How is A Piece of Metal Powder Coated?

Iron and steel are used for making big machines while other parts are made of copper and nickel. Metal is used for making machines and machine parts because it is stronger than wood and functional than stone. But metal is also not free from defects. Visit here :- https://www.behance.net/gallery/25192131/How-is-A-Piece-of-Metal-Powder-Coated