Choosing a 180 ton injection moulding machine: five checks and what each one tells you
| Check | A standard 180 t machine is enough when | Look at a different build when |
|---|---|---|
| Clamp | Area × upper factor × 1.1 stays at or under 180 t | It exceeds 180 t: a higher clamp class |
| Mould size | Mould width and height fit the tie-bar gap; thickness sits inside the shut height range | The mould needs a wider tie-bar gap or more shut height at the same clamp |
| Opening stroke | Stroke clears the core, the part and the gripper | Deep parts need a longer stroke or more daylight |
| Shot | Shot is about 20% to 65% of barrel capacity | Shot exceeds 65%: a larger screw or injection unit |
| Speed and pressure | Fill time and pressure are within normal moulding | Thin walls need fast fill, high pressure and a fast clamp |
If all five checks pass for every mould you plan to run, a standard 180 t machine is enough. When choosing a 180 ton injection moulding machine, move to a bigger frame, a larger injection unit or a faster hydraulic system only when a specific check fails. A higher clamp is a separate decision.
Machines sharing a 180 t rating can differ in tie-bar gap, opening stroke, screw size and pump capacity. That is why the clamp figure alone cannot settle the choice.
Key Takeaways
- Clamp is one of five checks; mould size, opening stroke, shot share and fill speed can each rule out a standard machine at the same tonnage.
- Keep the shot between about 20% and 65% of barrel capacity; below that, long residence time can degrade the melt.
- Thin-wall work calls for fast fill, high pressure and fast clamp movement that a general-purpose machine may not offer.
- A machine larger than the job needs carries a higher base load, which shows on a kVAh electricity bill.
What Should You Check When Choosing a 180 Ton Injection Moulding Machine?
Check five things in order: clamp, mould size, opening stroke, shot share and fill speed. A standard 180 t machine is enough when all five pass for every mould you plan to run. If only one fails, look for the build that fixes that one item.
Clamp comes from projected area and a tonnage factor, as the applications article in this series explains. Mould size comes next. The mould's width or height must pass between the tie bars, and its closed thickness must sit inside the machine's minimum and maximum mould height. A wide tray or grille mould can fail here while using little clamp.
Opening stroke matters for deep parts. The mould must open far enough to clear the core, the part and the gripper or drop path. As a rough check, add the part depth twice plus a working clearance, and compare that with the stroke and daylight on the data sheet.
How Do You Know the Injection Unit Is Big Enough?
Compare the shot volume with the barrel's swept volume. Plastics Technology columnist John Bozzelli advises keeping the shot between about 20% and 65% of barrel capacity. Below that, long residence time can degrade the melt; above it, melt quality suffers. Work in volume, not PS grams.
Machine shot ratings are usually given in grams of polystyrene. Bozzelli's method converts your part to volume using melt density, given as 0.945 g/cm³ for PS and about 0.74 g/cm³ for PP, adds 10% for check-valve leakage and melt uniformity, and then sizes the barrel so the shot is no more than 65%.
Bigger is not always better. Bozzelli notes that big screws tend to mean lower plastic pressure, because the same hydraulic force acts on a larger screw area. If your moulds span a wide range of shot sizes, he also notes that a second barrel ordered with a new machine can be low cost, and a skilled operator can swap one in under 30 minutes.
When Do Thin Walls or Fast Cycles Call for a Different Build?
When fill must happen in under a second at high pressure and the clamp must move fast. Thin-wall articles with flow length to wall ratios of 100:1 to 200:1 can need injection pressures above 30,000 psi (about 2,068 bar), which a general-purpose injection unit may not reach.
Gary Tremblay's PlasticsToday article describes thin-wall machines with accumulator-assisted clamps, extra-thick platens and, on better machines, a tie-bar distance to platen thickness ratio of 2:1 or less. It also suggests a smaller barrel so the shot is at least 40% of its size. The food containers article in this series covers the clamp side.
Our view: buy the build for the mould list you have, not the one you might win. A faster or larger machine that runs at half its capability costs more to buy and more every month to run.
What Does a Larger Machine Cost to Run?
More base load. An ExxonMobil, AMI and Tangram Technology energy guide says a standard hydraulic machine's base load can be 75% or more of its energy, and a high base load can mean the machine is too large. All-electric and hybrid machines sit near 10 to 20%.
The same guide found that ten-year energy cost exceeds purchase cost in almost every case, so a running-cost comparison belongs next to the price comparison. Ask for measured power on a cycle like yours, not only the connected load.
In Maharashtra, MSEDCL bills demand on kVA and energy on kVAh, and MERC intended kVAh billing for HT consumers and LT consumers above 20 kW from 1 April 2020. At a power factor of 0.85, 15% of the power drawn does no useful work. Check your latest bill for current rates.
How Should You Make the Final Choice?
Run all five checks for every mould you expect in the first few years, starting with the largest and the deepest. If they pass, a standard 180 t machine is enough. If one fails, ask for the build that fixes it. See the 180 ton horizontal injection moulding machine page.
Frequently Asked Questions About Choosing a 180 Ton Machine
Can I fit a bigger screw on a 180 t machine later?
Sometimes. Some injection units accept more than one screw diameter, and a second barrel ordered with a new machine can cost less than one added later. A larger screw on the same unit gives more swept volume but less maximum injection pressure, so check that your hardest-to-fill mould still fills.
What happens if the shot is too small for the barrel?
The melt stays in the barrel for many cycles, which raises residence time and the risk of degradation, discolouration and black specks. Keep shots above about 20% of capacity. Lower barrel temperatures and frequent purging can help one small mould on a large barrel, but a smaller screw is the better fix.
Does tie-bar spacing matter for a top-loaded mould?
Yes. The mould still sits between the tie bars once it is closed, so whichever dimension lies across the tie bars must fit the gap. Some machines let a tie bar be pulled for loading, but the mould must still fit the platen, the locating ring and the ejector pattern.
Is a hybrid machine always cheaper to run than a hydraulic one?
Not on every job. The ExxonMobil, AMI and Tangram guide puts all-electric and hybrid base loads at about 10 to 20%, against 75% or more for some standard hydraulic machines. The gap matters most where the machine idles often or runs long cooling times, so compare on your actual cycle.
How do I read opening stroke and daylight on a data sheet?
Stroke is the distance the moving platen travels; daylight is the largest gap between the platens. Subtract your mould's shut height from the daylight, then compare both that figure and the stroke with the space needed to clear the core, the part and the gripper. The smaller figure decides.
Related Articles
- What Can You Make on a 180 Ton Injection Moulding Machine?
- 180 Ton Machine for Food Containers, Bowls and Trays
- Moulding Larger Electrical Housings on a 180 Ton Machine
Sources & References
- Plastics Technology, J. Bozzelli: A Simpler Way to Calculate Shot Size vs. Barrel Capacity
- PlasticsToday, G. Tremblay (Sabic Innovative Plastics): Never too thin
- ExxonMobil, AMI and Tangram Technology: An Energy Saving Guide for Injection Moulders
- Maharashtra State Electricity Distribution Co. Ltd (MSEDCL): kVAh Billing: Frequently Asked Questions
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.
