Coating thickness measurement
The measuring method chosen will depend on the combination of materials and the issue in hand. There is no single standard measuring procedure that would be suited to measuring all coating thicknesses. This is why the Institute has at its disposal so many different measuring systems for determining coating thicknesses.
Non-destructive measuring techniques
X-ray fluorescent method
Non-destructive & non-contact layer thickness and material analysis of metallic coated materials to DIN to DIN EN ISO 3497. This measuring technique enables us to define the layer thicknesses and the compositions of individual layers, multiple layers and alloyed layers.
It is also possible to measure coating systems with up to three layers at the same time or the simultaneous measurement of the thickness and the composition of layers having up to three integral components.
Advantages of this process:
- Virtually no restrictions on part geometry
- Accurate positioning of the measuring point
- Very small measuring area
- Little time required
Combined interaction of the layer (or layers) and the substrate with a powerful X-ray beam.
Magnetic inductive testing / magnetic processes
Measuring the thickness of non-magnetic coatings (including enamel coatings) on metallic substrates to DIN EN ISO 2178. Suitable for individual layers with thicknesses of 1 to 1000 µm and relatively smooth surfaces.
The measuring principle is based on the magnetic attraction between a permanent magnet and the substrate and the changes in the flow of the magnetic force field resulting from the presence of the coating. The measurable magnetic flux depends on the thickness of the non-magnetic coating.
Eddy current method
Measurement of the thickness of electrically non-conducting coatings on non-magnetic metallic substrates to DIN EN ISO 2360 This technique is particularly suitable for measuring the thickness of most oxide layers generated in an anodic process and with paint layers.
An eddy current is generated in the substrate by applying a high-frequency electromagnetic alternating field. The change in the eddy current through the coating is a measure of the coating thickness.
Destructive measuring techniques
Common methods of analysing the thickness of many different layers using microscopic processes.
- Metallic coatings
- Oxide coatings
- Enamel coatings
- Paint coatings
- Sprayed coatings
- Conversion layers
Depending on the type of coating and its thickness, the exact coating thickness can be analysed by means of a ground sample, spherical abrasion or an oblique section.
Incident-light microscope (magnification 50 to 1000 times) and stereoscopic microscope (up to 100 times) with state-of-the-art, digital recording and image processing systems.
One of the most frequently used methods for measuring coating thickness is microscopical analysis to DIN EN ISO 1463. This method can be applied to nearly all types of coating such as metallic, oxide, enamel coatings, paints and sprayed coatings and many more. This measuring procedure is well suited to coating thicknesses ≥3 µm. Where the coating is thinner, measurement uncertainty increases disproportionately. For thinner coatings, spherical abrasion or an oblique section should be used, and the Institute can also perform these tests.
The microscopical method of measuring coating thickness is often used as a reference method for cross-checking and calibrating all other measurement methods.
The thickness of the coating is measured using optical methods oat the surface of the cross section.
Spherical abrasion test
The spherical or micro-abrasion wear ("dimple-grinder") test is used for measuring the thickness of PVD, CVD or electrochemically applied coatings from 0.3 to 30 µm.
A rotating steel ball is used to abrade a dimple-like recess through the coating into the substrate. Through a projection technique, the coating whose thickness is to be measured is worn away in a broad crater. This crater is then measured accurately and the coating thickness calculated from that.
Oblique section test
Oblique section testing is a variant of the ground sample test. This method is suitable for thin, mainly hard coatings. By grinding the section at an angle, the coating thickness is visually "stretched", which makes it easier to measure accurately. The precise coating thickness can then be calculated once the angle of the specimen is known. This test method is suitable for coating thicknesses ≤1 µm with a correspondingly low measurement uncertainty.