The main differences between castings and forgings are as follows:
1. Castings are formed by casting the material as a whole in the mold. Its stress distribution is uniform and there is no restriction on the direction of compression. The forging is made by the same direction of force, its internal stress is directional, and can only withstand directional pressure. Castings and forgings of the same material and wall thickness are superior to castings in terms of strength and crystal phase structure.
2. For valves, the wall thickness of casting valves of the same pound class and material is thicker than that of forgings. Its compressive strength is equal to that of forgings.
3. Castings have relatively high requirements for the casting process. The biggest feature is that they can make more complex shapes. The structure of the valve body and the flow channel are irregular. The casting can be formed at one time. the valve body. The compactness of the forgings is relatively good, but for too complex flow channels and shapes that cannot be formed at one time, they often need to be modularized, forged separately and then welded together, so the size of the forgings is limited to a certain extent.
4. Forgings are often unable to process complex and streamlined runners. The processing of the runner is made by turning, and many sharp corner transitions are formed inside, and it is easy to cause uneven stress and cracking at these sharp corners.
5. At the same time, the design of modular welding, the diameter of the valve seat of the forged valve is relatively fixed, and in some valve sizes, its diameter is too small, which affects the flow capacity. This will increase the flow resistance of the valve and reduce the efficiency of the entire system.
6. Due to the limitations of the forging process for large-sized valves, and at the same time to save costs, many manufacturers currently use the structure of the central part of the valve body and the forgings at both ends.
7. Whether it is casting or forging. During processing, there may be product defects. The main defects of castings are manifested in trachoma, bubbles, etc.; the main defects of forgings are manifested in large grains, chill phenomenon, cracks, cracks, etc. In order to obtain qualified product quality, the corresponding castings need heat treatment to eliminate the stress in the casting process, and X-ray, magnetic particle inspection, penetration inspection and other detection methods are used at the same time. For forgings, the strict heat treatment of the weld and the corresponding testing methods are guaranteed. Forgings often require ultrasonic inspection. In addition, it should be mentioned that the welding process is very strict, and the qualification of welding engineers is also the key to ensuring product quality.
8. No matter what kind of raw material the valve uses, the manufacturer needs to have strict quality control procedures and standard testing procedures to ensure the quality of the valve.