The main difference of castings and forgings are the following:
1, casting is a casting material in the mold in the whole of its uniform stress distribution, for there is no limit to the compressive direction.
And forgings is composed of the same direction of force to crack down on, its internal stress has the directivity, only has a direction under pressure.
The same material, same thickness of castings and forgings, on the intensity and the phase structure, forging is better than castings.
2, for the valve, the same class, same materials of casting wall thickness thicker in the forging of the valve. It is the compression strength of forgings with equal.
3, casting is taller to the requirement of casting process, the biggest characteristic is to make more complex shapes, valve body structure and flow are irregular, casting can be one-time molding, as long as the process, can be cast out of the large diameter of the valve body.
The density of forgings is better, but for too complex flow channel and appearance to a molding, often need to be modular, forging welding together again separately, thus the size of the forgings.
4, forgings often can't work out complex, streamlined flow channel. Port of machining by cutting and become, within many sharp-angled transition, at the sharp corners to cause uneven stress, cracking.
5, the modular design of welded together at the same time, the forging of the valve seat diameter is relatively fixed, on some valve size, its diameter is small, influence the flow capacity. Cause of valve flow resistance increase, lower efficiency of the whole system.
6, due to the limitation of big size valve forging process, at the same time to save costs, many manufacturers usually USES the body center of castings, forgings on both ends of the structure.
7, whether castings and forgings. When processing, are likely to defect.
The main defects of the castings in trachoma, bubbles, etc.; Performance in the big grain, the main defect of forgings cold hard phenomenon, crack, crack, etc.
In order to obtain qualified product quality, the corresponding casting needs in the process of heat treatment to eliminate casting stress, at the same time using X-ray, magnetic powder flaw detection, detection means such as penetrant inspection.
And for forgings, which requires strict of weld heat treatment and the corresponding detection means to ensure that. Forgings are often required to ultrasound. In addition, to mention is the welding process is very strict, qualification of welding engineer is also the key to guarantee product quality.
8, regardless of the valve adopts the raw materials, manufacturers need to have strict quality control procedures, standard testing procedures to ensure that the quality of the valve.
