CLICK HERE FOR INDEX PAGE

GALVANISING STEEL AND IRON - 2

V. Ryan 2008 - 2009

 

VIDEO - GALVANISING IRON AND STEEL  
 

PDF FILE - CLICK HERE FOR PRINTABLE WORKSHEET

TASK
Carefully cut a small piece of galvanised steel sheet with tin snips. The edges will be shape so handle it with care. Scratch the surface with an engineers scriber and leave it outside in the rain for a few days. Compare it to a piece that has not been scratch and has also been left outside for the same length of time.

What do you think will happened to the surface of each piece of galvanised steel?

You will probably find that rust has formed along the scratched line. If the steel was to be left outside for longer the rust would spread out and damage the surface considerably. Eventually the rust would ‘eat’ its way through the thin sheet metal. It would eventually be possible to bend and break the steel quite easily.

ELECTROPLATING - ELECTRO-GALVANISED

   

In industry electroplating is often the process used to galvanise steel products as it is more efficient and more cost effective than the hot dipping process. Also, it is easier to control the entire process. For instance, the thickness of the coating can be determined with great accuracy.

A good example of this can be seen in car manufacturing. Galvanising of steel car bodies is now standard practise although twenty years ago only the must prestigious of cars such as Rolls Royce had galvanised bodies.
The steel car body is electrically charged as negative and is suspended in a conducting solution known as the electrolyte. As the car body is negatively charged it is known as the cathode. Rods of pure zinc are positively charged and it is the zinc from these rods that is eventually deposited on the surface of the steel. The rods are suspended in the electrolyte.
A current passing through the electrolyte causes the zinc already in the solution to migrate towards the cathode (the car body). At the same time zinc from the anode (the zinc rods) pass into the electrolytic solution. The rods eventually need replacing.

 
The diagram above shows a car body about to be lowered into the electrolyte solution
   
1. List a range of products that have been treated in an electrolyte solution and galvanised.
 
 
 
 
 
 
2. Why are car bodies galvanised?
 
 
 
 
 
 
 
CLICK HERE FOR FIRST PAGE ON GALVANISING STEEL
     
CLICK HERE FOR EQUIPMENT AND PROCESSES INDEX PAGE
     
CLICK HERE FOR RESISTANT MATERIALS INDEX PAGE
     
 
Google
 
Web www.technologystudent.com