| 摘要 |
PROBLEM TO BE SOLVED: To provide a valve casing of butterfly valve and a valve casing manufacturing method in which the material quality and hardness are uniform over whole inner cylinder to constitute the valve casing of the butterfly valve, there is no risk of generating stress corrosion or uneven deformation, dispersion in the quality and performance of the valve casing is not generated, and it is possible to select the inside diameter, thickness, etc., of the inner cylinder to any desired values. SOLUTION: The valve casing 8 of the butterfly valve is structured so that an inner cylinder 6 furnished with end walls 5a and 5b directed to the outer cylinder at the two ends of a cylindrical portion 3 is fitted in the outer cylinder 2 and flanges 4a and 4b are formed at the peripheral edges of the end walls 5a and 5b, and further the outer cylinder 2 and inner cylinder 6 are joined at the flange peripheral surfaces with a hollow interposed in between so that a single piece structure is embodied, wherein the inner cylinder 6 is formed in a single piece molding from one sheet of plate material through a turning processing. This eliminates necessity for welding of the cylindrical portion 3 with the end walls 5a and 5b to allow the material quality and hardness of the inner cylinder 6 to remain uniform, and there is no risk of generating stress corrosion or uneven deformation, and it is possible to enhance the quality of the valve casing 8 and select the inside diameter, thickness, etc., of the inner cylinder to any desired values.
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