What Are The Characteristics Of The Casting System For Steel Castings That Deserve Our Attention
The characteristics of cast steel are high melting point, poor fluidity, large shrinkage, and easy oxidation, requiring rapid and smooth filling of the molten metal.
1. Characteristics of casting steel:
1.1 Cast steel has high shrinkage, and castings are prone to defects such as shrinkage cavities, porosity, cracks, and deformation. For castings with significant differences in thickness and wall thickness, a directional solidification principle is used to set up a sprue and riser system. It is best for the liquid to flow through the sprue and enter the mold cavity to enhance the sprue's ability to compensate for shrinkage; For shell castings that are prone to cracking and deformation, the internal runners should be evenly distributed on the thin walls of the castings, and the mechanical obstruction of the runners to the castings should be minimized as much as possible.
1.2 The pouring temperature of cast steel is high and prone to oxidation, so it is usually poured with a leakage package. Leakage casting has good slag blocking effect and does not require high slag blocking effect on the casting system. Therefore, the casting system has a large cross-sectional area and is open, which does not require high slag blocking function, but needs to quickly and smoothly fill the mold. The pouring pressure of the leaking package is high, and it is easy to damage the sprue. Therefore, the pouring system should strive for a simple structure, strong and impact resistant. The sprues for large and medium-sized castings, as well as the transverse and inner runners with a steel flow rate exceeding 1T, should be composed of refractory brick pipes. The pouring system for small steel castings can be composed of water glass, resin sand, or all surface sand, and ensure sufficient strength.
2. Characteristics of cast steel pouring system:
The pouring system is the process of distributing the casting liquid. The setting of the pouring system should minimize the flushing of the casting, minimize the turbulence of the steel liquid in the mold cavity, and follow the rule of sequential solidification as much as possible to allow the steel liquid to rise smoothly in the casting cavity. Among them, the setting of the sprue is the most important. The pouring system should try to shorten the solidification time of the casting as much as possible and implement on-demand distribution. For parts that require a large amount of steel water, additional layers should be added. If designed based on the shape of the casting, a layer should be set at a height of 400-500 and a layer should be set at a length of 400-500. This way, the time for the molten steel to flow through the pouring channel is long, but the time for it to enter the casting is short, which is beneficial for the lower part to solidify first, the middle to supplement the lower part, and the upper to supplement the middle part, forming a sequential solidification state. Imagine if we only consider the bottom injection type, within 90 seconds of pouring, the molten steel in the mold cavity will continue to move continuously. Which is better than the imagined smooth rise and layer by layer solidification caused by layered pouring? The hot nodes brought by the bottom injection gate and the cold steel water in the The yield of risers and the solidification of castings have a significant impact. Therefore, it is reasonable to use bottom injection for some castings with low height and large heat nodes, but it has a significant impact on completely using bottom injection for castings with small heat nodes and high height.
