Injection molding of crosslinking polymers

Abstract

Non-time dependent measured variables are used to effectively determine an optimal hold profile for an expanding crosslinking polymer part in a mold cavity. A system and/or approach may first inject molten expanding crosslinking polymer into a mold cavity, then measure at least one non-time dependent variable during an injection molding cycle. Next, the system and/or method commences a hold profile for the part, and upon completing the hold profile, the part is ejected from the mold cavity.

What is claimed is: 
     
         1 . A method for determining whether an expanding crosslinking polymer part is ready to be ejected from a mold cavity during an injection molding cycle, the method comprising:
 injecting molten expanding crosslinking polymer into a mold cavity;   measuring at least one non-time dependent variable during the injection mold cycle;   commencing a hold profile for the expanding crosslinking polymer part; and   upon completing the hold profile, ejecting the part from the mold cavity.   
     
     
         2 . The method of  claim 1 , wherein commencing the hold profile comprises:
 upon the measured at least one non-time dependent variables reaching a first threshold value, commencing the hold profile;   restricting additional molten expanding crosslinking polymer from being injected into the mold cavity; and   upon the measured at least one non-time dependent variables reaching a second threshold value, terminating the hold profile.   
     
     
         3 . The method of  claim 2 , wherein the first threshold value is indicative of the mold cavity being substantially full of molten expanding cross linking polymer. 
     
     
         4 . The method of  claim 2 , wherein the second threshold value is indicative of the part being structurally sound. 
     
     
         5 . The method of  claim 2 , wherein the measured at least one non-time dependent variable comprises a cavity pressure value. 
     
     
         6 . The method of  claim 5 , wherein the first threshold value comprises a nominal increase in cavity pressure. 
     
     
         7 . The method of  claim 5 , wherein the second threshold value comprises a substantially constant cavity pressure value over a period of time. 
     
     
         8 . The method of  claim 2 , wherein the measured at least one non-time dependent variable comprises a temperature value. 
     
     
         9 . The method of  claim 8 , wherein the first threshold value comprises a nominal increase in cavity temperature. 
     
     
         10 . The method of  claim 8 , wherein the second threshold value comprises a substantially constant cavity temperature value over a period of time. 
     
     
         11 . The method of  claim 1 , wherein the hold profile is commenced at a substantially constant pressure.