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Entry type: FAQ Entry ID: 109759489, Entry date: 08/02/2018

SIMOGEAR, 2KJ1/2KJ3: Reasons why bearings fail

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Bearing failures – identifying causes & avoiding failures

How can you prevent bearing failures?

Rolling bearings are predominantly manufactured in high unit quantities. Products from manufacturers released and approved by Siemens are very reliable, and have been optimized so that failures as a result of material defects or manufacturing failures are very uncommon. Having said this, all machine elements have a limited service life. If the bearing fails far earlier than its theoretical service life, then generally the rolling bearing itself is not the cause, but external effects.

The term "rolling bearing damage" applies to all identifiable changes to the bearing raceway and rolling bearing surfaces over the complete usage period. This also applies to slight changes that do not restrict the ability of the bearing to operate or indicate a pending failure. In practice, the visible damage profiles involve several superimposed damage mechanisms and operating conditions, so that it is difficult to make any statement about what initiated the damage in the first place. Their optical appearance and the mechanisms that initiated the damage are comparable to those of gearing; however, the different motion sequences, load distribution and lubrication conditions must always be taken into consideration as well.

Far more than 50 percent of all premature bearing failures can be avoided. After detailed investigations, the causes and the frequency of all bearing failures (depending on the source) can be classified according to four groups:

  1. Poor lubrication (approx. 35% - 55%)
  2. Dirt and pollution (approx. 14% - 18%)
  3. Assembly/installation faults (approx. 16% - 17%)
  4. Overload and/or fatigue (approx. 10% - 34%)

It can be clearly seen that lubrication plays a central role here.

Unsuitable lubricant - in this case, the excessively low viscosity or inadequate amount of additives play an important role. However, inadequate physical/chemical attributes - such as foaming behavior, corrosion protection etc. - must also be taken into consideration when selecting a suitable lubricant. If the oils listed in the operating instructions that are approved and released by Siemens are used, then this issue can be ruled out as fault source.

Lack of lubricant in the contact zone - involves the (motor) design and the selection of a suitable lubricant. This is a design feature of our geared motors, and can only be influenced to a limited extent.

Dirt and pollution in the lubricant - always reduce the bearing lifetime irrespective of whether dirt and pollutants enter along with the fresh oil or enter the lubricant as a result of external effects or as particles arising from the aging process or abrasion in the gearbox itself. This is the reason that regular oil changes are very important.

Changes to the lubricant properties - taking into account the inner and outer operating conditions, these must be taken into consideration over the complete lifetime to ensure that they have no negative effects. This is another reason why regular oil changes are very important.

Overlubrication (for grease lubrication) - this also has a negative effect and must be definitely avoided. The instructions and information provided in the Operating Instructions must be strictly complied with.

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