How the Different Types of Viscometers Work

In previous blogs, we discussed the “what” and “why” of viscometers — what they are and why they are useful in measuring ink viscosity. In this blog, we will be going over the “how” — that is, how different process viscometers work. This list is by no means exhaustive; there are other types of viscometers out there, but not all of them are useful for industrial ink control and flexographic printing processes.

Here are the four types we’ll cover:

• Falling piston and ball viscometers
• Rotational viscometers
• Torsional viscometers
• Vibrational viscometers

#1 – Falling piston and ball viscometers

Falling piston viscometers used in manufacturing or flexography, due to their ease-of-use, simple maintenance, and long life. They consist of a piston of a diameter determined by the viscosity range of the fluid, a cup to collect the sample in process, a rod assembly on which the piston is attached, an air cylinder to lift the piston/ rod assembly and a switch to count the time of fall. They function by drawing the fluid into the piston cylinder while the piston is lifted; the time it takes the piston to fall (time-of-fall seconds) due to the resistance of the fluid determines the viscosity. 

Falling ball viscometers work in a similar fashion to falling piston viscometers. With this type of viscometer, a ball is lifted and dropped into a cylinder of the ink being measured in process. The dimensions of the ball are already known, so viscosity is determined by timing how long it takes the ball (again, using time-of-fall seconds) to fall through the fluid via gravity. 

#2 – Rotational viscometers

Rotational viscometers use a rotating spindle immersed in the fluid to measure viscosity. The amount of power (torque) required to turn the spindle indicates the viscosity of the fluid, and because rotational viscometers do not require gravity to function, their measurements are based on the internal shear stress of the printing ink.

#3 – Torsional oscillating viscometers

Torsional oscillating viscometers consist of a probe oscillating at a resonance frequency with amplitudes in the micro- to nanometer range. A fluid in contact with the probe dampens the torsional oscillation. The degree of damping depends on the ink density and viscosity, making this tool ideal for real-time monitoring in high-precision ink metering systems used in flexographic presses.

#4 – Vibrational viscometers

Vibrational viscometers use a powered, resonant frequency, tuning fork, (or “oscillating electromechanical resonator,” according to Wikipedia) to measure viscosity. Different fluids are resistant to vibrations depending on how viscous they are. Therefore, by measuring the power needed to overcome the dampening of the fluid, or by measuring how quickly the vibration of the viscometer dies off once power is switched off, viscosity can be determined. Vibrational viscometers are popular in flexo press automation because they offer maintenance-free operation, high sensitivity, and no moving parts, making them perfect for continuous ink viscosity monitoring.

Conclusion 

Precise ink viscosity control is critical for achieving consistent color density and print quality in flexographic printing. Each type of ink viscometer serves different applications, from inline process monitoring to laboratory formulation testing.

For more information, please contact INKSPEC.  Sales@inkspec.com  +14504415005  www.inkspec.com