In this post you'll learn
Introduction to Metal Coatings
Metal coatings are used to improve the physical and chemical properties of ferrous metals. Corrosion, thermal and impact resilience are the main properties that can be improved through the surface coating. The process of coating is also commonly used to provide metals with visually pleasing finishes. Deciding which coating process to use for which preferred result can be challenging. In this article, we will take an in-depth look at different processes, and compare the advantages or disadvantages along with economical parameters.
Galvanization
Most commonly known as hot-dip galvanization, is the process of dipping the base material into a molten bath of zinc. Molten zinc attaches to the base material and reacts with the free oxygen in the air to create a powerful zinc oxide layer. High-temperature levels under which the galvanization occurs create a strong chemical bond between the base material and the zinc to prevent flaking. Galvanized metal has a non-reflective grey color with a crystallized appearance.
Oxidation resistance is the biggest strength of galvanization. A vast range of materials and equipment can be galvanized to achieve oxidation resistance. Metal supports, pipes, and construction materials are some of the most commonly galvanized materials.
In the case of welding after galvanization, the welding point must be repaired with a special touch-up painting material which includes zinc, the base component of galvanization to prevent rust build-up from the welding damaged area.
Galvanization also offers a good amount of chemical corrosion resistance, making it a viable option for coating petrochemical plant components.
Surface strength is not the strongest property of galvanization. Therefore if the intended result is a hardened surface, this method of coating may not be the best option. If the physical impact is expected, galvanization may not last as long as other options since the impact will create cracks that will break the seal of zinc around the base material, allowing oxidation to penetrate deeper into the steel.
The thickness of the coating is the most essential parameter to determine the quality of the galvanized metal. The industry standard for most applications is 40 microns. However, this value can change between a range of 15 to 50 microns. Not all galvanization is the same, so correct thickness specification is critical to ensure desired results.
Powder Coatings
Powder coatings have been covered more in-depth by one of our articles however to sum it all up, this is the process of spraying the bare metal surface with electrically charged particles. The base material is cured under 200 Fahrenheit after the initial application of coating material to seal the surface.
To achieve the best results with powder coatings, intensive surface preparation is essential. The base material surface must be cleaned off of contaminants to prevent flaking. Another key surface preparation step is to reduce the roughness of the surface.
Powder coatings don’t offer much improvement when it comes to chemical resistance. The main attraction of this application is to achieve visually presentable results. Therefore, powder coatings are most commonly used for parts that are not expected to endure corrosion or surface impact but need to be visually pleasing.
Powder coating provides an environmental alternative to conventional painting due to the lack of solvents in the coating material.
Aluminum Coating
The aluminum coating is the process of applying a protective layer of aluminum-based material against corrosion and other contaminants. The process itself is quite straightforward. The base material is dipped into an acidic degreaser for decontamination so that the dirt and debris wouldn’t be buried under the coating material. After the degreaser, the material is dipped into a rinsing bath to get rid of the degreaser solution. Aluminum coating sticks onto the surface through the principle of attraction of opposite poles, therefore the base material needs to get electrically charged before coating. Charged material is dipped into the coating solution, which is charged as well and dissolved in deionized water. This is a very similar process to powder coating. When the coating is done, the base material gets taken into a drying oven.
Aluminum coating provides the base material with excellent oxidation and chemical resilience. In addition, aluminized material can be shaped without damaging the coating which makes aluminum coating unique in terms of reformability.
Electroplating
Electroplating, also known as electrodeposition, involves depositing a thin layer of one metal on the surface of another metal. During electroplating, both metals are placed in an electrolytic solution. The metal to be coated acts as the anode, while the coating metal acts as the cathode. An electric current is applied to the electrolytic cell, causing metal ions to move from the cathode to the anode, thus forming the coating.
Electroplating has excellent resistance against oxidation and corrosion. It also provides the base material with a visually pleasing finish. However, a uniform thickness should not be expected with this process since homogeneity is determined by how equally the electrical charges have been distributed across the material.
Due to the use of harmful chemicals and solutions used in this process, the disposal of electroplated metals must be performed with care for the environment.
Porcelain Enamel Coatings
Most commonly seen in cast-iron cookware, enamel coatings provide a smooth and consistent coating that is resistant to stains and scratches. The coating also prevents corrosion. Since they are resistant to stains, enamel coatings provide easy cleaning for surfaces prone to graffiti. Porcelain enamels are used most often on toilet-room partitions.
Summary
It might be challenging to decide on the correct surface coating method. Required physical, chemical, and visual parameters must be studied correctly to make informed decisions.
