Photothermal coating thickness measurement in motion
As is well known, photothermal coating thickness testing is a non-contact process for paints, powder coatings and glazes on metallic and non-metallic substrates. The different thermal properties of the coating and substrate are utilised to determine the coating thickness. The surface of the coating is heated up by a few degrees with a short, intense light pulse and then cools down again by dissipating the heat into deeper areas. The thinner the coating, the faster the temperature drops. The temperature curve over time is recorded by a highly sensitive infrared sensor and converted into the coating thickness. The process works contactlessly and non-destructively with both freshly applied and cured powder and paint coatings.
The PaintChecker Move is a new, scanning photothermal coating thickness measurement system.
The new scanning 3D inspection process complements previous fields of application with the non-contact, fast and precise measurement of large workpieces and moving objects. For the new process, the OptiSense development team extended the heating range of the test system to enable a greater heat input. However - and this is revolutionary - with the innovation presented here, the heated area does not have to cover the entire surface to be tested, but only a small section, usually just a few centimetres. As an interesting side effect, it is also no longer necessary to stimulate with pulsed light. On the contrary - constantly illuminated excitation sources are actually an advantage.
The detector used is an integrated matrix of IR sensors with a relatively small field of view and a low number of pixels, which covers a measuring field approximately the size of the heating area.
The temperature curve is recorded on a pixel basis to determine the coating thickness with localised resolution. In simple terms, the image of the previously excited (heated) workpiece moves from pixel to pixel in the sensor due to the relative movement. The temperature profile of each individual surface element of the workpiece can thus be determined by continuously analysing the pixels over time. This temperature curve is then converted into the corresponding coating thickness, as in conventional photothermal technology.
The PaintChecker Move Sensor
As the component moves along the sensor, it first passes through an excitation zone (red), in which the coating is heated by a few degrees by light radiation. It then enters the measuring zone (blue), in which the local temperature is recorded at several hundred points simultaneously. As the component passes through the measuring zone, the cooling of the coating is measured periodically and the coating thickness is calculated from the temperature curve. The temporally overlapping evaluation results in continuous, uninterrupted recording.