Standard Test Method for Automatic Determination of Low-Temperature Viscosity of Automatic Transmission Fluids, Hydraulic Fluids, and Lubricants Using a Rotational Viscometer

Importancia y uso:

5.1 The low-temperature, low-shear-rate viscosity of automatic transmission fluids, gear oils, torque and tractor fluids, power steering fluids, and hydraulic oils are of considerable importance to the proper operation of many mechanical devices. Low-temperature viscosity limits of these fluids are often specified to ensure their suitability for use and are cited in many specifications.

5.2 The manual test method, Test Method D2983, was developed to determine whether a gear oil or an automatic transmission fluid (ATF) would meet low-temperature performance criterion originally defined using a particular model viscometer.4 The viscosity range covered in the original ATF performance correlation studies was from less than 1000 mPa·s to more than 60 000 mPa·s. The success of these correlations and the development of this test method with gear oil and ATF performance has over time been applied to other fluids and lubricants such as hydraulic fluids, and etc.

5.3 Some formulated fluid types may form a structure, presumably due to the presence of wax, when soaked at or below a certain low temperature. The viscometer’s spindle rotation can degrade this structure during the viscosity measurement, which may result in a decrease in the apparent viscosity as the step time increases. This decrease in a fluid’s apparent viscosity is often referred to as shear thinning. A sample that exhibits a high initial apparent viscosity may impede the lubrication of certain machinery, such as automatic transmissions.4 However, it is not unusual to see a sample exhibit shear thinning behaviour when measuring high viscosity products such as gear oils, especially those formulated using solvent refined base stocks. It is recommended, that if this phenomenon is observed in ATF or similar low viscosity products, the suitability of the fluid for the application should be carefully considered. If desired, Test Method D5133 or D6821, may be used to study the behavior of these fluids.

5.4 The viscosity determined by this test method using option A was found to be statistically indistinguishable from Test Method D2983 – 16 measurements based on the ILS data to establish this test method’s precision. The ILS results were consistent with the data obtained on numerous ATF and gear oils evaluated in developing this test method.5

5.5 Due to the shorter time at test temperature, results from the abbreviated thermal conditioning (Option B) may differ from results obtained with the 14 h soak at test temperature (Option A). For the samples used in developing this test method, results obtained with the abbreviated procedure (Option B) tended to be less than 14 h soak (Option A). This difference seemed to be larger for products that contained high wax base stock.

Subcomité:

D02.07

Referida por:

D8278-20, D2983-23, D8164-21, D2983-23, D2983-23

Volúmen:

05.05

Número ICS:

75.100 (Lubricants, industrial oils and related products)