If the lubricant passes routine tests, is it necessary to change it?

This post was last edited by CHANGBAISHI on 2020-12-23 at 15:49; no replacement is necessary as long as the physical and chemical parameters match those specified in the manual. The so-called conventional items are not suitable as a basis for judgment. For reference.

These few indicators are not sufficient for making a determination; it depends on what type of bearing is being used – sliding or rolling, whether it is used solely for lubrication or in combination with hydraulic regulation systems such as those in engines. Factors such as cleanliness, emulsibility, foaming tendency, and defoaming ability also need to be analyzed

Personally, I think it’s fine with no issues; I agree with the opinions from the 2nd and 3rd floors. If the duration is long, the oil quality analysis test can be added. Currently, there are also online oil filtration systems available to remove harmful impurities and extend the service life of the lubricant

If there are problems with cleanliness, emulsifying ability, foaming capacity, or defoaming ability, they can be seen with the naked eye. If the four parameters that cannot be detected visually – viscosity, moisture, mechanical impurities (or, more advanced methods such as spectroscopy), and acid value – are all within normal limits, it indicates that the quality of this oil is the same as that of the oil when it was first used. There should be no parameters beyond these 4 indicators. If properties such as flash point, viscosity index, and pour point change, then the viscosity will certainly also change

There are two ways of replacement: based on schedule and based on quality; for maintenance at the second level or above, replacement is still necessary

How can it be determined by the naked eye? Each parameter needs to be analyzed using corresponding **standards; if it’s already obvious that it fails the standards, there’s no need to analyze indicators such as water content and mechanical impurities. What’s meant here is that although the existing parameters have passed the analysis, more in-depth tests are required. For example, just because the mechanical impurity level is within acceptable limits doesn’t mean the cleanliness level is satisfactory, as cleanliness is measured in micrometers and is determined using a laser particle size analyzer. In particular, particles between 5-15 micrometers cause the most damage to sliding bearing surfaces, and mechanical impurity analysis cannot reveal this information. The same applies to other indicators as well

I’m glad to continue the discussion. So, as you suggested, mechanical impurities can be replaced by ferrography (which is also inexpensive). In other words, the four parameters to consider are viscosity, water content, ferrography, and acid value: viscosity represents its physical properties, acid value represents its chemical properties, while water content and ferrography represent its microscopic characteristics. If there are no changes, does that mean the oil doesn’t need to be replaced? Is there anything else we haven’t thought of?

These basic physical and chemical parameters cannot truly determine the service life of oils; certain tendencies of the paint film, as well as spin oxidation, are also important factors in assessing the service life of oils. There are many cases in rail transit where the service life cycle of oils is inferred through decomposition analysis, and I can share this information with you.

1. From the perspective of device management (shifting responsibility), tests or replacements should be carried out in accordance with the specifications required by the manufacturer, as long as those requirements are met. 2. In terms of equipment classification, air compressors and small rotating devices generally do not require testing; according to the maintenance schedule, it is sufficient to simply replace them with new lubricant. 3. It is generally large-scale units that require testing, such as centrifugal compressors, steam turbines, or gas turbines. The five main parameters to be tested are viscosity, mechanical impurities, acid value, flash point, and moisture; parameters such as iron content, demulsification ability, and antifoaming properties can also be checked. However, if these requirements are met, there is no need for replacement. Regular use of a vacuum oil filter to treat the lubricating oil, along with increased frequency of testing to monitor trends in each parameter, is sufficient for making judgments. 4. Changing the oil in large-scale units is very expensive; this needs to be considered comprehensively

Ordinary equipment can be used as long as its specifications are suitable