Quick answer: A 75 ton machine makes small plastic parts. Typical 75 ton injection moulding machine applications include screw caps and flip-top closures, switch and socket components, plug tops, cable clips, drip and sprinkler fittings, small gears, toy and stationery parts, and single-cavity lids about the size of your palm. The clamp sets the limit, not the part name. At a common starting factor and a 10% reserve (a starting margin, not a rule), 75 t holds roughly 160 cm² of projected area per shot, shared across every cavity and the runner.
This guide shows which part families fit that limit, how to check your own part on paper, and the signs that a job has outgrown the size.
Key Takeaways
- Clamp force limits projected area. At about 0.42 t/cm² and a 10% reserve, 75 t covers roughly 160 cm² of parts and runner per shot.
- Cavities share the clamp. A lid that runs comfortably in one cavity can need well over 75 t in two.
- Machine shot ratings are usually quoted in polystyrene grams, so convert your PP or nylon shot with melt density before you compare.
- Mould size matters as much as tonnage. The mould has to pass between the tie bars and sit inside the machine's mould height range.
What Are Typical 75 Ton Injection Moulding Machine Applications?
Small parts with a modest projected area suit it best: caps and closures, modular switch parts, plug tops, socket inserts, cable clips, small gears, irrigation fittings, toy parts and stationery. Multi-cavity moulds for light parts are common, provided the total projected area stays inside the clamp.
The table groups the usual work by part family. The right-hand column matters more than the left, because it tells you what normally stops a job from running well at this size.
Typical part families for a 75 t class machine
| Part family | Usual materials | What usually limits it |
|---|---|---|
| Screw caps and flip-top closures | PP, HDPE | Cavity count against clamp, cooling time |
| Modular switch and socket parts | PC, nylon | Drying, tolerance on snap-fits |
| Plug tops and small housings | PC, nylon, PP | Insert loading, wall thickness |
| Cable clips, ties and saddles | Nylon, PP | Long flow in thin sections |
| Drip and sprinkler fittings | PP, HDPE, POM | Core pulls and thread release |
| Small gears and bushes | POM, nylon | Shrinkage control, gate position |
| Toy and stationery parts | ABS, PP, PS | Colour changes, cavity balance |
| Single-cavity lids and small tubs | PP | Projected area, opening stroke |
Electrical accessories can be a steady source of this work in India. BIS covers switches under IS 3854 and plugs and socket-outlets under IS 1293, and its own guidance notes that these parts are made from both thermoset and thermoplastic materials. The ETD 14 committee's programme of work lists IS 3854:2023, so ask your customer which edition their tests follow.
Thermoset parts need a machine set up for thermosets. Confirm the material family before you size anything else.
How Do You Check Whether Your Part Fits Within 75 t?
Multiply the total projected area of all cavities and the runner by a tonnage factor for your material, then add a reserve. RJG suggests 3 US tons per square inch as a starting point, which is about 0.42 t/cm². Below roughly 68 t, the clamp is comfortable.
Projected area is the shadow the part casts on the parting line, seen in the direction the mould opens. A 110 mm round lid casts a 95 cm² shadow no matter how deep its skirt is. Add the runner if it sits on the parting line, because the melt pushes on it too.
RJG also says to subtract any cored-out area, such as a window or a large through hole, and to multiply by the number of cavities before you add the runner. The factor itself varies with material and wall thickness, and the 75 t vs 100 t comparison in this series shows how far it can move the answer.
Here is the flat opinion. A mould that calculates at 72 t is a bad plan for a 75 t machine, not a tight fit. Material lots change, moulds wear and the factor you assumed may be low, so leave the reserve in place.
Will the Shot Weight Be Enough for Your Part?
Compare the machine's rated shot, usually quoted in polystyrene grams, with your own shot converted to the same basis. John Bozzelli of Plastics Technology recommends working between 25% and 65% of barrel capacity, and converting with melt density rather than solid density.
Bozzelli gives melt densities of about 0.945 g/cm³ for PS and 0.74 g/cm³ for PP. So a 40 g PP shot fills the barrel like 51 g of PS. Ignore the conversion and a mould that looks fine on paper comes up short on the machine.
Both ends of the range cause trouble. Above about 65%, he notes melt quality problems such as unmelted granules and long screw recovery. Very small shots leave melt sitting in the barrel for many cycles, which matters most for heat-sensitive grades. In a follow-up column he adds that PP and PE can wear metal off the screw flights when shots run above 65% of barrel capacity.
Moisture is the other shot-side trap. Nylon usually arrives dry in sealed bags, but in the Indian monsoon a bag opened beside the hopper sits in humid air all shift. If your clips and ties are nylon, plan a dryer on the machine from the start rather than after the first brittle batch.
When Has a Job Outgrown a 75 Ton Machine?
A job has outgrown the size when the calculated clamp passes about 68 t, the mould will not pass between the tie bars, the shot needs more than 65% of the barrel, or the opening stroke cannot clear the part. Any one of these is enough reason to move up.
Mould fit catches many first-time buyers: tie-bar spacing, mould height range and opening stroke all have to suit the mould, and the 75 t vs 100 t article in this series covers those checks in detail.
The machine also tells you on the shop floor. Flash at the parting line with the clamp already near maximum points to a clamp that is too small. Screw recovery that takes longer than the cooling time means the barrel cannot melt the shot in time, and the cycle stretches to wait for it.
Repeated short shots at full injection pressure are a third warning sign, though check gates, vents and material first.
Growth is the quiet reason. A cap mould that starts at 8 cavities often moves to 16 or 24 as orders build, and the clamp, barrel and tie-bar space all have to follow.
What Should You Send Before Choosing a Machine?
Send the part drawing or a sample, the material grade, part and runner weight, cavities, mould dimensions and monthly volume. With these, the clamp, shot and mould fit can all be checked on paper before you commit. See the 75 ton horizontal injection moulding machine page.
Frequently Asked Questions About What a 75 Ton Machine Can Make
Can a 75 ton machine make plastic buckets?
Not in practice. A bucket has a large projected area, a deep cavity that needs a long opening stroke, and a shot weight far above what a small barrel melts well. Even before the clamp calculation, the mould would usually be too big to pass between the tie bars of a machine in this class.
Can a 75 ton machine run a family mould with different parts?
Yes, if the clamp holds the combined projected area of every part and the runner, and the shot covers their combined weight. The harder part is filling unequal cavities evenly. Balance the runner so each cavity fills at about the same time, or the smallest part will flash while the largest one is still short.
Is a 75 ton machine suitable for thin-wall packaging?
Only for small items, and only if the injection unit is fast enough. Thin walls freeze quickly, so they need high injection speed and pressure as well as clamp. Check the rated injection rate and pressure on the specification sheet against what your mould maker expects, not the tonnage alone.
Can a 75 ton machine mould PC and nylon?
Yes, if the barrel heating suits the grade and the material is dried to the resin maker's moisture limit. Both PC and nylon absorb water from the air, and moulding them wet causes silver streaks and brittle parts. The companion article on caps and small electrical parts gives the drying figures.
Why are machine shot weights given in polystyrene grams?
It gives buyers one common basis for comparing barrels. Your own material is usually lighter in the melt. Plastics Technology gives melt densities of about 0.945 g/cm³ for PS and 0.74 g/cm³ for PP, so multiply PP grams by about 1.28 to get the polystyrene-equivalent figure.
Related Articles
- Moulding Caps and Small Electrical Parts on a 75 Ton Machine
- 75 Ton vs 100 Ton Injection Moulding Machine: Which Do You Need?
- Starting a Small Moulding Unit With a 75 Ton Machine
Sources & References
- Bureau of Indian Standards: Standards for Plugs-Socket-Outlets and Switches (BIS blog)
- RJG / Plastics Technology: Clamp Tonnage: More Is Better...Right?
- Plastics Technology (J. Bozzelli): Revisiting Shot Size vs. Barrel Capacity
- Bureau of Indian Standards: ETD 14 Electrical Wiring Accessories Sectional Committee: programme of work
- Plastics Technology (J. Bozzelli): A Simpler Way to Calculate Shot Size vs. Barrel Capacity
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.
Limitation of Liability: Pratishna Engineers makes no representation or warranty, express or implied, regarding the completeness, accuracy or suitability of the information for any particular application. To the extent permitted by applicable law, Pratishna Engineers shall not be liable for any loss, damage, cost or consequence arising from reliance on or use of the information contained in this document. Final machine selection, configuration and application suitability should be confirmed with Pratishna Engineers based on complete and accurate project requirements.
