PET Preform Mould Cooling System Design: Why It Determines Your Cycle Time
Cooling accounts for 50–70% of total injection moulding cycle time. In PET preform production where cycle times of 6–14 seconds are standard, even a 1-second cooling improvement translates to millions of extra preforms per year. Here is how cooling system design makes or breaks your output.
The Physics of Cooling in PET Preform Moulds
Every preform enters the mould as liquid PET at ~280°C. The cooling system must remove enough heat for the preform to reach a safe ejection temperature (typically below 70°C for the preform skin) while simultaneously quenching fast enough to prevent crystallisation in the preform body.
Core Cooling vs. Cavity Cooling
| Zone | Design Challenge | Critical Parameter | Hexamech Approach |
|---|---|---|---|
| Core pin (inside preform) | Narrow geometry limits channel size; turbulence harder to achieve | Water flow must remain turbulent (Re > 4000) | Optimised core bore diameter; bubble jet or spiral inserts for turbulence |
| Cavity (outside preform) | More geometric freedom but must not compromise wall strength | Channel proximity to mould surface; uniform distribution | Strategically placed channels; CFD-verified flow distribution |
Cooling Water Specifications
| Parameter | Specification | Effect if Out of Range |
|---|---|---|
| Water temperature | 8–15°C (chilled) | Higher temp = longer cooling, risk of body haze |
| Flow regime | Turbulent: Re > 4,000 | Laminar flow reduces heat transfer efficiency 50–80% |
| Water quality | Treated, low hardness | Scale builds up; cooling efficiency degrades over time |
| Pressure | 3–6 bar at mould inlet | Low pressure = insufficient flow velocity = laminar risk |
Cooling circuit scale is one of the most common and under-recognised causes of cycle time creep and quality drift. A mould that runs at 9 seconds in year 1 can drift to 12 seconds by year 3 if cooling circuits are not periodically descaled and inspected. Hexamech includes cooling circuit documentation with every mould — recording baseline flow rates at commissioning so deviations are immediately identifiable.
Cooling Design That Delivers Your Target Cycle Time
Hexamech calculates cooling circuit requirements before the mould is designed — not after the first trial shows a problem.
Discuss Your Cycle Time Target