What a 120 ton household moulding machine can carry: largest total projected area across all cavities, with a 10% reserve (a starting margin, not a rule)
| Product group | Tonnage factor (US t/in²) | Largest total area at 120 t | What that can mean |
|---|---|---|---|
| PP storage containers and lunch boxes | 2 to 3 | 259 to 388 cm² | One 180 × 130 mm box (234 cm²) per shot at either factor |
| Lids for those containers | 2 to 3 | 259 to 388 cm² | The same cavity count as the box, plus any cold-runner area |
| PP mugs and tumblers | 2 to 3 | 259 to 388 cm² | Four 85 mm round mugs (227 cm²) at either factor |
| Bowls and serving dishes | 2 to 3 | 259 to 388 cm² | Two 140 mm bowls (308 cm²), but only near the lower factor |
| Small pails and tubs | 2 to 3 | 259 to 388 cm² | One 200 mm round pail (314 cm²), only near the lower factor |
| Thin-wall tubs and lids | 5 to 8 | 97 to 155 cm² | One 120 mm round lid (113 cm²), only at the lower factor |
A 120 ton household moulding machine suits PP storage containers, lunch boxes, lids, mugs, tumblers and bowls, in one to four cavities depending on size. The limit is total projected area. With a 10% reserve, 120 t carries about 259 to 388 cm² of conventional PP work, but only about 97 to 155 cm² of thin-wall work.
Clamp is the first filter, not the last. Opening stroke, tie-bar space and shot size can each rule out a mould that the clamp would accept. Those checks are covered in the other articles in this series.
Key Takeaways
- Clamp needed is projected area, minus through-holes, times cavities, plus any cold runner, times a tonnage factor for the resin.
- PP sits at about 2 to 3 US t/in², so 120 t holds roughly 259 to 388 cm² of PP parts with a 10% reserve.
- Single-cavity PP parts up to about 180 mm round fit at either factor; small mugs and tumblers fit four to a mould.
- For anything that touches food, pick a PP grade the resin supplier lists as complying with IS 10910.
How Do You Work Out What Fits on 120 t?
Take the projected area of one part, subtract through-holes, multiply by the cavity count and add any cold runner. Multiply that total by a tonnage factor for the resin and add a reserve. If the answer stays under 120 t, the clamp can hold the mould shut.
This is the method set out in a Plastics Technology column by RJG trainer Jeremy Williams. It gives typical factors of 2 to 10 US tons per square inch and recommends 3 as a starting point when nothing better is known. With a hot runner, only the cavities count, because the runner melt stays inside the manifold.
Factors vary by resin. An SPE Plastics Engineering article puts the range at 2 to 8 US t/in², with polyethylene at the low end, polycarbonate toward the high end and PP at 2 to 3. Flow length, wall thickness, gate size and gate count all move the figure for a given part.
Published factors are in US tons per square inch, while Indian machines are rated in metric tonnes and drawings are in millimetres. One US ton is 0.9072 t and one square inch is 6.4516 cm², so 1 US t/in² is about 0.141 t/cm². The table above uses those conversions.
The 10% reserve in the table is a starting margin, not a rule. It covers small swings in melt temperature and fill speed from shot to shot. You can run tighter or wider once trials show how the mould behaves.
Which Products Fit a 120 Ton Household Moulding Machine?
Single-cavity PP parts up to about 180 mm round, or 254 cm², fit at either PP factor. Smaller items fit in multiples: four 85 mm mugs use about 227 cm². Thin-wall tubs and lids are the exception, because their much higher factor cuts the usable area to well under half.
Storage boxes and lunch boxes are the core work. A 180 × 130 mm box fits as one cavity with room for a cold runner. Its lid has a slightly larger footprint, so check the lid on its own, because it is often the mould that sets the clamp.
Mugs, tumblers and scoops are small in plan view, so cavity count is limited by shot size and mould width more than clamp. Bowls and small pails are the opposite: wide parts where one cavity can use most of the clamp. Deep parts also need a long opening stroke, which the mugs and bowls article in this series works through.
Handles, knobs, spoons and small organiser parts fill out a range. They are tiny in plan view, so even eight or more cavities use little clamp. For these, the shot size and the mould width decide the cavity count, and the clamp check is a formality.
Our view: plan houseware moulds at the upper PP factor of 3 and treat any mould that fits only at 2 as a trial job, not a programme. A mould that needs the whole clamp on a good day will flash on a warm afternoon.
Which PP Grades and Rules Apply to Houseware?
Houseware can be moulded in PP homopolymer where stiffness matters, or in PP impact copolymer where parts must survive drops. For anything that touches food, choose a grade the supplier lists as complying with IS 10910, the Indian standard for PP in food contact.
Reliance's Repol H110MAS is one example. It is a nucleated PP homopolymer the TDS lists for rigid packaging, furniture and houseware, with an MFR of 11 g/10 min, a flexural modulus of 1,650 MPa and an HDT of 110 °C. It complies with IS 10910 and is marked as not for single-use items banned under the PWM Rules.
Where toughness matters more than stiffness, an impact copolymer trades one for the other. Copolymer grades resist cracking on impact, especially in the cold, but flex more under load. Buckets and children's tumblers may favour the tougher grade, while thin rigid boxes may favour the stiffer one.
Thin-wall work is a different class. A PlasticsToday article by Sabic's Gary Tremblay puts thin-wall clamp at 5 to 8 US t/in², against 3 to 5 in conventional moulding, and calls adapting conventional machines for it usually unwise. Treat thin-wall tubs as a separate decision from houseware.
What Should You Send Before Choosing a Machine?
List every houseware mould you plan to run in the first few years, with part drawings, cavity counts, runner type and resin grade. Run the clamp check for each at the upper factor, then check stroke and shot size. See the 120 ton horizontal injection moulding machine page.
Frequently Asked Questions About a 120 Ton Household Moulding Machine
Can a 120 ton machine mould plastic chairs?
No. A chair seat of about 450 × 450 mm projects around 2,025 cm². At a PP factor of 2 US t/in², that alone needs roughly 570 t before the back and legs are counted. Chairs belong on much larger machines, while 120 t suits smaller houseware such as boxes, mugs and bowls.
Can I run a family mould for a box and its lid together?
You can, if the combined projected area of box, lid and runner stays inside the clamp limit at the upper factor. The catch is balance: a box and lid differ in volume, so one can overpack while the other short-fills. Runner sizing or valve gates are often needed to fill both evenly.
Why does the table give a range instead of one figure?
Because the tonnage factor is a range. PP sits at about 2 to 3 US t/in² depending on flow length, wall thickness and gating. The low end gives the most area and the high end the least. Size on the high end unless trials on the actual mould show you need less.
Is PP homopolymer or copolymer better for buckets?
It depends on the load. Homopolymer is stiffer, so a bucket wall flexes less when full. Impact copolymer resists cracking when dropped, especially in cold stores. For buckets carried full by a handle, a sensible start is an impact copolymer, with stiffness checked on a moulded sample.
How many cavities should a first houseware mould have?
Start from the clamp limit at the upper factor, then check shot size and mould width. Within those limits, fewer cavities cost less to build and are easier to balance. Starting with one or two cavities, then adding a second mould once demand and cycle time are proven, keeps early tooling spend down.
Related Articles
- Moulding Mugs, Bowls and Lunch Boxes on a 120 Ton Machine
- 120 Ton vs 125 Ton Machine: Which Suits Houseware?
- Starting a Houseware Unit With a 120 Ton Machine
Sources & References
- Plastics Technology, J. Williams (RJG): Clamp Tonnage: More Is Better...Right?
- SPE Plastics Engineering, A. Urbina: Mastering Clamping Force Calculation
- Reliance Industries: Repol H110MAS Technical Data Sheet
- PlasticsToday, G. Tremblay (Sabic Innovative Plastics): Never too thin
Technical Disclaimer
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