By Sinopec Online Technical Team
Injection moulding machines depend on stable hydraulic performance for clamp force, injection control and repeatable cycle times. Correct hydraulic oil choice and disciplined upkeep protect pumps and valves, control temperature, and help prevent unplanned stops.
Key properties required
- Stable flow behaviour in the machine’s operating range
- Hydrodynamic sealing support between moving components
- Oxidation resistance to limit varnish and sludge
- Rust and corrosion protection
- Load carrying capability and anti wear performance
- Rapid separation of water and entrained air when the system is at rest
- Compatibility with seals and elastomers used by the equipment maker
- Low foam tendency to maintain smooth hydraulic response
Hydraulic oil type used in moulding plants
Mineral anti wear hydraulic oils are most common in injection moulding machinery. These fluids contain zinc anti wear chemistry for film strength and reliable pump protection.
Viscosity grades and selection
Machine manuals define the viscosity grade. Grades frequently used are ISO VG 32, ISO VG 46 and ISO VG 68. Choose the grade that delivers the required viscosity at the normal running temperature so that pumps and servo valves operate within their design window.
Selection checklist
- Follow the equipment maker specification for oil type and viscosity grade
- Confirm oxidation stability and air release performance suit the duty cycle
- Check demulsification to allow fast removal of free water
- Verify filterability and cleanliness targets for servo valve systems
- Confirm seal compatibility
Routine checks in service
- Keep the oil level above the midpoint of the sight gauge
- Warm up before loading the system in cold conditions
- Maintain typical running temperature near 45 to 50 °C unless the machine maker states otherwise
- Monitor filter condition and differential pressure
- Listen for pump noise that may indicate air ingress or high viscosity
- Inspect hoses, joints and seals for leaks
Oil condition monitoring
- Compare new and used oil visually for clarity and colour
- Use a blot paper drop test to screen for deposits
- Laboratory analysis for viscosity shift, oxidation, water and particles on a planned interval
Oil replacement and system cleanliness
- Drain and clean the tank, refill through a clean filter, and keep fill points protected
- Allow the system to stand for three to five hours after filling so air and suspended material can separate
- Flush when contamination is confirmed or when instructed by the machine maker
Troubleshooting reference
| Condition observed | Likely causes to check |
|---|---|
| High oil temperature | Restricted cooling, prolonged high pressure operation, pump wear or internal leakage |
| Abnormal noise | Air entry at suction, blocked filter, incorrect viscosity, coupling misalignment, valve issues |
| Unstable cycle or slow response | Viscosity outside target range, aeration, sticking valves, temperature variation |
| Leakage | Seal wear, loose fittings, hose damage |
Related lubrication on the machine
Gear trains, slides and linkages require oils and greases specified by the equipment maker. Store greases and oils clean and dry, away from heat and direct sunlight.
Recommended Sinopec resources
Cross-references
- What Goes Into Machine Lubricants
- Benefits of Regular Maintenance for Industrial Machines Using Lubricants
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Published by Sinopec Online Technical Team
