MOLD FOR RESIN-COATED STEEL BALL

PROBLEM TO BE SOLVED: To provide a mold with the capability of uniformly forming the wall thickness of cushioning outer shell upon forming a resin-coated steel ball having the entire surface of a steel ball to be core material coated with a cushioning outer shell such as urethane rubber. SOLUTION: The mold for forming a resin-coated steel ball is of a formation having six pieces of gates set on an annularly configured runner 12 with the size of surrounding a ball set within the cavity, forming 1.7-1.9 times each injection cross-sectional area of a pair of subsequent tow pieces of gates Y, Y spaced away from a supply port in order relative to each injection cross-sectional area of a pair of two pieces of gates X, X nearest the supply port, and forming 1.4-1.6 times each injection cross-sectional area of a pair of subsequent two pieces of gates Z, Z. Altering the size of each injection port cross-sectional area every two piece allows molten rubber 20 flowing in the cavity to be balanced in its injection rate, thus making the wall thickness of a cushioning outer shell uniform.