分类归档： Industry News

Due to incorrect installation of the slewing bearing raceways and rolling elements, overload operation, poor heat treatment, unreliable sealing devices, etc., premature failure of the slewing bearing raceways and rolling elements. The typical damage symptoms are listed below and the main causes of the damage and the effects on the slewing work are described.

1. Slewing bearing raceway peeling off

The slewing bearing raceway is also called the raceway erosion. This phenomenon is generally caused by poor heat treatment. Usually, the surface hardness of the raceway is too high and the hardened layer is relatively thin, and the interface layer of high hardness and low hardness is caused by the alternating stress. It is characterized in that the exfoliate is in the form of a sheet. This damage can also occur at the junction of the raceway tempering soft belt.

2. Slewing bearing raceway and roller damage

(1) If the roller is skewed or the axis of the race is skewed, it will cause raceway scratches.

To avoid scratching the raceway at the end of the roller, the length of the roller in the slewing bearing of the cross roller is usually shortened by 0.5-1 mm from its diameter. If the roller is excessively shortened or the upper and lower races are separated due to slack of the connecting bolt, the gap between the end face of the roller and the raceway is increased. The skew of the roller increases the skew angle between the end face of the roller and the raceway. If there is a defect in the raceway (low hardness, unevenness, etc.), the roller edge is damaged due to the increased skew of the roller. In addition, if the roller is stuck in the diagonal direction, the end face chamfer in the diagonal direction of the roller is damaged, and even the slewing bearing is braked.

(2) The surface of the slewing bearing raceway is insufficient in quenching hardness, which may cause partial raceway scratches.

(3) When the slewing bearing is assembled, if the slewing bearing is inadvertently impacted, the roller is skewed and the force applied during assembly is too large, the raceway of the raceway may be damaged.

3. Slewing bearing raceway wear

There are several reasons for the wear of the slewing bearing raceway:

(1) Due to dust, sand, dirt and other particles mixed in the lubricating oil, the abrasive acts on the raceway and the rolling element, causing invisible metal peeling or peeling, which can be felt in severe cases. Degree. In order to prevent such wear, the support should be provided with a reliable sealing protective device to prevent external media such as dust, dirt and moisture from intruding into the raceway.

(2) When the lubricating oil is lacking in the slewing bearing or the lubricating oil is insufficient, under the action of heavy load, the raceway wear will be intensified due to the dry friction or semi-dry friction of the rolling element and the raceway.

4. The reason for the slewing bearing raceway to produce the grain

(1) The material itself is defective or improperly heat treated.

(2) When the rolling element and the raceway rotate, the contact fatigue stress is large and fatigue cracking occurs.

5. Wear of the slewing bearing rolling elements

The cross roller slewing bearing has a plurality of sliding friction surfaces, the end faces of the rollers and the friction between the outer rollers and the raceway surfaces. The latter type of friction is often point contact at the beginning, the unit contact pressure is high, and it is in dry friction and semi-friction state, resulting in wear, but as the contact area increases, the unit pressure decreases, and the lubrication condition of the contact surface is improved. , so that the degree of wear is controlled. After this stage, a 2, 4 mm wide wear band is formed on the outer circumference of the roller, which does not impair the working ability of the roller and the support.

6. Slewing bearing steel ball fragmentation

Steel ball fragmentation may occur due to defects in the material or heat treatment of the steel ball, as well as improper holding or use of foreign objects. This can be judged from the sudden increase in the rotational resistance of the support and the abnormal sound at the time of turning. If it is not eliminated in time, the broken steel ball can scrape off the large metal of the raceway, and even the thickness of the raceway is reduced. The head of the fastening screw on the support moves down to the fixed frame, causing the machine to lose the turning ability. In addition, sometimes the broken steel ball is embedded between other steel balls and theraceway, which also causes the machine to lose its ability to turn.

As the core component of the machine tool spindle and turntable, the bearing plays a decisive role in the performance of the machine tool. This paper mainly describes the selection of spindle bearings and the selection of rotary table bearings.

As a key component of the machine tool, the spindle directly affects the parameters such as the rotation accuracy, rotation speed, rigidity, temperature rise and noise of the machine tool, which in turn affects the machining quality of the workpiece, such as the dimensional accuracy of the part and the surface roughness.

Therefore, in order to maintain excellent machine tool processing capabilities, high-performance bearings must be used. The accuracy of the bearings used on the machine tool spindle should be ISO P5 or higher (P5 or P4 is the ISO accuracy level, usually from low to high is P0, P6, P5, P4, P2), and for high-speed CNC machine tools, machining centers, etc. For high-precision machine tool spindle bearings, ISO P4 or higher accuracy is required; spindle bearings include angular contact ball bearings, tapered roller bearings, and cylindrical roller bearings.

Among the above types of bearings, precision angular contact ball bearings are the most widely used. We all know that the rolling element of an angular contact ball bearing is a ball; because it is a point contact (distinguished from the line contact of the roller bearing), it can provide higher speed, smaller heat generation and higher rotation. Precision. In some ultra-high-speed spindle applications, hybrid bearings with ceramic balls (typically Si3N4 or Al2O3) are also used. Compared with the traditional fully hardened steel ball, the ceramic ball material itself gives the ceramic ball bearing the characteristics of high rigidity, high rotation speed, high temperature resistance and long service life, so as to meet the demand of high-end customers for machine tool bearing products.

In terms of the contact angle of the angular contact ball bearing, the contact angles of 15° and 25° are currently popular; usually the contact angle of 15° has a relatively high rotational speed performance, and the contact angle of 25° has a high axial direction. Carrying capacity. Because the choice of preloading has a great influence on the application of precision angular contact ball bearings, for example, in high load bearing and high rigidity, medium or heavy bearing preloading is generally used; for some high speed and high precision applications. In the early selection of bearings, we need to pay attention to choose the appropriate preload, generally light preload is more common. Preloading is generally divided into three types: light, medium and heavy. In order to facilitate the use of customers, several major bearing manufacturers in the world generally provide pre-grinded bearing end faces and preloaded bearings, which is what we usually call universal matching precision. Angular contact ball bearing form. This type of bearing eliminates customer preload regulation and saves installation time.

Precision tapered roller bearing

In some machine applications with heavy loads and speed requirements – such as the forging of forgings, the wire machine of oil pipelines, heavy duty lathes and milling machines, the selection of precision tapered roller bearings is an ideal solution. . Because the roller of the tapered roller bearing is designed for line contact, it can provide high rigidity and load to the main shaft. In addition, the tapered roller bearing is a pure rolling bearing design, which can reduce the bearing operation. Torque and heat to ensure spindle speed and accuracy. Since the tapered roller bearing can adjust the axial preload (play) during installation, this allows the customer to better optimize the bearing clearance adjustment throughout the life of the bearing.

In addition, in some high-speed applications where the inner ring rim speed is greater than 30 m/s, some specially designed tapered roller bearings can also meet the requirements, such as TSMA bearings or Hydra-Rib hydraulic floating rib bearings. The rib of the TSMA bearing has a plurality of lubricating oil holes in the axial direction, which can be lubricated by circulating oil or oil mist. The centrifugal force can distribute the oil to the contact area between the roller and the rib, so that the bearing can be more fully lubricated and the bearing can be improved. Rotating speed. The Hydra-Rib hydraulic floating rib bearing is designed to optimize the preload of the spindle system. The bearing has a floating rib that is in contact with the large end of the roller, unlike the common bearing with a fixed inner ring rib; The floating rib is positioned by the “pressure” system, which ensures that the bearing will perform at its best under all conditions and has been successfully used in domestic customers.

The rotary table commonly used in CNC machine tools has an indexing table and a CNC rotary table. When machining certain parts of CNC machine tools, in addition to the linear feed motion of the three coordinate axes X, Y, and Z, sometimes there is a need for circular motion around the three axes of X, Y, and Z. For A, B, C axis

The CNC rotary table can be used to achieve a circular feed motion. In addition to the circular feed motion, the CNC rotary table (referred to as the CNC rotary table) can also complete the indexing movement. The function of the indexing table is to transfer the workpiece to the surface, and the automatic tool changing device can be used together to realize the multiple installations of several surfaces in one installation of the workpiece, thus greatly improving the working efficiency. The shape of the CNC turntable and the indexing table are not much different, but the structure has a series of features. Since the CNC rotary table can realize the feed motion, it has much in common with the feed drive mechanism of the CNC machine. The difference is that the drive mechanism realizes the linear feed motion, and the CNC rotary table realizes the circular feed motion.

The rotary table is widely used in various CNC milling machines, boring machines, various vertical cranes, and vertical milling machines. In addition to requiring the rotary table to withstand the weight of the workpiece well, it is also necessary to ensure its rotation accuracy under load. The turntable bearing, as the core component of the turntable, not only has a high load carrying capacity during the operation of the turntable, but also needs to have high rotation precision, high anti-overturning capability, and high rotational speed capability. In the design of the rotary table, the types of bearings used are roughly divided into several types:

Thrust ball bearing + cylindrical roller bearing

Thrust ball bearings can withstand certain axial forces, so the bearings are mainly used to bear the weight of the workpiece; cylindrical roller bearings are mainly used for radial positioning and external radial forces (such as cutting force, milling force, etc.) . This type of design is widely used and relatively inexpensive. Since the thrust ball is a point contact bearing, its axial bearing capacity is relatively limited, and it is mainly used in small or medium-sized machine tool rotary table. In addition, the lubrication of the thrust ball is also difficult.

Hydrostatic bearing + precision cylindrical roller bearing

A hydrostatic bearing is a plain bearing that supplies pressure oil externally and establishes a static pressure bearing oil film in the bearing to achieve liquid lubrication. Hydrostatic bearing always works under liquid lubrication from start to stop, so there is no wear, long service life and low starting power. In addition, this bearing also has the advantages of high rotation precision, large oil film stiffness, and can suppress oil film oscillation. Precision cylindrical roller bearings have good radial bearing capacity, and thanks to the use of precision bearings, the rotary table’s rotation accuracy is also well guaranteed.

The rotary table designed with this type can withstand high axial forces. Some workpieces weigh more than 200 tons and the turntable has a diameter of more than 10 meters. However, this type of design also has some shortcomings. Because the hydrostatic bearing must be equipped with a special oil supply system to supply the pressure oil, the maintenance is complicated and the cost is relatively high.

Crossed roller bearing

The application of crossed roller bearings on the turntable is also relatively common. Crossed roller bearings are characterized by two raceways in the bearing and two rows of rollers arranged in a row. Compared with the traditional thrust bearing + radial centering bearing combination, the cross roller bearing is compact, compact and simplifies the table design, thus reducing the cost of the turntable.

With the advancement of technology, the application of slewing bearings in construction machinery is more and more extensive. If we find that the slewing bearing can’t move, how can we deal with it? The following methods can help you to eliminate this problem.

1. The newly purchased products are not flexible. Please check the production date of the slewing ring. If the time is long (such as more than half a year) and the weather is cold, there may be impurities such as salt spray in the raceway, which may cause malfunction (cold area, winter is more prominent). Remedy: If you can work after the afterburner and no other abnormalities can be used normally.

2. The operation is not flexible during use. The sealing strip is damaged, causing foreign matter to enter the raceway if the working condition is poor, the dust is immersed in the raceway, etc.); check the meshing of the large and small gears, whether there is any foreign matter or broken teeth.

3. The operation after installation is not flexible. It may not work well with the mounting surface of the mainframe and the mounting surface of the slewing bearing. As a result, the axial clearance of the slewing bearing after installation cannot compensate the deformation of the slewing bearing. The slewing bearing is in the negative clearance state, and the rolling elements are in the raceway. Difficulties in operation (sometimes accompanied by abnormal noise); or poor meshing of large and small gears; or foreign objects in the large and small gears.

Remedy: Rework the main machine installation plane so that the installation plane meets the requirements; re-adjust the gear meshing backlash according to the requirements, especially pay attention to the gear runout position; check to ensure that the large and small gear meshing position has no foreign matter; exchange a slightly larger slewing bearing .

This is a common situation in which the slewing ring can not be turned. In fact, it is far more than just these. In fact, as long as we install it correctly and regulate the operation, many problems can be avoided.

Slewing bearings are a common mechanical part in industrial equipment. They have many good properties and advantages that can increase productivity in industrial production. However, in the long-term use of the slewing bearing, various failures will inevitably occur. The methods for solving various failures are as follows:

1. The newly purchased slewing bearing product is not flexible. Please check the production date of the slewing bearing. If the time is long (such as more than half a year) and the weather is cold, there may be a large viscosity of the grease in the raceway, which may cause malfunction (cold area, winter is more prominent).

Remedy: If it can work after the afterburning and no other abnormalities can be used normally; if there is abnormal noise, check whether there is serious trauma during transportation, and feedback the information to our company’s sales service department.

2. It is not flexible after installation. It may be that the mounting surface of the main assembly does not cooperate well with the mounting surface of the slewing bearing, so that the axial clearance of the slewing bearing after installation cannot compensate for the deformation of the slewing bearing, and the slewing bearing is in a negative clearance state, and the rolling elements are difficult to operate in the raceway (sometimes accompanied by different Sound); or poorly meshed gears; or foreign objects in the large and small gears. Remedy: a. Rework the host installation plane so that the installation plane meets the requirements; or use the gasket filling method.

b. Resize the gear meshing backlash as required, paying particular attention to the maximum position of the gear runout.

c. Check that there is no foreign matter in the meshing position of the large and small gears.

d. Replace a slewing bearing with a slightly larger gap.

(3) Inflexible operation during use

a. Lack of grease, fill as required

b. The sealing strip is damaged, causing foreign matter to enter the raceway (if the working condition is poor, the dust in the raceway invades the dust, etc.).

c. Check the meshing of the large and small gears, with or without foreign objects or broken teeth. If the above measures are taken, the slewing bearing cannot be rotated, and there may be a failure in the raceway. Please inform our after-sales service department.

2. The slewing bearing that has just been shipped from the factory will give a uniform sound of the rolling of the steel ball during idling, which is normal. The slewing bearing is accompanied by a different kind of abnormal sound when it is installed after installation, which is called abnormal noise.

(1) The slight abnormal sound of the new product when it is idling, it will naturally disappear after turning for dozens of laps. If it does not disappear, it may be caused by slight deformation of the slewing bearing during transportation. However, if the operation is flexible and normal, it can be installed and used with confidence, and it will disappear naturally after a period of use. If the sound is loud or after a period of use (usually 2-4 months) has not disappeared, you should contact me in time.

(2) After the assembly, abnormal operation occurs during the test run. It should be checked whether the installation surface is level and meet the requirements. If the unevenness of the installation surface does not meet the requirements, the negative gap of the raceway will be generated and the noise will be abnormal. The treatment method is the same as “the operation after installation”. “Flexible”; or poorly meshed gears, loose when tight, and excessively tight at the maximum position of the tooth jump to produce abnormal noise.

(3) Abnormal noise is generated during use. (First of all, it should be determined whether the sound is emitted by the slewing ring. Some steel structures or other components make a sound, which is often mistaken for the sound of the slewing ring. Therefore, the rotation of the slewing ring can be stopped. Other components are in normal operation to discriminate the source of the sound. There are several reasons: the grease is missing in the raceway, and the rolling body and the block collide to make a sound. This sound can be eliminated after oiling in time; the raceway is mixed with foreign matter such as sand and iron. Such as scraping, this situation is often accompanied by difficulty in turning (generally this situation is prone to occur in harsh environments). At the same time, it should also pay attention to whether the sealing strip is damaged; the mounting bolt is loose, resulting in elastic deformation of the slewing bearing, negative gap in the deformation position, etc., to eliminate the above situation, such as the slewing bearing still has abnormal noise, please contact me.

 

3. After the slewing bearing is loaded, the clearance is about 3-5 times of the factory inspection (three-point inspection method), and can be used continuously within this range.

(1) The mounting bolts are loose, causing them to shake during work. Please inspect all inner and outer ring mounting bolts and tighten as required.

(2) The steel structure supporting the slewing bearing is not rigid enough, and elastic deformation occurs during loading, resulting in overall swaying of the slewing bearing. Increase the strength of the supporting slewing bearing steel structure.

(3) Check whether the operation is overloaded and operate in strict accordance with the regulations.

(4) Long-term overloading and causing the raceway to collapse, and the clearance is too large. Please let me know if this happens.

 

4. When there is a broken tooth in the broken tooth slewing bearing, the site should be protected and the company’s after-sales service department should be notified immediately for analysis and processing. (1) Broken teeth are often directly related to installation, and there are mainly the following reasons:

a. When installing the large and small gears, the side gap is not adjusted properly, and the requirements are not met, resulting in poor gearing of the two gears during operation. The backlash should be adjusted as required.

b. The meshing gap adjustment is not performed with the pinion gear at the maximum position of the tooth jump as required, causing the pinion gear to become stuck when the meshing gear is engaged with the maximum position of the large gear tooth jump. The meshing adjustment should be made with the pinion in the position where the green paint is applied, and the test operation should be carried out after adjusting according to the requirements.

c. The axis of the large and small gears is not parallel. After installation, the large and small gears mesh poorly, causing broken teeth. It should be ensured that the two gear axes are parallel.

d. The slewing bearing mounting bolts are not tightly fixed, and the large and small gears are poorly engaged, causing broken teeth. The bolts should be tightened as required.

(2) aspects of use

a. Violation of the operating procedures, overload and tell the rotation, the host collides (sweep) obstacles and so on. It should be operated strictly in accordance with the operating procedures.

b. Foreign matter is caught when the slewing bearing is engaged with the pinion. The size of the gears should be clean and checked frequently. Common faults and troubleshooting methods for slewing bearings

Slewing bearing is an important device of industrial machinery. It is a mechanical “joint”. Without slewing mechanical equipment, there is no good activity. Therefore, daily troubleshooting is very important, which not only guarantees the service life of the slewing bearing, but also Improve the utilization of slewing bearings, reduce maintenance costs and reduce costs. The slewing bearing is a more professional mechanical device, and it is also a special load that can withstand large axial loads, radial loads and overturning moments, and combines various functions such as support, rotation, transmission and fixing. Large bearing with structure. In the course of use, it will inevitably cause damage to the bearing. Its maintenance and maintenance also needs to be very careful. What is the specific maintenance operation procedure? Below, I will summarize some points for you to pay attention to, and we will introduce the common faults and troubleshooting methods of the slewing bearing device.

 

1. Rolling surface metal peeling The slewing bearing rolling elements and the inner and outer ring raceways are subjected to periodic pulsating loads, thereby generating cyclically varying contact stresses. When the number of stress cycles reaches a certain value, fatigue peeling occurs on the rolling element or the inner and outer ring raceways. Measures: First remove the roller or steel ball in the slewing ring to separate the inner and outer rings; then clean the raceway with gasoline; then use a sander (grinding wheel) to carefully produce around the needle stripping area of ​​Microsoft Corporation of the United States. Grinding the hardened layer of the crack, grinding the bottom of the stripping layer; preheating the welding torch with the welding torch for the raceway, and welding with the medium carbon steel electrode (the electrode must be dried before use and used with baking) ), to make the solder layer slightly higher than the surface of the raceway 1-2mm.

2. The high-precision slewing bearing of the burned burn of the slewing bearing has a tempering color on the raceway and the rolling element. The causes of burns are generally insufficient lubrication, the quality of the lubricant does not meet the requirements or deterioration, and the bearing assembly is too tight. Measures: partial repair welding or insert repair, the local repair welding method is: firstly grind the residual crack base of the damaged part with a portable grinding wheel, clean it with gasoline (oil); use the welding torch to preheat in this part, when it reaches After a certain temperature, the medium carbon steel electrode is used to weld the shape of the tooth in the damaged part of the tooth, so that it is 1-2mm higher than the tooth surface of the party; the experienced machine repair fitter is selected according to the tooth shape test until the tooth The shape meets the requirements.

 

3. Plastic deformation of slewing bearing Non-uniform pits appear on the contact surface between the raceway and the roller with high precision slewing bearing, indicating that the bearing is plastically deformed. The slewing bearing is subjected to a large static load or impact load, and the local stress of the working surface exceeds the yield limit of the material, which generally occurs on a low-speed rotating bearing. Measures: If the deformation is serious or the area is large, the layered welding should be carried out in layers, and the temperature of the base metal should not be too high to cause deformation; this avoids the rapid cooling to produce welding cracks, and the heat preservation measures should be taken immediately after welding to gradually cool him. . After cooling, use a sander to smooth the repair layer so that it is slightly higher than the raceway surface. Gradually repair the repaired weld layer with a whetstone or metallographic abrasive cloth to make it conform to the height of the normal surface of the raceway, with the corresponding original curvature. The sample is tested until it is qualified; the grease is cleaned on the raceway and the roller (steel ball) and assembled into one.

4, the slewing bearing seat crack bearing seat ring cracks may be caused by high-precision slewing bearing too tight, high-precision slewing bearing foreign or inner ring loose, bearing containment parts deformation, mounting bearing surface processing and so on. Action: When a whole seat is damaged, it can be cut along the root of the tooth, and then the root of the tooth ring is shaped into a certain shape. Then, a tooth is registered and cut on the same kind of waste seat ring, and processed into a shape corresponding to the base material, and then placed in the groove, and the positioning is clamped by the seat-shaped template. In order to ensure the consistency of the seat distance, and use the double wire clamp to increase the value, and then weld around the seat with low carbon steel. Finally, the weld is flattened with a tool such as a file.

The Ministry of Industry and Trade of the Russian Federation initiated an anti-dumping investigation on rolling bearing products originating in China. On December 13, 2007, the Russian federal government decided to adopt anti-dumping measures against rolling bearing products originating in China, and implemented a 31.3%-41.5% anti-dumping tax rate, valid for 5 years. On September 18, 2012, the Eurasian Economic Commission launched the first anti-dumping sunset review investigation on the products involved in China.

On September 17, 2013, the Eurasian Economic Commission made an anti-dumping sunset review of the products involved in China, and extended the anti-dumping measures for five years. On September 18, 2017, the Eurasian Economic Commission launched a second anti-dumping sunset review investigation on China’s rolling bearing products. The investigation period of dumping and damage in this case was from July 1, 2016 to June 30, 2017.

Bearing anti-dumping

Such a high anti-dumping duty will bring a heavy blow to China’s bearing export to the Russian market! China’s bearing export enterprises are forced to give up the Russian market! However, we know that Russia’s bearing requirements for China are relatively large. It is a pity that such a large market will give up because of anti-dumping duties!

In order to enable our country’s bearings to export Russian enterprises to continue to maintain the Russian market after anti-dumping, our company has opened up a channel for bearing the third country’s entrepot trade, and entered the Russian market through the third country curve, thus achieving the purpose of avoiding Russian anti-dumping duties.

We know that Russia does not have anti-dumping duties on bearings in all countries, so our solution comes: We first transport the goods to a third country (such as Malaysia, Thailand, etc.). After the goods arrive in a third country, we arrange customs clearance. Change the cabinet, issue a full set of documents from a third country (such as certificate of origin, packing list, INV, bill of lading, etc.), and then re-export to Russia. After the goods arrive in Russia, the customs clearance is a full set of documents from the third country. Such high anti-dumping Tax can be effectively avoided. This is what we call entrepot trade. We have started to operate after obtaining the consent of domestic and foreign customers, especially some foreign BUYER, I really like…

Bearing anti-dumping

The process of re-export operation is as follows:

1) Our company starts to carry goods from any port in China (Tianjin, Qingdao, Shanghai, Ningbo, Shenzhen, Guangzhou Port, etc.), and sends the goods safely to the transit port of the third country. The consignee is designated by our company. Our company is responsible for Re-export port import customs clearance.

2) When the goods are ready to leave the mainland, our company will arrange a two-way schedule according to the needs of the guests, and do BOOKING. After the arrival of the first-way (China-transit port), the container will be put in time and replaced at the terminal. Photographs of changing cabinets will be taken when changing cabinets to ensure the integrity and safety of the goods.

3) After completing the change of the cabinet, take the second-pass (transfer port-destination port) ship, get the bill of lading within 3-5 working days, and make the certificate of origin with the bill of lading. Prior to this, our company will be more correct with the Chinese shipper to do the documents.

4) After all the documents (Bill of Lading, FORM A/CO, INV, Bill of Lading, K2, etc.) are published, we will send the full set of original documents to your company or directly to the destination port. The destination port is used for customs clearance. A full set of documents from the three countries.

I hope that we can win more international markets for more enterprises in China that have encountered trade barriers through this third country re-export!