1. Field of the Invention
The present invention relates to method of the production of a golf ball having dimples on the surface thereof.
2. Description of the Related Art
For the formation of a golf ball, injection molding or compression molding has been employed. In either case, a mold having upper and lower mold half having a hemispheric cavity is used. Upon formation, material for the molding leaks outside from the parting line between the upper and lower mold half. Due to this leakage, a ring-shaped flash is generated in the part corresponding to the parting line (hereinafter, referred to as “seam”) on the surface of the ball body. Although a gate is provided on the parting line of the mold for the injection molding, a flash is also generated in the part corresponding to this gate. These flashes need to be removed.
The flash is removed by bringing the flash into contact with a grinding device while rotating the ball body. Examples of the grinding device for use include sand belts, whetstone, sand paper and the like. Such procedures of removal are disclosed in JP-A No. 60-232861.
Golf balls have numerous dimples on the surface thereof. A role of the dimples involves causing turbulent flow separation through disrupting the air flow around the golf ball during the flight. By causing the turbulent flow separation, a separating point of air from the golf ball shifts backwards leading to the reduction of a drag coefficient (Cd). The turbulent flow separation promotes the differentia between the separating points at the upper and lower sides of the golf ball, which result from the backspin, thereby enhancing the lift force that acts upon the golf ball. Flight distance of the golf ball is prolonged on behalf of the reduced drag and enhanced lift force.
FIG. 9 is a cross sectional view illustrating a part of a ball body 2 after the molding. What is indicated by a chain double-dashed line E in FIG. 9 is an equatorial line. This equatorial line E corresponds to a parting line. A flash 4 is generated on the equatorial line E. What is indicated by a reference numeral 6 in FIG. 9 is a dimple which is positioned in the vicinity of the equatorial line E.
FIG. 10 is a cross sectional view illustrating a golf ball 8 obtained from the ball body 2 shown in FIG. 9. This golf ball 8 is obtained by grinding/removing the flash 4 from the ball body 2. Along with the grinding of the flash 4, a part of the ball body 2 is also cut away. What is indicated by a chain double-dashed line M in FIG. 10 is the ball body 2 prior to the grinding. In light of being affected by the grinding, the vicinity of the equatorial line E of the golf ball 8 is a specific region. A golf ball having dimples with considered specificity in the vicinity of the equatorial line E is disclosed in U.S. Pat. No. 5,090,705.
FIG. 11 is a front view illustrating a dimple 6 of the golf ball 8 shown in FIG. 10. According to the grinding, the edge on the side of the equatorial line E of the dimple 6 shifts from the position indicated by a double-dashed line to the position indicated by a solid line. In other words, the dimple 6 is deformed according to the grinding. The deformation causes deterioration of the appearance of the golf ball 8. The deformation may adversely affect the aerodynamic properties of the golf ball 8.
An object of the present invention is to provide a method of the production in which a golf ball that is excellent in appearance is obtained.