What are the reasons for slag inclusion in lost foam casting?

Slag inclusion defects refer to the defects formed by the dry sand, paint and other inclusions as the molten iron enters the casting during the casting process. On the surface of the casting after processing, white or dark gray inclusion spots can be seen, distributed individually or in pieces, and white is quartz sand particles. Black and gray are residues and other inclusions after pyrolysis of slag, paint, foam model. This kind of defect is commonly known as "sand in" or "slag inclusion", which is a very common defect in the production of lost foam casting. Factories that almost use lost foam casting are ubiquitous and difficult to eradicate completely. Only by adopting various measures and careful operation in each process can the "slag inclusion" be reduced to the limit and achieve a satisfactory result.

Before the lost foam castings are cooled and unboxed and not cleaned, according to the surface conditions of the castings and the pouring system, it can be judged whether there is sand entry and slag inclusion missing. If the gate cup, sprue, cross-runner, in-runner and gate surface or connection and the surface of the casting are seriously sticky or there is crack-like sticky sand, it is basically certain that the casting has slag inclusion and sand entry defects. If you smash the sprue rod or the sprue of the sprue, you can see white spots on the fracture. In severe cases, the fracture forms a circle of white spots. Such castings, especially plate-shaped, cake-shaped castings will be processed on the processing surface. There is white. Black and gray speckle defects. If the operation procedures are not strictly controlled. The castings produced seriously affect the quality of castings and the progress of order completion.

Causes of slag inclusion and sand entry defects

After long-term observation in the production practice, it has been proved that from the gate cup, the sprue, the cross-runner, the in-runner to the casting, all parts may cause sand intrusion, especially the combination of the pouring system and the casting. During the production process, the paint peeling and cracking on the surface of the white mold of the pouring system, the paint peeling and cracking at the joint of the white mold, the paint peeling and cracking of the surface of the foam plastic white mold, and the tightness of the direct sprue are not tightly closed. The main reason.

Secondly, the selection of process parameters, such as the size of the net head of the casting system, the pouring temperature, the size of the negative pressure, the dry sand particle size, and the model transportation process and packing operation, etc., are all very important for the casting slag inclusion and sand entry defects. Big impact. Only by taking systematic measures and careful operation in these links can the slag inclusion defects of castings be reduced and basically eliminated, and high-quality castings can be obtained.

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