Methods and measures to improve bearing fatigue life

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Bearings are key machine parts that bear load and transmit motion. The challenges brought about by the increasing power density of modern equipment manufacturing industry have put forward higher requirements on the bearing capacity and reliability of bearings. Today, the editor will come to talk with you about methods and measures to improve bearing fatigue life.

Bearings in specific applications will fail prematurely, and their service life only accounts for 5%-10% of the calculated rated life. Many early failure bearings have a typical feature-a large-area subsurface crack network with “white etching morphology”, that is, white etching cracks.

There are many factors affecting white etching cracks, including raw materials, bearing design, lubrication, stress, surface and many other aspects. Among them, the bearing steel as a raw material, its composition design, purity, carbides, internal pores and other improper control will cause white corrosion cracks and cause early failure of the bearing. In order to obtain a high and stable fatigue life, the following aspects of the bearing steel production process must be done:

Slewing bearing

1. According to the application environment and characteristics of the bearing, select and design suitable bearing steel varieties, establish chemical composition internal control standards, and focus on the control of residual and harmful element content.

2. The oxygen content of the bearing steel, non-metallic inclusions and other purity indicators are improved through measures such as the control of the oxygen content of the steel in the primary furnace, the control of the amount of slag, the control of the slag composition, the control of the refining and pouring process, and so on.

3. According to different carbide quality requirements, choose different smelting processes such as vacuum degassing, electroslag, and self-consumption to obtain the corresponding level of carbide level. At the same time, we will do a good job in the process of temperature injection speed control, high temperature diffusion and other aspects of process optimization, to further improve the size and distribution of carbide particles, and reduce the risk of bearing fatigue life reduction caused by residual stress caused by microstructure changes.

4. For the rolling elements, the control of the microscopic pores in the bearing steel is even more important because there is no longer any thermal deformation treatment in the bearing manufacturing process. In the production process, it is necessary to focus on the control of processing methods, processing ratios, heating systems, etc.

5. Establish a complete bearing steel inspection system. On the one hand, it is necessary to formulate detailed laboratory sample preparation inspection plans, make full use of laboratory testing capabilities, objectively evaluate the physical quality level of each heat, and do a good job of high-frequency water immersion The promotion and application of new methods such as flaw detection and maximum extreme value detection; on the other hand, make full use of on-site surface and internal automatic flaw detection equipment to prevent the outflow of defective steel. Through the implementation of the above measures, the product quality level and quality stability are improved, thereby reducing the bearing white corrosion crack defects caused by raw materials.

Bearing manufacturing is a systematic engineering, and every link and step is very important. Therefore, in the design and production of bearing steel components, bearing manufacturing, heat treatment, processing and assembly, etc., qualified bearing products must be produced in strict accordance with the requirements of the standard.

Why the slewing bearing is not installed smoothly or even cannot rotate?

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Sometimes the technical indicators were normal when the rotation performance was tested in the factory, but the newly installed slewing bearing and slewing ring showed inflexible rotation. In addition, why the slewing bearing is not installed smoothly or even cannot rotate?

Reasons for the unsmooth installation of the slewing bearing

1, mounting hole. The threaded hole of the mounting hole is not standardized, the thread is not completely, and the thread is defective, which causes the bolt to be unable to be screwed in.

2. The center diameter and chord length of the mounting hole are out of tolerance too much, such as 3-5mm, causing the bolt to fail to perforate.

3, the positioning hole and the step size are out of tolerance and cannot be matched.

4. The bearing after heavy load has a dead center or ellipse in rotation, causing it to fail to operate normally.

5. The bearing is not in the installation direction of the installation design drawing, resulting in the opposite direction of the taper pin, which has potential safety hazards.

6. Interference of installation parts, such as tooth tip interference, there will be teeth gnawing phenomenon, and individual parts conflict with each other.

7. The negative clearance design is unreasonable, resulting in oblique force, unbalanced load and clearance after installation.

8. The equipment structure design is unreasonable, causing the debugging to not be carried out normally.

The slewing bearing may be difficult to rotate or unable to rotate

1. Idling of newly purchased products is not flexible

Please check the production date of the slewing bearing. If it takes a long time (such as more than half a year) and the climate is cold, it is possible that the salt mist and other temperament in the raceway will double the rotation resistance, which will make the slewing ring not work properly (cold areas, more prominent in winter) ) Elimination method: If it can run without other abnormalities, it can be used normally.

2, the operation after installation is not flexible

It may be that the surface of the main machine device and the surface of the slewing ring are not properly matched, resulting in that the axial clearance of the slewing ring behind the device cannot compensate for the deformation of the slewing ring. The slewing ring is in a state of negative clearance, and the rolling elements are difficult to run in the raceway (sometimes with abnormalities). Noise) or poor meshing of the large and small gears; or foreign matter stuck in the large and small gears. Elimination method: re-process the plane of the main machine device to make the device plane meet the requirements; re-adjust the gear meshing backlash according to the requirements, especially pay attention to the gear jump position; check to ensure that there is no foreign matter in the meshing position of the large and small gears; exchange a slewing bearing with a larger gap .

3, the operation is not flexible during use

The sealing strip is damaged, causing foreign matter to enter the raceway (such as poor working conditions, dust immersed in the raceway, etc.), and the isolation block is deformed and difficult to operate; there are hard objects or other conditions at the meshing of the large and small gears, such as broken teeth.

The above is an analysis of the annoying reasons why the slewing bearing is not installed smoothly or even cannot rotate. I hope everyone will be helpful after reading it. When testing the rotation performance of the new bearing, it can rotate lightly, but at this time, it does not represent a reasonable index. The contact point, contact angle, and relative position of the connecting point of the channel are in line, and whether the two circles are close to the perfect circle. The two circles are completely or close to positive balance. In layman’s terms, just like the two rails of a train, they should be close to theoretical parallel, high and low parallel, so that the train will be stable, high-speed, orderly and safe. Therefore, to test the rotation performance, the loading experiment is a very important basis and effective means.

Technical Difficulties of Fault Diagnosis for Ladle Turret slewing bearing

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The ladle turntable is one of the important key equipment of the continuous casting machine. Once these key equipment fails, it may cause the entire production line to stop production, disrupt the normal production rhythm, and seriously affect the normal production and economic benefits of the enterprise. In the structure of the ladle turret, the ladle slewing bearing is the key component of the stable and efficient work of the ladle turret. In order to ensure the normal operation of the supporting bearings, the factory will require on-site workers to conduct high-density inspections. However, due to the harsh on-site environment, on-site inspections are difficult, which not only increases the labor intensity of the workers, but may also threaten their lives.

The fault diagnosis of ladle turret slewing bearing has the following technical difficulties:

1. The speed of the equipment is low, and the impact energy caused by bearing damage is very low; and the equipment is greatly interfered by external forces, and the noise can easily cover the bearing fault characteristics; therefore, the conventional bearing detection methods cannot effectively find the bearing damage characteristics, such as time domain analysis, frequency Domain analysis, envelope demodulation spectrum, etc.
2. The bearing is subjected to complex forces, and it bears axial force, radial force and overturning moment at the same time;
3. During the operation of the equipment, personnel are not allowed to enter due to the harsh on-site environment; and a single offline monitoring cannot effectively evaluate the mechanical state of the equipment, and the amount of data is insufficient to support the judgment of the mechanical state of the equipment;
4. It is not only necessary to judge whether the equipment is faulty, but also to predict the residual life of the bearing, guide the direction of maintenance and repair, give play to the value of the equipment, and gain time for the preparation of spare parts and spare parts;
5. In order to ensure the accuracy of vibration analysis, diagnostic personnel need to have a very high level of professionalism and rich field experience. Even if the above conditions are met, the accuracy of diagnostic analysis cannot be guaranteed.

At this stage, there is no effective detection method for the bearing, and after the hidden trouble of failure, the fault signal characteristics are not obvious, it is difficult to find the bearing failure, and there is a high probability of causing secondary damage to the equipment, resulting in increased maintenance costs, and additional costs for the enterprise economic burden.

Therefore, the condition monitoring and fault diagnosis of the ladle turret slewing bearing not only guarantees the normal production needs of metallurgical enterprises in the continuous casting process, but also promotes the reform of the equipment management system, and will surely bring huge benefits. Condition monitoring and fault diagnosis are needed to reduce maintenance workload and maintenance time.

What is the impact of the amount of grease injected on the bearing?

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We all know that grease has good adhesion, wear resistance, temperature resistance, rust resistance and lubricity, can improve high temperature oxidation resistance, delay aging, can dissolve carbon deposits, and prevent metal wear debris and oil stains. Poly, to improve the wear resistance, pressure resistance and corrosion resistance of machinery, it will be commonly used in bearing products. For sealed bearings, appropriate grease has been filled during production; for open bearings, a sealing device is also installed in the host to prevent grease leakage. Today, the editor will talk to you about the impact of the amount of bearing grease on the bearing?

The amount of grease injected into the bearing will have a certain impact on its operation. If the amount of grease is too small, it is easy to cause lack of grease or dry friction, which will affect the life span. Too much grease will cause the bearing temperature to rise. A large amount of grease leakage not only pollutes the environment, but also causes waste. It can be seen that the amount of grease injected into the bearing should be as small as possible on the premise of ensuring sufficient lubrication of the bearing.

After understanding the movement process of grease in the bearing, it will naturally come to a conclusion: the grease in the bearing should not be too much. Too much grease is not only a waste, but also harmful. The higher the speed of the bearing, the greater the harm.

The more grease is filled, the greater the friction torque. With the same filling amount, the friction torque of the sealed bearing is greater than that of the open bearing. After the grease filling amount is equivalent to 60% of the internal space volume of the bearing, the friction torque no longer increases significantly. This is because most of the grease in the open bearing has been squeezed out, and the grease in the sealed bearing has also leaked out.

With the increase of the grease filling, the temperature rise of the bearing increases linearly. The temperature rise of the sealed bearing is higher than that of the open bearing at the same filling amount.

Slewing ring

It is generally believed that the grease filling amount of sealed rolling bearings should not exceed about 50% of the internal space. Tests have shown that 20% to 30% of ball bearings is appropriate.

Correct lubrication and regular maintenance can avoid bearing damage caused by lubrication problems. To ensure reasonable lubrication:

• Follow the instructions set by the device manufacturer for each device;

• When adding grease, it should be filled between the rolling parts of the bearing and the housing (or retainer) to ensure that sufficient grease enters and the surface of the key raceway is fully lubricated;

• Pay attention to when the bearing should be greased (Re-lubrication);

• Monitor the indicating instruments of the equipment, so as to find signs of problems as early as possible, such as temperature fluctuations and/or abnormal high temperatures;

• Pay attention to equipment noise or abnormal vibration;

• Observe lubricating oil leakage;

• Regularly sample the lubricating oil and check for contamination.

When injecting grease in addition, the site should be clean and clean, and the tools used should be cleaned with gasoline. After the grease is filled, other parts should be assembled as soon as possible to prevent the grease entering the bearing from entraining dust and sundries, especially sand and iron filings.

What is the slewing ring gear module?

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Slewing bearing is one of the important parts of many modern machinery and equipment. It is called “joint of machine”. Many people are familiar with various parameters of slewing bearing, including clearance, inner and outer diameter, friction coefficient, etc. Many of my friends don’t know the module of supporting gear, so let’s follow the editor today to understand it.

 

  1. what is the slewing ring gear module

 

The length of the arc (gear)/straight line (rack) occupied by a single gear tooth in the indexing circle (gear)/or line (rack), its length is π * m, and m is the modulus.

 

What does the module of the slewing ring represent: The module of the slewing ring represents the product of the tooth pitch and the number of teeth of the slewing ring gear, which is the circumference of the index circle. The gear modulus of the slewing ring determines the size of the tooth. The gear modulus is a basic parameter for the calculation of the gear size. The symbol is “m”. Gear cutters can be standardized, so that the standard modulus of gears can be standardized for mass production. Facilitate the replacement of later accessories. In the same way, “modulus” refers to the ratio of the pitch t between the tooth profiles of two adjacent gear teeth on the same side and the circumference ratio π (m=t/π), in millimeters.

 

If the number of teeth of the slewing ring gear is constant, the larger the gear modulus, the larger the radial dimension of the gear. The teeth of a gear with a large modulus are thick, and for two gears with the same number of teeth, the outer circle of the gear with a large modulus is larger. Therefore, the modulus of the gear in a watch is very small, and the modulus of the flywheel and transmission gear on the mechanical punching machine is large. The modulus of the two meshing gears must be the same. Modulus is the basic parameter of gear design, and it is used in many calculations of gear design.

 

 

  1. Reasonable selection of gear modulus

 

When designing a gear, one of the important parameters is this modulus. The gnawing of the gear will produce gnawing pulsation. The main reason is that it has a great relationship with the elastic deformation of the gear teeth. It is a basic part of the gear design. Parameter-gear modulus, if it is a relatively large modulus (that is, a gear with a relatively large size), it will also have a relatively large load-bearing capacity. The modulus parameter is inversely proportional to the degree of bending of the gear teeth. The increase of the modulus means that the rigidity of the gear teeth is improved, so that the elastic deformation of the gear teeth will not be great when the gnawing transmission is carried out, which greatly reduces the impact force formed by the gear teeth, thereby achieving The purpose is always greatly reduced. Therefore, from this point of view, the modulus should be increased appropriately, but the error generated when machining gears is also related to the modulus. If the modulus is increased, the tooth profile and pitch will also be increased. At this time, the error of gnawing noise will also increase accordingly, so the choice of modulus should be determined according to the specific situation.

 

In the case of keeping the modulus unchanged, the diameter of the gear is proportional to the number of teeth, so the change of the number of teeth will also change the bending amount and elastic stiffness of the gear teeth: the strength of the noise generated by the sound source is not only related to the energy of the vibration source It is related to the size of the radiation area. If the radiation area is increased, the radiation power will also increase. Increasing the diameter of the gear will increase the noise radiation area, which will greatly affect the gear. Effective noise control. Therefore, in the relevant design, within the permissible range of ensuring the strength of the gear, the number of teeth and the small modulus should be used as much as possible, and the reasonable selection of materials and heat treatment methods can be combined to promote the improvement of the strength of the gear teeth, thereby Reduce the gear tooth diameter to achieve the purpose of reducing gear noise.

 

The above is the relevant introduction about the slewing ring gear module. In the slewing ring selection process, the first two sets of data listed in the national standard parameters of the slewing ring module should be selected first, which is more important for the adaptation of the bearing and the replacement of accessories. Convenient, but non-standard gears with customized bearing module requirements for bearings used in special machines are not within the above constraints.