMMA was used to produce low carbon steel castings,the surface increased carbon content less than 0.1%,the volume increased carbon content less than 0.015%,the chemical composition and various mechanical properties met the quality requirements of bridge bearings.The research conclusion of this thesis can guide the production of low carbon steel castings for bridge bearings,and met the requirements of production enterprises for product quality and economic benefits.