| 摘要 |
<p>The tennis ball of semi-hard type having no pressure or low pressure, is suitable for the beginner and the old who periodically keep on exercising to enhance the health. The tennis ball is mainly made from nature rubber, synthetic rubber and flexible synthetic resin having high tensile strength. Such tennis ball is produced by press molding and unifying the outer surface of rubber core ball and inner surface of cover in die. Said outer surface has a thickness of 3.0-3.4 mm, a weight of 39-41 g, and inner surface has a thickness of 3.0-3.5 mm, a wight of 9-11 g. In this case, hollow of ball is at no pressure or low pressure(less than 5 psi), outer diameter of the ball is 63-65 mm and total weight of the ball is 48-52 g. Meanwhile, rubber core ball is formed as follows; uniformly mixing rubber composition in roll and mixer; press molding the mixture to the die(for half shell) to form half shell; and press molding the produced half shell to the die(two core ball) to form hollow sphere.</p> |
