【Q&A Question 140】2016.09.07
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【Q&A Question 140】September 7, 2016: Why must the lubricating oil temperature be no lower than 25 degrees Celsius before starting the cyclic hydrogen compressor, and no lower than 30 degrees Celsius during speed-up? The answer key will be available after responding; scoring is based on answering the key points. The viscosity of turbine oil is greatly affected by temperature; when the oil temperature is too low, its viscosity increases, leading to uneven distribution of the oil, increased friction losses, and even bearing wear. Therefore, the oil temperature must not be lower than 25 degrees Celsius at startup. As the speed increases, frictional losses rise as well, which demands higher standards for the lubricating oil; hence, the oil temperature needs to be even higher, not falling below 30 degrees Celsius.
Centrifugal compressors operate at relatively high speeds, and there are specific requirements regarding the temperature of the lubricating oil before startup. In particular, the dynamic viscosity of the lubricating oil must be above 25 degrees Celsius as one of the conditions for starting the machine. This is especially true in winter; if the temperature of the lubricating oil is too low before startup or during the acceleration process, it can result in an overly thick oil film between the shaft and the bearings, which impairs the lubrication of the shaft and prevents the shaft temperature from dropping appropriately. This can even lead to excessive vibration
The oil temperature is too low, resulting in no lubrication effect
Different oil film stabilities are required under different conditions, and the viscosity of lubricating oil varies at different temperatures.
Ensure the fluidity of the lubricating oil, prevent poor film formation by the lubricant, and avoid damage to the rotating components of the press
The temperature is too low, resulting in poor lubrication; a proper oil film cannot be formed, and cooling is also not achieved. Before starting the machine, its temperature is low; after startup, the temperature rises over time to prevent the lubricating oil temperature from increasing too rapidly.
At low oil temperatures, the viscosity is high, which increases frictional losses; these losses increase as the speed rises, so a higher oil temperature is required
If the lubricant temperature is too low, its viscosity is too high, resulting in poor flowability, which hinders the lubrication of rotating components.
Answer: The viscosity of turbine oil is greatly affected by temperature. If the oil temperature is too low, the viscosity of the oil increases, which leads to uneven distribution of the oil, increased friction losses, and even bearing wear. Therefore, the oil temperature at startup is specified to be no lower than 25°C. At startup, friction loss increases as the speed rises. Therefore, the requirement for lubricating oil is not to be lower than 30°C.
Because the lubricant temperature is below 25 degrees Celsius, its viscosity is too high, resulting in poor lubrication.