Applications of viscometers

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.

Measuring viscosity is important when considering process conditions for materials that need to be pumped or piped. Viscosity also affects dipping and coating performance, which is particularly relevant to paints and inks.

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.

Example 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.

Since changes in viscosity reflect changes to molecular weight, viscometers are used to characterize plastics. They are particularly useful in polymer synthesis since the flow rate can be used to determine the change of polymer length through different processes.

In many industrially useful cases, viscosity decreases as enzymatic activity increases. Viscometers are used to determine the activity of enzymes such as cellulase, protease, amylase, and pectinase.

Types of viscometers

There are many ways to measure viscosity, but they break down into two basic methods. Either an object, such as a sphere or a rotor blade, moves through a stationary material, or the material flows through or past a stationary object. In either case, the resistance to flow is measured.

Capillary viscometers

Also known as u-tube or glass viscometers, capillary viscometers are often used in laboratory settings. Viscosity is measured by timing how long it takes for a transparent or translucent fluid to flow between two points of a capillary tube.

For opaque liquids, it is hard to determine when the sample has passed a point in the tube, so it is necessary to use reverse-flow viscometers that only wet the timing section of the viscometer capillary during the actual measurement. The Cannon-Fenske Opaque, Zeitfuchs Cross-Arm, and BS/IP/RF Viscometers from CANNON Instrument Co. (State College, PA; ..........com) are all reverse-flow types. Reverse-flow viscometers must be cleaned, dried, and refilled before a repeat measurement can be made.

Capillary viscometers can be manual or automatic. Automatic instruments use infrared optical sensors for transparent samples, or thermal sensors for opaque samples.

Rotational viscometers

Simple rotational viscometers, also known as Brookfield type viscometers, use a torsion spring to measure the torque required to rotate a spindle in the material. Changing rotor speed and size allows for the measurement of different ranges of viscosity.

Rotational viscometers

Simple rotational viscometers, also known as Brookfield type viscometers, use a torsion spring to measure the torque required to rotate a spindle in the material. Changing rotor speed and size allows for the measurement of different ranges of viscosity.