Coil coating is a continuous and highly automated process for coating metal roofing pre-fabricates before fabrication. In one continuous process, a coil of metal, almost 50 inches wide moving up to 700 feet per minute, is unwound and both the top and bottom sides are cleaned, chemically treated, primed, oven cured, top coated, oven cured again, rewound and packaged for shipment.

In Precoat Metals Coating Facility, bare DML USA metal coils are placed on an uncoiler where the metal is observed for defects. The metal is then cleaned and chemically treated in preparation for painting.
Brushes can be used to physically remove contaminants from the sheet, or the metal may be abraded by flap sanders to further enhance the surface. Pretreatments may be used to provide the bond between the metal and the coating, in addition to adding any corrosion resistance.

After drying, the strip enters a coating room for a coat of primer usually on both sides of the sheet. The pickup roll transfers the coating liquid from the pan to the applicator roll. The liquid is then pumped into the pan, and then overflows back to the supply reservoir, where it is remixed and filtered.

The direction of the rotation of the applicator roll plays a part in determining the type of coating. Reverse roller coating, when the applicator roll turns in the opposite direction of the strip, is used to apply thick coatings. Direct roller coating, turning in the same direction as the strip, is used for thinner coatings, 0.5 mils or less.

The paint sheet then enters an oven in which the coating is cured at high temperatures for 15 to 30 seconds. The strip exits the oven and is cooled with air and water. DML USA Metal Roofing specifications call for two coats (primer and top coat) on each side of the sheet, requiring a pass through a second coater room and oven. The fully painted sheet then exits the second oven and is cooled before inspection and rewind.

Since the process allows metals to be finished in one continuous pass, there is flexibility in how the metal is coated and the types of coatings. Prepainted coils can also be printed, striped and embossed to create special visual effects.

Coil coating provides for controls that are virtually impossible to attain with most other painting processes. Dealing with a flat sheet allows for mechanical cleaning in addition to the spray cleaning. The flat sheet also enables excellent control of coating weights of both the pretreatment and the paint to within a tenth of a mil or less, depending upon the equipment and the paint system being applied. Such advantages, along with the economic and environmental benefits, make coil coating the right choice for many manufacturers.

Coating Layers

 

 

 

 

 

 

 

 

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