In a hydraulic injection moulding machine, the purchase price of the oil is only one part of the operating cost. Much larger losses can arise from unplanned downtime, unstable cycles, filter or valve problems, pump wear, overheating and unnecessary oil changes.
A good lubrication strategy therefore focuses on total cost of ownership (TCO): selecting the correct hydraulic fluid for the machine, keeping it clean and in the right condition, and monitoring changes before they develop into costly failures.
Key takeaways
- For hydraulic injection moulding machines, oil is both a power-transmission medium and a lubricant for hydraulic components.
- The correct viscosity grade and specification must come from the machine or hydraulic-system manufacturer, not from a generic “best oil” recommendation.
- Oil cleanliness, water contamination, air release, oxidation stability and varnish control can directly affect valves, pumps, filters and cycle repeatability.
- Condition monitoring can help optimise oil-change intervals and identify developing problems before they cause unplanned downtime.
- Shell positions Tellus S4 ME as an energy-efficient synthetic hydraulic fluid for specialist applications and also highlights the newer Tellus S4 VE in its plastics-industry portfolio.
- Claims such as energy savings or extended oil life are application-dependent and should not be treated as guaranteed results for every injection moulding machine.
Where do the operating costs of an injection moulding machine come from?
An injection moulding machine converts polymer feedstock into repeatable moulded parts through a controlled cycle that includes plasticising, injection, holding, cooling, mould opening and part ejection. In hydraulic machines, the hydraulic system supplies power to important machine functions such as clamping, injection and other actuated movements.
From a maintenance perspective, the most expensive lubrication-related issue is rarely the price of a drum of oil by itself. A more useful calculation includes:
- planned and unplanned downtime,
- maintenance labour,
- replacement filters and components,
- lost production and scrap,
- oil consumption and disposal,
- energy use,
- the effect of unstable hydraulic performance on cycle repeatability.
What does hydraulic oil actually do?
Hydraulic fluid must transmit power while also supporting lubrication, wear protection, corrosion protection, heat transfer, air release and contamination management. The balance of these properties matters because hydraulic systems contain pumps, valves and precision clearances that can be sensitive to changes in viscosity and contamination.
| Oil function or property | Why it matters | Possible consequence when control is poor |
|---|---|---|
| Correct viscosity | Supports efficient power transmission and lubrication across the intended operating temperature range. | Higher losses, slow or unstable response, increased wear or leakage depending on whether viscosity is too high or too low. |
| Wear protection | Protects pumps and other loaded hydraulic components. | Accelerated component wear and loss of efficiency. |
| Air release and foam control | Helps the hydraulic system transmit power consistently and limits compressibility effects caused by entrained air. | Noisy operation, unstable response, cavitation risk and reduced control precision. |
| Water separation | Allows free water to be removed where the system and oil type are designed for demulsibility. | Corrosion, additive degradation and poorer lubrication. |
| Oxidation and varnish control | Helps keep valves, filters and oil-wetted surfaces clean over long service periods. | Deposits, sticking valves, restricted filters and shortened oil life. |
| Cleanliness | Protects precision hydraulic clearances from hard particles and abrasive contamination. | Wear, valve malfunction, filter loading and reduced reliability. |
Why oil selection should start with the machine specification
The correct hydraulic oil is not simply the highest-tier or most expensive product. The starting point is the viscosity grade, performance specification and approvals required by the machine manufacturer and hydraulic components.
Before changing oil, verify:
- required ISO viscosity grade,
- hydraulic-fluid specification such as HM/HLP, HV/HVLP or another required class,
- OEM approvals or recommendations,
- operating and start-up temperatures,
- seal and material compatibility,
- current oil type and the flushing or changeover procedure,
- filtration and cleanliness requirements.
How can a higher-performance hydraulic oil reduce TCO?
A higher-performance fluid can create value in several ways, but the actual result depends on the machine and process.
Longer oil life
Better oxidation stability can help extend oil-drain intervals when the oil remains clean, cool and within its operating limits. Longer service intervals can reduce maintenance labour, oil consumption and waste, but the interval should be determined by OEM requirements and oil-condition data rather than by a headline marketing number alone.
Wear and deposit control
Good wear protection and resistance to sludge and varnish formation can help maintain pump, valve and filter performance. This is particularly relevant in continuously operated machines where a sticking valve or blocked filter can interrupt production.
Hydraulic efficiency
Some hydraulic fluids are formulated specifically to improve system efficiency. Shell reports application-dependent efficiency benefits for its energy-efficient Tellus grades. These results should be treated as measured case or test results, not guaranteed savings for every machine.
Shell Tellus S4 ME: what can be stated accurately?
Shell Tellus S4 ME 46 is listed by Melkib for industrial hydraulic applications including injection moulding machines. Shell describes Tellus S4 ME as an energy-efficient, zinc-free hydraulic fluid based on synthetic PAO technology.
Shell materials indicate that selected premium synthetic Tellus technologies can provide up to four times standard oil life compared with other oils in the Shell range under the referenced test conditions.
Shell also reports that, in a controlled injection-moulding test cycle, energy savings of up to 6.4% were measured when using Tellus S4 ME. Actual savings depend on the application, previous oil, maintenance procedures, equipment condition, operating conditions and the intensity of hydraulic power use.
What about the newer Shell Tellus S4 VE?
Shell's current plastics-manufacturing materials also highlight Tellus S4 VE as a premium energy-efficient hydraulic fluid. Shell reports test-based benefits including up to 6% hydraulic productivity improvement and up to 21% lower pump energy loss compared with a mineral oil under the stated test conditions.
This does not mean that an existing machine should automatically be switched from S4 ME or another approved oil to S4 VE. Any change should be checked against the machine manufacturer's requirements, the current fluid, compatibility and the planned changeover procedure.
Oil condition monitoring: replace by condition, not guesswork
Fixed oil-change intervals are easy to manage, but they do not always reflect the actual condition of the fluid. A machine operating in a clean, temperature-controlled environment may age oil differently from the same model exposed to high temperature, moisture or contamination.
Condition monitoring can help maintenance teams determine whether the lubricant is still serviceable and detect abnormal trends before a failure occurs. Shell LubeAnalyst is designed to support proactive issue identification, maintenance optimisation and equipment-performance trending.
What should be monitored?
The exact test package depends on the oil and equipment, but a hydraulic-oil monitoring programme may include:
- viscosity,
- particle contamination / cleanliness,
- water content,
- oxidation or degradation indicators,
- wear metals and other elemental data,
- acid number or other chemistry-specific indicators where relevant,
- trend comparison with previous samples.
Sampling quality matters
A laboratory result is only as useful as the sample. Use a repeatable sampling point and procedure, avoid introducing dirt during sampling and record machine hours, oil hours, recent top-ups, filter changes and abnormal operating events. Trend data is usually more valuable when samples are taken consistently over time.
Melkib's English offer includes industrial oil testing / Shell LubeAnalyst for hydraulic systems and other industrial equipment.
Practical maintenance checklist for hydraulic injection moulding machines
- Confirm the approved oil specification. Use the machine manual and current OEM guidance.
- Control cleanliness during filling and top-up. New oil should not automatically be assumed to meet the machine's target cleanliness level.
- Monitor filters and differential pressure. A rapidly loading filter can indicate contamination or degradation.
- Track operating temperature. Persistent temperature increases can accelerate oil ageing and may indicate a system problem.
- Investigate water and air ingress. Both can affect hydraulic stability and fluid life.
- Check leaks instead of only topping up. Frequent top-up can mask a maintenance issue and continuously alter the oil condition.
- Use oil analysis as a trend tool. Compare results over time instead of reacting to a single number in isolation.
- Record oil changes and product changes. Traceability helps explain later changes in performance.
Hydraulic products relevant to injection moulding machines
The products below represent hydraulic lubricants and related solutions available in the Melkib range. Final selection should always be based on the machine specification, viscosity grade, operating conditions and OEM requirements.
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For the broader range, see Hydraulic oils or the complete Lubricants section.
FAQ – hydraulic oil and injection moulding machine operating costs
Can a more expensive hydraulic oil really reduce operating costs?
Yes, but only when the selected product is suitable for the machine and produces measurable benefits such as longer service intervals, lower maintenance requirements, improved efficiency or reduced failure risk. Compare total cost of ownership rather than purchase price alone.
Should hydraulic oil be changed at a fixed interval or based on analysis?
Follow the machine manufacturer's mandatory maintenance requirements first. Where condition-based maintenance is permitted, regular oil analysis can help refine the change interval and identify degradation or contamination earlier.
What are common warning signs of hydraulic-fluid problems?
Rising operating temperature, noisy pump operation, unstable machine response, repeated filter loading, varnish or sludge, water contamination and abnormal oil-analysis trends all justify investigation. These symptoms can also have mechanical causes, so the oil should be assessed as part of the complete system.
Is Shell Tellus S4 ME always the best choice for an injection moulding machine?
No. The correct product must meet the viscosity, performance and OEM requirements of the specific machine. Tellus S4 ME is one energy-efficient specialist option, while Shell's current portfolio also includes newer S4 VE and other Tellus grades for different requirements.
Can oil analysis detect a machine failure before it happens?
Oil analysis can reveal developing contamination, degradation and wear trends that support earlier maintenance decisions, but it cannot predict every failure. It works best together with machine inspections, operating data and other condition-monitoring methods.
Need to optimise a hydraulic-oil maintenance programme?
Start with the machine model, required viscosity grade and approvals, current oil, operating temperature, filtration, change interval and recent oil-analysis history. These details make it possible to assess whether the biggest opportunity lies in product selection, contamination control or condition monitoring.
Technical sources
- Melkib – current Polish counterpart of this article.
- Melkib – current English article page.
- Shell – plastics manufacturing lubrication materials.
- Shell – Tellus hydraulic fluids technical and portfolio materials.
- Melkib – Hydraulic oils.
- Melkib – Shell LubeAnalyst / industrial oil testing.
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