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Reading Selection, Lesson 24

The Work Never Ends

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The Golden Gate bridge

The Golden Gate Bridge (San Francisco, California) is an example of steel used in close proximity to saltwater.

The Golden Gate Bridge is one of the world's great bridges. It spans 2.7 kilometers across the Golden Gate Strait at the end of San Francisco Bay. More than 1.5 billion cars have crossed over it. It contains 75 million kilograms of steel. It can withstand powerful tides, hurricane winds, and major earthquakes. But one thing could send it tumbling into the bay below: corrosion. The iron in steel combines with the oxygen in air to form iron oxide, or rust. Water and salt, which the bridge is constantly exposed to, greatly speed up rust formation. To keep the mighty bridge from crumbling apart, maintenance crews must constantly battle rust.


Preventing Rust
Dry steel rusts very, very slowly. But wet steel rusts very quickly. If steel is in contact with saltwater, it rusts even faster. Paint prevents rust by keeping oxygen, water, and salt away from the steel surface.

Applying the Paint
Worker painting the Golden Gate Bridge

Paint is applied to combat the rust problem. Paint prevents the iron in the steel from coming into contact with water and oxygen, the other reactants in the rusting equation.

A painter puts down a primer coat. Primer sticks to the metal, but it isn't that tough or waterproof. So after the primer dries, the painter puts on two protective top coats of paint that keep out air and water.

Touching Up
Whenever rust spots appear on the bridge, maintenance crews go to work scraping off the rust and worn paint. Metal workers then cut out and replace any corroded metal.

Repainting
Although it is called "Golden," the Golden Gate Bridge has always been painted International Orange. The bridge was first painted in 1937, the year it opened. Between 1965 and 1995, the entire bridge was repainted. Bit by bit, all of the old paint was scraped off and a new, tougher acrylic formula was put on. But even the new paint can break down in spots. Maintenance crews constantly inspect the bridge and touch up any rusted areas.

Question

How do car or bicycle manufacturers stop or reduce rusting? Draw a simple sketch of either a car or a bike and label all the different methods of rust prevention you can identify.

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