The pre-foamed parts of low-pressure castings are usually more precise in size and less likely to deform. Compared with sand casting, its internal quality has fewer pores, smooth surface, and can achieve various mechanical properties. The vanishing foam has matured in ordinary cast iron technology.

When lost foam is used to produce steel castings, the castings undergo surface carburization, volume carburization, and local carburization. Carburizing mainly occurs in low-pressure cast low-carbon steel castings, and the carbon mass fraction is usually0.08-0.4%, there is a large inhomogeneity in the re-carburizing of steel castings. For castings with different molten steel compositions, the carburization of the same different parts of the same part is also different, which depends on the model material, the position of the inner runner and the pouring speed. Regarding the size, the carbon addition of steel castings will reduce the processing performance of the castings, thereby affecting the quality of welding heat treatment, and even scrapped.

The reason is that, in the low-pressure casting process, the pattern undergoes pyrolysis and gasification under the action of high-temperature molten steel. Some of the pyrolysis vapor is discharged from the casting mold, and another part of the pyrolysis product collects in the coating between the molten steel or in the gap between the mold and the molten steel. Carbon diffuses in the liquid and solid phases of molten steel. It can be seen that the diffusion activity of free carbon on the interface between molten steel and solidification is much greater than the diffusion coefficient during filling and condensation, allowing convective mass transfer and carbon diffusion into molten steel. Mass transfer will result in increased carbon content in low pressure castings.

How to prevent carbon increase;

1,There are many reasons for the increase of carbon in castings. According to different process measures, the way of reducing carbon increase and usingEPMMA,STMMA copolymer foam material or low density EPS to reduce carbon increase and reduce the carbon content of pyrolysis gasification

2、Increase the temperature and pouring speed of molten steel, make the gasification speed as balanced as possible, reduce the contact time of pyrolysis liquid and molten steel, and speed up the gasification speed. The permeability of the coating is increased in order to discharge the pyrolysis products as quickly as possible.

3,The vapor can be quickly discharged from the low pressure casting mold by selecting the appropriate vacuum degree and air flow rate. Excessive vacuum may cause sand particles to stick.

4,Adopting a suitable pouring position and introducing the inner runner from the thin wall is beneficial to the accumulation of pyrolytic substances in the riser and reduces the carbon increase of the low-pressure casting.