Operating specifications
A circle method adhesion tester is an instrument that applies scratches to the surface of a coating by a specific scratch tool to evaluate the adhesion strength between the coating and the substrate. This specification is designed to provide standardized operating procedures to ensure the reliability and repeatability of test results.
Instrument structure and principle
The instrument is mainly composed of a scratching device, a sample loading platform, a loading system and an observation system. Its working principle is that under controlled load, the scribing needle moves in a uniform circular motion along the surface of the coating to form continuous scratches. By observing the scratch morphology and coating peeling, the adhesion level is evaluated according to relevant standards. Adhesion levels are typically related to scratch spacing, load, and coating failure mode.
Preparation before operation
Before operation, it is necessary to confirm that the environmental conditions meet the standard requirements, usually the temperature should be controlled at 23±2°C and the relative humidity should be 50±5%. Check whether the parts of the instrument are intact, and the tip of the scribing needle should be free of wear or contamination. Prepare the sample to be tested, ensuring its surface is clean, flat, and dry.
Procedure:
First, the sample is securely fixed on the sample loading platform. Select the appropriate load and scratch spacing according to the test criteria, and install the corresponding scribing pins. Start the instrument so that the scribing needle draws overlapping rings on the surface of the coating at a constant speed. The scratching process should be smooth and free of abnormal vibrations. Once done, remove the sample and use a soft-bristled brush to remove debris from the scratched area.
Result evaluation and recording
In sufficient light, observe the scratched area with the help of a magnifying device. The adhesion grade of the coating is evaluated against the standard map. Common grading is based on the position of the first ring where the coating peels off continuously. Records should include test conditions, sample information, rating grades, and any anomalies.
Notes:
The scribing needle is a consumable item and needs to be checked regularly and replaced in time to avoid affecting the quality of the scratch. Different coating types or thicknesses may need to adjust the test parameters, so it is recommended to explore the parameters in advance. The instrument should be calibrated regularly to ensure load and movement accuracy. After testing, the instrument should be cleaned, especially the sample loading platform and the scribing area.
Maintenance and calibration
Routine maintenance includes cleaning up dust and checking the tightness of mechanical components. It is recommended to calibrate the load cell and motion mechanism every six months or after every 500 tests. Calibration should be performed according to the instrument manual using standard weights and measuring tools.
Safety Notes
Avoid physical contact with moving parts during operation. When changing the scribe or cleaning, make sure the instrument is powered off. Waste samples and consumables should be disposed of in accordance with laboratory regulations.
Cited Literature
GB/T 9286-1998 Colored paints and varnishes - Scratch tests
ASTM D3359-17 Standard Test Method for Measuring Adhesion by Tape Testing
ISO 2409:2013 Coloured paints and varnishes - Grid tests