94 Steels: Metallurgy and Applicationscoated with a primer, which is cured, and the top coating is then applied by
the reverse-roll method. Finally, the topcoat is cured in a finishing oven. Where
embossing is required, typically on PVC coatings of 200 ~tm, a patterned steel
roll is applied to the hot PVC as it emerges from the finishing oven. The mate-
rial is then immediately quenched in water in order to 'freeze' in the embossed
texture. Coil-coated strip is marketed in the UK under the name Colorcoat.
In the laminate coating, an adhesive and backing coat are applied by roller-
coating and the strip is passed through an oven to activate the adhesive and cure
the backing coat. The coating film, generally PVC, is bonded to the steel and
cooled immediately by water quenching. The material is marketed in the UK
under the name Stelvetite and is intended for internal applications.
Organic-coated strip is specified in Euronorm 169-85. The following infor-
mation on the characteristics of the more important coatings has been derived
from Annex A of Euronorm 169-85 and a British Steel publication: 14s
9 PVC Plastisol (200 ~tm)-a plasticizer-bearing coating with very good
flexibility. Can be drawn and formed easily. Suitable for embossing for
decorative purposes and can be used in internal and external applications.
Typical applications- roofing and cladding on buildings, curtain walling,
furniture, vehicle fascia panels, garage doors.
9 PVC Organosol (50 ~tm) - a coating with good flexibility and specially recom-
mended for deep-drawn parts. Not recommended for exterior use. Typical
applications- electric light fittings, cable trunking, deep-drawn parts.
9 Acrylic (25 ~tm)- unplasticized coating with good flexibility. Suitable for
continuous operation at temperatures up to 120"C. Good resistance to chemical
attack.
9 Epoxy (5-15 ~tm)- hard, chemical-resistant coating with good flexibility.
Typical applications - used extensively as a primer for two-coat systems. Good
adhesion to polyurethane foam. Not recommended for external use.
9 Polyesters (25 am) - widely applied coatings with good flexibility and suitable
for continuous exposure at temperatures up to 120"C. Various formulations are
available that offer good deep-drawing properties, resistance to chemical attack
and that are suitable for exterior use. Typical applications - consumer durables,
deep-drawn components, building components.
9 PVF2 (27 l~m) - a coating with good flexibility and highly resistant to chem-
icals and solvent attack. Highly resistant to weather and particularly suitable
for exterior use. Typical applications - building components.
As indicated above, many of these coatings exhibit good formability and are
amenable to forming operations such as press braking and folding, roll forming
and deep drawing. However, the flexibility of the coatings varies with ambient
temperature and, to minimize the risk of cracking during forming, it is recom-
mended that the liquid film and laminate-coated materials should be allowed to
attain minimum temperatures of 16 and 200C respectively. 149
The resistance welding of organic-coated steel is not possible by conventional
methods because the coating prevents the flow of current across the electrodes. On
the other hand, resistance welding is possible if the coating is removed locally, or