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Jan 05, 2024

Purging Hot runners: Open or closed methods

Running purging compound through hot runner channels can remove residual

Running purging compound through hot runner channels can remove residual materials while leaving a minimal amount of residue behind. This ensures continued proper and efficient operation of a molding machine.

Prior to starting the process, make sure that the purging compound is the proper grade for one's hot runners. For external heating systems, raise the manifold temperature 35-55 degrees to improve flow. If you are running heat-sensitive resins, do not exceed the top safe operating temperature of the material.

If using an internal heating system, make sure to consult with a purging compound provider to ensure proper use.

For purging hot runner channels with the mold plates open, after the screw and barrel have been cleaned thoroughly using your choice of purging compound, set the nozzle into the mold, and open the plates.

The mold plates should be open, and a surface set up for collecting the purgings. Then, verify that the mold safety door is closed and add enough purging compound to fill the barrel about halfway.

At this point, extrude the purging compound through the hot runner system, first at a medium velocity. Then, increase screw speed to the maximum safe level for maximum cleaning.

Once the purging compound is flowing through all of the gates, injection shots can be performed with the mold plates open.

Finally, inspect purgings for any color or carbon contamination, repeating the final three steps, if needed. Any remaining purging compound can be purged at the maximum safe screw speed. Adjust the barrel temperatures and hot runners for the processing parameters for the next resin to be used. Flush the system with some of the resin until no compound is seen, and resume production.

Hot runner channels also can be purged with mold plates closed.

The screw and barrel are cleaned, and the nozzle is set into the mold, and the mold safety door is closed.

Cooling time in the hot runner cavities is reduced and the cavities are sprayed with mold release to reduce the slight chance of purging compound parts getting stuck in the hot runner cavities.

The pack and hold pressures and velocities are removed and purging compound is injected using short-shot molding, while using only as much shot as is needed to safely remove parts from cavities, not to exceed 90 percent.

Parts should be ejected while warm and inspected for color and/or carbon contamination until parts are clean.

Repeat the last three steps until purging compound is visually free of color and/or carbon contamination and has returned to a clean appearance.

Flush the system with the next resin to be processed, molding parts until the purging compound can no longer be seen in the next resin. Now, one is ready to resume production.

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