Practical use of micropitting test results according to FVA 54/7 for calculation of micropitting load capacity acc. To ISO/TR 15144-1

This paper aims at giving a practical guideline for setting the right test parameters for micropitting tests according to FVA 54/7 and using the obtained results for calculation of micropitting load capacity according to ISO/TR 15144-1 for specific gear drives under given operating conditions. The micropitting test according to FVA-Information Sheet 54/7 consists of two parts and is carried out for a specific oil under fixed conditions regarding oil temperature and circumferential speed. First, a step test for predefined load stages with increasing torque is performed. Result of this step test is a classification of the lubricant regarding the micropitting load capacity expressed as a failure load stage (SKS). The failure load stage (SKS) is defined as the load stage, in which the defined failure criterion (profile form deviation f_fm) is exceeded. In a second part, a subsequent endurance test usually is performed which provides information about the progress of micropitting at a higher number of load cycles. This approved, standardized and widely used test method can be used for deriving the micropitting load capacity of all types of gear oils. Whereas the micropitting test according to FVA 54/7 provides information about the micropitting performance of a specific lubricant, the calculation method for micropitting load capacity acc. ISO/TR 15144-1 allows the evaluation of a safety factor against micropitting for a specific gear drive under given load (torque, circumferential speed and lubricant temperature). The calculation is based on a comparison of the actual specific lubricant film thickness and the permissible specific lubricant film thickness. Test results from a micropitting test (e.g. acc. FVA 54/7) can be used to determine the permissible specific lubricant film thickness. To achieve reliable results for the safety factor, particular attention has to be paid to the used test parameters in the lubricant test. This paper gives a detailed guideline on setting these parameters right.