| 摘要 |
A baseball or softball having a size, weight, sound and rebound in accordance with standards set for the game. The ball is formed of a spherical plastic shell covered with a conventional sewn cover. The plastic shell is a thermoplastic consisting of a mixture of "Surlyn" ionomer with about 50% ethylene vinyl acetate. The proportions are variable to achieve the desired characteristics, the "Surlyn" providing strength and sound while the EVA provides softness and ease of thermo-welding. The shell is made by injection molding hemispheres and thermally welding two hemispheres together. As an alternative, the shell can be formed with a hole, and liquid components of an expanded plastic placed into the shell and expanded to fill the shell. The shell still provides all characteristics desired, and the expanded plastic is for weight only.
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