14th December 2018

QC FOR DECORATIVE ANODIZED COATINGS

Beyond their protective function, decorative anodized coatings must also meet certain design requirements. The exact coloring plays an important role, but even small differences in the aluminum alloy can significantly affect the final hue. Therefore, an accurate review of the raw materials during incoming goods inspection is necessary to achieve consistent coloration and to prevent waste.

Not every aluminum alloy can be anodized for decorative purposes; therefore, mainly AL99, AIMg or AlMgSi alloys are used. For best results, anodizers need to use high quality aluminum alloys.

But even with supposedly the same alloys, slight differences in composition may occur from manufacturer to manufacturer and from batch to batch, which can then lead to significant color deviations during the anodizing process. For decorative anodized finishes, the exact hue is actually an important aspect of the quality; discrepancies in coloration can drive manufacturing costs up with extensive reworking to correct problems or even a new production run.

To avoid these issues, it is necessary to know whether one is indeed working with the exact same aluminum alloy – or not. The best way to check this is to determine the electrical conductivity of the raw material or semi-finished products before the anodizing process, as this parameter is sensitive to even small variances in composition.

The conductivity of the plates was measured with the Sigmascope SMP350 and the FS40 probe, from Fischer. Using the non-destructive phase-sensitive eddy current method, this instrument quickly and accurately determines the electrical conductivity of nonferrous metals.

The FS40 probe can handle a wide range of measuring frequencies (60-480 kHz), making it suitable for a variety of material thicknesses. Since the electrical conductivity is affected by temperature, it also has an integrated temperature sensor. To accommodate for rounded parts, the diameter of the sample’s curvature is simply entered into the instrument.

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