A 320 ton container moulding machine suits large PP storage containers and square tubs, paint and industrial pails in one or two cavities, crate and bin lids, and high-cavity thin-wall lids. With a 10% reserve (a starting margin, not a rule), it carries about 690 to 1,034 cm² of conventional PP area, or about 259 to 414 cm² of thin-wall work.
At this size, clamp is often not the first limit. Deep pails and tall tubs can run out of opening stroke or mould height first, and the shot for a heavy pail can outgrow the barrel. Those checks are covered below and in the other articles in this series.
Key Takeaways
- With a 10% reserve, 320 t carries about 690 to 1,034 cm² of PP container area at factors of 3 and 2 US t/in².
- One 230 × 230 mm square tub fits at either PP factor; two cavities need about 327 to 491 t.
- Slots in crate and bin lids are deducted from the projected area, which can decide whether a lid fits.
- Food tubs must be made from plastics that meet the Indian Standards listed under the FSSAI Packaging Regulations, such as IS 10910 for PP.
What Can a 320 Ton Container Moulding Machine Make?
Large rectangular and square tubs, storage containers, paint and industrial pails, pail lids, crate and bin lids, and thin-wall tubs or lids in high cavity counts. The table shows how much projected area each product group can use across all cavities once a 10% reserve is held back.
Largest total projected area on a 320 ton container moulding machine, with a 10% reserve
| Product group | Tonnage factor (US t/in²) | Largest total area at 320 t | What that can mean |
|---|---|---|---|
| Large PP storage containers and square tubs | 2 to 3 | 690 to 1,034 cm² | One 230 × 230 mm tub (529 cm²) at either factor |
| Paint and industrial pails | 2 to 3 | 690 to 1,034 cm² | One 300 mm round pail (707 cm²), only at the lower factor |
| Crate and bin lids | 2 to 3 | 690 to 1,034 cm² net | A 400 × 300 mm lid fits once slots remove about 14% to 43% of its area |
| High-cavity thin-wall tubs and lids | 5 to 8 | 259 to 414 cm² | Four 100 mm round lids (314 cm²) up to a factor of about 6.5 |
Lids need the same clamp as the containers they close, because the rim outline is the same, but far less stroke and shot. Thin-wall work raises the factor, so high-cavity tools fill the clamp quickly even with small parts.
How Is the Clamp Worked Out for a Large Container?
Take the projected area of one part as seen from the parting line, subtract through openings such as slots, multiply by the cavity count and add any cold-runner area. Multiply by a tonnage factor for the resin and wall, convert to metric, add a reserve and compare with 320 t.
This is the method John Williams of RJG sets out in Plastics Technology. He suggests 3 US t/in² as a starting factor where no better data exists, within a typical range of 2 to 10. One US t/in² equals 0.1406 t/cm², so factors of 2 and 3 become 0.281 and 0.422 t/cm².
SPE Plastics Engineering's guide by A. Urbina places PP at 2 to 3 US t/in² and polyethylene at the low end of the range. Flow length, wall thickness and gate design move the factor. For thin walls, Gary Tremblay's PlasticsToday article gives 5 to 8 US t/in², against 3 to 5 for conventional moulding.
For a container, the projected area is the rim outline, not the surface area of the walls. A deep 20 litre pail and a shallow tray with the same rim need the same clamp; they differ in stroke, shot and cooling.
Which Limits Besides Clamp Apply to Large Containers?
Opening stroke, mould height, tie-bar gap, shot size and ejector stroke. A deep pail mould is thick and must open far, a wide lid mould must pass between the tie bars, and a heavy pail shot must suit the barrel. Any of these can fail first.
Stroke and daylight for deep, labelled containers are covered in the large IML containers article in this series, which also deals with ejector stroke. Pail sizes, resins and lids are covered in the paint pail article.
When stroke, mould height or machine length are the limits rather than clamp, a different clamp design may suit better. The two-platen article in this series compares that option with a toggle machine of similar tonnage.
Spare clamp is not a reason to use it all. Williams describes a mould that needed about 100 tons but was clamped at a 400-ton machine's maximum; the cavity block split in two places. Set the clamp from the calculation plus a modest reserve, not from the machine's rating.
Which Rules Apply to Food Tubs and Pails in India?
Tubs and pails in direct food contact fall under the FSSAI Packaging Regulations 2018. Plastics must conform to listed Indian Standards, such as IS 10910 for PP and IS 10146 for PE, and meet an overall migration limit of 60 mg/kg or 10 mg/dm², tested to IS 9845.
Food businesses need a certificate of conformity from an NABL-accredited lab for packaging in direct food contact. Pigments must meet IS 9833 and printing inks IS 15495, which matters for printed or labelled tubs. Paint and industrial pails are outside these rules but have their own recycled-content questions, covered in the paint pail article.
Our view: on a 320 t machine that runs both food tubs and industrial pails, keep separate resin, masterbatch and regrind streams for the two. The machine can switch jobs in a shift; a traceability gap takes far longer to close.
What Should You Send Before Choosing a 320 t Machine?
Send the rim size, height, wall thickness, part weight, resin grade and target cavity count for each container and lid, plus the mould's closed thickness if the mould exists. Clamp, stroke, mould height, tie-bar fit and shot can then be checked together. See the 320 ton horizontal injection moulding machine page.
Frequently Asked Questions About Container Moulding at 320 t
Can a 320 t machine run a 20 litre pail?
On clamp, often yes: a 300 mm round rim needs about 219 t to 328 t at PP factors of 2 to 3 with a 10% reserve. The harder checks are opening stroke, mould height and shot weight, because a 20 litre pail mould is tall and the part is heavy. Check those first.
How many thin-wall lids can a 320 t machine carry?
It depends on the factor your fill study supports. At 5 to 8 US t/in² with a 10% reserve, 320 t carries about 259 to 414 cm². Four 100 mm round lids use about 314 cm², which fits up to a factor of about 6.5. Smaller lids allow more cavities.
Do slots in a crate lid really reduce the clamp needed?
Yes. Through openings carry no melt pressure, so their area is deducted from the projected area. A 400 × 300 mm lid covers 1,200 cm², which exceeds the 1,034 cm² that 320 t carries at a factor of 2; removing about 14% of the area as slots brings it within reach.
Is a cold runner acceptable on large container moulds?
It can be, but its area adds to the clamp and its weight adds to the shot and regrind. On a one or two-cavity pail mould, a hot runner or direct sprue gate removes the runner altogether. Count any runner area in the clamp calculation and weigh regrind handling against the hot-runner cost.
Should I buy 320 t if most of my jobs need 200 t?
Usually not for clamp alone. A larger machine costs more to buy and to run when it idles at part load. Buy 320 t when stroke, mould height, tie-bar gap or shot on your largest regular mould demands it, and keep smaller jobs on a smaller machine.
Related Articles
- Paint Pail Moulding on a 320 Ton Machine
- When to Move From a 320 Ton Toggle Machine to a Two Platen Machine
- Large IML Containers: Daylight and Ejector Stroke on a 320 Ton Machine
Sources & References
- Plastics Technology, J. Williams (RJG): Clamp Tonnage: More Is Better...Right?
- SPE Plastics Engineering, A. Urbina: Mastering Clamping Force Calculation
- PlasticsToday, G. Tremblay (Sabic Innovative Plastics): Never too thin
- 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.
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