Bearing clearance refers to the total distance of radial movement of one bearing ring relative to the other (radial internal clearance) or the total distance of axial movement (axial internal clearance). Working clearance: The clearance under the actual working and operating conditions of the bearing, its size has an impact on the rolling fatigue life, temperature rise, noise, etc. of the bearing. Original clearance: the clearance before the bearing is installed The clearance value is divided into basic group, small clearance group (C2), and large clearance group (C3, C4). The large clearance group is suitable for large interference fit between the inner and outer rings, or large temperature difference between the inner and outer rings, deep groove ball bearings need to bear large axial loads or need to improve the self-aligning performance, or need to increase the limit speed of the bearing and reduce the bearing speed. friction torque etc. The small clearance group is suitable for high rotation accuracy, where the axial displacement of the housing hole needs to be strictly controlled and the vibration and noise need to be reduced. When selecting the bearing clearance, it is generally advisable for the clearance group to be zero or slightly positive. Whether the choice of bearing clearance is correct or not has a great influence on the mechanical operation accuracy, bearing life, friction resistance, temperature rise, vibration and noise. If the clearance of the radial bearing is too small, the number of rolling elements bearing the load will increase, the contact stress will decrease, and the operation will be more stable, but at the same time, the friction resistance will increase and the temperature rise will also increase. On the contrary, it is also true. Therefore, we need to consider the following factors when selecting the bearing clearance: 1. The tightness of the fit between the bearing and the shaft housing bore will affect the variation of the clearance value. Generally, the clearance value will be reduced after installation. 2. During the operation of the bearing, due to the different heat dissipation conditions of the shaft and the housing, the temperature difference and the clearance value decrease 3. Due to the different expansion coefficients of the shaft and housing materials, the clearance value increases or decreases. Usually, the most suitable working clearance of radial bearings is the clearance of the basic group specified in the standard. Under special conditions, when the clearance value of the basic group cannot be used, the auxiliary clearance value can be used. For example, the third, fourth and fifth groups of deep groove ball bearings are suitable for interference fit or mechanical parts with excessive temperature difference between inner and outer rings. Appropriate installation clearance contributes to the normal operation of rolling bearings. If the clearance is too small, the temperature of the rolling bearing will rise and cannot work normally; if the clearance is too large, the vibration of the equipment will be large, and the noise of the rolling bearing will be large. The lubrication of bearings is divided into three types: grease lubrication, oil lubrication and solid lubrication. 1. grease lubrication It is mostly used in places where the bearing seat, sealing structure and lubrication facilities are simple and easy to maintain, and can prevent the intrusion of water, air, dust and other impurities to a certain extent. It is a semi-solid lubricant made from base oil, thickener and additives. (Bearing Encyclopedia WeChat: zcbk2014) Among them, the base oil is synthetic oil such as mineral oil, which mainly plays a lubricating role; the thickener plays an important role in the temperature characteristics and water resistance of the lubricant; Rust and other performance aspects play a role. The cone penetration (needle penetration) of the grease is an indicator of its performance, which indicates the flow performance of the grease. The larger the value, the softer the grease, which is not suitable for high temperature occasions. The dropping point of a grease is an indicator of its performance, expressing the performance of the service temperature. The larger the value, the higher the usable temperature. After installation, if there is too little grease during the operation of the bearing, there will be no effective oil film protection between the raceway of the ring and the surface of the rolling element, and the surface will be damaged due to wear. If too much, it will cause the bearing to generate a lot of heat during operation and damage the bearing. Therefore, the general grease filling amount G inside the bearing G=0.005DB Among them, G: Filling amount (g) D: Bearing outer diameter (mm) B: Bearing width (mm) Ng: Limiting speed of bearing grease (r/min) N: Actual working speed of bearing (r/min) When Ng/N<1.25, the amount of grease filling accounts for 1/3 of the inner space of the bearing When 1.25<ng p=”” 3<=”” 3～2=”” n<5, the amount of grease filling occupies 1> of the inner space of the bearing When Ng/N>5, the amount of grease filling accounts for more than 2/3 of the inner space of the bearing 2. oil lubrication Commonly used lubricating oil methods: (1) Oil bath lubrication It is mostly used for the lubrication of low and medium speed bearings (2) Drip oil lubrication Mostly used for small bearings with higher speed (3) Splash oil lubrication The bearing is lubricated by the splash generated by the rotation of the gear mounted on the shaft. Widely used in automotive gearboxes, machine tool gearboxes, etc. (4) Circulating oil lubrication (5) Jet lubrication (6) Oil mist lubrication (7) Oil-air lubrication A piston-type quantitative distributor is used to provide oil regularly. Its small amount of supply reduces the pollution to the surrounding environment, and the amount of oil is small and stable, the friction torque is small, and the temperature rise is low, which is especially suitable for high-speed bearings. Viscosity is one of the important indicators of lubricating oil. If the viscosity is too low, it will not be easy to form an oil film, which will lead to a decrease in the service life of the bearing; if the viscosity is too high, it will cause heat due to viscous resistance and increase power loss. In general, low-viscosity lubricating oil is used for high-speed applications. When the operating temperature is below 50°C, the lubricating oil can be replaced once a year. When it reaches 100°C, replace it every three months. Problems prone to occur during installation (1) The shaft and the inner hole of the bearing are too loosely matched (commonly known as “inner ring”), and the sliding friction generated by sliding will cause heat and damage the bearing. (2) The matching between the housing aperture and the bearing outer diameter is too loose (commonly known as “outer ring”), and the sliding friction generated by sliding will cause heat and damage the bearing.  

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