| 摘要 |
<p>PROBLEM TO BE SOLVED: To firmly adhere semi-spherical bodies with each other which constitute a spherical core by a method wherein the spherical core and an external layer which covers the core are formed of a thermoplastic resin, and at the same time, the spherical core is integrally formed by spin-welding the semi- spherical bodies. SOLUTION: As core constituent parts, a protruding semi-spherical body 2a made of a thermoplastic resin, having a ring-shaped protruding rib 8 on the bonding end face, and a recessed semi-spherical body 2b made of the thermoplastic resin, having a ring-shaped recessed groove 9 on the bonding end face, are used, and the protruding rib 8 is fitted in a recessed groove 9, and while both semi-spherical bodies 2a, 2b are pressed to each other, one of the semi- spherical bodies is rotated at a high speed, and the bonding end faces of both semi-spherical bodies 2a, 2b are melted by the frictional heat with each other, and bonded and integrated, and a spherical core is formed. Then, an external layer is formed by an injection forming in a manner to cover this spherical core. By this method, cracks and a breakage of a ball due to repeated hittings can be prevented from occurring.</p> |
