1. Defect analysis
(1) There is a great difference in the wall thickness between the cylinder body and the shaft head, and the hot spot is prone to shrinkage defects;
(2) Before the completion of liquid shrinkage, the feeding channel is closed in advance;
(3) The amount of liquid feeding is insufficient.
2. Preventive measures
(1) The formed cold iron is placed at the joint of shaft head and cylinder body, and the thickness of cold iron adopts empirical formula δ=（ 3 ~ 0.8) t, the diameter of hot spot circle is 88 mm, the coefficient is 0.6, and the thickness of cold iron is 55 mm. The size of the die mouth should be 2 ~ 3mm larger than the theoretical size, so that the cast iron size can fully fit with the roller model and play the role of chill.
(2) When there are many roller models, make two “small ears” on the cold iron, mark the identification number on the top, and formulate the corresponding on-site document table to facilitate workers’ operation. The two “small ears” are convenient to take and fix the sand on the cold iron, as shown in the figure.
(3) One insulating overflow riser is set at the ends of two shafts. The riser neck adopts the principle of short, thin and wide, and long × wide × Thickness = 40 mm × 80 mm × The closing time of liquid feeding channel was verified by CAE simulation to ensure sufficient liquid feeding amount and make full use of the self feeding characteristics of ductile iron.