The classification of lubricants by ISO viscosity grade system

 ISO viscosity grades are a standardized system used to classify lubricants based on their viscosity, or thickness, at various temperatures. Viscosity refers to a fluid's resistance to flow, and it's a critical property in determining how effectively a lubricant will protect machinery and reduce friction.

The ISO viscosity grade system assigns a numerical value to each grade, which indicates the viscosity of the lubricant at 40 degrees Celsius (104 degrees Fahrenheit). For example, ISO VG 32 has a viscosity of 32 centistokes at 40°C. The higher the number, the thicker the oil.

Here's a breakdown of the ISO viscosity grade system:

1. ISO VG 2 to ISO VG 10: These grades are considered very light oils, suitable for extremely low-temperature applications or for use in very fine instruments where minimal friction is essential.

2. ISO VG 15 to ISO VG 22: These are light oils, commonly used in applications where low viscosity and good fluidity at low temperatures are required. They're often used in refrigeration systems, small engines, and hydraulic systems.

3. ISO VG 32 to ISO VG 68: These grades are referred to as medium oils and are among the most common. They're used in a wide range of applications, including hydraulic systems, industrial gearboxes, and circulating systems.

4. ISO VG 100 to ISO VG 150: These grades are considered heavy oils and are typically used in applications where greater film thickness and lubricant longevity are required, such as large industrial gearboxes and certain hydraulic systems.

5. ISO VG 220 to ISO VG 680: These grades are very heavy oils, used in applications where extreme pressure and load-bearing capabilities are necessary, such as in heavy machinery and gearboxes operating under severe conditions.

6. ISO VG 1000 and above: These are extremely heavy oils, typically used in specialized industrial applications such as open gearing and certain large-scale machinery.

Additionally, ISO viscosity grades may be followed by a suffix indicating the viscosity index (VI) improver used, such as ISO VG 32 with VI, indicating that it has a viscosity index improver added to improve its viscosity-temperature relationship. This helps maintain consistent viscosity across a range of temperatures.