Thickness Gauges to Measure Anodized Coatings

In addition to x-ray fluorescence analyzers, Eastern Applied Research offers a complete line of eddy-current and magnetic thickness gauges for metal finishing quality control interests.  When applicable, these nondestructive gauges provide a fast check on a variety of paint and metal coatings at a much lower cost than what x-ray fluorescence options would list at.

One of the most common uses of contact gauges is for the quality control of anodized coatings.

The process of anodizing aluminum (a popular example) involves creating a coating of aluminum oxide grown from the aluminum.  You may already know that this is accomplished by passing an electrical current through an acid electrolyte bath and immersing the aluminum item in it.  So, this type of coating is different than other coatings our clients would measure because anodized coatings are actually a ‘manipulation’ of one type of metal so that the top portion (or layer) is oxidized.  In contrast, applications that would use other gauges or XRF Analyzers would have one type of metal on top of a substrate of a different metal (or metals).

Anodized aluminum coatings are one of the only finishes in the metals industry that provides the high performance benefits of durability, color stability, ease of maintenance, etc.  The unique properties of anodized aluminum coatings make it of interest for a variety of products and industries.  Since slight changes in the process involved can affect the coating, most plating facilities will use multiple methods of process controls – one of the most critical quality controls for anodizing is thickness and the only way to measure the thickness is with eddy-current gauges.

In short, the eddy-current method uses a probe containing a coil that creates an oscillating magnetic field.  In closed circular paths, the depth of penetration is inversely proportional to the square root of the probe frequency and also to the square root of the electrical conductivity of the material in which the eddy-currents flow.  The eddy-currents create a counter magnetic field, which in turn reacts upon the probe by reactance and alters its output voltage.  The change in output voltage created is used to calculate the thickness.  Review the full eddy-current technology overview.

While these gauges do provide reliable measurements, the end-user needs to know that some aspects of a sample can affect readings.  Users should take note of factors that can influence readings such as distance to the edge of the part, sample curves, and surface roughness among others.  ASTM B 244 details these influences and you can work with an Application Specialist at Eastern Applied to develop a corrective calibration when appropriate.

DeFelsko Thickness GaugeIf you are adding anodized coating capabilities or are simply looking for an accurate method to insure proper plating, then Eastern Applied offers options from the DeFelsko Positector line of thickness gauges.  Contact our Application Specialists to discuss measuring anodized coatings or any other thickness measurement interests you may have.

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