Automotive
Application: Automotive Body Painting - Car Manufacturer Measures Paint Thickness and Zinc Thickness at the Same Time (Duplex Corrosion Protection)
In the quality control of duplex coatings, it is beneficial to measure both the organic coating as well as the zinc coating. The portable instrument Phasescope® PMP10 Duplex with a probe ESG 20 combines a magnetic induction method and a phase-sensitive eddy current (see figure 1).
Varying Zinc Coating Thicknesses
Galvanized steel sheet is used with increasing popularity in the automotive industry. The zinc coating is already applied by the sheet metal supplier either by galvanic deposition or in a zinc dip bath. If the zinc coating thickness were uniform, the thickness of the subsequently applied paint coating could be measured using a conventional magnetic induction coating thickness measuring instrument. One would simply have to deduct a constant value from the actual reading.
However, this uniformity of the zinc thickness is typically given within a batch on the supplied sheet that has still to be formed. When the body parts are formed, flowing or even scraping off of the zinc coating may occur in the areas of severe bending radii, and this may vary its thickness by between 3 and 9 μm, and occasionally remove the coating altogether.
Similar situations are encountered when repairing a body area that has coating defects due to sanding and subsequent re-painting of the defective area. In this case too, the zinc coating may be sanded away as well, leading to an apparent reduction in the paint thickness if the above-mentioned conventional paint coating thickness measurement system is used. This is not only problematic for the inspection of the finished painted body but also particularly critical in the quality monitoring of a cataphoretic paint, because that thickness is typically only about 20 μm and a defect in the coating thickness measurement of 5 or 6 μm through a reduced zinc coating cannot be tolerated.
Measuring Paint and Zinc Thicknesses at the Same Time with Automatic Method Selection
The "Phascope® PMP10 Duplex" is ideally suited for measuring the paint thickness and the zinc thickness at the same time (and on the same spot - see figure 2). The repeatability precision of the zinc thickness measurement is as low as a few tens of nanometres, and that of the paint thickness measurement is below 0.5 μm.
In order to reduce vehicle weight, the use of aluminium is becoming increasingly popular for non-safety, relevant components of the body. Therefore, the measuring instrument is also equipped with a conventional eddy current channel to measure the paint thickness on these parts according to a standard. Without any action by the operator, who may not even know which parts are made of steel and which parts are made of aluminium, the instrument automatically selects the required measuring method - duplex or eddy current - immediately after the probe touches down and stores the paint thickness data in the same application, in such a way that a simple evaluation of the paint thickness distribution is possible regardless of the type of sheet metal.
Click for the Phascope ® PMP10 Duplex Technical Product Brochure
Or to view the Phascope® PMP10 Duplex technical specification online, please click on www.fischergb.co.uk
View the next page for an application case study demonstrating the measurement of two coating thicknesses at the same time in a 100% automated production line...