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Machine tool experts must know the bearing type selection analysis data, you must not know!

2020-03-28

As the core component of machine tool spindle and turntable, bearing plays an important role in the performance of machine tool. This paper mainly describes the selection of spindle bearing and turntable bearing. As a key component of machine tool, spindle performance will directly affect the rotation accuracy, speed, rigidity, temperature rise, noise and other parameters of the machine tool, and then affect the processing quality of the workpiece. In order to maintain excellent machining ability of machine tools, high performance bearings must be used. < / P > 1 Selection of spindle bearing < / P > the bearing accuracy used for machine tool spindle should be isop5 or above (P5 or P4 is the ISO precision level, usually from low to high is (P0, P6, P5, P4, P2), but for the spindle support of high-speed and high-precision machine tools such as CNC machine tools and machining centers, the accuracy of isop4 or above should be selected. Spindle bearings include angular contact ball bearings, tapered roller bearings, and cylindrical roller bearings. Precision angular contact ball bearing is widely used, the rolling element of angular contact ball bearing is ball, because it is a kind of point contact (different from linear contact of roller bearing), so it can provide higher speed, smaller heat output and higher rotation accuracy. In some ultra-high speed spindle applications, ceramic ball (generally Si3N4 or Al203) hybrid bearings are used. Metalworking reporter thinks that compared with the traditional fully hardened steel ball, the characteristics of ceramic ball material endow ceramic ball bearing with high stiffness, high speed, high temperature resistance and long service life, so as to meet the needs of high-end customers for machine tool bearing products. In terms of contact angle of angular contact ball bearings, the contact angles of 15 and 25 are more popular at present; generally, the contact angle of 15 has higher speed performance, while the contact angle of 25 has higher axial bearing capacity. Because the selection of preload has a great impact on the application of precision angular contact ball bearings, for example, in the case of high load and high rigidity, the medium or heavy bearing preload is generally selected; for some high-speed and high-precision applications, it is necessary to pay attention to the selection of appropriate preload in the early selection of bearings. Metal processing experts said that preload is generally divided into light, medium and heavy three kinds, generally light preload is more common. In order to facilitate the use of customers, at present, several major bearing manufacturers in the world generally provide pre grinding bearing end face and preloading bearing, which is commonly known as universal matching precision angular contact ball bearing. This kind of bearing eliminates the customer's preload adjustment, thus saving the installation time. In the application of machine tool spindle, double row precision cylindrical roller bearing will also be used, usually combined with precision angular contact ball bearing or thrust bearing. This kind of bearing can bear larger radial load and allow higher speed. Two rows of rollers are arranged in a cross way in metalworking on-line bearing. The fluctuation frequency is greatly increased and the amplitude is reduced by 60% - 70% when rotating. This kind of bearing usually has two forms: NN30, nn30k two series bearing inner ring with rib, the outer ring can be separated; nnu49, nnu49k two series of bearing outer ring with rib, inner ring can be separated, of which nn30k and nnu49k series inner ring are tapered hole (taper 1:12), with the conical Journal of the spindle, axial movement of the inner ring can make the inner ring swell, so that the bearing clearance can be reduced or even pre emptive Tight bearing (negative clearance state). The cylindrical bore bearing is usually hot installed, using interference fit to reduce bearing clearance, or preloading bearing. For nnu49 series bearings with separable inner rings, the raceway is generally machined after the inner ring is installed with the spindle to improve the spindle rotation accuracy. In some heavy load machine tool applications with certain speed requirements, such as rough grinding of forgings, thread turning machine of oil pipeline, heavy lathe and milling machine, the selection of precision tapered roller bearing is an ideal scheme. Because the roller of tapered roller bearing is linear contact design, it can provide high rigidity and load for the main shaft; in addition, tapered roller bearing is a pure rolling bearing design, which can well reduce the bearing running torque and heat, so as to ensure the spindle speed and accuracy. Because tapered roller bearings can adjust axial preload (clearance) during installation, this allows customers to better adjust the bearing clearance during the entire service life of the bearing.