Page 677 - Corrosion Engineering Principles and Practice

630 C h a p t e r 1 4 P r o t e c t i v e C o a t i n g s 631

Detonation Front Explosive

Cladder

Jet Metallurgical
Weld Line
Backer
Collision Point

FIGURE 14.12 Manner in which explosives bond a layer of cladding metal to
a base: explosive; cladding metal; base metal; and "jet" securing cladding
layer to base.

In roll bonding, layers of two metals are mated by heavy rolling
in a mill after the surfaces have been thoroughly cleaned and treated.
Clad thicknesses of 5 to 10 percent of the base steel thickness are
common. Some small areas of unbonded metal will be present. Two
metals may also be coextruded through a die.
Cladding can also be accomplished by other methods such as arc
or gas welding in which relatively thick layers of weld metal are
deposited either by manual or machine methods on surfaces. The
interior of pulp digesters or other pressure vessels requiring an alloy
composition to resist the chemical conditions can be constructed in
this manner.

Laser Welding Propeller
In explosion bonding, a base metal and a covering metal coating are
contacted, placed in an appropriate enclosure with the coating
material on top. A layer of explosive is placed over the coating metal.
When the explosion is activated, the resulting shock wave merges the
two materials, as shown in Fig. 14.12.

14.8.5 Metallizing (Thermal Spray)
The metallizing technique for applying metal coatings consists of
thermally spraying one type of metal onto a metallic substrate, most
often steel, or reinforced concrete to provide cathodic protection to
the rebar material as discussed in Chap. 13. The technique is
accomplished in several ways. Table 14.6 shows the main metallic
materials that have been used for the production of spray coatings
and Table 14.7 summarizes the limits and applicability of each
technique.
Coatings can be sprayed from rod or wire stock or from powdered
materials. The material (e.g., wire) is fed into a flame, where it is
melted. The molten stock is then stripped from the end of the wire
and atomized by a high-velocity stream of compressed air or other