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What kinds of bearings are commonly used in machine tool spindles?

Update:01-09-2020
Summary:

There are five types of bearings commonly used in machi […]

There are five types of bearings commonly used in machine tool spindles: deep groove ball bearings, angular contact ball bearings, two-way thrust angular contact ball bearings, double row cylindrical roller bearings, and tapered roller bearings.
Deep groove ball bearings 1. This type of bearing is generally only used to bear radial load. Since the clearance is not adjustable, it is often used in occasions that require low precision and do not need preload, such as ordinary drilling machine spindles. 2. Angular contact ball bearings can bear radial and axial loads at the same time. Because they will cause internal axial forces when they bear radial loads, they should be installed and used. The configuration methods are "back to back" and "face to face". , "Series" and "multiple", etc., and the rigidity of the main shaft can be improved by pre-tensioning. This type of bearing has three contact angles of 15°, 25°, and 40°. The B7000CY high-precision angular contact ball bearing with a contact angle of 15° is a special bearing specially designed for the spindle of a high-speed grinder. The bearing has an internal structure design. In addition to the change, the rings and rolling elements are made of high-quality electroslag bearing steel.
The material of the cage is phenolic laminated cloth tube, with tolerance grades of 5, 4 and 2. Therefore, this type of bearing has high rotation accuracy and limit speed, low friction and low temperature rise. 3. Two-way thrust angular contact ball bearings usually use 230,000-type two-way thrust angular contact ball bearings, with a contact angle of 60°, which is held by a seat ring with lubricating oil holes, two shaft washers, a spacer ring and two sets of steel balls. Frame components. Choosing the right spacer height can make the bearing have the required preload after assembly.
This type of bearing can bear bidirectional axial load, has good rigidity, low temperature rise during normal lubrication, high speed, and easy to assemble and disassemble. As a new structure, it is currently mostly used for spindles such as grinding machines, lathes, boring machines, milling machines, drilling machines, etc. Above, it is often combined with double row cylindrical roller bearings in use. 4. Double-row cylindrical roller bearings are able to withstand larger radial loads and allow higher speeds. The two rows of rollers in the bearing are arranged in a crossed manner, the fluctuation frequency during rotation can be doubled compared with the single row bearing, and the amplitude is reduced by 70%.
There are two types of commonly used bearings of this type: NN30/W33, NN30K/W33 two series bearings with ribs on the inner ring and separable outer ring; NNU49/W33, NNU49K/W33 two series bearings with ribs on the outer ring and inner The inner ring can be separated. The inner ring of NN30K/W33 and NNU49K/W33 series has 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 to reduce Small bearing clearance even pre-tighten the bearing. Cylindrical bore bearings are usually hot-mounted to reduce the bearing clearance by using interference fit, or to achieve the purpose of preloading. For NNU49 series bearings with a separable inner ring, the raceway is generally processed after the inner ring is equipped with a spindle to obtain high spindle rotation accuracy. 5. Tapered roller bearings can bear radial and axial loads at the same time, and double-row tapered roller bearings can bear bidirectional axial loads.
Due to the sliding friction between the big end of the tapered roller and the rib of the inner ring, the limit speed is often lower than that of cylindrical roller bearings of the same size. Hollow tapered roller bearings can use oil to cool the rollers to reduce the temperature rise and increase the allowable speed. However, the manufacturing process of this kind of bearing is complicated, and the requirements for the lubrication system of the machine tool are also high, and it is generally only used on the horizontal spindle with special requirements.

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