Principle
The pendulum hardness test method is a physical method to evaluate the mechanical hardness and viscoelasticity of the coating by measuring the damping time of the swing attenuation of the pendulum rod on the surface of the coating. Its core principle is based on the theory of energy dissipation: when the spherical or cutter edge contact point of the pendulum rod swings freely on the coating surface, the resistance of the coating to the movement of the pendulum rod will cause the swing amplitude to be attenuated. The higher the hardness and the more elastic components of the coating, the less energy absorption of the pendulum rod and the longer the swing attenuation time. Conversely, the softer or more viscous the coating, the greater the energy absorption and the shorter the decay time. This test does not directly measure the indentation depth, but indirectly reflects the coating's ability to resist plastic deformation through damping time, which belongs to the category of dynamic mechanical testing.
Test instruments
The standard pendulum hardness tester is mainly composed of a pendulum system, a support seat, a ruler and a timing device. A pendulum bar system typically consists of a rigid pendulum bar with two steel balls, with a pointer at the end to indicate the amplitude. The support base ensures that the pendulum bar contact point is perpendicular to the coating surface and the pressure is constant. During the test, the pendulum lever is adjusted to the initial angle (usually 6°), released and allowed to swing freely, and the time (seconds) required for the amplitude to decay from one specified angle to another is recorded by the timing device. Depending on the design difference, the common types of pendulum rods are König pendulum and Persoz pendulum, which have different quality, shape and swing cycle, and are suitable for coatings with different hardness ranges.
Operational points
Ensure that the coating is evenly applied to a flat, rigid substrate and cured well under standard temperature and humidity conditions before testing. Place the specimen horizontally on the base of the durometer and adjust the instrument so that the pendulum contact point is in contact with the coating surface without additional pressure. Release the pendulum lever and start the timekeeping, recording the time when the amplitude decays from the specified start angle to the end angle. Multiple measurements are often taken to average for reliability. During operation, it is necessary to avoid vibration and airflow interference, and regularly calibrate the instrument with standard glass plates to ensure that the damping time of the pendulum rod meets the standard value.
Influencing factors
The test results are directly expressed as damping time (seconds), with longer times indicating higher coating hardness. The interpretation of the results should refer to the relevant product standards or comparison of reference samples. Coating thickness, curing degree, ambient temperature and humidity, and substrate rigidity can all have a significant impact on the test results. For example, a coating that is too thin or a substrate that is too soft can lead to an abnormally short damping time; Coatings that are not fully cured will have reduced damping time due to residual stickiness. Therefore, the tests are carried out under strict control conditions and the relevant parameters are indicated in the report.
Applications:
This method is widely used in quality control and R&D evaluation in coatings, inks, plastic coatings, and other fields, and is especially suitable for evaluating the hardness properties of organic coatings such as varnishes and color paints. A number of domestic and foreign standards regulate test methods, such as ISO 1522, ASTM D4366, etc., which provide detailed regulations on instrument specifications, test conditions and calibration procedures to ensure the repeatability and comparability of test results.
Technical parameters
| Pendulum type | König pendulum, Persoz pendulum |
| Typical swing cycle | 1.4±0.02s (König)、1.0±0.02s (Persoz) |
| Initial amplitude angle | Usually 6° |
| The results show | Damping Time (Seconds) |
| Suitable coating types | liquid, powder-cured coatings, etc |
| Standard environmental conditions | 23±2°C，50±5% RH |
Summary
The pendulum hardness tester provides an effective means to evaluate the dynamic mechanical properties of coatings, which reflect the hardness and elasticity balance of the coating through damping time. This method is relatively simple to operate, non-destructive to coating, and has practical value in industrial quality control and R&D. Standard procedures should be strictly followed during testing, and the influence of coating systems and environmental variables should be fully considered to ensure the accuracy and comparability of data.
References
ISO 1522:2006, Paints and varnishes – Pendulum damping test.
ASTM D4366-16, Standard Test Methods for Hardness of Organic Coatings by Pendulum Damping Tests.
GB/T 1730-2007, Colored paints and varnishes - Pendulum damping tests.