The gating system is mainly composed of sprue. Molten steel enters the mold through the sprue. The sprue is divided into direct sprue, transverse sprue and internal sprue. The quality of sprue design will directly affect the quality of steel castings. For large steel castings, the design principles of gating system are as follows:
(1) Within the specified time, molten steel can fill the cavity to ensure the structural integrity of steel castings.
(2) Reasonably select the direction and position of molten steel entering the mold to make the liquid metal flow smoothly and avoid turbulence, which is conducive to the sequential solidification of steel castings and prevent local overheating.
(3) It has good slag retaining ability to prevent inclusion and pore defects.
(4) Ensure proper rising speed of molten steel in the mold cavity to prevent wrinkle and cold shut defects.
(5) Avoid the direct impact of molten steel on the mold wall and mud core.
The calculation of gating system of large steel castings generally adopts the weight speed calculation method and rising speed calculation method. According to the weight of the steel casting and the diameter of the casting hole, the appropriate method is to calculate the diameter of each casting hole according to the casting weight and casting time. The latter method is to determine the appropriate rising speed of steel castings during pouring according to the factors such as the structure and weight of steel castings, select the cladding hole diameter according to the rising speed, calculate the pouring time of steel castings, and then check the rising speed according to the height and pouring time of the mold. The latter method is widely used in the production of large steel castings.