01 Making Coil Coating

Coil coating is a continuous and highly automated process for coating metal before fabrication. In one continuous process, a coil of metal, up to 1.80 meter wide moving up to 213 meter per second, 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.

Coil coating provides beautiful topcoats, durable surfaces, innovative applications, green benefits, and cost savings as compared to other substrates and other coating options.

Innovative coil coating production methods and processes are used that generate consistent production runs.  Coil Coat caters to many leading manufacturers that include roofing, cladding, composite panels, ceilings, window blinds, sporting goods and appliances.

An overview of coil coating

Bare coils of metal are placed on an unwinder or decoiler 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 are used to provide the bond between the metal and the coating, in addition to adding any corrosion resistance. The type of chemical treatment varies with the type of metal being used.

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 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. A majority of 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.

Coil coating process line

The following steps take place on a modern coating line:

  • Stitching the strip to the previous coil
  • Cleaning the strip
  • Power brushing
  • Pre-treating with chemicals
  • Drying the strip
  • Applying primer on one or both sides
  • Curing (often only 15 to 60 seconds!)
  • Cooling the strip
  • Top coating on one or both sides
  • Second curing
  • Cooling down to room temperature
  • Rewinding of the coated coil

coil

Benefits of coil coating

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. Organics and inorganics, such as polyesters, epoxies, vinyls, plastisols, acrylics, water-born emulsions, fluorocarbons, dry lubricants, treatment and primer combinations, can be applied.

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.