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Characteristics of cracks defects in medium and large steel castings

Hot crack: the crack is an irregular curve, the inner surface is rough and black brown iron oxide. Cold crack: the crack line is relatively straight, and the inner surface of the crack is clean and metallic luster.

Fig. 1 JIS rodless anchor claw root arc surface thermal crack and Fig. 2 double claw anchor claw arc surface thermal crack are caused by shrinkage stress of large steel castings during solidification of molten steel.

Fig. 3 the internal thermal crack after polishing the upper surface of the root of JIS rodless anchor claw is visually characterized by the thermal crack caused by sand inclusion. The cause is that the molding sand falls into the mold cavity when closing the box and is not removed, which is caused by floating sand.

Fig. 4 crack at the inner gate of anchor shackle and Fig. 5 hot crack at the connection root of rib plate of stern column steel casting are caused by the resistance of molding sand during solidification shrinkage of medium and large steel castings.

In Fig. 6, the surface of medium and large steel castings is cracked, which is visually characterized by crack distribution such as turtle shell pattern. The main causes are premature unpacking and quick cooling.

Fig. 7 is the main reason for the stress on the root of large anchor claw and the stress on the anchor hole in the circular arc. Fig. 8 is the main reason for the stress on the anchor claw.

The crack defect at the top of shackle of medium and large steel castings in Figure 9 and the hot crack at the root of anchor bolt riser in Figure 10 are caused by too small arc at the root of riser or too unpacking.

Figure 11 hot cracks are easy to occur at the junction of casting process tie bar and workpiece, which is mainly caused by improper size of process tie bar or premature unpacking.

Photo 12 defective parts after rough machining of stern shaft hole and 13 crack defects after rough machining of stern shaft hole are visually characterized by hot cracks caused by sand inclusion. The main reason is the insufficient strength of molding sand.