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, whereupon a cure profile is commenced.
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:
during the injection molding cycle, injecting molten expanding crosslinking polymer into a mold cavity;
during the injection molding cycle, measuring at least one non-time dependent variable during the injection mold cycle;
during the injection molding cycle and upon the at least one non-time dependent variables reaching a first threshold value, commencing a hold profile for the expanding crosslinking polymer part, the hold profile comprising:
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,
during the injection molding cycle and upon completing the hold profile, ejecting the molded part from the mold cavity; and
during the injection molding cycle and upon ejecting the molded part, commencing a cure profile for the molded part whereby the molded part expands to a final form, the cure profile comprising:
measuring a different non-time dependent variable,
upon the measured different non-time dependent variable reaching a third threshold value, transferring the molded part to a stabilization tunnel in which the molded part cools for a duration dependent on the third threshold value,
wherein the at least one non-time dependent variable and the different non-time dependent variable is selected from the group consisting of a pressure value, a temperature value, a rate of change in pressure values, or a hardness value.
2. The method of claim 1 , wherein the first threshold value is indicative of the mold cavity being substantially full of molten expanding cross linking polymer.
3. The method of claim 1 , wherein the second threshold value is indicative of the molded part being structurally sound.
4. The method of claim 1 , wherein the measured at least one non-time dependent variable comprises a cavity pressure value.
5. The method of claim 1 , wherein the hold profile commences at a substantially constant pressure.
6. The method of claim 1 , wherein the third threshold value is indicative of the molded part being essentially fully formed for further processing.
7. The method of claim 1 , wherein the measured different non-time dependent variable comprises a pressure value.
8. The method of claim 1 , wherein the step of commencing the cure profile comprises allowing the molded part to cool for a predetermined amount of time.