Bearing clearance refers to a bearing circle relative to another bearing circle radial movement of the total distance (radial internal clearance) or axial movement of the total distance (axial internal clearance). Work clearance: bearing actual working operating conditions clearance, its size on the bearing rolling fatigue life, temperature rise, noise, etc. have influence. Original clearance: bearing not installed before the clearance Clearance value is divided into basic group, small clearance group (C2), large clearance group (C3, C4). Large clearance group is suitable for inner and outer ring with interference amount is large, or inside and outside the circle temperature difference is large, deep groove ball bearing need to bear larger axial load or need to improve the alignment performance, or need to improve bearing limit speed and reduce bearing friction torque and other occasions. Small clearance group is suitable for higher rotational accuracy, need to strictly control the axial displacement of the shell hole and need to reduce vibration and noise occasions. When choosing the bearing clearance, the general clearance group is zero or slightly positive is appropriate. Bearing clearance selection is correct or not, on mechanical running accuracy, bearing life, friction resistance, temperature rise, vibration and noise has a great influence. Such as to the heart bearing clearance selection too small, will make the load bearing rolling body number increase, contact stress is reduced, running more smoothly, but at the same time friction resistance increased, temperature rise also increased. On the contrary, also like this. Therefore, we need to consider the following factors when choosing the bearing clearance: 1. 1, bearing and shaft housing hole with the tightness will affect the clearance value of the change. Generally after the installation will make the clearance value reduced. 2, bearing operation process, due to the shaft and shell heat dissipation conditions are different, resulting in temperature differences, clearance value decreases 3、Because the shaft and shell material expansion coefficient is different, lead to the clearance value increase or decrease. Usually, the most suitable working clearance to the heart bearing for the standard specified in the basic group of clearance. In special conditions, can not use the basic group of clearance value, can use auxiliary clearance value, such as deep groove ball bearing 3rd, 4th, 5th group suitable for interference fit or inner and outer ring temperature difference is too large mechanical parts. Appropriate installation clearance helps rolling bearing normal work. Clearance is too small, rolling bearing temperature rise, can not work properly; clearance is too large, equipment vibration, rolling bearing noise. Bearing lubrication is divided into grease lubrication, oil lubrication and solid lubrication three kinds. 1. Grease lubrication Mostly used in the bearing seat, sealing structure and lubrication facilities are simple, easy maintenance, to a certain extent can prevent the invasion of water, gas, dust and other impurities. It is made of base oil, thickener and additives made of semi-solid lubricant. (Bearing Encyclopedia WeChat: zcbk2014) Among them, the base oil is synthetic oil such as mineral oil, which mainly plays the role of lubricity; thickener plays an important role in the temperature characteristics and water resistance of lubricant; additives play a role in enhancing the performance of lubricant such as anti-oxidation and rust prevention. The cone degree of grease (needle degree) is an indicator of its performance, indicating the fluidity of grease. The larger the value, the softer the grease is, and it is not suitable for high temperature occasions. The drop point of grease is an indicator of its performance, indicating the performance of the use of temperature. The larger the value, the higher the temperature that can be used. After installation, if the bearing operation process grease is too little, will make the collar raceway and rolling body surface between the lack of effective oil film protection, the surface will be bad due to wear. If there is too much, it will make the bearing heat up during the operation and damage the bearing. Therefore, the general grease filling amount inside the bearing G G=0.005DB Where, G: filling amount (g) D: bearing outer diameter (mm) B: bearing width (mm) Ng: bearing grease limit speed (r/min) N: bearing actual working speed (r/min) When Ng/N<1.25, the amount of grease filling accounts for 1/3 of the internal space of the bearing When 1.25<ng p=”” 3<=”” 3～2=”” n<5, the grease filling amount accounts for 1> of the internal space of the bearing When Ng/N>5, the amount of grease filling accounts for more than 2/3 of the internal space of the bearing. 2. Oil lubrication Commonly used lubrication methods. (1) Oil bath lubrication Mostly used for low and medium speed bearing lubrication (2) oil drip lubrication Mostly used for higher speed of small bearings (3) Splash lubrication Use the splash generated by the rotation of the gears mounted on the shaft to lubricate the bearings. 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 dispenser is used to supply the oil regularly. Its micro supply reduces the pollution to the surrounding environment, and the oil quantity is less child stable, the friction torque is small, the temperature rise is low, especially suitable for high speed bearings. Viscosity is one of the important indexes of lubricating oil, viscosity is too low, it is not easy to form oil film, and then cause the bearing service life to decrease; viscosity is too high, it causes heat because of viscous resistance, and expand the power loss. Generally speaking, low viscosity lubricant is chosen for high speed. When the operating temperature is lower than 50°C, the lubricant can be replaced once a year. When it reaches 100°C, it should be replaced once every three months. Problems that may occur during installation (1) Shaft and bearing bore fit too loose (commonly known as “go inner ring”), sliding friction caused by sliding heat, will damage the bearing. (2) shell aperture and bearing outer diameter with too loose (commonly known as “go outer ring”), sliding friction caused by the sliding heat, will damage the bearing.

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