Injection moulding tonnage: how to size the clamp for your product mix.
TL;DR: Clamp tonnage is set by your largest part's projected area (roughly 0.3–0.8 t per cm², resin-dependent) — not by ambition. For most African packaging producers the answer lands in the 150–350t workhorse band (closures, cups, thin-wall containers, housings). Buy for the product mix you can sell today plus one realistic step, and put the saved capital into the mould — tooling quality decides your economics more than the machine's badge does.
What clamp force actually does
Injection pressure tries to blow the mould open; the clamp holds it shut. Too little tonnage and parts flash at the parting line; far too much and you've paid for iron, floor loading and electricity you never use — every cycle, for a decade. The sizing rule of thumb the industry runs on: roughly 0.3–0.8 tonnes of clamp per cm² of projected part area (the part's shadow, including runners), with the multiplier set by resin flow — easy-flowing PP at the low end, engineering resins and thin walls at the high end. Your mould maker confirms the exact number; the table below is how the bands map to real products.
The tonnage bands, matched to products
| Clamp force band | Typical products | Notes |
|---|---|---|
| 50–150 t | Small closures, caps, fittings, small technical parts, thin-wall lids | High-cavity tooling common; fast cycles; entry tier |
| 150–350 t | Closures (multi-cavity), cups, small containers, housings, thin-wall food packaging | The workhorse band for African packaging |
| 350–650 t | Buckets, larger containers, small crates, automotive-adjacent parts | Larger shot sizes; higher energy draw |
| 650–1,300 t | Crates, small pallets, large containers, bumpers | Heavy structural parts; significant utilities |
| 1,300 t+ | Large pallets, bulk bins, large automotive | Specialist; high capex; niche in most African projects |
Budget context: complete entry moulding cells (machine, mould, chiller, dryer, granulator) sit in the US$150k–400k equipment band; mid-scale multi-machine plants run US$400k–900k. Landed and installed, apply ×1.25–1.45 coastal or ×1.45–1.60 landlocked.
Four buying rules that survive contact with reality
- Size to the largest part in your sellable mix — then check the machine's shot size and tie-bar spacing against that part too. Tonnage is one of three constraints, not the only one.
- The mould is the product. A mid-range machine with excellent tooling beats a premium machine with a cheap mould, every day, in every market. Put capital saved on the machine into cavities, hot runners and steel quality.
- Count the whole cell. Chiller, dryer, granulator, and — in most of our markets — the power stabilisation that keeps barrel heats steady. An injection machine on a sagging grid makes scrap with great confidence.
- Plan the wear parts on day one: heater bands, thermocouples, screw and barrel wear, nozzle tips, mould springs. All of it moves on our one-week channel — but the kit should be specified with the machine, not discovered at 2 a.m.
The failure mode — the 650t trophy: a producer whose entire sellable mix needs 250t buys the 650-tonne machine "for the crate contract we might get". The big machine cycles slowly on small parts, burns power it can't bill anyone for, and the crate contract goes to whoever already had crate tooling. If the future product is real, buy it when its tooling is — machines in this class hold value, and capacity can be added in steps.
Where the demand is, in our footprint
Nigeria is the largest plastics-machinery market we serve — US$86.3M in 2024, the biggest single category anywhere in our footprint 2024 · UN Comtrade. Ghana grew 40.4% to US$27.3M including recycling; Tanzania holds US$31.3M. In all three, the winning combination is the same: the workhorse band, excellent tooling, honest power engineering, and parts in days not months.
What parts do you want to mould?
Send photos or samples of the products and your target volumes — we'll come back with tonnage, cell configuration and an honest budget band.