Viscosity: A Key Performance Index of Lubricating Oil

Viscosity is a major performance index of lubricating oil. Different refrigerants have different requirements for viscosity. For example, R12 is miscible with lubricating oil, which will reduce the oil’s viscosity. Therefore, lubricating oil with higher viscosity should be selected.

Neither too high nor too low viscosity is suitable for compressors. Excessively high viscosity will increase friction power and heat generation, enlarge starting torque, and reduce machine efficiency. If viscosity is too low, the required oil film cannot be formed, accelerating wear on bearings and other components. Thus, viscosity must be moderate.

The viscosity of lubricating oil changes greatly with temperature. For instance, when the temperature rises from 50°C to 100°C, the viscosity of mineral oil drops to 1/3 to 1/6 of its original value. For this reason, lubricating oil with small viscosity variation over temperature should be used.