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What are the main damage forms of engine spindle bearings

Update:18-03-2021
Summary:

The main shaft bearing is a very important part of the […]

The main shaft bearing is a very important part of the engine. If the main shaft bearing is damaged, the engine cannot be used normally.

1. Bearing peeling damage

The metal particles fall off due to the expansion of fatigue cracks in the stress field, and the arc crater visible to the naked eye is called spalling. Spalling is the most common failure mode of engine spindle bearings. According to the cause of the spalling, it can be divided into subsurface fatigue spalling and spalling caused by surface damage.

On the subsurface of the bearing raceway or the stress concentration position of the rolling element, the fatigue peeling caused by the material micro-tear is the subsurface fatigue peeling. This is due to the formation of the subsurface fatigue peeling on the subsurface when the rolling elements are squeezed and rolled on the raceway. It is caused by the maximum orthogonal shear tensile stress with an inclination of about 45°. The main influencing factors are the magnitude of the load, the number of actions and the residual stress state of the subsurface. With the improvement of materials and processes, it is difficult for bearings to undergo subsurface fatigue spalling in a short period of time under normal working conditions. However, under certain special working conditions, such as a large negative working clearance in the radial direction of the bearing or a serious tilt of the inner and outer rings of the bearing due to changes in the temperature field, sub-surface fatigue spalling will occur in a short time when the maximum Hertzian stress reaches a certain value.

The spalling caused by surface damage is mostly caused by the microscopic crack propagation of the surface defects caused by the rolling marks, scratches, slipping scratches, foreign body damage, corrosion, etc. on the working surface. The spalling starts in the form of scaly.

This kind of peeling does not require a large stress level and a large number of actions. The peeling of the bearing will cause engine vibration and increase the noise. In severe cases, it will cause the loss of bearing function and threaten the safety of the engine. Under the premise of selecting suitable bearing materials, changing the residual tensile stress on the surface and subsurface of the material to compressive stress and preventing surface damage are the most effective methods to prevent bearing spalling.

2. Bearing damage caused by particles

Some metallic, inorganic or vegetable particles of varying sizes will leave marks when stuck or embedded in some parts of the bearing

According to the analysis of 200 sets of bearings removed from the field engine by the Massachusetts Institute of Technology and GE, the damage caused by particles is the most common failure mode of the main shaft bearing of the field engine.

The main cause of particle damage is lubricating oil pollution. The pollution source mainly comes from the debris scraped from the sealed runway coating, sand and dust brought in by the sealed gas, and the products of wear or peeling of bearing components.

The effects of damage caused by particles mainly include:

1) The greatly increased surface roughness causes micro-cracks on the bearing working surface and severely damages the oil film, thereby greatly reducing the life of the bearing;

2) Reduce the accuracy of the working surface, affect the uniformity of the load distribution and the motion posture of the rolling elements, thereby causing abnormal damage to the bearing;

3) Increase the load of the cage, and even cause the cage to vibrate, causing damage to the cage.

3. Calendering impression

Calendering marks are plastic deformation marks that occur on the surface of bearing components, linear or circular, with random directions. This is caused by particles passing between the bearing elements when the bearing is running. The bottom of the impression is generally the same as the surface of the bearing element.

If the lubricating oil contains hard particles, it can not only cause damage to the abrasive particles, but also may cause indentations on the surface of the rolling elements and raceways. In addition, assembling and disassembling bearings, the work of the whole machine and its components, or excessive impact during transportation may cause indentation on the surface of the raceway or rolling element. The appearance of calendering marks will increase the noise of the bearing, and produce super stress (ie edge effect) at the edge of the imprints, which becomes the starting point of fatigue spalling, and may also make the bearing clearance disappear and become stuck during rotation.

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