The gating system is usually divided into three types according to the different ways of liquid metal note of cavity.
3 different types of gating system
- The top type:
The metal from the cavity at the top of the note. Its advantage is that it can make the metal from the lower cavity to the gate of directional solidification, and the compact structure of castings can be achieved.
Prone to splash liquid metal casting is a weakness. The impact of the mold is big. Easy to make casting slag inclusion and porosity. The bigger the casting of this defect is, the more significant it is. So, this form is only applicable to low-altitude of castings.
2. The bottom type:
The advantages of this approach is that the liquid metal can smoothly from the bottom of the shell injection, gas in the cavity can be free from the top (riser or the outlet) escape, therefore, has a good gas discharge effect (serpentine gate better slag), pouring casting surface is bright and clean. This form is especially suitable for casting copper, aluminum, and other non-ferrous alloy castings.
Its defect is at the bottom, and the top of the liquid metal temperature difference is big. And it is easy to produce the defects such as shrinkage cavity, porosity, and crack disease.
Therefore, there must be a corresponding high-pressure head and increased casting speed or from the top to fill water with high-temperature metal liquid to reduce the overall shell temperature difference.
3. Side type (dendritic):
the impact on the shell and the exhaust performance is better than the top note, the integral type shell temperature difference is smaller than the bottom note type. And a sprue weldable multiple investments is very widely used and the process production rate is higher.
What are the basic requirements for the gating system?
- As a supporting precision casting gating system of the whole mold type and the role of the shell, it must have sufficient strength.
- Because of the gating system and riser role, so must ensure that the castings to gate partial order set. The casting solidification process can fully make the feeding. And the shrinkage cavity can stay in the water in the mouth.
- Ensure that the metal liquid flow rate is to a certain extent and can fill the cavity smoothly.
- For nonferrous alloy casting and gating system should have a good ability of slag.
- In the case of ensuring the above requirements, as far as possible to reduce the metal weight of the gating system. In order to improve the process of casting production rate.
A precision casting gating system usually consists of the following units: pouring basin, sprue, runner, and gate. In addition, according to the need to sometimes attach other units. Such as slag removal device, buffer, the riser section (wax) mouth.