When molten metal passes through the gate, its filling methods can be divided into three types: laminar filling, jet filling and atomization filling. When the gate speed is low, the filling mode is laminar flow; When the speed increases, the molten metal no longer flows out continuously, but is ejected in the form of coarse particles; At higher speeds, water will be ejected as fine particles in the mist. Laminar flow filling or fog flow filling can produce satisfactory castings, but coarse particle flow filling is not good because of the large heat loss during filling. Generally speaking, the thinner the gate, the higher the gate speed to reach the atomized flow state.

The flow state of molten metal entering the cavity is determined by the form of runner and inner gate. At present, there are two widely used channels: fan channel and cone channel. The gating system consists of three parts: straight runner, horizontal runner and inner runner. Fan runner is more suitable for products with shorter inner gate length, and cone runner is suitable for products with longer inner gate length. Whether it is a fan-shaped runner or a cone-shaped runner, the cross-sectional area from the runner to the inner gate should be gradually reduced to ensure the control of the flow pattern of alloy liquid and prevent gas from being involved in the gating system. The runner should have a certain length, which can flow stably and guide the molten metal.

Generally, the design of gates and runners should follow the following principles:

1). The most difficult place to fill in is preferred.

2).

The size of each gate should be distributed in proportion to the casting quantity of its main filling part.

3).

The gate position should avoid the place where the liquid flow is easy to block or directly impact the core.

4). The cross-sectional area of runner and gate must be balanced.

5) Protruding parts or buffer bags should be set at the corners or tail of the runner to buffer and absorb impurities.

6). Avoid sharp turns of the runner and sudden changes in cross section, so as not to cause turbulence in the air.

7). When the runner turns, the cross-sectional area should be appropriately reduced to avoid being involved in the air.

In order to improve the quality of die casting, the gas in the cavity should be removed as much as possible during the filling process of molten metal, and the molten metal mixed with gas and contaminated by coating residue should be removed. Therefore, it is necessary to set up overflow and exhaust system, including overflow tank and exhaust tank.

The overflow tank has the following functions:

A, play a role in discharging sundries and gases;

B, maintaining the temperature balance of the mold;

C, improve the flow direction (drainage);

D, play the role of ejection platform;

E, receiving the first cold metal flow (collecting slag).

The depth of the slag outlet of the zinc alloy overflow trough is generally 0.2-0.3mm, and the depth of the exhaust pipe behind the overflow trough is generally 0.05-0.12mm. ..

V In order to fully exhaust the gas in the cavity, the cross-sectional area of the exhaust groove is generally 20%-50% of the cross-sectional area of the inner gate.