Standard Test Method for Measuring the Thread Length and Pull-off Force of a Lubricating Grease by using the Falex TAA Instrument

Abstract

5.1 This method is used to characterize a grease using the described instrument to obtain a quantitative measurement of properties defined in this method as thread length and pull-off force. These properties are measured under repetitive and consistent testing conditions as defined by this method. This standard uses a copper ball to isolate a single thread out of a grease volume (see Fig. 2). Previously, tackiness was evaluated qualitatively by subjective methods without controlled retraction speeds or temperatures, or by indirect methods such as water washout, hammer impact, etc. A widely used quick test is known as the finger test (see Fig. 2). The finger test indicates major differences in grease tackiness, specifically the thread formation, but it lacks control and is subjective to the operator's execution. It does not result in quantitative data that can be used to classify or compare lubricating greases. FIG. 2 Thread Formation Illustrated in Qualitative ‘Finger Test’ (left) and Copper Ball Isolating a Single Thread in Instrumented Indentation-retraction Experiment (right) 5.2 This test standard will allow quantitative data to be measured for the characterization of lubricating greases. The test results can be correlated with requirements of field applications of lubricating grease and for use in specifications, the significance is to be determined by the user of this method. 5.3 In applications, thread formation can be a desirable or undesirable quality. For example, a higher tackiness is desired in industrial machinery, agricultural and automotive equipment, open gears and one sliding surfaces, where transfer and refreshment of the grease between contacts is essential to maintain lubrication. On the other hand, low tackiness may be favorable in lubrication of processing machines in food industry, where grease transfer can cause contamination of the product and should be avoided.