【Weekly Topic】Topics related to bearing usage

The topic is quite broad; this is just a tentative suggestion. It seems that for high-speed and light-load applications, rolling bearings are lubricated with oil or grease, while for low-speed and heavy-load applications, sliding bearings are lubricated with oil

I) Types and characteristics of sliding bearings 1. Sliding bearings are classified according to the loads they bear as follows: (1) Centrifugal sliding bearings (radial sliding bearings); they mainly bear radial loads; (2) Thrust sliding bearings, which mainly bear axial loads. 2. Sliding bearings are suitable for low-speed, high-precision, heavy-load applications as well as those where a split design is required. It is also often used in low-speed and impactful applications. 3. Centrifugal sliding bearings: (1) Integral type, split type. The split type generally consists of a bearing cover, a bearing housing, bearing shells, and coupling bolts, etc. (2) Bearing shells are key components in bearings. The bearing bush material should possess properties such as a low friction coefficient, good thermal conductivity, a low coefficient of thermal expansion, wear resistance, corrosion resistance, strong resistance to adhesion, sufficient mechanical strength, and ductility. (3) Requirements for bearing bush materials: bearing alloys (Babbitt alloy), bronze, bearing materials with special properties, etc. 4. Thrust sliding bearings (for understanding) (1) Thrust sliding bearings come in fixed and tilting types. (2) The thrust surface of the thrust sliding bearing can utilize the end face of the shaft, or a shoulder can be created in the middle of the shaft or a thrust disc can be installed. (II) Types and characteristics of rolling bearings 1. Classification of rolling bearings Based on the shape of the rolling elements, they are divided into ball bearings and roller bearings. 2. Characteristics of rolling bearings (1) Advantages: Compared with sliding bearings, rolling bearings have advantages such as low frictional resistance, quick start-up, high efficiency, easy lubrication, and ease of replacement. (2) Disadvantages: Poor impact resistance, noise at high speeds, and a shorter service life compared to sliding bearings with liquid lubrication.

Rolling bearings are used for high-speed, light-load applications, while sliding bearings are used for low-speed, heavy-load applications

Based on their friction properties, bearings can be divided into rolling (friction) bearings and sliding (friction) bearings. It is obvious that rolling bearings have less frictional resistance, start more quickly, and operate with higher efficiency – these are the advantages of rolling bearings. Compared to sliding bearings, rolling bearings have larger radial dimensions, poorer vibration damping capabilities, a shorter lifespan at high speeds, and generate more noise. That is its drawback. The shape of the rolling elements is not limited to balls only; there are also cylindrical rollers, tapered rollers, needle rollers, as well as the needle rollers shown on the right side of the image. Based on the type of rolling element, rolling bearings are divided into ball bearings and roller bearings. Under identical other conditions, roller bearings operate smoothly and can handle high speeds, but their load-bearing capacity is relatively low ； Roller bearings do not operate as smoothly as ball bearings, but they have a higher load-bearing capacity and greater resistance to impacts. The most basic structure of a sliding bearing consists of a bearing shell and a shaft journal (is it obvious that this has a simple structure?) ). There is a fundamental difference between sliding friction and rolling friction (one involves point contact while the other involves surface contact), which in turn leads to fundamental advantages and disadvantages. Advantages: 1. High load-bearing capacity ； (Reason for large contact area) 2. Simple structure, easy to manufacture, process, and disassemble ； 3. Good impact resistance and excellent vibration absorption properties, ensuring smooth operation and high rotational accuracy. Disadvantages: 1. Complex maintenance requirements, with high demands on lubrication conditions ； 2. Boundary-lubricated bearings experience significant friction and wear. (This is also a disadvantage of a large contact area). In summary, sliding bearings are used in applications that involve high speeds, high precision, heavy loads, as well as in machines subject to low-speed impacts. Besides that, rolling bearings are widely used in most applications.

**It can be found in the standards; I can’t remember which standard it is. It is also specified in API610.

Rolling bearings are precision mechanical components that convert the sliding friction between a rotating shaft and its housing into rolling friction, thereby reducing friction losses. Sliding bearing: A bearing that operates under sliding friction. Difference: The forms of friction are different; one is rolling, and the other is sliding. Although the friction of rolling is lower than that of sliding, sliding bearings are also used in places where it is inconvenient to install rolling bearings, such as the engine crankshaft.

I don’t know where the one on the 5th floor came from How is the distinction made between high-speed and low-speed applications? In my case, high-speed applications usually use sliding bearings, such as those in turbines and compressors, while low-speed pumps, motors, and similar devices generally use rolling bearings.

I checked clause 5.10.1.1 of API 610, version 2004: for centrifugal pumps that meet the requirements of this standard, rolling bearings are to be used when all of the following three conditions are satisfied: a) the speed factor nXdm for the rolling bearings must not be greater than 500,000, where n is the shaft speed in RPM and dm is the average bearing diameter in mm； For example, if the rotational speed is 3000, sliding bearings should be used when the average diameter of the bearing is greater than 170 mm. b. The expected service life of the rolling bearing shall not exceed its basic rated service life. Note: This requires reference to ISO 281; I don’t have it handy, so I’m not sure what this means. c. The energy intensity of the bearing, which is the product of its rotational speed (RPM) and power (kW), when this value is less than 4,000,000. If the rotational speed is 3000, then if the power is greater than 1300 kW, sliding bearings are required. Reading from the script, haha~~~~

After reading everyone’s replies, I’ve received a lot of feedback; thank you!