“Golf balls have undergone substantial evolution since the early days of the game. A modern golf ball 100 is made with multiple layers, including an outer layer called a "cover" and an inner body called a "core." Many modern golf balls have at least one additional layer, called a "mantle", situated concentrically outside the core. The cover is typically formed around the mantle so that the cover is concentric with the mantle and the mantle and core are sealed inside the cover. For purposes of description herein, the term "core" is used generally herein to denote the portion of a golf ball located inside the cover and providing the surface on which the cover is formed, regardless of whether the core comprises one or more layers. “

“Conventional techniques used for forming the cover include casting, compression molding, and injection molding. The surficial dimples are formed at the same time as the cover. Injection molding is usually used for forming covers of thermoplastic materials. Compression molding is used for forming covers of polyisoprene (e.g., "balata" or gutta percha) and of certain polyurethane materials. Casting is usually used for forming covers of a thermoset material such as polyurethane, which is formed by reaction of diisocyanate, polyol, and polyamine.”

“Casting (also called "cast-molding") is performed in a ball cavity formed by bringing together two mold halves that define respective hemispherical cavities. Casting is especially suitable for forming the cover of a thermoset material. A precise amount of liquid thermoset resin is introduced into the hemispherical cavities and partially cured ("gelled"). The core is placed in the hemispherical cavity of one mold half and supported by the partially cured resin. The second mold half is placed relative to the first mold half to enclose the core and resin in the resulting ball cavity. As the mold halves are brought together, the resin flows around the core and forms the cover. The mold body is heated briefly to cure the resin, then cooled for removal of the ball from the mold body. Advantages of casting are that it achieves substantial uniformity of cover thickness without having to use centering pins, and it can be performed at a much lower pressure inside the mold than injection molding or compression molding. Indeed, casting can be performed at substantially zero gauge pressure.”

[Kuttappa, US Patent 8,021,590 (9/20/2011)]

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