Why do bearings adopt interference fit assembly?

In general, the bearing can be used only when it is matched with the shaft and bearing seat. Do you know how to use the bearing interference fit assembly? Some people will ask: “interference fit assembly does not mean that the shaft or sleeve parts are installed into the hole, is the size of the shaft or sleeve and the hole slightly larger than the hole?” Can the bearing work well? According to the understanding below, answer everyone’s doubts.

1、 Why do bearings adopt interference fit assembly?
When the load on the bearing rotates relative to the ring, that is to say, when the direction of the radial load is unchanged, but the ring rotates; or when the ring is stationary, but the load rotates around the ring, the contact deformation will occur at the position bearing the load on the fitting surface, and at the same time, there will be a gap at its opposite position. As a result, the perimeter of the inner part and the outer part of the mating surface will be inconsistent, and the inner part will slide in the inner diameter plane of the outer part. This slip is slow and is generally referred to as creep. After creep, due to the poor lubrication of the mating surface and the ploughing effect of the abrasive particles, the mating surface will be seriously worn, resulting in poor rotation, heating or internal wear of the bearing, which will eventually lead to bearing damage. In order to prevent this phenomenon, it is necessary to use interference fit so that there is no gap between the fitting surfaces. In addition, interference fit is also required when the ferrule is strictly positioned.

2、 Advantages of interference fit
1. The connection is firm and can be tightened more than key connection and pin connection.
2. Interference connection reduces the number of parts and simplifies the mechanical structure.

Due to the above advantages, interference fit is suitable for the connection bearing impact load and infrequent disassembly.

3、 It can be seen that the reliability of interference fit is related to the assembly method. The following figure and text illustrate the assembly method of bearing interference fit:

According to the ratio of interference to basic size, interference fit is divided into light, medium, heavy and extra heavy.

The interference is small and belongs to light interference fit.
Assemble with steel hammer or press. For the fit used for precise positioning and overhaul before disassembly or without disassembly, due to the small interference, most of the above fits cannot transfer the load by the generated tightening force. If the torque or axial force needs to be transferred, the fasteners shall be tightened. For example, the matching of winch rope wheel and hub, worm gear bronze gear ring and hub, and connecting rod small end and bushing.

Medium interference, medium interference fit.
It is used for permanent or semi permanent combination of iron and steel parts by means of press, hot expanding hole or cold shrinking shaft. It is not necessary to tighten the fasteners when transferring medium load. If it bears larger load or dynamic load, it should be tightened. Such as the matching of water pump seat and housing hole, crank pin and crank hole, coupling and shaft, engine valve seat and cylinder head hole.

The interference is large and belongs to heavy interference fit. Assemble by hot expanding hole or cold shrinking shaft method.
It can be used to transfer large torque or bear large impact load, and ensure firm combination completely depending on the tightening force produced by interference. Because of the large interference, it is not necessary to tighten the fasteners, but the parts are required to have good rigidity and high material strength. Such as train wheel and shaft fit, diesel engine pin shaft and housing hole fit.

The interference is very large, which is a very heavy interference fit. Assemble by hot expanding hole or cold shrinking shaft method.
It can bear large torque and dynamic load. At present, it is rarely used and can only be applied after testing. Such as diesel engine pin shaft and housing fit.

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