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Bearing selection and use matters needing attention

Bearing selection and use matters needing attention

2020-07-03

1. Large clearance shall be used in situations where tight fit is adopted, the difference in temperature between inner and outer rings is large, the friction torque needs to be reduced, the deep groove ball bearing bears a large axial load or the centering performance needs to be improved.

2. When the rotation accuracy is high or the axial displacement is strictly limited, the small clearance group should be adopted.

Ii. Factors related to clearance of imported bearings:

1. Coordination between bearing inner ring and shaft.

2. Coordination between bearing outer ring and housing hole.

3. The influence of temperature.

Note: The reduction of radial clearance is related to the actual effective interference size of matching parts, the size of matching axle diameter and the wall thickness of shell hole.

The selection of imported bearings and matters needing attention when using Bearings Selected Outline The types, types and dimensions of rolling bearings are varied.In order to give the expected performance of the mechanism, it is very important to select the most suitable bearing.In order to select bearings, it is necessary to analyze many important reasons and study and evaluate the procedures for bearing selection from various angles. There is no special specification, but the general sequence is as follows:

(1) Master the use conditions of mechanical devices and bearings, etc

(2) Clear requirements for bearings

(3) Select the bearing type

(4) Select the bearing configuration mode

(5) Select bearing size

(6) Select bearing specifications

(7) Select the mounting method of the bearing

It is the premise to select the suitable bearing to correctly grasp the use position and use condition of the bearing in the mechanical device.For this purpose, data and information in the following aspects are required:

(1) Function and structure of the mechanical device

(2) The use part of the bearing

(3) Bearing load (size and direction)

(4) Rotation speed

(5) Vibration and impact

(6) Bearing temperature (ambient temperature, temperature rise)

In general, the shaft is supported by two bearings in radial and axial directions. At this time, the bearing on one side is called the fixed side bearing. It bears two kinds of loads, namely, radial and axial loads, and plays the role of relative axial displacement between the fixed shaft and the bearing box.The other side is called free side, which only bears radial load, and the axial direction can move relatively, so as to solve the telescopic part of the shaft caused by temperature change and the spacing error of mounting bearing.For fixed side bearings, select bearings that can be moved axially with a rolling surface (e.g., cylindrical roller bearings) or with an assembly surface (e.g., radial ball bearings).On shorter shafts, bearings (e.g., centrist-thrust ball bearings) that move in a fixed, unidirectional axial direction are used when there is little difference between the fixed and free sides.Selection of Bearing Type It is very important to have a comprehensive grasp of the conditions of bearing use when selecting the bearing type.The following table lists the major analysis items: analysis item selection methods

1) Bearing installation space can be accommodates within the bearing installation space. As the rigidity and strength of the shaft are emphasized in the design of the shaft system, the axle diameter, namely the bearing inner diameter, is generally determined first.But the rolling bearing has a variety of sizes and types, should choose the most appropriate bearing type. 

The size, direction and nature of the bearing load [the bearing capacity is represented by the basic rated load, the value of which is shown in the bearing size table] The bearing load is variable, such as the size of the load, whether there is only radial load, whether the axial load is unidirectional or bidirectional, the degree of vibration or impact, etc.After considering these factors, then choose the most suitable bearing type.In general, the radial load capacity of bearings of the same inner diameter increases in the following order: deep groove ball bearing < angular contact ball bearing < cylindrical roller bearing < tapered roller bearing < self-aligning roller bearing

3) speed can adapt to mechanical bearing type [to benchmark the threshold of the bearing rotating speed in limiting speed, its value is shown in table bearing size] bearing limit rotational speed is not only to take on bearing type is limited to the bearing size, cage type, precision grade, load condition and lubrication method, etc., therefore, when the choice must consider these factors.The following bearings are mostly used for high-speed rotation: deep groove ball bearings, angular contact ball bearings, cylindrical roller bearings

Type of bearing with desired rotation accuracy [bearing dimensional accuracy and rotation accuracy have been standardized by GB according to bearing type] Machine tool spindles, gas turbines, and control machines require high rotation accuracy, high speed, and low friction, respectively. In this case, class 5 or higher precision bearings should be used.The following bearings are commonly used: deep groove ball bearings, contact ball bearings, cylindrical roller bearings

5) just performance to meet required for mechanical shafting rigid bearing type [bearing the load, the part of the rolling element and raceway contact will produce elastic deformation. "high rigidity" refers to the deformation of the elastic deformation smaller] reduction device at the end of the spindle and auto parts, such as in improving shaft rigidity at the same time, also must improve bearing rigidity.Roller bearings bear less deformation under load than ball bearings.The rigidity can be increased by applying preload (negative clearance) to the bearing.The method is suitable for angular contact ball bearing and tapered roller bearing. 

6) Analysis of the relative tilt between the inner and outer rings of the bearing and the factors that cause the relative tilt between the inner and outer rings of the bearing (such as deflection of the shaft caused by load, poor precision of the shaft and housing or installation error), and select the bearing type that can adapt to such service conditions.If the relative tilt between the inner ring and the outer ring is too large, the bearing will be damaged by the internal load.The bearing type that can withstand this dip should therefore be chosen.In general, tilt angles (or pitch angles) are allowed to increase in the following order: cylindrical roller bearings, tapered roller bearings, deep groove ball bearings (angular contact ball bearings), self-aligning roller bearings (ball)

7) Installation and disassembly frequency and methods of periodic inspection, etc. In case of frequent installation and disassembly, it is convenient to use cylindrical roller bearings with detachable inner ring and outer ring, needle roller bearings and tapered roller bearings.Taper hole dimming ball bearings and taper hole dimming roller bearings can be easily assembled and disassembled by using fasteners or detachable sleeves. 

Bearing structure of the selected type of machinery is not the same, the use of the bearing conditions will be different, the performance requirements are not the same, but in general, a shaft used at least two bearings.Moreover, in order to facilitate axial positioning, one bearing is mostly used as fixed end bearing, while the others are used as free end bearing.The following table lists the options for fixed-end and free-end bearing structures.

The fixed end bearing is used to position and fix the bearing in axial direction. The bearing that can bear both radial and axial loads should bear bidirectional axial loads. The corresponding strength should be considered according to the size of axial loads during installation.

Deep groove ball bearing combination angular contact ball bearing Double row angular contact ball bearing self-aligning cylindrical roller bearing with side guard (NUP type, NH type) double row self-aligning roller bearing free end bearing is used to avoid the expansion of the shaft caused by temperature change during operation and the axial position used for adjusting the bearing.It is advisable to choose bearings that only bear radial load and can be separated between inner and outer rings.When using non-separating bearing, clearance fit is generally adopted between outer ring and housing, so that axial avoidance can be done together with bearing when the shaft is telescopic.It is used to avoid the expansion of the shaft caused by the temperature change during operation and the axial position of the bearing.It is advisable to choose bearings that only bear radial load and can be separated between inner and outer rings.When using non-separating bearing, clearance fit is generally adopted between outer ring and housing, so that axial avoidance can be done together with bearing when the shaft is telescopic.Two angular contact ball bearings or tapered roller bearings which can bear axial load shall be configured and used on the front or back when the bearing spacing between fixed end and free end is small and the influence of shaft expansion is not big.Adjust the installed axial clearance with nut or gasket.Angular contact ball bearing tapered ball bearing cylindrical roller bearing (NJ, NF) tapered roller bearing tapered roller bearing is used for vertical shaft. The fixed end of tapered roller bearing is selected to bear both radial and axial loads.When the axial load of the bearing is large, the thrust bearing is combined with the axial bearing.The same free end can only bear radial load bearing, in order to avoid the expansion of the shaft.Fixed end combination angular contact ball bearing (back combination) double row tapered roller bearing (type 37000) thrust bearing and radial bearing combined installation bearing belong to precise mechanical parts, do not open the package before installation to avoid rust.For lubricated bearings and both sides with oil seal or dust cover, seal ring bearings can be installed directly without cleaning.

Methods A principle must be mastered during the installation of bearings, that is, the installation force or torque can only be transmitted through the corresponding ring.When the inner ring of the bearing fits tightly with the shaft, and the outer ring fits loosely with the hole of the bearing seat, the bearing can be first pressed on the shaft by a press, and then the shaft and the bearing together are put into the hole of the bearing seat. During the pressing, an assembly bushing (copper or mild steel) made of soft metal is mounted on the end face of the inner ring of the bearing.Bearing outer ring and bearing seat hole are tightly matched. When the inner ring and shaft are loose, the bearing can be first pressed into the bearing seat hole. At this time, the outer diameter of the sleeve assembly should be slightly smaller than the diameter of the seat hole.If the bearing ring is closely matched with the shaft and the seat hole, the inner ring and outer ring shall be pressed into the shaft and seat hole at the same time, and the structure of the sleeve shall be able to tighten the end face of the inner ring and outer ring at the same time.Heating fit An installation in which a tight fit is converted into a loose fit by heating a bearing or bearing housing.Is a common and labor-saving installation method.This method is suitable for the installation of bearing with large interference. Before hot loading, the ring of the bearing or separable bearing is put into the oil tank and heated evenly at 80-100℃. Then, it is taken out from the oil and installed on the shaft as soon as possible.When the bearing outer ring is tightly matched with the bearing seat made of light metal, the hot loading method of heating the bearing seat can avoid the abrasion of the bearing surface.Heating tank with bearing and should be at a certain distance from the bottom of a mesh, hanging hooks in the bearings, bearing on the bottom, in case of heavy impurities into the bearing or uneven heating, fuel tank must have a thermometer, strictly control the oil temperature shall not exceed 100 ℃, in order to prevent the tempering effect, reduce the hardness of the ring.The fit between thrust bearing and shaft is generally a transition fit, and the fit between seat ring and bearing seat hole is generally a clearance fit. Therefore, this kind of bearing is easy to install. The center shaft of bidirectional thrust bearing should be fixed on the shaft to prevent rotation relative to the shaft.The mounting method of the bearing is generally in the case of shaft rotation, so the coordination between the inner ring and the shaft is excessive and the coordination between the bearing outer ring and the bearing chamber is clearance coordination.

Bearing operation inspection Bearing installation after the inspection, should ensure that the bearing installed in place, flexible rotation, no stuck phenomenon, such as improper installation of the bearing, the bearing temperature will rapidly rise and damage, or even bearing stuck fracture and other major accidents.(1) When the bearing is in use, keep the surrounding environment clean and do not stick to sweat and dirt on the hand.It should be used by personnel who are familiar with bearings, especially for injury, indentation, underdamage, etc.In order to ensure the performance of the bearing, the bearing should be regularly maintained, maintained and overhauling according to the operating standard of the equipment, including monitoring the running state, lubricant supplementation and regular disassembly and inspection.(2) Bearing shall not be stored directly on the ground (above 30cm from the ground) to avoid direct light and cold walls.In order to prevent rust, the bearing should be kept in an environment with a temperature of about 20℃ and humidity below 65%. The bearing should be placed in acid air, which is easy to rust and change color. It is necessary to wipe the bearing, shaft and shell with gloves and kapok return wire.


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