To give full play to bearing performance and maintain its expected service effect for a long time, it is necessary to carry out cleaning, maintenance, lubrication and other related operations on bearings. Among them, bearing lubrication plays a crucial role in the operation of bearings. Under normal circumstances, grease is the main lubricant for bearing lubrication. A suitable grease can not only reduce the operating friction of bearings but also extend their service life to a certain extent. Then, how to select grease for bearings?
### I. Grease Selection Methods
#### 1. Clarify Personal Requirements
(1) Bearing Operating Temperature Mechanical bearings used indoors (such as those for machine tools, hand tools, precision machinery, and intermittently started motors) usually have an operating temperature range of 10-50℃; the operating temperature of bearings for outdoor working machinery such as transportation machinery, engineering machinery, and agricultural machinery changes with the atmospheric temperature — in most areas of China, the atmospheric temperature varies from -40℃ to 40℃. In addition, factors such as increased load, higher rotational speed, elevated ambient temperature, excessive grease filling, and long-term continuous operation will cause the temperature of rolling bearings to rise. For example, the temperature of truck wheel bearings traveling along trunk highways can reach 40-80℃; the maximum temperature of large generator bearings can reach 80-90℃; and the temperature of rolling bearings for equipment such as aircraft landing gear and high-temperature motors can even reach 150-200℃ or higher.
(2) Bearing Working Environment Bearings operating in humid environments should be matched with grease with excellent anti-corrosion performance. If machinery works in a humid environment and needs to be parked for a long time, condensed water will form on the bearing surface due to cooling. To prevent rusting, water-insoluble calcium-based grease should be selected; when there is a lot of dust around the bearing and a labyrinth seal is adopted, the grease is required to have a sealing effect at the same time, and in this case, grease with a small penetration should be chosen; if the medium in contact with the bearing has a strong chemical effect, grease containing anti-corrosion additives must be selected.
(3) Bearing Motion Performance For bearings lubricated with grease, if special friction characteristics or low-temperature starting friction torque are required, similar grease made of synthetic base oil with low viscosity and large penetration should be selected; for small motor bearings requiring low noise, filtered stearin or high-viscosity base oil grease should be used to reduce bearing noise.
#### 2. Understand the Inherent Characteristics of Grease
After clarifying the required type of grease, you can start screening products. However, the quality of grease on the market is uneven. How to judge the quality of grease and select high-quality products? You can refer to the following methods:
(1) Check the Production Date Generally, the storage time of grease should not be too long, and it is recommended to select products with a storage period of no more than 1 year; grease with a storage period of more than 1 year can only be used after passing inspection. If the storage time exceeds 1 year or the shelf life has expired, the grease should not be selected — such grease is not only difficult to play its role but may even damage the bearings.
(2) Observe the Appearance Different types of grease have different colors, but regardless of the color, they should be in the form of a paste with uniform viscosity. Phenomena such as uneven color, skin hardening on the surface, excessive oil separation on the surface, a significant drop in viscosity, or emulsification and whitening of the surface due to water mixing all indicate that the grease has deteriorated and cannot be used.
(3) Smell the Odor After opening the package, if an obvious rancid odor of fatty acids is smelled, it means the grease has deteriorated and cannot be used. Forcible use will not only fail to lubricate but also damage the bearings.
(4) Manual Kneading When kneading grease without fillers by hand, it should feel smooth and non-irritating; a rough feel may indicate uneven dispersion of the thickener or mixing of impurities, which will increase the operating resistance of the bearing after use, and such products should not be selected. It should be noted that grease containing filler powder will have a slight granular feel, which needs to be distinguished.
(5) Burn with Fire Pick up a small amount of grease with an iron wire and burn it with a lighter. If the grease softens and drips, it indicates a low dropping point and is an inferior product that cannot be used. It should be noted that this method can only identify inferior grease with an extremely low dropping point — since the flame temperature of a lighter does not exceed 120-130℃, and the dropping point of most greases is higher than this temperature, they will not drip when burned with a lighter.
(6) Sun Exposure Put a small amount of grease into a cup and place it in the sun for 1-2 days. If the grease changes significantly (such as oil separation and discoloration), it indicates unstable performance and cannot be used; if there is no obvious change in the grease after a period of exposure, it means the grease has relatively stable performance and can be considered for selection.
(7) Water Addition Test Put a small amount of grease into a cup, add a few drops of clean water, and stir with a glass rod. If turbidity or whitening occurs, it means the grease is easy to emulsify and has poor water resistance; if there is no obvious change after adding water, it indicates acceptable water resistance and the grease can be considered for selection.
#### 3. Evaluate the Manufacturer
(1) Production Scale It is recommended to choose manufacturers with a large production scale and a long production history — such manufacturers usually have richer production experience and more guaranteed product quality. More importantly, manufacturers that can produce stably for a long time prove that they have competitiveness in the industry and pay attention to technological innovation; otherwise, they are easily eliminated by the market.
(2) Brand Reputation When selecting a grease manufacturer, priority should be given to brands with a good reputation, which can effectively avoid fraud or purchase of inferior products. You can compare multiple enterprises and choose the one with a high reputation under the same conditions.
(3) Product Quality Products with a high reputation but poor quality cannot meet the usage requirements. Therefore, while evaluating the reputation, it is also necessary to carefully inspect the quality of the grease, which is a key consideration when selecting a manufacturer.
(4) After-sales Service The use of grease is not just "buy and fill", and there are many precautions during its use. Therefore, it is necessary to pay attention to the after-sales service of the manufacturer when making a selection — if problems are encountered during use, professional guidance can be obtained through consultation and communication at any time.
### II. Precautions for Grease Selection
1. The selected grease must match the intended use For lubricating grease, it should be selected in a targeted manner according to the friction type, working conditions, environmental conditions and grease supply method; for protective grease, it should effectively protect metal from corrosion (for example, to protect parts in contact with seawater, aluminum-based grease with strong adhesion and good water resistance should be selected), and protective grease can usually be made of solid hydrocarbon thickened high-viscosity base oil; for sealing grease, special attention should be paid to its tolerance to the solvent of the sealing medium.
2. Minimize the types of grease to improve economic benefits On the premise of meeting the usage requirements, it is recommended to give priority to general-purpose greases such as lithium-based grease, complex soap-based grease and polyurea grease. This can not only reduce the types of grease and simplify grease management but also reduce grease costs and maintenance costs by virtue of the long service life of multi-effect grease.
3. The selected grease must adapt to the working state of the friction pair When the equipment has large vibration, grease with high viscosity, strong adhesion and vibration reduction effect should be selected, such as complex soap-based grease thickened with high-viscosity naphthenic or mixed base lubricating oil.
