Study on manufacture of container heads by two-step hydro-bulging of single-curvature polyhedron

Container heads are indispensable components of pressure vessels, which have a wide application in industry. The traditional method for manufacturing a large size container head is to form double-curvature petals and polar shell plates, then assemble and weld them into a container head, which needs large size dies and heavy presses. This paper presents a two-step hydro-bulging method for the manufacture of ellipsoidal container heads. The method involves formation of a single-curvature sector shell, which is assembled and welded into an enclosed tubular polyhedron, then the cylindrical and transition zones are formed through the primary hydro-bulging. Next, the polar zone is formed through the secondary hydro-bulging of the container head. Finally, the shell is cut to reveal the container heads. This paper also describes hydro-bulging experiments of a tubular polyhedron and an enclosed shell obtained from the tubular polyhedron. The results show that the two-step hydro-bulging technology of the single-curvature polyhedron can be used to manufacture large container heads without using large size dies and heavy presses.