Hi David,

The residence time of plastic material in the barrel and hot runner is a critical parameter that must be carefully monitored, especially for heat-sensitive materials.

If the residence time is too long compared to the cycle time, the material may undergo thermal degradation, leading to issues such as discoloration, burn marks, loss of mechanical properties, or increased viscosity.

Ideally, the residence time in the hot runner system should be kept as short as possible while maintaining a stable melt temperature and good flow balance. The general guideline is to ensure that the total residence time (barrel + hot runner) does not exceed the material supplier’s recommended limit depending on the polymer.

In short:

• Monitor residence time regularly, especially for long cycle molds or large hot runner systems.

• Avoid excessive residence time by optimizing barrel capacity, injection speed, and cycle time.

• Purge material if the machine remains idle for extended periods to prevent degradation.

Monitoring these factors helps ensure consistent melt quality and prevents thermal damage to the polymer.

In Moldex3D , you can check what is residence time of material in the Process summary page and try to keep it as low as possible.

In trials  for temperature sensitive material  keeping minimum cushion in previous cycle is recommended.

I hope this clarifies your query.

Best regards,
Abhishek Tiwari
Regional Manager – North & West India | Moldex3D