What types of rotary table bearings are there?
Writer： admin Time：2019-11-23 15:42 Browse：℃
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. It is 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 only to transfer the workpiece to the surface, and the automatic tool changing device is used together to realize the multiple installations of several surfaces in one installation of the workpiece, thereby 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 many similarities in structure to the feed drive mechanism of the CNC machine tool. 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 rotary table 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.
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 to conventional thrust bearing radial centering bearing assemblies, cross-roller bearings are compact, compact and simplify the table design, reducing the cost of the turret.
In addition, due to the use of optimized preload, this type of bearing has a high stiffness, so the rigidity and accuracy of the turntable are also guaranteed. Thanks to the design of the two-row cross-roller, the effective span of the bearing can be significantly improved, so this type of bearing has a high anti-overturning moment. In the cross-roller bearing, it is divided into two types: * is a cylindrical cross-roller bearing, and the second is a conical cross-roller bearing. In general, cylindrical cross-roller bearings are less expensive than conical crossed roller bearings and are suitable for use in turntable applications where the rotational speed is relatively low. Conical crossed roller bearings use a purely rolling design of tapered rollers, so this type of bearing has
• Reduce shaft length and machining costs, thermal expansion leads to limited geometric variations
• Nylon separator, low moment of inertia, low starting torque, easy to control angular division
• Optimized preload, high stiffness, small jitter
• Line contact, high rigidity, high precision of guide roller operation
• Carburized steel provides excellent impact resistance and surface abrasion resistance
• Simple but fully lubricated
When the bearing is installed, the customer only needs to pre-tension the crossed roller bearing to the recommended value without having to have a complicated installation adjustment process like the hydrostatic bearing. The cross roller bearing is easy to install and easy to adjust the original installation or maintenance method. Crossed roller bearings are suitable for all types of vertical or horizontal boring machines, as well as applications such as vertical mills, vertical stands and large gear milling machines.
All in all, the bearing, as the core component of the machine tool spindle and turntable, plays a decisive role in the performance of the machine tool. In order to be able to choose the right size and type of bearing, we need to consider a variety of working conditions, such as operating speed, lubrication, installation type, spindle stiffness, accuracy and other requirements. As far as the bearing itself is concerned, we can only exert the bearing performance if we fully understand its design features and the advantages and disadvantages.