Why, under the same pressure, are the valve bodies of valves made from forgings much larger and heavier than those made from castings?
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Why are forgings larger and heavier than castings?
Because of forging. Because of the pressure rating.
Castings can be shaped to match the required shape of their internal cavity, while forgings require consideration of processing and material shaping issues. The valve in the image is a ball valve; the component used for internal pressure control is a sphere that rotates. The required shape of the internal cavity can be similar to that of a sphere, and castings can be formed along this contour (through die casting). Forgings are generally produced by free forging, and their shape requires thorough processing; they can only have simple shapes. Die forging isn’t an option in such cases, as it results in shapes similar to those of castings (die forging molds are expensive and not cost-effective, and large-scale forging equipment is also costly)