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Which probes can be used to measure the layer thicknesses in 'paint on hot-dip galvanized steel' duplex coating systems in heavy corrosion protection?

Use the duplex probes FDX10 and FDX13H. These probes require a minimum coating thickness of 70 ยตm for hot-dip zinc in order to measure correctly.

What do I have to watch out for when calibrating the duplex probes FDX10 and FDX13H?

These duplex probes have two measuring channels. The magnetic induction channel measures the total thickness of the paint plus the zinc. The amplitude-sensitive eddy current channel measures just the thickness of the paint layer on top of the zinc.

Calibration requires a completely uncoated steel part that corresponds to the original part, as well as a galvanized part with at least 70 microns of zinc. The magnetic-inductive channel of the probe is calibrated on the uncoated steel part. The calibration foils used should encompass the expected range of the overall coating thickness (paint + zinc).

The galvanized part is used for calibration of the amplitude-sensitive eddy current channel. The calibration foils used should encompass the expected thickness range of the paint layer.

Which probes can be used to measure the layer thicknesses in 'paint on thinly galvanized steel' duplex coating systems?

The probes ESG2 and ESG20 are appropriate for thin zinc layers. These probes can only be used if there is no diffusion layer between the zinc and the steel. This is usually the case with electroplated and very thin hot-dip zinc coatings (e.g. in automotive engineering). Hot-dip zinc coatings in heavy corrosion protection, which are often more than 70 ยตm thick, usually form a distinct diffusion layer between the steel and the zinc. In this case, the ESG2 and ESG20 probes cannot be used.

What do I have to watch out for when calibrating the duplex probes ESG2 and ESG20?

These duplex probes have two measuring channels. The magnetic induction channel measures the total thickness of the paint plus the zinc. The phase-sensitive eddy current channel measures just the thickness of the zinc layer under the paint.

Calibration requires a completely uncoated steel part that corresponds to the original part, as well as a galvanized part with a typical zinc layer.

The magnetic-inductive channel of the probes is calibrated on the uncoated steel part. The calibration foils used should encompass the expected range of the overall coating thickness (paint + zinc).

The probeโ€™s phase-sensitive eddy current channel is calibrated on the galvanized part. No calibration foils may be used here, since the zinc layer itself is the calibration layer: just measure the galvanized part. The thickness of the zinc coating does not need to be measured as a reference before calibration. The calibration target/set value for the zinc coating is provided by the magnetic-inductive channel as calibrated in the first step.

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