No matter what the feed coil type, the strip must be pre-treated before paint is applied to obtain any acceptable level of prolonged paint adhesion and corrosion resistance.
Prior to pre-treatment the feed is cleaned to remove oil and any other surface contaminants. This is done in high pressure spray tanks with contact times of between 2 and 5 seconds. The solution is normally hot (60 -70 degC) alkali although acid based cleaners are also available. Following the cleaning tanks usually two hot (50 -60 degC) water spray tanks are used to be sure that the alkali from cleaning is not carried through to the pre-treatment stage. Between each spray tank rubber squeegees also prevent carry through of the solution from one tank to the next.
Following cleaning, the pre-treatment is applied. This is usually chromic or phosphoric acid based although chromium free systems are now available. The pre-treatment performs a dual function.
● It creates a very high bond between the paint and the base metal.
● It provides corrosion protection. Without the pre-treatment protection, any cuts,