Powder coating companies are familiar with the challenge of applying coatings to parts in such a way that the color, coverage level and gloss remain consistent after curing. The critical parameter is the thickness of the cured powder, and this is determined by the settings of the powder coating shop and the shape of the components.

A new photothermal measuring device enables the thickness of powder coatings to be measured before the curing process, including coatings applied to curved components. The device is highly versatile and easy to use.
   

The Existing Technology: Air Ultrasonic Systems

The thickness of coatings needs to be checked regularly - both after a change of color or component, and also during the normal application process. Otherwise, there is the risk of producing components that are not fully coated, where the amount of powder is too small, or of incurring unnecessarily high costs, where too much powder is used. It is particularly important to measure the coating before it is cured, in particular in corners and on edges, because any areas that have not been adequately coated can easily be rectified at this early stage.

The only manually operated, nondestructive measurement procedure available until now was air ultrasonic technology. However, this solution can only be used to measure coatings up to a thickness of around 100 micrometers on flat surfaces. It was generally not possible to determine the thickness of powder coatings on curved components.

The Alternative: Photothermal Measurement

The alternative to the ultrasonic process is photothermal measurement. This uses thermal waves instead of sound waves to measure the coating thickness. The waves are generated by the absorption of optical radiation into the powder. When it absorbs the radiation, the coating heats up in a characteristic way and the thickness can be determined by its behavior over time. This is also a noncontact, nondestructive process and is described in the DIN EN 15042-2 standard published in 2006. It has advantages over the ultrasonic procedure, which include the measurement of components of almost any size and shape, a much larger measurement area and the more flexible positioning of the sensor during the measurement. In addition, the procedure is ideal for use with a variety of coatings on different substrates.
 

Mobile Device for Coaters

OptiSense GmbH & Co. KG has worked with TQC to develop the first battery-powered, fully mobile photothermal measuring device for powder coatings on the basis of this procedure. The new device is known as the PowderTAG.

OptiSense has almost 20 years of experience in optical process measuring systems and supplies both mobile devices and easy-to-use sensors for in-line coating thickness measurement. TQC is one of the leading suppliers of testing and measuring systems in the surface technology industry and has more than 30 years of experience with powder coatings.

The PowderTAG makes it possible to carry out systematic and random measurements of the coating thickness and to evaluate the layer of powder accurately before it is cured. It can measure over large areas and on curves, corners and weld seams. Three dots of light help the user to position the measuring point, which  means that even small structures can be accurately targeted.

Because the measuring device provides reliable results, even when the probe is angled through ± 15°, areas that are difficult to access can be evaluated much more easily than when using the ultrasonic procedure. The measurement point is 2 x 2 square millimeters in size, which enables the device to make measurements on rough substrates and coarse powder coatings. The process can easily compensate for any unevenness in the coatings or substrates.

The device uses invisible light for excitation purposes, which means that users are not affected by reflected light. The OptiSense Lares technology has been incorporated into this system, in the same way as in the company’s other measuring devices. This guarantees that no harm can be caused to users’ eyes and that no additional protective measures are required.

A Variety of Uses

The new photothermal measuring device can measure the thickness of more than 95 percent of the powder coatings currently on the market, including normal, textured and metallic products. A special evaluation procedure allows coatings more than 200 micrometers thick to be measured using a single setting. In addition, the thickness of cured coatings can also be assessed. The benefits of this process, which is not dependent on the shape of the component, also apply in this case, meaning that measurements can be made in areas that were previously inaccessible. The PowderTAG is a robust, versatile, easy-to-use measuring device for powder coaters, which is highly flexible and suitable for all types of components in the coating shop.

For more information, e-mail joel@tqc-usa.com, or visit www.tqc.eu or www.optisense.com.