Keywords: spindle bearings, machine tool bearings, angular contact ball bearings, deep groove ball bearings, cylindrical roller bearings.
Bearing, as the core component of machine tool spindle and turntable, plays a decisive role in the operating, performance of machine tools. Spindle as a key part of the machine tool, the performance will directly affect the rotation accuracy of the machine tool, speed, rigidity, temperature rise, noise and other parameters, and then affect the quality of the workpiece processing. In order to maintain excellent machine tool processing capacity, must be equipped with high-performance bearings.
Machine tool spindle bearings are commonly used in five categories: deep groove ball bearings, angular contact ball bearings, two-way thrust angular contact ball bearings, double row cylindrical roller bearings, tapered roller bearings.
Deep Groove Ball Bearing
This kind of bearing is generally only used to bear radial load. Because the clearance can not be adjusted, it is often used on occasions where the accuracy is not high and there is no need for tightening, such as the common drilling machine spindle.
Angular Contact Ball Bearing
This kind of bearing can bear radial and axial load at the same time. Because it will cause internal axial force when bearing radial load, it should be installed and used, and its configuration mode is “back to back”, “face to face”, “series” and “multi-connection”, etc., and the stiffness of the spindle can be improved by pre tightening. This kind of bearing has three kinds of contact angles: 15°, 25° and 40°. B7000CY type high-precision angular contact ball bearing with 15° contact Angle is specially designed for the spindle of the high-speed grinder. In addition to the change of internal structure design, the ring and rolling body of this bearing is made of high-quality electro slag bearing steel. The cage is made of phenolic laminated cloth tubes with tolerance classes 5, 4 and 2. Therefore, this kind of bearing has high rotation accuracy and limit speed, small friction, low-temperature rise.
Bidirectional Thrust Angular Contact Ball Bearings
Bidirectional thrust angular contact ball bearings are usually 230000 type bidirectional thrust angular contact ball bearings with a contact Angle of 60°, which are composed of a seat ring with a lubricating oil hole, two shaft rings, a spacer ring and two groups of steel balls and cage components. Selecting the proper height of the spacer can make the bearing have the required pre-load after assembly. This kind of bearing can bear bidirectional axial load, has good rigidity, the normal lubrication temperature rise is low, high speed, and easy to assemble and disassemble, as a new structure, is widely used in grinding machine, lathe, boring machine, milling machine, drilling machine and other spindles, often used with double row cylindrical roller bearing combination.
Double Row Cylindrical Roller Bearings
Double row cylindrical roller bearings this kind of bearings can withstand a large radial load and allow a higher speed. The two rows of rollers in the bearing are arranged in a crossway. When rotating, the fluctuation frequency is twice as high as that of a single row bearing and the amplitude is reduced by 70%.
The commonly used such bearings have two forms: NN30/W33, NN30K/W33 two series bearing inner ring with a guard, the outer ring can be separated; The outer ring of NNU49/W33 and NNU49K/W33 series bearings has a flanged edge and the inner ring can be separated. Among them, the inner ring of NN30K/W33 and NNU49K/W33 series has a taper hole (taper 1:12), which is coordinated with the taper journal of the main shaft. By moving the inner ring axially, the inner ring can be enlarged to reduce bearing clearance and even retighten the bearing. Cylindrical bore bearings are usually heated, and interference fit is used to reduce bearing clearance or to achieve the purpose of pre-tightening. For the NNU49 series bearings with separable inner ring, the inner ring is generally mounted on the main shaft and then the raceway is finished to obtain high spindle rotation accuracy.
Tapered roller bearings
Tapered roller bearings can bear radial and axial loads at the same time, double row tapered roller bearings can bear bidirectional axial loads. Because of the sliding friction between the big end of the tapered roller and the inner ring, its limit speed is often lower than that of cylindrical roller bearings of the same size. Hollow tapered roller bearings can cool the roller with oil, so that the temperature rise is reduced, thus increasing the allowable speed. But this kind of bearing manufacturing process is complex, the machine tool lubrication system requirements are also high, generally only used in the horizontal spindle with special requirements.
