There are certain specifications and requirements for lost foam casting, and the following aspects should be paid attention to in the molding process: lost foam casting generally uses silica sand, and its silica content is required to be more than 85% ~ 90%. In terms of air permeability and fire resistance, silicon sand with particle size of 0.850 ~ 0.300mm is generally selected for steel castings and iron castings. First, lay a layer of dry sand with a thickness of about 100mm on the bottom of the sand box, then place the EPS mold and pouring riser painted with paint in the center of the sand box, fill the sand while vibrating, stop adding sand until the dry sand is about 50mm away from the top surface of the sand box, cover the dry sand with plastic film, then place the gate cup on the top of the straight gate, and remove a layer of loose sand on the film to prevent molten iron splashing during pouring and burning through the film, resulting in air leakage and box collapse.
In the lost foam casting process, the whole process includes seven links, and each link has a great impact on the quality of lost foam casting. Of course, the pouring process is also a crucial link in the whole lost foam casting process. Mastering the precautions of pouring process and strictly controlling every detail of pouring process are the key to the production of high-quality lost foam casting.
The pouring process of lost foam casting is the process of liquid steel filling and the vaporization of foam mold. In the whole process, it should be noted that: (1) the sprue should be filled with liquid steel from beginning to end. If it is dissatisfied, due to the limited strength of the coating layer, molding sand collapse and air inlet are easy to occur, resulting in casting defects. (2) When pouring molten steel, be sure to hold it to ensure stability, accuracy and speed. Fill the sprue cup instantaneously and keep the flow fast. The ton of molten steel is about one minute. If the molten steel in the same box is cut off, air will be sucked in, which may cause sand collapse or increase air holes in the casting, resulting in the scrapping of the casting. (3) lost foam casting adopts negative pressure closed type and must be closed below the gate cup. When the molten steel enters the molding mold, it begins to liquefy and burn, vaporize and disappear, and a temporary cavity is formed at the front end of the molten steel in a short distance. Therefore, the design speed of liquid steel filling is roughly the same as that of the foam model. In order to prevent the molten steel from melting other models in the same box by high temperature radiation, the sprue shall be properly far away from the casting model. The lowest position of the whole box casting shall be selected for the position of the vertical sprue. During pouring, pay attention to adjust and control the negative pressure and vacuum degree within a certain range. After pouring, keep it under a certain negative pressure for a period of time. After the negative pressure stops and the liquid steel condenses, it will be discharged from the box.