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    浙江本盛軸承有限公司

    Zhejiang Bensheng Bearing Co.,Ltd.

    HOME >> NEWS >>Industry dynamic >> How to Choose High Quality Machine Bearing
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    How to Choose High Quality Machine Bearing

    As the core parts of the spindle and turntable of machine tool, bearing plays a pivotal role in the performance of machine tool. As a key part of machine tool, the performance of spindle will directly affect the machine tool rotation accuracy, speed, rigidity, temperature rise and noise parameters, and then affect the quality of the workpiece. In order to maintain excellent machining ability, high performance bearings must be used.

    How to Choose High Quality Machine Bearing

    First, the selection of spindle bearings

    Bearing accuracy on the spindle of the machine tool should be ISOP5 or above(P5 or P4 is the ISO accuracy level, usually from low to high(P0, P6, P5, P4, P2), For the spindle support of high-speed, high-precision machine tools such as CNC machine tools and processing centers, the accuracy of ISOP4 or above is required. The spindle bearings include angular contact ball bearings, conical roller bearings, and cylindrical roller bearings.

    1, dense corner contact ball bearings

    The precision corner contact ball bearings are widely used. The angular contact ball bearing's roller body is the ball because it is a point contact(different from the line contact of the roller bearing), so it can provide higher speed and smaller heat. And higher rotation accuracy. In some ultra-high-speed spindle applications, mixed bearings with ceramic balls(usually si3N4 or Al203) are also used. Metal processing reporter believes that compared with the traditional fully hardened steel ball, the characteristics of the ceramic ball material itself give the ceramic ball bearing the characteristics of high stiffness, high speed, high temperature resistance, and long life, so as to meet the high-end customers 'needs for machine tool bearing products.

    As far as the contact angle of the corner contact ball bearing is concerned, the contact angles of 15 and 25 are more popular at present; Usually the contact angle of 15 has a relatively high rotational speed performance, while the contact angle of 25 has a higher axial bearing capacity. Because the pre-loading choice has a great influence on the application of precision corner contact ball bearings, such as in the case of high load and high rigidity, medium-sized or heavy bearing preloading is generally used; For some high speed and high precision applications, in the early selection of bearings, it is necessary to pay attention to the selection of suitable preloading. Metal processing experts said that preloading is generally divided into light, medium, and heavy, and light preloading is more common. In order to facilitate the use of customers, several major bearing manufacturers around the world generally provide pre-grinding bearings with pre-loaded bearings, which is commonly referred to as universal pairing precision corner contact ball bearings. This type of bearing eliminates the customer's pre-load adjustment, thus saving installation time.

    2, precision cylindrical roller bearings

    In the application of machine tool spindle, double-row precision cylindrical roller bearings are also used, usually in combination with precision corner contact ball bearings or thrust bearings. Such bearings can withstand larger radial loads and allow higher rotational speeds. The two rows of rollers in the metal machining online bearings are arranged in a cross-mode, and the frequency of fluctuations during rotation is significantly higher than that of single bearings, and the amplitude is reduced by 60-70 %. Such bearings usually have two forms: NN30, NN30K two series of bearings with a block edge, the outer ring can be separated; The NNU 49 and NNU 49K two series of bearings have outer rings with bounding edges, and the inner rings can be separated. The inner rings of the NN 30K and NNU 49K series are cone-holes(cone-degree 1:12), and they cooperate with the conical shaft neck of the main axis, and the axial movement of the inner ring, The inner ring can be enlarged so that the bearing clearance can be reduced or even pre-tightening the bearing(negative clearance state). Cylinder bore bearings are usually hot mounted, with excess balance to reduce the clearance of the bearings, or to pre-tighten the bearings. For the NNU 49 series bearings that can be separated in the inner ring, the main shaft is generally installed in the inner ring and then the Raceway is refined to improve the rotation accuracy of the main shaft.

    3, precision cone roller bearings

    In some heavy load machine tool applications with certain speed requirements, such as forgings, oil pipelines, heavy lathes and milling machines, the choice of precision conical roller bearings is an ideal solution. Since the roller of the cone roller bearing is designed for line contact, it can provide high stiffness and bearing load for the spindle; In addition, conical roller bearing is a pure rolling bearing design, which can reduce the operating torque and heat of the bearing, so as to ensure the speed and accuracy of the spindle. Since conical roller bearings can adjust axial preload(clearance) during installation, this allows customers to better optimize bearing clearance during the entire life cycle of bearings.

    Selection of bearings for turntable

    The rotary worktables commonly used in CNC machine tools include fractional worktables and numerical control rotary worktables. When machining certain parts, CNC machine tools sometimes require circular motion around the X, Y, and Z axes in addition to the linear feed motion of the X, Y, and Z axes, which are called A, B, and C axes, respectively. The CNC rotary table can be used to realize the circular feed movement. In addition, it can also complete the fractional motion. The function of the sub-table is only to change the face of the workpiece and use the automatic knife changing device to achieve a variety of processes that can be completed on several sides at a time. Therefore, the work efficiency is greatly improved. There is not much difference between the shape and the scale table of the on-line CNC turntable of metal machining, but it has a series of characteristics in the structure. Since the CNC turntable can realize the feed movement, it has many similarities in structure and the feed drive mechanism of the CNC machine tool. The difference is that the driving mechanism realizes the linear feed movement, while the CNC turntable realizes the circular feed movement.

    The rotary work table is widely used in a variety of CNC milling machines, boring machines, various standing vehicles and milling machines. In addition to the requirement that the rotary worktable can withstand the weight of the workpiece well, it is also necessary to ensure its rotary accuracy under the load. As the core part of the turntable, the turntable bearing must not only have high bearing capacity during the turntable operation, but also have high rotary accuracy, high anti-overturning ability, and high rotational speed ability.

    1, thrust ball bearing cylindrical roller bearing

    The thrust ball bearing can withstand a certain axial force, so the bearing is mainly used to withstand the weight of the workpiece; Cylinder roller bearings are mainly used for radial positioning and bearing external radial forces(such as cutting force, milling force, etc.). This kind of design is widely used and the cost is relatively low. Since the thrust ball is a point-contact bearing, its axial bearing capacity is relatively limited and is mainly used for small or medium-sized machine tool rotary worktables. In addition, the lubrication of the thrust ball is also difficult.

    2, static pressure bearings precision cylindrical roller bearings

    Static bearing is a kind of sliding bearing that can be lubricated by establishing the oil film of static bearing in the bearing by external supply of pressure oil. Static bearing is always working under lubrication from start to stop, so there is no wear, long service life, and low starting power; In addition, this kind of bearing also has the advantages of high rotation accuracy, large oil film stiffness, and can suppress oil film oscillation. Precision cylindrical roller bearings have very good radial bearing capacity, and the rotary precision of the rotary table can also be guaranteed due to the use of precision bearings. The rotary worktable using this type of design can withstand high axial force. Some workpieces weigh more than 200t and the turntable diameter exceeds 10m. However, this kind of design also has some shortcomings. Since the static bearing must be accompanied by a special oil supply system to supply the pressure oil, the maintenance is relatively complicated and the cost is relatively high.

    3, cross roller bearings

    The application of cross roller bearings on Turntable is quite common. The cross roller bearing is characterized by two raceways in the bearing and two rows of crossed raceways. Compared with the traditional combination of thrust bearing radial centring bearings, the cross-roller bearings are compact and compact, and the design of the workbench is simplified, thus reducing the cost of the turntable. Due to the use of optimized preloading force, this type of bearing has a high stiffness, so the stiffness and accuracy of the turntable are also guaranteed. Due to the design of two rows of cross rollers, the effective span of the bearing can be significantly improved, so this type of bearing has a high anti-overturning moment. In cross roller bearings, there are two types: the first is a cylindrical cross roller bearing, and the second is a conical cross roller bearing. Generally, the price of cylindrical cross roller bearings is lower than that of conical cross roller bearings, which is suitable for applications with relatively low rotational speed; The tapered cross roller bearing adopts the pure rolling design of tapered roller, which has the advantages of high operation accuracy, strong speed, and reduced shaft length and processing cost. Cross-roller bearings are suitable for various types of vertical or horizontal boring machines, as well as vertical grinding, standing and large gear milling machines.

    To sum up, in order to be able to select the proper size and type of bearings, it is necessary to comprehensively consider various working conditions, such as running speed, lubrication, installation type, Spindle stiffness, precision, etc.. As far as the bearing itself is concerned, only by fully understanding its design characteristics and the advantages and disadvantages brought about by it, can the performance of the bearing be fully realized. As the core parts of the spindle and turntable of machine tool, bearing plays a pivotal role in the performance of machine tool.


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    TEL:+86 0635-2262222

    ADD:Shandong Linqing Yandian Bearing market


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