Put a few drops of oil on the filter paper and take a clean red filter paper. After the lubricating oil leaks, if there is black powder on the surface, and there is a sense of astringency when you touch it, it means that there are many impurities in the lubricating oil. Good lubricating oil has no powder. Grease is very critical if, in the process of using SKF bearings. The use of metamorphic grease will not only fail to function as it should, but will also damage SKF bearings. ① Oil flow observation method One of the lubricating oil to be checked, take two measuring cups. The other is empty on the table, lift the measuring cup full of lubricating oil 30-40 cm away from the table and tilt it, let the lubricating oil slowly flow into the empty cup, observe its flow, good quality lubricating oil flow It should be slender, uniform, and continuous from time to time. If the oil flow is suddenly fast and slow, and sometimes large pieces flow down, it means that the lubricating oil has deteriorated. ② The lubricating oil with better hand twisting method has lubricity, less wear debris and no friction in the hand, and the lubricating oil is twisted between the thumb and the index finger for repeated grinding. If you feel a large friction such as sand between your fingers, it indicates that there are too many impurities in the lubricating oil and can no longer be used, and new lubricating oil should be replaced. ③ Lighting method Use a screwdriver to lift up the lubricating oil, on a sunny day. At a 45-degree angle to the horizontal. Observe the oil droplets against the sunlight. Under the light, you can clearly see that there is no wear debris in the lubricating oil, which is good and can continue to function. If the wear debris is too much, the lubricating oil should be replaced.