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The approach to investigating a failure

Tooth fracture
Tooth fracture

As an independent engineering company, we investigate machine failures in order to identify the associated root cause and recommend appropriate counter measures. Most of our cases are related to the following applications:

  • Automotive
  • Railway
  • Agricultural and construction equipment
  • Industrial drives
  • Mining
  • Rolling mills
  • Water turbines
  • Wind energy converters

Initial Inspection & Endoscopy

Endoscopic inspection of a wind energy converter
Endoscope

At the beginning of an investigation, typically the entire system must be inspected. This yields a first impression of which parts are affected, what kind of damages are present, and which parts may need to be replaced. Additionally, an on-site inspection allows for the precise identification of operating conditions and ensures that all traces of use can be identified and considered later on.

Especially in the case of large or hard to access machinery such as wind energy converters and large industrial gearboxes it can be useful to perform an inspection with endoscopy. Elgeti Engineering has 3 m long endoscopes with a bi-directional swiveling camera available to avoid the necessity of dismantling the machinery. Routine gearbox endoscopy can also be part of preventative maintenance, e.g. to detect damaged bearings and gears or extraordinary wear at an early stage.


Identifying the failed part

Getriebeschaden einer Windenergieanlage
Fracture of inner ring of cylindrical roller bearing

Once a failed part is identified, its traces of use and damage pattern are assessed with a visual inspection. Based on the documented findings, one can decide what manner of further investigations are necessary to fully understand the root cause of the failure.


Fracture face investigation

Schwingbruch eines Innenrings
Fatigue fracture of the inner ring of a cylindrical roller bearing

In the case of this cylindrical roller bearing, a fracture of the inner ring has been detected. An investigation of the fracture face identified fatigue as the relevant damage mechanism and discovered the origin of the crack. Both contribute valuable information to the description and understanding of the root cause of the damage.

Fracture face investigation is typically carried out by means of optical microscopy or scanning electron microscopy.


Material analysis & Metallography

Metallographie
Material structure of a bearing

A metallographic investigation can reveal conspicuous microstructures, internal defects, inclusions, etc. In addition to grain size and degree of cleanliness, both chemical composition and hardness are part of the investigation.
In our materials laboratory, we have the capability to take material samples, even out of larger parts, without thermal influences and to prepare them for metallographic assessment. This is typically done via optical microscopy.


Simulation

Finite Elemente Methode
Finite Elements Analysis

Possible scenarios or responses to specific loading conditions, taking different load cases into account, can be studied by means of finite element analysis.Stress distributions, deflections, vibrations and thermal behavior are considered.
The suitability of a part for regular operating conditions can be verified by a structural analysis. In these cases, an analytic strength assessment according to the relevant standards is carried out after the numerical simulation.


Testing

Bearing test rig EELPAX-320
Bearing test rig EELPAX-320

In order to reproduce very specific damage mechanisms, extreme conditions can be simulated on our bearing test rigs. For example, the influences of poor or contaminated lubrication on the lifetime of a part or on the damage pattern itself can be investigated in order to verify a damage hypothesis. Such investigations are also helpful during verification of counter measures.


Measurements of operational loads and vibrations

DMS
Strain gauge

In some cases, it is necessary to measure loads and vibrations during regular operation. For this purpose different kinds of sensors such as strain gauges and piezo sensors are used and must be applied to the relevant parts.


Final assessment and definition of appropriate countermeasures

If the investigations lead to a clear result, the associated scenario will be described and explained in a detailed report. The resultant understanding of the associated issues will then be used to define appropriate countermeasures in order to prevent further damages of the same kind in the future.