The difference between oil lubrication and grease lubrication in bearings.

Aug 27, 2024

As the key component of mechanical equipment, bearings' selection of lubrication methods is directly related to the equipment's operating efficiency, service life and maintenance costs. In the field of bearing lubrication, oil lubrication and grease lubrication are the two most common lubrication methods, each with unique characteristics and scope of application.

1. Physical state and properties of lubricants.

First of all, from the perspective of the physical state of the lubricant, oil lubrication uses liquid lubricating oil, while grease lubrication uses semi-solid grease. Lubricating oil has good fluidity and can quickly penetrate all parts of the bearing to form a uniform oil film. In contrast, grease is in the form of a paste, which has low fluidity but strong adhesion and can form a stable lubricating layer on the bearing surface.

There are also significant differences in properties between oils and greases. Lubricating oil has strong fluidity and slightly high volatility. It can quickly take away a large amount of heat generated during the operation of the bearing and play a cooling role. Due to its semi-solid characteristics, grease has low fluidity, is not easy to leak, and can form a strong oil film, which is beneficial to the sealing use of bearings. In addition, the adhesive properties of the grease enable it to provide adequate lubrication when the rolling bearing is started and stopped, reducing starting friction.

2. Lubrication effect and scope of application.

In terms of lubrication effect, oil lubrication and grease lubrication have their advantages. Oil lubrication, due to its good fluidity, can form sufficient oil film thickness when the bearing operates at high speed, effectively reducing friction and wear. At the same time, lubricating oil can also take away the heat generated during the operation of the bearing and have a significant cooling and cooling effect. It makes oil lubrication more suitable for high-speed, high-temperature, and high-precision applications, such as automotive wheel bearings, high-speed motors, etc.

Grease lubrication performs better at low or medium speeds. Its adhesion ensures that the bearings are fully lubricated when starting and stopping, reducing starting friction. In addition, grease also has certain sealing properties, which can effectively prevent external impurities and moisture from intruding into the interior of the bearing, thereby protecting the bearing from corrosion and contamination. It makes grease lubrication more suitable for situations with low speed, heavy load, and high sealing requirements, such as engineering machinery, metallurgical equipment, etc.

3. Complexity and maintenance of lubrication system.

In terms of the complexity of the lubrication system, the oil lubrication system usually requires the addition of accessories such as oil pumps and oil pipes and requires regular maintenance work such as replacing the lubricating oil and cleaning the oil circuit. It makes the operation and use of the oil lubrication system relatively cumbersome and increases the maintenance burden of rolling bearings. The grease lubrication system has a relatively simple structure and only needs to be replenished or replaced with grease regularly, making it relatively easy to maintain.

However, it is worth noting that overfilling with grease may cause the bearing temperature to rise and affect the lubrication effect. Therefore, during the maintenance process of grease lubrication, the filling amount of grease needs to be strictly controlled to ensure that it can provide a sufficient lubrication effect without overheating the bearing due to excess.

4. Adhesion, temperature range and pressure resistance.

Grease lubrication offers significant advantages in terms of adhesion. When the friction part is in a stationary state, the grease lubrication can maintain its original shape and will not automatically lose due to gravity, nor will it slip on vertical surfaces and drip out from gaps. Oil lubrication cannot guarantee its original shape and will be lost directly. It makes grease lubrication more advantageous in situations where lubrication needs to be maintained for a long time.

In terms of temperature range, grease lubrication generally has a wider operating temperature range than oil lubrication. For example, general-purpose lithium grease can be used in the minus 20 to 120 degrees Celsius range, while oil lubrication is used in a much narrower temperature range. It makes grease lubrication more suitable under extreme temperature conditions.

In terms of pressure resistance, the adsorption capacity of grease lubrication on metal surfaces is much greater than that of lubricating oil, and it can form a relatively strong oil film and withstand a relatively high workload. The reason is due to the large amount of polar substances contained in grease lubrication. It makes grease lubrication more advantageous under heavy and high-load conditions.

5. Comprehensive comparison and selection.

To sum up, oil lubrication and grease lubrication each have their unique advantages and scope of application in bearing lubrication. Oil lubrication is more suitable for high-speed, high-temperature, and high-precision applications because of its good fluidity and significant cooling effect, while grease lubrication is more suitable for low-speed, heavy-duty applications because of its strong adhesion, good sealing, and easy maintenance. Occasions with high load-bearing and sealing requirements.

When selecting a lubrication method, comprehensive consideration should be made based on factors such as the specific use conditions, maintenance requirements, and cost considerations of the bearing. Correct lubrication methods can not only improve the service life and efficiency of bearings but also reduce equipment failure rates and maintenance costs. Therefore, when selecting the bearing lubrication method, scientific and reasonable decisions must be made based on the actual situation.

In short, oil lubrication and grease lubrication are the two main methods of bearing lubrication, each with its characteristics and scope of application. In practical applications, the appropriate lubrication method should be selected depending on specific working conditions and needs to ensure the stable rotation of the bearing and the long-term stability of the equipment.