Definition
A hardness tester is a portable hardness measurement instrument typically used in a field or laboratory setting to perform a fast, non-destructive approximation of the surface hardness of a material. It evaluates the hardness value of a material by pressing an indenter of known hardness into the surface of the material to be measured under constant pressure and evaluating the hardness value of the material based on the indentation or scratch generated.
Principle
The hardness test pen works based on the material's ability to resist local plastic deformation or scratches. At its heart is the principle of mechanical contrast: inside the test pen is a test needle (usually made of tungsten carbide or hardened steel) that has been calibrated for a specific hardness. Under standard spring or constant load, the test needle is pressed vertically into the surface of the sample under test. The hardness range of a material is inferred by looking at whether the surface is indented or scratched, or by measuring the indentation depth and comparing it with a pre-calibrated hardness scale such as Mohs, Wechsler, or Rockwell approximates.
Some electronic hardness test pens convert the indentation depth into an electrical signal through a sensor, and the conversion relationship can be approximately expressed as:H ≈ k * (F / d), where H represents the hardness value, F is the applied load, d is the indentation depth or related displacement, and k is the conversion coefficient related to the shape and ruler of the indenter. This formula is a simplified illustration, and the actual instrument needs to be strictly calibrated.
Measurement method
When measuring with a hardness test pen, it is necessary to follow a standardized operating procedure to ensure consistent results. First, the surface of the material to be tested needs to be cleaned to ensure that it is flat and free of oil and oxide layers. According to the estimated hardness of the material, select the appropriate test pen model and the corresponding hardness scale. Apply pressure with a smooth, uniform force by placing the test pen perpendicular to the sample surface and hold it for a specified time. Then remove the test pen and use the built-in magnifying glass or tactile to determine if there are visible indentations or scratches on the surface. Finally, according to the test results, the hardness comparison table provided by the instrument is used to read the corresponding hardness value or hardness range. Each test point should be spaced far enough apart, and it is recommended to take representative results from multiple measurements.
Influencing factors
The measurement results of a hardness test pen are influenced by a variety of factors. Material factors include uniformity, anisotropy, surface roughness, and thickness of the sample being tested, and thinner or uneven samples may result in insufficient support or biased readings. Environmental and operational factors include the temperature during the test, the speed and angle of force, the stability of the pressure applied by the operator, and the calibration status of the test pen. The instrument's own factors include wear of the test needle, changes in spring elasticity, and the scope of application of the ruler. In addition, there is no direct linear conversion relationship between different hardness scales (such as Mohs, Webster, and Barp), and it is crucial to choose a scale that matches the target material to obtain valuable data.
Application
Due to its portability and easy operation, hardness test pens are widely used in many fields. In the metalworking and manufacturing industry, it is often used in the field to quickly evaluate the heat treatment effect or work hardening of metal materials (e.g. aluminum, steel, copper alloys). In material research and quality control, it can be used to screen and compare the hardness of plastics, coatings, composites, etc. In the construction and stone industry, it can be used to test the surface hardness of building materials such as marble and tiles. It also serves as an intuitive hardness assessment tool for jewelry appraisal, wood processing, and educational presentations. It is important to note that the test results are approximate and are typically used for process control or rapid screening, rather than as a substitute for arbitration testing with laboratory precision hardness testers.
Selection
Choosing the right hardness test pen requires a combination of factors. First, the type of material to be tested and the estimated hardness range should be clarified, and the model covering the corresponding scale should be selected accordingly, such as a special pen for softer materials (such as plastic, aluminum) or harder materials (such as hardened steel and ceramics). Secondly, considering the measurement accuracy and resolution requirements, for high-quality control occasions, electronic models with digital display and depth sensors can be selected. The environment is also an important factor, and on-site inspection may require a more robust, shock-resistant design. In addition, it is important to pay attention to the calibration method of the instrument, whether it complies with relevant industry standards (such as ASTM or ISO guidelines), and whether the accompanying hardness conversion table is applicable. Finally, ease of operation, data logging capabilities, and maintenance costs should also be within the scope of the decision.