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 Zinc Finish Finishes.. Zinc plated deposits protect by corroding before the steel of the component is attacked. Therefore there are two corrosion phases to consider when specifying a zinc finish. The first phase is the time it takes for the zinc deposit to show the first signs of corrosion, often called "White Rust" as zinc oxide in its pure form is white in practice its colour can range from grey to black. At this point the finish maybe unattractive but the component is still potected by the zinc deposit. The second phase is the time it takes for the steel itself to start to corrode with evidence of the familiar "Red Rust". From this point on the structure of the component is being degraded.
Extending the time to "White Rust" Using a chromate passivation that modifies the surface of the zinc deposit and thus improving its corrosion resistance. This process colours the deposit and the resultant colour is often used to specify the correct film, e.g: clear or yellow Passivate. Adding a lacquer "Sealing" coat to the deposit after the passivation process can attain further improvement.
Extending the time to "Red Rust" Once the barrier coat of the chromate film has been penetrated the zinc will start to corrode. The thickness of the zinc will determine the time it takes for "Red Rust" to appear. Specifying a thicker zinc coat will increase the time to "Red Rust". Improving the design features of the component so that a more even deposit is achieved will also extend the time to "Red Rust" |
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