Viscometer

viscometer
Tribology Wikipedia > Viscometer

What is viscometer?

Viscosity refers to the fluid’s resistance in its ability to move. A high-viscosity (or “thick”) liquid flows much slower than a low viscosity (or “thin”) liquid. his can be seen with the speed of oil’s flow compared to the one of water when they’re both at the same temperature.

When dealing with fluids in manufacturing, understanding their viscosity is crucial for various reasons: quality control, possible overheating, preamature wear of the parts, leakages, etc. having the right viscosity is key for the succsful operation of a machine.

A viscometer (also known as the viscosimeter) is a tool utilized to determine the substance’s viscosity. In the case of liquids with viscosities that differ according to the flow conditions, the instrument known as a Rheometer is typically used. This is why a Rheometer may be described as a distinct kind of viscometer. Viscometers are only able to measure in one flow state.

Why are Viscometers Important?

Viscometers can help ensure that the viscosity of your fluid complies with the specified tolerances. In doing this, they help guarantee consistent operation results.

In the past, if you didn’t have monitoring, you could encounter various problems with viscosity. Viscosity, whether thicker or thinner, can impact the way your equipment processes the fluids you’re working and, if it’s not uniform, there could be problems like:

  • Colour shifts and inconsistencie
  • Many quality imperfections
  • Material (i.e. paint or ink) materials (i.e. ink or paint)
  • Excessive solvent usage
  • In-process or rework work that isn’t necessary

It’s no surprise that your customers will not be satisfied with products that are affected by these problems. This is why it’s essential to check the viscosity of your processes.

Be Aware of Fluid Viscosity.

If you decide to start using the viscometer regularly to measure the viscosity of your fluids, it is possible that you’re not achieving the proper tolerances. If you’re experiencing this, you should try these steps:

  • Make sure you have calibrated your viscometer. Some viscometers require periodic calibration.
  • Make sure you test the mix that your liquid has. Does it look consistent? Did it change recently?
  • Examine your equipment. It could need cleaning or other types of maintenance.

Six types of viscometers

  • Viscometers with orifices
  • Capillary viscometers
  • Falling piston viscometers
  • Rotational Viscometers or in simple term Viscometer that rotate
  • Viscometers for falling balls
  • Vibrational viscometers

Viscometers with orifices

An orifice viscometer typically consists of a glass with a hole through which fluid flows. Viscosity is measured by measuring the time it takes the cup to empty. It is calculated in seconds of a cup. Viscometers for orifices are easy to operate manually because they’re placed in the fluid to be used; they are a popular tool in the painting industry. They can be found in Zahn Cups, Ford Cups and others.

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Figure 1. Orifice viscometer.

Capillary viscometers

Also called U-tube viscometers, capillary viscometers are two types: the Ostwald and Ubbelohde variants. They’re easy to operate, comprising the shape of a U-shaped glass tube, which has 2 bulbs (one higher than the other). The fluid flows from the upper bulb into the lower via a capillary. The viscosity is determined by determining the time for the fluid to move within the tube.

Figure 2. Capillary viscometers.

Falling piston viscometers

The viscometers for falling pistons were developed in the late 1800s by Austin Norcross, which is why they’re also known as Norcross viscometers. They work by drawing the liquid being determined into the piston-cylinder when the piston is elevated; the time it takes for the piston to lower (time-of-fall seconds) because of the fluid’s resistance can be used in determining the viscosity. Viscometers for falling pistons are easy to operate and maintain and provide longer service life.


Figure 3. Falling piston viscometers.

Viscometers that rotate

Viscometers that rotate measure viscosity by submerging a rotating spindle into the liquid to be tested. The force (torque) required to rotate the spindle determines the viscosity of the liquid as they don’t rely on gravity for work; the fluid’s internal shear force determines their calculations.

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Figure 4. Viscometer that rotates.

Viscometers for falling balls

The falling ball viscometer works the same way as the fall piston viscometers. When using this type of viscometer, a small ball is dropped into the fluid that is being studied. Dimensions of the ball are well-known, so the viscosity is determined by the amount of time it takes for the ball (again using time-of-fall second) to drop into the fluid through gravity.

Vibrational viscometers

Vibrational viscometers employ a powered vibrating rod for measuring viscosity. Certain fluids can be more receptive to vibrations based on the degree of viscosity. So by measuring the dampening effect of the vibration or by observing the speed at which the vibroometer’s frequency decreases, the viscosity is assessed. Vibrational viscometers are extremely popular due to their highest sensitivity without moving components.

Accuracy

The precision or accuracy depends not just on the instrument’s design but also on how the temperature is controlled.

Viscosity standards can be used to test the precision of a viscometer. It is a crucial factor in determining conformity with the industry’s quality standards. Make sure the manufacturer has standards that meet your requirements. Brookfield Silicone and Mineral Oil Standards provide a viscosity of the fluid that is constant at 25 degrees Celsius. The company suggests replacing the standards annually.

Consideration before purchasing viscometers

The selection of a viscometer is an intricate process based on the type of sample and viscosity, the opacity and quantity of sample available, the required throughput and the degree of automation required. At the minimum, these factors must be taken into consideration:

  • Viscosity range
  • Accuracy
  • Control of temperature
  • Microvolume and sample volume capabilities
  • Computer interfacing and automation
  • Industry standards and regulatory requirements.

The article is written by Riya Veluri, an editorial team member of Industrial Lubricants. After her graduation, Riya works as a website developer & SEO specialist in Lubrication & Tribology Industry & writes technical articles on Lubricants, Lubrication, Reliability & sustainability.