on the test rig
High-quality lubricating oils are used in gear wheels and worm gears; these are either mineral oils or synthetic oils depending on their area of application. The high specific loads applied to modern gearboxes set high standards for the quality of the gear oils. Suitable oil additives help to improve the scuffing, micro-pitting and pitting load capacity of the gear wheels at the tooth flank. Additives also influence the aging resistance and the foaming characteristics of oils. Excessive foaming has a negative impact on the load capacity of the gear wheels and bearings. Excessive foaming of gear oils may also cause oil leakage at the shaft seals and bleeders.
As a rule, oil manufacturers test the foaming characteristics of their oils in accordance with the ANSI / ASTM D 892 method and/or a similar method pursuant to DIN 51566, i.e. by injecting air into an oil sample over a preset time. As the results from this test frequently do not match the foaming characteristics detected in gearboxes, it was necessary to develop a test setup focusing on actual operating conditions. In the foaming test rig, a gear pair rotates in the oil to be tested and thus mixes an air-in-oil dispersion. The surface foam, the volume change of the air-in-oil dispersion as well as its reduction are tested under marginal conditions which occur in gearboxes.