How to test the low temperature performance of lubricating oil?

January 08, 2024

How to test the low temperature performance of lubricating oil?

Main body

The low temperature performance index of lubricating oil is a set of very important parameters in the technical index system of lubricating oil, which determines the actual performance of lubricating oil in low temperature environment. Usually, pour point test, freezing point test, cloud point test and freezing point test are carried out in the experiment to evaluate the performance indexes such as freezing point, pour point, cloud point, freezing point and low temperature dynamic viscosity.

Application of low temperature performance test of lubricating oil

Application of pour point and freezing point test

(1) The pour point and condensing point of lubricating oil are expressed in ° C. Are used to measure the low temperature fluidity of the conventional indicators, under normal circumstances, the pour point of the same oil is slightly higher than the freezing point of about 3 ° C, the past commonly used freezing point, now the international common pour point; Almost all lubricating oil technical indicators have a pour point (or freezing point), which is one of the required items of the factory batch of lubricating oil manufacturers.

(2) The pour point (or freezing point) is an important reference index of the ambient temperature of the lubricating oil, and the pour point (or freezing point) is high, and the low temperature fluidity of the oil is poor. When choosing lubricating oil, it is usually necessary to consider the pour point (or freezing point) of lubricating oil, the pour point (or freezing point) of lubricating oil should be 5 to 20 degrees lower than the minimum temperature of the use environment, and different types of oil requirements are different.

(3) The storage, transportation and transportation of lubricating oil also consider the pour point (or freezing point) of lubricating oil, otherwise it cannot be carried out.

(4) Pour point (or freezing point) is one of the important indicators to measure the low temperature flow performance of lubricating oil, but they cannot fully reflect the low temperature performance of oil for internal combustion engine oil.

Application of cloud point test

(1) The turbidity point test of lubricating oil is an indicator of the microcrystalline content in lubricating oil. When the temperature drops to a certain temperature, the microcrystalline precipitation is the turbidity point, which is the lowest temperature indicator that can be effectively used for specific purposes. Too much wax crystallization will block the filter of the lubrication system.

(2) turbidity point is an important technical index of Class II and III Base Oil, and the turbidity point is higher than the limit value of the technical index.

(3) turbidity point is the main quality index of refrigerant oil, when the temperature is reduced to a certain value, the paraffin begins to precipitate in the refrigerant oil, the refrigerant oil begins to become cloudy, this temperature is the turbidity point; The refrigerant oil used in the refrigeration compressor, its turbidity point should be lower than the evaporation temperature of the refrigerant, the refrigerant oil dissolved in the refrigerant flow with the refrigerant to the refrigeration system, if there is paraffin precipitation in the oil, it will cause system blockage.

Low temperature performance of lubricating oil In addition to pour point, turbidity point, different types of lubricating oil products, low temperature performance focus is different.

For the low temperature performance of internal combustion engine oil, it is necessary to consider the apparent viscosity (CCS) core boundary pumping viscosity: (cold start simulation experiment (CCS) to determine. CCS simulates the cold start condition of the cylinder liner and piston of the engine, and has a good correlation with the cold start of the engine. Therefore, the apparent viscosity can be used as a viscosity index to predict whether the engine can start smoothly under low temperature conditions. Apparent viscosity is a measure of the internal friction force of multigrade oil measured at low temperature and high shear rate. Under the same low temperature condition, the smaller the viscosity value measured, the better the cold starting performance of the oil.

The boundary pumping viscosity is the maximum viscosity at which the oil is continuously and fully supplied to the engine oil pump inlet at a certain temperature. The shear stress required when the lubricating oil starts to flow is called the yield stress, the maximum yield stress that can make the lubricating oil flow to the filter inlet is called the critical yield stress, and the temperature at which the lubricating oil reaches the critical yield stress or critical viscosity in the engine oil specification is called the boundary pumping temperature, above which the oil pump can continuously and smoothly transport the lubricating oil to the lubrication system.

For Gear Oil, it is also necessary to consider the low temperature dynamic viscosity, which represents the indicator of the low temperature maneuverability of the oil. Excessive viscosity will cause the gear shift lever of the vehicle transmission to manipulate and weigh, and speed change is difficult.

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