ISO Viscosity Grades
ISO 3448 viscosity classification system for industrial lubricating oils, providing a standardized method for specifying oil viscosity at 40°C.
The ISO viscosity grade (VG) system provides a standardized method for classifying industrial lubricating oils by their kinematic viscosity at 40°C. This allows consistent communication of viscosity requirements between equipment manufacturers, oil suppliers, and end users.
How to Read ISO VG Numbers
The ISO VG number represents the approximate kinematic viscosity in centistokes (cSt) at 40°C:
- ISO VG 32 = approximately 32 cSt at 40°C
- ISO VG 100 = approximately 100 cSt at 40°C
Viscosity Selection Principles
Higher Viscosity (Higher VG Number)
- Better load-carrying capacity
- Slower speeds
- Higher temperatures
- Rough or worn surfaces
Lower Viscosity (Lower VG Number)
- Higher speeds
- Lower temperatures
- Better heat dissipation
- Energy efficiency
Operating Temperature Considerations
ISO VG is measured at 40°C, but equipment operates across a temperature range. Key considerations:
- Viscosity Index (VI): Indicates how much viscosity changes with temperature
- Minimum Viscosity: At highest operating temperature, must maintain adequate film
- Maximum Viscosity: At lowest start-up temperature, must allow circulation
Relationship to Other Systems
| ISO VG | SAE Crankcase | SAE Gear | AGMA |
|---|---|---|---|
| 32 | 10W | 75W | 0 |
| 46 | 15W | 75W-80 | 1 |
| 68 | 20W | 80W-90 | 2 |
| 100 | 30 | 80W-90 | 3 |
| 150 | 40 | 85W-90 | 4 |
| 220 | 50 | 90 | 5 |
| 320 | 60 | 90 | 6 |
Classification Table
| ISO VG | Kinematic Viscosity at 40°C (cSt) | Viscosity Range (Min-Max) | Typical Applications |
|---|---|---|---|
| 2 | 2.2 | 1.98-2.42 | Spindle oils, instrument oils |
| 3 | 3.2 | 2.88-3.52 | Spindle oils, air tool oils |
| 5 | 4.6 | 4.14-5.06 | Light spindle oils |
| 7 | 6.8 | 6.12-7.48 | Spindle oils |
| 10 | 10 | 9.0-11.0 | Spindle oils, hydraulic oils |
| 15 | 15 | 13.5-16.5 | Spindle oils, hydraulic oils |
| 22 | 22 | 19.8-24.2 | Hydraulic oils, slideway oils |
| 32 | 32 | 28.8-35.2 | Hydraulic oils, circulating oils |
| 46 | 46 | 41.4-50.6 | Hydraulic oils, general purpose |
| 68 | 68 | 61.2-74.8 | Gear oils, circulating oils |
| 100 | 100 | 90-110 | Gear oils, compressor oils |
| 150 | 150 | 135-165 | Gear oils, way oils |
| 220 | 220 | 198-242 | Gear oils, way oils |
| 320 | 320 | 288-352 | Gear oils |
| 460 | 460 | 414-506 | Gear oils, worm gear oils |
| 680 | 680 | 612-748 | Gear oils, heavy-duty |
| 1000 | 1000 | 900-1100 | Gear oils, open gears |
| 1500 | 1500 | 1350-1650 | Open gears, heavy-duty |
Typical Applications
| Grade/Class | Common Applications |
|---|---|
| VG 2-10 | High-speed spindles, instruments, pneumatic tools |
| VG 15-32 | Hydraulic systems, light-duty bearings, spindles |
| VG 46-68 | General hydraulic systems, circulating systems |
| VG 100-220 | Enclosed gear systems, compressors |
| VG 320-1500 | Heavy-duty gears, worm drives, open gears |
Notes & Limitations
- - ISO VG number is the midpoint viscosity in centistokes at 40°C
- - Each grade allows ±10% viscosity tolerance
- - Adjacent grades differ by approximately 50% (following R 20 preferred number series)
- - Viscosity at operating temperature is more relevant than 40°C viscosity for film thickness calculations
Sources
- ISO 3448:1992 - Industrial liquid lubricants -- ISO viscosity classification
- ASTM D2422 - Viscosity System for Industrial Fluid Lubricants
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