Reduced Size Runner for an Injection Mold System

Abstract

A runner system for a multi-cavity injection molding system, the runner system having runners of reduced size.

What is claimed is: 
     
         1 . A method of operating an injection molding machine having a mold with multiple cavities, the method comprising, during each molding cycle:
 injecting a molten thermoplastic polymer through a nozzle, then through a runner system with multiple runners, including a set of runners in closest proximity to the mold, and then into multiple cavities of a mold;   filling the cavities of the mold while maintaining the molten thermoplastic polymer at a substantially constant melt pressure that fluctuates no more than 30% with respect to a desired pressure, wherein the melt pressure is measured at the nozzle; and   forming molded parts that essentially duplicate the shapes of the cavities;   wherein, during the molding cycle, the molten thermoplastic polymer experiences a peak melt pressure, measured at the nozzle;   wherein a particular cavity from the multiple cavities molds a particular part that has a particular length to thickness ratio, which is a particular L/T;   wherein, a particular runner from the set of runners leads to the particular cavity, and the particular runner has a particular hydraulic diameter, which is a particular DH, measured in inches;   wherein the particular DH is sufficiently large so as to permit the flow of the molten thermoplastic polymer through the particular runner, and the particular DH is in the range of 0.020″ to 0.130″; and   wherein, for the particular runner leading into the particular cavity, the particular DH is less than or equal to 20 times the peak melt pressure divided by the particular (L/T) −1 .   
     
     
         2 . The method of  claim 1 , wherein the peak melt pressure is 6,000 psi or less. 
     
     
         3 . The method of  claim 1 , wherein the peak melt pressure is 6,000 psi to 15,000 psi. 
     
     
         4 . The method of  claim 1 , wherein the particular L/T is greater than 100 but less than 1000. 
     
     
         5 . The method of  claim 1 , wherein the particular L/T is greater than 200 but less than 1000. 
     
     
         6 . The method of  claim 1 , wherein the particular part has an average thickness of less than 0.394″ (10 millimeters). 
     
     
         7 . The method of  claim 1 , wherein the particular part has an average thickness of less than 0.197″ (5 millimeters). 
     
     
         8 . The method of  claim 1 , wherein for the particular runner leading into the particular cavity, the particular DH is less than or equal to 8.25 times the peak melt pressure divided by the particular (L/T) −0.889 . 
     
     
         9 . The method of  claim 1 , wherein:
 each of the cavities molds a part that has a length to thickness ratio, which is L/T; and   wherein, each of the runners leads to one of the cavities, and each of the runners has a hydraulic diameter, which is DH, measured in inches;   wherein each DH is sufficiently large so as to permit the flow of the molten thermoplastic polymer through its runner, and each DH is in the range of 0.020″ to 0.130″; and   for each runner leading into each cavity, its DH is less than or equal to 20 times the peak melt pressure divided by its (L/T) −1 .   
     
     
         10 . The method of  claim 9 , wherein the peak melt pressure is 6,000 psi or less. 
     
     
         11 . The method of  claim 9 , wherein the peak melt pressure is 6,000 psi to 15,000 psi. 
     
     
         12 . The method of  claim 9 , wherein each L/T is greater than 100 but less than 1000. 
     
     
         13 . The method of  claim 9 , wherein each L/T is greater than 200 but less than 1000. 
     
     
         14 . The method of  claim 9 , wherein the particular part has an average thickness of less than 0.394″ (10 millimeters). 
     
     
         15 . The method of  claim 9 , wherein the particular part has an average thickness of less than 0.197″ (5 millimeters). 
     
     
         16 . The method of  claim 9 , wherein for each runner leading into each cavity, its DH is less than or equal to 8.25 times the peak melt pressure divided by its (L/T) −0.889 .