TEDIN Bearing Co., Ltd.
Tel.: 0086-379 67301199
M.P: 0086-136 63889399
As the key component of machine tool, the performance of spindle will directly affect the rotation precision, rotation speed, rigidity, temperature rise and noise of the machine tool, and then affect the machining quality of the workpiece. Bearing accuracy for spindle of machine tool should be ISOP5 or above (P5 or P4 is the precision grade of ISO, usually from low to high to P0 / P6 / P5 / P4 / P2).
Spindle bearings include angular contact ball bearings, tapered roller bearings, and cylindrical roller bearings.
1. Precision angular contact ball bearings:
Precision angular contact ball bearings are widely used for machine tools. Their rolling elements are balls, because it is a point contact (different from the line contact of roller bearings), so it can provide higher rotational speed, but with smaller heat and higher precision of rotation.
As far as the contact angle of angular contact ball bearings is concerned, the contact angles of 15 and 25 are popular at present, and usually the contact angles of 15 have higher rotational speed performance and 25 have higher axial bearing capacity. Because bearing preload has a great influence on the application of precision angular contact ball bearing, for example, for high bearing load and high rigidity applications, the medium or heavy bearing preload is generally used. For some high-speed and high-precision applications, in the early selection of bearings, we should pay attention to the selection of appropriate preload. In order to easily be assembled, at present, some famous bearing manufacturers in the world generally provide pre-grinding endface for pre-loading the bearing, which is commonly known as universal paired precision angular contact ball bearings. This type of bearing eliminates the customer to adjust the bearing before installation, thus saving time.
2. Double row cylindrical roller bearings (NN type):
In the application of machine tool spindle, double-row precision cylindrical roller bearings are also used, usually combined with precision angular contact ball bearings or thrust bearings. This type bearings can withstand larger radial loads and higher speeds. The two rows of rollers in the bearing are arranged in a cross way. The frequency of fluctuation is greatly increased than that of the single row bearing, and the amplitude is reduced by 60-70. This type bearing usually comes in two forms: NN30, NN30K, their inner ring with flange, outer ring can be separated; NNU49, NNU49K, their outer ring with flange, inner ring can be separated. The inner rings of NN30K and NNU49K series are with conical holes (1:12 taper), which are matched with the tapered journal of the spindle. Axial movement of the inner ring can cause the inner ring to swell, so that the bearing clearance can be reduced or even preloaded (negative clearance state). The bearings with cylindrical holes are usually hot-packed, interference fit is used to reduce bearing clearance, or preload bearing. For the NNU49 series bearings with detachable inner ring, the inner ring is installed with the spindle and then the raceway is finely machined to improve the rotation accuracy of the spindle.
3. Precision tapered roller bearings:
In some applications of heavy load machine tools with certain requirements for speed, such as the waste grinding of forgings, oil pipeline wire machines, heavy duty lathes and milling machines, it is an ideal scheme to select precision tapered roller bearings. Because the roller of tapered roller bearing is the design of line contact, it can provide high rigidity and bearing capacity for spindle. In addition the tapered roller bearing is a kind of pure rolling bearing design which can reduce the running torque and heat of the bearing and ensure the rotation speed and accuracy of the spindle. Since tapered roller bearings can adjust axial preload (clearance) during installation, this allows customers to better optimize bearing clearance adjustment throughout the bearing life cycle.