Factors That Affect Viscosity Measurements

2021/06/19

Factors That Affect Viscosity Measurements

Although the viscosity of a fluid seems easy to analyze, accurate measurement of this fluid can be a difficult task. In order for the measurement to be valid, several factors must be known and kept constant, including:

Temperature

In terms of importance, temperature is to viscosity what viscosity is to base oil. The sole responsibility of the temperature control bath is to ensure that the entire viscosity measurement experiment is maintained at a precise temperature (usually 40 or 100 degrees Celsius) and controlled within 0.02 degrees Celsius. This is why more complex viscometers include a temperature-controlled bath system as part of the unit.

Viscometer

Viscometer

Viscometer glass

The accuracy of the capillary viscometer depends not only on the temperature, but also on the precise inner diameter of the tube. For this reason, these glass tubes are formed from fully annealed, low-expansion borosilicate glass, and the viscometer constant associated with the tube is often used as a correction factor. The usual practice is to recalibrate the constant of the viscometer according to the temperature of use every year to ensure as little error as possible.

The size of the viscometer

Due to the wide variety of viscosities to be tested, the size of the viscometer is also different. It is recommended that the viscometer take at least 200 seconds from one mark to another (manually measured with a stopwatch) to avoid human error.

Measurement between cleanings

Another key viscometer test factor is the quality of the rinse in the tube between measurements. Generally, the washing, rinsing and drying stages are carried out using various residual-free solvents. In the laboratory, the sample runs continuously on the high-capacity viscometer, and the built-in cleaning system ensures cleaning efficiency. Nevertheless, a visual inspection is still required to determine if a second rinse cycle is required, especially the used oil.

Other important factors affecting viscosity measurement include the method and accuracy of the timing device, proper sample handling, and in-depth and continuous quality control.

Over the years, viscosity measurement has evolved into various styles and methods. Viscometer testing methods, procedures, calibration, cleaning and other factors have also been developed to ensure accuracy and consistency between different viscometers.

After all, viscosity is the most important physical property of the base oil. The effort to measure viscosity through careful methods and strict standards can be equated with more reliable mechanical lubrication, which ultimately leads to longer mechanical life.

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