The gating system is mainly divided into three types as shown in the figure: pressurized (closed) gating system, decompression (open) gating system and non pressurized gating system. Other types of gating systems can be regarded as the mixture of at least two types above, which are collectively referred to as mixed (semi closed and semi open) gating systems.
The key feature of the pressurized gating system is the cross-sectional area of the gate, which is calculated according to the formula of free falling body and considering the friction force. When metal is introduced into the gate, the cross-sectional area of the sprue and the sprue will increase by 10-20% every time the gate is changed by 90 ° from the inner gate, and the cross-sectional area is always upward toward the gate cup
This creates pressure at the inner gate as soon as the gating system is filled with metal due to the pressure generated by the height of the metal (measured from the surface of the liquid metal in the upper part of the gate cup to the inner gate). In this system, the metal velocity at the gate will be the main factor to determine the filling time.
The key feature of the pressurized gating system is the cross-sectional area of the inner gate and the runner connecting the inner gate,
The other parts of the gating system are always pressurized towards the gate cup. The free fall formula similar to the pressurized gating system can be used for calculation. The cross-sectional area leading to the decompression part will be the main factor determining the filling time.
The characteristic of non pressurized gating system is that during the whole pouring process, the metal pressure of the main part of the system is zero, and the complete metal pressure will come at the end of the pouring process. Therefore, the non pressurized gating system is usually called “sewage system”,
This gating system may look similar to the other systems shown, where the upper horizontal runner is the same as the other gating systems shown, but will remain open thereafter. In this way, the cross-sectional area of the horizontal runner near the gate cup will be the main factor determining the pouring time.