Steels_ Metallurgy and Applications, Third Edition

Low-carbon strip steels 127

Figure 1.124 A comparison of the sound level from a garage door made from sheet steel
and from sound-deadened steel. The average difference was 10 dB (After Mathieu 193)

that the noise reduction may be accompanied by a weight reduction as a result
of the elimination of the conventional materials that would otherwise be needed
to reduce noise, such as felt.
The formability of the composite depends on the formability of the steel and
the adhesion of the polymer since the latter influences the tendency for wrinkling
in areas of a pressing subject to in-plane compression. During forming the two
sheets may move relative to each other to give an offset of the edge. Holes for
fixing must, therefore, be made after forming. The polymer acts as an insulator.
Spot welding may, therefore, be achieved by the use of shunts which lead to
local heating and softening of the core material. This enables it to be compressed
and allows the weld current to pass and make a satisfactory weld.
The material already has many applications in the manufacture of cars,
including engine enclosures, oil sumps and rocker covers and its use is spreading
to other industries where noise control is becoming increasingly important.

Vitreous enamelled products

Vitreous enamelling is a long-established finishing process and one that is being
applied to an increasing range of steel products. Cold-reduced steel is the most
widely used substrate and the grade is selected according to the strength and
formability required and the enamelling process that is used. After fabrication,
the product is degreased, pickled, rinsed and dried and in the most common
process, a ground coat enamel slip or slurry is applied to the component, either
by dipping or spraying. After drying, the enamel is fused by firing at temperatures
above 800~ A second coat, the cover coat enamel, is applied, dried and fired
in a similar way. Some enamel is applied by means of a single-coat process
and also by means of a two-coat one-fire process. The ability to produce a
satisfactory product depends on the nature of the steel as well as on the nature of