This study determines the optimum feed zone temperature and screw speed settings.

The optimal feed zone temperature is the temperature that results in the shortest and most stable screw recover time. This is the temperature where the polymer sticks best to the screw, and it’s conveyed most efficiently.

Once the optimal feed zone temperature is determined, the screw rotational speed is adjusted so that the screw recovery time consumes 80 % of the overall cooling time.

Note that the back pressure used during screw recovery should be high enough to provide a consistent recovery time and consistent mixing.

The recovery time should not vary more than 5% from shot to shot, and 10% from material lot to material lot.

Keep in mind when setting feed throat temperature

• Too low temperature wastes heating from the rear barrel heating zone.
• A low temperature can allow moisture to get in or on plastic granules. Keep the feed throat hot enough so that it will never condensate.
• Too high 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.
• Make shure the temperature is well below the softening point of the resin to avoid bridging.

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 50° C. Materials that have a low melt temperature range normaly run better with a lower feed throat temperature. Typically 16° to 21° C.

If you have equipment with digital communication interface, we can automate this study and make it even better with integrated evaluation of information and send alerts when deviations occur!!