Definition
A laboratory pendulum hardness tester is an instrument used to assess the resistance of surfaces of non-metallic materials such as coatings, plastics, composites, etc. to mechanical pressing or scratching. The measurement results are usually expressed in the form of pendulum damping time or hardness value, which is an important means to evaluate the mechanical properties of the material surface, especially the curing degree and wear resistance of the coating. The instrument is widely used in coatings, inks, furniture, automotive industry, and electronic product coating inspection.
Principle
The measurement of the pendulum hardness tester is based on the damping oscillation principle of the physical pendulum. The core of the instrument is a pendulum rod with a defined shape and quality and a steel ball of a specific size at the end. To test, place the support ball of the pendulum bar on the surface of the sample to be tested and allow it to swing freely from the initial maximum swing angle (usually 5° or 6°). The steel ball of the pendulum rod will roll slightly on the surface of the material, and its swing amplitude will gradually decay due to the resistance of the material surface to the rolling of the steel ball (i.e., the hardness of the material). The harder the surface of the material, the less resistance to the swing and the longer it takes for the pendulum bar to swing or the time it takes to decay from the initial swing angle to a smaller swing angle. By measuring the damping time or the number of swings of the pendulum bar, the corresponding hardness value can be calculated according to the relevant standard formula.
There are two common hardness scales, König and Persoz, and the main differences are the pendulum structure, mass, swing period, and measurement time interval. The swing period of the Koenig pendulum is about 1.4 seconds, measuring the time to decay from 6° to 3°; The Persaz pendulum has a swing period of about 1 second and measures the time to decay from 12° to 4°. The hardness value (t) can be understood by the following basic relations: t ∝ (N) or t ∝ (T), where N is the number of oscillations and T is the damping time.
Measurement method
Before measurement, the sample and instrument need to be conditioned under a standard temperature and humidity environment (e.g., 23±2°C, 50±5% relative humidity). The sample should be flat, stiff, and thick enough to avoid bending during testing. Place the sample horizontally on a stable tabletop, ensuring that the pendulum supports the ball contact point away from the edge. Carefully lift the pendulum bar to the specified initial angle and lock it tightly, then release the pendulum bar to allow it to swing freely. The operator records the time (seconds) or number of swings required for the pendulum amplitude to decay from the initial angle to the specified termination angle via an optical scale or electronic sensor. The same specimen should be measured multiple times at different locations, and the average value should be taken as the final result to improve the repeatability of the measurement. After the measurement is completed, the measured time is converted to a standard hardness value according to the corresponding standard conversion table or formula, depending on the type of pendulum used (Koenig or Persaz).
Influencing factors
The accuracy of the measurement results is influenced by several factors. Ambient temperature and humidity are significant factors, and increasing temperature or humidity can cause some coatings to soften and shorten the measured damping time. The characteristics of the sample itself, such as the thickness and uniformity of the coating, the rigidity of the substrate, and the degree of curing of the coating, directly affect the resistance to wobbling. The condition of the instrument is also crucial, and the cleanliness and lubrication of the pendulum bearing, the cleanliness and wear of the steel ball, and the levelness of the worktable may introduce errors. In addition, operational normativeness, such as whether lateral forces are introduced when releasing the pendulum bar and whether the readings are accurate, can also affect the results. Therefore, strictly following standard test procedures and regularly calibrating and maintaining instruments are the basis for ensuring data reliability.
Application:
Laboratory pendulum hardness testers are mainly used in areas where the mechanical properties of material surfaces need to be quantitatively evaluated. In the coatings and inks industry, it is used to test the drying and curing process and final hardness of coatings such as varnishes and color paints, and is a key indicator for controlling product quality. In the field of plastics and polymer materials, it can be used to evaluate the surface hardness of molded products or sheets. In furniture manufacturing and wood painting, it is used to test the abrasion resistance and durability of wood paint films. The automotive industry often evaluates the hardness properties of body coatings and interior parts. In addition, it also has corresponding applications in industries such as printing and leather treatment. It provides a relatively fast and non-destructive testing method that is valuable for production process control and product development.
Selection
Choosing the right laboratory pendulum hardness meter takes into account testing needs, standard compliance, and operating environment. The test standards to be followed (e.g. ISO 1522, ASTM D4366, GB/T 1730, etc.) should be specified first, and the standard usually specifies the type of pendulum bar to be used (Koenig pendulum or Persaz pendulum). Secondly, according to the expected hardness range of the material to be tested, choose the appropriate range of the model, and confirm the measurement ability of the instrument for very soft or very hard coatings. The instrument reads two types: visual scale and electronic automatic detection, which can reduce human reading errors and improve efficiency and repeatability. The overall structural stability of the instrument, the ease of calibration, and the presence of a leveling device should also be considered. For laboratories with strict environmental control requirements, models with temperature and humidity monitoring accessories are available. Finally, technical support, calibration services, and compliance with relevant metrology certifications from the supplier are also aspects to consider to ensure the long-term reliable operation of the instrument.