In the field of coating, the measurement of dry film thickness is a crucial task. The performance evaluation of the coating, coating engineering construction quality acceptance and overall control, accurate measurement of dry film thickness plays an indispensable role. This paper will discuss the significance of dry film thickness measurement, the importance of measuring instruments and calibration.

Significance of dry film thickness measurement
The measurement of dry film thickness is a key index in coating engineering, which can directly reflect the protective performance of coating film and the rationality of coating process. In the evaluation of coating performance, dry film thickness is usually with coating corrosion resistance, durability and so on are closely related. In addition, the dry film thickness and the appearance of the coating quality, use efficiency is closely related to the factors such as coating material. Therefore, accurate measurement of dry film thickness is very important to ensure coating quality and prolong coating life.

Dry film thickness measurements: important step before coating quality assessment

Measuring instruments and methods
The measurement of dry film thickness can be divided into destructive test and non-destructive test. Destructive tests need cross engraved on coating such as traumatic operation, rather than a destructive test coating will not cause damage. Typically, non-destructive testing methods are more commonly used, but destructive testing methods are more persuasive when disputes arise or arbitration is required.

1, non destructive measurement methods:

Micrometer meter

This is a common non-destructive measurement method, suitable for coating thickness thinner. However, it is in the measurement of complex curved surface or uneven surface has some limitations.

Magnetic thickness gauge

Apply to measure metal coating on the surface of the substrate, but note that magnetic thickness gauge is only applicable to magnetic metal substrate, such as steel.

Eddy current thickness meter

Suitable for coating on the surface of the metal substrate measurements, especially suitable for nonmagnetic metal substrate, such as aluminum and stainless steel.

Dry film thickness measurements: important step before coating quality assessment

2, destructive measurement:

Microscopy (ISO2808)

The method by cutting film, coating thickness measuring cutting. Not only can the total thickness of the coating be measured, but also the thickness of each layer in the multilayer coating can be measured. It is recommended as an arbitration method for coating thickness.

Dry film thickness measurements: important step before coating quality assessment

Thickness gauge calibration
A thickness gauge must be calibrated before it can be used to make a measurement. No matter which thickness gauge is used, calibration is the key to ensuring the accuracy of the measured data. Calibration data is meaningless.

The way of calibration depends on the state of the surface. There is some controversy as to whether calibration is performed on smooth surfaces after sandblasting steel surfaces. Some standards, such as ISO2808 (third edition) method 10, provide for calibration on smooth surfaces. However, in practice, the surface after sandblasting will affect the measurement results of the coating thickness. In general, when the coating thickness is about 5~6 times of the roughness, the influence of the roughness can be ignored.

In summary, accurate measurement of dry film thickness is a critical step to ensure coating quality. Different measuring methods are suitable for different situations. Choosing the right measuring instrument and carrying out proper calibration can guarantee the quality of coating, improve the performance of coating and prolong the life of coating.