A new 16-cavity mould arrives for the 220 t press. On day one, two nozzle zones will not hold temperature, the valve gates close late and the preforms show strings at the gate. The mould is fine; the machine side was not ready. Hot runner preform moulds need the machine to provide enough controlled heater zones, valve-gate air at the right pressure, chilled water at the rated flow, and platens that carry the mould and keep it parallel.
This article covers each of those needs and what to agree with the mould maker before the mould is built.
Key Takeaways
- Count one controller zone for every nozzle, plus the manifold and sprue zones, and keep spare zones for failures.
- The PETplanet Rapid Guide gives valve-gate air of typically 8 to 10 bar, with water flow to the mould and robot at the mould maker's rating.
- Nozzle tip heat decides gate quality: too hot and the gate strings, too cold and the gate area turns crystalline.
- Check mould weight on both platens, platen parallelism and the locating ring before the mould is built, not on the day it arrives.
What Must the Machine Supply to Hot Runner Preform Moulds?
Three utilities: heater power with a controlled zone for every nozzle, manifold and sprue heater; compressed air for the valve gates; and chilled water for cavities, cores, neck splits and the take-out robot. Each must match the mould maker's figures, not the machine's defaults.
The PETplanet Rapid Guide to Perfect Preforms, in its section on wavy bodies, gives valve-gate air of typically 8 to 10 bar. It also asks for water flow to the mould and to the robot's receptacles at the mould maker's rating. The higher-cavity article in this series covers mould water temperature.
Air quality matters as much as pressure. Wet or dirty air can make valve stems slow to close, and the gate then behaves like an open gate. Fit a dryer and filter on the line to the mould, and a gauge where an operator can read it.
What hot runner preform moulds need from the machine side
| Utility | What the mould needs | What to confirm on the machine |
|---|---|---|
| Heater zones | One per nozzle, plus manifold and sprue | Controller zone count, spare zones, thermocouple type |
| Valve-gate air | Typically 8 to 10 bar, clean and dry | Regulated supply, dryer and filter at the mould |
| Chilled water | Flow at the mould maker's rating | Pump and chiller capacity for mould and robot together |
| Platens | Carry the mould weight, stay parallel | Maximum mould weight on each platen |
How Does Nozzle Tip Heat Affect the Preform Gate?
Directly. In the PETplanet Rapid Guide's section on stringing, nozzle tip heat has a major effect on the gate. Too high keeps the dome and gate nub hot, and the gate strings. Set it low enough to freeze the nub, but not so low that crystallinity forms.
The same section links stringing to a gate that is too hot, usually on moulds without valve gates or where valve stems do not close. That puts the burden on the machine's controller: every tip zone needs a stable, correct reading, because one drifting thermocouple shows up as one bad cavity.
Our view: for production preforms, specify valve gates and a controller with spare zones. Open gates save on mould cost, but the time lost to gate defects and tip tuning soon outweighs it on a 220 t machine running many cavities.
Can the Platens Carry a Hot Runner Mould?
Check before you order. A hot runner preform mould carries a manifold plate, many cores and neck splits, so it can be heavy for its size. Bruce Catoen's sizing guide in MoldMaking Technology says to check the maximum mould weight for both platens, not only the moving one.
The same guide gives platen level and parallelism of 0.025 to 0.05 mm as generally acceptable on machines under 500 t. It notes that most moulds use a 101.6 mm or 120 mm locating ring, and that the mould thickness must fall between the machine's minimum and maximum shut height.
Ask the mould maker for the mould weight and thickness early, while the design can still change. A mould that is too thick for the shut height, or too heavy for the fixed platen, is far cheaper to fix on paper than on the shop floor.
Wiring is the last fit check. Agree where the heater and thermocouple connectors sit on the mould, and that their type and pin layout match the controller cables. A mismatch here can hold up the first trial while new cables are made.
Does Recycled Content Change the Hot Runner Question?
It can. The PWM (Amendment) Rules notified on 31 March 2026 require rigid plastic packaging to contain at least 30% recycled material in 2025-26, rising to 60% by 2028-29. Bottles outside food contact may need rPET, and recycled feed brings contamination risks for hot runner tips.
The same rules exempt packaging where FSSAI and similar rules restrict recycled content, and FSSAI's own position on recycled PET for food is set out in the applications article in this series. If you plan rPET in non-food bottles, ask the hot runner maker about melt filtration and tip design for recycled feed.
Keep records too. Whoever files the recycled-content return, your buyer will ask what share of each preform batch was recycled and from which supplier. Log it with the resin lot from the first run.
What Should You Agree With the Mould Maker Before the Mould Is Built?
Agree the heater zone count and thermocouple type, valve-gate air pressure, water flow per circuit, mould weight, thickness and locating ring size. Check each against the machine before the design is frozen, so the mould runs on day one. See the 220 ton PET injection moulding machine page.
Frequently Asked Questions About Hot Runner Preform Moulds
Can the machine controller run the hot runner, or do I need a separate one?
Either works if it has enough zones, the right thermocouple type and stable control. A machine-mounted controller keeps settings in one place, while a separate unit can move with the mould. What matters is zone count, spare capacity and how quickly a failed zone can be found and fixed.
Why does one cavity keep stringing when the rest are fine?
Look at that cavity's nozzle tip zone first. A tip running hot keeps the gate nub soft, and a faulty or loose thermocouple can read low while the heater runs high. On valve-gated moulds, check that the stem closes fully. Then check water flow to that cavity.
What happens if valve-gate air pressure drops?
The stems may close slowly or not fully, so gates behave like open gates and can string or leave long nubs. Fit a pressure switch that alarms or stops the machine on low air, and keep a gauge at the mould so operators can see the pressure.
How long should a hot runner take to heat up before moulding?
Follow the hot runner maker's start-up sequence. Heating everything at full power at once can damage heaters or leave zones uneven. A controller with a soft-start mode drives moisture out of the heaters first. Allow time for the manifold and nozzles to settle before the first shot.
Do I need a separate water circuit for the robot?
The take-out robot's receptacles keep cooling the preforms after ejection, so they need water at the flow the mould maker or robot supplier rates. Size the chiller and pump for mould and robot together, or the robot will steal flow from the mould on warm days.
Related Articles
- What PET Products Can You Make on a 220 Ton Machine?
- Higher-Cavity Preform Moulds on a 220 Ton Machine
- Three Screw Options for PET on a 220 Ton Machine Explained
Sources & References
- PETplanet Insider, R. Unterlander and O. Brandau: The Rapid Guide to Perfect Preforms, part 34: Wavy Body
- PETplanet Insider, R. Unterlander and O. Brandau: The Rapid Guide to Perfect Preforms, part 28: Stringing
- MoldMaking Technology, B. Catoen: Machine Sizing and Specification for Optimal Mold Performance, Part 1
- Polymerupdate, D. K. Jha: India eases plastic recycling regulations
Technical Disclaimer
Disclaimer: The information provided in this document is for general informational and educational purposes only. It is based on technical references and industry information available at the time of preparation and may be subject to change. It does not constitute engineering, technical, commercial or professional advice, nor does it constitute a quotation, specification, warranty or contractual commitment by Pratishna Engineers.
Actual injection moulding machine and process requirements vary according to the component design, material, mould, production volume, machine configuration and operating conditions. The information, examples, calculations and recommendations provided should be independently evaluated and verified for the specific application before making any equipment, process or production decision. Information obtained from third-party sources remains subject to the accuracy and limitations of those sources.
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