| 摘要 |
PURPOSE:To obtain ribbed tubes having ribs with a sharp sectional shape by making a groove bottom width at the rib work beginning position of a plug to or wider than than that at the rib work finishing position. CONSTITUTION:Line groove 13 are cut on the plug body 12 of a plug 11 and the groove bottom width is constant from the rib work beginning position A to the rib work finishing position B or the width at the position A is wider than that at the position B. Groove sides 14 incline so that the groove 13 expands toward the periphery of the plug 11. The slope of the groove sides 14 at the position A is smaller than that at the position B and gradually increases toward the position B.
|
