75 ton PET machine applications: what each product group needs and what to check first
| PET product | What matters most | First check on a 75 t machine |
|---|---|---|
| Still water and juice bottle preforms, small sizes | Low acetaldehyde, clarity, a neck that suits the closure | Shot weight against the barrel, and cavities that fit between the tie bars |
| Pharma syrup and tablet bottle preforms | Colour, clean handling, small batches | Mould changes and colour purging |
| Cosmetic, hair oil and disinfectant bottle preforms | Clarity or tint, many neck finishes and weights | Number of SKUs each mould must cover |
| Wide-mouth jar preforms | Large neck diameter | Mould width and projected area per cavity |
| Sample and trial preforms | Quick changes, small shots | Barrel size against a small shot |
The 75 ton PET machine applications that fit best are small bottle preforms for still water, juice, pharma, cosmetic, hair oil and disinfectant bottles, plus wide-mouth jar preforms and trial samples. Clamp is seldom the limit, because a preform's projected area is only its cross-section. Shot size, mould space and opening stroke decide what runs.
This article sets out each product group, why the clamp check comes out small for preforms, what does limit a small PET machine, and the Indian food-contact rules for bottles made from your preforms.
Key Takeaways
- A preform's projected area is its widest cross-section, so even an eight-cavity mould can need only about 31 t of clamp at a 400 bar guide pressure.
- Shot against the barrel, mould width between the tie bars and opening stroke decide what a 75 t PET machine can run, more often than clamp.
- Opening stroke should be at least about 2.5 times the part height, so a 100 mm preform needs about 250 mm.
- Under the FSSAI Packaging Regulations, PET in food contact must conform to IS 12252, and packaged drinking water bottles need at least 85% transparency.
Which 75 Ton PET Machine Applications Fit Best?
Small preforms in modest cavity counts fit best: bottles for water, juice, syrups, cosmetics, hair oil and disinfectants, from a few grams up to the weight the barrel handles well. Wide-mouth jar preforms can fit if the mould passes between the tie bars and the stroke clears the core.
Cavity count is where small and large PET machines differ. A preform mould holds its cavities in rows, each with its own core, neck splits and hot-runner nozzle, so the number that fits depends on mould width and the gap between tie bars as much as on clamp.
Our view: buy a 75 t PET machine for range, not for volume. It earns its place on short runs, many neck finishes and sample work, where a large machine would sit idle during changeovers or run a small shot in a big barrel.
Pharma and cosmetic preforms bring their own colour and changeover questions, covered in the pharma and cosmetic preforms article in this series.
Why Is Clamp Rarely the Limit for Preforms?
Because a preform mould sees each cavity end-on. The projected area is the circle of the widest diameter, usually the support ledge below the thread, not the length of the body. A few square centimetres per cavity needs little clamp, even with eight cavities and a high cavity pressure.
The method comes from a Plastics Technology article by John Williams of RJG: projected area of one part times cavities, plus any cold-runner area, times a tonnage factor. A preform mould built with a hot runner counts only the cavities, so there is no runner area to add.
Where you have no tonnage factor for the resin, SPE's Plastics Engineering magazine suggests a cavity pressure of 400 bar as a guide value. That is about 408 kg/cm², or 0.408 t for every square centimetre of projected area. The worked example below applies it to an eight-cavity mould.
A low clamp need does not mean any setting will do. The same RJG article warns that over-clamping can crush vents, roll the parting line and crack cavity blocks. Set clamp from the calculation plus a reserve, such as 10% (a starting margin, not a rule).
What Does Limit a Small PET Machine?
Three things: the shot against the barrel, the mould against the tie bars, and the opening stroke against the preform length. Each can rule out a mould that the clamp would accept, so check all three before you fix the cavity count with your mould maker.
Stroke first. Bruce Catoen's machine sizing guide in MoldMaking Technology puts the opening stroke at least 2.5 times the part height. For a 100 mm preform that is about 250 mm. A preform also has to clear a long core and open its neck splits, so ask the mould maker for the stroke the tool needs.
Mould size next. Catoen's guide says the parts' projected area must sit wholly inside the tie bars, because platens can pull in near the bars and wear the parting line. Wide rows of cavities reach the tie bars before they reach the clamp limit.
Shot last. A small shot in a large barrel stays hot for longer, and PET loses viscosity when held in the melt. The trial moulds article in this series works through barrel sizing and IV loss, and the start-up article covers the dryer.
Which Indian Rules Apply to Bottles Made From Your Preforms?
If the bottle will hold food, drinks or drinking water, the FSSAI Packaging Regulations 2018 apply. PET for food contact must conform to IS 12252, and bottles for packaged drinking water need a transparency of at least 85%. Your customer will ask for proof.
The regulations also set an overall migration limit of 60 mg/kg or 10 mg/dm², tested to IS 9845, and require pigments to meet IS 9833. Food businesses need a certificate of conformity from an NABL-accredited lab for packaging in direct food contact, so keep resin lot records with every batch of preforms.
Recycled PET is a separate question. FSSAI allows recycled plastics in food contact only as and when it frames standards and guidelines for them. Check the current position before you plan rPET in a food preform; the start-up article in this series covers recycled-content targets under the PWM Rules.
What Should You Send to Check a PET Product on 75 t?
Send the preform drawing with weight, length, neck finish and support-ledge diameter, the resin grade, the target cavity count and the bottle it will be blown into. With those, clamp, stroke, mould size and shot can be checked together. See the 75 ton PET injection moulding machine page.
Frequently Asked Questions About PET Products on a 75 t Machine
Can a 75 t machine make preforms for 1 litre bottles?
It can, if the shot sits well inside the barrel and the mould fits between the tie bars. Clamp is unlikely to stop it. The limits are the preform weight against barrel capacity and the cavity count the mould width allows, so check the preform weight and length with the machine supplier first.
Does a hot runner matter for preform moulds?
Yes. On a hot runner only the cavities count toward projected area, there is no runner to regrind, and each cavity is gated close to the preform base. A cold runner adds its own area and waste, and PET regrind brings drying and IV questions of its own.
Why are PET preforms clear when PET resin chips are white?
Bottle-grade chips are supplied crystallised, which makes them opaque and lets them be dried without sticking. Melting removes that structure, and fast cooling in the mould freezes the preform in a clear, amorphous state. A white haze in a preform can therefore point to slow cooling or too thick a wall.
Can I make wide-mouth jar preforms on a 75 t machine?
Yes, at low cavity counts, if the mould fits. A wide neck raises the projected area and the mould width per cavity, so check both against the clamp and the tie-bar gap. Jar preforms are also short, which helps the stroke check. Take the area from the largest outer diameter.
What clamp reserve should I add for a preform mould?
A 10% reserve is a reasonable starting margin, not a rule. Raise it if you are using a guide pressure rather than data for your resin and wall. Do not run the clamp at the machine maximum because the mould is small; over-clamping can crush vents and damage the mould.
Related Articles
- Small Pharma and Cosmetic Bottle Preforms on a 75 Ton Machine
- Running Trial Preform Moulds Before Scaling Up Production
- Starting PET Preform Production With a 75 Ton Machine
Sources & References
- Plastics Technology, J. Williams (RJG): Clamp Tonnage: More Is Better...Right?
- SPE Plastics Engineering, A. Urbina: Mastering Clamping Force Calculation
- MoldMaking Technology, B. Catoen: Machine Sizing and Specification for Optimal Mold Performance, Part 1
- Food Safety and Standards Authority of India (FSSAI): Food Safety and Standards (Packaging) Regulations, 2018, compendium
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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