When purchasing grease, the operating temperature range is an important factor to consider. Grease has a certain operating temperature range, and different greases have different applicable temperature ranges. The components of lubricating grease are Base Oil, thickener and additives, and the operating temperature of lubricating grease is also related to these three components. For a certain lubricating grease, the manufacturer will give a maximum operating temperature and a minimum operating temperature. The user should remember that when selecting, the user needs to consider the maximum and minimum temperature of the lubricated part (usually the minimum temperature at startup). 1. Minimum operating temperature of grease The hardness of the grease will increase when the temperature drops, affecting the normal delivery, causing the grease to not reach the lubrication point sufficiently, and the lack of lubrication when the machine is cold started. The minimum operating temperature of the grease must be higher than the minimum ambient temperature during cold start. At lower temperatures (such as close to -30°C), synthetic greases, such as those using PAO as the base oil, should be used. The maximum service temperature of grease: one of the indicators of grease is the dropping point, but the dropping point is not equal to the maximum service temperature. The maximum allowable use temperature of the grease is generally 30°C to 50°C lower than the dropping point. Do not use it at excessive temperature, especially is a high temperature that lasts for a period of time. Even if the grease exceeds the dropping point, the performance has been destroyed even if it cools down, and it is not suitable for use.
2. Performance of grease at high temperature The direct harm of over-temperature use of lubricating oil is to accelerate oxidative deterioration and generate acidic substances. It is worth noting that if local high temperature occurs at the lubrication point, it will also cause oxidative deterioration of grease and gradually spread. Local high temperature may be caused by poor bearing installation, too much or insufficient grease, wrong oil selection, vibration, and excessive load. The temperature characteristics of lubricating grease are also different within the range of use of grease. As mentioned above, grease is mainly lubricated by base oil. If the base oil has good viscosity-temperature characteristics (high viscosity index), then the temperature changes During the process, the viscosity is relatively stable. The classification of base oil is stipulated by API. There are currently five classifications. It is necessary for users to understand the base oil composition of lubricating grease when purchasing. Although the main components of lubricating grease are base oil and thickener, the degree of influence of temperature on base oil and thickener is not the same. Generally speaking, base oil is relatively more affected by temperature changes. Consistency, which changes slowly until the dropping point is reached. Therefore, when purchasing grease, it is necessary to understand the performance of the base oil.
3. Low temperature performance of grease At low temperature, the grease will become thicker, that is, the hardness will increase, and the low temperature performance of the grease is also directly related to the base oil. Just like cooking oil, it is liquid at room temperature, but at low temperature it will reduce its fluidity or even stop flowing. When it drops to a certain temperature, the lubricating oil stops flowing. This temperature is called the pour point. Lubricating oil with a low pour point can be used at a lower temperature. The pour point of mineral oil is generally -20 ~ -30 ℃, but the pour point is generally required to be lower than the operating temperature. Low temperature torque is one of the important indicators of low temperature performance of grease. At low temperature, grease thickens and increases hardness, which will block the bearing. The low temperature torque is the degree to which the grease retards the rotation of the rolling bearing at low temperature (below -20°C). The low temperature torque of the grease is expressed by the average value of the starting torque and the torque after running for a period of time. The smaller the starting torque value of the grease measured at low temperature, the smaller the starting power consumption; on the contrary, if the low temperature starting torque of a certain grease is large. The bearing may be stuck, and it is not suitable for use at low temperature. Therefore, when purchasing grease, the operating temperature (maximum and minimum temperature) of the lubricating point must be taken into account, and the allowable operating temperature range of the grease should include the operating temperature range of the grease. The indicators related to temperature include dropping point, maximum service temperature, minimum service temperature, pour point of base oil, low temperature torque, viscosity index of base oil and so on.
