How it works:
The Stormer viscometer is a rotary viscometer used to determine the viscosity of non-Newtonian fluids, which is widely used in coatings, inks and other industries. The core principle is to calculate the viscosity value in Krebs units (KUs) by measuring the load weight or torque required to maintain a fixed rotational speed (typically 200 rpm) by rotating a specific shape in a specifically shaped paddle. KU viscosity is one of the key indicators of workmanship and construction performance of latex paint products in the coating industry.
The basic working formula of the instrument is:
KU = (W - C) × K
where W is the applied load weight (grams), C is the internal friction compensation constant when the instrument is running without load, and K is the instrument-specific conversion coefficient. This formula establishes a linear relationship between the load weight and the KU viscosity value, making the measurement results readable directly or through calibration charts.
Determine significance
The KU viscosity of latex paint directly affects its storage stability, pumpability, painting feel and final film formation quality. too low viscosity may lead to pigment settling and coating film sagging; Excessive viscosity may cause construction difficulties and obvious painting marks. Standardized measurements by stormer viscometers can provide objective and reproducible data for production quality control, formulation adjustments, and construction applications to ensure product performance meets expectations.
Assay method
The determination process should be performed under a standard temperature and humidity environment, and the sample should be thoroughly agitated and air bubbles eliminated. The specific steps are as follows: First, load an appropriate amount of latex paint sample into a container of the specified size, and the liquid level must reach the specified height. The Stormer viscometer blade is then immersed vertically into the sample to a specified depth. Start the instrument and gradually increase the load until the blade speed stabilizes at 200 rpm. The load weight applied at this time is recorded, and the corresponding KU viscosity value can be obtained through the calibration table or calculation formula built into the instrument. Clean the paddle and container thoroughly after each measurement.
Notes:
The accuracy of the assay is affected by a variety of factors. Ambient temperature is the primary factor, and temperature changes can significantly alter the apparent viscosity of latex paints, so testing should be performed under constant temperature conditions. The sample is preprocessed, such as stirring speed and time, to ensure consistency. The calibration status of the instrument is critical and needs to be checked regularly with standard viscosity oil. In addition, the size of the test vessel, the immersion depth of the paddles, and the presence of air bubbles during the test can introduce errors and must be strictly followed in accordance with standard operating procedures.
Relevant standards
The determination of KU viscosity of latex paint mainly follows the following domestic and foreign standards, which make detailed regulations on instrument specifications, test conditions, operating procedures and result reports.
| Standard code | Standard name |
| ASTM D562 | Standard test method for determining paint viscosity using a stormer viscometer |
| GB/T 9269 | Determination of viscosity of architectural coatings by stormer viscometer method |
| ISO 2884-1 | Color paints and varnishes Determining viscosity with a rotary viscometer Part 1: Cone plate viscometer with high shear rate |
In actual testing work, the specific standard version should be clarified and followed.
Data interpretation
The measured KU viscosity value should be judged in conjunction with the product specification or internal quality control range. Typically, latex paints have a KU viscosity range of 75 to 110, depending on the type of product and application. This data is not only used to judge whether a single batch of products are qualified, but also to track the stability between different batches, or to assist R&D personnel in formula optimization, adjust the type and dosage of rheology additives, and accurately control rheological performance.
Summary
Determining the KU viscosity of latex paints using a stormer viscometer is a well-established, efficient, and standardized method. By understanding how it works, following standard operating procedures, and taking into account various influencing factors, you can obtain reliable, repeatable viscosity data. These data are of irreplaceable value for ensuring the performance consistency of latex paint from production to construction, and are an important technical bridge connecting product formulation design and practical application effect.
References
1. American Society for Testing and Materials. Paint viscosity determination standard: Stormer viscometer method (ASTM D562).
2. National Standardization Administration of China. Determination of viscosity of architectural coatings (GB/T 9269).
3. International Organization for Standardization. Viscosity determination of colored paints and varnishes (ISO 2884 series).
4. Coating technology related textbooks and industry technical manuals.