How to Make the Roll Stability Work Where the Worked Stability Doesn't Work

摘要

For many years, Worked Stability or Prolonged Worked Penetration test has been the standard test for the evaluation of the mechanical stability of greases. The majority, if not the totality of the specifications developed for the greases used by the military and the civil aviation, as well as the ground equipment, were subject to this requirement. To simulate the conditions of actual applications, the test is commonly conducted in the presence of water or even with sea water. The magnitude of the penetration change as result of the worked stability test (in wet or dry conditions) provides information on the resistance of the grease. The grease will shear when subjected to an extensive mechanical work, thus to some extent, prolonged worked penetration can help predict the component service life. ASTM D 217 or equivalent test methods are far from simulating the actual application conditions. A large amount of grease is pushed up and down in a closed cup through a perforated plate for a specified number of double strokes. The grease is not subjected to the load, temperature, or rotational speed that is usually experienced in the field. The method in which water is added to the grease was and is still subject of discussion. The results of the worked stability are dependent on the method used to emulsify the grease. Unlike the Worked stability test, the Roll Stability test seems to overcome all these limitations. Small amounts of grease are used in this test to simulate an actual bearing. A bearing works by squeezing a thin film between two steel surfaces under a load with a unidirectional rotation at a given speed. This bearing simulation can run at temperatures similar to the temperatures of application. Water is simply added to the grease in one step eliminating any variability associated with a multi step process. In addition to these advantages, the roll stability test is also an efficient and effective tool for evaluating grease compatibility which can be conducted under actual temperatures. This study will encompass extensive data involving greases made with different thickening systems, various base oils viscosities and in the presence or absence of water.