How to Choose a PET Preform Machine: Cavities, Tonnage and Neck Finish

Three numbers you already know — preforms per hour, preform weight and neck finish — decide the preform machine. The clamping force and cavity count follow from them.

This guide follows the order buyers usually work in: the bottle, the output, the machine size, the series, then the equipment around the machine. We supply PET preform injection molding machines and cut the PET preform moulds in our own workshop. We have been in business since 2007.

Watch: the machine running

What you will see: a multi-cavity preform mould at work and the clear preforms dropping onto the take-off conveyor.

Step 1: Start from the bottle — volume, preform weight and neck finish

Everything about the machine follows from the preform, and the preform follows from the bottle. Before you compare machines, write down three things about the bottle you want to make:

• The bottle and its use. Its volume, and whether it is still or carbonated, hot-fill or ambient.
• The preform weight, in grams. If you do not know it yet, the bottle and its use are enough for us to work from.
• The neck finish. This is the thread standard of the bottle neck, for example PCO 1881, PCO 1810 or a 30 mm neck such as 30/25. If you do not know what yours is called, send us a cap or a dimensioned drawing.

The neck finish is moulded into the preform and does not change when the bottle is blown, so it has to match your cap and your filling line — a taller PCO 1810 and a shorter PCO 1881 neck, for example, take different caps. How the neck insert is built into the mould is explained in PET preform mould design.

Heavy preforms for jars, wide-mouth and large-format bottles need a bigger shot; the 328-ton machine in Step 3 is listed for them. A wide-mouth jar is blown from a wide-mouth preform, so tell us if your container has a wide opening.

Step 2: From preforms per hour to cavities

Hourly output is simple arithmetic:

Preforms per hour = cavities in the mould × shots per hour
Shots per hour = 3,600 ÷ cycle time in seconds

Preforms have thick walls, so cooling is normally the longest part of the cycle.

For example, you want 12,000 preforms per hour and your preform runs a 12-second cycle. That is 3,600 ÷ 12 = 300 shots per hour, so you need 12,000 ÷ 300 = 40 cavities. Moulds come in standard layouts, so you step up to the next one, 48 cavities, which gives 48 × 300 = 14,400 preforms per hour before downtime. A shorter cycle needs fewer cavities; a thicker or heavier preform has a longer cycle and needs more. This is an illustration only and does not describe any machine on our list: the real cycle depends on the preform weight and wall thickness, and we confirm it for your preform.

Figures from our range:

• One machine in our Efficient series makes up to 20,000 PET preforms per hour with a 72-cavity mould.
• Our Economical series runs moulds from 8 to 48 cavities; the Efficient series goes up to 96.
• Common preform moulds have 16, 24, 32, 48 or 72 cavities.

Output and cycle time tell you how many cavities you need. More cavities mean a larger hot-runner mould and a bigger machine to carry it, so we check that the clamping force, shot size and platen size of the machine can carry that mould. We work it out from your output target, list the workable options in the quotation and explain the trade-offs in plain words. For the mould side of this choice, see cavitation in PET preform mould design.

Step 3: Size the preform machine — clamping force and injection weight

Two numbers size the machine:

• Injection weight (shot size), in grams. The preform weight times the number of cavities gives the shot the injection unit has to deliver every cycle. The shot also sets the screw size. As a working rule, choose a machine whose rated shot sits well above this figure, so that your shot uses roughly a third to three-quarters of it: too close to the limit and the machine struggles to fill and recover, too small and the PET sits too long in the barrel.
• Clamping force, in tons. The clamp has to hold the mould shut against the pressure of the melt. The force needed follows from the combined projected area of all the cavities and the injection pressure, so it rises with the cavity count. The mould must also fit the machine: the tie-bar spacing, platen size, mould thickness and opening stroke all have to match.

Examples from our range:

For 0.5–2 L water bottles there is also a 16- to 96-cavity PET preform machine, with the cavity count matched to your bottle.

Your preform weight and cavity count decide which size fits. Send them and we recommend the model, or tell us the machine you already have and we design the mould to fit it. For how a machine and mould are matched in general, see how an injection molding machine works.

Send your preform weight and cavity count Ask on WhatsApp

Step 4: Economical or Efficient series

If you are starting a new line or need a medium output, start with the Economical series. If you need high cavity counts and large volume, look at the Efficient series. Not sure? Send your preform weight, neck finish and hourly output and we recommend the series, the cavity layout and the mould.

Drive. Preform machines come with two kinds of drive. A servo-hydraulic machine uses a servo motor to drive the hydraulic pump, so it saves energy compared with a fixed-speed pump and keeps the high force of hydraulics, which suits large, heavy moulds. An electric machine drives its movements directly with servo motors, which suits work where precise, repeatable shots and low energy use matter most. Tell us which your plant prefers and we match the model to it.

Send your preform weight, neck finish and output Ask on WhatsApp

Watch the footage

Footage: an Efficient-series PET preform injection molding machine with automated take-out producing PET preforms.

Step 5: What goes with the preform machine

A preform machine is one part of a PET bottle line. You will need these around it:

• Dryer and chiller. PET is dried before it is melted, normally in a desiccant dryer down to below about 50 ppm moisture, because water left in the resin breaks the polymer chains when it melts and the preforms come out hazy or streaky. The chiller sends cold water through the mould, often at around 10 °C, so the thick preform walls cool quickly and stay clear; warmer water makes the cycle longer.
• Take-out robot. A robot takes the hot preforms out of the open mould, holds them in cooling tubes so the mould can close again sooner, and then sets them on a conveyor, as in the footage on this page.
• The blow step. A preform machine does not blow bottles. To turn the preforms into bottles you need a stretch blow machine with a PET stretch blow mould, or you make preform and bottle on one machine with a one-step injection stretch blow molding machine.
• The preform mould. We cut the PET preform mould in our own workshop to your neck finish and preform weight, and the mould takes 40–60 days from approved drawings. Order it with the machine and we ship machine and mould as one set, tested and tuned together. We also cut preform moulds for machines you already have, whether or not the machine came from us.

Figure 1. Two routes to a PET bottle: a preform machine and a stretch blow machine, or one machine that does both.

After the machine ships

We install and commission the machine on site and train your operators. The warranty covers mechanical parts for 2 years and electrical parts for 1 year, for faults not caused by misuse.

What to send us for a PET preform machine quote

Send these five facts and we quote the machine, the mould, or both:

1. Neck finish, or a sample cap or a dimensioned drawing.
2. Preform weight, or the finished bottle: volume, still or carbonated, hot-fill or ambient.
3. Output per hour you need.
4. Your machine, if you only need the mould: its make and model.
5. Resin and colour.

Send what you have — a photo of your bottle is enough to start. Get an exact quote within 24–48 hours.

Send your drawing or photo Ask on WhatsApp

FAQ

Related: PET preform moulds · PET stretch blow moulds · PET preform mould design · How PET preforms are made and blown into bottles · One-step injection stretch blow molding machines