Yudo HOT RUNNER - Process Adviser; Color Change; Glass Fiber; Material Degradation

UH-02-Aug16-ENG P 19 / 21
5. P ROCESS A DVISER
The process of injecting plastic parts involves several areas of the technical knowledge bringing us to an
immense and complex puzzle of technical definitions and parameters that can be put together in a huge
number of different configurations.
Not aiming to approach this complex subject, in this handbook we just offer some basic generic guidelines for
typical issues that involve directly the parameters set up of the hot runner.
5.1. C OLOR C HANGE
The process of changing color in injected plastic parts is complex and depend of many factors with big
variation.
The optimal performance is then a combination of factors that can only be achieved on the basis of a case by
case study, that has toinclude a battery of validation tests.
Nevertheless there are some generic recommendations that we advise to our customers:
- Whenever possible use front removable inserts. Thus the tips become accessible for cleaning.
- Adjust the machine sprue diameter to the hot runner inlet diameter.
- The first slot should be non coloured material.
- For the color change decrease barrel temperature by 20 - 40°C and change to natural material.
- Purge the barrel with natural material first, the Hot Runner system afterwards.
- When approx. 95% of the purged material contains of natural material, increase the temperature of
the Hot Runner by 30 - 50°C and continue to purge with natural material until no further improvement
can be achieved. You can also increase the injection speed from 10 to 20%.
- Set temperature back to standard settings.
- Start molding with new color.
ATTENTION: Please observe the guidelines of the material manufacturer!
5.2. G LASS F IBER
- Do not stop production with the runners filled with glass fibre filled resin. Use non filled or purging
material. If, for some reason, it is not possible, at least stop production with valve pin stopped in open
position.
5.3. M ATERIAL D EGRADATION
- Respect plastic material specifications.
- Check the technical data sheet of the plastic material previously to process initiation.
- Residence time of the material specifications shall be taken into consideration when mold stop.
- Overtime at too high temperature may cause serious problems.
- Use standby temperatures according to material specifications.