Some people say that forged ball valves are durable and perform good sealing. While some people say that cast ball valves are low cost, which can be mass-produced quickly, meeting the requirements of most working environments. But which ball valve is better in fact? Today’s article will explain it for you.
Forging is a material technological process that uses forging machinery applying pressure to metal blanks, aiming to produce plastic deformation to obtain mechanical properties, certain shape and size. While forging metals, it is necessary to exceed the elasticity limit but not the strength limit. Therefore, ductile materials are suitable for forging, which means materials that have those two limits sufficiently far apart. Forging methods includes rolling (sheet metal), forging, drawing, extrusion.
Types of Forging
1.According to the temperature of the workpiece during processing, forging can be divided into: hot forging, warm forging and cold forging.
2.According to the tools used for forming, it is divided into free forging and die forging.
3.According to whether the forging are with flash, it is divided into open forging and closed forging.
Forged Ball Valves
Forging ball valve uses forging machinery to apply pressure to metal blanks, causing plastic deformation to obtain forgings with certain mechanical properties, shape and size. Forging and stamping are both plastic processing, both means forging.They are generally used in pipelines with high grades. The diameter is relatively small, generally below DN50. And the pressure is high, such as forged ball valves, usually the highest pressure of his forged ball valves to 4500LB. Among forged ball valves, forged steel ball valves are more common.
Casting is a method of producing various objects by pouring liquid (molted) metal (steel), or another liquid or suspension capable of solidifying into the mold of the required shape. Casting is primarily suitabe for products with complicated shapes, which cannot be produced by a different method, or made in complicated or expensive way (e.g., by machining or welding). After pouring the steel into the mold, the liquid steel immediately contact with the cold wall, which decreases the temperature of the steel and its crystallization. The casting temperature, for example of carbon steel, is around 1 450 °C.
Casting Ball Valves
Cast ball valves are produced when the steel is put into the furnace for melting, and then formed by casting. Generally, the pressure level of cast ball valves is relatively low, such as PN16, PN25, PN40. But there are also high pressure ones, which can reach 1500Lb, 2500Lb. And most of the calibers are above DN50.
The Differences Between Forged Ball Valves and Cast Ball Valves
1. The compactness of the forged ball valve is relatively good. Owing to the complicated flow channel and appearance, it is impossible to form at one time. And it often needs to be modularized, forged separately, welded together. so the size of the forging is limited to a certain extent.
2. Moreover, forgings usually cannot produce flexible streamlined runners. The runners are machined by turning. And many sharp corners are formed inside, which can easily lead to uneven stress and cracking. In the modular welded design, the seat diameter of the forged valve is relatively fixed, and in some valve sizes, the diameter is relatively small, affecting flow.
3. Because of the limitation of large valve forging process, in order to save cost, many manufacturers usually adopt the structure of valve body center casting and both ends forging, so no matter casting or forging, there may be product defects during processing.
4. Casting ball valves can be cast into large diameter ball valves, and castings have higher requirements on the casting process. They can be made into more complex shapes. For valve body structure and irregular flow channel, casting can be formed at one time. Therefore, the large diameter valve body can be cast with high technology level.
5. The main defects of cast ball valves are trachoma, bubbles. While the main defects of forgings are large grains, chill phenomenon, cracks. In order to produce qualified products, the castings need heat treatment to eliminate the stress in the casting process. And at the same time, run test with different inspection methods such as X-ray, magnetic particle inspection, and penetrant inspection. Besides, it is necessary to carry out strict heat treatment and corresponding inspection of the weld to forgings. Usually, ultrasonic inspection is required to ensure the quality of the product.
6. Cast ball valves are used for large balloon valves (DN50 – 6.4MP). And forged ball valves should be used for those above DN50 and 6.4MP. For ball valves above DN50 and pressure above 6.4MP, forged ball valves can be used.
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