Determination method and step of coating thickness of dry film

Four methods can be used to measure the coating thickness of color-coated plates, namely, magnetic Thickness Gauge method, micrometer method, metallographic microscope method and drilling destructive microscopic observation method. The choice of measurement method can be negotiated between the supplier and the buyer.

Magnetic Thickness Gauge Method

This method is applicable to the determination of the coating thickness of color-coated sheets with cold-rolled sheets and galvanized sheets as substrates. This method is not applicable if the coating thickness is less than 3 μm.

micrometer method

1. Scope and description

This method is applicable to the determination of the coating thickness of color-coated plates with various materials as substrates. This method is not applicable to coatings that are easily deformed under the load of the micrometer measuring device, and this method is also not suitable for measuring too thin coating films. The US ASTMD 1005 standard stipulates that the film thickness is not less than 12.7 μm.

Using micrometers, lever micrometers and other instruments to measure the thickness of the coating film is to detect the coating thickness by measuring the difference between the thickness of the color-coated plate before and after the coating is removed.

2. Instruments and Materials

(1) Micrometer: lever micrometer or digital display handheld micrometer, the instrument display error is ±0.001mm; (2) Solvent or paint remover (remove coating, not corrode certain materials); (3) Marker pen.

3. Measurement method

(1) Carry out zero calibration according to the instrument manual.

(2) In the area not less than 10mm from the edge of the template, select 3 different parts to mark, measure the thickness of the marked part with a micrometer and record it.

(3) Use an appropriate solvent (or paint remover) to remove the coating film at the mark (the sample cannot be deformed, scratched or scratched during the stripping process), and then use a micrometer to measure the thickness of the substrate where the coating film is removed, Record the thickness value.

4. Result representation

Calculate the difference between the two thickness readings at each scene measurement site, and this value is the coating thickness at this site.

The arithmetic mean value of the coating film thickness at three different viewing locations is the thickness of the sample coating, expressed in microns (μm).

5. Reference standard

National standard GB/T 13448 "Test method for color coated steel plate and steel strip".

metallographic microscopy 

1. Scope and description

This method is suitable for the determination of the coating thickness of color-coated plates with various materials as substrates. This method can be used as a referee test method. The coating thickness of the color-coated plate is measured by using the difference in light reflectance between the section coating of the color-coated plate and the metal substrate.

2. Instruments and Materials

(1) Metallographic microscope: the measurement accuracy should be better than 2 μm; (2) Metallographic sandpaper of appropriate grade; (3) The material (such as resin) used to fix the test plate should have no damage to the paint film, and its color is obviously different in the coating. 3. Measurement method

(1) Use appropriate materials to fix the test plate. During the plate making process, the test plate should be kept perpendicular to the observation surface.

(2) Grind and polish the prepared test plate to make it smooth enough to observe the coating section under a microscope. Be careful to keep the test board at right angles to the sandpaper surface during operation.

(3) Use the ruler on the metallographic microscope to measure the coating thickness at 5 different parts of the sample section and record the value.

4. Result representation

The arithmetic mean of the coating thickness at 5 different positions is the coating thickness of the test plate, expressed in microns (μm).

5. Reference standard

National standard GB/T 13448 "Test method for color coated steel plate and steel strip".

American standard ASTM D 4138 "Determination of dry film thickness of protective coating system by destructive method".

borehole destructive microscopy

1. Scope and description

This method is applicable to the determination of the coating thickness of color-coated plates with various materials as substrates. When the interface of each coating can be clearly distinguished, it is also applicable to the separate determination of the thickness of each coating (primer, topcoat).

This method is to use a drilling machine to drill a round hole with a certain taper in the coating of the color-coated plate, observe the coating through an optical microscope, locate the coating interface, measure the horizontal distance and convert it into the thickness of the coating according to the taper .

2. Instruments and Materials

(1) Microscopic Thickness Gauge: It consists of an automatic drilling device and a microscopic video image system, and the measurement accuracy should be better than 10% of the coating thickness; (2) Marker pen.

3. Measurement method

(1) Put the sample on the drilling table, adjust the drilling depth control wheel of the automatic drilling device, so that the drill bit just penetrates the substrate, and drill a circular shallow-angle shrinkage hole on the sample.

(2) Put the sample on the measuring table, adjust the microscopic video image system, so that each interface of the coating at the shrinkage cavity can be clearly imaged on the video. The thickness of each coating can be read directly by using the scale of the microscopic video image system.

4. Result representation

Take the arithmetic mean value of at least 3 different measuring positions in the shrinkage cavity of the measured hole, which is the coating thickness of the sample, expressed in microns (μm).

5. Reference standard

National standard GB/T 13448 "Test method for color coated steel plate and steel strip".

American Standard ASTM D 5769 "Determination of Dry Film Thickness of Coil Coatings by Drilling Equipment".