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High Temperature Bearing
High Temperature Bearing
2021-12-11
Turntable Bearing
Turntable Bearing
2021-12-11

Spindle Bearing

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, and then affect the machining quality of the workpiece, such as the dimensional accuracy and surface roughness of the parts. Therefore, in order to maintain the processing capacity of the machine tool, high-performance bearings must be used. The bearing accuracy used on the spindle of the machine tool shall be ISO P5 or above (P5 or P4 is the accuracy grade of ISO, usually P0, P6, P5, P4 and P2 from low to high). For the spindle support of high-speed and high-precision machine tools such as NC machine tools and machining centers, the accuracy of ISO P4 or above shall be selected; Spindle bearings include angular contact ball bearings, tapered roller bearings, and cylindrical roller bearings.

 

Precision angular contact ball bearing

Among the above bearings, precision angular contact ball bearings are widely used. We all know that the rolling element of angular contact ball bearing is a ball; Because it is a point contact (different from the line contact of roller bearing), it can provide higher speed, less heat and higher rotation accuracy. In some ultra-high speed spindle applications, hybrid bearings with ceramic balls (generally Si3N4 or Al2O3) will also be used. Compared with the traditional fully quenched steel ball, the characteristics of ceramic ball material endow ceramic ball bearing with the characteristics of 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.

Spindle Bearing

In terms of the contact angle of angular contact ball bearings, 15? And 25? Contact angle; Usually 15? The contact angle has relatively high speed performance, while 25? The contact angle has high axial bearing capacity. Because the choice of preload has a great impact on the application of precision angular contact ball bearing, for example, medium or heavy bearing preload is generally selected in the occasion of high load and high rigidity; For some high-speed and high-precision applications, we need to pay attention to the selection of appropriate preload in the early selection of bearings. Generally, light preload is common. Preload is generally divided into light, medium and heavy; In order to facilitate the use of customers, at present, several major bearing manufacturers in the world generally provide bearings with pre grinding bearing end faces and preloading, that is, what we usually call universal paired precision angular contact ball bearings. This type of bearing eliminates the customer’s preload adjustment, thus saving installation time.

 

Precision tapered roller bearing

In some machine tool applications with heavy load and certain requirements for speed, such as raw grinding of forgings, threading machine of oil pipeline, heavy lathe and milling machine, selecting precision tapered roller bearing is an ideal scheme. Because the roller of tapered roller bearing is designed in line contact, 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 running torque and heating of the bearing, so as to ensure the speed and accuracy of the main shaft. 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.

 

In addition, in some high-speed applications where the linear speed of inner ring flange is greater than 30 m / s, some specially designed tapered roller bearings can also meet the requirements, such as TSMA bearing or Hydra rib hydraulic floating flange bearing. The retaining edge of TSMA bearing has multiple lubricating oil holes in axial direction, which can be lubricated by circulating oil or oil mist. The centrifugal force can distribute the oil to the contact area between the roller and the retaining edge, so as to more fully lubricate the bearing and improve the bearing speed. The Hydra rib hydraulic floating flange bearing is designed to optimize the preload of the main shaft system. The bearing has a floating flange that contacts the big end of the roller, unlike the common bearing with a fixed inner ring flange; The floating flange is positioned by the “pressure” system, which can ensure that the bearing can play an excellent performance under various working conditions, and has been successfully used in domestic customers.

 

For the accuracy selection of tapered roller bearings, ISO P5 bearings are mainly used in traditional lathes and milling machines; For machining center, grinder and other applications, precision bearings of ISO P4 or above are usually selected. In the design of spindle, there are two common layout of tapered roller bearing. One is that the front end and the rear end adopt a tapered roller bearing respectively, and the face-to-face installation method is adopted; This kind of design has compact structure, high stiffness and easy installation and adjustment. The second is that two tapered roller bearings are installed face to face as the front end of the main shaft, while the rear end uses a double outer ring and two single inner ring bearings (TDO) as the floating end; Due to its floating capacity, this kind of design can well bear the axial thermal expansion of the spindle, and has high stiffness, which ensures the accuracy of the machine tool.
Precision cylindrical roller bearing

 

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 large radial load and allow high speed. The two rows of rollers in the bearing are arranged in a cross manner. When rotating, the fluctuation frequency is significantly higher than that of the single row bearing, and the amplitude is reduced by 60% ~ 70%. This kind of bearing usually has two forms: NN30 and nn30k series bearing, the inner ring has a retaining edge, and the outer ring can be separated; The outer rings of nnu49 and nnu49k series bearings are provided with retaining edges, and the inner rings can be separated.

 

Among them, the inner rings of nn30k and nnu49k series are tapered holes (taper 1:12), which cooperate with the tapered Journal of the main shaft and move the inner ring axially, which can expand the inner ring, so that the bearing clearance can be reduced or even preload the bearing (negative clearance state). Cylindrical bore bearings are usually hot installed, using interference fit to reduce bearing clearance, or preloading bearings. For nnu49 series bearings with separable inner ring, the raceway is generally finished after the main shaft is installed on the inner ring, so as to improve the rotation accuracy of the main shaft.

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