Epoxy is an extraordinarily versatile coating with applications ranging from the automotive industry to do-it-yourself at home projects. Both waterborne and powder based epoxies are employed because of their high level of adhesion, and resistance to corrosion and heat—they can be clear or opaque, and with additives can easily be manipulate to resemble a variety of other materials, such as finished concrete or granite. Fusion bonded epoxy coating (FBE), a powder-based coating, possesses the same properties as traditional epoxy and is used to coat and protect steel pipeline, piping connections, and valves. It earns its name “fusion bonding” from the process by which it adheres to a substrate—when the hardener and epoxy react and the coating takes solid form, the chemicals involved are cross-linked—the process is irreversible, even with severe heat applications.
Fusion Bonded Epoxy Components
What enables chemical cross-linking, and makes FBE such a strong coating, is a combination of four separate components: resin, hardener, fillers, and color pigments. Resin and hardener comprise the adhesive element of FBE, and are often referred to as the “binder.” The epoxy resin, also known as “oxirane” is comprised of resin molecules that each carry one oxygen atom and two carbon atoms, which are highly reactive. When mixed with hardener, the resin and hardener react and adhere to the substrate.
The hardener itself is what determines many qualities of the final fusion bonded epoxy mix, such as flexibility and chemical resistance. The addition of fillers and pigment can alter properties such as hardness, thickness, permeability, and color. Resin, hardener, fillers, and pigment are usually solid in form.
How FBE Powder is Manufactured
After all four components are mixed and blended, the resulting dry mixture enters an extruder, where the mixture is compressed, heated, and melted until semi-liquid. The temperature of the extruder barrel is kept between 50-100 degrees C so as not to significantly alter the chemical properties of the ingredients while they are evenly mixed together. The mixture is then extruded and passed between rollers until it forms a solid sheet. The sheet is then cut into tiny pieces, which are then ground up into powder. The final powder mixture is then packaged.
Applying Fusion Bonded Epoxy Coating
Fusion bonded epoxy coating application takes place in three general stages. First, the metal surface or substrate must be cleaned. After adequate cleaning, the metal should be heated to the appropriate temperature for FBE powder application (because heat is needed in order for the powder to assume liquid form and adhere). The last stage involves properly applying the FBE powder.
To properly clean the metal, blast cleaning is commonly used. Because dust and rust and other grit and grime can inhibit proper coating adhesion, blast cleaning effectively removes such build-up, making the surface rough and clean. In order to remove oil and grease, a solvent cleaning agent may be used.
After the metal has been sufficiently cleaned, it must be heated. Induction heating, which requires that the metal be exposed to alternating electric currents, is a common method; other common choices are oven heating and infra-red heating. Once the metal is heated, the coating process can begin. The epoxy power is applied with an electrostatic spray gun—the powder is literally ionized and charged, so as to adhere to the metal—and as the molten powder meets the metal it forms a strong, irreversible bond. After the powder sits for a few seconds, it assumes solid form.
The application process is quick, produces limited amounts of waste, and enables quick and smooth production. Since the coating dries quickly, the end products are able to be moved shortly after the process ends.