It mainly includes oxidation stability, free acid and free alkali, corrosivity, etc
1. Oxidation stability: the ability of lubricating grease to resist oxidation during storage and use. Oxidation stability is one of the Chemical Properties important properties that affect the service life of grease, especially for grease used at high temperature for a long time.
2. Free acid and free alkali: free acid and free alkali refer to the organic acid and excess alkali after the grease is not fully saponified in the production process. The free alkali content is expressed by the mass fraction containing KOH. Significance of free organic acids and free bases in use:
1) A very small amount of free alkali has little effect on the quality of Chemical Properties grease, and it is allowed or even necessary to contain a small amount of free alkali. In the long-term storage of lubricating grease, due to oxidation,
some hydrocarbon substances deteriorate and become organic acids, which will reduce and neutralize the content of free alkali. Therefore, the existence of a certain amount of free alkali is necessary to inhibit the oxidative deterioration of lubricating grease.
However, when the amount of free alkali in the grease is too large, the colloidal stability and mechanical properties of the grease will be Chemical Properties affected, resulting in stratification, oil separation and loss of lubricating performance.
2) Free acids are not allowed in lubricating grease, especially low molecular organic acids, which will corrode metals. When the grease is acidic, the grease skeleton will fail Chemical Properties and the grease will become soft and thin.
3. Corrosivity: whether the grease has corrosive effect on the metal. The main reasons why grease corrodes metals are as follows: first, it contains corrosive substances, such as water, free acid, alkali and active sulfide; Another reason is due to organic acids produced by oxidation.
（3） Practical performance
Mainly including: mechanical stability and lubricity.
1. Mechanical stability: refers to the performance that the structure of Chemical Properties lubricating grease is damaged and the consistency changes after being subjected to mechanical force. It is expressed by the change of cone penetration before and after shear.
2. Lubricity: the lubricating performance of grease is closely related to its use. For heavy-duty equipment, especially chains and Chemical Properties gears, it is required to have high comprehensive wear value and sintering load,
so as to prevent the equipment from being worn if the performance fails to meet the requirements. The commonly used methods to evaluate the anti-wear and extreme pressure properties of lubricating grease are four ball machine method and Timken test machine method.
Koyo bearing shows the characteristics of late failure. The time from the occurrence of serious failure (generally bearing damage, Chemical Properties such as shaft holding, burn, sand frame crack, raceway, bead wear, etc.) is mostly less than one week.
The larger the equipment capacity, the faster the speed, and the shorter the interval. Therefore, in the actual bearing fault diagnosis, once the late fault characteristics are found, the fault of one-way bearing should be determined and the maintenance should be arranged as soon as possible.
The manufacturing of Koyo bearings usually involves forging, Chemical Properties heat treatment, turning, grinding and assembly. The rationality, advanced nature and stability of all the processing technologies will also affect the life of unidirectional bearings.
The thermal treatment and grinding processes that affect the quality of bearings are often more directly related to the failure of bearings. In recent years, the research on the degenerative layer of the bearing working surface shows that the grinding process is closely related to the bearing surface quality.
1. The Koyo bearing has been damaged and should be replaced immediately.
2. There is too little or too much bearing grease or impurities such as iron filings. The capacity of one-way bearing grease shall not exceed 70% of the total volume, and those with impurities shall be replaced.
3. The fit between shaft and bearing is too tight or loose. If it is too tight, it shall be grinded again, and if it is Chemical Properties too loose, the rotating shaft shall be sleeved.
4. The fit between bearing and end cap is too tight or loose. When it is too tight, the bearing chamber shall be processed, and when it is too loose, the steel sleeve shall be embedded in the end cover.
5. The covers at both ends of the motor or bearing covers are poorly assembled. Install and level the end cover or bearing cover stop, and tighten the screws.
6. The belt is too tight or the coupling is poorly assembled. Adjust the belt tension and correct the coupling.
7. The lubricating oil of one-way bearing is too little, there are impurities or the oil ring is stuck. The oil ring shall be repaired or replaced if oil is added or replaced.
After moving for a period of time, the vibration and noise maintain a certain level, and the spectrum is very single, with only one or two times the frequency. The frequency spectrum above three times of power frequency rarely appears,
and the state of one-way bearing is very stable and enters the stable working period. After continued operation and entering the later stage of use, the bearing vibration and noise began to increase, and sometimes abnormal sound appeared, but the change of vibration increase was slow.
At this time, the kurtosis value of Koyo bearing began to suddenly reach a certain value. We believe that the bearing shows initial failure at this time.
The primary obligation of Koyo bearing service life analysis is to find out the primary elements of bearing failure according to a large number of matching data,
analysis data and failure mode pattern, so as to put forward targeted improvement measures, delay the retirement period of one-way bearing and avoid sudden early failure of Koyo bearing.