In this post you'll learn
Introduction
Painting a finished product is vital to ensure its presentability and longevity. Due to new advances in surface finishing technologies, wet painting is no longer the only option to finalize a product. Many industries utilize surface coating over painting for various reasons.
Benefits of Surface Coating
Due to its efficient application, surface coating is decidedly cost-effective compared to wet painting. Coating applications are very well automated, meaning little to no supervision is needed to run a coating process. In addition, the coating is not a labor-intensive process; therefore, labor and training costs are considerably lower with coating compared to conventional methods of surface finishing. Moreover, the waste coating material can be easily reused: meaning less waste material cost.
Another benefit of surface coating is its longevity. Surfaces finished by coating are much more durable compared to surfaces with wet paint. Due to the contents of the coating material, surfaces finished by coating have higher levels of impact strength. This makes coating a perfect surface finishing process for products that are expected to endure impacts during their life span.
Aesthetics is another category in which the coating is superior to traditional methods. Since the coating material can level itself on the surface automatically and doesn’t drip, it’s almost impossible to achieve better visual results with other methods.
Finally, the coating is safer and more environmentally friendly. Wet paint contains carcinogens and volatile organic compounds (VOC) such as benzene, making them dangerous to work with and hazardous to nature. Since the coating material does not contain VOCs, the process is safer to work with and is more sustainable.
Surface Preparation
Regardless of the method chosen to finish a surface, proper surface preparation is critical to ensure long-lasting, visually presentable results. Correct use of tools for surface preparation is critical to ensure desirable results. Some work areas require special tools to achieve perfection in surface preparation such as subsea applications and oversea platforms’ splash zones. Check out our collection of equipment for subsea applications and splash zones. Without a well-prepared surface to work on, desired results are impossible to achieve, no matter how well the coating is performed. To achieve coating-ready surfaces, SSPC standards must be studied and followed.
The Society for Protective Coatings (SSPC) is a nonprofit organization for professionals in the industrial protective and marine coatings industry.
This association was formed in 1950 and was originally known as the Steel Structures Painting Council. The name was changed to the Society for Protective Coatings in 1997, but the organization retained its original acronym. In 2020, the SSPC and the National Association of Corrosion Engineers International (NACE) announced a merger agreement.
The SPPC oversees coatings industry standards, technical publications, training and certification courses, painting contractor certification programs conferences, and events that achieve standardization of the industry.
SSPC Standards of Surface Preparation
There are numerous standards published by the SSPC for different surface preparation methods. Standards of surface preparation are mentioned down as follows:
SSPC-SP1 Solvent Cleaning: Solvent cleaning is intended to clean any visible oil, grease, and all soluble compounds off of the surface. Solubles make it difficult for finishing products to bond with the surface; therefore, their removal is critical to achieve the desired results.
SSPC-SP2 Hand Tool Cleaning: This standard covers the removal of loose mill scale, rust, paint, and other foreign contaminants from the surface with the use of non-powered hand tools.
SSPC-SP3 Power Tool Cleaning: SP3 oversees the removal of similar contaminants as SP2 but with power tools to achieve a well-detailed surface preparation.
SSPC-SP5 White Metal Blast Cleaning: Blast cleaning will remove all coatings from the surface such as old coatings, rust, and corrosive products by blasting small particles onto the surface.
SSPC-SP7 Brush Off Blast Clean: This standard states a brush of blast clean will allow as much of an existing adherent coating to remain as possible and to roughen its surface before coating application.
SSPC-SP10 Near-White Metal Blast Cleaning: Near-White Metal Blast Cleaning provides a greater degree of cleaning than commercial blast cleaning, but less than white metal blast cleaning. The SSPC-SP10s definition of a near-white metal blast clean requires the surface to be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products, and other foreign matter when viewed without magnification.
SSPC-SP11 Power Tool Cleaning To Bare Metal: This surface preparation standard is similar to that of some less aggressive blast cleans. The standard requires the surface to be free from all visible oil, grease, dirt, dust, rust, coating, oxides, mill scale, corrosion products, and other foreign matter when viewed without magnification. However, some rust remaining at the bottom of pits is acceptable if the surface was pitted in the beginning.
SSPC-SP12 Surface Preparation and Cleaning of Metals by Waterjetting Before Recoating: Waterjetting is the use of standard jetting from a nozzle at high pressures (10,000 psi or higher) to prepare a surface for coating. Intended primarily for carbon steel, but it also applies to other metals.
SSPC-SP16 Brush-Off Blast Cleaning of Coated and Uncoated Galvanized Steel, Stainless Steel, and Non-Ferrous Metals: This surface preparation standard roughens and cleans the bare substrate including a hot-dip galvanized coating to create a profile suitable for painting.
Surface preparation under international standards is the final step before coating a surface. After choosing and applying the best suiting surface preparation method, the next decision is to decide which type of coating shall be applied.
Powder Coating
Powder coatings are based on polymer resin systems, combined with curatives, pigments, leveling agents, flow modifiers, and other additives. These ingredients are melted mixed, cooled, and grinded into a uniform powder.
The coating material is electrically charged and sprayed onto the metal surface using a process called electrostatic spray deposition (ESD). The spray gun electrically charges the particles to enable them to stick to the grounded metal surface. After application, the painted surface is heated up in a curing oven to dry off and finalize the process. The implementation of heat starts a chemical reaction resulting in a long-lasting, cured painted surface bonded together by cross-link density. Powder coatings can also be applied to non-metallic substrates such as plastics and medium-density fiberboard (MDF).
Powder coating is cost-effective, durable, presentable, and environmentally friendly. These properties make the process a popular finishing method for various industries. However, powder coating can leave a textured finish on the applied surface. If a smooth and seamless finish is preferred, other alternatives can be considered. Even though the process itself is highly cost-effective, the initial setup costs are relatively high due to the required equipment and automation.
Overall, powder coating is an excellent finishing solution preferred by various industries. Its ease of application on various materials explains its popularity. However, it’s not the only method of coating a surface.
E-Coating
E-coating, also known as electrodeposition coating, is a method of painting that uses electrical current to deposit paint on a surface. The process utilizes the elementary physics principle of opposite charges attracting one another.
After appropriate surface preparation, the surface is dipped into an electrocoating bath. The electro-coating bath includes 90% deionized water and 10% coating material. The water must be deionized; otherwise, the charged coating material would be attracted to the water instead of the surface. The coating material is primarily made up of resin along with other additives such as curative and color pigmentation. During the coating process, a modulated amount of voltage is applied to the surface. The amount of voltage applied determines the thickness of the coating. After the initial bath, the surface is rinsed to enhance the quality of the coating and to remove the excess coating material. Once the post-rinsing is complete, the coated surface enters an oven to cure the coating. E-coating can be applied to almost every metal, making it the preferred choice to various industries.
The main benefit of e-coating is that it ensures perfect coverage of tight and difficult-to-reach areas. Since the coating material is not sprayed, dipping the material into the coating allows tight areas to be coated with ease. In addition, e-coating enables better control over the top coat thickness due to the moderation of voltage applied on the surface. Much thinner levels of coating can be applied through e-coating compared to powder coating.
In contrast to the benefits of e-coating, surfaces that are finished by e-coating are vulnerable to sunlight. UV lights dissolve e-coating; therefore, if the finished product is expected to be exposed to sunlight, a protective topcoat is needed. In addition, color changes are almost impossible to achieve. The process is designed to coat the surface with one color only due to the part being dipped into the coating bath. Lastly, the initial set-up cost of an e-coating system is considerably higher than a powder coating system.
Final Words
Coating applications provide a more economical, visually presentable, long-lasting, and nature-friendly alternative to conventional methods of surface finishing. However, correct surface preparation and the use of correct tools are critical to achieving the desired results.
