What Is the Viscosity Index?
English name: Viscosity Index.
Viscosity index
discuss
- Chinese name
- Viscosity index
- Foreign name
- Viscosity Index.
- Viscosity index
- Viscosity index indicates the viscosity of all fluids
- Calculate
- The viscosity index must be calculated using a formula
- English name: Viscosity Index.
- The viscosity index indicates the degree to which the viscosity of all fluids changes with temperature. The higher the viscosity index, the less the viscosity of the fluid is affected by temperature, and the less sensitive the viscosity is to temperature.
- Lubricants can be divided into three grades according to the viscosity index: 35-80 are medium viscosity index lubricants; 80-110 are high viscosity index lubricants; 110 and above are extra-high viscosity index lubricants. The motor oil with a viscosity index of 100-170 is a high-grade multi-grade lubricating oil. It has a smooth viscosity-temperature curve change and good viscosity-temperature properties. At lower temperatures, the high molecular weight organic compound molecules in these viscosity index improvers have low solubility in the oil, and the molecules curl into small compact groups, so the viscosity of the oil increases little; at high temperatures, it is in the oil As the solubility increases, the tortuous linear molecules expand and extend, thereby increasing the viscosity, which makes up for the viscosity of the base oil that decreases due to the temperature increase. So the higher the viscosity index, the smaller the change in viscosity with temperature.
- Calculation of viscosity index
- The viscosity index must be calculated using a calculation formula. The viscosity index is lower than 100 and the algorithm is different. The method of ASTM D2270 is divided into two parts, one is method A, and the other is method B. Method A is actually the old method of ASTM D567, which uses a calculation method to measure the viscosity index. Rule B is designed for oils with a viscosity index exceeding 100.
- Algorithm A for Viscosity index:
- If the viscosity index is between 0 and 100, this method is adopted. The calculation formula is: Viscosity Index VI = [(LU) / (LH)] * 100
- The viscosity of a known oil with a viscosity index of 100 at 100 ° F (or 40 ° C), but its viscosity at 210 ° F should be the same as that of an unknown oil at 210 ° F (or 100 ° C). Because its viscosity index is very high, it uses the H (High) alphabet.
- L viscosity of a known oil with a viscosity index of 0 at 100 ° F (or 40 ° C). However, its viscosity at 210 ° F (or 100 ° C) should be the same as that of an unknown oil at 210 ° F (or 100 ° C). Because its viscosity index is very low, it uses the L (Low) alphabet.
- U Raw material of unknown viscosity index, viscosity at 100 ° F (or 40 ° C).
- Algorithm B for Viscosity index:
- Designed for oils with viscosity index over 100.
- If the result calculated by the old method for an oil material exceeds 100, it must be recalculated using this method, and a report based on the calculation method of the B method must be used. It is expressed by VI (E), VI (Extended), VIe, or "epitaxial viscosity index". The calculation formula is as follows:
- VI (E) [(Antilog N) 1 / 0.0075] In formula 100, N increases the viscosity of the oil sample at 210 ° F, making it equal to the index required for the ratio of H and U at 100 ° F. which is
- N (H-U) / (KV210), or
- KV210N H / U
- KV210 kinematic viscosity at 210 ° F (or 100 ° C) (KV is the abbreviation for Kinetic Viscosity)
- H Known a known oil with a viscosity index of 100 by method A. Its kinematic viscosity at 100 ° F (or 40 ° C) (can be found in Table 24)
- Dynamic viscosity of U oil sample at 100 ° F (or 40 ° C) (at this time H U)
- For example: the kinematic viscosities of an oil sample at 100 ° F and 210 ° F are 24.71 and 5.15 cSt, respectively. Try to find its viscosity index.
- Check from the table (proportion method) H 31.69, and substitute it into the formula
- There is a problem with the H value!
- Viscosity index H value table
- In the actual query table [1] , it is found that there is no H value corresponding to 5.15, the value corresponding to 5.10 is 29.46, the value corresponding to 520 is 30.43, and the value corresponding to 5.15 should be between the two, which is obtained by linear interpolation The average is 29.945, which is calculated by plugging into the formula. The viscosity index is 142, which is very close to the result 143 calculated on the website. The calculation tools on the website are available. [2]
- N HU / KV210
- 31.6924.71 /5.15
- 0.15180
- VI (E) [(AntilogN1 / 0.0075] 100
- (Antilog 0.151801 / 0.0075] 100
- 1.4181 /0.0075 100
- 155.7 or 156