GAOTek provide exceptional selection of high-quality rotational viscometers. Rotational viscometers determine the function of the fluid’s viscosity by measuring the point when the torque starts rotating the disk or bob at a known speed.

“Cup and bob” viscometers work by determining the exact volume of a sample which is to be trimmed within a test cell. This works only when the torque achieves a certain rotational speed and then it is measured and plotted. There are two classical geometries in “cup and bob” viscometers known as “Couette” or “Searle” systems.  In some cases, the rotating cup is preferred, because it reduces the onset of vortices at a very high shear rates. However, the rotating bob is commonly used due to its flexible design for other geometries.

“Cone and plate” viscometers use a narrow-angled cone in close proximity to a flat plate. It allows the shear rate between the geometries to be constant at any given rotational speed. The viscosity can easily be calculated from shear stress from the torque and shear rate from the angular velocity.

Calculating shear rate and shear stress form factors differ for each measuring system. Each measuring system will have an associated “form factors” to covert torque to shear stress and to convert angular velocity to shear rate.

• C1 is shear stress form factors and the shear rate factor is C2.

Shear stress = C1 × torque

Shear rate = C2 × angular velocity / gap

Viscosity = shear stress / shear rate

The following sections show how the form factors are calculated for each measuring system.

Cone and plate

C1 = 3 / 2 × r3

C2 = 1 / θ

where: r = radius of the cone

θ = cone angle in radians

Parallel plates

C1 = 3 / 2 × r3

C2 = 3r / 4

where r = radius of the cone

NOTE: The shear stress varies across the radius for a parallel plate. The above formula refers to the 3/4 radius position

Coaxial cylinders

C1 = ra²H / 3

C2 = 2ri²ro² / ra² (ro² - ri²)

where:

ra = (ri + ro) / 2

ri = inner radius

ro = outer radius

H = height of cylinder

NOTE: C1 takes the shear stress as that occurring at an average radius position ra.

GAOTek’s viscometers are made up of these features:

•         Collects data accurately and effectively
•          Gorgeous display of test data with ultra-bright LCD screen
•         Able to determine the absolute viscosity of Newtonian and Non-Newtonian liquids (including, but not limited to greases, oil paints, plastics, pharmaceutics, coatings, adhesives, detergents, asphalt, hot sol, paraffin, high polymer, etc.)
•         Able display data in real time, and print out measurement data
•        Microcomputer technologies for temperature control, data collection, and data process
•        High speed rotational spindle efficiently measures viscosity
•        Simple interface allows for easier operation
•         Effective in various environments

Viscometers have wide and varied applications in the materials science and chemical industries for materials such as oil, asphalt, plastics, wax, paints, coatings, and adhesives. They are also used for food and beverages and personal-care products such as cosmetics, shampoo, and toothpaste.

Viscosity is a very useful indirect measure of material properties including molecular weight and density, both of which affect flow behavior. Viscometers can therefore be used to monitor batch consistency and quality control.

Some examples of these applications include:

·         Measuring the flow of engine oil under different temperature conditions

·         Analyzing the flow properties of milk to design suitable piping systems

·         Checking the viscosity of jams and syrups to ensure batch consistency