Tribo Contacts in Gears

The GMBU tribosensor concept (DE 10 2014 103 231) was developed to record acoustic emissions (AE), in which a sensor is placed in close proximity to a lubricated sliding friction contact.
The concept was developed on a tribometer (Download four-ball apparatus) and extended to the monitoring of tooth flanks rolling against each other [1,2].
In plain bearings, the transition from the EHL range to mixed friction could be detected. The concept is also suitable for detecting wear damage in rolling bearings.

THE ORIGIN OF AE IN LUBRICATED TRIBOLOGICAL CONTACTS

The lubricated frictional contact between two solid bodies is a complex process. The Stribeck curve describes the various friction scenarios as a function of surface pressure and relative speed.
In the area of fluid friction, the solids are separated by a lubricating film. In the area of mixed friction, there is sporadic contact between the solids. Ad hoc vibrations and AE occur due to the elastic deformation. Frictional heat is released. In the long term, plastic deformation of the solids occurs and microcracks and mass erosion occur at the contact surfaces.
This scenario is the basis for indirectly modelling the friction and wear processes with AE measurements [3].

DETECTION OF MIXED FRICTION IN SLEEVE BEARINGS

Plain bearings are operated in the transition from fluid friction to mixed friction. In large industrial bearings, maintaining the optimum friction regime is linked to controlling the oil pressure. For operating cost reasons, it is very important to maintain the optimum operating point.
With the aid of an AE sensor, which is mounted in the hollow shaft of the plain bearing, the lubricant film breakdown can be detected and the optimum operating range for the hydrodynamically lubricated bearing can be specified. (Download plain bearing).

CHARACTERISATION OF ROLLING SLIDING CONTACTS AT MESHING TEETH FLANGES

Gear flanks are affected by wear in particularly. This occurs when the load-bearing lubricating film breaks down under high surface pressure and tooth flanks briefly touch each other. Acoustic emissions occur immediately (Figure below centre). The AE
change significantly in the event of abrasion damage or the absence of lubricant (illustration below right). In the medium term grey spotting occurs and in the long term, seizure processes (pitting) or flank breakouts occur.
The adaptation of the tribosensor concept for monitoring tooth flank contact offers the opportunity to gain detailed insight into the rolling-friction process (Download Tooth meshing). The high-resolution temporal recording of the AE thus offers the prerequisite for condition monitoring and predictive maintenance concepts.

REFERENCES

[1] L. Ledig, U. Bauerschäfer, S. Gai, Erfassung und potentieller Nutzen hochfrequenter akustischer Emissionen in Tribosystemen am Beispiel des VKA, GETLUB Tribologie- /Schmierstoffkongress Mannheim, 26./27. März 2014

[2] S. Gai. U. Bauerschäfer, L. Ledig, K. Krüger., Zustandsdiagnose an Maschinen auf der Grundlage hochfrequenter akustischer Emissionen, NetUs 2020 Workshop VIU Akademie, 01/2020

[3] S. Schnabel, Monitoring of Wear in Elasto-Hydrodynamic Lubricated Contacts, ISBN 978-91-7439-855-7