A plant head with a free 260 t machine gets an enquiry for three parts: a round dustbin of about 13 litres (260 mm rim, 300 mm tall), a larger one of about 28 litres (320 mm rim, 420 mm tall) and a 320 × 230 mm storage box, 200 mm deep. Which can a dustbin making machine at 260 t run? The small bin and the box, yes. The large bin needs about 249 t even at the low PP factor and about 1,050 mm of opening, which points to a bigger machine.
This article works through the three checks behind that answer: clamp from the footprint, opening stroke from the height, and shot from the weight, followed by the resins that suit bins and boxes.
Key Takeaways
- Clamp follows the footprint: a 260 mm round bin needs about 164 to 246 t at PP factors of 2 to 3, with a 10% reserve.
- Opening stroke follows the height: plan at least 2.5 times the bin height, so a 300 mm bin needs about 750 mm.
- A box lid can need more clamp than its box, because its outline is slightly larger.
- Impact copolymer PP suits bins and boxes that are dropped, kicked and stacked full.
How Much Clamp Does a Dustbin Making Machine Need?
Enough for the bin's footprint seen from the opening direction, times PP's tonnage factor of 2 to 3 US t/in², plus a reserve. At 260 t, round bins up to about 267 mm across fit at either factor; larger bins and boxes need a factor near 2.
Clamp and opening stroke per cavity for dustbins and boxes (sizes assumed; PP factor 2 to 3 US t/in²; 10% reserve, a starting margin, not a rule; stroke at 2.5 × height)
| Part | Projected area | Clamp needed | Highest factor at 260 t | Opening stroke |
|---|---|---|---|---|
| Round bin, 260 mm rim, 300 mm tall | 531 cm² | 164 to 246 t | 3.17 | 750 mm |
| Rectangular bin, 300 × 220 mm, 320 mm tall | 660 cm² | 204 to 306 t | 2.55 | 800 mm |
| Round bin, 320 mm rim, 420 mm tall | 804 cm² | 249 to 373 t | 2.09 | 1,050 mm |
| Storage box, 320 × 230 mm, 200 mm deep | 736 cm² | 228 to 342 t | 2.28 | 500 mm |
| Box lid, 330 × 240 mm, 30 mm deep | 792 cm² | 245 to 368 t | 2.12 | 75 mm |
The projected area method behind these numbers is set out in the applications article in this series. Note the last row: the lid has a slightly larger outline than the box it closes, so it needs more clamp, even though it is shallow. Size the lid mould from its own drawing.
Pedal bins and swing-lid bins add small parts such as pedals, hinges and inner liners. Those belong on smaller machines, which keeps the 260 t machine free for the bodies and lids that need its clamp.
How Tall a Bin Can a 260 t Machine Open For?
Plan at least 2.5 times the bin height as opening stroke, then check that the closed mould fits the machine's mould height range and that mould plus opening fits within maximum daylight. A 300 mm bin needs about 750 mm of stroke; a 420 mm bin needs about 1,050 mm.
The 2.5 times rule comes from Bruce Catoen's guide to machine sizing in MoldMaking Technology. The logic is geometric. The core stands as tall as the bin, and once the bin is pushed off the core it needs as much space again to fall clear, so about twice the height plus clearance is the bare minimum.
Catoen also gives the daylight checks. On a toggle clamp, maximum daylight equals maximum mould height plus stroke, so the whole stroke is available at any mould height. On a direct hydraulic clamp, maximum daylight equals minimum mould height plus maximum stroke, so a thick bin mould reduces the opening left over.
Bin moulds are tall and heavy, with a long core, a deep cavity block and often a stripper plate. Catoen advises checking maximum mould weight for both platens, so ask for the mould weight early.
Our view: for dustbins, read the opening stroke on the data sheet before the tonnage. A machine with clamp to spare but too little stroke cannot run the bin at any setting, while a bin near the clamp limit can sometimes be helped by gate and wall changes.
How Heavy a Shot Do Dustbins and Large Boxes Need?
Convert the part weight to melt volume using PP's melt density of about 0.74 g/cm³, add 10%, and keep that between about 20% and 65% of the barrel's swept volume. Shot ratings in grams usually refer to PS, so convert before comparing a bin with a machine.
John Bozzelli gives this method in Plastics Technology, with melt densities of 0.945 g/cm³ for PS and about 0.74 for PP. He links shots above 65% of the barrel to melt-quality problems and shots below 20% to long residence and degradation.
For a 420 g bin, 420 ÷ 0.74 × 1.1 gives about 624 cm³, so the barrel must sweep at least 960 cm³, about 908 g on a PS rating. Heavier bins and boxes can reach the top of a mid-size machine's barrel before they reach its clamp limit.
Which Resins Suit Dustbins and Storage Boxes?
PP impact copolymer suits bins and boxes, because they are dropped, kicked and stacked full. HDPE can suit bins kept outdoors in cold weather. Boxes that hold food need a grade listed against IS 10910 and IS 16738:2018, the Indian food-contact standards for PP.
Reliance's Repol B120MA is one example of a medium-impact copolymer for general purpose moulding. Its TDS lists an MFR of 12 g/10 min, notched Izod of 85 J/m at 23 °C, flexural modulus of 1,000 MPa, compliance with IS 10910 and IS 16738:2018, and BIS designation IS 10951-3-MBJ-C.
Lids must fit their boxes after shrinkage, so mould both in the same grade and colour where you can. The flat trays article in this series explains why colour and wall thickness change shrinkage.
What Should You Send for a Dustbin or Box Check?
Send the drawings with footprint, height, wall thickness and part weight for each body and lid, the resin grade, and the closed mould thickness if the mould exists. Clamp, stroke, daylight and shot can then be checked together for 260 t. See the 260 ton horizontal injection moulding machine page.
Frequently Asked Questions About Dustbin and Storage Box Moulding
Why is a dustbin mould so much heavier than a bucket mould?
A dustbin is taller, so its core and cavity block are longer and the mould is thicker and heavier. Many bins also need a stripper plate and air valves to release from the core. Ask the mould maker for the weight early and check it against the machine's platen limits.
Can a rectangular bin run on the same machine as a round one?
Yes, if each fits the clamp and stroke. A rectangular bin has more projected area than a round bin of similar width, so it needs more clamp. In the table, a 300 × 220 mm bin needs about 204 to 306 t against 164 to 246 t for a 260 mm round bin.
How do I stop dustbins wedging when stacked?
Stacking depends on draft, wall stiffness and a stacking feature such as lugs or a step near the rim that stops bins nesting too deeply. Settle the stacking feature in the drawing, because adding it later means re-cutting steel. Test stacks of warm and cold bins before approving the mould.
What makes a storage box lid fit loosely?
The lid and box shrink by different amounts. Different grades, colours, wall thicknesses or mould temperatures between the two moulds can all cause it. Mould both in one grade and colour, keep cooling similar, and measure fit after the parts have rested, since PP keeps shrinking for up to about 48 hours after moulding.
Can dustbin bodies use regrind or recycled PP?
They can, since bins are non-food parts, but impact strength and colour may change with each share. Fix the share, keep regrind clean and dry, and repeat drop tests whenever the share or supplier changes. Check customer specifications before adding recycled content to branded or contract products.
Related Articles
- What Can You Make on a 260 Ton Household Moulding Machine?
- Large Flat Trays Without Warp on a 260 Ton Machine
- Pump Flow and Cycle Time on Large Household Machines
Sources & References
- MoldMaking Technology, B. Catoen: Machine Sizing and Specification for Optimal Mold Performance, Part 1
- Plastics Technology, J. Bozzelli: A Simpler Way to Calculate Shot Size vs. Barrel Capacity
- Reliance Industries: Repol B120MA Technical Data Sheet
- SPE Plastics Engineering, A. Urbina: Mastering Clamping Force Calculation
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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