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Spindle Bearing
Spindle Bearing
2021-12-11
Rod End Joint Bearing
Rod End Joint Bearing
2021-12-11

Turntable Bearing

The rotary worktable commonly used in NC machine tools includes indexing worktable and NC rotary worktable. When NC machine tools process some parts, in addition to the linear feed motion of the X, y and Z coordinate axes, sometimes there is a circular motion around the X, y and Z coordinate axes, which are called a, B and C axes respectively. CNC rotary table can be used to realize circular feed motion. CNC rotary table (referred to as CNC turntable) can not only realize circular feed motion, but also complete indexing motion.

 

The function of the indexing worktable is only to transpose and change the surface of the workpiece, which is used together with the automatic tool change device to realize the installation of the workpiece at one time, and can complete a variety of processes on several surfaces. Therefore, the work efficiency is greatly improved. The shape of NC turntable is not much different from that of indexing worktable, but it has a series of characteristics in structure. Because NC turntable can realize feed movement, it has many similarities with the feed drive mechanism of NC machine tool in structure. The difference is that the driving mechanism realizes linear feed motion, while the NC turntable realizes circular feed motion.

 

Rotary worktable is widely used in various CNC milling machines, boring machines, various vertical turning, vertical milling and other machine tools. In addition to the requirement that the rotary table can well bear the weight of the workpiece, it is also necessary to ensure its rotation accuracy under load. As the core component of the turntable, the turntable bearing should not only have high bearing capacity, but also have high rotation accuracy, high anti overturning capacity and high speed capacity during the operation of the turntable. In the design of rotary worktable, the types of bearings used are roughly divided into the following types:

 

Thrust ball bearing cylindrical roller bearing

Thrust ball bearing can bear certain axial force, so the bearing is mainly used to bear the weight of workpiece; Cylindrical roller bearings are mainly used for radial positioning and bearing external radial forces (such as cutting force, milling force, etc.). This kind of design is widely used and the cost is relatively low. Because the thrust ball is a point contact bearing, its axial bearing capacity is relatively limited. It is mainly used in the rotary worktable of small or medium-sized machine tools. In addition, it is difficult to lubricate the thrust ball.

Turntable Bearing
 
Hydrostatic bearing precision cylindrical roller bearing

Hydrostatic bearing is a kind of sliding bearing which supplies pressure oil from the outside and establishes hydrostatic bearing oil film in the bearing to realize liquid lubrication. Hydrostatic bearing always works under liquid lubrication from start to stop, so it has no wear, long service life and low starting power; In addition, the bearing also has the advantages of high rotation accuracy, large oil film stiffness and suppression of oil film oscillation.

Precision cylindrical roller bearings have good radial bearing capacity, and the rotation accuracy of the rotary table can be well guaranteed due to the use of precision bearings. The rotary table with this design can bear high axial force. The weight of some workpieces is more than 200 tons and the diameter of the turntable is more than 10 meters. However, this kind of design also has some shortcomings. Because the hydrostatic bearing must be attached with a special oil supply system to supply pressure oil, the maintenance is more complex and the cost is relatively high.

 
Cross roller bearing

Cross roller bearings are also widely used in turntable. The cross roller bearing is characterized by two raceways and two rows of cross arranged rollers in the bearing. Compared with the traditional combination of thrust bearing and radial centering bearing, the cross roller bearing has compact structure and small volume, and simplifies the design of the workbench, thus reducing the cost of the turntable. In addition, due to the use of optimized preload, this kind of bearing has high stiffness, so the stiffness and accuracy of the turntable are also guaranteed.

Thanks to the design of two rows of cross rollers, the effective span of the bearing can be significantly improved, so this kind of bearing has high overturning moment. In the cross roller bearing, it is divided into two types: one is cylindrical cross roller bearing, and the second is conical cross roller bearing. Generally, the price of cylindrical cross roller bearing is lower than that of conical cross roller bearing, which is suitable for turntable applications with relatively low speed;

 

The tapered cross roller bearing adopts the pure rolling design of tapered roller, so this kind of bearing has
• high operation accuracy

• high speed capability

• reduced shaft length and processing costs, limited geometric changes due to thermal expansion

• nylon separator, low moment of inertia, low starting torque, easy to control angular division

• optimized preload, high stiffness and small runout

• line contact, high rigidity and high roller operation accuracy

• carburized steel provides excellent impact resistance and surface wear resistance

• simple but well lubricated

 

During bearing installation, customers only need to pre tighten the cross roller bearing to the recommended value, instead of having a complex installation and adjustment process like hydrostatic bearing. The cross roller bearing is simple to install and easy to adjust the original installation form or maintenance method. Cross roller bearings are suitable for various types of vertical or horizontal boring machines, as well as vertical grinding, vertical turning and large gear milling machines.

 

In a word, bearing, as the core component of machine tool spindle and turntable, plays an important role in the operation performance of machine tool. In order to select the appropriate size and type of bearing, we need to comprehensively consider various working conditions, such as operating speed, lubrication, installation type, spindle stiffness, accuracy and other requirements. As for the bearing itself, only by fully understanding its design characteristics and the advantages and disadvantages, can we give full play to the performance of the bearing.

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