JPS5574847A - Metal mold for molding synthetic resin lid cap - Google Patents

Abstract

PURPOSE: To prevent shrinkage of molded synthetic resin lid cap and to provide good appearance thereof by avoiding its unbalanced shrinkage after its separation from mould in suck a way that inner face of mould cavity is designed in a specific configuration.

CONSTITUTION: Mould cavity 10 is constituted by a space between mould core 20 and outer mould 11 having flat ceiling face 12 of which annular corner has radius R of curvature terminating at its lowest point A. Straight imaginary line l is defined by the point A and the lowermost point B of the outer mould 11. Desired thickness 2 of side wall of completed lid cap is determined by the thickness at the lowest point D of core packing land which extends in parallel with the line l. Thickness of the cavity 10 at the uppermost point of the packing land is designed suck that it is thicker than the desired thickness α by an additional thickness β which is represented by a segment EF extending radially outwardly from the line l and which is determined by the shrinkage coefficient of the thickness α. The inner side face of the outer mould 11 is determined by a curved line between point A and F and a straight line between points F and B, and these lines AF and FB are to be smoothly extended without discontinuty from the ceiling face 12 including corner R. A synthetic resin lid cap molded in the cavity 10 will have its slightly swelled out side surface on its packing land by the additional thickness β when it is separated from the moudls 11 and 20, but it will shrink to the desired thickness 2 with no unbalanced shrinkage as it is cured, resulting in a well molded lid cap with good appearance and no deformation.

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