Three cable connector bodies, each 70 × 45 mm across the parting line, plus a 6.5 cm² runner, project 101 cm². At 3 US t/in² with a 10% reserve (a starting margin, not a rule), that needs about 47 t. At 2 US t/in² it needs about 31 t. That is the 40 ton vs 55 ton vertical machine question in one part.
Two cavities of the same connector need about 32 t at the upper factor and fit 40 t. The third cavity is the step that may need 55 t, depending on the compound. For small plugs, grommets and strain reliefs, the clamp is seldom the deciding point, as the applications article in this series shows.
Key Takeaways
- 55 t holds 37.5% more projected area than 40 t, which matters for larger connectors and higher cavity counts.
- A shot that uses too little of a large barrel leaves PVC sitting hot, and one flexible PVC guide sets a 10-minute limit.
- A larger machine on small parts can add connected load, and MSEDCL bills demand charges on kVA.
- Decide from the clamp check at the upper factor, then the shot-to-barrel ratio, then mould size.
Where Does the Clamp Run Out on a 40 Ton vs 55 Ton Vertical Machine?
With a 10% reserve, the usable clamp is about 36.4 t at 40 t and 50 t at 55 t. At a tonnage factor of 3 US t/in², that is about 86 cm² against 119 cm² of parts and runner. The larger machine holds 37.5% more area at any factor.
Largest total projected area (parts plus cold runner) with a 10% reserve, by tonnage factor
| Tonnage factor (US t/in²) | At 40 t | At 55 t |
|---|---|---|
| 2 | 129.3 cm² | 177.8 cm² |
| 2.5 | 103.4 cm² | 142.2 cm² |
| 3 | 86.2 cm² | 118.5 cm² |
| 4 | 64.7 cm² | 88.9 cm² |
| 5 | 51.7 cm² | 71.1 cm² |
The method behind these figures is the one RJG's Jeremy Williams sets out in Plastics Technology, with typical factors of 2 to 10 US t/in² and 3 as a starting point. The applications article in this series walks through it for cable parts.
More clamp is not free insurance. Williams describes a mould needing about 100 tons that was clamped at a 400-ton machine's maximum and split its cavity block in two places. On a cable mould, excess clamp can also crush the jacket at the shut-offs, so set clamp to the job, not to the machine's rating.
Does a Bigger Barrel Help or Hurt PVC Cable Parts?
It can hurt. A small cable shot in a large barrel spends longer at melt temperature, and PVC is heat sensitive. Plastics Technology's John Bozzelli warns that shots below 20% of barrel capacity bring long residence and degradation, and advises against buying the biggest screw by default.
His working window is 20% to 65% of barrel capacity, figured in volume rather than PS grams, with 10% added for check-valve leakage and melt uniformity. Flexible PVC asks for more: the Teknor Apex guide wants each shot to use at least 50% of the overall shot capacity.
The same guide says flexible PVC must not sit for more than 10 minutes, as the grommet article in this series explains. Hand-loaded cable cells run long cycles, so a small shot on a large barrel can approach that limit even with no stoppage.
Our view: for PVC cable parts, match the barrel to the shot first and the clamp second. A bigger frame bought for headroom, with a barrel sized for parts you may never mould, can cost you in degraded compound every day.
What Does the Larger Machine Cost to Run?
More, if the extra size sits idle. A larger machine can carry a bigger motor, pump and heater load, and for Maharashtra consumers on kVAh billing, demand charges follow it. The MSEDCL kVAh billing FAQ explains that demand charges are levied on kVA and energy charges on kVAh.
Power factor adds to the bill. The same FAQ notes that at a power factor of 0.85, 15% of the power drawn does no useful work, and it recommends capacitors or APFC panels. A motor running well below its rating also tends to run at a poorer power factor, so check it on your own meter.
To compare the two machines fairly, ask for the connected load of each and work out the kVA demand each adds to your contract, not just the motor kW. Then weigh that against the output the extra clamp would actually earn on your parts.
When Is 55 t the Right Call?
When the part needs it on the numbers. That means connector bodies or heavy-cord strain reliefs that pass 36 t at the upper factor, cavity counts the operator can load in time, or a mould too large for the smaller platens. If none applies, 40 t is the closer fit.
Heavy cords bring larger strain reliefs and longer flow along the tail, which raises both the tonnage factor and the shot. Larger connectors with several cable exits do the same. Run the clamp check at the upper factor and the shot check in volume for each part.
Mould size works both ways. A mould too large for the 40 t platens rules that machine out, but a small mould on large platens is also a risk, because the platens can bow under clamp and flash the centre of the mould. Ask for each machine's minimum mould size.
Cavity count is the last check. Two cavities of a large part can fit 55 t on clamp yet slow the cell if two long cords take much longer to load than one.
How Should You Decide Between the Two?
List each cable part you plan to run, with outline, shot volume, compound, cycle and cavities. Run the clamp check at the upper factor, then the shot-to-barrel ratio and residence, then mould size. Choose the smaller machine that passes all three. See the 40 ton vertical injection moulding machine page.
Frequently Asked Questions About 40 Ton vs 55 Ton Vertical Machines
Can I start on 40 t and add a 55 t machine later?
Yes, and it can be the lower-risk route. Start with the parts that fit 40 t at the upper factor, prove cycle times and demand, then add the larger machine when a real part needs it. Design early moulds so that any you may later move fit both machines.
Will the same moulds fit both machines?
Not automatically. Check platen size, minimum and maximum mould height, locating ring size, ejector pattern and the cable exit positions against each machine. A mould built for one can need spacers, adaptor plates or a new ejector layout on the other. Ask for both machines' mould data before tooling.
Is a 55 t machine faster than a 40 t machine?
Not on cable parts in a manual cell. The cycle is set mostly by loading and by cooling, and cooling time depends on wall thickness, not on clamp size. A larger machine can even open and close more slowly. Faster output comes from fixtures, cavities and loading method.
What if my parts sit between the two machines?
Size on the parts you expect to run for the next few years, not on one borderline mould. If most fit 40 t comfortably and one needs 55 t, compare the cost of a smaller mould or fewer cavities for that part with the cost of the larger machine.
Do both machine sizes need the same PVC screw?
The PVC requirements are the same at either size: a chrome-plated general purpose screw, a 2:1 to 3:1 compression ratio, chromed or stainless tooling, and no dead spots in the melt path. What changes is the barrel size, which should follow your shot, as the worked example shows.
Related Articles
- What Can You Make on a 40 Ton Vertical Moulding Machine?
- Moulding Power Cord Plugs on a 40 Ton Vertical Machine
- Cable Grommets and Strain Reliefs: Mould and Machine Setup
Sources & References
- Plastics Technology, J. Williams (RJG): Clamp Tonnage: More Is Better...Right?
- Plastics Technology, J. Bozzelli: A Simpler Way to Calculate Shot Size vs. Barrel Capacity
- Teknor Apex: Processing Guide for Injection Molding of Apex Flexible PVC Compounds
- 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.
