Valve nozzle for injection molding

Abstract

An injection molding valve nozzle comprises a nozzle head with a gate dividing a flow passage into two sections, a spool slidably attached to the gate and including axial grooves in its outer surface and a spring for urging the spool rearward. The valve nozzle is so arranged that the gate is closed by the spool because the grooves do not reach the gate upon lower pressure of resins below a certain level, but that the spool may slide forward to extend the grooves over the gate, communicating a front passage with a rear passage upon higher resin pressure above a certain level and that when the pressure differential between the front and rear passages decreases or the resin pressure descends below a certain level, the spool slides rearward by the spring for closing the gate. Thus, the gate is closed by the spool until the resin pressure rises up to a certain level. The engaging portions of the gate and the spool may be made long depending on the pressure and viscosity of the resin so that the gap between the gate and the spool can be determined to be approximately 10 .mu.m. Therefore, easy manufacturing of the valve nozzle is realized. Further, although the resins flow into the gap, the spool surely slides forward during injection to spout the resin by the resin from the rear without remaining, deterioration and dissolution. Therefore, the life of the valve is improved.