Steels_ Metallurgy and Applications, Third Edition

126 Steels: Metallurgy and Applications

plastics. The formability requirements are not high and steel drums are normally

made from uncoated, Fe POI strip. However, limited use is made of galvanized

steel to provide greater corrosion resistance against particular products.

For the future, there is the prospect of using higher strength steels in lighter

gauges in an attempt to stem the greater penetration of the market by plastics.

However, attention must also be given to improved designs in order to preserve

adequate rigidity in down-gauged drums.

Sound deadened steel

Since 1991 there has been in Europe a regulation requiring that noise levels
must be below certain specified values that would otherwise cause damage to
hearing. An indication of the noise level that could damage heating is given
in Figure 1.123. In addition, a low noise level has become an important selling
point for cars and other products. This may be achieved by appropriate design but
noise levels may also be reduced by the application of various sound absorbing
materials, such as mastic, onto hidden surfaces.
A special product is now available from at least five companies in Europe to
provide sound absorption without the need for the application of any additional
material. It is known as sound deadened steel and consists of two sheets of steel
enclosing a thin layer of a viscoelastic polymer. 194 In use, vibratory shear strains
are developed in the polymer by relative motion of the two sheets and this leads to
the damping of the vibration and the development of a small amount of heat. The
polymer may be formulated to give maximum damping at various temperatures
up to 150"C as required and is stable up to 200"C. It does not, therefore, lose its
damping capability as a result of paint baking. The degree of damping achieved
depends on the shape of the component and the method of support. 195 It also
varies with the frequency of the vibration, as illustrated in Figure 1.124, which
gives an example of the effect of sound deadened steel on the airborne noise
from a garage door. 193 It is seen that the noise is reduced by an average of about
10% within the frequency range 200-10000 Hz. Another possible advantage is

Figure 1.123 Noise levels expected to have an effect on hearing ability (After Mathieu 193)