Correct installation of bearings is very important, but in actual operation it is always easy to go astray and problems arise in endlessly. The reason is that some details were not paid attention to, causing the bearing to be damaged during installation. This article shares several examples of errors in bearing installation, as well as correct installation methods and techniques.
Demonstration of common errors in bearing installation
1
Take the inner circle
The fit between the shaft and the inner hole of the bearing is too loose (commonly known as "walking the inner ring")
Because the fit between the shaft and the inner hole is too loose, slippage occurs between the shaft and the inner hole surface. Sliding friction will cause heat and damage the bearing due to heat.
Traces of sliding between the shaft and the inner hole surface
1. Cracks occur due to friction and heat between the inner ring end face and the shaft shoulder.
When "moving the inner ring", the sliding friction between the inner ring and the shaft will generate high temperature. Since the contact surface between the inner ring end face and the shaft shoulder is small, the temperature will be higher. Hot cracks will occur on the end face of the inner ring. The continuous extension of hot cracks will cause the inner ring of the bearing to break during use.
2. Adhesion occurs after heat is generated between the shaft and the inner hole surface.
Due to the "inner ring" sliding friction occurs between the inner hole and the shaft surface, the high temperature caused melts the surface metal and causes adhesion.
2
Go outside the circle
The shell aperture and the bearing outer diameter are too loosely matched (commonly known as "outer ring running")
Because the housing aperture and the bearing outer diameter are chosen to fit too loosely, sliding occurs between their surfaces. Sliding friction will cause heat, causing the bearing to become heated and damaged.
There are traces of sliding between the shell aperture and the outer diameter surface of the bearing.
1. Hammer directly hits the bearing
When installing a bearing with an interference fit of the inner ring (or outer ring), it is forbidden to directly hit the end face of the bearing inner ring (or outer ring) with a hammer, as this will easily damage the rib. It should be installed by placing the sleeve on the end face of the inner ring (or outer ring) and hitting the sleeve with a hammer.
2. Transmit installation force through rolling elements
When installing a bearing with an interference fit in the inner ring, force cannot be transmitted to the inner ring through the outer ring and rolling elements. This will damage the bearing raceway and rolling element surface, causing the bearing to produce noise during operation and cause premature damage. The correct method should be to use a sleeve to directly apply force on the end face of the inner ring.
3
Heating temperature is too high
Some users use an acetylene spray gun to heat the inner hole of the bearing. When the heating temperature exceeds 727°C (the phase transformation temperature of the bearing steel), the metallographic structure inside the bearing steel will change. When a bearing cools, the bearing bore does not return to its original size and is usually larger than before heating.
After being heated by an acetylene spray gun, the surface of the bearing turns black.
Correct installation method of bearings
Bearing installation should be carried out in a dry, dust-free area as far as possible, and should be kept away from equipment that generates metal debris and dust. When it must be installed in a complex environment, contamination should be minimized.
When installing bearings, mechanical, heating or hydraulic methods should be selected according to type and size.
1
Cylindrical bearing installation
1. Cold installation
When installing a small bearing that is not too tight, you can use a sleeve and hammer it to gently tap the sleeve to install the bearing into the appropriate position. When knocking, the impact should be as even as possible on the bearing ring to prevent the bearing from tilting or skewing.
Most bearings are installed using the press-fit method. If you want to install the inner and outer rings of the bearing on the shaft and the bearing seat at the same time, you must ensure that the same pressure acts on the inner and outer rings at the same time, and the contact surface with the installation tool must be on the same plane.
2. Hot installation
Typically, mounting of larger bearings without heating the bearing or housing is not possible because as the size increases, the greater the force required for mounting. The temperature difference between the bearing ring and the shaft or bearing seat required for hot installation mainly depends on the interference amount and the diameter of the bearing fit. The temperature at which open bearings are heated must not exceed 120°C. It is not recommended to heat bearings with seals and dust caps above 80°C (make sure the temperature does not exceed the allowable temperature of the seals and grease).
When heating the bearing, it must be heated evenly and there must be no local overheating.
Bearing induction heater
2
Tapered bearing installation
Most of the inner rings of bearings with tapered holes are installed with an interference fit.
The amount of interference is determined by the axial advancement distance of the inner ring on the conical shaft diameter, adapter sleeve or withdrawal sleeve. The greater the advance distance on the conical mating surface, the smaller the radial internal clearance of the bearing. The amount of interference can be determined by measuring the clearance reduction or the axial advance distance.
For small and medium-sized bearings, you can use a bearing installation tool or preferably a locking nut to push the inner ring into the appropriate position on the conical shaft diameter. When using an adapter sleeve, use a socket nut that can be tightened with a hook or impact wrench. Use the bearing installation tool or the end plate to push the withdrawal sleeve into the bearing inner hole.
Larger bearings require greater force to install, so hydraulic nuts should be used. The hydraulic nut can install the tapered bore bearing on the tapered shaft diameter (Figure 1), the adapter sleeve (Figure 2), and the withdrawal sleeve (Figure 3).
Oil injection method
The working principle of the oil injection method is: hydraulic oil passes through the oil holes and oil grooves under high pressure and is injected into the mating surface between the bearing and the shaft diameter to form an oil film. The oil film separates the mating surfaces, greatly reducing friction between them. This method is usually used when the bearing is mounted directly on the conical shaft diameter.
The necessary oil holes and grooves should be part of the overall shaft design. If the adapter sleeve and withdrawal sleeve have been processed with oil holes and oil grooves, this method can also be used to install the bearing on the adapter sleeve or withdrawal sleeve.
