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

Hi Biswanath,

The gate size depends primarily on three key factors:

1. Wall Thickness at Gate Location:
   The gate depth should ideally be 75–80% of the wall thickness of the face where the gate is placed. Exceeding this ratio may lead to poor gate sealing and flow imbalance.

2. Shear Rate of the Plastic Material:
   Since PEEK is a high-temperature engineering polymer, excessive shear can cause material degradation or burn marks due to shear heating.

   • Maximum allowable shear rate at gate: 30,000 s⁻¹

   • Recommended range: 10,000–20,000 s⁻¹
     To maintain this range, use a larger gate size and optimize the injection speed to control shear rate effectively.

3. Gate Freeze Time:
   While increasing gate size helps reduce shear, it should not result in an excessively long gate freeze time. Ensure the gate freeze time is shorter than the End of Packing (EOP) so that adequate packing can occur before the gate freezes.

In summary:

• Keep gate depth ≤ 75–80% of wall thickness.

• Maintain shear rate within 10,000–20,000 s⁻¹.

• Ensure gate freeze time < EOP, with proper packing completed before gate freeze.

All these parameters can be easily monitored and validated using Moldex3D Fill and Pack results.

I hope this clarifies your query. Thank you for reaching out to us through the forum.

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