What's the failure analysis and renovation of slewing ring bearings?

Slewing bearings are special types of bearings usually used in heavy machinery.The difference between these types of bearings and ordinary bearings is that  they have high pitch value diameters, the way they are mounted on a structure, generally "static" working properties, high load capacity and a large number  of rolling elements.

The slewing bearing is usually selected according to the static load which is calculated by the axial and radial force and the tilting moment.Some  parameters, such as speed, load and working temperature, are needed to properly select the rotating bearing.There are some assumptions to consider:
1) The bearing is made of high-quality materials without manufacturing defects.
2) Select bearing according to load calculation.
3) The bearing mounting is suitable.
4) The grease quality is good and it can reach every corner of the bearing.
5) The bearing is sealed with high-quality seals.
6) The bearing working temperatureis within the range.
7) Ensure proper maintenance.



If the above conditions are met, the maximum bearing life can be ensured.However, consideration must be given to the fact that life depends more on actual  conditions than on theoretical values.

Slewing bearings, like other ball bearings and roller bearings, are worn by the continuous torque within the rolling element (ball or roller).Bearings  capable of maintaining calculated service life operation are affected by natural wear.Compared with traditional roller bearings, slewing ring work in  relatively harsh environments where they are subjected to heavy loads to very heavy loads within restricted operating ranges.Uneven load distribution,  distortion in the raceway, proper lubrication of the rolling element, all these parameters affect the service life of the bearing.In addition to natural wear  and tear, these conditions, if not taken care of, will greatly shorten the slewing bearings service life.

When rotating the bearing, the rolling element rolls in a circular mode on the inner raceway.Because the rotating speed is very low (mostly less than 1RPM),  gradual pitting and fragmentation occur.Pitting is caused by the heavy load on the roller element.The durability of rotary bearings subjected to incorrect  induction heat treatment is more prone to failure in the early stages of the operating cycle.If this happens, the bearing must be replaced or repaired  immediately, as failure to do so will result in more pitting and may cause the rolling element in the bearing to become stuck.If not noticed, this can also  cause the ring to break in extreme conditions.

The fault is mainly due to excessive bearing load.Another reason may be the unusual clearance between the rolling elements, which may cause the bearings to  relax.This type of failure may be due to inappropriate infrastructure for mounting bearings.Similarly, if the hardened layer is small, the bearing can cause  catastrophic failure.The bearing layer thickness should be selected appropriately according to the bearing stress.

For some slewing bearings, fatigue may occur due to improper internal lubrication.In this case, spalling occurs on the raceway surface, leading to premature  wear and eventual pitting.Furthermore, there is a risk of corrosion if the race is not properly lubricated.This accelerates premature wear due to surface  flaking.

Finally, it is concluded that the axial clearance in bearings, especially those with larger diameters, should be considered.This is usually an important  factor for a bearing with a roller as its rolling element, which may result in failure.Surface subjected to induction heat treatment is subject to strict  inspection procedures to ensure that there are no microcracks.These microcracks then develop into larger cracks and the bearings fail instantaneously.

The failures mentioned in these articles are often perceived failures, and not necessarily limited to those failures.

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