| 摘要 |
PURPOSE:To accomplish biaxially stretching of tubular product of polymer by inserting a tubular polymer product, in a heated and softened state, having small outer diameter into an outer mold, inserting an elastic tubular body into said product, and expanding said body from the innermost side of the outer mold by blowing air thereinto so that the polymer product is stretched and brought into close contact with the inner surface of the outer mold. CONSTITUTION:Into an outer mold 1 with cylindrical inner surface a tubular polymer product 2 having an outer diameter (d) smaller than that of the inner surface of the mold is axially inserted. An elastic tubular body 3 having an interior 3A into which compressed air can be introduce and whose outer surface has a high coefficient of friction is axially inserted into the product 2. The body 3 is expanded successively from the innermost side 1A of the mold 1 by gradually introducing air thereinto to expand the product radially outwardly until said product comes into close contact with the inner surface of the mold. Since the body 3 has a high coefficient of friction and is expanded radially and at the same time axially stretched, axial and radial expansion of the product can be accomplished at a time, so that any special device such as a chuck is not needed and another forming process after the stretching is not required. |
