Kinematic viscosity is the fluidity index of the oil, when its value is larger, it means that its viscosity is higher, the smaller the value is, the lower the viscosity is. This number will change as the temperature changes, the higher the temperature, the lower the viscosity will be. On the contrary, the lower the temperature, the larger the value will be, and the higher the viscosity will be.

Summary of kinematic viscosity test methods: Determine the time for a sample to flow through a viscometer of a calibrated volume at a given temperature. The product of the measured flow time and the viscometer calibration constant is the kinematic viscosity of the sample (mm²/s). According to the formula: v=C*t v is the kinematic viscosity, the unit is quadratic millimeters per second (mm²/s); C is the viscometer calibration constant, expressed in quadratic millimetres per quadratic second (mm²/s²); t indicates the process time, expressed in seconds (s).

Knowledge sharing: Difference between kinematic viscosity and viscosity index

So what does the viscosity index mean? In fact, it represents the extent to which the oil changes with temperature, the higher the viscosity index, the less the oil viscosity is affected by temperature, the less the viscosity is sensitive to temperature, and the oil has been able to maintain a stable viscosity. The viscosity index can be measured by the testing equipment of the known 40℃ and 100℃ kinematic viscosity value of the oil, and then the viscosity index value is obtained according to the formula in GB/T 1995 standard.

The higher the viscosity index is, the better the viscosity temperature characteristics of the oil, and to a certain extent, the better the quality of the oil, which is an important control index in the production process of the lubricant manufacturer. According to the different viscosity index, the lubricating oil is divided into three levels: 40-80 is the intermediate viscosity index; > 80 is the high viscosity index; > 120 is a very high viscosity index; > 140 is a super high viscosity index oil.

So some customers will ask, does the higher the viscosity index of the lubricating oil mean the better the quality of the oil?

We should be clear that the viscosity index is a performance indicator of lubricating oil, not a quality indicator.

Knowledge sharing: Difference between kinematic viscosity and viscosity index

The choice of lubricating oil or according to the use of conditions, not just look at the level of the viscosity index, different types of lubricating oil for the application of different surface, the corresponding viscosity index requirements will be different, and the quality of the lubricating oil itself has nothing to do with. The choice of lubricating oil is related to temperature, speed, load and working environment. Or according to the actual use of conditions, choose their own lubricating oil.

For example: pure electric vehicle reducer oil (NB/SH/T 6042-2021) standard for the viscosity index of the quality index requirements ≥120; Heavy duty vehicle gear oil (GB 13895-2018) standard for viscosity grades 90, 110, 140 oil viscosity index quality index requirements ≥90. It can be seen that for different types of lubricating oil, it is necessary to select the appropriate lubricating oil with reference to the oil indicators specified in the corresponding national standards.

Knowledge sharing: Difference between kinematic viscosity and viscosity index
The following to introduce our Shanghai Changji test kinematic viscosity equipment.

Instrument according to GB/T 265 standard

Knowledge sharing: Difference between kinematic viscosity and viscosity index

Conforms to SH/T0956 ASTM D7279 better than GB/T 265

Comparison of kinematic viscosity test methods

Knowledge sharing: Difference between kinematic viscosity and viscosity index