Thermal valve pin

Abstract

This invention relates to an improved valve pin for a valve gating injection molding system. Heat transfer to the gate area is extremely critical in valve gating systems and this is even more so when new high density glass filled materials are being molded. Thus it is necessary to provide substantially increased and more uniform heat transfer to the gate area. Accordingly, the invention provides an improved valve pin having at least a portion of the valve pin adjacent the tip end being formed of an elongated hollow sealed tube which contains a vaporizable fluid under a partial vacuum. The back end of the tube receives heat from the surrounding heater cast to vaporize the fluid in the area. The vapor pressure establishes circulation of the vapor towards the cooler tip end of the tube. The energy required to evaporate a liquid is the latent heat of vaporization and this energy is released by the vapor when it condenses upon encountering a cooler portion of the tube as it moves towards the tip end. The condensed liquid then returns to the back end of the tube where it is again evaporated. Circulation may be very rapid to provide a very greatly increased rate of heat transfer along the tube and the temperature drop along the length of the tube is reduced to a minimum. This allows minimum injection pressures and valve pin forces to be used with consequent decreases in manufacturing and operating problems and expense.

Dependencies are inferred from the claim text.