1. Selection of bearings (1) The main factors that should be considered in the selection of bearings with cylindrical inner holes are as follows: ① Type of load According to the load acting on the bearing, the rotation of the ring can be adjusted The load is divided into three types: fixed load, swing load and swing load. a. Fixed load The resultant radial load is borne by the local area of u200bu200bthe raceway of the ring, and is transmitted to the corresponding local area of u200bu200bthe matching surface of the shaft or housing. This load is called a fixed load. The characteristic of the fixed load is that the combined radial load is relatively static with the ferrule. Ferrules that bear a fixed load generally choose a looser fit. b. Rotary load The synthetic radial load vector acting on the bearing ring rotates along the circumferential direction of the raceway, which is borne by each part of the raceway in turn, and is transmitted to each part of the surface of the shaft housing hole accordingly. This kind of load is called swing load, also known as cyclic load. The characteristic of the slewing load is that the resultant radial load vector rotates relative to the ferrule. The ferrule and shaft or housing hole that bear the rotary load should be filtered or interference fit. If they are installed with a clearance fit, slippage will occur between them, which will lead to friction and heating of the contact surface, which will cause the temperature to rise sharply and the bearing will be damaged quickly. The size of the interference fit depends on the operating conditions. The principle is that when the bearing works under load, it will not cause the ferrule to crawl on the matching surface of the shaft or the housing hole. C. The synthetic radial load vector acting on the bearing ring by the swing load swings relatively in a certain area of u200bu200bthe raceway of the ring, is borne by a certain area of u200bu200bthe raceway, and is transmitted to a certain area of u200bu200bthe surface of the shaft or the housing hole, Or the load acting on the bearing is an impact load or a vibration load, and the direction or value of the load often changes. This kind of load is called a swing load, also known as a non-directional load. When the bearing is subjected to a swing load, especially when it is subjected to a heavy load, the inner and outer rings should adopt an interference fit. When the inner ring oscillates and rotates, the inner ring is usually fitted with a rotating load. However, sometimes the outer ring must be able to move in the bearing direction outside and inside the housing or when the load is light, a fit slightly looser than the rotating load can be used. ②The magnitude of the load Under the action of the radial component of the load, the bearing ring will be compressed in the radial direction, which is easy to cause loose fit, especially in the case of heavy rotating load, it is easy to cause slippage. Therefore, for heavy-duty applications, the fit should usually be tighter than for light-load and normal-load applications. In short, the heavier the load, the larger the fit should be. ③ Working temperature When the bearing is running, because the working temperature of the ring is usually higher than the temperature of the adjacent parts, the inner ring of the bearing may become loose with the bearing due to thermal expansion, and the outer ring may affect the axial clearance of the bearing due to thermal expansion, so , When choosing a fit, you must pay attention to the temperature difference between the ferrules and the direction of heat conduction. ④Rotation accuracy When the requirements for the rotation accuracy and running stability of the bearing are high, in order to eliminate the influence of the elastic deformation and vibration of the bearing components, the clearance fit should be avoided as much as possible. ⑤The structure and material of the shaft and the casing If the hole surface of the shaft and the casing (box) is irregular in shape, it will cause abnormal deformation of the inner and outer rings of the bearing, and uneven force. For the split casing (box) body, it is not advisable to use interference fit with the outer ring of the bearing, but the outer ring should not be rotated in the hole of the casing (box). When the bearing is installed on the thin-walled, light alloy housing (box) hole or hollow shaft, in order to ensure that the bearing has enough bearing surface, it should be installed in a thick-walled housing (box) body, cast iron housing (box) body or solid The fit selected on the shaft is tighter. ⑥Installation and disassembly In many complex structural applications, in order to facilitate installation and disassembly, clearance fit is required. According to the operating conditions of the bearing, if it must be installed with an interference fit, a separable bearing (cylindrical roller bearing, needle roller bearing, tapered roller bearing and thrust bearing can be installed separately on the inner and outer rings) or a tapered bearing can be used. Bearings with inner holes make it easy to install and remove. ⑦Axial displacement of non-fixed end bearing This displacement refers to the requirement that a ring of the bearing installed on the non-fixed end can have a certain free play in the axial direction. The ferrule (usually the outer ring) that bears the fixed load is usually installed with a clearance fit. If the cylindrical roller bearing (type 2000 and 3200) or needle roller bearing without ribs on the inner ring or outer ring or needle roller bearing is installed on the non-fixed end, the inner and outer rings are installed with interference fit. (2) Bearings with conical inner holes Bearings with conical inner holes are more convenient to install and disassemble, and can be directly installed on the conical journal or the intermediate sleeve (adapter sleeve, retractor) with a conical cylindrical surface on the outside. Unloading sleeve), and then installed on the cylindrical shaft together with the middle sleeve. The matching between the outer ring of the bearing and the hole of the shell (box) is the same as that of the cylindrical inner bore bearing. Non-separable bearings with adapter sleeves or withdrawal bushings can be used for bearings with large tolerances, but the shape and position tolerances of the shaft must be strictly controlled. 2. The cooperation between the bearing and the shaft and the housing The cooperation between the bearing and the shaft adopts the base hole system, and the cooperation between the bearing and the housing adopts the base shaft system. The fit between the bearing and the shaft is different from the tolerance fit system used in the machine manufacturing industry, and the inner diameter tolerance of the bearing is mostly negative tolerance.