Various casting defects often occur in the production of steel castings. How to prevent these defects has always been the concern of casting manufacturers. This paper mainly introduces the author’s understanding and practical experience in this area.
Our workshop mainly uses the traditional green sand casting process to produce steel castings. In the long-term production, it is found that the following casting defects mainly appear in the steel castings: sand hole, sand sticking, air hole, shrinkage hole, sand inclusion scab, sand expansion, etc.
There is a small hole filled with mold (core) sand in the inner or surface of the sand hole defect. Sand hole is a common casting defect, which often leads to casting scrap. The sand hole is caused by the sand particles (blocks) flushed down from the surface of the sand mold cavity by the metal liquid, or the sand particles (blocks) falling into the mold cavity in the molding and closing operation are too late to float into the pouring system and remain in the internal or surface of the casting.
Precautions for sand holes:
1.1 strictly control the properties of molding sand, improve the surface strength and compactness of sand core, reduce burr and acute angle, and reduce sand flushing.
1.2 before closing the box, the floating sand on the surface of the cavity and sand core shall be cleaned and the box shall be closed stably. If it is an open riser or through the air hole, the loose sand shall be avoided from falling into the cavity. After closing the box, pouring shall be carried out as soon as possible.
1.3 set up correct and reasonable pouring and pouring system to avoid excessive scouring force of metal liquid on mold wall and sand core.
1.4 the surface of sprue cup shall be smooth without floating sand.