Recently Developed Procedures and Tests to Investigate the Lubricating Capability of Different Types of Hydraulic Fluids * 2002-01-1402

Traditionally, various testing methods are used to determine the lubrication properties of hydraulic fluids. The specific standard for mechanical testing of hydraulic fluids is based on a special type of hydraulic power unit, the vane pump (DIN 51 389, DIN 51 524). Numerous other procedures for mechanical testing of lubricants are used, the most important one being the gear rig test by the FZG-method (DIN 51 354), in which the tested fluid is exposed to a certain load by shearing it in a gear set. Moreover industry uses several non-standard ‘in-house’ testing methods.

This situation can not be satisfying in many respects: Since only part of the interaction between fluid and component is tested with the existing test procedures, the validity of test results is limited, especially in the case of the vane pump test. Run under the same conditions, some tests lead to results of widespread variation with a problem of reproducibility; due to the number of necessary test procedures, cost and time expense is too high.

In order to overcome this a new application-related test procedure is developed at the authors' institute. This paper describes the systematic development of the newly created procedure and shows some first experimental results with the test apparatus, where the lubricating properties of a mineral oil-based and an ester-based fluid are compared.