Mold-Masters Hot Runner, User Manual, Page: 104 / 319

Section 9 - Color Change
WARNING
Ensure that you have fully read “Section 3 - Safety” before purging the Hot
Runner system.
Although it is not possible to make a generic color change procedure
that will give the best performance in all circumstances because the flow
characteristics of the plastic polymers in use can influence color changes,
there are specific procedures which work to enhance color changes.
9.1 General Tips
• Always process a natural / clear color for the first shot on an empty Hot
Runner system to coat the melt channel walls and gate bubbles with a
neutral color.
• Ensure the hopper and conveying system are free of all contamination
from the previous production color. Many times the previous color will
hang up in the hopper or conveying system and be slowly released into
the mold resulting in contaminated parts. Also, make sure there is no
contamination in the resin being used in production.
• Schedule color changes from light to progressively darker.
• Understand the economics of your color change to decide if it is
economically better to take the time to latch over the cavity plate and
clean out the gate bubbles or just run scrap parts slightly longer to clean
out the gate bubble area.
• Use purge compounds for color change in the machine barrel and Hot
Runner.
9.2 Procedure A: Simple and Effective
WARNING
To avoid serious burns when purging, wear safety clothing consisting of a
protective heat-resistant coat, heat-resistant gloves and a full face shield
over safety glasses.
Use adequate ventilation for fumes. Some plastics develop gases that
may be dangerous to personal health. Follow the plastics supplier’s
recommendations.
Do not look directly into the feed throat of a hopper - use a mirror.
Unexpected release of resin may cause serious burns.
Never handle plastic purgings or drool until they have completely cooled.
Purgings may appear solid but may still be hot and cause serious injury.
1. Empty hopper of existing color and clean thoroughly.
2. Increase Hot Runner system temperature on all zones 20°C (68°F) above
processing temperatures. On
Mold-Masters
controllers, simply push
the boost button on the controller to increase temperatures for a pre-
determined time and temperature.
9-1 COLOR CHANGE
Hot Runner User Manual
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