In the process of casting production, the causes of blow hole defects are:
① The excessive velocity of molten iron during pouring causes local sand mold to be washed;
② The molding sand falls due to carelessness during molding;
③ When running the core, it touches the sand mold and causes the molding sand to fall;
④ The sand core strength is too low due to insufficient sand mixing or too high sand temperature;
⑤ The sand mold is not cleaned after repair;
⑥ The surface stability of sand mold is poor;
⑦ The sand mold is scoured by molten iron for a long time;
⑧ Free sand in the sand mold is not cleaned;
⑨ The sand mold collides with the sand box when the box is closed;
⑩ The design of gating system is unreasonable.
In view of the above causes of blow holes, the preventive measures for their defects are:
① Adjust the settings of sprue, runner and ingate;
② Avoid touching the cavity wall during the molding process;
③ Design the shape of core head for easy placement and adopt correct core laying method;
④ Measures such as increasing binder ratio, cooling molding sand, fully mixing sand and removing sand balls were taken to improve sand mold strength;
⑤ Carefully clean the scraping surface and cutting surface of the sand mold;
⑥ The runner and ingate shall be painted;
⑦ The casting process in which the molten iron does not directly wash the molding sand or the filter screen is used to make the molten iron flow smoothly;
⑧ Thoroughly blow the sand mold inside;
⑨ Adjust the size fit of core head and core seat;
⑩ Fillet the root of the ingate to improve the fluidity of molten iron.