Definition
A scratch hardness pen is a handheld testing tool used to evaluate the scratch resistance of a material's surface. It quickly determines the relative hardness or scratch resistance level of the material surface by scratching the tip of a known hardness on the surface of the material with a specific pressure to observe whether visible scratches are formed. The tool is widely used in quality control and R&D testing in coatings, plastics, metals, ceramics, and composites.
Principle
The working principle of a scratch-resistant hardness pen is based on the scratch testing principle of a Mohs hardness scale or pencil hardness scale. The core of the test pen is to mechanically contact and move the test pen tip with fixed hardness with constant pressure to the material surface, and use the hardness difference between the pen tip and the material surface to produce scratches or deformation on the material surface. If the surface hardness of the material is higher than that of the pen tip, there will be no obvious scratches; Otherwise, visible scratches will occur. Test results are usually expressed as "pass" or "fail" nibs for a specific hardness rating, or the maximum scratch hardness value of a material is determined through a series of tests.
Measurement method
Place the sample on a flat and stable table to ensure that the test area is clean and free of contamination. Select a test pen of the appropriate hardness, align it vertically with the sample surface, hold the pen barrel at an angle of about 45 degrees, and push the tip forward in a straight line, applying pressure that meets the requirements of the relevant standards (such as the pencil hardness test method specified in ASTM D3363 or ISO 15184). The pushing distance is usually 6 mm to 10 mm, and the speed is maintained uniformly. Once done, remove surface residue with a soft cloth and observe the scratches under standard lighting conditions. If the scratch length exceeds 3 mm and is visible to the naked eye, it is judged that the hardness level has not passed. By replacing the nib of different hardness for a series of tests, the critical value of the material's scratch hardness can be determined.
Influencing factors
Test results are influenced by a variety of factors. The flatness and cleanliness of the material surface can change the contact state of the pen tip, which in turn affects the uniformity of the scratch. Ambient temperature and humidity can cause small changes in the surface properties of the material, resulting in differences in hardness performance. Push speed and pressure stability during testing are key parameters, and pressure fluctuations can lead to inconsistent scratch depths. The wear of the nib can also affect test accuracy and need to be checked and replaced regularly. In addition, the lighting conditions and angles of observation during scratch observation may have a subjective impact on the judgment results, and it is recommended to verify it from multiple angles under a standard light source.
Applications
Scratch resistant hardness pens have a wide range of uses in industrial testing. In the coatings industry, it is used to evaluate the surface hardness and scratch resistance of coatings after curing. In the automotive industry, it is commonly used to test the durability of interior plastic parts, exterior coatings, and glass surfaces. In the field of electronic products, it can be used for quality inspection of screen protectors and shell coatings. The furniture and building materials industry is used to evaluate the scratch resistance of wood coatings, metal finishes or composites. In addition, in scientific research and teaching experiments, this tool provides a simple comparative testing method for the study of material surface properties.
Selection considerations
When choosing a scratch-resistant pen, consider testing needs and standard compliance. First, the type of test material and hardness range should be clarified to select a pen set that covers the corresponding hardness level. The nib hardness scale needs to match common industry standards, such as pencil hardness scales (9B to 9H) or Mohs hardness scales. The structure of the pen body should be designed to ensure smooth force application, and some models are equipped with pressure adjustment devices to improve test repeatability. The convenience of nib replacement and the sustainability of consumables supply also need to be considered. For applications where quantitative recording is required, an electronic version with integrated pressure sensor is available. The final selection should be based on the actual test standard requirements, sample characteristics and test environmental conditions for comprehensive evaluation.