The shear thinning index and the degree of thixotropy can vary greatly between different paints, and is temperature-dependent. This test method allows you to calculate the degree of shear thinning and thixotropy, which is especially important for the application behavior of paints and coatings. Test method B: Determination of the degree of shear thinning and thixotropy under changing speed conditions. If this is the case, the measurement has to be stopped after a specified period of time, e.g. When measuring thixotropic paints, the reading might not stabilize. Once the viscosity reading has stabilized, stop the viscometer. Simply select a speed on the rotational viscometer so that the torque reading is between 10 % and 95 %.

Test method A: Determination of the apparent viscosity at 25 ☌ at a certain speed. In the next chapters, you will learn how to measure the viscosity of different chemical samples with such a spring-type viscometer. In case of low-viscous substances, the spring needs to be sufficiently sensitive, whereas for samples in the high viscosity range, a more robust spring is required. Different spring-types of rotational viscometers allow measuring substances from low to high viscosity. Optical sensors detect the deflection and, as a result, we get the viscosity of the sample. The rotation (torque) of the spindle deflects the spring. A spring connects the motor of the viscometer and the spindle. The sample in the cup follows this movement and in further consequence the torque (force) required for turning the spindle against the fluid’s viscous forces is measured. The speed on the viscometer is preset and the spindle starts to rotate. A typical rotational viscometer used for quality control measures the viscosity according to the “ Searle principle”.Ī cup is matched with a so-called spindle that is placed in the sample. Before we get started with how to measure viscous materials, let’s have a quick look at how a rotational viscometer works.

How to test viscosity of small volumes