The quality indicators of bearing lubricating oil can be divided into two categories: one is the physical and chemical performance indicators of oil products, and the other is the application performance indicators of oil products. (mainly introduce several main physical and chemical indexes)
a. Color: the color of lubricating oil, like all substances, has a corresponding and fixed color, which is related to the refining system of base oil and the additives added. However, in the process of use or storage, it will deteriorate due to its oxidation, so as to change the color,
and the degree of discoloration is related to the degree of deterioration. If it is milky white, it indicates the presence of water or bubbles; Darker color indicates oxidative deterioration or pollution.
b. Viscosity: viscosity is the degree of internal friction resistance of lubricating oil, that is, the measure of internal friction. Viscosity is usually divided into dynamic viscosity, kinematic viscosity and relative viscosity.
Viscosity is the main index of classification, classification, quality evaluation, selection and substitution of various lubricating oils.
Dynamic viscosity: dynamic viscosity is a measure of the internal friction of a liquid flowing under a certain shear stress.
Relative viscosity: relative viscosity refers to the viscosity expressed in conditional units measured by different specific viscometers. Generally, there are three expression methods: Engler viscosity, Sayer viscosity and Rayleigh viscosity.
Kinematic viscosity: kinematic viscosity is a measure of the internal friction of a liquid flowing under the action of gravity. Unit of measurement: mm2 / S; In China, the viscosity of lubricating oil is divided into 20 grades according to its size, which is called viscosity grade.
two two two point two 1.98～2.42
three three three point two 2.88～3.52
five five four point six 4.14～5.06
seven seven six point eight 6.12～7.48
ten ten ten 9~11
fifteen fifteen fifteen 13.5～16.5
twenty-two twenty-two twenty-two 19.8～24.2
thirty-two thirty-two thirty-two 28.8～35.2
forty-six forty-six forty-six 41.4～50.6
sixty-eight sixty-eight sixty-eight 61.2～74.8
one hundred one hundred one hundred 90~110
one hundred and fifty one hundred and fifty one hundred and fifty 135~165
two hundred and twenty two hundred and twenty two hundred and twenty 192~242
three hundred and twenty three hundred and twenty three hundred and twenty 288~352
four hundred and sixty four hundred and sixty four hundred and sixty 414~506
six hundred and eighty six hundred and eighty six hundred and eighty 612~748
one thousand one thousand one thousand 900~1100
one thousand and five hundred one thousand and five hundred one thousand and five hundred 1350~1650
two thousand and two hundred two thousand and two hundred two thousand and two hundred 1980~2420
three thousand and two hundred three thousand and two hundred three thousand and two hundred 2880~3520
Viscosity is an important quality index of lubricating oil. If the viscosity is too small, it will form semi liquid lubrication or boundary lubrication, which will accelerate the wear of friction pairs and easily leak oil;
Excessive viscosity, poor fluidity, poor permeability and heat dissipation, large internal friction resistance, difficult overshoot and high power consumption. Therefore, the reasonable selection of viscosity is the guarantee of sufficient lubrication of friction pairs.
c. Viscosity temperature characteristics: the characteristics of lubricating oil change with temperature into viscosity temperature characteristics.
At present, viscosity index VI is often used to express the quality of viscosity temperature characteristics. The greater the VI value of general oil, the greater the change of its viscosity value with temperature, so it is more suitable for occasions with variable temperature or wide range of change.
The better the viscosity temperature characteristics of the oil. Oil with VI = 0 is represented by 0 VI, and oil with VI = 100 is represented by 100 VI. Viscosity index is an empirical value, which is obtained by comparing the viscosity of 40 ℃ and 100 ℃
with two lubricating oils with good viscosity performance (viscosity index is set as 100) and poor viscosity performance (viscosity index is set as 0).
Classification of viscosity index
classification Viscosity index range
Low viscosity index ＜ thirty-five
Medium viscosity index 35~80
High viscosity index 80~110
Higher viscosity index ＞ one hundred and ten
d. Freezing point and pour point
Freezing point: the freezing point refers to the high temperature at which the lubricating oil stops under the specified cooling conditions;
Pour point: the pour point refers to the low temperature at which the lubricating oil can continue to flow under the specified conditions.
Both pour point and pour point represent the low-temperature performance of lubricating oil, but the pour point better reflects the low-temperature fluidity of oil, which is better than the pour point in actual use. Therefore, at present,
the pour point is mainly used to represent the low-temperature performance of lubricating oil in the world. The pour point is about 3 ℃ higher than the pour point, and the working temperature of general lubricating oil is 3 ~ 4 ℃ higher than the pour point.
e. Lightning: the flash point refers to the low temperature when the lubricating oil is heated and the evaporated oil vapor is mixed with air under the specified conditions to a certain concentration to produce a short flash fire when in contact with the flame.
f. Acid value: acid value refers to the mass of potassium oxide required to neutralize the organic acid contained in 1g lubricating oil, in mgKOH / g.
Acid value has different meanings for new oil and old oil. For new oil, the acid value indicates the refining depth of the oil, and for 110 oil, the acid value indicates the degree of oxidation and deterioration of the lubricating oil during use. Excessive acid value indicates serious oxidation and deterioration.
g. Moisture: moisture refers to the mass percentage of water content in lubricating oil. Due to the existence of water, when the temperature drops below 0 ℃, the viscosity temperature characteristics will become worse.
When the temperature rises, the water will vaporize, produce bubbles, destroy the oil film, emulsify the oil, reduce the viscosity and deteriorate the lubrication effect.
h. Mechanical impurities: all solid impurities suspended and precipitated in lubricating oil are collectively referred to as mechanical impurities. The existence of mechanical impurities will destroy the lubricating oil film and accelerate the wear of friction pairs.
k. Carbon residue: carbon residue refers to the coke like residue generated after the lubricating oil is heated, vaporized and decomposed with air, which is expressed as a percentage of the oil.