Guidelines for Selecting a Viscometer Based on Sample Type

Selecting the right viscometer for a specific sample requires consideration of the sample properties, measurement principle, viscosity range, and testing conditions. Several types of viscometers are widely used in industry, with Rotational Viscometers and Capillary Viscometers being two major types that operate on different measurement principles and are suited to different applications.

The key factors to consider before purchasing a viscometer include the following:

• Measurement Principle: Choose the instrument type that best matches the sample characteristics and testing objectives.

Rotational Viscometer: Suitable for liquids with a wide range of viscosities, such as paints, printing inks, adhesives, cosmetics, creams, gels, and certain food products. Some models can also be used to study the flow behavior of materials at different rotational speeds or shear rates.

Capillary Viscometer: Measures viscosity based on the flow of a liquid through a capillary tube, using the flow time under specified test conditions. This type of instrument is commonly used to measure the kinematic viscosity of suitable liquids, such as fuels, lubricating oils, and petroleum products, particularly in applications requiring testing in accordance with standards such as ASTM D445. The selection of the capillary tube and test conditions must comply with the applicable test standard.

• Viscosity Range & Sample Properties: Select an instrument that covers the viscosity range of the actual samples to be tested. Consider whether the material exhibits Newtonian or non-Newtonian flow behavior.
• Temperature Control: Temperature directly affects viscosity, making stable temperature control essential for measurement accuracy and result comparability. Rotational Viscometers may feature integrated temperature control or require additional accessories, depending on the model. Capillary Viscometers typically require a thermostatic bath to maintain the temperature of the capillary tube and sample in accordance with the specified test method.
• Measurement Parameters & Results: Verify whether the instrument can directly measure or calculate the required parameters.

Rotational Viscometers are commonly used to measure dynamic viscosity. Depending on the model and the appropriate accessories and software, some instruments can also determine shear rate, shear stress, and other flow characteristics.

Capillary Viscometers use flow time and the capillary constant to calculate kinematic viscosity. When dynamic viscosity is required, it can be calculated from the kinematic viscosity and the sample density measured at the same temperature.