INJECTION MOLDING OF CROSSLINKING POLYMERS
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.
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.