Briefly describe the advantages and disadvantages of precision castings and common problems:

Precision casting iron castings can be made into complex shapes and very complex inner walls, such as shells and cylinder blocks. Integration coverage is wide. Forging, waste parts and cutting with low cost can be used immediately, and the cost of machinery and equipment is low. The specifications and quality of castings are basically not restricted. The appearance and specifications of the castings are very close to the parts, so the labor of drilling production and processing is reduced, and a lot of metal composite materials can be saved.
The defects of precision casting are that the manufacturing process is diverse, the whole process of the processing technology is difficult to manipulate, and the casting is easy to cause defects. The castings have poor specification uniformity and low specification precision. Compared with steel castings of the same appearance and specification, the intrinsic quality of infrared carbon-sulfur meter castings is poor, and the bearing capacity is not as good as steel castings. The office environment is poor, with high temperature, a lot of smoke and dust, and high labor efficiency.
After the deep processing of the outer wheel gallery of the iron castings, there should be no welding defects such as vent holes. Sand (slag) holes appear on the surface of the castings with small uneven cracks, which are generally irregular, with different shades and less smooth internals, and there is no cold mouth condition. The key is because the steelmaking furnace is untidy, the weld bead infiltrates during pouring, and the sand is shoveled when the impurity removal sheet is released.
The small sand particles remaining in the mold rush into the cavity with the steelmaking furnace. When clamping the mold, the middle of the mold or the middle of the mold and the sand core are extruded to cause the sand to fall. Poor characteristics of casting sand (such as low water content, poor compressive strength, etc.) in the design scheme, too fast water ingress can easily lead to sand washing. The key reason is that the pebbles in the cavity are not quiet. Pebbles were invaded from openings such as sprue or riser before pouring. The sand mold has insufficient compressive strength and falls due to external forces.
Pouring is not continuous or the pouring rate is very slow, so that the small stones in the cavity cannot float to the riser perfectly, and stay in the lower temperature area.
A layer of air oxide on the outer surface of steel castings, also known as black skin. It can be removed by sandblasting, and naturally it can also be removed by mechanical processing. Inconvenient areas can be removed by pickling passivation. After this layer of air scale, because this layer of air scale will fall off, the appearance becomes less and less beautiful, it is not easy to adopt anti-corrosion countermeasures such as paint electroplating process, if it is immersed in liquid, the liquid will appear residue. It should be said that there are not many negative effects.