What’s the detection methods for coating thickness measurement(1)

Coating thickness gauge is an important process parameter and plays an important role in the product quality, process control and cost control. Now, technicians can use many different kinds of instruments and methods to measure the thickness of a coating or film. There are many factors to consider when is selecting the most appropriate measurement method, including the type of coating, the substrate material, the thickness range of the coating, the shape and size of the device underwater test, and the cost of measurement.

Coating thickness measurement gauges techniques generally include non-destructive measurement methods such as magnetic measurement, eddy current measurement, ultrasonic measurement, and micrometer measurement; in addition, destructive measurement methods such as cross-section measurement and gravimetric analysis. For powder and liquid coatings, some effective methods can be used to measure the film thickness before drying and curing. Let's take a look at the commonly used non-destructive measuring instruments and methods.

2, the principle of operation
Magnetic thickness gauges mostly use one of two operating principles: magnetic stretching or magnetic/electromagnetic induction.

(1) Magnetic tensile thickness gauge
The magnetic tensile thickness gauge is mainly used for a permanent magnet, a calibration spring and a scale. The attraction between the magnet and the magnetic steel matrix pulls the two together, and as the thickness of the coating gauge increases, the magnet becomes easier to pull out.Therefore, the aluminium sheet thickness gauge is mainly determined based on this drawing force. Thinner coatings generally have greater magnetic attraction, while thicker film coatings have relatively less magnetic attraction. Magnetic tensile thickness gauges are very sensitive to measure the surface roughness, curvature, substrate thickness, and composition of metal alloys.Magnetic thickness gages are rugged, it is simple, inexpensive, and portable, usually do not require calibration adjustments. If only a small amount of reading is required during production, they will be a good low-cost measurement solution.Tensile thickness gauges are usually in the form of a pencil or rollback dial. The pencil model uses a magnet mounted on a coil spring (perpendicular to the surface of the coating).

Most pencil-type tensile gauges use larger magnets and are specifically designed to work in only one or two locations that complement some of the effects of gravity. By using a tiny, precise magnet, it can be made into a more accurate version for measuring small or hard-to-reach surfaces. The triple indicator ensures measurement accuracy when the gauge is pointing downwards, upwards or horizontal tolerances of ±10%.

The dial type is the most common form of magnetic tensile thickness gauge. A magnet is attached to one end of the rotating balance arm and attached to the calibrated balance spring. By rotating the dial with a finger, the spring increases the force on the magnet and pulls it out of the surface.These gauges are easy to use and have a balance arm that allows them to work in any position, independent of gravity. In addition, they are equally safe to use in the explosive environments, and coating contractors use more powder coating operations with measurement deviations of around ±5%.

(2) Magnetic / electromagnetic induction thickness gauge

A magnetic induction thickness gauge uses a permanent magnet as the magnetic field source and utilizes a hall effect generator or a magnetoresistive resistor to sense the magnetic flux density at the magnetic pole of the magnet.The electromagnetic induction thickness gauge uses an alternating magnetic field and uses a soft ferromagnetic rod wound with a thin coil to generate a magnetic field. The other coil is used to detect changes in magnetic flux.These electronic instruments are effective for measuring changes in magnetic flux density on steel surfaces near the surface of the magnetic probe. The magnitude of the magnetic flux density on the surface of the probe is directly related to the distance of the steel substrate. Therefore, by measuring the magnetic flux density, the coating thickness can be determined.

These electronic electromagnetic meters come in many shapes and sizes. They typically use a constant pressure probe to provide data that is not subjective to the operator, and the measurement readings are clearly displayed on a liquid crystal display (LCD). They can choose to store measurements or perform an immediate analysis of the readings and output the results to a printer for further inspection. The measurement deviation of this instrument is generally about ±1%.In order to obtain more accurate measurements, the operator should carefully follow the manufacturer's instructions. Test methods can refer to international standards such as D7091, ISO 2178 and ISO 2808.