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Hardness Testing of Anodized Layers and Glass

The inside of a pair of binoculars contains a high degree of experience and technological expertise. Manufacturers are working on eliminating any negative effects such as refraction, reflections and dispersions, by manually incorporating more than 70 different types of glass. Within the framework of product development and quality assurance, hardness testing of thin, dark layers—the anodized layer—is a particularly difficult challenge.A leading manufacturer chose a hardness testing machine from ZwickRoell to carry out this test task.

Anodized layers

Anodized layers are oxidic protective coatings on aluminum. In the first step, the aluminum component is degreased and pickled. Pickling removes the thin natural oxide layer. After that the actual anodizing process takes place. Sometimes colorant is added to the freshly prepared porous layer and then sealed. The anodizing procedure is an electrolytic process. It is carried out with direct current and acid electrolytes. The layer is then sealed so that a deposit of corrosion-promoting substances is prevented and the pores become more narrow and then close. As a result, these coatings have a high degree of hardness and are highly wear resistant. They are often also used as decorative layers and have very good corrosion properties.

The tough challenge for this application is finding the right test method for the anodized layer, since it is both very thin and very dark. In addition, glass has to be tested, since the glass is subjected to a goods inwards check and quality control must be implemented. Which test method is the most suitable must be determined empirically.

The Knoop method for hardness testing

Since the anodized layer is very thin, low test forces must be used. With the DuraScan 20, it has been possible to perform a test directly on the layer. The Knoop impression does not penetrate very deep into the material and is therefore ideal for thin layers. The Knoop method is also suitable for hardness testing on glass. The test force to be used depends on the glass.

Use of the turret facilitates the test. Especially when testing anodized layers, it is sometimes necessary to test several measurements to determine the optimal test force. Since due to the turret, manual tool changes are unnecessary and the evaluation of the indentation is fully automated, a lot of time is saved. After finishing the measurement, a customized test report is created so that traceability of the test results is always provided.