| 摘要 |
A golf ball 1 has a core 2 and a cover 3. For molding a core 2, a rubber composition is extruded from a kneading machine, and cut at a predetermined length to obtain a preforming material. The preforming material is placed in a mold and the mold is clamped. An upper portion and lower portion of the mold mate for more than or equal to 15 seconds, and thereafter they are unclamped until a clearance between the upper and lower portions becomes from 3 mm to 8 mm, then, the mold is shut. The shutting time is determined to be from 0.5 second to 5.0 seconds. By this unclamping of the mold, a residual air in a spherical cavity is released, which results in elimination of defective products.
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