1. Defect analysis
(1) The inner cavity of the cylinder body is a long strip-shaped sand core, and the gas generation speed of the sand core is fast. If it can not be discharged in time, it is easy to produce choking fire, resulting in porosity defects in the casting;
(2) The sealing treatment of the exhaust rope at both ends of the sand core is not good, and the air passage is blocked by the molten iron during pouring;
(3) The gas entrained by molten iron precipitates out of pores.
2. Preventive measures
(1) The groove of the ventilation rope is preset on the cast iron core bone model, as shown in Fig. 1, which is convenient for fixing the position of the ventilation rope and preventing the thickness of the sand layer of the ventilation rope from being too thin;
(2) The sand filling groove leading out the air rope is preset at the upper core of the model, as shown in Figure 2. The air rope ensures that the thickness of the sand layer sealed by the air rope is greater than 20 mm;
(3) Keep ladle dry to prevent air hole caused by incomplete baking.