PET 125 ton vs 150 ton: clamp-side comparison (factor 5 US t/in² and 10% reserve, assumed for illustration; shot and mould width come from each machine's own data)
| Point | 125 t | 150 t |
|---|---|---|
| Clamp after 10% reserve | 113.6 t | 136.4 t |
| Projected area covered | 161.6 cm² | 194.0 cm² |
| Cavities of a 33 mm ring preform, by clamp | 18 | 22 |
| Cavities of a 70 mm jar preform, by clamp | 4 | 5 |
| Shot and plasticising rate | From the barrel data | From the barrel data |
| Mould width | From the tie-bar gap | From the tie-bar gap |
In the PET 125 ton vs 150 ton choice, the extra 25 t buys about 20% more projected area, which adds one jar cavity and a few narrow-neck cavities. For a narrow-neck preform mould like the one in the worked example, it is not the deciding number. The shot weight against the barrel, and the mould width against the tie bars, decide which machine fits.
So start with the mould drawing and the preform weight, not with the tonnage. The sections below show how to turn both into requirements you can compare against two specification sheets.
Key Takeaways
- 150 t covers about 20% more projected area than 125 t at the same factor and reserve.
- Convert preform shot weight to volume at PET's melt density of about 1.15 g/cm³, then compare with the barrel.
- Keep the shot, plus a 10% allowance, at or below 65% of the barrel's swept volume.
- A mould should cover at least about 70% of the tie-bar gap, so a larger machine can be too large for a small mould.
How Do You Convert Preform Shot Weight Into Barrel Size?
Add the preform weights across all cavities, divide by PET's melt density of about 1.15 g/cm³, add 10%, and divide by 0.65. The result is the smallest swept volume that keeps the shot within 65% of the barrel. Multiply by 0.945 to read it against a PS rating.
The melt density comes from Ottmar Brandau's preform guide, extracted in PETplanet Insider, which gives 1.15 g/cm³ for PET melt and 1.335 for solid amorphous PET. John Bozzelli, in Plastics Technology, notes that barrel ratings are usually quoted in grams of PS, and gives PS melt density as 0.945 g/cm³.
Bozzelli also explains the allowance and the limits. He adds about 10% for check-valve leakage and melt uniformity, and sizes the barrel so the shot uses no more than 65% of it. Below about 20%, he warns, resin sits too long and can degrade, which matters for PET.
A quick ratio helps when reading specification sheets: 1.15 ÷ 0.945 is about 1.22, so a barrel rated at a given weight of PS holds about 22% more PET melt by weight at full stroke.
PET 125 Ton vs 150 Ton: When Does 150 t Earn Its Place?
When the barrel or the mould outgrows the 125 t machine: a shot above about 65% of its barrel, a hot runner mould wider than its tie bars allow, or a fifth jar cavity. If none of these applies, the extra clamp only adds weight and cost.
Check the plasticising rate too. Multiply shots per hour by shot weight to get kilograms per hour, and compare it with the screw's rated output on the specification sheet. A shot that fits the barrel can still be more than the screw can melt evenly in the cycle.
Our view: when a mould sits between two machines, size by the barrel first. Too little barrel shows up as unmelts and drifting weights from the first day; a slightly oversized clamp only costs some energy.
How Does Mould Size Limit Each Machine?
From both sides. A mould too wide for the tie bars cannot be mounted, and a mould too small for the platen lets the platens bow under clamp. A Plastics Technology mounting guide gives a rule of thumb that the mould should cover at least 70% of the tie-bar gap.
The same guide, by Witaszek, Klees, Fattori, Di Siro and Bozzelli, warns that platens bending under clamp on a small mould can cause flash in the mould centre, and that very small moulds can cause catastrophic platen damage. It notes that most machine manuals give a minimum mould size.
This is where the bigger machine can go wrong. A narrow eight-cavity preform mould that suits 125 t well may fall below the 70% mark on a 150 t frame with a wider tie-bar gap. Check the mould width against both machines' minimum and maximum before you decide.
Does a Bigger Machine Cost More to Run?
It can. A larger machine on a small job heats more barrel and runs a bigger motor below its best point. In Maharashtra, MERC directed kVAh billing for HT consumers and LT consumers above 20 kW from April 2020, so a lightly loaded machine shows on the bill.
Demand charges are levied on kVA. MSEDCL's kVAh billing FAQ notes that at a power factor of 0.85, 15% of the power drawn does no useful work, and it recommends capacitors or APFC panels. Matching machine size to the mould is the first step; power factor correction is the second.
Use your latest electricity bill for rates rather than any published figure, since tariffs and orders change. Then compare the two machines on what each would draw for your actual mould, not at full load.
What Should You Send to Compare 125 t and 150 t?
Send each mould's drawing with overall width, height and shut height, the preform weight and cavity count, and the expected cycle. With those, shot share, plasticising rate, clamp and tie-bar fit can be checked on both machines side by side. See the 125 ton PET injection moulding machine page.
Frequently Asked Questions About PET 125 Ton vs 150 Ton
Can I run a 125 t mould on a 150 t machine later?
Yes, if it mounts and the shot sits inside the larger barrel's working range. Check the mould width against the 70% rule for the larger tie-bar gap, and reduce clamp to what the mould needs rather than running at the machine's maximum.
What if my shot falls between the two barrels?
Pick the barrel where the shot, with its 10% allowance, sits nearer the middle of the 20% to 65% window. If the larger machine leaves the shot near 20%, residence time rises, which PET does not tolerate well. A different screw size on the smaller machine may solve it.
Why use melt density rather than solid density for PET?
The barrel holds melt, and melt is less dense than the solid preform. Using PET's solid density of about 1.335 g/cm³ instead of 1.15 would understate the volume needed by about 14% and could put a shot that looks comfortable beyond 65% of the barrel.
Does mould height matter as much as width?
Yes, in a different way. The mould's shut height must sit between the machine's minimum and maximum, and the opening must allow the preforms and take-out to clear. Send the mould's shut height and preform length so both machines can be checked.
Is it worth buying 150 t for future moulds?
Only if those moulds are already defined. Buying ahead for an unknown mould can mean a small barrel share and a mould that undershoots the tie-bar gap on today's jobs. A clear list of current and planned moulds gives a better answer than headroom.
Related Articles
- What PET Products Can You Make on a 125 Ton Machine?
- Edible Oil Bottle Preforms on a 125 Ton Machine
- Controlling Haze and Acetaldehyde in PET Preforms
Sources & References
- Plastics Technology, J. Bozzelli: A Simpler Way to Calculate Shot Size vs. Barrel Capacity
- PETplanet Insider, O. Brandau: Practical Guide to Injection Moulding of Preforms, Injection parameters part 17 (Vol. 16, 01+02/2015)
- Plastics Technology, P. Witaszek, J. Klees, J. Fattori, E. Di Siro, J. Bozzelli: How to Mount an Injection Mold (June 2017)
- MSEDCL: kVAh Billing: Frequently Asked Questions
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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