| 摘要 |
An injection mold for optical discs has a stamper mounted on any one of mold surfaces defining a mold cavity, a cylindrically shaped center pressing member being inserted into and engaged with a center portion of the stamper, and a cylinder piston being placed at a center portion of the mold and movable in forward and backward directions by a fluid pressure in relation to the center pressing member so as to make the center pressing member in contact with the top of the cylinder piston whereby the stamper is detachably mounted on the mold by the center pressing member. The injection mold for optical discs is characterized in that a plurality of crews are provided on the center pressing member at its contact portion to the cylinder piston at circumferentially constant pitch and projections to be engaged with the crews are provided on the top of the cylinder piston, wherein the crews of the center pressing member, the projections and grooves of the cylinder piston, a receiving surface of the mold for positioning the insertion position of the center pressing member with reference to the mold are placed in concentric circle.
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