Bearing selection and matters needing attention when using bearing selection profile the types, types and sizes of rolling bearings are various.It is essential to select the most suitable bearing for the desired performance of the mechanism.In order to select the bearing, it is necessary to analyze a number of important reasons, and study and evaluate the bearing selection procedures from various angles. There is no special specification, but the general order is as follows:
(1) master the operating conditions of mechanical devices and bearings
(2) specify requirements for bearings
(3) select the bearing type
(4) select the bearing configuration
(5) select bearing size
(6) select bearing specifications
(7) select the installation method of bearing
The use condition and environment condition of bearing it is the premise of selecting suitable bearing to correctly grasp the use position of bearing in the mechanical device and the use condition and environment condition.In order to do this, data and information are required in the following areas:
(1) function and structure of mechanical device
(2) use site of bearing
(3) bearing load (size and direction)
(4) rotation speed
(5) vibration and impact
(6) bearing temperature (ambient temperature, temperature rise)
(7) the surrounding atmosphere (corrosion, clean, lubricity) the choice of the ways of bearing configuration, usually axis in two bearings in the radial and axial support, at this point, called the bearing on one side of the fixed side bearing, it bear radial and axial load, the fixed axis and the relative axial displacement between the bearing box.The other side is called the free side, which can only bear the radial load, and the axial direction can be moved relatively, so as to solve the problem of the expansion part of the shaft caused by the temperature change and the spacing error of the mounting bearing.For fixed side bearings, select bearings that can be moved axially by rolling surfaces (such as cylindrical roller bearings) or by assembly surfaces (such as centripetal ball bearings).In the case that there is little difference between the fixed side and the free side on the shorter shaft, a bearing (such as a centripetal thrust ball bearing) with only one-way fixed axial movement is used.When choosing the bearing type, it is very important to master the use conditions of the bearing.The following table lists the main analysis items: analysis item selection methods
1) the mounting space of the bearing can accommodate the bearing type in the bearing mounting space. Due to the emphasis on the rigidity and strength of the shaft when designing the shaft system, the shaft diameter is generally determined first, that is, the bearing inner diameter.However, there are a variety of bearing size series and types, should choose the most appropriate bearing type.
2) bearing load size, direction and nature of bearing load [bearing load capacity is expressed by the basic rated load, its value is contained in the bearing size table] bearing load varies, such as the size of the load, whether there is only radial load, axial load is one-way or two-way, the degree of vibration or impact, and so on.After taking these factors into consideration, then choose the most suitable bearing type.Generally speaking, the radial load capacity of the bearing with the same inner diameter increases in the following order: deep groove ball bearing < angular contact ball bearing < cylindrical roller bearing < tapered roller bearing < centering 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
4) rotation precision bearing type with required rotation precision [the dimensional accuracy and rotation precision of the bearing have been standardized by GB according to the bearing type] machine tool spindle, gas turbine and control machine respectively require high rotation precision, high speed and low friction, at this time should be used more than grade 5 precision bearing.Generally use the following bearings: 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.Preload (negative clearance) is applied to the bearing to improve rigidity.The method is suitable for angular contact ball bearings and tapered roller bearings.
6) the relative tilt analysis of the inner ring and the outer ring causes the relative tilt of the bearing inner ring and the outer ring (such as the deflection of the shaft caused by the load, the accuracy of the shaft and the shell is poor or the installation error), and the bearing type that can adapt to this operating condition is selected.If the relative inclination between the inner ring and the outer ring is too large, the bearing will be damaged due to the internal load.Bearing types that can withstand this tilt should therefore be selected.Generally speaking, the inclination Angle (or centering Angle) is allowed to increase in the following order: cylindrical roller bearings, tapered roller bearings, deep groove ball bearings (angular contact ball bearings), centering roller (ball) bearings
7) installation and disassembly regular inspection and disassembly frequency and disassembly method when disassembling frequently, it is more convenient to use cylindrical roller bearings with detachable inner ring and outer ring, needle roller bearings and tapered roller bearings.Tapered hole aligning ball bearings and tapered hole aligning roller bearings are easy to assemble and disassemble through the use of fasteners or unmount sleeves.
The type of bearing structure of the selected machinery is not the same, the bearing conditions will be different, the performance requirements are not the same, but generally speaking, a shaft on the use of no less than two bearings.In addition, in order to facilitate axial positioning, most of the use of a bearing as a fixed end bearing, the rest is used as a free end bearing.The following table lists the choice of fixed end and free end bearing structures.The fixed end bearing is used for bearing axial positioning and fixing. The bearing that can bear both radial and axial loads is selected to bear two-way axial loads.
Deep groove ball bearing combination angular contact ball bearing double row angular contact ball bearing centering ball bearing cylindrical roller bearing with retaining edge (NUP type, NH type) double row roller bearing centering roller bearing free end bearing is used to avoid shaft expansion caused by temperature change during operation, and the axial position of the bearing.It is advisable to choose bearings which only bear radial load and can be separated from inner ring and outer ring.When using non-detached bearing, clearance is generally used between the outer ring and the housing, so that when the shaft telescopic bearing together with the axial avoidance.Used to avoid shaft expansion caused by temperature change during operation and to adjust the axial position of the bearing.It is advisable to choose bearings which only bear radial load and can be separated from inner ring and outer ring.When using non-detached bearing, clearance is generally used between the outer ring and the housing, so that when the shaft telescopic bearing together with the axial avoidance.When the fixed end and free end are not divided, the front or back side of the two angular contact ball bearings or tapered roller bearings which can bear the axial load will be used when the bearing spacing is small and the influence of the shaft telescopic is not big.Adjust the axial clearance after installation with nut or gasket.Deep groove ball bearing angular contact ball bearing centering ball bearing cylindrical roller bearing (NJ type, NF type) tapered roller bearing centering roller bearing when used for vertical shaft, the fixed end is selected to bear both radial load and axial load.When the axial load of the bearing is large, the thrust bearing and the centripetal bearing are used together.The same free end can only bear the radial load of the 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 centripetal bearing installation bearing belongs to precision mechanical parts, do not open the packaging before installation, to avoid rust.For grease lubricated bearings and oil seal or dustproof cover on both sides, seal ring bearings can be installed directly without cleaning.In the process of bearing installation, one principle must be mastered, that is, the installation force or torque can only be transmitted through the corresponding ring.Press in with bearing inner ring and shaft to make tight fit, outer ring and bearing seat hole is relatively loose, can be used to press the bearing on the shaft, and then the shaft and bearing together into the bearing seat hole, pressing on the bearing inner ring end face, pad a soft metal material assembly sleeve (copper or mild steel).The bearing outer ring is closely matched with the bearing seat hole. When the inner ring is loose with the shaft, the bearing can be pressed into the bearing seat hole first. 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 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 assembly sleeve shall be able to tighten the end faces of the inner ring and outer ring of the bearing at the same time.Heating fit an installation method of heating a bearing or bearing housing and transforming a tight fit into a loose fit by means of thermal expansion.Is a common and labor-saving installation method.This method is suitable for the installation of bearings with large interference. Before hot loading, put the rings of bearings or separable bearings into the oil tank and heat them evenly at 80-100℃. Then take them out of the oil and install them on the shaft as soon as possible.When the outer ring of bearing is closely matched with the bearing seat made of light metal, the heat loading method of heating the bearing seat can avoid the abrasion of the matching 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.Installation of thrust bearing overall thrust bearing and shaft fit is generally transition fit, seat ring and bearing seat hole fit is generally clearance fit, so this kind of bearing is easier to install, two-way thrust bearing shaft spring should be fixed on the shaft, in order to prevent rotation relative to the shaft.Bearing installation method, generally, is the majority of the shaft rotation, so the inner ring and the shaft for over-win cooperation, bearing outer ring and the bearing chamber for clearance cooperation.* bearing operation inspection after the bearing is installed, it should be checked to ensure that the bearing is installed in place, flexible rotation, no stuck phenomenon, such as improper bearing installation, the bearing temperature will rise rapidly and damage, or even major accidents such as bearing stuck fracture.Use and storage of bearings (1) when using the bearings, keep the surrounding environment clean, do not adhere to hand sweat and dirt.It should be used by the person who is familiar with the bearing.In order to ensure the performance of the bearing, the bearing shall be regularly maintained, maintained and repaired according to the operating standards of the equipment, including monitoring the running status, adding lubricant and regular disassembly inspection.(2) the bearing shall not be stored directly on the ground (above 30cm above the ground), avoid direct light and cold walls.In order to prevent rust, the bearing is kept in an environment with temperature around 20℃ and humidity below 65%. The bearing is placed in acidic air, which is prone to rust and discoloration. Gloves and kapok silk are used to wipe the bearing, shaft and shell.