Archive for year: 2019

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.

Definition and operation principle of crossed cylindrical roller slewing bearing

Definition: Cross-roller type slewing bearing consists of two races. It is compact in structure, light in weight, high in manufacturing precision, small in assembly clearance, high in installation accuracy, and 1:1 cross-arrangement of rollers. The force, tipping moment and large radial force are widely used in lifting and transportation, construction machinery and military products.

Cross cylindrical roller principle: Cylindrical rollers are arranged at right angles to each other at intervals between the inner and outer rings of the bearing. They can withstand loads from all directions (such as axial, thrust or momentum loads). The internal structure of the crossed roller bearing is arranged at 90° perpendicular to each other by rollers, and spacers or spacers are arranged between the rollers to prevent the inclination of the rollers and the friction between the rollers, thereby effectively preventing the rotational torque. increase.

In addition, the contact phenomenon or the locking phenomenon of the roller does not occur, and since the inner and outer diameters are divided structures, the gap can be adjusted, and even if the preload is applied, a high-precision rotational motion can be obtained.

Application field of cross cylindrical roller slewing bearing

Cross cylindrical roller bearings have a split inner ring, a split outer ring, and an integral inner and outer ring from the outer structure. From the internal structure, there are full roller type, metal window cage and so on. Therefore, it is widely used in various occasions: joint parts or rotating parts of industrial robots, rotary tables of machining centers, rotating parts of robots, precision rotary tables, medical instruments, measuring instruments, and IC manufacturing equipment.

Use cases and technical analysis of crossed cylindrical roller slewing bearings in the robot industry:

Industrial robots typically use an articulated mechanical structure. The drive motor is independently installed in each connector, and the power amplifier circuit of the drive unit is controlled by a computer to realize the operation of the robot. The structure of an industrial robot is a closed loop system. Through the motion controller, servo drive, robot body, sensor and other components, the key products of the functional robots that people need are completed: welding robot, handling robot, painting robot, transmission robot.

The development of modern industrial robots tends to be lighter, and the bearings must be installed in a limited space that must be small and lightweight, ie lightweight. At the same time, the robot has high load, high rotation precision, high running stability, fast positioning speed, high repeatability, long life and high reliability. The required robot bearings must have high load capacity, high precision and high. Rigidity, low friction torque, long life and high reliability. Lightweight and high performance is a contradiction.

Technology: Industrial robots with thin-walled bearings not only have to ensure sufficient capacity, but also require precise positioning and flexible operation. Therefore, bearing design analysis determines the main parameters, not just the dynamic rated load as the objective function, and the rated motion Load, stiffness and friction torque are used as objective functions for multi-objective optimization design. At the same time, the finite element analysis method of thin-walled bearings based on ferrule and frame deformation is adopted.

1. Which carriers use slewing rings to operate in high temperature environments

The slewing bearing of the ladle turret has a relatively poor working condition and is subject to high axial load and overturning moment. These loads are transmitted and received by the ring gear, the raceway of the raceway and the gear, so the slewing bearing is on the selected material. It is necessary to consider the tensile strength, compressive strength and fatigue strength of the material to be high and have sufficient toughness and wear resistance. The single-row four-point contact slewing bearing can simultaneously bear radial force, axial force and overturning moment, and is widely used.

In view of the bearing capacity of the slewing bearing in high temperature environment, based on the thermal stress analysis of the slewing bearing, the contact angle, the rolling element radius r, the raceway radius R and the rolling element radius r ratio, the hardened layer depth and Five aspects of the raceway hardness are proposed to improve the bearing capacity of the slewing bearing. Orthogonal test analysis is carried out for these factors, and the optimal combination of parameters is found to reduce the contact stress on the slewing bearing raceway and improve the slewing bearing at high temperature. The bearing capacity provides a theoretical basis for the structural optimization of the high-temperature single-row four-point contact slewing bearing.

2. Precautions for slewing bearing high temperature operation

The slewing bearing is a new type of mechanical parts that has gradually emerged in the world for nearly forty years. The slewing bearing is a mechanical force transmission basic component that needs relative rotation between the two parts and simultaneously receives axial force, radial force and overturning moment. Its basic function is to fix it on the upper and lower supports of the mechanical equipment by bolts. The force transmission and transmission realize the relative rotation between the two parts of the mechanical equipment. The domestic slewing bearing market was originally mainly in the construction machinery industry.

The largest single-row four-point contact ball slewing bearing accounted for more than 95% of the total market share, and the diameter of the raceway was between Φ500 and Φ1500mm. Most of them have a small processing difficulty, a broad market, and low equipment cost. With the continuous development of engineering machinery, wind power industry, heavy-duty vehicles, metallurgical machinery, petroleum industry, military industry, etc., slewing bearings have been more widely used, and are also required to have more and better performance, one of which is the requirement With high temperature resistance, bearing raceways, cages, seals and lubricants can withstand certain high temperatures and maintain their performance.

High temperature slewing bearings for specific applications, in addition to withstand the alternating pressure, also withstand alternating temperature changes, which will produce fatigue, creep and their interaction. In order to ensure the mechanical properties and life of the product, higher requirements are put forward from material selection, machining process, heat treatment process, to corresponding tooling equipment and testing instruments.

3. How to maintain the slewing ring running in high temperature environment

The slewing ring is rolled to the inside with a small amount of grease. The activation allows the user to refill the new grease according to different working conditions.

The slewing bearing raceway should be filled with grease regularly. Generally, the ball support is refueled once every 100 hours of operation, and the roller type support is refueled every 50 hours. The special working environment, such as tropical, humid, dusty, large temperature difference and continuous operation, should shorten the lubrication cycle. New grease must be added before and after the machine has been shut down for a long time. For each lubrication, the raceway must be filled with grease until it seeps out from the seal. When filling grease, slowly turn the slewing ring to make the grease fill evenly.

The tooth surface should always be cleaned of debris and coated with the corresponding grease. There should be a lot of comprehensive work factors, and users can also choose the best grease according to specific requirements.

After the slewing bearing has been running for the first time for 100 hours, the pre-tightening force of the bolts should be checked. After every 500 hours of operation, the pre-tightening force must be maintained. Pay attention to the operation of the slewing bearing during use. If noise, shock and power suddenly increase, stop the machine immediately, check the fault, and dismantle it if necessary.

4. Quality requirements for slewing bearings in high temperature environments (blanks and accessories)

There are many manufacturers of slewing bearings, and the quality and price are also uneven. However, the factors affecting the price are mainly the product quality. The product quality gap is also mainly reflected in the quality of raw materials. The price of raw materials and the price of non-tempered products differs by 1000. Multivariate/ton, because the hardness of the material that is not tempered is only 140-170HB and the hardness of the material after quenching and tempering is 207-262HB, which is the biggest gap.

Secondly, the hardness of the raceway also affects the quality of the product. The hardness of the raceway of the Xuzhou Wanda slewing bearing is ≤3mm, and the depth of the hardened layer of the raceway quenching affects the service life of the product.

Once again, the precision control of each process in product processing, our products in the process of processing more than two other processes to ensure that the product is flexible, does not cause jamming or shaking.

Quality is the foundation of an enterprise’s survival and the soul of its development. Therefore, Luoyang Hengguan slewing bearing will provide you with the most cost-effective products. Quality products will also make us go further and further on the road in this industry. Getting better and better.

Deep groove ball bearings are the most common type of rolling bearings. The basic deep groove ball bearing consists of an outer ring, an inner ring, a set of steel balls and a set of cages. The deep groove ball bearing types are single row and double row. The deep groove ball structure is also divided into two types: sealed and open. The open type refers to the bearing without sealing structure. The sealed deep groove ball is divided into dustproof seal and oil proof. seal. The dust seal cover material is stamped from steel plate, which is simple to prevent dust from entering the bearing raceway. The oil-proof type is a contact type oil seal, which can effectively prevent the grease inside the bearing from overflowing.

Deep groove ball bearings are mainly subjected to radial loads and can also withstand radial loads and axial loads. When it is only subjected to radial loads, the contact angle is zero. When the deep groove ball bearing has a large radial clearance, it has the performance of an angular contact bearing and can withstand a large axial load. The deep groove ball bearing has a small friction coefficient and a high limit speed.

The deep groove ball bearing has a simple structure and is easy to achieve high manufacturing precision compared with other types, so it is easy to be mass-produced in series, and the manufacturing cost is also low, and the use is extremely common. In addition to the basic type, deep groove ball bearings also have various modified structures, such as: deep groove ball bearings with dust cover, deep groove ball bearings with rubber seals, deep groove ball bearings with snap grooves, and Deep groove ball bearings with large load capacity of ball notches, double row deep groove ball bearings.

Deep groove ball bearings generally use steel stamped cages or brass solid cages. When the outer diameter is less than 400 mm, the steel stamping cage is not added with a post code. When the outer diameter is larger than 400 mm, the brass solid cage is not used with a post code.

1.Self-aligning ball bearing

The self-aligning ball bearing is a bearing equipped with a spherical ball between the inner ring of the two raceways and the outer ring of the spherical raceway.
The center of curvature of the outer raceway surface is identical to the center of the bearing, so it has the same self-aligning function as the self-aligning ball bearing. When the shaft and outer casing are deflected, they can be adjusted automatically without increasing the bearing load.

Spherical roller bearings can withstand radial loads and axial loads in both directions. The radial load capacity is large, and it is suitable for heavy load and impact load. The inner ring inner diameter is a tapered bore bearing that can be mounted directly. Or use the adapter sleeve and the removal cylinder to mount on the cylindrical shaft. The cage uses a steel stamping cage, a polyamide forming cage and a copper alloy cage.

The self-aligning ball bearing has two structures of a cylindrical hole and a tapered hole, and the material of the cage is steel plate, synthetic resin and the like. The characteristic is that the outer ring raceway has a spherical shape and has self-aligning property, which can compensate the error of the heart ball bearing by different degrees of heart and shaft deflection, but the relative inclination of the inner and outer rings must not exceed 3 degrees.

Can withstand large radial loads while also withstanding a certain axial load. The outer ring raceway of this type of bearing is spherical, so it has the function of self-aligning. When the shaft is bent or tilted so that the center line of the inner ring and the center line of the outer ring are inclined no more than 1°~2.5°, the bearing can still work.

The inner diameter of the self-aligning ball bearing is cylindrical or conical. The conical inner bore has a taper of 1:1 2 or 1:30. In order to enhance the lubrication performance of the bearing, an annular oil groove and three oil holes are machined on the outer ring of the bearing.

It is mainly subjected to radial loads and can withstand small axial loads. The axial displacement of the shaft (housing) is limited to the clearance limit, and has automatic self-aligning performance, allowing normal operation under the condition that the inner and outer sides are relatively inclined, and is suitable for the parts in which the support seat hole cannot strictly guarantee the coaxiality.

The self-aligning ball bearing with dust cover and sealing ring has been filled with the proper amount of grease. It should not be heated or cleaned before installation. It does not need to be relubricated during use. It can adapt to operating temperature – 30 °C to + 120 °C. between. Main purpose of self-aligning ball bearings: Suitable for precision instruments, low noise motors, automobiles, motorcycles and general machinery, etc. It is the most widely used type of bearing in the machinery industry.

2. Cylindrical roller bearing

Cylindrical rollers and raceways are line contact bearings. Load capacity, mainly bear radial load. The rolling element has little friction with the ferrule rib and is suitable for high speed rotation. According to the ferrule with or without ribs, it can be divided into single row cylindrical roller bearings such as NU, NJ, NUP, N, NF, and double row cylindrical roller bearings such as NNU and NN. The bearing is a structure in which the inner ring and the outer ring are separable.

Cylindrical roller bearings with no ribs on the inner or outer ring, the inner and outer rings can move relative to the axial direction, so they can be used as free end bearings. A cylindrical roller bearing with a single rib on one side of the inner and outer rings and a single rib on the other side can withstand a certain degree of axial load in one direction. Steel stamping cages or copper alloy solid cages are generally used. However, some use polyamide shaped cages.

The cylindrical roller is in line contact with the raceway and has a large radial load capacity. Suitable for both heavy and shock loads, as well as for high speed rotation.

Cylindrical roller bearing raceways and rolling elements are geometric. After the improved design, the new load-bearing capacity, the new structural design of the rib and the roller end face not only improve the axial bearing capacity of the bearing, but also improve the lubrication conditions of the contact area between the roller end face and the rib, and improve the lubrication condition. Bearing performance.

The cylindrical roller is in line contact with the raceway and has a large radial load capacity. Suitable for both heavy and shock loads, as well as for high speed rotation.

Cylindrical roller bearing raceways and rolling elements are geometric. After the improved design, the new load-bearing capacity, the new structural design of the rib and the roller end face not only improve the axial bearing capacity of the bearing, but also improve the lubrication conditions of the contact area between the roller end face and the rib, and improve the lubrication condition. Bearing performance.

3.Single row angular contact ball bearings

Single row angular contact ball bearings can only withstand axial loads in one direction and will cause additional axial forces when subjected to radial loads. And can only limit the axial displacement of the shaft or housing in one direction. Angular contact ball bearings have a contact angle of 40 degrees and can withstand large axial loads. Angular contact ball bearings are non-separable designs with different shoulder heights on the sides of the inner and outer rings. In order to increase the bearing capacity of the bearing, the shoulder on one side is machined lower, so that the bearing can be loaded with more steel balls.

Double row angular contact ball bearings can withstand large radial loads and mainly combine radial and axial load and moment loads, limiting axial displacement of both sides of the shaft. Mainly used to limit the axial displacement of the shaft and the shell. The tiltability between the inner and outer rings of the double row angular contact ball bearing is limited. The allowable tilt angle depends on the internal clearance of the bearing, the bearing size, the internal design and the action.

The force and moment on the bearing, and the maximum allowable tilt angle should ensure that there is no excessive additional stress in the bearing. If there is a tilt angle between the inner and outer rings of the bearing, it will affect the life of the bearing, and at the same time, the bearing running accuracy will decrease and the running noise will increase. Double row angular contact ball bearings typically use a nylon cage or a brass solid cage.