Page 678 - Corrosion Engineering Principles and Practice

632 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 633

Type Coating General Qualities
Aluminum Highly resistant to heat, hot water, and corrosive gases.
Excellent heat distribution and reflection.
Babbitt Excellent bearing wearability.
Brass Machines well, takes a good finish.
Bronze Excellent wear resistance; exceptional machineability;
dense coatings (especially Al, Bronze).
Copper High heat and electrical conductivity.
Iron Excellent machining qualities.
Lead Good corrosion protection fast deposits and dense coatings.
Molybdenum Self-bonding for steel surface preparation.
(Molybond)
Monel Excellent machining qualities; highly resistant to corrosion.
Nickel Good machine finishing; excellent corrosion protection.
Nickel-Chrome High-temperature applications.
Steel Hard finishes, good machineability.
Chrome Steel Bright, hard finish, highly resistant to wear.
(Tufton)
Stainless Excellent corrosion protection and superior wearability.
Tin High purity for food applications.
Zinc Superior corrosion resistance and bonding qualities.

TABLE 14.6 Spray-Coating Materials

gas, which propels the material onto a prepared substrate or
workpiece. Depending on the substrate, bonding occurs either due to
mechanical interlock with a roughened surface, due to localized
diffusion and alloying, and/or by means of van der Waals forces (i.e.,
mutual attraction and cohesion between two surfaces). There are
three basic categories of thermal spray technologies:

• Feeding a wire or metal powder into oxyacetylene or oxyhy-
drogen flames (Fig. 14.13).
• Feeding a wire into the heated zone created by electrodes
arcing alternating current from which molten metal is
impelled by a stream of compressed air toward the surface to
be coated (Fig. 14.14).
• Blowing metallic particles suspended in a gas through a blow-
pipe flame, twin-arc (Fig. 14.15) or plasma (Fig. 14.16), a process
that can be used to coat inside pipes and tubes.