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Technical Committee Lubricants

Examination of Compound Distribution in Lubricating Greases

The components of a lubricating grease are the base oil, the thickener and additives. During their production, lubricating greases are subjected to homogenization in a final process. The aim of the process is to equalize the distribution of all components and optimize the structure of the thickener. Automation of homogenization could reduce the costs of lubricant production, but has not yet been realized, because until now there was no known parameter which could be measured on-line during homogenization and with which the degree of homogenization could be quantified.

The aim of the research project was to test a series of measurement methods to determine whether they are suitable for on-line use to determine the condition of a grease during the homogenization process. In the project, the thickener structure was investigated using model greases of a lithium soap grease and a urea grease with the aim of contributing to a definition of homogeneity. The following methods were used: optical microscopy, scanning electron microscopy and optical coherence tomography (OCT). The result of the investigations is that the homogenization leads to a refinement of the thickener structure.

Second, the project applied the following measurement techniques to the model greases as candidates for use in real-time monitoring:

refractometry (measurement of refractive index), photospectrometry, Fourier transform infrared (FTIR) spectrometry with attenuated single reflection (ATR), and ultrasound propagation.

A correlation between measurement signal and homogeneity of the grease was shown by FTIR-ATR spectrometry and refractometry and only for urea grease by photospectrometry. Using the refractive index or integral area of the thickener band in the FTIR-ATR spectrum, different degrees of homogenization could be differentiated with the same sensitivity for both urea grease and lithium grease. The determination of the distribution of extreme-pressure (EP) additives was not possible or only possible by combining both methods.


The IGF project (20867 N) of the research association DGMK Deutsche Wissenschaftliche Gesellschaft für nachhaltige Energieträger, Mobilität und Kohlenstoffkreisläufe e.V.. Große Elbstraße 131, 22767 Hamburg, Germany, was funded by the German Federal Ministry of Economics and Climate Protection through the German Federation of Industrial Research Associations (AiF) as part of the program for the promotion of joint industrial research (IGF) on the basis of a resolution of the German Bundestag.

OWI Science for Fuels gGmbH
An-Institut der RWTH Aachen
Dr. Helen Ackermann
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