False Brinelling

Called False Brinelling on German also " arrest ", "mark fluting " or " troughing " is a wear phenomenon in seemingly stationary rolling bearings. By vibrations or elastic deformations are introduced into the micro- movements of the contact surfaces between the rolling elements and the tread. These lead after only a few thousand load cycles to damage. During further operation, these markers are rolled over and lead this cause runout and later premature failures. The micro-movements are initiated for example by machine and head vibrations but also by driving dynamic effects of road and rail-bound transport.

A clear definition of what is meant by False Brinelling, it does not yet exist. Just unsystematic are so far the laboratory test methods that are used to simulate such damage and will be used for the development of suitable lubricants. Most often the tests according to ASTM D 4170 ( Fafnir test), the SNR test ( SNR FEB 2 ) or HRE - IME checker tester mentioned in the literature. The problem is that these devices work with very different tilt angles that go from 12 ° when Fafnir testing to real micro vibrations in the HRE IME checker tester. This makes the devices test different lubricant properties and provide when using the same lubricant completely different results.

Strongly affected by this form of damage are currently wind turbines. General occur critical operating conditions but also with all bearings, which are excited by auxiliary units, internal combustion engines, hydraulic power units or similar to vibrations (eg, machinery, pumps, bearings etc. ).

State of the art

From practice it is known that grease lubricated bearings against arrest markings are more vulnerable than oil-lubricated what the conclusion suggests that the flow behavior has a great influence on the development. In addition to these general findings, there has been only few systematic studies on the causes of arrest markings and on critical parameters. On the Influence of grease components on the lubrication behavior at the operating conditions mentioned above are just a few basic tests are documented in the literature as well. Previously published research on this very special treat most cases of operation (eg, the influence of moisture ) or are very old (see bibliography). In recent years, the issue has found more attention, so that projects are currently underway at several German research institutions.

Definition of Terms

The term False Brinelling is derived from the known Brinell hardness test, which was developed by the Swedish engineer Johan August Brinell in 1900 and presented at the World Exhibition in Paris. Under " Brinelling " thus means a beyond the elastic limit beyond overloading of the bearing. This can occur, for example at a single shock or impact load.

The concept of " False Brin Elling " was created in the raceways of bearings due to the often false interpretation of trough- like depressions. Inexperienced maintenance staff has such wells often attributed to a purely mechanical overload, although this is a tribological indexed injury. On a large scale false Brinelling damage occurred for the first time on the ship transporting cars to America. New vehicles were already unloaded from ship wheel bearing damage. Cyclic vibration excitation by the low-speed diesel engines, and the relatively poor absorption of the transport deck had been sufficient to produce permanent markings in the running surfaces of the wheel bearing.

A typical damage ( cap ) can be divided into three areas: in the middle of the label is an area that does not experience any Realtivbewegung despite the micro-movements due to the high load and static friction and is therefore not affected. At this range, the severely damaged area closes sharply demarcated in which it comes to sliding movements under relatively high pressure between the friction partners. A third also clearly demarcated area may be designated as zone of influence. In this area, it also comes to sliding movements. However, the pressures are so low that no significant damage occurs.

Causes for the emergence of arrest marks

Possible causes for the emergence of arrest marks different mechanisms are:

Firstly, slide the micro-movements under high load the lubricant right out of the friction point out; there is a lack of lubrication phenomena. In addition, these micro-movements ( the contacting micro- contacts on the roughness peaks specifically ) stimulate the surface energy on. This leads to chemical reactions until a few nanometers in depth. This part of the damage correlated with the knowledge to tribo-chemical reaction ( fretting corrosion ). Another important and often -noticed point are microcracks that are caused by the cycling of the surfaces at the transition between the inner adhesive zone and slip zone and barely visible on superficial examination. These cracks lead but when rolling over under heavy load inevitably rapidly progressing damage. Good approaches for describing the contact mechanical effects are based on the investigations of Cattaneo (1939) and Mindlin (1949 ). You are in the standard work "contact mechanics" of KL Johnson summarized.

As a result of these three damage mechanisms mentioned in the formation of wear particles and reaction products which can hardly escape from the friction due to the lack of "real" relative motion and thus act as emery paste. This correlates, for example, with the development of fretting corrosion ( Tribo corrosion) and usually leads to a progressive loss experience and deep hollows, no longer leave the original damage mechanisms seen. In the further claims experience and during the rotational movement of the bearing overlap more wear mechanisms and disguise the true origin causes.

The standard laboratory test methods Fafnir or SNR test based on the assumption that it is a wear and tear damage to the fluting. In Fafnir test will swing angle of / -6 °, down in the SNR test / -3 °. It comes to "real" Abwälzvorgängen and not to in practice is considered as critical micro-movements. The greater the tilt angle is, the greater the importance of the Nachfließverhaltens the lubricant. In micro-movements, however, this point plays a subordinate role.

Avoid arrest marks

Current research projects are aimed at how to prevent the emergence of arrest marks by the use of suitable lubricants, materials and surface treatment processes. So far, however, been shown that good lubricants the damage progress can curb though; complete prevention of the damage, in critical operating conditions, but did not appear to have been possible. Investigations on the influence of the materials ( ceramic balls, surface finish, coatings) run at the Competence Centre tribology the University of Mannheim. Relatively safe can avoid the damage if it is ensured that the vulnerable bearings are moved regularly. For large machines transports this auxiliary drives will be mounted that provide at defined time intervals to ensure that the bearings are twisted.