The adhesion of the coating refers to the degree of adhesion between the coating and the substrate, and is one of the important indicators to evaluate the performance of the coating. There are many methods for measuring adhesion, one of which is the circle method. This paper will introduce the principle, instrument, measuring method and result expression of the method.

1. Scope and description

The loop method is a method used to determine the adhesion of coating. In this method, the template is fixed to a movable platform, and then a stylus is used to scratch through the coating as the platform moves, creating overlapping circular lines. The adhesion of the coating is expressed in grades according to the degree of coating integrity within the scratch range of the circular roll line.

Overview of the adhesion determination method by circle method

2. Instruments and materials

Adhesion measuring instrument: the instrument includes a test bench, a rotating needle, a load plate, a pin plate and other components. The lead screw pitch of the test bench is 1.5mm, the needle is turned with a specific specification stylus, and the no-load pressure is 200g. Weights can be placed on the load tray with masses of 100g, 200g, 500g and 1000g respectively. The turning radius of the needle can be adjusted, and the standard turning radius is 5.25mm.

Quadruple magnifying glass

Paint brush: Width between 25 ~ 35mm.

3. Determination method

(1) Check the instrument

Before testing, first check whether the stylus of the adhesion tester is sharp, if not, it needs to be replaced. Also check whether the scratch is consistent with the standard turning radius, if not, it is necessary to adjust the turning radius.

(2) Adjust the instrument

Adjust the turning radius of the instrument to ensure that it is the same as the standard turning radius of 5.25mm. This step involves loosening the bolt behind the pin tray, adjusting the radius of turn, and then tightening the bolt until the scratch matches the standard roll line.

(3) Measurement

Place the template coating facing up on the test bench and tighten the fixing template adjusting bolts.

Move the rod backwards so that the tip of the needle touches the coating.

Evenly shake the crank in the clockwise direction to control the speed at 80 ~ 100r/min.

Draw a circle on the coating to form a circular line scratch. The standard length of the scratch is (7.5 soil 0.5)cm.

Overview of the adhesion determination method by circle method

(4) Check and rating

After finishing the scratch, move the lifting rod forward, lift the pin tray, loosen the bolt holding the template, and remove the template. Then, a paint brush is used to remove the paint chips from the scratch, a quadruple magnifying glass is used to inspect the scratch and grade it.

According to the integrity of the coating on the scratch, the scratch of different parts is marked 1, 2, 3, 4, 5, 6, 7 seven parts, and divided into seven grades. The recommended adhesion is grade 1, and the worst is grade 7. The result is consistent with the level of at least two samples.

4. Result presentation

The result of adhesion is expressed as the lowest grade of coating integrity. This means that if the degree of coating integrity of a certain part reaches a certain standard, then the overall adhesion level will be based on the grade of this part.

Overview of the adhesion determination method by circle method

5. Reference standards

In the determination of adhesion, you can refer to the national standard GB/T 1720 “Paint film adhesion determination method”.

The coiling method is a commonly used method to measure the adhesion of the coating to the substrate. The coiling line scratch is used to evaluate the adhesion between the coating and the substrate. This method is simple and easy to evaluate the adhesion properties of coatings quickly and accurately, which is of great significance for quality control and product evaluation in the coating industry.