Principles and Common Problems of Setting the Position of Inner Gate in Precision Casting

Principles and Common Problems of Setting the Position of Inner Gate in Precision Casting

The solidification and shrinkage method of precision casting castings is closely related to the position of the inner gate. Generally, it is required that the opening position of the inner gate should comply with the solidification and shrinkage method of the casting. Today, precision casting manufacturer Tianyao Metal will talk about the principles and common problems of opening the inner gate position of castings.

1、 The principle of opening the position of the internal sprue of the casting:

1. For precision castings that require simultaneous solidification, the inner runner should be set at the thin-walled part of the casting, with a large number and dispersed arrangement, so that the metal liquid can quickly and evenly fill the mold cavity and avoid local overheating of the sand mold near the inner runner.

2. For precision castings that require directional solidification, the inner runner should be set at the thick wall of the casting. If there is a feeding and shrinking riser, it is best to place the riser between the casting and the inner runner, so that the metal liquid can be introduced into the mold cavity through the riser to improve the feeding and shrinking effect of the riser, such as ductile iron crankshafts, gears, and cast steel gears. Sometimes, in order to avoid significant shrinkage stress caused by large temperature differences in castings, an inner runner can also be set up at the secondary wall thickness of the casting.

3. For precision castings with complex structures, the so-called "weaker directional solidification" principle of combining directional solidification and simultaneous solidification is often used to arrange the position of internal runners. That is, internal runners are set for each filling zone according to the requirements of directional solidification, while multiple internal runners are used for dispersed punching of the entire casting according to the requirements of simultaneous solidification. This setting can fully fill and shrink the thick parts of the casting without producing shrinkage holes and looseness, while minimizing stress and deformation.

4. When there is a significant difference in wall thickness of precision castings and it is necessary to introduce molten metal into the inner runner starting from the thin-walled area, attention should be paid to using cold iron to accelerate solidification at the thick wall and increase the riser. During pouring, process measures such as point riser should also be taken to ensure shrinkage at the thick wall.

2、 When setting up the position of the internal runner, it is not only necessary to consider the solidification and shrinkage method of the casting, but also to consider and pay attention to the following issues:

1. Do not open the inner gate in areas with high quality requirements for castings, as the grains near the inner gate are coarse. It is also best not to open it on non machined surfaces to avoid affecting the appearance quality of castings. For pipe castings with pressure resistance requirements, the inner runner is often set at the flange to prevent shrinkage and loosening at the pipe wall;

2. The inner sprue should not be directly facing the sand mold, sand core, or other weak protruding parts to prevent sand erosion. For rotating castings, the inner runner should be introduced tangential and the direction should be consistent to concentrate impurities and discharge them into the riser or corresponding process protrusion;

3. Do not open the inner runner near the cold iron or core support to avoid reducing the effect of the cold iron or causing premature melting of the core support;

4. The inner runner should allow the metal liquid to be injected along the mold wall, and not allow the metal liquid to fall on the surface of the mold wall for a long time, causing local overheating of the sand mold;

5. The opening of internal runners should be conducive to smooth punching, exhaust, and slag removal. The flow direction of the metal liquid entering the mold cavity from each internal runner should strive to be consistent to avoid confusion in the flow direction, which is not conducive to the discharge of slag and gas;

6. For alloys with a high tendency for shrinkage, such as steel castings, the setting of internal runners should not hinder the shrinkage of the castings, avoiding the occurrence of significant stress or cracking due to shrinkage obstruction;

7. The internal pouring channel should be set up on the parting surface as much as possible to facilitate the shaping operation;

8. The position of the internal sprue should be easy to open the box, clean the casting, and remove the pouring system, without affecting the use and appearance of the casting;

9. On the premise of meeting the pouring requirements, the metal consumption of the pouring system should be minimized as much as possible, and the size of the sand box should be kept as small as possible to reduce the consumption of molding sand and metal liquid;

Precision machining