Lost foam casting process includes riser system design, pouring temperature control, pouring operation control, negative pressure control and so on.
Gating system plays a very important role in lost foam casting process and is a key to the success or failure of casting production. Due to the wide variety and shape of castings, the specific production process of each casting has its own characteristics and varies greatly. These factors directly affect the accuracy of gating system design results.
The gating system design is different from the traditional sand casting. In the design of gating system, the particularity of this process should be considered. The section size of each part of gating system is related to the size of castings, the combination mode of model clusters and the number of pieces per box.
The combination of model clusters can basically reflect the characteristics of castings and the feeding form of castings. Due to the existence of model clusters, the behavior of molten metal after pouring is very different from that of sand casting. In the pouring process, the mold gasification needs to absorb heat, so the pouring temperature of lost foam casting should be slightly higher than that of sand casting.
When designing the section size of each part of the gating system, the resistance caused by the existence of the model during the liquid metal pouring of lost foam casting should be considered, and the minimum resistance flow area should be slightly larger than that of sand casting.
Negative pressure is a necessary measure for lost foam casting of ferrous alloy. The operation of negative pressure is an important guarantee measure to increase the strength and stiffness of molding sand, and it is also the main measure to eliminate the gasification products of the model. The magnitude and holding time of negative pressure are related to the casting material, model cluster structure and coating.
The most taboo of lost foam casting pouring operation is intermittent pouring, which is easy to cause cold insulation defects of castings, that is, the temperature of the molten metal poured first decreases, resulting in cold insulation between the molten metal poured later and the molten metal poured later. In addition, closed gating system is often used in lost foam casting gating system to maintain the stability of pouring. In this regard, the form of gate cup is closely related to the stability of pouring operation. The liquid level in the gate cup shall be kept stable during pouring, and the dynamic pressure shall be flat and stable during pouring.