| 摘要 |
PURPOSE:To solve the problem of adverse effects caused by welding heat by reversing both end faces of a metallic pipe in the direction of the outer periphery of the pipe by means of roll molding so as to bring both end faces into contact with each other, and welding both end faces together to form a hollow circular body, and rolling the hollow circular body into a required shape to form a valve box main body. CONSTITUTION:A valve box comprises a welded body of a valve box main body 4 and a valve rod supporting portion 5. The process of producing the valve box main body 4 includes reversing both end faces 1 of a stainless pipe in the direction of the outer periphery of the pipe by means of rolling work, bringing both end faces into contact with each other at approximately the center portion of the outer periphery, and welding these contact faces together so as to form a hollow circular body having a cross section approximating a deformed circle, both end faces 1 of the stainless pipe having respective bearing storage portions 16,17 both of which are molded from a base member by means of press working (or bulging). Next, rollers are pressed against the hollow circular body from three directions to mold the hollow circular body into a required shape to form the valve box main body 4. Both residual stress and thermal stress are therefore small and the amount of deformation of the valve box is decreased and the degree of concentricity of the two bearing storage portions and the accuracy of the inner and outer peripheral portions of the valve box and the bearing storage portions relative to each other are equal to the high accuracy of the valve box which is finished by cutting process after forging. |
