Energy Consumption of PET Preform Injection Moulding

Injection molding machine energy consumption is the cost line nobody in a preform plant can quote from memory. The press is bought on clamping force and cycle time, the tool on cavity count, the chiller on tonnes of refrigeration — and then the electricity bill arrives once a month as a single number that nobody can attribute to a product, a tool or a shift.

That matters more than it used to. Energy is now a competitive variable: a plant that knows its consumption per kilogram can price work accurately, spot a machine drifting out of condition within days, and argue a sustainability claim with a meter reading instead of an estimate. A plant that does not know it can only pass on whatever the utility charges.

Sailwin has built injection moulding machines for PET preforms for 15+ years, with 500+ machines delivered to 60+ countries, manufacturing under ISO 9001:2015 with CE marking and a 2-year machine warranty. The SW-P series covers 14 models from 170 kN to 5500 kN, runs dedicated PET screws and barrels with far-infrared nano heater rings, and supports 64-cavity valve-gate hot runner tools. This guide explains why a single kWh/kg figure is a property of your cell rather than of a machine, how to establish yours in one shift, and which machine choices move it.

1. Why No One Can Quote You a Single Figure

The energy needed to make a preform is not fixed by the machine. It is fixed by the work the machine does, and the work changes with every decision made around it.

A heavier preform needs more heat and more cooling. A higher cavity count spreads the same clamp and injection work over more parts but demands more cooling capacity and a larger hot runner load. A shorter cycle reduces the time over which fixed loads are amortised, so the fixed loads — heaters, dryers, chillers, control and hydraulics idling — make up a larger share of each kilogram. Thin-wall or hot-fill grades need tighter thermal control, which usually means more cooling energy rather than less.

This is why an honest supplier will not hand you a single number. What a supplier can do is tell you the installed power, the drive architecture, the temperature control accuracy and the expected consumption of the auxiliary services, and then help you measure the result. The calculation itself is simple:

Specific consumption (kWh/kg) = metered energy over a stable run (kWh) ÷ good preforms produced (kg)

Run that for a full shift, then again for each product on each machine. The first run gives you a baseline; the comparison between products is where the useful information appears, because a tool consuming noticeably more per kilogram than a similar tool is telling you about its cooling circuits or its cycle, not about the price of electricity.

2. Where the Energy Actually Goes

Chasing the total without breaking it down leads to the wrong investment. Five loads matter on a preform cell, and each answers to a different lever.

Two loads are easy to overlook. Rejects are the most expensive energy in the plant, because the material, the heat, the cooling and the labour have all been spent on a part that is scrapped — which is why temperature control at approximately ±1 °C under PID is an energy argument as much as a quality argument. Idle time is the second: dryers, chillers and heaters left running through a long changeover consume without producing anything, and mould changes that take under 30 minutes directly reduce that waste.

3. Establishing Your Baseline in One Shift

You do not need a permanent monitoring system to start. You need one metered shift and a repeatable method.

1. Meter the right boundary. Decide whether the figure covers the press alone or the whole cell including chiller, dryer and automation, and keep that boundary identical every time you measure. A number that changes boundary is not a benchmark.
2. Wait for steady state. The first hour after a cold start is not representative. Measure after the tool, the barrel and the water circuit have stabilised.
3. Record preforms in kilograms, not pieces. Weigh the output of the measured period, and count good parts only.
4. Log the conditions with the result. Cycle time, melt temperature, tool water temperature and ambient temperature belong beside the figure, because each of them changes it.
5. Repeat per product and per machine. One figure is a curiosity; a table of figures per tool is a management tool. Sailwin machines log 40+ process parameters in real time, so the machine record can be aligned with the meter reading for the same window.
6. Compare against installed power. A machine drawing a high fraction of its installed power while producing at its rated cycle is working normally; the same draw at half the expected output is the signal to investigate the tool, the cooling or the material.

4. Case Study: Making Energy Visible on a Preform Cell

A preform producer running a high-cavity hot runner tool could quote material cost per thousand pieces to the cent, but could not say what a thousand pieces cost in electricity.

Composite scenario from preform plant engineering work, with no customer-identifying detail. Plant-specific figures are confirmed during engineering review.

5. Machine Choices That Move the Number

Once you have a baseline, the machine decisions that reduce it are concrete rather than theoretical.

• Drive architecture. Servo drive systems cut energy use by up to 30 percent compared with a conventional hydraulic arrangement, because the pump only works when the cycle calls for it instead of holding pressure continuously.
• How heat reaches the polymer. Sailwin injection machines use a dedicated PET screw and barrel with far-infrared nano heater rings, chosen for heat-transfer behaviour into the melt rather than for installed kilowatts alone.
• Temperature stability. PID control holding approximately ±1 °C keeps the cycle repeatable and reduces rejects, and a rejected preform has already consumed its full share of heat, cooling and drive energy.
• Correct machine size. The SW-P series spans 14 models from 170 kN to 5500 kN, and matching clamping force and injection unit to the tool avoids carrying oversized loads through every cycle.
• Changeover speed. Mould changes completed in under 30 minutes reduce the idle time during which heaters, dryers and chillers consume without producing.
• Air-side recovery. High-pressure exhaust recovery reduces compressor load by around 20 percent, which shows up in the plant total rather than on the press meter alone.
• Automation interface. An EUROMAP 67 robot interface lets handling equipment be integrated to the cycle so that robots and conveyors stop when the machine stops.

Machines are FAT tested at full load before shipment, so the power and utilities behaviour is documented before the machine leaves the factory rather than discovered on site. Standard delivery is 30–45 days and 45–60 days for custom configurations, with installation and commissioning on site taking 3–7 days, common wear parts shipped within 48 hours and remote support available 7×24.

Frequently Asked Questions