The raceway of the slewing bearing generally needs to be heat treated. In the heat treatment process, because the diameter of the raceway circle of the slewing bearing is relatively large, flame surface quenching is usually used. The method is to use acetylene to heat the surface of the workpiece to be hardened and then add water to cool it. , this process is completed continuously.

1. How is the slewing bearing soft belt produced?

During the production and processing of the slewing bearing, the raceway of the device generally needs to be heat treated. The usual processes are: forging → rough machining → quenching and tempering treatment → finishing → raceway surface flame surface quenching → raceway surface grinding and other processes . One of the raceway surfaces is flame quenched to form a soft band.
The so-called soft belt is the area that has not been heat treated. The formation of the soft band is necessary for the heat treatment process. In the heat treatment process of the slewing bearing, because the diameter of the raceway circle of the slewing bearing is relatively large, flame surface quenching is usually used. The method is to use acetylene to heat the surface of the workpiece to be hardened and then add water to cool it.

The heated flame spray gun and water gun are mounted together while making a circular motion along the circle of the workpiece. When the movement is close to 360 degrees, the heating and water spray are stopped immediately. That is, the circular areas of heating and water spray do not overlap. Cracks in the workpiece can occur if the circle areas where the heating and water spray occur overlap (heat treatment at an angle greater than 360 degrees on the circle). The tangential width of the unheated area is typically 15 mm. This 15 mm area is called the soft belt in the slewing bearing, that is, the so-called soft belt is the area without heat treatment. The formation of the soft band is essential to the heat treatment process.
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Under normal circumstances, the steel character “S” is marked on the position where the soft belt exists in the workpiece to indicate the specific soft belt position. The installation position of the soft belt is essentially to improve the life of the bearing. From the perspective of the user and the manufacturer, it is still a reasonable position to install the upper and lower ring soft belts of the slewing bearing. Therefore, the manufacturer of the slewing bearing should accurately mark the position of the soft belt of the slewing bearing, and the manufacturer and installer should reasonably install the position of the soft belt of the slewing bearing as needed.

2. The installation position of the soft belt

Usually the upper loop flexible belt of the slewing device is installed at a position perpendicular to the projection line of the pitching rotation plane. For example, the upper loop flexible belt of the slewing device of a ship loader or stacker-reclaimer should be installed at a position perpendicular to the center line of the cantilever and cut through the center of rotation , that is, standing at a 90-degree position facing the left or right side of the cantilever on the center of rotation. In the usual mechanical design, the soft belt does not have the stress state of the support roller of the slewing bearing device at this position.

The installation position of the lower ring soft belt of the slewing device should be determined according to the center of gravity of the equipment and the range of the slewing angle. If the rotation angle is 100 degrees left and right, and the center of gravity of the upper part of the rotation is in the front, it is recommended to install the lower ring soft belt at the rear, that is, at a position of 180 degrees. If the change position of the center of gravity of the upper part of the rotation is the same in the front and rear positions, the angular position of the lower ring soft belt can be installed arbitrarily.
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Because of the inevitability of the soft belt on the slewing bearing device, it is required that the user who uses and selects the slewing bearing device should install the position of the soft belt reasonably, so as to improve the service life of the bearing. The general principle is to try to install the soft belt in a position where the soft belt is under less pressure during the load change.

There are many classifications of slewing bearings, each type has different characteristics, and the scenarios used are also different. You may not be very clear about the selection type. Generally, the selection type should be considered: slewing accuracy, bearing capacity, working temperature, In terms of running speed, etc., let’s take a look at the specific method with the slewing bearing manufacturer~

Classification of slewing bearings

1. Three-row combined roller slewing bearing

The three-row roller slewing bearing has the upper and lower and radial raceways of the three races separated, so that the load of each row of rollers can be accurately determined. It can bear various loads at the same time, has a firm structure, and has large shaft and radial dimensions. It is suitable for heavy machinery requiring large diameters.

2. Double row angular contact ball slewing bearing

The double-row ball slewing bearing has three races, and the steel balls and spacers can be directly discharged into the upper and lower raceways. According to the stress conditions, two rows of steel balls with different diameters are arranged. The axial and radial dimensions of the double-row ball slewing bearing are relatively large, and the structure is firm, especially suitable for machinery that requires a medium or larger diameter.

3. Single row cross roller slewing bearing

The single-row cross-roller slewing bearing is composed of two races, with compact structure, high manufacturing precision, light weight, small assembly clearance, and can bear axial force, large radial force and tipping moment at the same time.

4. Single row four-point contact ball slewing bearing

The single-row four-point contact ball bearing slewing bearing is composed of two races, with compact structure, light weight, four-point contact between the steel ball and the arc raceway, and can bear axial force, radial force and tipping moment at the same time.

Factors to consider when choosing a slewing ring bearing type

1. Carrying capacity

The bearing capacity is one of the factors that determines the size of the bearing. In general, the four-point contact ball slewing bearing can withstand heavier radial loads, so it may be more suitable for the occasions where the heavier load and the size and direction of the load may change The four-point contact is a slewing bearing.

2. Rotation accuracy

If the bearing positioning capability is required to be high, the crossed roller slewing bearing can be selected.

3. Working temperature

In general, the operating temperature of the slewing ring bearing mainly depends on the sealing material, grease, isolation block, and the operating temperature range is -25 to +70 °C.

4. Running speed

The four-point contact ball slewing ring bearing has a high limit speed, and the friction force generated is smaller than that of the cylindrical roller slewing ring.

5. Sealing conditions

Qualified seals used in slewing bearings can provide good moisture and pollution protection, and ensure sufficient quality in the bearing, which can prolong the service life of the bearing, so the seal is very important for the performance of the slewing bearing.

6. Vibration

For vibration applications, both four-point contact ball slewing rings and crossed cylindrical roller slewing rings are suitable.

The above article describes the classification of slewing ring bearings in detail, and the factors that need to be considered when choosing the type. I hope it can help you. If you have other questions about slewing ring bearings, you can leave us a message~

The failure of the bearing raceway will directly lead to the overall failure of the slewing bearing. The life of the slewing bearing raceway is affected by its own quality and later maintenance. Therefore, the daily maintenance of the slewing bearing raceway is very important.

When we find that the raceway fails, there are mostly five manifestations: large bearing clearance, oil leakage from the bearing, stuck running of the bearing, abnormal noise from the bearing, iron powder or iron lumps in the slewing bearing raceway. The four forms of track failure will be briefly introduced to you, and at the same time, I will share with you some daily maintenance skills for the slewing bearing raceway.

Four forms of slewing bearing raceway failure

1. Surface peeling

The main reason for the surface peeling of the slewing bearing raceway is that the hardened layer is too thin and the hardness transition zone is too narrow. There are many reasons for contact fatigue failure, which may be excessive axial load, poor lubrication, poor alignment, excessive impact load during installation, etc., which can cause contact fatigue failure of bearings. Intermediate frequency equipment with lower frequencies should be used to deepen the hardened layer. At the same time, the quenched and tempered hardness should be appropriately increased to reduce the hardness gradient of the raceway section.

2. Corrosion pitting

The chemical or electrochemical reaction occurs between the metal surface and the environmental medium, and the surface damage caused by it is called corrosion failure. Corrosion is divided into three categories: chemical corrosion, electrical corrosion, and fretting corrosion, mainly manifested as the corrosion of the inner bearing surface of the bearing. The intrusion of corrosive medium, condensation of moisture in the air, sparks generated when the current passes, fretting and other factors can cause the corrosion failure of the slewing bearing raceway.

Pitting corrosion mainly occurs on the raceway treated with quenching and tempering. The reasons are low hardness and unreasonable design of raceway structure, causing sliding friction and contact fatigue stress, resulting in defects such as pitting and indentation.

3. Plastic deformation

Under the action of external force, the local plastic flow or overall deformation of the surface of the part, such as the deformation of the raceway or the distortion and warpage of the cage, etc., cause the failure of the slewing bearing to not work properly, which is called plastic deformation failure. This situation often occurs after a period of use. At this time, most of the high-hardness layer has been worn, and after the load and friction force suddenly increase, the metal inside and outside the raceway is squeezed into piles. Steel grades with high hardenability should be used instead.

4. Wear

The relative sliding friction between the surfaces leads to the continuous wear and tear of the metal on the working surface, resulting in failure. Wear will increase the fit clearance and change the shape of the raceway surface, and also affect the lubricating function of the lubricant, causing the bearing to lose its rotational accuracy or even fail to operate normally. Raceway wear is divided into normal wear and abnormal wear.

Normal wear and tear is the process of gradually increasing the gap in the whole life cycle to complete the task of the whole life cycle. Abnormal wear has manufacturing problems, standard parts problems, grease problems and post-maintenance problems.

The post-maintenance skills of the slewing bearing raceway

1. Slewing bearing raceway lubrication

(1) Selection of grease: For the slewing bearing, grease is equivalent to the relationship between fish and water. If the best quality product does not pay attention to the lubrication of the raceway, it is the state when the fish leaves.

The general grease used for slewing bearings used in general construction machinery is usually 2# or 3# lithium-based grease. It is recommended to use lithium molybdenum disulfide grease for heavy-duty products, and low-temperature lubricating grease is used in severe cold areas. Grease, in high temperature environment is high temperature grease, the grease used in wind power slewing bearing is usually NLGI1.5 to 2 grade lithium-based, complex lithium-based, calcium grease, the choice of different environmental greases are differentiated .

(2) Grease filling frequency: In dry and clean occasions, it is recommended to refill once every 500 hours of operation, and once every 250 hours of operation for construction machinery in outdoor environments, and once every 50 to 100 hours of operation in harsh environments. In some closed dust environments, continuous filling is recommended.

Some equipment is going to be stopped for a long time. It is recommended to fill up the grease when stopping the operation, and squeeze out the old grease. When re-operating, it is recommended to refill the grease again. At this time, only a small amount of lithium base grease is needed to be replenished. Newly purchased equipment is recommended to be filled with grease.

(3) Grease filling method: one is manual filling, and the other is automatic filling equipment on the equipment, which adopts automatic filling.

2. Maintenance of slewing bearing sealing ring

The sealing ring is the first wall of the slewing bearing, which can be used to prevent foreign objects such as sand outside the slewing bearing from entering the raceway, causing wear of the rolling elements and the raceway. If the sealing ring is damaged, the problem is the leakage of grease. And dust and dirt enter the raceway, resulting in the rapid wear and failure of the raceway.

In terms of the maintenance of the sealing ring, firstly, after the main engine is working in acid and alkali occasions, it should be cleaned in time; secondly, check whether the lower sealing ring is damaged or fall off each time oil is injected; thirdly, check whether the sealing ring is worn at least once every three months. Seriously, whether there is an oil leak.

If there are any of the above three phenomena, it is recommended to replace the sealing ring immediately. It is not recommended to replace the sealing ring personally. You should ask a technician to replace it, so as to ensure the service life of the sealing ring.

The failure manifestations and causes of the slewing bearing raceway have been introduced in detail above. We do a good job in the daily maintenance of the slewing bearing raceway in daily use, which can also prolong the service life of the bearing.

There are many factors that affect the life of the slewing bearing. Different working conditions, different materials, and different bearing types will affect the service life of the bearing. For this reason, the life is not a standardized number but depends on the materials, processes, and production levels during production. , as well as the use method during use, maintenance and lubrication conditions and other factors are comprehensively determined.

How long is the service life of the slewing bearing in general

According to the influence of the bearing material, assembly, tolerance fit, lubrication and other factors, the service life of the slewing bearing under normal conditions ranges from 10,000 to 192,000 hours. We generally say that the service life of bearings is also different for different types of bearings.

Like ordinary bearings, the service life of the bearing refers to the failure of use, such as pitting, spalling, etc., which cannot work normally. For spindle bearings, precision bearings, etc., which require high precision, when the running accuracy of the bearing fails to meet the requirements, it will fail, but it is far from the standard of failure of ordinary bearings. So this is also the reason for the different service life of the slewing bearing.

Factors affecting the service life of slewing bearings

1. Manufacturing factors

(1) Design: Whether the diameter, number, ring wall thickness, effective length of rolling contact, tightness, radian and size of the contact surface of the raceway of the bearing are compatible with the matching equipment.

(2) Material: Martensite in the quenched steel, impurities in the steel, chemical composition, gas, cracks, etc., during the bearing production process, the impact of the material on the quality of the bearing is a hard injury, which cannot be compensated by technology in the later stage.

(3) Manufacturing: In the process of producing slewing bearings, the hardness of bearing parts, bearing metallographic structure, surface burns, bumps and scratches, roughness, poor parts grouping, production accuracy, bearing clearance, cleanliness, residual magnetism and parts Residual stress on the working surface will affect the service life of the bearing, and the impact in the manufacturing process is similar to the congenital quality problem. The bearing with defects manufactured under the same working conditions has a shorter life than the standard and qualified bearing.

2. Use factors

(1) Selection: In terms of selection, such as bearing load, hardness, operating environment, etc., a good bearing design will first make the bearing reach the upper limit of theoretical life.

(2) Assembly: the installation accuracy of the bearing, the degree of fit between the bearing shaft and the seat hole, the selection of each part, size, shape and position accuracy, the selection of assembly tools, and the cleanliness of the installation. Whether impurities are mixed in, including the assembly position and assembly of each part Clearance, preload size, lubricant selection and filling amount, etc.

(3) Working environment: The working temperature and the cleanliness of the working environment will affect the service life of the bearing. If the bearing is used in a harsh environment or in a high temperature, high heat, low temperature and cold environment, it may affect the performance and performance of the bearing. The service life has a certain impact.

(4) Load: Each bearing has a rated load during production, and there is a range for the load that the bearing bears during operation, that is, the stress condition. If it exceeds this range for long-term overload operation, it may cause serious damage to the performance of the bearing. influence, which in turn affects the service life.

(5) Lubrication: Bearing lubrication is a key factor to reduce the friction between the various parts of the bearing and reduce the occurrence of damage and deformation. For this reason, whether the bearing lubrication is appropriate, timely and reasonable will have a certain impact on the service life of the bearing.

The above is my answer about how long the service life of slewing bearings is generally. In fact, if you want to extend the service life of the bearing, you only need to do the correct selection and assembly, maintain a good working environment, and use the correct maintenance and lubricating oil. Supplementation can increase the service life of the bearing