The appearance of the crack is a straight or irregular curve. The surface of the hot crack is strongly oxidized and becomes dark grey or black without metallic lustres. The surface of the cold crack is clean with metallic lustres. Usually, external cracks can be seen directly in x-ray inspection machine castings, but internal cracks can only be seen by other means. Cracks are usually associated with defects such as shrinkage porosity and slag entrapment. They are mainly found in the interior of the casting sharp corners, the junction of thick and thin walls and the hot connection area where the pouring riser is connected to the casting.
Reasons: metal mould X-ray inspection equipment castings are easy to be cracked, for the metal mould itself does not shrink and the cooling rate is fast. It is easy to increase internal stress in the casting, open the hole too early or too late. The pouring angle will be too small or too large, and the coating is too large. Thickness and other conditions are easy to cause cracking of the casting. In addition, the cavity with cracks is also easy to be cracked.
Cold barrier refers to the surface gap with a straight seam or chamfer, separated by oxide. When the cold barrier is serious, it will become "underground". Cold barrier often appears on the top wall of x-ray inspection equipment castings, horizontal or vertical thin surfaces, the junction of thick and thin walls or thin auxiliary plates.
Reasons: metal mould exhaust design is not reasonable; working temperature is too low; paint quality is not good (artificial, material); the position of the runner opening is incorrect; pouring speed is too slow, etc.
Relatively regular holes are formed on the surface or inside of the casting, and the shape of the holes is consistent with the shape of the sand grains. When just out of the mould, we can see the sand embedded in the surface of the X-ray inspection equipment castings, and we can take out the sand grains.
Reasons: Sand grains falling from the surface of the core are wrapped in copper liquid and form holes on the surface of the casting. The surface of the core is fragile, burnt or not fully cured. The size of the core does not match the external mould and will be compressed when the mould is closed. Sand cores may break. The mould is immersed in graphite water contaminated with sand. Sand wiped off between the sand core and runner of the casting ladle is flushed into the cavity with copper water.