A process for injection molding polyester premixes

Claim 1

A process for injection molding thermosetting polyester premixes, comprising the steps of forcing under pressure raw material which is a thermosetting polyester premix in putty-like lumps containing glass fiber-like reinforcement material into the upstream end of a screw-containing heating cylinder through a converging feed path extending radially toward the screw and then tangential to and in the direction of rotation of the screw for a distance less than the circumference of the screw while raising the temperature of the raw material by externally heating the material in the converging path sufficiently so that the externally supplied heat and the heat due to the advancement and shearing action raise the temperature of the raw material to a temperature at which it is plastic and yet is below the thermosetting temperature of the raw material, advancing the thus fed material by the rotation of said screw in said heating cylinder from the upstream end to the downstream end while controlling the temperature thereof by externally heating said cylinder sufficiently so that the externally supplied heat and the heat due to the action of the screw on the raw material keep the temperature of the raw material at a temperature at which it is plastic and still below the thermosetting temperature of the raw material, further advancing the material in the cylinder downstream of the check valve means, and injecting the material into a die heated to the thermosetting temperature of the raw material while checking reflux of the material from the die while at the same time heating the downstream end portion of said heating clyinder downstream of said check valve means to maintain the temperature of the raw material at least said last mentioned temperature and below the thermosetting temperature of said raw material.