By using ProCAST numerical simulation software to study the lost foam casting process of the representative steel and steel bearing in bridge bearing, the advantages and disadvantages of horizontal pouring and vertical pouring are compared and analyzed. The influence of pouring temperature, negative pressure degree and pattern density on riser feeding of cast steel is studied and analyzed by orthogonal test, and the optimal combination scheme of process parameters is determined. At the same time, taking into account the production cost, economic benefits and other factors of the enterprise, the process scheme is further optimized, and the bridge bearing cast steel products with high process yield and high quality are produced. On this basis, the influence of different foams on the carburizing defects of steel castings and the influence of different foam materials on the chemical composition and mechanical properties of cast steel castings are studied. Finally, the following conclusions are drawn
1) for the steel and steel bridge bearing, the side bottom injection and vertical casting combined process are adopted. The metal liquid filling is more stable, the liquid level rises faster and the foam pattern gasification is more sufficient, which can effectively reduce the carbon defect, and can produce the steel castings with excellent internal quality.
2) The influence of pouring temperature, negative pressure degree and pattern density on feeding effect of steel support cast steel riser was studied by orthogonal test. The order of influence degree is: pouring temperature > pattern density > negative pressure degree. The optimal parameters combination scheme is as follows: pouring temperature 1680 ℃, pattern density 20g / L, negative pressure degree 0.05Mpa.
3) By adding external cold iron and adopting riser heating covering agent, the size of riser is reduced, and the process yield is increased to 65%. The numerical simulation analysis and small batch production verification show that the secondary optimization scheme can obtain lower cost and better quality of bridge bearing steel castings.
4) Based on the experimental study of carburizing defects in low carbon steel castings, the distribution law of carburizing defects in low carbon steel castings is analyzed as follows: from the inner gate along the soft moving direction of liquid metal, the longer the soft moving distance is, the more serious the carburizing degree is; when the soft moving distance is the same, the later the solidification time is, the more serious the carburizing degree is.
5) When EPS is used to produce low-carbon steel castings, the surface carburization is between 0.1% and 0.3%, and the volume carburization is between 0.01% and 0.04%. The chemical composition and impact toughness do not meet the quality requirements of bridge bearings; when using stmma to produce low-carbon steel castings, the surface carburizing amount is less than 0.1%, and the volume carburizing amount is less than 0.015%. The chemical composition and mechanical properties meet the quality requirements of bridge bearings.
6) It is found that the uneven distribution of pearlite and the edge angle of grain boundary are the main reasons for the unqualified mechanical properties of steel castings produced by EPS; the pearlite and ferrite are evenly distributed and the grain boundary is smooth in steel castings produced by stmma, which is beneficial to ensure the mechanical properties. Therefore, stmma is more suitable for the production of low carbon steel castings.
The above research conclusions have been applied and produced in ZHY casting, and obvious economic benefits have been obtained. This process scheme can be extended to other cast steel products with similar structure and material, and has certain practical value and promotion theory.