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Countermeasures for bearing housing under heat

by:JNSN     2021-12-22
Generally, more than two rolling bearings with seat are used on one shaft. If the installation interval of the seated rolling bearing is small or the shaft expansion and contraction caused by temperature is small, each bearing assembly can be installed as a fixed end. However, when the installation interval is large or the shaft is subjected to heat, one seated bearing can be installed as the fixed end to determine the position of the shaft, and the other seated bearing can be installed as the free end. This is because when the shaft is subjected to heat, it will elongate in the axial direction, so that a large axial load acts on the bearing, and there is a risk of early damage to the bearing. Therefore, the expansion and contraction of the shaft can be absorbed by the free end bearing. The relationship between temperature rise and shaft elongation is shown in equation (9.1). When the shaft expands and contracts greatly due to heat, the countermeasures are as follows. (1) The method of using a set screw with a pin at the free end. When the shaft is stretched due to heat, the shaft or bearing with a seat must be installed so that it can move freely in the axial direction. When the speed is low, the free end assembly adopts the method of machining the keyway on the shaft, and installing the set screw (special symbol G6) with the pin on the top of the bearing. Insert the pin at the top of the stop screw into the key groove of the shaft to guide the axial movement of the shaft. The free-end assembly processes the keyway on the shaft, and the structure diagram of the set screw with the pin at the top is shown in Figure 9.1. The keyway dimensions for stop screws with pins at the top are shown in Table 9.7. When using this method, the tolerance zone of the shaft adopted by the free end assembly is recommended to h7. When the temperature of the shaft is higher than the temperature of the inner ring of the bearing, the shaft used should adopt a tolerance zone that can form a larger fit gap. In addition, with this method of free-end components, the mating surface of the bearing inner ring and the shaft may sometimes be abraded. In order to prevent the occurrence of abrasion, it is recommended to apply grease to the inner diameter surface of the bearing when installing the bearing. (2) The method of using the ring seat bearing at the free end is high speed or vibration, it is recommended to use the method of ring seat bearing at the free end. The installation hole of the machine and the outer diameter surface of the bearing box can be Relative axial movement. An example of a structure that uses a ring seat bearing as a free end component is shown in Figure 9.2. When a bearing with a ring seat is subjected to heat, it is necessary to take countermeasures against the axial expansion and contraction of the shaft, and at the same time, it is necessary to calculate the reduction in the internal clearance of the bearing and correctly select the internal clearance of the bearing (refer to 7 Operating temperature and bearing specifications).
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