How to choose Viscometers
A viscometer is an instrument that quantifies the viscous resistance of a fluid by measuring the ratio of shear stress to shear rate under specified flow conditions.
Newtonian & Non-Newtonian Fluids
Newtonian fluids: Newtonian fluids are those whose viscosity, at any given temperature, does not change with shear rate (i.e., the rotational speed of the viscometer).
Non-Newtonian fluids: Their viscosity varies with shear rate (i.e., rotational speed) or shear time. They must be measured using a rotational viscometer or a rheometer, and multiple rotational speeds are required; otherwise, the data are incomplete.
Rotational Viscometers
Special Types of Rotational Viscometers
Brookfield Viscometer (General-Purpose Type)
Offers a wide variety of spindles and accessories. It is suitable for measuring an extensive range of samples and for conducting in-depth rheological studies (such as generating rheological curves).
Krebs Stormer Viscometer (Industry-Specific Type)
Designed for the paint and coatings industry. Unlike other rotational viscometers that measure absolute viscosity in mPa·s (or cP), the Krebs Stormer viscometer measures the weight (grams) required to maintain a constant rotational speed of 200 RPM and then converts this value to Krebs Units (KU) using a specific logarithmic function.
Viscosity Measurement Range
Low Viscosity Range (1–1,000 mPa·s)
Characteristics: Flows very quickly, similar to water.
Typical materials: Water, milk, beverages, vegetable oil, low-viscosity engine oil, solvents.
Medium Viscosity Range (1,000–100,000 mPa·s)
Characteristics: Flows slowly.
Typical materials: Honey, syrup, paint, cream, lotion, shampoo, ketchup.
High Viscosity Range (above 100,000 mPa·s)
Characteristics: Hardly flows under its own weight.
Typical materials: Peanut butter, toothpaste, silicone, sealants, asphalt (in molten state), polymer melts.
Rotational Speed
Fixed speeds
(0.3, 0.6, 1.5, 3, 6, 12, 30, 60) r/min, or 6, 12, 30, 60, or 5, 10, 20, 50 RPM, or 200 RPM (Krebs Stormer).
Stepless speed control
0.1–200 RPM or 0.1–99.9 RPM or 1–60 RPM.
1. Selecting the Spindle
High-viscosity samples: Use a smaller spindle and a lower rotational speed. A small spindle has a smaller contact area and lower rotational resistance, preventing excessive torque and overrange errors.
Low-viscosity samples: Use a larger spindle and a higher rotational speed. A large spindle has a larger contact area, amplifying the torque signal and improving measurement accuracy.
2. Leveling the Instrument
Adjust the leveling feet on both sides of the instrument base so that the bubble in the spirit level is centered.
3. Instrument Settings
Select the spindle model and set the rotational speed (RPM).
4. Temperature Control
Constant-temperature water bath (for viscometers without built-in temperature control):
Place the sample beaker in a water bath to heat or cool the sample until it reaches a stable temperature (e.g., 25°C, 40°C).
Heating chamber (for viscometers with built-in temperature control):
Heat the sample inside the instrument’s integrated heating chamber.
5. Validity of Measurement Values
The ideal torque range is 20%–80%.
Torque too low (<10%): Signal-to-noise ratio is poor, resulting in inaccurate data.
Torque too high (>80%): Approaches the instrument’s physical limit and may cause measurement errors.
Precautions
The sample must be free of air bubbles before measurement.
The liquid level must cover the spindle’s immersion line to ensure valid measurements.
The spindle must not touch the container walls during measurement.
