False brinelling
False Brinelling , also called “standstill marking ” , “corrugation” or “troughing” in German, is a phenomenon of wear in rolling bearings that is caused by micro-oscillations. Vibrations or elastic deformations initiate micro-movements in the contact surfaces between the rolling elements and the running surface. These can lead to damage after just a few thousand load changes. Further operation can lead to the wear marks being rolled over and encourage premature failure of the bearing. The micro-movements are initiated, for example, by machine and unit vibrations, but also by the dynamic effects of road and rail-bound means of transport. Blade bearings in wind turbines are severely affected by this type of damage . In general, however, critical operating states also occur with bearings that are excited to vibrate by auxiliary units, internal combustion engines, hydraulic units or the like (e.g. construction machines, pumps, wheel bearings, etc.).
State of the art
It is known that grease-lubricated bearings are more susceptible to standstill markings than oil-lubricated ones, which suggests the conclusion that the after-flow behavior has a major influence on the formation. In addition, the influence of various parameters, such as the size of the swivel amplitude, the swivel frequency, the number of swivel cycles and the load situation, was researched.
The distinction between false brinelling and fretting corrosion is difficult. Essentially, false brinelling occurs when there is lubricant in the contact area, while fretting corrosion occurs under dry contact conditions. The lubrication condition is strongly influenced by the contact and operating conditions and the number of swivel cycles.
Definition of terms
The term False Brinelling is derived from the Brinell hardness test , which was developed by the Swedish engineer Johan August Brinell in 1900 and presented at the World Exhibition in Paris . “Brinelling” is understood to mean an overload of the rolling contact that exceeds the elastic limit. This can arise, for example, in the event of a single shock or impact load.
The term “False Brinelling” was coined due to the often incorrect interpretation of trough-like depressions in the running surfaces of roller bearings. The maintenance staff has often attributed such depressions to a purely mechanical overload, even though the damage is tribologically induced. False Brinelling damage occurred on a large scale for the first time when cars were shipped to America. New vehicles showed damage to their wheel bearings when they were unloaded from the ship. The cyclical vibration excitation by the slow-running diesel engines and the relatively poor damping on the transport decks were sufficient to cause permanent damage to the running surfaces of the wheel bearings.
A typical damage (spherical cap) of a ball bearing can be divided into three areas: In the middle of the marking there is an area which, despite the micro-movements due to the high load and static friction, does not experience any relative movement and is therefore not damaged. This area is sharply delimited by the severely damaged area, in which sliding movements occur with relatively high pressure between the friction partners. A third, also clearly delimited area can be called the zone of influence. There is also sliding movement in this area. The pressures are so low, however, that no significant damage occurs.
Causes of the standstill markings
Various mechanisms can be considered as possible causes for the formation of the standstill markings:
On the one hand, the micro-movements push the lubricant out of the friction point under high load; insufficient lubrication occurs . In addition, these micro-movements stimulate the surfaces (especially the contacting micro-contacts at the roughness tips) energetically. This leads to chemical reactions down to a few nanometers . This part of the damage correlates with knowledge of the tribochemical reaction ( fretting corrosion ).
As a result of the damage mechanisms mentioned, wear particles and reaction products are formed which, due to the lack of "real" relative movement, can hardly escape from the friction point and thus lead to abrasive wear. This correlates, for example, with the formation of fretting corrosion (tribochemical corrosion) and generally leads to a progressive course of damage and deep depressions that no longer reveal the original damage mechanisms. In the further course of the damage and during the rotational movement of the bearing, further wear mechanisms overlap and hide the real causes.
Simulation of false brinelling
The simulation of false brinelling is possible with the help of the finite element method. For the simulation, the relative displacements (slip) between the rolling elements and the raceway, as well as the pressure in the rolling contact, are determined. The friction work density, which is the product of the coefficient of friction, slip and pressure, is used to compare simulation and experiments. The simulation results can be used to determine critical application parameters or to explain the damage mechanisms.
Avoidance of standstill markings
Current research is aimed at how to prevent the formation of standstill markings through the use of suitable lubricants, materials and surface processes. So far, however, it has been shown that good lubricants can curb the progress of damage; a complete prevention of the damage, but in critical operating conditions is apparently not possible so far. However, critical operating states can be identified with the help of special simulation models. The damage can be avoided with relative certainty if you ensure that the endangered bearings are regularly moved. In the case of large machine transports, auxiliary drives are attached to this, which ensure that the bearings are rotated at defined time intervals.
Individual evidence
- ↑ a b Christian Shadow: Standstill, grease-lubricated roller bearings under dynamic stress. Shaker Verlag, accessed June 27, 2017 .
- ↑ Fabian Schwack, Gerhard Poll: Problem Faced in Service Life Estimation of Blade Bearings. WindTech-International, October 2016, accessed on May 2, 2017 .
- ↑ F. Schwack, M. Stammler, G. Poll, A. Reuter: Comparison of Life Calculations for Oscillating Bearings Considering Individual Pitch Control in Wind Turbines . In: Journal of Physics: Conference Series . tape 753 , no. 11 , January 1, 2016, ISSN 1742-6596 , p. 112013 , doi : 10.1088 / 1742-6596 / 753/11/112013 ( iop.org [accessed May 2, 2017]).
- ↑ Markus Grebe: False Brinelling and Standstill Markings in Rolling Bearings. ExpertVerlag, accessed October 10, 2017 .
- ↑ Fabian Schwack: Time-dependent analyzes of wear in oscillating bearing applications . In: Society of Tribology and Lubrication (Ed.): 72nd STLE Annual Meeting . Atlanta May 21, 2017 ( researchgate.net ).
- ↑ Taiskue Maruyama, Tsuyoshi Saitoh, Atsushi Yokouchi: Differences in Mechanisms for Fretting Wear Reduction between Oil and Grease Lubrication. Retrieved June 27, 2017 .
- ^ Matthias Stammler, Andreas Reuter: Blade bearings: Damage mechanisms and test strategies (PDF Download Available). Retrieved June 27, 2017 (English).
- ↑ M. Grebe, P. Feinle, B. Blaskovits: Influence of various factors on the development of standstill markings - Technical Information Library (TIB). Retrieved June 27, 2017 .
- ↑ Fabian Schwack, Artjom Byckov, Norbert Bader, Gerhard Poll: Time-dependent analyzes of wear in oscillating bearing applications (PDF Download Available). Retrieved June 27, 2017 (English).
- ^ MH Zhu, ZR Zhou: On the mechanisms of various fretting wear modes . In: Tribology International . tape 44 , no. 11 , October 1, 2011, p. 1378–1388 , doi : 10.1016 / j.triboint.2011.02.010 ( sciencedirect.com [accessed June 27, 2017]).
- ↑ Robert Errichello: Another perspective: False brinelling and fretting corrosion (PDF Download Available). Retrieved June 27, 2017 (English).
- ↑ Douglas Godfrey: fretting corrosion or False brinelling | Wear | Surface Science. Retrieved June 27, 2017 (English).
- ↑ D. Tonazzi, E. Houara Komba, F. Massi, G. Le Jeune, JB Coudert: Numerical analysis of contact stress and strain distributions for greased and ungreased high loaded oscillating bearings . In: Wear (= 21st International Conference on Wear of Materials ). 376–377, Part B, April 15, 2017, pp. 1164–1175 , doi : 10.1016 / j.wear.2016.11.037 ( sciencedirect.com [accessed June 27, 2017]).
- ↑ Fabian Schwack, Artjom Byckov, Norbert Bader, Gerhard Poll: Time-dependent analyzes of wear in oscillating bearing applications (PDF Download Available). Retrieved June 27, 2017 (English).
- ↑ Fabian Schwack, Felix Prigge, Gerhard Poll: Frictional Work in Oscillating Bearings - Simulation of an Angular Contact Ball Bearing under Dry Conditions and Small Amplitudes. Retrieved June 27, 2017 (English).
- ↑ JO Almen: Lubricants and false brinelling of ball and roller bearings . In: Mechanical Engineering . tape 59 , no. 6 , p. 415-422 .
- ↑ Fabian Schwack, Felix Prigge, Gerhard Poll: Frictional Work in Oscillating Bearings - Simulation of an Angular Contact Ball Bearing under Dry Conditions and Small Amplitudes. Retrieved June 27, 2017 (English).
- ↑ Douglas Godfrey: fretting corrosion or False brinelling | Wear | Surface Science. Retrieved June 27, 2017 (English).
- ↑ Fabian Schwack, Felix Prigge, Gerhard Poll: Finite element simulation and experimental analysis of false brinelling and fretting corrosion . In: Tribology International . tape 126 , p. 352-362 , doi : 10.1016 / j.triboint.2018.05.013 ( sciencedirect.com ).
- ^ Christian Schadow: Standstill, grease-lubricated roller bearings under dynamic stress. Retrieved June 27, 2017 .
- ↑ Felix Prigge, Fabian Schwack, Gerhard Poll: FE simulation of an angular contact ball bearing in an oscillating application. Retrieved October 10, 2017 .
- ↑ Markus Grebe: Rolling bearings in operation with small swivel angles or under vibration loads: False Brinelling in use . expert, 2017, ISBN 978-3-8169-3351-9 ( amazon.de [accessed June 27, 2017]).
- ↑ Adjustable, self-aligning rotor locking device for an aerogenerator . November 13, 2007 ( google.com [accessed June 27, 2017]).