Solution of air gap defect in crankshaft casting of large engine

The air-conditioner of the defective product is mainly located at the highest point of the mold, i.e. 2 and 5 turns (as shown in Fig. 1, the dark position). Through the simulation and analysis, it is found that the filling speed of the mold becomes slower, the filling ability becomes worse, and even there is a situation that the molten iron can not be poured into the mold for a short time, which indicates that the reaction of the liquid iron by the air pressure in the mold cavity is relatively large. In this case, the pressure difference of molten iron is insufficient, and the gas in the mold cavity can not be discharged in time, which hinders the flow of molten iron. The corresponding specific rectification measures are as follows.

Increase the static pressure of molten iron

The height of the gate cup is increased from 200 mm to 300 mm ~ 350 mm, and the height difference between the gate cup and the highest point of the mold is increased, so as to obtain the pressure difference between the two highest points of the gate cup and the molten iron, and improve the filling capacity of molten iron (as shown in Fig. 2).

Set vent

The process optimization and improvement of the iron mold were carried out, and the vent holes were set at the highest points of 2 and 5 turns and other necessary positions. The exhaust needle (Tooling) is installed from the back of the upper iron mold and is injected together with the iron mold. After installation, there is about 10 mm sand covering gap between the exhaust needle (Tooling) and the mold. After the injection, remove the exhaust needle (Tooling) from the back of the iron mold, so that there is only left between the upper surface of the iron mold and the casting mold When the thickness of sand covering is about 10 mm, compared with the previous airtight iron mold or the perforation with thick film coated sand, the exhaust capacity is more powerful, thus solving the problem of poor exhaust performance of casting mold. The exhaust needle structure is shown in Fig. 3.