| abstract |
A mold comprises a spherical cavity, a support pin capable of being moved forward and backward with respect to the cavity, and a vent pin ( 8 ). The vent pin ( 8 ) includes two slits (S), an annular groove ( 20 ) and a vertical groove ( 22 ). An upper end ( 24 ) of the slit (S) is opened toward the cavity. A lower end ( 26 ) of the slit (S) is opened toward the annular groove ( 20 ). The annular groove ( 20 ) is coupled to the vertical groove ( 22 ). The lower end of the vertical groove ( 22 ) is opened toward air. A width (W) of the slit (S) is preferably equal to or greater than 1 μm, is more preferably equal to or greater than 3 μm, and is particularly preferably equal to or greater than 5 μm. A depth (D) of the slit (S) is preferably equal to or greater than 10% of a diameter (φ), is more preferably equal to or greater than 15% of the diameter (φ), and is particularly preferably equal to or greater than 20% of the diameter (φ). It is preferable that the same slit ( 3 ) should be formed on the support pin. |