Coil coating is the continuous painting of a coiled metal strip. The process consists of a
number of stages along the travel path of the strip as a coil of bare metal is unwound,
processed and rewound into a finished painted coil.
The entry end of a continuous coating line includes two uncoilers, a coil-splicing unit,
and an accumulator.
The bare coil is loaded onto one of the uncoilers for entry into the coating line. The head
of the coil is spliced to the tail of the running coil. The accumulator allows the splicing
to occur by stopping the running coil without stopping the movement of the strip through
the line and letting the strip loop shorten and lengthen as required.
After the coil exits the accumulator, it goes through a series of clean and rinse tanks after
which it is air dried and then passes through a chemical pretreatment section.
The chemical pretreatment can be applied either by passing the strip through a spray tank
or applying dry with a coater. Its purpose is to provide a good adhesive layer for the
paint.
The strip then passes through a paint roll coater, which applies the paint to one or both
sides of the strip. The roll coater has an applicator roll to apply the paint against the strip
surface, a pickup roll to transfer the paint from a paint well to the applicator roll, and
support rolls to guide the strip through the coater.
The strip then is heated continuously in a curing oven at a temperature consistent with the
specification and thickness of the paint.
(Note: To apply a second coating requires passing the strip through another coater and
curing oven. )
After exiting the oven, the strip is cooled via a water quench or air-cooling section ,
finally passing through an exit accumulator section to be recoiled on one of two
recoilers.
When the end of the coil is reached, it is cut at the splice, which links the tail of the coil
to the head of the trailing coil. The accumulator provides a buffer to keep the line running
while making the stationary cut. The coil is then removed from the recoiler while the new
coil is wound on the other free recoiler.