Where servo pump energy saving applies on a hydraulic moulding machine and its plant, from the ExxonMobil, AMI and Tangram guide and R. Kent
| Load | Reported share or effect | Does a servo pump change it? |
|---|---|---|
| Hydraulic pump drive | Base load of a standard hydraulic machine can be 75% or more of its energy | Yes, the main target: the pump slows or stops when little oil is needed |
| Barrel heating | 10% to 25% of a machine's energy input | No; barrel insulation can cut it by up to 50% |
| Idle running | Idling machines measured at 52% to 97.5% of full moulding energy | Partly; pump draw falls, heaters keep drawing |
| Chillers and cooling water | 11% to 16% of plant energy | No; 1 °C warmer chilled water cuts chiller cost by about 3% |
| Compressed air | Up to 10% of energy cost; leaks 20% to 40% in typical plants | No; fix leaks and pressure separately |
A servo pump cuts the energy the hydraulic drive wastes when the machine needs little oil, mainly during cooling, holding and pauses. On a 200 t two-platen machine running crates and dustbins with long cooling times, that is much of each cycle. It does not touch heaters, chillers or compressed air, so measure the whole machine, not only the pump.
Key Takeaways
- Hybrid and all-electric machines are reported to have base loads of about 10% to 20%, mostly barrel heating, against 75% or more on standard hydraulics.
- A university study of a hydraulic machine converted to servo motors reported similar cycle times and about 40% energy saving.
- Heaters, chillers and compressed air stay the same, so plant-level savings are smaller than machine-level ones.
- Under kVAh billing in Maharashtra, power factor affects billed units, so check it alongside the drive.
How Does a Servo Pump Save Energy?
A conventional machine runs its motor at constant speed and diverts or throttles oil it does not need. A servo-driven pump changes speed with demand: fast for injection and clamp movement, slow or stopped during cooling and hold. Energy follows the oil actually used, not the oil available.
Large, thick parts spend most of the cycle cooling, when the clamp is locked and the screw has already recovered. On a fixed-speed pump that time still costs motor power; on a servo pump it costs little more than standby. So the longer the cooling share of the cycle, the more a servo drive has to save.
The energy guide produced by ExxonMobil, AMI and Tangram Technology puts the base load of a standard hydraulic machine at 75% or more of its total energy, and notes that a high base load can mean the machine is too large for the job. All-electric and hybrid base loads are about 10% to 20%, mostly barrel heating.
Servo Pump Energy Saving: How Much Is Realistic?
Reported savings vary with the machine, the cycle and what the drive is compared with. A 2020 study measured about 40% on a converted hydraulic machine; a consultant recorded 22% from a variable-speed drive. Treat any single figure as a guide and measure your own cycle.
Hongsik Yun and Sungdong Kim of Kumoh National Institute of Technology compared a conventional hydraulic machine with the same machine after its induction motors were replaced by servo motors. They report production cycle times similar to the original and an energy saving of about 40%.
Moulding energy consultant Robin Kent, writing in PlasticsToday, recorded one hydraulic machine using 22% less energy with its variable-frequency drive switched on. He also measured idling machines drawing 52% to 97.5% of their full moulding energy, and suggests that stops longer than about 1.5 hours may be cheaper to shut down and restart.
The ExxonMobil guide adds context: modern hydraulic machines are at least 25% more efficient than 1997 designs, all-electric savings of up to 60% are possible, and the energy to run a machine for ten years exceeds its purchase price in almost every case. That makes drive choice a ten-year cost decision.
What Else Draws Power Around a 200 t Machine?
Barrel heaters, mould and oil cooling, chillers, dryers and compressed air. These loads stay whatever pump is fitted, and together they can match or exceed the drive's share once a servo pump has cut it. They are the next place to look after the drive.
The same guide puts barrel heating at 10% to 25% of a machine's energy input and says insulation can cut it by up to 50%. Drying can use up to 15% of process energy, and compressed-air leaks run at 20% to 40% in typical plants. Halving air system pressure cuts its cost by three quarters.
Kent's article also suggests a practical check: a clamp-meter data logger can measure a machine in as little as 30 minutes, and rising energy on the same job can be an early sign of screw or barrel wear. Log before and after any change so the saving is measured, not assumed.
How Do Maharashtra Tariffs Change the Payback?
Under kVAh billing, MSEDCL levies demand charges on kVA and energy charges on kVAh, so a poor power factor raises the units billed. A drive that saves kWh but leaves power factor low saves less on the bill than the kWh figure suggests.
MSEDCL's FAQ notes that at a power factor of 0.85, 15% of the power drawn does no useful work, and recommends capacitors or automatic power factor correction panels. It says MERC intended kVAh billing for HT consumers and LT consumers above 20 kW from 1 April 2020. Use the rates on your latest bill for payback sums.
Our view: compare drives on measured kWh per kg of good parts on your own heaviest regular job, logged over a full shift. A brochure percentage tells you nothing about a 50-second dustbin cycle in your plant with your chiller.
What Should You Measure Before Comparing Drives?
Log the machine for a full shift with a clamp-meter data logger, and record cycle time, good shots, shot weight and idle time. Note the power factor and billing basis from your bill. Then compare kWh per kg and cost per good part. See the 200 ton two platen injection moulding machine page.
Frequently Asked Questions About Servo Pump Energy Use
Does a servo pump make the cycle slower?
It need not. The Kumoh study reported cycle times similar to the original hydraulic machine after conversion to servo motors. Response depends on the drive, pump and control tuning, so check the dry cycle and the real part cycle during a trial rather than assuming either faster or slower results.
Will a servo pump reduce oil temperature?
It usually means less oil is churned through relief valves when no movement is needed, which reduces the heat put into the oil. That can lower the cooling water needed for the oil cooler. Measure oil temperature and cooling water flow before and after, since the effect depends on the cycle.
Is an all-electric machine better than a servo-hydraulic one?
On energy alone, all-electric machines can save more, with savings of up to 60% reported against hydraulics. For large, deep parts, a hydraulic two-platen clamp offers long strokes and high forces, which can outweigh the energy gap. Compare measured kWh per kg on the parts you will run, along with price and service.
Can an older hydraulic machine be retrofitted with a servo pump?
Often yes. Retrofit kits replace the motor and pump with a servo motor and suitable pump and link them to the existing control. Results depend on the machine's condition and cycle, so log energy before and after on the same job and check hydraulic seals and valves at the same time.
What is a realistic kWh per kg target?
There is no single figure, because part weight, wall thickness, cycle and resin all change it. The ExxonMobil guide puts site variable load at typically 0.9 to 1.6 kWh/kg across a whole plant. Track your own machine figure over time and against similar jobs rather than chasing a published number.
Related Articles
- What Can You Make on a 200 Ton Two Platen Machine?
- Crates and Dustbins on a 200 Ton Two Platen Machine
- Choosing Between 55 mm and 60 mm Screws on a 200 Ton Machine
Sources & References
- ExxonMobil, AMI and Tangram Technology: An Energy Saving Guide for Injection Moulders
- PlasticsToday, R. Kent: Getting to know your real energy use and cost
- H. Yun and S. Kim, Kumoh National Institute of Technology (via KoreaScience): A Study on Cycle Time and Power Saving Effect of a Hydraulic Hybrid Injection Molding Machine using a Servo Motor (2020)
- 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.
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