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Reasonable selection of bearings for machine tool spindles and rotary tables
Source: China Bearing Network Time: 2013-01-09
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Reasonable selection of spindle bearings For bearing precision on machine tool spindles should be ISO P5 or above (P5 or P4 is ISO accuracy grade; generally from low to high is P0, P6, P5, P4, P2); For the spindle support of high-speed, high-precision machine tools in the middle of machining; ISO P4 or higher accuracy is required. Spindle bearings include angular touch ball bearings, tapered roller bearings, and cylindrical roller bearings.
1. Fine angle touch ball bearings are among the above mentioned bearings; the fine angle touch ball bearings (Fig. 1) are the most widely used. The roll of the angular touch ball bearing is the ball; because it is a point touch (different from the roller) Bearing line touch); therefore can supply higher speed, smaller heat and higher rotation accuracy. In some ultra-high speed spindle applications; ceramic ball (usually Si3N4 or Al2O3) is also used. Type bearing. Compared with the traditional fully hardened steel ball; the characteristics of the ceramic ball material give the ceramic ball bearing the characteristics of high rigidity, high speed, high temperature resistance and long service life; then satisfied with the demand of high-end customers for the bearing products of the machine tool.
The fine angle touch ball bearing is in terms of the touch angle of the angular touch ball bearing; the current popular touch angle is 15 and 25, generally the touch angle of 15 has a relatively high speed function; and the touch angle of 25 has a higher axis. Because of the preloading selection, the influence on the application of the fine-angle touch ball bearing is very large; for example, in the case of high load bearing and high rigidity; the medium or heavy bearing preload is generally selected, and some high speed and high are aligned. The application of precision; in the early selection of bearings; the demand pays attention to the selection of suitable preload. The preload is generally divided into three types: light, medium and heavy; general light preload is more common. In order to facilitate the use of customers; the current world Several major bearing manufacturers all supply pre-grinded bearing end faces and preloaded bearings; that is, the all-purpose pairing fine angle touch ball bearing method is generally mentioned. This type of bearing eliminates the customer's preload conditioning; then saves equipment time.
2. Fine tapered roller bearings are used in some heavy-duty machine tools where there is a certain need for speed; such as the forging of forgings, the wire machine for oil pipelines, heavy-duty lathes and milling machines; the selection of fine tapered roller bearings is a comparison The plan of ambition. Because the roller of the tapered roller bearing is a line touch; therefore it can supply the spindle with high rigidity and load, and the other; the tapered roller bearing is a purely tumbling bearing depiction; it can be very Goodly reduce the bearing torque and heat generation; then ensure the spindle speed and accuracy. Because the tapered roller bearing can adjust the axial preload (play) during the equipment process; this allows the customer to better in the entire operating cycle of the bearing Optimize bearing clearance conditioning
In addition, in some high-speed applications where the inner ring rim speed is greater than 30 m/s; some specially described tapered roller bearings are also satisfactory; such as TSMA bearings or Hydra-Rib hydraulic floating bearing (Figure 2) The rib of the TSMA bearing has a plurality of smooth oil holes in the axial direction; the circulating oil can be smooth or the oil mist can be smooth; the centrifugal force can spread the oil to the roller and the rib touch area; then the bearing can be more smoothly smoothed; Bearing speed. Hydra-Rib hydraulic sling bearing is designed to optimize the preload of the spindle system; the bearing has a rib that can float; touch with the big end of the roller; unlike the common bearing has a fixed inside The rim is positioned, and the damper is positioned by the “pressure†system; this ensures that the bearing can perform the best functions under all working conditions and has been successfully used in domestic customers.
The spindle with hydraulic lifting bearing is drawn to the accuracy of the tapered roller bearing; the ISO P5 bearing is mainly used in traditional lathes and milling machines, if it is used in machining, grinding, etc.; generally select ISO P4 Fine bearing or above. In the description of the main shaft; there are two kinds of common tapered roller bearing designs. The first one is to use a tapered roller bearing for each of the front end and the rear end; and the device method facing the surface is selected; Compact layout; high stiffness and easy equipment and conditioning.
The second is to use two tapered roller bearings to face the front end of the machine as the main shaft; while the rear end uses a double outer ring and two single inner ring bearings (TDO) as the floating end, because it has the ability to float; The class description can well accept the axial thermal expansion of the spindle; and the stiffness is high; the accuracy of the machine is ensured.
3. Fine cylindrical roller bearings are used in machine tool spindles; double row fine cylindrical roller bearings are also used; generally used in combination with fine angle touch ball bearings or thrust bearings. These bearings can accept large radial loads and It promises a higher speed. The two rows of rollers in the bearing are placed in the interspersed manner; the shaking frequency is greatly improved compared with the single-row bearing when rotating; the amplitude is reduced by 60% to 70%. There are generally two methods for such bearings: NN30, NN30K The inner ring of the two series of bearings has a rib; the outer ring can be separated, and the outer rings of NNU49 and NNU49K bearing the outer ring; the inner ring can be separated; the inner ring of NN30K and NNU49K series is a taper hole (taper 1:12); Cooperate with the tapered journal of the main shaft; move the inner ring axially; the inner ring can be inflated; thus the bearing clearance can be reduced or even pre-tensioned (negative clearance condition). Cylindrical bore bearings are generally hot-fitted; Interference cooperation reduces bearing clearance; perhaps pre-tightening bearings. NNU49 series bearings that can be separated from the inner ring; generally the inner ring is fitted with the main shaft and then the raceway is finished; to improve the spindle rotation accuracy.
Reasonable selection of rotary table bearings The reversing workbench commonly used in CNC machine tools has an indexing table and a CNC reversing table. The time when the CNC machine tool processes certain parts; except for the line that requires three axes of X, Y and Z Outside the feed movement; sometimes the demand also has a circular motion around the three axes of X, Y, Z; do not call the A, B, C axis.
The CNC reversing workbench can be used to complete the circumferential feed motion; in addition to this; it can also complete the indexing movement. The function of the indexing workbench only transforms the workpiece into a face; cooperate with the active tool changer; Once the equipment can complete several processes of several faces; therefore; greatly improve the efficiency of the work. The shape of the CNC turntable and the indexing workbench are not much different; but the layout has a series of features. Because the CNC turntable can be completed It gives motion; therefore, it has many things in common with the feed drive organization of CNC machine tools. The difference is that the drive organization is finished with linear feed motion; and the CNC turntable is finished with circular feed motion.
The reversing workbench is widely used in various CNC milling machines, boring machines, various vertical vehicles, and vertical milling machines. In addition to the demand reversing workbench, it can well accept the workpiece component; it also needs to ensure its reverse under load. Accuracy. Turntable bearing; as the core component of the turntable; in the working process of the turntable; not only has a high carrying capacity; it also needs to have high reversal accuracy, high anti-overturning ability, and high speed.
1. Thrust ball bearing + cylindrical roller bearing Thrust ball bearing can accept a certain axial force; therefore, the bearing is mainly used to accept the component of the workpiece, while the cylindrical roller bearing is mainly used for radial positioning and receiving external radial force ( Such as cutting force, milling force, etc.). This type of painting is widely used; and the cost is relatively low. Because the thrust ball is a point-touch bearing; so its axial bearing capacity is relatively limited; The medium-sized machine tool reverses the workbench. In addition, the smoothness of the thrust ball is also difficult.
2. Hydrostatic bearing + fine cylindrical roller bearing The hydrostatic bearing is a kind of externally supplied pressure oil; a static pressure bearing oil film is built in the bearing to complete the smooth sliding bearing of the liquid. The hydrostatic bearing has been smooth under the liquid from start to stop. Work; so there is no wear; long life; start power. Huai sent 猓 庵 庵 å²¢ å²¢ å²¢ å’•å“‚ å’•å“‚ å’•å“‚ æ’¸ æ’¸ æ’¸ æ’¸ æ¹ã˜æ–© æ¹ã˜æ–© æ¹ã˜æ–© æ¹ã˜æ–© . 精细 精细 精细 精细 精细 精细 精细 精细 精细 精细 精细 精细 精细 精细 精细 精细 精细 精细 精细Good radial bearing capacity; and because of the selection of fine-grade bearings; the reversal accuracy of the reversing workbench can also be ensured. The reversing workbench depicted in this class can accept high axial forces; some workpieces The component exceeds 200t; the diameter of the turntable exceeds 10m. However, there are some shortcomings in this type of depiction; because static pressure bearings need to supply a special oil supply system to supply pressure oil; the protection is more complicated; and the cost is higher.
3. The interspersed roller bearing interspersed roller bearing (Fig. 3) is more widely used on the rotary table. The interspersed roller bearing is characterized by two raceways in the bearing, two rows of inserted rollers, and a conventional thrust bearing + The radial centering bearing combination is comparable (Fig. 4); the interspersed roller bearing is compact and compact; it simplifies the drawing of the workbench; then reduces the cost of the turntable.
Others; because of the optimized pre-tightening force; this kind of bearing has high rigidity; therefore, the rigidity and precision of the turntable are also ensured. Thanks to the drawing of the two rows of inserting rollers; the useful span of the bearing It is obviously improved; therefore, this type of bearing has a high anti-overturning moment. In the interspersed roller bearing; there are two types of reddening: the first is a cylindrical interspersed roller bearing; the second is a conical interspersed roller bearing. Cylindrical interspersed roller bearings are less expensive than conical insert roller bearings; they are suitable for use in rotary turrets with relatively low rotational speeds, while conical interspersed roller bearings are characterized by pure tumbling of tapered rollers; with high precision; Reduced shaft length and processing cost, etc. The interspersed roller bearings are suitable for various types of vertical or horizontal boring machines; as well as vertical grinding, vertical lathes and large gear milling machines.
In short, the bearing is the core component of the machine tool spindle and turntable; it plays an insignificant effect on the machine tool's work. In order to select the appropriate size and type of bearing; we need to summarize the various working conditions; for example, working speed, smooth, equipment Type, spindle stiffness, precision, etc.. As far as the bearing itself is concerned; as long as it fully understands its depiction characteristics and the advantages and disadvantages brought about by it; it can carry out the best function of the bearing.
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