| 摘要 |
PROBLEM TO BE SOLVED: To provide a manufacturing method of a formwork for forming a through- hole of concrete moldings, which can be easily removed from the concrete moldings, by flattening an outer peripheral face of a rubber cylindrical body while preventing the rubber cylindrical body from being deformed in the process of vulcanization. SOLUTION: After fitting an elastic tube 8, whose peripheral length is shorter than that of a rubber cylindrical body 1, to this unvulcanized rubber cylindrical body 1, a reinforcing cloth 9 is wound around them, and vulcanization is performed. By this method, the following effects can be obtained. First, the swelling deformation of the rubber cylindrical body 1 can be prevented in the process of vulcanization with the aid of the reinforcing cloth 9 and, even in the case of changes in the shape (particularly, changes in a diametral length, an axial length and a sectional shape) of the rubber cylindrical body 1, it is not necessary to change the reinforcing cloth 9. Secondly, on account of interposition of the elastic tube 8, a cloth mark of the reinforcing cloth 9 and an edge mark of the spiral reinforcing cloth 9 are not transferred to an outer peripheral face of the rubber cylindrical body 1, and these marks are not further retransferred to an inner peripheral face of a through-hole of concrete moldings. |
