Detailed description of rolling bearing precision grade and selection

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Bearing is one of the commonly used parts in mechanical equipment, due to the different precision requirements of the equipment,
plus the bearing precision provided by different manufacturers are also different.But no matter how the requirements of the bearing precision,
for the bearing precision or there is a level of standard, in addition, the choice of the bearing is also a strict standard.Today xiaobian to tell you about the accuracy of rolling bearings and selection

The precision of bearing includes dimension precision and rotation precision.Dimensional accuracy is the required item for mounting a bearing on a shaft or bearing box. It includes inner diameter, outer diameter, width, chamfering dimensional tolerances or allowable values.
The geometric accuracy includes internal diameter deviation, average internal diameter difference, external diameter deviation, average external diameter difference and allowable value of the ring end face parallel difference.The precision of rotation is specified for the pendulum during rotation, including radial and axial swing of inner and outer rings, and vertical tolerance range of inner ring side swing and outer diameter surface.

One.Bearing accuracy class code

1.China bearing previous code accuracy class code
The standards developed by each country are based on ISO standards, which are generally related to ISO- and are individually stricter than ISO standard

The precision is divided into dimension precision and rotation precision,It is divided into level 0, level 6, level 6, level 5, level 4 and level 2
The old code standard of Chinese bearings before is :G class (0 class) E class (6 class) D class (5 class) C class (4 class) B class (2 class)。

2.Current code generally adopts German DIN standard
Accuracy level has been standardized and divided into P0 (0 level), P6 (6 level), P5 (5 level), P4 (4 level), P2 (2 level)

The precision of bearing is improved successively from level 0. PO level is a national standard, and it is also a common standard in the bearing industry, so it is also called ordinary level.
At present, most manufacturers in China also produce PO level products, while P2 level is a precision level, and specific technical parameters are also standardized

General standard grade P0, reflected in the bearing type is omitted, only P6 or above, the grade code appears in the bearing type

For example: 6205 and 6205/p5, where the precision level of 6205 is PO, but it is omitted, which gives people the impression that the PO level is non-precision level bearing

Two.The selection of bearings with different precision
1.Grade 0: in the rotation accuracy of more than 10 m of the general bearing system, it is widely used such as the common machine tool speed change mechanism feed mechanism automobile tractor speed change mechanism,
common motor water pump and agricultural machinery and other general machinery of the rotation mechanism

2, Grade 5: In precision bearing systems with rotation accuracy of 5-10 m or higher rotation speed, such as bearings used in ordinary lathes (5 for front support, 6 for rear support),
more precise instruments, instruments, and precise rotating mechanisms。

3 ,Grade 2: In ultra-precision instruments with rotation accuracy of less than 5 m or at very high speeds, such as precision jig boring machines, gear systems for precision grinding machines, precision instruments, meters and high-speed cameras.

A good bearing is important is used in the appropriate place, the bearings suitable place, there must be precision grade to divide.In mechanical equipment, it is impossible for a high precision bearing to replace the general bearings, general bearings can not replace the high precision class of bearings.

Maintenance work of the rotary mechanism of the drilling rig

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During the use of the drilling rig, the problems that are prone to occur in the slewing system are the wear of the slewing bearing steel ball, the pitting of the output gear of the slewing reducer, and the wear of the slewing brake friction plate. How to reduce the occurrence of the above-mentioned problems through daily operation and maintenance?

 

In the actual construction process, the performance requirements of rotary drilling rigs are increasingly strengthened. How to ensure that the drilling rig can exert maximum performance in the actual construction process? This requires not only a good initial performance index of the drilling rig, but also the later use process. Careful maintenance.

 

  1. slewing bearing lubrication

 

The entire slewing ring is actually an enlarged bearing. During the rotation of the bearing, the steel balls inside must always be lubricated with lubricating oil to avoid dry grinding of the steel balls in the slewing ring. Before adding lubricating oil to the slewing bearing, the grease nipple should be cleaned to prevent foreign impurities from entering the slewing bearing during the lubricating process.

 

The slewing bearing is located under the base of the boom, and lubricating oil is added through the oil nozzle until the lubricating oil overflows from the bearing seal. At this time, it can be considered that the steel ball of the slewing bearing is completely protected by the lubricating oil.

 

  1. Replace the lubricating oil of the rotary drive unit

 

Check the lubricating oil level of the rotary drive device:

 

1) The dipstick for the lubricating oil of the turntable driving device is on the turntable device behind the boom base, and the dipstick is taken out.

 

2) Check the oil dipstick: Keep the oil level between the top of the dipstick and the mark on the dipstick. If necessary, add oil through the dipstick tube.

 

3)  Insert the dipstick.

 

  1. Lubricate the slewing ring gear

 

Note: Incorrect lubrication may cause damage to the parts of the drill. To avoid damage, make sure that the amount of grease added to the turntable drive is correct. Too much grease in the turntable gear chamber will increase the stirring loss, thus accelerating the deterioration of the grease. Deterioration of grease will cause damage to the pinion and inner ring of the turntable drive device; insufficient grease will result in poor gear lubrication.

1) Remove the inspection cover near the base of the boom and check the grease.

 

2) Remove the bolts, washers, lower cover and gaskets to drain water.

 

3) Check the gasket. If there is obvious damage, the gasket should be replaced; check the grease surface, the grease should be evenly distributed on the bottom of the groove.

 

4) Check whether the grease is contaminated and discolored. If the grease is contaminated or discolored due to water, replace the grease.

 

5) Raise the starter arm, turn the upper structure 1/4 turn, pause for a while after every 1/4 turn, and then perform the rotation work to ensure that the lubricant in the slewing ring can be evenly distributed to the surface of the slewing ring gear.

 

The above is the introduction to the maintenance work of the rotary mechanism of the drilling rig. Although the above-mentioned operations cannot completely avoid the aging of the drilling rig as the working time increases, these daily maintenance and maintenance will make the drilling rig work better and reduce the occurrence of serious failure, Reduce operating costs.

What is the difference between single row ball slewing bearing domestic and overseas?

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Slewing bearing is very popular both in China and abroad, especially in Germany, France, the United States and Britain is a major manufacturer of slewing bearing of single Chinese slewing bearing single appeared in the early 20th century in the early 1980 s, using the German technology and combining with the domestic technology, formed the slewing bearing of single bearing technology, however, compared with abroad, is still a big gap between product quality and level of The following is a comparison of single ball slewing bearing from four aspects domestic and overseas

1.Design Technology

Foreign only need to input in the computer such as working conditions, installation size, speed and other data, such as CAD program automatically complete product structure design, loading capacity calculation, and the output of various shapes and curves at the same time, and using finite element analysis of slewing bearing load simulation analysis and single foreign company’s new products emerge in endlessly, at least a dozen, but in China is less than 10, so every year there are many special requirements,single row ball slewing bearing need to be imported from abroad

2. Technology
Slewing bearing manufacturer abroad single CNC machine tool has been widely used for processing and it has the advantage of greatly simplifies the process, reduce the frequency of the workpiece clamping, avoid the processing and the measurement error, greatly shorten the production cycle, and to ensure that the internal and external assembly, at the same time improve the quality of the product percent of pass due to the use of the nc machine tool, it provides conditions for the scene to realize the drawing operations from product contract to product design (CAD), process design (CAPP) and CNC machine design, the computer system can be connected to the whole operation process is very efficientAnother foreign manufacturer has many unique features for single volley type rotary bearings in heat treatment, roll rolling and other processes

3. Test technology
The design of the single ball slewing bearing is inspired by a large number of long-term experiments and practices, so the experimental equipment and methods have attracted wide attention.For this, lack of in-depth research and implementation, should gradually improve the life test, temperature test, bolt strength test, gear strength test equipment.

4. Quality control

There is still a large gap between domestic production plants and international standards.There are almost no full-time inspectors in foreign production workshops, but all kinds of inspection data are accurate and reliable, and transmitted timely.We do not have a lot of advanced testing equipment, such as nondestructive testing, coordinate measurement, so the domestic quality control level is low.

A single row ball slewing support is often referred to as the connecting part of a machine tool.This is an essential transport link for the machine.The macros of a single row ball slewing support are called supports.Support parts are commonly used as basic tools for CNC machines, including rocker arms and turret.And the bed, and the beam, and the elevator.

One of the supports is called the auxiliary support.Auxiliary supports certainly play a role in limiting the degree of freedom in increasing the stiffness of the workpiece.In fact, the two meanings play the same role: to achieve and improve machining accuracy and efficiency through machining, corresponding to the different installation methods of single volleyball slewing bearing. When constraints are applied, the inner ring can be all or all of the constraints.The constraint is applied to the outer surface of the outer ring

The Mises stress of the elliptical raceway is less than that of the circular raceway, that is to say, the bearing capacity of the single volleyball slewing bearing is better than that of the single volleyball raceway bearing.Single volleyball slewing supports, these components are relatively large in size, so they are also known as large single volleyball slewing supports, which can withstand the combined load of large bearings.The latter can withstand greater axial loads, radial loads and sloping turning moments.In order to ensure the normal and stable operation of the equipment, the large bearing is of closed construction, so that the true function of the bearing can only be seen when the top of the heavy structure is lifted to a certain height.

What sealing device used for bearing? What material are there? How to choose?

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Bearings are one of the common important mechanical parts in our lives and are called mechanical joints. Because the bearing is affected by the working environment, it needs to be dust-proof and sealed to protect the normal operation of the bearing and increase the service life. So do you know what sealing device is used in the bearing? What material is it made of?

 

  1. Bearing sealing device

 

In order to protect the bearing’s dust-proof and sealing effect, corresponding sealing devices will be installed on both ends of the bearing. There are dust cover and sealing ring. The two performances are different, one is dustproof and the other is sealed. The seal is to keep the grease (oil) inside the bearing from being lost during use, and the grease from the outside is not easy to flow in, so as to ensure that the bearing is in a lubricated state; dust prevention is to protect the outside of the bearing from dust or harmful gases from entering the bearing Cavity to prevent damage to the bearing.

 

It is often seen that different bearing seals are used on different bearings, so that the components can give the bearing a good sealing effect, and indirectly protect the use effect and service life of the bearing. The common ones are rubber or engineering plastic seals, as well as steel stamped seals (or dust caps). The sealing structure of the sealing ring is various, and the sealing effect is also different. If there is a gap between the sealing ring and the rotating shaft, it is called non-contact sealing. The smaller the gap, the better the sealing effect, but the lower the allowable shaft speed; the opposite is true. There is no gap between the seal ring and the rotating shaft, which is called a contact seal. The larger the contact area of ​​the seal ring contact lip, the better the sealing effect, but the lower the speed of the shaft, the opposite is true.

 

 

How to express the bearing dustproof and sealing: Z is used for dust control, and S is used for seal (felt ring seal is expressed by FS; rubber seal is expressed by LS).

 

1). dust cover

 

ZZ: Retaining ring steel plate bearing dust cover, used for miniature bearings, and the structure in which the stamped metal steel plate is fixed on the outer ring with a spring tight ring.

 

2Z: Stamping steel plate bearing dust cover to reduce grease leakage, and the structure of metal steel plate reinforced on the outer ring by stamping.

 

2). Sealing ring

 

TT: Retaining ring type Teflon bearing seal ring, mainly used for miniature bearings. The structure of the Teflon seal ring added with glass fiber is fixed on the outer ring with a spring tight ring.

 

2RS: Contact rubber bearing seal ring, which effectively prevents the intrusion of foreign matter. The rubber seal ring is embedded in the outer ring of the bearing, and the seal ring is in slight contact with the inner ring.

 

  1. Material of sealing device

 

Depending on the specific use environment of the bearing, the materials used for the dust cover and the sealing ring are also different. The following briefly introduces several materials used for dust cover and sealing ring.

 

1) bearing dust cover material

 

The standard material of the dust cover of the bearing is cold-rolled electro-tinned steel plate, and sometimes ASI-300 stainless steel is used.

 

2) bearing seal ring material

 

Bearing seals mainly use nitrile rubber as the material. For high temperature environments, fluorine rubber and silicone rubber are also widely used.

 

①Silicone rubber: MQ/PMQ/VMQ/PVMP, temperature range: -70~200 degrees Celsius; hardness: 25~80; features: resistance to high temperature and drying, high abrasion resistance, resistance to sunlight and ozone aging; Limitations: poor surface wear and crack resistance.

 

②Hydrogenated (nitrile rubber): HNBR/NEM, temperature range: -35~165 degrees Celsius; hardness: 50~90; features: heat resistance, high ductility, chemical corrosion resistance; restriction: not suitable for ultra-low temperature conditions, avoid sunlight Direct sunlight and chemical erosion.

 

③Fluorine rubber: FKM/FPM, temperature range: -28~200 degrees Celsius; hardness: 50~95; features: high temperature resistance, significant chemical corrosion resistance, corrosion resistance to petroleum products; limitation: not suitable for low temperature working conditions .

 

④Polypropylene rubber: ACM Rubber, temperature range: -18~175 degrees Celsius; hardness: 40~90; features: strong resistance to hot oil, sunlight and ozone erosion and strong crack resistance; restrictions: Poor waterproof performance, not suitable for ultra-low temperature working conditions.

 

 

  1. The choice of bearing sealing device

 

Whether the bearing uses a dust cover or a sealing ring depends on the requirements of the bearing. The dust cover does not contact the inner ring of the bearing and is installed in a non-contact type. The sealing ring is in contact with the inner ring of the bearing and is a contact installation. Therefore, the limit speed of the dust cover bearing is higher than that of the seal ring bearing, and the protection level of the seal ring bearing is higher than that of the dust cover. The seal ring bearing has good waterproof performance, and the seal ring bearing can better prevent the grease from flowing out. .

 

The above is a brief introduction to what kind of sealing device the bearing adopts. In recent years, bearings with different sealing rings have appeared in various rolling bearings. Therefore, sealing is one of the important directions for the development of bearing technology. Bearings with different structures and different working conditions require different structures and materials of the sealing ring. Common sealing methods are divided into three categories: contact, non-contact, and combined sealing. Which will be refined according to the actual situation.

Pretightening requirements for turntable bearing bolts

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The connection of the turntable bearing depends on fasteners such as bolts, so the quality choice of bolts and the way of loading and unloading will affect the performance of the turntable bearing.Today, let us introduce you about the pre-tightening requirements of the turntable bearing bolts.
The purpose of preloading is to increase the reliability and tightness of the connection so as to prevent gaps or relative slippage between the connected parts after loading.It has been proved by experience that the proper selection of large preload is beneficial to the reliability of the threaded connection and the fatigue strength of the joint。

Turntable bearing

According to the provisions related to the main engine, the bolt tightening mode should ensure a certain pre-tightening force, except for special provisions, the general pre-tightening force is 0.7 times the bolt limit.Allow a little oiling at the threads while tightening.Preload torque or preload.

“Cross-fixation” is a form of mounting and configuration of turntable bearings, in which each turntable bearing is positioned one way on the shaft and in the opposite direction.This combination is mainly used for short axes.All radial disc bearings capable of bearing at least one axial load in one direction are applicable, including deep groove and angular contact ball bearings, tapered roller bearings, and NJ type cylindrical roller bearings. In some cases, preload must be applied when angular contact ball or tapered roller bearings are used.

After radial positioning of the turntable bearing, cross tighten the mounting bolts according to the star, and check the rotation of the bearing.In order to ensure the bearing transmission is stable, the gear side clearance should be checked and adjusted before the mounting bolts are not tightened completely.When tightening bolts, there should be enough preloading force, which should be 70% of the yield limit of bolt material.The mounting bolt shall be equipped with a tempered flat washer and a spring washer is strictly prohibited.

slewing bearing

The axial preloading method can be divided into positioning preloading and constant pressure preloading.In positioning preload, the appropriate preload can be obtained by adjusting the size of bushing or gasket.The starting friction torque can also be measured or controlled to adjust the appropriate pretightening;Also can be directly used to pre-adjust the pretension of a pair of twin rotary bearings, at this time generally do not need to adjust, in short, after the axial pretension of the rotary bearings, its relative position will certainly not change.
Constant pressure preloading is the use of spiral spring, dish spring and so on to get the proper preloading of the rotary bearing method.The rigidity of the preloaded spring is much smaller than the rigidity of the turntable bearing, so the relative position of the fixed-pressure preloaded turntable bearing will change in use, but the preloaded amount will remain roughly the same.
After the initial operation of the rotary bearing for 100 hours, the bolt pre-tightening force shall be checked, and the bolt pre-tightening force shall be checked once every 500 hours after the operation.

Influence of bearing steel material on turntable bearing

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The wide application of slewing bearings requires the production industry to continuously innovate product forms and improve product performance in product design. Because it’s main performance is closely related to product material selection, there are multiple considerations in manufacturing and material selection. Today, the editor will analyze and explain the influence of bearing steel materials on slewing bearings.

According to the working conditions of the slewing bearing, the material is selected. The slewing bearing that works at room temperature uses chromium bearing steel. The working temperature is higher than 150℃ and lower than 250℃, chromium bearing steel is also used, but it needs special heat treatment (200℃ or 300℃ tempering is required); According to the size of the impact load, the slewing bearing with strong impact load is generally selected. Do not use chromium bearing steel, most use high-quality carburized structural steel, impact-resistant tool steel or quenched and tempered structural steel.

 

The quality of steel determines the fatigue life and reliability of slewing bearings. Therefore, how to improve the performance of metal materials is an important entry point for the improvement and innovation of slewing bearings. The purity and uniformity of steel depend on the level of metal smelting and processing technology.

 

 

The bearing has the characteristics of long life, high accuracy, low heat generation, fast speed, good rigidity, low noise, and high wear resistance. Therefore, bearing steel is required to have: high hardness, uniform hardness, high elastic limit, and high contact fatigue. The strength of the atmospheric lubricant, the necessary toughness, a certain degree of hardenability and corrosion resistance. In order to meet the above performance requirements, the uniformity of the chemical composition of the bearing steel, the content and type of non-metallic inclusions, the size and distribution of carbides, and decarburization are strictly required. Bearing steel generally develops in the direction of high quality, high performance and diversification. Bearing steels are classified into high-carbon chromium bearing steels, carburized bearing steels, high-temperature bearing steels, stainless steel bearing steels and special bearing materials according to their characteristics and application environment.

 

Due to the characteristics of bearing steel, the requirements for smelting quality are much stricter than general industrial steel, such as the chemical composition, purity, structure and uniformity of the steel. Strict chemical composition requirements the general bearing steel is mainly high-carbon chromium bearing steel, that is, a hypereutectoid steel with a carbon content of about 1%, 1.5% of chromium, and a small amount of manganese and silicon. Chromium can improve heat treatment performance, improve hardenability, structure uniformity, tempering stability, and can also improve steel’s rust resistance and grinding performance. But when the chromium content exceeds 1.65%, after quenching, it will increase the retained austenite in the steel, reduce the hardness and dimensional stability, increase the unevenness of carbides, and reduce the impact toughness and fatigue strength of the steel. For this reason, the chromium content in high carbon chromium bearing steel is generally controlled below 1.65%. Only by strictly controlling the chemical composition of the bearing steel can the structure and hardness that meet the bearing performance be obtained through the heat treatment process.

 

For general use occasions, ordinary bearing steel smelted in acid open hearth furnace or alkaline electric furnace is often used. With the continuous improvement of smelting methods, new smelting methods such as current remelting, vacuum smelting, and electron beam furnace smelting have emerged. The life of the slewing bearing made of bearing steel smelted by the above method has been correspondingly improved.

 

Due to the continuous changes in bearing working conditions, especially the rapid development of science and technology, the working environment of machines has become more and more complicated. For example, the speed of the shaft is getting faster and faster, the load is getting heavier and the working temperature is getting higher and higher, the bearing becomes more and more complicated (except for gravity, there is also multidirectional thrust). All of these require the bearing to be competent, and the support shaft can operate stably as required. Therefore, bearing steel must keep up with the development of the times and technology in terms of strength, rigidity, wear resistance, hardness, uniformity of physical and mechanical properties, and contact fatigue strength function.

Slewing bearing maintenance is very important. What are the precautions?

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Bearings are used in many mechanical equipment. Among them, slewing bearings are widely used. Let’s say slewing bearings. When in use, maintenance is an important thing to do. Then we need to repaBearings are used in many mechanical equipment. Among them, slewing bearings are widely used. Let’s say slewing bearings. When in use, maintenance is an important thing to do. Then we need to repair and maintain slewing bearings. What should I pay attention to?

Slewing bearing maintenance and repair matters:
(1) The mounting support of the slewing ring must have sufficient rigidity and the mounting surface must be flat. Before assembling the slewing ring, the bearing should undergo stress relief, and the slewing bearing and slewing ring should be repaired and maintained to reduce the deformation of the slewing bearing. The contact surface between the support and the slewing ring must be cleaned up during assembly.
(2) When using slewing bearing and slewing ring, attention should be paid to changes in noise and slewing resistance torque. If there is any abnormal phenomenon in the maintenance of slewing bearing and slewing ring, it should be disassembled and inspected.
(3) The slewing bearing must be hoisted or stored horizontally, and do not hoist or store vertically to avoid deformation.
(4) Before the bolts are tightened, the slewing bearing and the slewing support should be checked for meshing of the gear. The meshing condition should meet the requirements of gear accuracy: that is, the contact spots distributed on the tooth surface after the gear pair runs under slight braking The height of the teeth is not less than 25%, and the length of the teeth is not less than 30%.
(5) The slewing bearing and slewing ring tooth surface work 10 shifts should be cleaned of secondary debris and re-coated with grease.
(6) Slewing bearing and slewing ring In order to ensure the reliability of bolt work and avoid the lack of bolt pre-tightening force, the slewing bearing and slewing ring should be checked for the pre-tightening torque of the bolts after 100 hours and 500 hours of operation. . After that, check the preload torque every 1000 hours of work.
(7) The bolts and nuts connecting the slewing ring are all high-strength bolts and nuts; double nuts are used for fastening and preventing loosening.
(8) When tightening nuts for slewing bearings and slewing rings, lubricate the threads and nut surfaces of the bolts, and use a torque wrench to tighten them symmetrically and evenly in the circumferential direction. When tightening later, the pre-tightening torque on each bolt should be roughly uniform.
(9) 4 oil cups are evenly distributed on the upper surface of the ring gear of the slewing ring that is aligned with the raceway, thereby adding grease to the raceway. In general, the slewing ring should be lubricated every 50 hours. You must add enough oil each time until the grease leaks out from the seal.
Only with frequent maintenance, the possibility of slewing ring damage will be reduced, and we will be more at ease when using it.
ir and maintain slewing bearings. What should I pay attention to?

 

What should we pay attention to when buying slewing bearing,swing bearing

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Slewing bearings are widely used in all kinds of machinery and equipment.So, what to pay attention to when buying slewing bearing?how to select the high quality of the slewing bearing
let us teach for you

There are many issues that need to be paid attention to when purchasing a slewing bearing, such as load, bolt strength, and whether there is a series of bolt holes.

One,Whether the bearing load is reasonably distributed

Bearing mounted in a lack of a unified support surface, in the design phase of the support structure is a common mistake is to assume that the slewing bearing structure is rigid enough.However, local deformation can change the load, causing the bearing to have different load sizes.If appropriate steps are not taken, it is easy to cause slewing bearing failure.

Two.The bolts must be strong enough

Be sure to select the right slewing bearing product for your installation.This phase is often overlooked, leading to the possibility of a system failure.Typically, the device designer is responsible for determining the correct type of fasteners required for the project.However, fastener suppliers and manufacturers should really get a measure of what a specified fastener can stand.They will be able to assist in the greater calculation of the integrity of bolt load confirmation fasteners

What should I pay attention to when buying slewing bearing

Three、Is there a uniform bolt hole design

Fasteners need to be placed in more places in larger load areas.Bolt holes can be used as hazardous support structures only in areas where heavy loads occur and should not be overlooked in the overall design of the product.It is important to remember that a large amount of exercise load exists, not just the installation part.Uniform bolt loops help reduce bending and load distribution in bearings, fasteners, and support structures.
In addition, When we purchase the rotary bearing, also want to pay attention to the toughness of the product, because the parts are very thin, so a lot of parts are look good, but in the use of machine before long will be reimbursed, you first choice, in fact you can buy a few more brands, carries on the practice in the middle of the practical.

Above on the purchase of slewing bearing matters need to pay attention , in the purchase of slewing support products, must see the plate printed on the slewing bearing words, label, etc.Most of the products in the factory use steel printing technology, the font is very small, and before the pressure before the treatment, so the font is small, but deep concave, very clear.The typefaces of the counterfeits are blurry, floating on the surface due to the rough printing technique, and some can even be easily wiped by hand