Evident
Precision Coating Inspection with Ultrasonic Thickness Gauges
This article first appeared in the Railway-News magazine, Issue 3 2022.
Because rail vehicles may operate through demanding conditions – such as rain and snow – as well as be exposed to rapidly changing temperatures, the lifespan of materials is a key issue in the rail industry.
In particular, the exterior coating must be able to withstand varying weather conditions, high mechanical stresses and airborne contamination while maintaining its aesthetics and protection capability.
Coatings are used for a wide variety of applications including to enhance the aesthetics of rail vehicles and to protect rail vehicles from corrosion. Although coatings can significantly increase the longevity of rail components, it is essential that they are applied properly to ensure maximal function. Specifically, thickness must be within the defined limits to ensure appropriate protection and aesthetics and minimally applied to avoid significant financial implications.
Coating inspection of rail vehicles not only ensures proper application during manufacturing but can also periodically evaluate quality, such as wear and tear of coatings and remaining thickness after rework. Ultrasonic thickness gauges offer a fast, reliable and non-destructive method for coating or substrate assessment that requires access to only one side of the test material. While ultrasonic approaches have previously been limited by their minimum thickness capabilities, Evident introduced the Olympus 72DL PLUS gauge which combines a robust design, streamlined interface, and the ability to measure thinner materials than ever before.
Measuring Microns with Higher Frequencies
An ultrasonic thickness gauge measures how long it takes a sound pulse to travel through a sample (or test piece) and reflect back from the inside surface or wall. Generally, higher-frequency sound pulses enable the measurement of thinner materials.
Historically, most precision ultrasonic thickness gauges have been limited to a maximum of ~20MHz frequency and to a corresponding minimum thickness capability of ~0.005 inches (0.125mm). However, improvements to technology have allowed increasing frequencies to be used in ultrasonic thickness gauges. For instance, the 72DL PLUS gauge drives frequencies up to 125MHz to measure ultra-thin materials – as low as 0.001 inches (0.025mm).
