In many scenarios of industrial production and mechanical equipment operation, bearings are key components, and the stability of their performance is directly related to the normal operation of the entire system. However, when the cold weather strikes, a series of complex and difficult problems will arise, which will have a rather adverse impact on the normal operation of the bearing.
Material Shrinkage
Bearings are usually made of metal (e.g. steel), which has the property of thermal expansion and contraction. The components of bearing, such as the inner and outer rings, rolling elements, will shrink In cold environments. For a standard-sized bearing, the inner and outer diameters may shrink by a few microns when the temperature drops from 20°C to -20°C. This shrinkage may cause the internal clearance of the bearing to become smaller. If the clearance is too small, the friction between the rolling body and the inner and outer rings will increase during operation, which will affect the rotational flexibility of the bearing, increase resistance, and the starting torque of the equipment.
Hardness Change
Cold weather will make the hardness of the bearing material change to a certain extent. Generally, metals become brittle at low temperatures, and their hardness rises relatively. In the case of bearing steel, although its toughness is good, it still be reduced in extremely cold environments. When the bearing is subjected to shock loads, this change in hardness may cause the bearing to be more prone to cracking or even fracture. For example, in outdoor mining equipment bearings, if subjected to the impact of ore falling in cold weather, it is more likely to be damaged than at normal temperature.
Grease Performance Change
Grease is one of the key factors to ensure the functional operation of bearings. In cold weather, the viscosity of grease will increase. Regular grease may become thicker and less fluid. This makes it difficult to form a good oil film between the rolling body and raceways of the bearing. In a motor bearing, the grease can be well filled in all the gaps inside at normal temperature. As the temperature decreases, the grease becomes sticky, and the rolling body cannot bring the grease uniformly to all the contact parts during rolling, which increases the friction and wear, and its rotational speed may fluctuate, which damages the surface quality and dimensional accuracy of the machined parts. In serious cases, it may lead to overheating or even seizing of the bearing.
Shortened Service Life
A combination of these factors, increased friction, reduced impact toughness and poor lubrication of bearings in cold weather can accelerate bearing wear. Under normal circumstances, bearings may be able to run thousands of hours, but in cold environments, due to increased wear, may run a few hundred hours will fail, such as rolling body wear, raceway pitting, etc., which greatly shortens the service life of bearings.
In the face of these adverse effects of cold weather on bearings, how should we alleviate them?
Choose Right Grease and Control the Amount
In cold weather, grease with good low temperature performance should be used. This type of grease can maintain good fluidity at low temperatures, such as products containing special additives (e.g., polyurethane-based greases). They are not too viscous and can effectively reduce the friction of bearings during start-up and operation. Generally speaking, the pour point (the lowest temperature at which a cooled specimen of oil can flow under specified test conditions) of low-temperature greases is very low, and some can be as low as -40°C or even lower, thus ensuring good lubrication of bearings even in cold weather.
The right amount of grease fill is also important for bearing operation in cold weather. Too little grease will result in insufficient lubrication, while excessively filling will cause the bearing to produce too much agitation resistance during operation. In cold weather, overfilling should be avoided due to the increased viscosity of the grease. Normally, for small and medium-sized bearings, the grease filling amount is about 1/3 – 1/2 of the internal space of the bearing. This ensures lubrication and reduces the resistance caused by excess grease.
Replace Grease Regularly and Strengthen the Seal
Even if proper grease is used, with the passage of time and the operation of the bearing, the grease will be contaminated, oxidized and so on. These problems may be exacerbated in cold weather. It is recommended that shorten the grease replacement cycle according to the operation of the equipment and environmental conditions. For example, in normal environment, the grease may be replaced once every six months, and under cold conditions, it can be shortened to every 3 – 4 months to ensure that the performance of the grease is always in good condition.
Good sealing can prevent cold air, moisture and impurities into the bearing. In cold weather, you can use high-performance seals, such as double lip seal or labyrinth seal. Double-lip seals have inner and outer lips to better block foreign objects and moisture outside. Labyrinth seals have a complex channel structure that makes it more difficult for outside substances to enter the bearing. This reduces damage to bearing internal structure caused by water icing expansion, as well as preventing the entry of impurities resulting in increased bearing wear.
The surface of the bearing can be coated with a protective coating, such as antirust paint or low-temperature protective coating. Antirust paint can prevent bearing from rusting in cold or wet conditions, while cryogenic protective coatings can mitigate the effects of temperature changes on the bearing material. Such coatings act as a guardian to protect the bearing surface from direct erosion in low temperature environments and also help to minimize changes in material properties due to temperature changes.
Equipment Warm-up
Warming up the entire unit before starting it is an effective method. For some small equipment, it can be placed in “Conservatory” for a period of time to let the bearing temperature to rise. For large equipment, such as large cranes bearing, can be used to add heat tape or hot fan or other equipment to preheat the bearing part. Preheating temperature can generally be controlled at about 10 – 20°C, which can make the bearing parts expansion and return to the normal clearance, while reducing the viscosity of the grease, which is conducive to the smooth start of the equipment.
For some bearings that can be disassembled, oil bath preheating is a good method. Put the bearings into the lubricating oil heated to the appropriate temperature, so that the bearings are evenly heated. This method not only expands the bearing material, but also allows the lubricant to fully enter the internal clearance of the bearing. Preheated oil temperature is generally about 30 – 40°C, the time can be controlled according to the size of the bearing and material and other factors in about 1 – 2 hours, which can effectively improve the bearing in cold weather starting performance.
Although the cold brings problems to the bearing, it can build a strong defense line by choosing the right grease, sealing and preheating protection. This not only ensures the reliable operation of bearings at low temperature, extends their life, but also promotes the stable development of the industry, so that TP can calmly walk towards a new industrial journey.
TP, Wheel bearing and auto parts manufacturer since 1999. technical specialist for Automotive Aftermarket! Get technical solution Now!
Post time: Dec-18-2024
