Industrial surface coating operations use several different methods to apply coatings to
substrates. Some of the more commonly used techniques include spraying, dipping, rolling, flow
coating, knife coating, and brushing. In addition to the application of coatings to substrates,
many surface coating operations also include surface preparation steps (e.g., cleaning and
degreasing), and drying and curing stages. Spraying operations are normally performed in a
spray booth using one of the following spray application methods: air atomization; airless
atomization; air-assisted airless; high-volume, low-pressure (HVLP); and electrostatic methods.
Dip coating involves briefly immersing the substrate in a tank containing a bath of paint. The
object is slowly removed from the tank allowing excess paint to drain back into the tank. Roller
coating is used to apply coatings and inks to flat surfaces. A typical roller coating machine
contains three or more power driven rollers, one of which is partially immersed in the coating
material. The paint is transferred to a second, parallel roller by direct contact. The sheet to be
coated is run between the second and third rollers, and is coated by transfer of paint from the
second roller. Flow coating is used on articles which cannot be dipped due to their buoyancy,
such as fuel oil tanks, gas cylinders, or pressure bottles. In this operation, the coating material
is fed through overhead nozzles, distributing the paint in a steady stream over the article to be
coated. Excess paint is allowed to drain from the coated object and is then recycled. Knife
coating is used primarily to coat paper or fabric webs. The adjustable blade or "knife" distributes
a liquid coating evenly over a moving surface.