Spherical Roller Bearing Fretting Damage Form

Time：2020.09.07  Source：Roller Bearings Suppliers

1. Common forms of spherical roller bearing fretting damage

In fact, the fretting state of spherical roller bearings is very complicated. Generally, according to the simplified plane contact model and according to different relative motion directions, fretting can be divided into four basic motion modes: tangential motion, radial motion, Rolling fretting, twisting fretting.In practice, the latter three types of fretting often occur or appear in a combination of two or more types of fretting. There are three main ways in which fretting damages bearings: bearing fretting wear, bearing fretting fatigue, and bearing fretting corrosion.

Among them, the fretting wear of spherical roller bearings is due to the relative displacement of the contact surface caused by external vibration, and the contact parts bear a large amount of local contact load, which causes the wear of the steel ball and raceway in the bearing; bearing fretting fatigue refers to the bearing bearing The fretting caused by the fatigue alternating stress caused damage to the bearing contact surface. Bearing fretting corrosion means that the bearing is used in rainwater, corrosive gas and other environments, and the contact surface of the bearing is damaged under the action of corrosive media.After the spherical roller bearing is subjected to the normal alternating load, the circular pit-like fretting damage is left on the inner and outer ring raceways of the inner and outer bearings. The fretting wear on the outer ring slows down as the load increases, and increases as the swing angle increases. As the number of cycles increases, the increase in wear decreases.

2. Damage distribution of fretting wear and fretting fatigue of spherical roller bearings

Spherical roller bearing fretting and fretting fatigue are the two most important forms of fretting damage. By observing the two contact surfaces of the friction pair, the boundary line between the wear zone and the crack zone is almost at the same position compared with ordinary fretting wear.The rapid formation of wear debris in the slip zone hinders the development of cracks. The boundary line between the crack zone and the non-damage zone obviously moves to the partial slip zone. The length and direction of crack propagation are the same as ordinary fretting wear.

In part of the slip zone, according to the measured maximum tangential force (ie frictional force), combined with the actual contact surface radius and the radius of the adhesion zone observed under an optical microscope, we can calculate the tensile stress of the contact surface according to Mindlin theory .

Spherical roller bearing fretting fatigue is caused by the relative movement of the two contact surfaces through external alternating load deformation. The characteristics of the fretting area under fretting fatigue are related to the fretting amplitude, contact pressure and other parameters.  There are enough stock for WSBC 22228 CCK/W33 bearings online , if you need , pls contact us . 

Spherical roller bearing fretting wear and fretting fatigue are caused by fretting, fretting wear is caused by external forces, and fretting fatigue is caused by the deformation of the specimen itself under the alternating fatigue force.

3. Measures to eliminate and prevent damage to spherical roller bearings caused by fretting

The easiest way to prevent fretting fatigue damage is to eliminate vibration sources, but in industrial production, vibration sources are usually inevitable. Therefore, only measures can be taken to slow down the fretting damage, and there are usually three ways to slow down the damage caused by the fretting damage to the bearing.

(1) Eliminate fretting slip and mixing zone

Material wear and cracks are mainly formed in the fretting slip zone and mixing zone. The fretting damage can be reduced by increasing the pressure (pre-tightening force) and the degree of interference, but the increase in normal pressure should be limited by the strength of the mechanism. However, the increase in pressure also means that the contact stress increases, and the local fatigue stress increases under the vibration environment, which increases the risk of fretting crack initiation.

It can also reduce the damage caused by fretting damage to the bearing by changing the mechanism design and manpower. The structural design changes change the pressure distribution of the contact area, the geometric contact mode and the stiffness of the contact surface, thereby changing the fretting operation area, which is beneficial to the relative movement in the partial slip area.

(2) Increase contact surface strength

The bearing can be changed by physical (laser shock, ion implantation, etc. to change the surface layer microstructure hardening technology), chemical (carburizing, nitriding and other surface hardening methods), mechanical (rolling and other methods to increase surface residual stress) and other technological means to change the bearing The structure and composition of the rolling elements and raceways can improve the wear resistance and fatigue resistance of the rolling parts of the bearing. The surface modification technology is very effective for fretting located in part of the slip zone and mixing zone, greatly improving the ability to resist fretting fatigue cracks. There are enough stock for WSBC 22230 CC/W33 bearings online , if you need , pls contact us . 

(3) Reduce friction coefficient

Another effective way to reduce the fretting damage of spherical roller bearings is to reduce the coefficient of friction and select suitable lubricating oil or grease. Add a polymer film interlayer on the bearing raceway to enhance the lubrication characteristics of the raceway contact surface, thereby improving the durability of the contact surface. At the same time, choosing the right cage material can also reduce the friction coefficient.

Under the condition of meeting the structural strength, choosing a material with good flexibility and large deformation can effectively absorb relative sliding, thereby reducing surface damage; choosing a parent material with high hardness and high fatigue strength can effectively reduce fretting Wear and inhibit the initiation and expansion of cracks; after reasonable selection of materials, the use of a small amount of third body generated at the initial stage of fretting for self-lubrication can also achieve the purpose of reducing further damage to the contact material.