Definition
A Circle Adhesion Tester is a specialized testing device used to evaluate the adhesion properties between a coating or film and a substrate. It applies a continuous load to the coating surface through a specific geometry of a scribing needle and makes a circular motion, forming a scratch trajectory that gradually deepens from the inside out, thereby systematically destroying the bonding interface between the coating and the substrate. The instrument has a wide range of application values in quality control and research and development in the coating, automobile, shipbuilding, building materials and electronics industries, and its test methods usually follow relevant international and domestic standards, such as ISO 2409, ASTM D3359, etc., to ensure the reliability and comparability of test results.
Principle
The core working principle of the scribing adhesion tester is based on the mechanical scratch method. The instrument is usually equipped with a scribing needle that applies a fixed vertical load, and the tip of the scribing needle is a hard material (such as tungsten carbide) with a specific radius of curvature. During the test, the sample is fixed on a horizontal platform and the scribing needle moves along a circular trajectory at a constant speed. As the scribing needle moves from the center of the circle to the periphery, the scratch depth gradually increases, and the coating undergoes elastic deformation, plastic deformation until it peels off from the substrate. By observing the peeling of the coating in the scratch trajectory, the adhesion can be quantitatively evaluated according to the standard map or grading method. The mechanical process can be roughly described by the following relationship: when the shear stress applied by the scribing needle exceeds the bond strength between the coating and the substrate, the interface failure occurs.
Measurement method
The measurement process typically includes four steps: sample preparation, instrument calibration, test execution, and result evaluation. First, the coating sample to be tested needs to be cured to the specified state in a standard environment and ensure that the surface is flat and clean. The scribing needle is then mounted to the tester and adjusted perpendicular to the sample surface by selecting the appropriate load according to the expected adhesion range of the coating. During the test, the scribing needle is completed at a constant speed (e.g. 80 rpm). After the test, a soft brush was used to remove loose coating fragments from the scratched area, and the adhesion grade was evaluated under standard lighting conditions. Common rating criteria divide adhesion into grades 0 to 5, where grade 0 indicates that the coating has no peeling and the best adhesion; Grade 5 indicates that the coating peels off in a large area and has poor adhesion.
Influencing factors
The accuracy of test results is influenced by various factors. The coating's own properties, such as thickness, hardness, flexibility, and curing degree, directly affect its shear resistance. The surface roughness, cleanliness, and chemical properties of the substrate can also change the interfacial bond strength. In terms of instrument parameters, the radius of curvature of the scribing needle tip, the application load, the scratching speed and the diameter of the scribing ring must be set strictly according to the standard, and any deviation may lead to a difference in rating. Environmental conditions such as temperature and humidity may cause changes in the physical state of the coating, so it is recommended to operate in standard temperature and humidity environments. Operator technical consistency, including sample placement, load application, and result interpretation, is also an important part of ensuring reproducibility of results.
Applications
The Circle Adhesion Tester is suitable for coating quality assessment in a wide range of industrial applications. In the automotive industry, it is used to test the adhesion properties of body paints, primers and anti-corrosion coatings. It is commonly used in marine and offshore engineering to evaluate the long-term durability of anti-rust coatings on metal substrates. The building materials industry pays attention to the bonding strength of decorative coatings and fireproof coatings on concrete, wood and other substrates. The electronics industry may be used for adhesion testing of printed circuit board protective films, insulating coatings. In addition, the instrument is also commonly used in scientific research institutions and quality inspection departments for new material development and factory inspection, providing data support for process optimization and standard formulation.
Instrument selection considerations
When selecting a model, it is necessary to comprehensively consider the testing needs, standard compliance and ease of operation. First of all, the coating type, substrate hardness and test standard requirements of the sample to be tested should be clarified to ensure that the load range and needle specifications of the instrument match the standard specifications. In terms of instrument construction, stable loading mechanisms, sophisticated motion control systems, and durable dicing materials help improve test repeatability. The operation interface should be clear and intuitive, which is convenient for parameter setting and result recording. Some models may integrate an optical observation device or a digital rating function to evaluate the inspection efficiency requirements. In addition, the ease of maintenance, availability of calibration services, and responsiveness of technical support are also reference factors for long-term use.