The selection of grease should be based on the specifications of the vehicle and machinery's operating manual, choosing the appropriate type and viscosity grade of grease that matches the working conditions of the lubricated part. Key factors to consider include: the purpose of using grease, the lubricated area, operating temperature, speed, load, working environment, and the method of grease application.
1. Define the Purpose of Lubricant Usage: When selecting a lubricant, it is crucial to first clarify its intended use. Based on the primary function of the lubricant, it is mainly categorized into three types: friction reduction, protection, and sealing. The choice of lubricant should depend on the main role it is intended to play in the application, and one should select the lubricant that meets the requirements.
2. Consider the working temperature of the lubrication areas: The temperature levels and variations of mechanical friction areas significantly impact the lubricating effect and service life of lubricants. The working temperature of the lubrication areas is a crucial factor in selecting the appropriate lubricant.
3. Consider the load on lubrication areas. Load refers to the pressure per unit area on the friction surface. Depending on high-load and low-load working conditions, extreme pressure grease (B) and non-extreme pressure grease (A) are respectively selected. Heavy machinery equipment such as gears, bearings, worm gears, and worm shafts all bear significant loads and must consider using lubricants with anti-wear extreme pressure additives. To enhance anti-friction effects and improve resistance to vibration and impact loads, lubricants with molybdenum disulfide, graphite, or other solid lubricants can also be considered.
4. Speed Considerations for Lubrication Points Since grease is a rheological system, its kinematic viscosity changes with shear rate. Therefore, the physical state and lubricating action of grease are particularly sensitive to the operating speed of the lubricated components, which differs from that of lubricating oils. The higher the operating speed, the greater the shear stress on the grease, the more severe the destructive effects on the thickener structure, and the shorter the service life. Thus, in conditions of the same load and temperature, speed is a major factor affecting the application of grease. For bearings, if d is the inner diameter of the bearing (mm) and n is the bearing speed, for d ≤ 50mm, when dn ≤ 300,000, grease lubrication is used; when dn > 300,000, oil lubrication is used. For d > 50mm, when dn ≤ 300,000, grease lubrication is used; when dn > 300,000, oil lubrication is used. Generally, for bearings with higher speeds, a thinner grease should be chosen; conversely, for slower speeds, a thicker grease is preferred. Exceptionally high-performance bearing greases can be used for bearings with dn values of 500,000 to 1,000,000. 5. Environmental Considerations for Lubrication Points and Media Contact The environment and media contacting the lubrication points have a significant impact on the performance of grease. Therefore, careful consideration should be given when selecting grease. (1) For areas prone to moisture or water contact, sodium-based grease should not be used; for areas that come into contact with large amounts of water or are frequently immersed in water, it may even be unsuitable to use lithium-based grease. Consider using better water-resistant complex aluminum, lithium-calcium-based grease, or polyurethane grease. (2) For areas exposed to acids or acidic gases, ordinary lithium-based grease, complex calcium, complex aluminum, and bentonite grease should not be used, as they are prone to thinning and loss. Consider using complex barium-based grease or polyurethane grease with better acid resistance. If contact with strongly acidic or strongly oxidizing media is expected, use full-perfluoro grease. (3) For areas contacting seawater or saltwater, complex aluminum-based grease can be used; for areas contacting rubber, grease made from base oils or esters with wax or silicone oil can be used. (4) For areas contacting fuel oils or mineral lubricating oils, grease made with inorganic thickeners (such as bentonite) and silicon oil synthetic oils can be used. 6. Considerations for Grease Filling Methods Grease filling methods include manual filling and centralized pump filling. Applying, filling, grease gun filling, and grease cup filling all fall under manual filling. 7. Considerations for Overall Benefits There are various types of greases that meet mechanical operating requirements. When selecting grease, one should not only consider the price but also look at whether it extends the lubrication cycle and reduces maintenance costs. Only greases with outstanding overall benefits are suitable. Cautionary Notes (1) Different types of greases should not be mixed, as this can soften the grease and decrease colloidal stability. When changing to fresh grease, the original grease must be cleaned off; otherwise, it will accelerate the oxidation and deterioration of the fresh grease. (2) Do not overfill grease, as this can increase operating resistance and raise working temperatures. (3) Generally, grease should not be mixed with oil. (4) Grease should be stored in a cool, dry place and should not be left outdoors. Prevent exposure to sunlight, rain, and the intrusion of dust and sand.
