The coil coating process is an engineering marvel. Coatings and film laminates are applied to coils of metal in a continuous and highly automated process prior to fabrication into final products. As a coil of metal – up to 72 inches wide and traveling as fast as 700 feet per minute – unwinds, both the top and bottom sides are cleaned, chemically treated, primed, oven-cured, top-coated, oven-cured again and recoiled for packaging and shipment.
Coil coating is recognized for its cost effectiveness, aesthetics, field performance and sustainability. The process is a closed loop system with greater than 98% VOC capture and conversion to fuel.
The European market sometimes refers to the finished product as "prepainted" or "precoated" metals or coils.
Metal coils, up to 60,000 pounds, are received and given a visual inspection. After inspection, the entry operator moves the coil to the uncoiler whereby the metal is placed on a pay-off arbor for unwinding.
At this stage, the end of the previous coil is mechanically joined to the beginning of the next coil. This function allows for the continuous feed of the coil coating line.
The accumulator is a structure that adjusts up and down to store material, which makes continuous operation of the coil coating process possible. This accumulation will continue to feed the coil coating processes while the entry end has stopped for the stitching process. As much as 750 feet of metal can be collected.
The cleaning and pretreating section of the coil coating process focuses on preparing the metal for painting. During the cleaning stage, dirt, debris and oils are removed from the metal strip. From there, the metal enters the pretreatment section and/or a chemical coater whereby chemicals are applied to facilitate paint adhesion and enhance corrosion resistance.
In this stage a chemical that provides enhanced corrosion performance is applied. This treatment can be chrome free if required.
During this stage, the strip enters the prime coat station whereby a primer is applied to the clean and treated metal. After the primer is applied, the metal strip travels through a thermal oven for curing. Primers are used to aid in paint adhesion, improve corrosion performance and enhance aesthetic and functional attributes of the top coat.
The S wrap coater design allows for primers and paints to be applied to the top and back side of the metal strip simultaneously in one continuous pass.
After the primer is applied and cured, then the metal strip enters the finish coat station where a top coat is applied. Topcoats provide color, corrosion resistance, durability, flexibility and any other required physical properties. Like primers, the top coat is cured using thermal cure ovens.
Coil coating ovens can range from 130 feet to 160 feet and will cure the coatings in 13 to 20 seconds.
Like the Entry Accumulator, the Exit Accumulator adjusts up and down to store metal while the recoiler is unloading a completed coil.
Once the metal is cleaned, treated and painted, the strip is rewound into a coil size prescribed by the customer. From there, the coil is removed from the line and packaged for shipment or additional processing.