Evaluation of zinc coating procedures : final report.
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1978-01-01
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Abstract:This research project was conducted in order to compare the existing procedure of zinc coating by hot-dip galvanizing with the other zinc coating systems of painting and electroplating.
Hardware coated by these processes was exposed to varied laboratory tests. Based upon the results of these tests, the protection afforded by the GS grade of electroplated hardware was determined to be equivalent to that of the hot-dip galvanized hardware having a coating thickness of approximately 2 ounces of zinc per square foot of surface area (0.061g/cm2). The LS grade of electroplated hardware was found to be inferior in performance to both the GS grade of electroplated and hot-dip galvanized hardware. The zinc-rich paints used as repair systems gave adequate protection to the hardware after being exposed in a hot and humid environment for 12 months.
Results using the scanning electron microscope showed a distinct difference in the layer of zinc deposited on the steel surface using the electroplating and hot-dip galvanizing procedures. The layer of zinc observed on a hot-dip galvanized washer showed the presence of an alloy layer. However, there was no alloy layer detected in the photomicrograph taken of an electroplated washer.
Four gears of field evaluation have been completed. The results showed that generally all the zinc coatings were performing satisfactorily. The only significant amount of corrosion was rusting of the bolt threads which were painted with an organic zinc-rich paint.
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