Large castings are not rare in iron mold sand coating process casting, but for large engine crankshaft castings with large cross-section and large transverse size, the sand coated iron moldis still lack of experience. In particular, as an important part of the engine, crankshaft bears the force from the connecting rod and outputs torque to the outside. In the engine work, the crankshaft is subjected to the combined action of centrifugal force of rotating mass, periodic gas pressure and reciprocating inertia force, which makes the crankshaft bear bending and torsion load. Therefore, the crankshaft casting is required to have sufficient stiffness and strength, and each working surface should be wear-resistant and smooth, so as to ensure its service life, safety and reliability.
The quality of C3000 crankshaft with sand coated iron mold developed by ZHY casting was unstable in the early stage of production, and the casting defect rate of air-conditioning spacer (Fig. 1), slag hole (Fig. 2) and sand hole (Fig. 3) remained high. Bad factors seriously affect the strength of the product, weaken the ability of the casting to bear load, reduce the mechanical properties of the casting, and even produce fracture, so the service life and reliability can not be guaranteed. Therefore, it is imperative to solve these kinds of defects, but the measures to solve the problems are large and broad. In this paper, combined with the principle and location of production quality problems in the early stage, the sand coated iron mold casting process is reasonably improved to control the formation of defects.
After the optimization and improvement of sand coating process for large engine crankshaft iron mold, the mature process has been applied in actual production. After long-term production verification, the defects such as cold shut, air trap, sand hole and slag hole have been significantly improved, and the comprehensive rejection rate has been reduced from 23.9% to less than 5%, which effectively reduces the quality cost of the product.