One of the core components of the machine tool spindle and turntable plays a decisive role in the performance of the machine tool.
As a key component of the machine tool, the performance of the spindle will directly affect the rotation accuracy, speed, rigidity, temperature rise, noise and other parameters of the machine tool, which in turn will affect the processing quality of the workpiece, such as the dimensional accuracy of the part, surface roughness and other indicators. Therefore, in order to maintain excellent machining capabilities of machine tools, high-performance bearings must be used. The accuracy of bearings used on machine tool spindles should be ISO P5 or above (P5 or P4 are ISO accuracy grades, usually P0, P6, P5, P4, P2 from low to high), and for high-speed CNC machine tools, machining centers, etc. , The spindle support of high-precision machine tools needs to use ISO P4 or above accuracy; spindle bearings include angular contact ball bearings, tapered roller bearings, and cylindrical roller bearings.
1. Precision angular contact ball bearings
Among the above-mentioned types of bearings, precision angular contact ball bearings (see Figure 2) are the most widely used. We all know that the rolling elements of angular contact ball bearings are balls; because it is a point contact (different from the line contact of roller bearings), it can provide higher speed, lower heat generation and higher rotation Accuracy. In some ultra-high-speed spindle applications, hybrid bearings with ceramic balls (usually Si3N4 or Al2O3) are also used. Compared with traditional fully hardened steel balls, the characteristics of ceramic ball materials endow ceramic ball bearings with high stiffness, high speed, high temperature resistance, and long life, so as to meet the needs of high-end customers for machine tool bearing products.
2. Precision tapered roller bearings
In some machine tool applications with heavy loads and certain speed requirements—such as the grinding of forgings, the wire-turning machine of petroleum pipelines, heavy-duty lathes and milling machines, etc., choosing precision tapered roller bearings is an ideal solution . Because the rollers of the tapered roller bearing are designed in line contact, it can provide high rigidity and load capacity for the main shaft; in addition, the tapered roller bearing is a pure rolling bearing design, which can reduce the bearing operation very well. Torque and heat to ensure the speed and accuracy of the spindle. Since tapered roller bearings can adjust the axial preload (clearance) during the installation process, this allows customers to better optimize the bearing clearance adjustment during the entire life of the bearing.
3. Precision cylindrical roller bearings
In the application of machine tool spindles, double row precision cylindrical roller bearings are also used, usually in combination with precision angular contact ball bearings or thrust bearings. This type of bearing can withstand larger radial loads and allow higher speeds. The two rows of rollers in the bearing are arranged in a crossed manner, and the fluctuation frequency during rotation is significantly higher than that of a single row bearing, and the amplitude is reduced by 60% to 70%. This type of bearing usually has two forms: NN30, NN30K two series bearings with ribs on the inner ring and separable outer ring; NNU49, NNU49K two series bearings with ribs on the outer ring and separable inner ring, among which NN30K and NNU49K series The inner ring is a tapered hole (taper 1:12), which is matched with the tapered journal of the main shaft. The inner ring can be moved axially to expand the inner ring, so that the bearing clearance can be reduced or even pre-tightened the bearing (negative clearance state). Bearings with cylindrical bores are usually hot mounted, using interference fit to reduce bearing clearance, or pre-tightening the bearing. For NNU49 series bearings with a separable inner ring, the raceway is generally processed after the inner ring is equipped with a main shaft to improve the rotation accuracy of the main shaft.
Post time: Sep-14-2021