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GALVANISING STEEL AND IRON - 1

V. Ryan 2008 - 2016

 

VIDEO - GALVANISING IRON AND STEEL  
 

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Steel is a very strong and versatile metal used to manufacture a large range of products. Steel surrounds us in our every day lives as it is used to construct buildings and structures. It is a versatile material although it has one weakness, corrosion.

If an exposed steel surface comes in contact with water or moisture rust can take hold. Rust can damage the surface of the steel  as seen on corroded car bodywork. It is possible that on a large structure such as a bridge rust can cause structural failure leading to collapse.

   

Steel is usually coated. For example, the Golden Gate Bridge in San Francisco receives a new coat of rust resistant bronze paint every five years. This prevents rust damaging the structural integrity of the bridge. On smaller manufactured items zinc is used to coat steel and this is an effective measure against rust. This process is called galvanising.

   

The bolt seen opposite shows the damage caused by rust. If this occurs to the bolts holding together the parts of a bridge, the bridge would be in danger of collapsing.

   

The steel tie ring (below) has also been attacked by rust. The magnified surface shows how deep the damage is and this will eventually mean that it needs replacing.

The galvanised tie ring is almost the same design. However, there is one crucial difference - it has been galvanised. The magnified surface shows the layer of zinc that protects the inner steel from the elements. This tie ring will last for many years whist the original unprotected steel tie ring (above) will last only two or three years.

1. Research the internet and compare the price of galvanised nuts and bolts to the steel equivalent.

2. List a range of steel products that are also supplied as galvanised.

3. Research how steel is galvanised.

 
   
HOT DIPPING - GALVANISING
   

Galvanised steel is steel that has been coated with zinc in order to prevent rusting / corrosion. Sometimes the galvanising process is referred to as hot dip galvanising. The zinc forms a barrier against corrosion in that the steel underneath does not come into contact with water / moisture in the air.

The hot dipping process applies quite a think layer of zinc to the steel by passing the steel through a molten bath of zinc. The temperature of the zinc is usually in the region of 460 degrees centigrade. The zinc forms a bond with the steel by forming an iron-zinc alloy. The zinc also forms a zinc oxide when it comes in contact with the air which also helps prevent corrosion.

   

The steel used in the manufacture of the bench seen below has been protected by adding a zinc coating. This is done by submerging the steel parts in molten zinc. The zinc becomes part of the steel outer layer.

     
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