SKF Bearing Lubricant Viscosity Parameters Application Notes

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Viscosity is a critical property of lubricants, especially for SKF bearings. It refers to the internal resistance of a fluid when it flows, and plays a vital role in preventing wear between moving parts. The viscosity of lubricating oil typically decreases as temperature increases. This characteristic is essential for ensuring proper lubrication and protection of mechanical components under varying operating conditions. Viscosity is one of the most important technical indicators of SKF bearing lubricants. However, the viscosity should not be too high, as excessive viscosity can lead to increased friction and energy loss. Most SKF bearing lubricants are classified based on their viscosity, which serves as the primary basis for selecting the right oil for different equipment. There are two main types of viscosity measurements: absolute (dynamic) and relative viscosity. Absolute viscosity includes dynamic and kinematic viscosity, while relative viscosity includes measures like Engler, Saybolt, and Redwood viscosities. In China, the commonly used methods for measuring viscosity are kinematic and dynamic viscosity. The standard method for determining kinematic viscosity is GB/T 265, which involves measuring the time it takes for a specific volume of liquid to flow through a calibrated glass capillary under gravity. The product of the capillary constant and the time gives the kinematic viscosity at that temperature. In foreign standards, ASTM D445 (USA), DIN 51562 (Germany), and JIS K2283 (Japan) are widely used for determining kinematic viscosity. For certain oil products like hydraulic fluids and gear oils, low-temperature viscosity is often measured using a Brookfield viscometer, with standards such as GB/T 11145 in China, ASTM D2983 in the US, and DIN 51398 in Germany. Using oil with excessively high viscosity can cause unnecessary wear on machinery. In practice, choosing an oil with the appropriate viscosity ensures smooth operation and reliability. For low-speed, high-load applications, a higher viscosity oil is recommended to maintain sufficient oil film thickness. Conversely, for high-speed, low-load situations, lower viscosity oil is preferable to ensure easier starting and reduced operational torque. If the engine oil has too high a viscosity, it may result in sluggish performance, high oil pressure, and poor circulation. This can prevent the oil from reaching all the necessary areas quickly, leading to potential damage under continuous operation. Additionally, if the oil filter has limited cleaning capacity, it may struggle to remove metal particles, carbon deposits, and dust effectively. High-viscosity oil can also increase friction between machine components, leading to greater energy consumption and reduced engine efficiency. Furthermore, slow oil circulation reduces cooling effectiveness, increasing the risk of overheating. Therefore, it's important to choose oil with the right viscosity to ensure proper lubrication across all operating temperatures. It’s a common misconception that higher viscosity is always better. In fact, under the condition of adequate lubrication, it's better to use oil with lower viscosity whenever possible. If the engine has larger clearances, a slightly thicker oil may be suitable. Always consider the operating environment and temperature when selecting the right lubricant.

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