Research on graphite casting technology of large size titanium alloy valve body

Titanium and titanium alloys are widely used in aerospace, Marine, petrochemical, medical and other fields because of their excellent properties such as low density, high specific strength, corrosion resistance, high temperature resistance and low thermal expansion coefficient. At present, with the improvement of the performance demand for titanium alloy products, higher requirements have been put forward for titanium alloy castings and their casting process, such as higher molding quality requirements, larger casting volume, and more complex forming structure.

At present, there are two main processes for titanium alloy molding, investment casting process and machining graphite molding process. Due to the difference in refractoriness of the molding material, the surface quality of the casting produced by investment precision casting is better than that of graphite casting, but the production cost is higher, and it is mainly suitable for small and medium-sized castings. For the casting process of large size titanium alloy castings, if the investment precision casting technology is used, it is difficult to make the shell, and the wax mold is easy to deform. The graphite mold casting process has the advantages of flexible parting surface selection, short preparation cycle and simple molding, which is suitable for the production of large-size titanium alloy castings, so the machined graphite mold casting process is adopted. Through graphite casting technology, Yan Ping successfully cast 120 kg titanium alloy castings with an overall size of 880 mm×740 mm×530 mm, and the wall thickness ratio of the shell castings reached the highest 1:10. The Ti321 alloy axle box castings produced by Fan Shixi have a profile size of 900 mm×350 mm×450 mm, which is relatively complex in structure, but the overall weight is about 69 kg. The titanium alloy graphite casting casting, although the overall size is large, but the casting quality does not exceed 150 kg.

The high speed centrifugal casting is used to improve the filling effect of liquid metal, and the centrifugal casting can also reduce the internal shrinkage and other defects of the casting to a certain extent. For large size and large mass titanium alloy castings, gravity casting is usually used to avoid damage to the cast due to metal liquid impact, but at the same time, the number of defects in the casting will increase under the action of losing centrifugal force.