Coating thickness gauges

Even before making a purchase, it is necessary to be clear about your requirements and measuring conditions. You should know the substrate under a coating, that is, whether the paint layer # is applied on steel or aluminum, for example. It is also important to know the material of the layer: Is it an organic, metallic, or plastic layer? Additionally, you should know in which measuring ranges you want to work and how accurately you need to take the measurements. If very precise measurements are required, not only the measurement accuracy of the coating thickness gauge itself plays a role. If measurements are to be taken on specific steel or aluminum alloys, the coating thickness gauge should also be able to store correction calibrations. This ensures that the ideal calibration is used for coating thickness measurements on alloys. This is necessary because the magnetic properties and conductivity of the alloys vary. If you want to measure under such specific conditions, we recommend contacting our competent service team by phone so that we can provide you with comprehensive advice on the topic of coating thickness gauge.

Example: A car dealer wants to be able to determine before purchasing a vehicle whether the vehicle in question has been repainted in some areas: He knows that the car paint will be measured on steel or aluminum. He is also aware that even a vehicle painted once has a layer thickness between 80 & 130 µm. Since the car dealer is only interested in determining whether the car has been painted once or multiple times, accuracy is of secondary importance to him. A measuring range of 1250 µm will certainly be sufficient.

Another example: An operator of an automated coating system is looking for a way to reduce costs. One option would be to optimize the paint consumption per coated part. This can be achieved by measuring the layer thickness during the coating process and adjusting the amount of paint in the coating system accordingly. The operator therefore needs a coating thickness gauge that measures the layer thickness non-destructively and contactlessly during the coating process.

As these two examples show, the conditions under which measurements are taken lead to completely different requirements for the coating thickness gauge. In the first case, a ComBi D3 or a ComBi D1000 would be completely sufficient. In the second case, the customer needs a CoatMaster Flex.

You are aware of your measuring conditions. Ideally, you have consulted with experts, ordered and already received your optimal layer thickness measuring device. Now it is up to you to pay attention to the small details in order to carry out as precise layer thickness measurements as possible. If you are measuring on an alloy, you have informed yourself about the specifics for precise layer thickness measurements on alloys with our competent team.

To ensure as error-free measuring as possible with your new coating measuring device, please follow the instructions below:

• Make sure that the probe, the zero plate, and your workpiece are as free from dirt as possible. Otherwise, you will also measure the thickness of the dirt layer.
• Zero the device for layer thickness measurement on the zero plate corresponding to the substrate (e.g. Fe zero plate for measurements on steel).
• Make sure to place the probe as stable as possible. Lift the probe at least 2-3 cm from the surface.
• Check the zeroing by performing a measurement on the zero plate. The device should display 0.0. Otherwise, perform zeroing again.
• Perform multiple measurements on your workpiece. Make sure to always place the probe slightly offset (about 0.5 - 1 cm), unless you want to measure exactly one point.
• The measured values should generally only vary minimally.

• Eddy current testing is an electrical method for non-destructive material testing. It is used for measuring the thickness of non-electrically conductive layers (such as paints, enamels, plastics, paper, glass, rubber, etc.) on non-magnetic, electrically conductive metals (e.g. aluminum, zinc, copper, brass). In this measurement method, an alternating magnetic field appears when a constant alternating current flows through a coil. The frequency of the generated magnetic field is the same as the alternating current and penetrates the tested material. If the material does not have electrical conductivity properties, the magnetic field remains unchanged. Otherwise, eddy currents are generated in the coated base material, which according to Lenz's law create a counter field and affect the overall impedance of the coil. The smaller the distance between the material and the coil, the greater the change in impedance (Figure 3). A layer thickness gauge determines the corresponding layer thickness from the change in impedance.

• In the Advanced Thermal Optics (ATO) process, the surface of the coating is heated with a light pulse. After a short heating of a few degrees, this surface is cooled down into deeper areas of the coating and the substrate through heat conduction. The cooling process at the surface in turn depends on the thermal properties of the coating and the substrate. The thinner the coating, the faster the surface temperature drops. The thickness and thermal properties of the coating are calculated from the dynamics of the surface temperature.