Viscosity — a measure of a fluid’s resistance to flow — is an important property of liquid and semi-liquid products that can be used for both process and product-quality control. While this rheological property can be measured via several different devices (flow cups, capillary tubes, and rotational viscometers), rotational viscometers have become the most popular choice, as it is relatively straightforward to operate and requires minimal testing and clean-up time. It is important to note, however, that the viscosity value obtained from a rotational viscometer depends on the shape and speed of rotation of the spindle.
This article provides an overview of viscosity and how it is used in the quality-control laboratory as well as on the production floor. While it describes the three most-popular measurement methods, the article focuses on rotational viscometers — outlining the different components and how to choose the right instrument for a particular purpose. Finally, the article discusses how to use viscosity data to control your process.