To obtain a piercing plug for a seamless metallic tube which restricts an adopted fault generating on the inside surface of a product tube and which does not reduce the life of the plug by making the thickness of scale skin film of a reeling part thinner than the thickness of scale skin film of a rolling part.
A plug 3 is formed in a bullet as the total shape, and it is composed of a rolling part 3a on the top end part, a reeling part 3b of the intermediate part and an escaping part 3c of the final end part. A scale skin film S is formed on a front face except the rear end face 3d connected to a core metal, and the thickness T2 of the scale skin film S of the reeling part 3b is made thinner than the thickness T1 of the scale skin film of the rolling part 3a. Therefore, the plug life is not reduced, and a hollow shell of a small roughness internal surface, that is, restricted degree of recessing and projecting parts is obtained. On the result, even in the case of extending or rolling this hollow shell, because the recessing and projecting parts on the internal surface are crushed, a product tube with few adopted fault is obtained.
YAMAKAWA TOMIO
NAKANISHI TETSUYA
