Lubricant manufacturers caution that the temperature range for use is a factor to consider when selecting grease. Grease has a certain temperature range, different grease temperature range is different.
The components of grease are base oil, thickener and additive. The maximum temperature of a grease is dropping point, but the dropping point is not equal to the maximum temperature. The allowable maximum temperature of a grease is usually 30℃ ~ 50℃ lower than the dropping point. Do not use it over temperature, especially if it lasts for a long time. Grease beyond the drop point, even if cooling down, performance has been damaged, should not be used.
The performance of grease at high temperature the direct harm of excessive temperature use of lubricating oil is to accelerate oxidation deterioration and generate acidic substances. It is worth noting that if local high temperature occurs at the lubrication point, oxidation deterioration of grease will also be caused and gradually spread out. Local high temperature may be caused by improper bearing installation, or by problems such as excessive or insufficient grease, wrong oil selection, vibration, or excessive load.
Grease oxidation color will become darker, the resulting acid will cause the thickener decomposition, the base oil from the thickener loss. Grease is the thickened lubricating oil. The thickener ACTS like a sponge to absorb the base oil and avoid excessive loss. If the base oil is lost, although the grease appears to exist on the surface, the lubrication capacity is almost non-existent. During the oxidation process, we can observe changes in the consistency of the grease, such as hardening or thinning and oil flow. Common lubricating grease is usually made of lithium based thickener and mineral base oil, which can meet the lubrication requirements of most ordinary working conditions. If there is a high temperature (above 60 degrees Celsius), grease will accelerate oxidation, when close to 90 degrees Celsius, common the oxidation of grease in the performance of the grease, these cases will need to use better grease, the use of synthetic oil and high-grade general thickener, such as compound lithium base, polyurea thickener and complex calcium sulfonate type. This type of grease performs better than ordinary greases at both ordinary and high temperatures.
Within the range of use, the temperature characteristics of greases are also different. As mentioned above, grease is lubricated mainly by base oil. If the base oil has good viscosity and temperature characteristics (high viscosity index), the viscosity will be relatively stable during the temperature change. The classification of base oils is specified by API. There are currently five classifications. It is necessary for users to know the base oil composition of grease when purchasing.
Although the main components of grease are base oil and thickener, base oil and thickener are not affected by temperature to the same degree. In general, base oil is more affected by temperature change, while the consistency of thickener changes slowly until it reaches the drop point. Therefore, it is necessary to understand the performance of base oil when choosing grease.