Definition
A single-pendulum pendulum hardness tester is a physical testing instrument used to determine the surface hardness of non-metallic materials such as coatings, plastics, and composites. Its working principle is based on the principle of single-pendulum damping attenuation, which evaluates the hardness of the material by measuring the time or number of times the swing amplitude attenuation of the pendulum rod on the surface of the specimen, which is often referred to as pendulum hardness. This instrument is widely used in coatings, inks, polymer materials and other fields, and its test results are related to the elasticity, viscosity and surface friction characteristics of the material.
Principle
The core principle of the single pendulum pendulum hardness tester is the energy decay method. The instrument consists of a freely swinging pendulum rod with a contact head of a specific shape (usually a steel ball or cylinder) at the end. When the pendulum bar is lifted to the initial angle and released, its contact head oscillates with a small amplitude on the surface of the specimen. Due to the friction between the specimen surface and the contact head and the viscoelasticity of the material itself, the swing amplitude of the pendulum rod will gradually decrease. The hardness value is calculated by measuring the time or number of swings it takes for the amplitude to decay from one angle to another, with longer decay times or more times indicating higher surface hardness of the material. Its basic relationship can be expressed as:
H = k · t
where H represents the hardness of the pendulum rod, t is the decay time, and k is the instrument constant. This formula demonstrates a positive correlation between hardness and decay time.
Measurement method
Before measurement, the specimen should be placed on a horizontal and stable platform to ensure a flat and clean surface. Adjust the instrument so that the pendulum contact head is in perpendicular contact with the specimen surface and apply the specified contact pressure. Raise the pendulum bar to a standard initial angle (e.g. 6° or 12°) and release the swing bar to swing freely. Use a chronograph device to record the time it takes for the pendulum amplitude to decay from the initial angle to a specified angle (e.g. 3°), or record the number of swings. Depending on the instrument type, the hardness value can be read directly or calculated. Tests should be performed in standard temperature and humidity environments, usually averaging multiple measurements to improve the reliability of the results.
Influencing factors
The surface condition of the specimen has a significant impact on the measurement results, and the surface roughness, flatness and cleanliness may cause data fluctuations. Ambient temperature and humidity may change the viscoelasticity of the material, which in turn affects the decay time. The shape, size and material of the pendulum contact head must comply with the standard regulations, and wear or deformation will lead to system errors. The consistency of the release of the pendulum bar during operation, the stability of the contact pressure will also introduce human factors. In addition, the thickness of the specimen and the substrate material may affect the oscillation behavior through vibration transmission. Therefore, standardized test conditions and standardized operating procedures are the basis for ensuring comparability of results.
Application:
The single-pendulum pendulum hardness tester is suitable for the determination of the hardness of coatings and varnish dry films, and is used to evaluate the degree of curing and wear resistance of coatings. In the plastics industry, it can be used to compare the surface hardness of different polymer materials. It is also commonly used in the fields of printing inks, adhesives, and composites for quality control. The instrument can also be used to study changes in surface properties during material aging, environmental exposure, and more. Because the test is non-destructive and easy to operate, it is valuable both on the production site and in the laboratory.
Selection
When selecting the model, it is necessary to consider whether the measurement range covers the hardness range of the material to be tested. There are differences in the instrument design parameters corresponding to different standards (such as ISO 1522, ASTM D4366), and the corresponding model should be selected according to the standards followed. The accuracy and repeatability of the instrument must meet the test requirements and refer to the technical parameters provided by the manufacturer. Ease of operation and degree of automation (e.g., automatic timing, digital display) may affect test efficiency. The stability of the instrument structure and the durability of the contact head material are related to the long-term stability of use. In addition, the availability of calibration services and the availability of accessories are also aspects of the actual selection.