Materials ~ Corrosion & Tarnishing

If a metal object is left unprotected it will change. It might be a minimal visual change or it could be a structural change after a period of time.

These changes are called ‘CORROSION’ or ‘TARNISHING’.

Make sure that you are able to understand the different effects that this has on different metals:

Iron and Steels will RUST because they contact IRON.

As you can see on this spanner (which was left outside in the weather) it has started to change from bright shiny metal (steel) to brown rust. It has not taken hold too much because the fine etching of the size of the spanner can be clearly seen just below the jaws.

Rust can be treated and prevented using chemicals.

Some metals become dull when exposed to the air. Silver is a good example of this, you can see on the spoon below it has become dull and ‘tarnished’. The only way to keep the surface shiny is to keep polishing it!

Huge structures like the Eiffel Tower have to be constantly attended to, to ensure that the metal used to make the the tower remain in good condition and structurally sound. A team of city workers constantly check, clean and repaint the tower.

 

Changes

I have been changing the layout of the pages and the contents to make things easier to find and navigate.

Tim

Joining metals with mechanical fasteners…..

Joining metal together………………………….

Joining to metal together is quite difficult at times particularly if you need it to move. It is quite common to see rivets used with ‘bell caps’. These are often seen on push chairs and other day to day folding items.

This is the inside of a bell cap, it consists of two parts, the cap and the star shaped sprung washer which grips the rivet shaft. It can only be removed by damaging the cap and sprung washer.

The cap is also used to hold wheels in place on pushchairs and childrens toys.

The picture shows the bell cap, round headed rivet and a snap or pop rivet.

Pop rivets are used a lot in the coach building, aircraft and vehicle industries. They are also used in fabrication and heating ducts/systems to help locate non-load bearing objects like ducts and pipes.

Pop rivets are inserted into a hole and then a tool used to pull the ballended pin through until it snaps off leaving the rivet clenching the metal sheets together.

This picture shows the rivet before use, the plain metal shaft is hardened steel and is gripped in the tool. On the left of the picture you can see the ball end which forces itself into the softer rivet body.

You can clearly see in this picture the ‘neck’ which fails when it reaches the top of the rivet body leaving the hardened steel pin in the tool to be discarded.