Automating ASTM D2983 Low-Temperature Viscosity Measurements

Abstract

Abstract The low-temperature viscosity of lubricants and hydraulic fluids is a key performance parameter in choosing an appropriate fluid. For gear oils, Automatic Transmission Fluids (ATF), and hydraulic fluids, ASTM D2983 is the primary test method for defining this low-temperature property. This article describes an approach to automatically measure this property for the aforementioned categories of products. It retains the critical aspects of D2983, which are the preheating, thermal conditioning from room temperature to test temperature, viscometer, rotor, and viscosity measurement criteria. Thermal conditioning follows that described in Annex 2 of D2983, and when complete, the viscosity is automatically measured. This requires a digital rotational viscometer with the capability to record viscosity and temperature as a key element in making the needed measurements. As described in D2983, viscosity measurements are made at discrete shear rate intervals (spindle speeds) for a set period of time. Upon the completion of a test, the data file contains a history of the thermal conditioning (time and temperature), plus the viscosity and torque at each spindle speed. By automating the procedure, the sample is undisturbed from the start of the test until the viscosity measurements begin. This eliminates errors due to sample preparation and temperature control throughout the test. Since the spindle is immersed in the sample throughout the test, the viscosity is measured on an undisturbed sample. All of this results in consistent thermal conditioning and a controlled temperature during viscosity measurement and eliminates operator-induced variance. Data on ASTM Proficiency Test Program samples and other commercial products indicate significant improvement in precision. The samples evaluated include ATF, automotive gear oils, and other products. An abbreviated procedure is described that could be suitable for some samples. This is achieved by shortening the soak time at the test temperature, but following the same thermal conditioning process prior to the soak at the test temperature.