We call all the channels of molten metal entering the mold cavity in the mold as the gating system, which includes sprue, sprue cup, transverse sprue and inner sprue. The design of gating system is very important, and whether the design of gating system of sand casting is reasonable or not will have a considerable impact on the quality of castings. According to the statistics of relevant departments, about three tenths of the casting wastes produced in the process of sand casting are caused by improper gating system design. Therefore, it can be seen that the importance of gating system design of sand casting, The design of gating system should follow the following basic design principles:
- When determining the position, direction and number of internal sprues of sand castings, the solidification principle or feeding method of sand castings shall be followed.
- The metal liquid shall fill the cavity within the specified time, and the temperature of the metal liquid shall not decrease too much during the flow in the gating system.
- Necessary filling head shall be provided to ensure that the outline and edges and corners of sand castings are clear.
- Try to make the metal liquid filling flow stable, avoid serious turbulence, and prevent the involvement of gas and excessive oxidation of metal.
- Have good slag resistance.
- When the liquid metal enters the mold cavity, its linear speed shall not be too high, and the splashing of liquid metal and scouring of mold wall or sand core shall be avoided.
- Ensure that the metal level in the mold cavity has sufficient rising speed, so as to avoid the formation of casting defects such as sand inclusion scar, wrinkle skin or cold septum.
- Do not damage the function of cold iron and core support.
- The metal consumption of the designed gating system should be as small as possible and easy to clean.
- Try to reduce the volume of the sand mold. The shape should be simple and easy to manufacture.
- The design of gating system shall not reduce the process yield.
According to the above design principles of sand casting gating system, the stepped gating system is adopted, and the dimensions of each gate are: straight gate is φ 140mmx1, transverse gate is φ 140mmx3, the inner gates of the first and second layers are φ 160mmx3, the third layer inner gate is φ 80mmx5, special gate for riser is φ 120mmx1, the total area ratio of each gate is ∑ a straight: ∑ a transverse: ∑ a inner = 1.0:3.0:3.8, as shown in the figure. When the liquid metal flows in this gating system, due to the larger and larger cross-sectional area, the flow speed becomes slower and slower. After the liquid metal flows from the sprue into the transverse sprue, the flow velocity in the transverse sprue and inner sprue is slow, and the flow is stable when entering the mold cavity.