A fluid’s resistance to flow is its viscosity—the ratio of force required to overcome internal friction between layers of fluid (shearing stress) to the change in speed between layers of fluid (velocity gradient). Many quality control measures are based on viscosity. For example, paint needs to be able to spread properly, but should not be dripping off of the brush. Ink must come out of a nozzle in a precise manner.
Technologies used to measure viscosity for various types of fluids include:
Falling ball viscometers measure the viscosity of fluids and some units can also measure the viscosity of gases.
Viscosity cups use gravity to allow a fluid to flow through an orifice located at the bottom in a precise amount, which can be measured over time to calculate viscosity.
Consistometers are metal troughs with graduations that measures materials as they flow at an incline under their own weight. These are typically used to measure paint viscosity to ensure conformity to military specifications.
Glass capillary viscometers are used mostly with test methods which conform to a particular ASTM. Use them with viscosity baths to maintain a stable temperature.Tuning fork vibration viscometers feature a level of 1% of reading with a high level of accuracy.
Rotational viscometersaccommodate wide ranges well into millions of centipoise and are considered the most versatile type of viscometer. Their digital readout and ease of use also provide a high degree of accuracy.