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Basic knowledge of bearings that you don't know

Basic knowledge of bearings that you don't know


The bearing has high working reliability and is easy to use and maintain. And what are the components of the bearing?

1. Outer ring - installed in the bearing seat hole, generally does not rotate

2. Inner ring—installed on the journal and rotates with the shaft

3. Rolling element - the core component of the bearing

4. Cage - evenly space the rolling elements to avoid friction

Spherical roller bearing structure: The bearing is generally composed of an inner ring, an outer ring, rolling elements and a cage. The inner ring is installed on the journal (called the shaft ring in the thrust bearing), and the fit is tight; the outer ring is installed in the bearing hole of the machine base or parts, and the fit is usually loose. There are raceways on the inner and outer rings, and when the inner and outer rings rotate relative to each other, the rolling elements will roll along the raceways. The function of the cage is to evenly space the rolling elements. In order to meet certain application requirements, some bearings can have no inner ring or outer ring, or have structures such as dustproof and sealing rings.

Monitoring of bearing working conditions and material performance requirements

1. Morphological characteristics of abrasive grains under normal conditions

During the running-in period and normal operation period of the bearing, the size of the abrasive fragments produced is generally 0.01-0.015mm, and some metal powder is mixed therein. The amount of abrasive debris produced by the new bearing during the running-in period is more than that during the normal operation period, and the amount of abrasive debris and metal powder will be significantly reduced after entering the normal operation period. Abrasive fragments appear thin and short under the microscope, with irregular cross-sections.

2. Morphological characteristics of faulty wear abrasive particles

The main failure mode of spherical roller bearings is fatigue pitting. The size of abrasive fragments formed by rolling fatigue and spalling is generally 0.025-0.05mm. Sometimes there are larger fragments mixed with some metal powder. Ball bearing debris generally takes the form of roughly circular, radially separated rose petals; raceway debris takes the form of roughly circular surface fractures; roller bearing roller debris It is usually in the form of a curled rectangle with a length equal to 2 to 3 times the width; the abrasive fragments of the raceway are generally in the form of an irregular rectangle.

Three major conditions for bearing storage

The bearing is a precision bearing with a special structure. It also requires special care when storing it. Only in a suitable environment can the accuracy and quality of the bearing be maintained.

1. Bearings should be stored in a clean and dry environment, and the temperature and humidity should be controlled during transportation and storage. The temperature and humidity should be within an acceptable fixed range and should be more than 30cm away from the ground.

2. Some bearings have a certain shelf life. For example, for bearings with dust covers and oil seals, when stored for a period of time, the starting torque of the bearings will be greater than that of new bearings. At the same time, the lubricating performance of the grease will be destroyed after long-term storage, so the bearings should be checked regularly. maintenance.

3. To ensure the normal and reliable operation of the bearing, sufficient lubrication must be applied to prevent direct metal contact between the rolling elements, raceways and cages, resulting in wear and corrosion of the bearing surface. Therefore, in various applications, the selection of the appropriate lubricant and lubrication method is extremely important, and at the same time, correct maintenance is also required.

The actual choice of lubricant is mainly based on the operating conditions, namely: temperature range and speed as well as ambient influences. If reliable lubrication can be guaranteed, when the amount of lubricant used in the bearing is the smallest, its operating temperature will increase, but at the same time it plays other functions, such as sealing or heat dissipation, the amount will increase. Therefore, when installing the bearing, generally fill the remaining space of the self-aligning roller bearing with grease, and only control 1/3-1/2 of the remaining space of the bearing box. Too much is easy to generate high temperature.

Four stages of bearing fault development

Check the disassembled bearings during the regular maintenance of the equipment, the operation inspection and the replacement of peripheral parts, so as to judge whether it can be used again or whether it is good or bad.

In the initial stage, the noise is normal and the temperature is normal, which can be measured by ultrasound, vibration peak energy, and acoustic emission. The bearing outer ring is defective, the total vibration is relatively small, there is no discrete bearing fault frequency peak, and the remaining life is greater than 10%.

In the second stage, the noise is slightly increased, the temperature is normal, ultrasonic, acoustic emission, vibration peak energy has a large increase, the outer ring of the bearing is defective, and the total vibration is slightly increased (total vibration acceleration and vibration velocity) logarithm The frequency of bearing failure can be clearly seen on the scale spectrum, which is rarely seen on the linear scale spectrum. The noise level is significantly improved, and the remaining life is 5%.

The third stage, noise can be heard, temperature rises slightly, very high ultrasound, acoustic emission, vibration peak energy, bearing outer ring is faulty, total vibration acceleration and vibration velocity have a large increase, online linear scale From the frequency spectrum, it is clearly seen that the bearing fault frequency and its harmonics and sidebands, the noise level of the vibration spectrum are significantly improved, and the remaining life is less than 1%.

In the fourth stage, the intensity of noise changes, the temperature rises significantly, ultrasound, acoustic emission, and vibration peak energy increase rapidly, and then gradually decrease, and the outer ring of the bearing is in a fault state before damage, total vibration velocity and total vibration displacement Significantly increased, the total amount of vibration acceleration is reduced, the vibration peak of the lower spherical roller bearing fault frequency is dominant, the noise level in the vibration spectrum is very high, and the remaining life is less than 0.2%.

Only when we, as industrial people, have a more accurate understanding of bearing-related knowledge and use and store bearings in a scientific way can we prolong the service life of bearings and reduce the production cost of enterprises.

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