To fully utilize and maintain the expected performance of bearings for a long time, it is necessary to carry out cleaning, maintenance, lubrication, and other related operations on the bearings. Especially, the lubrication of bearings plays a very important role in bearing operation. Generally, lubricating grease is mainly used for lubrication in bearings. Suitable lubricating grease can not only reduce the running friction of bearings, but also extend their service life to a certain extent. So, how to choose lubricating grease for bearings?
1、 Lubricating grease selection method
1. Understanding one's own needs
(1) Bearing operating temperature. For machine bearings used indoors, such as machine tools, manual tools, precision machinery, and intermittent starting motors, the general operating temperature range is 10-50 ℃. For mechanical bearings used for outdoor work such as transportation machinery, construction machinery, and agricultural machinery, the general working temperature will definitely change with changes in atmospheric temperature. In most regions of China, the atmospheric temperature changes from -40 to 40 ℃. Factors such as increasing load, accelerating speed, increasing ambient temperature, overfilling of lubricating grease, and long-term continuous operation all cause the temperature of rolling bearings to rise. For the wheel bearings of trucks driving along the main road, the temperature can reach 40-80 ℃. Large generator bearings can reach temperatures of up to 80-90 ℃, while rolling bearings such as aircraft landing gears and high-temperature motors can reach temperatures of 150-200 ℃ or higher.
(2) Bearing working environment. Bearings working in humid environments should use lubricating grease with good anti-corrosion performance. When machinery works in a humid environment and needs to stay for a long time, condensation water will form on the bearing surface due to cooling. To prevent rust, non absorbent calcium based grease should be selected. When there is a lot of dust around the bearing and a curved seal is used, it is hoped that the lubricating grease will also have a sealing effect, and a lubricating grease with a smaller penetration should be selected. When the bearing medium has strong chemical effects, lubricating grease with anti-corrosion additives should be selected.
(3) Bearing motion performance. For bearings lubricated with grease, when special friction is required or when starting friction torque at low temperatures is required, similar low viscosity and high penetration lubricating grease composed of synthetic base oil should be selected. For small motor bearings that require low noise, filtered hard grease or high viscosity base oil lubricating grease should be used to reduce bearing noise.
2. Understand lubricating grease
Once you have determined the type of grease you need, you can start choosing a grease. However, there is a mixed bag of greases in the market. What kind of grease is a good one, and how can you determine the quality of the grease? Let's take a look at the selection method of bearing grease together.
(1) Look at the production date. In general, the storage time of lubricating grease should not be too long. Users should choose grease with a storage period of no more than one year. Lubricating grease with a storage period of more than one year should be inspected and qualified before use. If it exceeds one year or is not within the shelf life, it cannot be selected. Even if such a lubricating grease is selected, its effect will not be significant, and it may even harm the bearings.
(2) Look at the appearance. Different types of lubricating grease have different colors, but regardless of the color of the grease, it should be a paste with uniform viscosity. If the color of the grease varies or the skin hardens, there is a lot of floating oil on the surface of the grease or the viscosity decreases significantly, or the surface of the grease emulsions and turns white due to the mixing of water, these phenomena all indicate that the grease has deteriorated and cannot be used.
(3) Smell the odor. If you smell a noticeable odor of fatty acid spoilage when opening the packaging, it indicates that the lubricating grease has deteriorated. Deteriorated lubricating grease cannot be used. If used persistently, it will not only have a certain effect but also harm the bearings.
(4) Hand twist. When twisting grease without fillers by hand, it has a smooth and non irritating feel; Otherwise, it may be due to uneven dispersion of the thickener or the inclusion of impurities, which will increase the resistance of bearing operation and cannot be used. But the lubricating grease containing filler powder has a slight tactile sensation, and everyone needs to pay attention to distinguishing it.
(5) Burn with fire. Pick up a piece of lubricating grease with iron wire and burn it with a lighter. If the lubricating grease softens and drips, it indicates that it is a low-quality lubricating grease with a low dripping point and cannot be used. It should be noted that this method can only identify low-quality lubricating greases with low drop points, as the temperature of the lighter flame does not exceed 120-130 ℃, and most lubricating greases have drop points above this temperature, so burning them with a lighter will not drip.
(6) Sunlight exposure. Take a piece of lubricating grease and place it in a cup in the sun for one or two days. If the grease changes significantly, causing oil separation or discoloration, it indicates that the performance of the grease is unstable and cannot be used. If there is no significant change in the grease body after a period of exposure to the sun, it indicates that the performance of the lubricating grease is relatively stable and can be considered for use.
(7) Water addition method. Take a small amount of lubricating grease into a cup, add a few drops of water to it, and then stir with a glass rod. If there is turbidity or whitening, it indicates that the grease is easy to emulsify and is not water resistant. If there is no significant change after adding water, it indicates that the water resistance of the lubricating grease is still acceptable and can be considered for use.
3. Look at the manufacturer
(1) Production scale. It is recommended to choose manufacturers with larger production scales and longer production years, as such manufacturers generally have more experience and guarantee quality. More importantly, if the production years are longer, it proves that this manufacturer is still capable in the industry and is also good at innovation, otherwise they will be eliminated long ago.
(2) Highly reputable. When choosing a lubricating grease manufacturer, it is important to choose a reputable one. This provides us with a guarantee that there will be no fraud or poor quality issues. You can compare several companies and choose one with high credibility under the same conditions.
(3) The quality is relatively good. Just having high credibility and poor quality is not enough, so when evaluating credibility, it is also important to carefully examine the quality of lubricating grease. This is also a noteworthy issue when choosing a manufacturer.
(4) Good service. The use of lubricating grease is not just about buying it back and filling it in directly. There is a certain level of attention in terms of usage, so when choosing, everyone needs to pay attention to the relevant services of the lubricating grease manufacturer, so that if you have any questions, you can consult and communicate at any time.
2、 Precautions for selecting lubricating grease
1. The selected lubricating grease should be suitable for its purpose of use. For lubricating grease, specific choices must be made based on the type of friction, working conditions, working conditions, environmental conditions, and grease supply method; For protective grease, it should be able to effectively protect metals from corrosion, such as protecting parts in contact with seawater. Aluminum based grease with strong adhesion and water resistance should be selected; Generally, protective grease can be made from solid hydrocarbon thickened high viscosity base oil. For sealing grease, attention should be paid to its resistance to the solvent of the sealed medium.
2. The selected lubricating grease should strive to reduce the variety of grease and improve economic efficiency. When meeting the requirements, it is recommended to use lithium based grease, composite soap based grease, polyurea grease, and other general-purpose lubricating greases as much as possible. This not only reduces the variety of fats and simplifies the management of fats, but also reduces the cost of using fats and maintenance costs due to the long service life of multi effect fats.
3. The selected lubricating grease should be suitable for the working state of the friction pair. When vibration is high, apply high viscosity, good adhesion, and vibration damping grease, such as high viscosity naphthenic or mixed base lubricating oil thickened composite soap based lubricating grease.