Bearings, as the core components of the machine tool spindle and turntable, play 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 Precision Spindle Assembly accuracy, speed, rigidity, temperature rise and noise of the machine tool, and then affect the processing quality of the workpiece. In order to maintain excellent machining capabilities of machine tools, high-performance bearings must be used.
The bearing accuracy used on the machine tool spindle should be ISOP5 or above (P5 or P4 is the ISO accuracy grade, usually from low to high (P0, P6, P5, P4, P2), and for high-speed CNC machine tools, machining centers, etc. , The spindle support of high-precision machine tools requires ISOP4 or above accuracy. Spindle bearings include angular contact ball bearings, tapered roller bearings, and 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 metal processing in-line bearing are arranged in a cross manner, and the fluctuation frequency during rotation is greatly increased compared with that of a single row bearing, and the amplitude is reduced by 60%-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, of 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 status). 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 spindle to improve the spindle rotation accuracy.