There are several ways to set the initial injection machine control settings for a specific molding job. On modern machines, the molding machine controller stores the settings from previously successful production runs. The technician simply loads the appropriate molding job into the controller.
If you are running an older injection molding machine that does not automatically store the control settings, use the set-up sheet to manually set the machine controls to an initial safe-operating state.
We’ll start with procedures for setting feed throat water temperature
The feed throat temperature setting is a process variable that is often overlooked. Some general guidelines to keep in mind when setting feed throat water temperature are:
- Too low a temperature wastes heating from the rear barrel heating zone
- A low temperature can also allow moisture to get in or on plastic granules
- Too high a temperature, or not turning on the throat cooling at all, can allow plastic granules to begin melting in the feed throat. This could block the flow of granules to the screw.
Tech Tip: The feed throat temperature setting will depend on the material being processed. With materials that have to be pre-dried and high temperature materials, the temperature setting can be set higher. The usual upper limit is about 120° F (49° C). Materials that have a low melt temperature range should be run with a lower feed throat temperature. Typically 60° to 70° F (16° to 21° C).
Don’t overlook the importance of setting the proper feed throat temperature. If incorrectly set, it can be very dangerous. For example, If you set too high a feed throat temperature, blockage in the hopper feed throat can occur. If this happens, you should immediately move the injection unit back away from the sprue bushing on the injection mold.
Also, if gas pressure due to degradation builds up in the barrel, the gas can escape out the nozzle. Excessive gas pressure can also blow out of the hopper throat without warning. That is a hazard to anyone who is near the injection molding machine. It also can seriously damage the molding machine. It is an expensive and completely avoidable mistake.
