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A brief introduction of commonly used machine tool spindle bearing types

by:JNSN     2021-11-04

Bearing, as the core component 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 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 accuracy of the bearings 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 The spindle supports of high-speed and high-precision machine tools such as CNC machine tools and machining centers need to use ISOP4 or higher accuracy. Spindle bearings include angular contact ball bearings, tapered roller bearings, and cylindrical roller bearings.

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1. Precision angular contact ball bearings

Precision angular contact ball bearings are widely used. The rolling elements of angular contact ball bearings are balls because it is a point contact (different from rolling The line contact of the sub-bearing), so it can provide higher speed, smaller heat generation and higher rotation accuracy. In some ultra-high-speed spindle applications, ceramic balls (usually si3N4 or Al203) are also used. Hybrid bearings. Metal processing reporters believe that compared with traditional fully hardened steel balls, the characteristics of ceramic ball materials endow ceramic ball bearings with high rigidity, high speed, high temperature resistance, and long life, so as to meet the needs of high-end customers. The demand for machine tool bearing products.

As far as the contact angle of angular contact ball bearings is concerned, the contact angles of 15 and 25 are currently more popular; usually the contact angle of 15 has a relatively high speed performance, while the contact angle of 25 The contact angle has a high axial load capacity. Because the choice of preload has a great influence on the application of precision angular contact ball bearings, such as high load and high rigidity occasions, medium or heavy bearing preloads are generally selected; For some high-speed and high-precision applications, in the early selection of bearings, you need to pay attention to selecting the appropriate preload. Metal processing experts said that preloads are generally divided into three types: light, medium, and heavy. Generally, light preload is compared. Common. In order to facilitate the use of customers, several major bearing manufacturers in the world generally provide bearings with pre-ground and preloaded bearing end faces, which is what people usually call the form of universal paired precision angular contact ball bearings. This type of bearing is free of charge. The customer’s preload adjustment is eliminated, thereby saving installation time.

2. 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. Such bearings can withstand larger radial loads and allow higher speeds. Two-row rollers in metal processing in-line bearings Subs are arranged in a cross pattern. The fluctuation frequency during rotation is significantly higher than that of single-row bearings, and the amplitude is reduced by 60%-70%. This type of bearing usually has two forms: NN30 and NN30K two series bearings with ribs on the inner ring and separable outer ring ; The outer ring of NNU49 and NNU49K series bearings has ribs and the inner ring can be separated. Among them, the inner ring of NN30K and NNU49K series has a tapered hole (taper 1:12), which is matched with the tapered journal of the main shaft to move the inner ring axially. , The inner ring can be expanded, so that the bearing clearance can be reduced or even pre-tightened the bearing (negative clearance state). Cylindrical bore bearings are usually hot mounted, using interference fit to reduce the bearing clearance, or Preload 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.

3. Precision tapered roller bearings

In some machine tool applications with heavy loads and certain speed requirements, such as forgings, oil pipelines For wire-cutting machines, heavy-duty lathes and milling machines, 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 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.

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