Installation of rolling mill bearings

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Installation of rolling mill bearings

The service life of rolling mill bearings is not only related to the quality of the bearing, but also closely related to its installation and use. To this end, attention should be paid to the technical requirements for bearing installation, and the relevant operating procedures should be followed.
1. Preparation before installation
(1) Before installation, carefully check the mating surfaces of the roll neck, bearing box, bearing ring and bearing box cover, etc., and check whether the size, shape and position accuracy and the mating male cover meet the technical requirements of the design. .
(2) The edges and burrs of the surface that matches the bearing, the roll neck, the bearing box hole, and the oil hole must be removed, cleaned and coated with lubricating oil.
2. Installation of four-row cylindrical roller bearings
(1) Install the labyrinth ring (waterproof cover)
The fit of the labyrinth ring and the roll neck is generally a tighter dynamic fit, and a copper rod must be used to tap lightly during installation. The two ends of the labyrinth ring must be parallel and closely fit the shaft shoulder and the inner ring of the bearing.
(2) Install the inner ring
The inner ring of the four-row cylindrical roller bearing has an interference fit with the roll neck. The inner ring should be heated to 90-100°C before installation. Do not exceed 120°C to prevent incomplete shrinkage of the inner ring after cooling. The heating method can be heating by oil tank or induction heating, and heating with open flame is absolutely prohibited.

Bearing selection method

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The market requirements for various mechanical devices and instruments using rolling bearings have become increasingly stringent, and the conditions and performance required for bearings have become increasingly diversified. In order to select the most suitable bearing from a large number of structures and sizes, it is necessary to study from various angles.

When selecting a bearing, generally, the bearing structure is roughly determined by considering the ease of arrangement, installation, and disassembly of the bearing as a shaft system, the allowable space and size of the bearing, and the marketability of the bearing. Secondly, while comparing and studying the design life of various machinery using the bearing and the various endurance limits of the bearing, the bearing size is determined. When selecting a bearing, it is often biased to consider only the fatigue life of the bearing. The grease life, wear and noise caused by the aging of the grease also need to be fully studied. Furthermore, according to different applications, it is necessary to select specially designed bearings for accuracy, clearance, cage structure, grease, etc. requirements.

However, there is no certain order and rules for selecting bearings. The priority should be the conditions, performance, and the most relevant matters required for the bearing, which is especially practical.

Maintenance method of backing bearing

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The eighteen-high rolling mill bearings adopt double-row needle roller bearings. When the copper foil is rolled at a high speed of 600m/min, the bearing speed reaches 3550r/min. The working conditions of the bearing are extremely bad, and improper assembly is prone to burns and scratches on the bearing surface. Needle roller fracture, wear, needle roller cage fracture and other problems.

The eighteen-high rolling mill has a total of 8 backing bearing rolls, each with 9 bearings, and a total of 72 bearings. The bearings have no inner ring and are assembled on 8 surface-hardened mandrels.
(1) Bearings should be tested for meat thickness before installation. The bearings should be tested and classified one by one. According to the requirements of the machine, the thickness deviation of the backing bearing on the same shaft should be less than 0.005mm, and they should be divided into 8 groups, especially during use for a period of time. Later, the needle rollers and outer ring of the backing bearing will have a certain degree of wear. Therefore, it is necessary to check the thickness of the bearing regularly.
(2) After the mandrel of the backing bearing is used for a period of time, the bearing surface will also have some wear. The bearing surface of the mandrel should be changed during assembly, which can prolong the use time of the mandrel.
(3) After a long-term use of the backing bearing in the middle part, the load it bears is different from that of the bearings on both sides, and the needle roller wear will be more serious. You can exchange positions with the bearings on both sides regularly to extend the use of the bearings. life.
(4) Regularly clean the oil injection hole on the mandrel to avoid clogging of debris and ensure that the bearing can have sufficient lubricating oil supply. Generally, compressed air can be used to blow out the oil hole at one end of the mandrel, and observe the oil outlet hole. Air pressure and air volume, if necessary, use a probe to clean up.
(5) After the bearing is installed, the side support roller can be used to carry out the pressing test, and the side support roller can be rotated, and more than half of the backing bearing can follow.

Analysis and Prevention of Burning Loss of Rolling Mill Bearings

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Rolling mill bearings occupies a relatively important position in my country’s rolling mills. Rolling mill bearings often cause mechanical burnout in daily production. How to reduce the number of rolling mill bearings burning, improve the level of rolling mill equipment, and increase the operating rate of rolling mills, especially for rolling mill bearings The cause of the burn was analyzed.

 

The reasons leading to the failure of rolling mill bearings can be roughly divided into two aspects:
1. Internal reasons, such as bearing quality.
2. External reasons, such as installation, maintenance, and maintenance. In order to find out the reasons, better targeted measures are taken, and it is very important to analyze the causes of the burn.

 

Analysis of the causes of burning
2.1, assembly problems

2.1.1. Since the manufacturing precision of the rolling mill is not very high, when the service life is long, the various accessories of the rolling mill will deform to different degrees, and the bearing seat will have a large difference in coaxiality, which makes the bearings at both ends of the rolling mill uneven. Insufficient lubrication is prone to generate high frictional heat, which may cause local pitting or seizure of the bearing. Combining the actual situation of the rolling mill, use cleaning agent before installation, clean the bearing, dry it with compressed air, and then check the roller, cage, and raceway. Use tools to rotate the cylindrical roller bearing. The bearing can be smooth and linear. Rotate to continue using. If the rollers and raceways have dents, pitting, etc., replace them.
2.1.2. The size, geometry and accuracy of the dynamic and static labyrinths are also issues that cannot be ignored that affect the burning of the rolling mill bearings, because the dynamic labyrinth follows the rotation of the roll. If the dynamic and static labyrinths are deformed, the waterproof ring may be affected by a certain local A point of intermittent friction during the rotation process will generate stress concentration locally. When the friction is frequent, a large amount of heat will be generated and transferred to the inside of the rolling mill bearing. When the heat is too high, the grease will not dilute to the outside of the seal ring. Loss, causing the bearing to burn or friction and smoke. Before assembling, check the integrity of the dynamic and static maze, remove the attached foreign matter and impurities, and compare the goodness of the fit to avoid wear caused by processing errors, and replace the ones that cannot be repaired in time.

2.2, insufficient lubrication
As long as there is movement, there must be friction. The most effective measure to reduce friction is to add lubricating materials. Rolling bearings have both fluid friction and sliding friction in motion. Cylindrical rollers are very hard rotating bodies. During operation, the inner and outer rings of the bearing rotate and slide. Therefore, the friction coefficient is very small. A good lubricating film can ensure good lubrication.
However, bearing burnt caused by lubrication problems often occurs during work, mainly due to the problem of oil volume and the method of refueling. At present, the rolling mill grease we use is a compound calcium sulfonate 3# grease with strong adsorption capacity and can form a high-strength oil film. In terms of oil volume, it is required that all the inner rings of the bearing must be coated with grease at the same time during assembly to ensure that the bearing has sufficient lubrication conditions. For a rolling mill that is used for a long time, the lubrication performance will gradually decrease during use and the wear will gradually increase. Regular lubrication should be used, and the lubricating gun of the pressure oil pump should be used for forced lubrication to ensure normal lubrication conditions.

2.3. Foreign body impact
Foreign matter is the so-called foreign impurity, mainly in several aspects:
1. Other impurities brought from grease;
2. Foreign matter enters the bearing during disassembly and assembly;
3. Partial damage caused by the impact of accessories during the assembly process;
4. Water and dust at work. One of the most common is the introduction of grease and foreign matter in the process of disassembly and assembly.
When the diameter of the foreign body is less than the working gap of the bearing, it can be stirred by grease to cause friction and strain on the working surface of the ball, which will cause the bearing to wear and fail in advance; when the foreign body is larger than the working gap, the foreign body will be crushed and a part of it will be embedded in the working surface, causing jam Dead, the fragments not embedded in the working surface will be involved in the grease, aggravate the wear surface of the bearing, cause the temperature of the working surface to rise sharply, and quickly wear the oil film, causing the bearing to burn when running in the dry grinding state. Therefore, strictly controlling the entry of foreign matter into the bearing is an important aspect of our work.
The bearing seal ring is also an important device to prevent water and foreign matter from entering, and it also serves to prevent the leakage of lubricating oil. Because the structure of the vertical rolling mill determines that the roll is rotating, water and impurities can easily pass through the gap between the sets. With the rotation of the roll, it enters the inside of the bearing, which will corrode the lubricating grease and reduce the lubrication effect. This is also the noteworthy part of our work. The sealing facility of the roll head cannot be easily removed.

2.4, overload damage
Under overload conditions, rolling bearings generally produce abnormal wear and fatigue damage. Combined with actual production, there are many reasons for bearing damage caused by cyclic load overload. Take the production of channel steel as an example to illustrate. The braking force is much larger than that of round steel, and the probability of bearing burning is also greater. Due to the requirements of the rolling process, some racks have a large amount of reduction, which makes the bearing work under a larger load when it is impacted, resulting in local rolling elements Fatigue cracks are initiated, causing fatigue wear and burning of the bearing.

2.5, the influence of external temperature
Rolling mill bearings are more sensitive to external factors in the long-term high temperature, high speed and frequent impact. Compound calcium sulfonate base 3# grease is suitable for the lubrication of high-load working mechanical bearings. The dropping point is greater than 300℃, the oil separation is about 2%, and the high temperature reversibility does not work. The 1/4 cone penetration difference is small . When the roll is working, due to various reasons, the cooling water cannot provide a good cooling effect, so the temperature of the roll itself is too high and will be transferred to the inside of the bearing. Once the temperature is ≥300 degrees, the grease will slowly become liquid. A large amount of lubricating oil will leak to the outside of the bearing, and the lubrication conditions will drop sharply, causing the temperature of the bearing to rise step by step, and finally causing the bearing to burn. Therefore, in the work, the management of the cooling water of the rolling mill is also an indispensable link to reduce the burning loss of the bearing.

 

Bearing Manufacturing Technology-Heat Treatment

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To meet the bearing performance requirements, heat treatment for the purpose of quenching and hardening is an indispensable process. The energy consumed in the heat treatment process accounts for about 25% of the total energy consumption in the bearing manufacturing process. Therefore, from the perspective of energy saving and environmental protection, the heat treatment in the bearing manufacturing process is analyzed. The main countermeasures include: high efficiency of the heat treatment process; small deformation heat treatment technology.

Bearing heat treatment method
There are many kinds of bearing heat treatment methods for the purpose of quenching and hardening. In most cases, it can be roughly divided into overall quenching, carburizing and quenching, high-frequency quenching, carbonitriding and so on.

Integral quenching is the most common bearing heat treatment process, and most of the materials use high carbon chromium bearing steel (GCr15). It is heated to about 840°C in a heat treatment furnace, and the carbide formed by spheroidizing annealing is appropriately and uniformly dissolved in the matrix, and then quenched and cooled, and then tempered at low temperature. Through undissolved carbides and carbides precipitated by tempering, a uniform precipitation structure is obtained, which can be used for bearings that require wear resistance.

Carburizing and quenching is to heat low-carbon alloy steel at about 930 ℃ in a heat treatment furnace, manage the carburizing gas in the furnace, infiltrate and diffuse the carbon from the surface to the inside, and perform quenching heat treatment. Due to the gradient of carbon concentration, after quenching The surface is hardened, because the internal hardness is lower than the surface hardness, it is used for bearings that require impact resistance.

High-frequency quenching is a heat treatment using induction heating. It is mainly used for medium-carbon steel and is used for bearings for automobile wheels with complex shapes. Only necessary parts are hardened.

Carbonitriding involves adding about 5% of ammonia to the carburizing gas to precipitate nitrides near the surface layer. Taking into account the difference in solubility of carbon and nitrogen in austenite, it is usually processed at 750~850 ℃ below the carburizing temperature, which is especially effective for extending the life of bearings used in an environment where foreign matter is mixed. .

 

Analysis on the Causes of the Damage of Rolling Mill Bearings

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The bearings used in the rolls of short-stress rolling mills are mostly rolling bearings
Rolling mill bearing burning refers to the phenomenon that the sliding heat generated by each part of the bearing increases sharply during the operation of the bearing, and plastic deformation causes the parts to stick, and the phenomenon of seizure caused by excessive wear. Each bearing has a pre-calculated service life. The life of the rolling bearing used in the rolling mill is to run under certain working conditions. The total number of revolutions of the rolling elements when fatigue corrosion points appear on the raceway or at a certain speed The total number of hours worked.
The failure of the bearing of the roll is damaged, causing the auxiliary bearing of the rolling mill to not be used normally. There are three failure modes of rolling bearings.


① Fatigue pitting
Using a period of time, under the action of cyclic contact stress between the bearing raceways and rolling elements, fatigue pitting damage will appear on the surfaces of the inner and outer raceways or rolling elements.
② Plastic deformation
Under the action of a relatively large static load or impact load, the local stress at the contact point between the rolling element and the raceway may exceed the yield limit of the material, resulting in uneven plastic deformation at the contact point, resulting in pits, increasing rotation resistance and The phenomenon of reduced rotation accuracy causes noise when the bearing is running.
③ Wear is mostly caused by poor lubrication of bearings or improper working environment. If the rotation speed is too high, it will cause damage to the bonding.

The Main Performance of Deep Groove Bearing

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The raceways of the inner and outer rings of deep groove ball bearings are all arc-shaped grooves, and the radius of the groove is slightly larger than the radius of the ball. It is mainly used to bear radial load, but also can bear certain axial load. When the radial clearance of the deep groove ball bearing increases, the angular contact ball bearing can withstand larger axial loads and is suitable for high-speed rotation. Deep groove ball bearings can still work normally when the housing hole and shaft are relatively inclined 8’～16′, but their service life will be affected. Thrust ball bearings can be used to bear pure axial load when the speed is high.

Deep groove ball bearings generally use two halves of riveted steel plate stamping cage, called wave cage, but large size or telling bearings use solid cage, this kind of cage is guided by the ball like the stamping cage, high speed and deep The cage of groove ball bearings is usually guided by the inner ring or outer ring ribs.

Compared with other types of bearings of the same size, deep groove ball bearings have low friction coefficient, low noise and high limit speed, and high accuracy. However, they are not resistant to impact and are not suitable for heavy loads.

Deep groove ball bearings are simple in structure and easy to use. They have the largest production batch and the widest application range. They are widely used in automobiles, tractors, machine tools, motors, water pumps, agricultural machinery, textile machinery and other fields. Its output accounts for 60% to 70% of the total output of bearings, which is the highest output, the most commonly used and the cheapest type of bearing in China.

Deep Groove Ball Bearings

The Main Structure of Deep Groove Ball

(1) Basic deep groove ball bearing 60,000 type
This structure can be used for parts that have no special requirements for installation, sealing, and coordination.
(2) Deep groove ball bearing 60000N type with brake groove on the outer ring
The deep groove ball bearing with brake and groove change is installed on the outer diameter of the outer ring. After the stop ring is installed, the axial positioning of the bearing in the bearing housing hole can be simplified, and the axial size of the component can be reduced. Small axial load.
The bearing code of this type of bearing with a stop ring is 60000NR.
(3) Deep groove ball bearings 60000-Z and 60000-2Z with dust cover
The deep groove ball bearing with dust cover is protected by steel dust cover to prevent grease leakage and foreign matter intrusion. The deep groove ball bearing with dust cover is divided into a dust cover on one side and a dust cover on both sides. There is a radial gap between the dust cover and the rib of the inner ring. It is a non-contact seal, so the friction torque is small. Compared with the bearing with sealing ring, its dustproof performance is poor, but the limit speed is higher.
The bearing has a dust cover on one side and a stop groove on the outer ring on the other side, its code is 60000-ZN.
(4) Deep groove ball bearing with sealing ring
Since sealed bearings can simplify the sealing structure of the support and improve the performance of the bearing, this type of product has developed rapidly and the demand is increasing, and it has accounted for about 90% of the output of deep groove ball bearings. There are also various types of bearing seals, including contact seals, non-contact seals and light contact seals to meet different needs. But the main function is to prevent the leakage of grease and the intrusion of foreign objects.

Causes of Bearing Noise, Detection and Treatment

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If the bearing is in a good state of continuous rotation, it will emit a low whining or buzzing sound. If there is a sharp hiss, squeak and other irregular sounds, it often indicates that the bearing is in a poor continuous rotation condition. The sharp squeaking noise may be caused by improper lubrication. Inappropriate bearing clearance can also cause metallic noise.

The dents on the bearing outer ring track will cause vibration and cause a smooth and crisp sound.

If there is intermittent noise, it means that the rolling parts may be damaged. This sound occurs when the damaged surface is rolled over, if there are contaminants in the bearing, it will often cause a hissing sound. Severe bearing damage will produce irregular and loud noises.

If it is caused by knocking scars during installation, noise will also be generated, and this noise will vary with the speed of the bearing.

Big metal noise
Reason 1: Abnormal load, countermeasures: correct the fit, study the bearing clearance, adjust and load, and correct the position of the housing shoulder.
Reason 2: Poor installation, countermeasures: machining accuracy of shaft and housing, improve installation accuracy and installation method.
Reason 3: Insufficient or unsuitable lubricant. Countermeasure: Replenish lubricant and select appropriate lubricant.
Reason 4: The rotating parts are in contact. Countermeasures: modify the contact part of the curved seal.

Regular noise
Reason 1: Indentation, corrosion or scars on the rolling surface caused by foreign matter. Countermeasures: Replace the bearing, clean the relevant parts, improve the sealing device, and use a clean lubricant.
Reason 2: (after steel carburization) surface deformation, countermeasure: replace the bearing, pay attention to its use.
Reason 3: the raceway surface is peeled off, countermeasure: replace the bearing.

Irregular noise
Reason 1: The clearance is too large. Countermeasures: Study the fit and bearing clearance, and modify the preload.
Reason 2: Foreign matter intrusion, countermeasures: study the replacement of bearings, clean relevant parts, improve the sealing device, and use clean lubricants.
Reason 3: Spherical surface injury, peeling, countermeasure: replace the bearing.

The Common Faults and Routine Maintenance of Rolling Mill Bearings

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1. Common faults and cause analysis
Rolling mill bearings may be damaged due to various reasons during operation, such as improper assembly, poor lubrication, intrusion of moisture and foreign matter, corrosion and overload, etc., may cause premature damage to the bearing. Even if the installation, lubrication and maintenance are normal, after a period of operation, the bearing will suffer fatigue peeling and wear and fail to work normally. In short, the reasons for the failure of rolling mill bearings are very complex, and the common failures and causes are now analyzed as follows.
1.1 Fatigue spalling
The inner and outer raceways and rolling element surfaces of rolling bearings bear both load and relative rolling. Due to the alternating load, cracks are formed at a certain depth below the surface (the maximum shear stress), and then they expand to the contact surface to cause the surface layer to spall pits. Finally, it develops to large flaking, this phenomenon is fatigue flaking. Fatigue spalling will increase shock load, vibration and noise during operation. Normally, fatigue spalling is often the main reason for the failure of rolling bearings.
1.2 Wear
Due to the intrusion of dust and foreign matter, the relative movement of raceways and rolling elements will cause surface wear. Poor lubrication will also aggravate wear. As a result of wear, the bearing clearance will increase, the surface roughness will increase, and the bearing operation accuracy will be reduced, as well as vibration. And the noise also increases accordingly. Therefore, to a certain extent, the amount of wear limits the life of the bearing.
1.3 Plastic deformation
When the bearing is subjected to excessive impact load or static load, or additional load caused by thermal deformation, or intrusion of foreign matter with high hardness, dents or scratches will be formed on the surface of the raceway. This will cause the bearing to produce severe vibration and noise during operation, and once there is an indentation, the impact load caused by the indentation will further cause the nearby surface to peel off.
2. Daily maintenance
2.1 Inspection of bearings during operation
In accordance with the maintenance procedures, the bearings are regularly listened to, observed and measured. Listening is to use a listening rod to face the axial end cover of the bearing and the radial housing of the bearing seat, and the other end to listen to whether the bearing is impacted or mechanically rubbed during operation. Observation is to observe the operating environment, installation location, vibration deviation, lubrication, etc., to see if there is any bad working condition. The measurement is to use a thermometer and a vibrometer to check the bearing seat regularly. Use these methods to periodically check the bearing to determine whether the bearing is in normal condition.
2.2 Inspection of the bearing at rest
Check the tightening of related parts to confirm whether the parts are in the correct position and whether there is any looseness or abnormality. In addition, the bearing lubrication is tested to detect whether there is foreign matter in the lubricating oil. When the diameter of the foreign matter is smaller than the minimum working clearance of the bearing, the foreign matter can be stirred with the lubricating oil through the clearance. Friction occurs on the working surface of the rolling element. When the diameter of the foreign body is larger than the working gap of the bearing, the foreign body is crushed or crushed into thin dust to adhere to the bearing surface or embedded in it. If the crushed foreign debris is not embedded in the working surface, but enters the lubricating oil, it will worsen the bearing wear. As a result, fatigue spalling of the bearing occurs. Causes the temperature of the working surface to rise. The lubricating oil then loses its effect. If the bearing fails, the foreign matter is crushed or embedded in the rolling elements, which quickly destroys the oil film, causing the bearing to be damaged by working and running in a dry friction state.
2.3 Inspection after disassembly of the bearing
After the roller is replaced, a cleaning agent can be used to clean the bearing, dry it with compressed air, and then inspect the roller, cage and raceway. If the rollers and raceways appear dents, pitting, etc., they should be replaced according to the specific conditions. At the same time, replace the necessary bearing seals to prevent poor seals from affecting the life of the bearings. If the bearing is not well sealed and the emulsion enters the bearing, it will cause water pollution to the lubricating oil or grease, resulting in a reduction in the fatigue strength of the bearing material and easy cracking. At the same time, the seal is not good, and the iron oxide scale during steel rolling enters the bearing to destroy the lubrication condition, causing abrasive wear on the surface of the bearing element.
2.4 Bearing installation
2.4.1 Press-in installation
Press-in installation generally uses a press, but also can use bolts and nuts. When it is necessary to use a hand hammer to install, it is necessary to pad the inner ring with a pad. This practice has repeatedly become the cause of damage to the bearing installation operation, so it is limited to the case of small interference and cannot be used for large or medium-sized bearings. For non-separable bearings such as deep groove ball bearings, the inner ring and outer ring need to be installed with an interference amount, so it is necessary to pad the work with the inner ring and the outer ring at the same time with a screw or oil pressure. The outer ring of self-aligning ball bearing is easy to tilt, even if it is not an interference fit, it is best to install it with a pad. For separable bearings such as cylindrical roller bearings and tapered roller bearings, the inner ring and outer ring can be installed on the shaft and housing respectively. When combining the installed inner ring and outer ring, the key is stability. Close the two firmly so that the center of the two does not deviate. Forcing it in will cause the raceway surface to jam.
2.4.2 Hot loading
Large bearings require a lot of force to press in, so it is difficult to press in. Therefore, the bearing is heated in oil to expand it, and then mounted on the shaft. This hot mounting method is widely used in the installation of large bearings. Using this method can make the bearing avoid unnecessary external force and complete the installation work in a short time. The heating temperature of the bearing is based on the size of the bearing and the required interference. Heat the bearing to about 100℃～120℃. In order to prevent the bearing from directly touching the bottom of the oil tank, it is best to consider placing the bearing on a metal mesh table, or hoisting the bearing, and heating the bearing to 20℃ higher than the required temperature～ 30°C, so that the inner ring does not become cold during operation and it is difficult to install. After installation, the bearing cools down and the width direction shrinks, so it must be tightened with a shaft nut or other appropriate method to prevent a gap between the inner ring and the bearing shoulder.
2.5 Inspection after the bearing is installed
After the bearing is installed, in order to check whether the installation is correct, it is necessary to perform a running check, which can be rotated by hand to confirm whether the rotation is smooth. The inspection items include improper operation caused by foreign objects, scars, and indentation, uneven rotation torque caused by poor installation, poor processing of the mounting seat, excessive torque caused by too small clearance, installation error, and seal friction Wait. If there is no abnormality, it can start to run. Check whether there is vibration, noise, whether the rotating parts are in contact, etc., and enter the power operation after confirming that there is no abnormality. The operation check starts from the no-load low speed, and slowly increases to the rated conditions for operation. The items to be checked during the test run are: whether there is any abnormal noise, bearing temperature shift, lubricant leakage and discoloration, etc. If an abnormality occurs during the trial operation, the operation should be stopped immediately, the mechanical equipment should be inspected, and the bearing should be removed for inspection if necessary.

How to ensure the safe operation of single-row ball slewing ring?

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Single-row ball slewing ring is one of the important parts of modern machinery and equipment, mainly composed of upper ring, lower ring and full ball. Its running speed is very low, and it is usually used in many mechanical products, for example, it is widely used in rotating equipment such as rotary conveyors, excavators, construction machinery, and small and medium-sized cranes. The safe operation of the single-row ball slewing bearing is very important, and it directly affects the working efficiency of the unloading equipment.