Chemical Conversion Coating

by Advanced Surface Technologies on Apr 4, 2023 Finance 137 Views
A chemical conversion coating is a process where a metal surface is treated with a solution of chemicals to produce a coating that offers corrosion resistance and improves paint adhesion.
 
Conversion coatings are a broad category that includes passivation, steel phosphating, and chromate coating. Typically, these conversion treatments are applied before electroless plating and painting, and they often increase the lifespan of a metal component.
 
The Basics
 
Chemical conversion coating is a process that provides corrosion protection and prepares a metal surface for better adhesion of primers and paints. Unlike passive coatings like paint or powder coat, which do not require any kind of mechanical or electrical action to protect your metal part, conversion coatings use special chemical reactions and/or acidic baths to help form a stable, anti-rust oxide layer on the underlying metal.
A common chemistry used for this coating is zinc phosphate (FOSTEX ZN), but there are also new, phosphate-free or low-phosphate technologies available today that have been gaining popularity among metal manufacturers.
Conversion coatings can have many different properties, including lubricity, hardness, color and increased corrosion resistance. Each conversion coating has its own unique benefits and can be applied to a wide range of metals.
 
Applications
 
A chemical conversion coating can be applied to any metal part in order to achieve desired surface changes. This process can include changing the color or hardness of the material.
 
Conversion coatings are often applied to produce a more durable finish or enhance the electrical conductivity of the material. They can also be used to provide corrosion protection.
 
Chromate Conversion Coating Mechanism are applied to a variety of metals and alloys including steel, aluminum, zinc, copper, cadmium, magnesium, tin, titanium and bronze. They can be used as a corrosion inhibitor, primer to promote the adhesion of paints and adhesives or as a decorative finish.
 
Chromate conversion coatings are a traditional and common post-treatment for many industries, although chromate is no longer a commonly used substance due to its carcinogenic properties. A new nontoxic, RoHS compliant and Nadcap-certified replacement process uses zirconium containing chemicals rather than hexavalent chromium. This reduces the total number of chemical stages and minimizes the environmental impact of the process.
 
Preparation
 
Chemical conversion coatings are a base for paint finishes and are used as a corrosion preventive film. They increase the surface area of the substrate material and change the chemistry of the surface, which increases the resistance to corrosion.
 
Conversion coatings are usually applied by spray or immersion. Before the chemical conversion coating process begins, the surface is degreased to remove all dirt, oil, grease and manufacturing residue.
 
Depending on the specific aluminum alloy, the surface may be treated in an acid or alkaline etch to remove alloying elements which might interfere with the conversion coating reaction. This is followed by thorough water rinsing and drying of the part.
 
The metal is then immersed in an aqueous coating solution to provide an in-situ protein conversion coating on the metal and cured for 5 days at room temperature and then painted or electroless plated. This aqueous conversion protective coating will afford oxidation resistance to the conversion coated metal for at least 200 hours when subjected to a salt fog at 95deg F.
 
Troubleshooting
 
A properly applied chemical conversion coating can add years to the life of a metal part while increasing its functionality. However, it can also cause problems if improperly installed. This is especially true for thin coatings, which can be easily damaged by bending, tinkering or heat treatment. Fortunately, many manufacturers offer professional installation of chemical conversion coatings to ensure the best possible result.
 
Before the conversion coating can be applied, the surface is cleansed with a non-etch, slightly alkaline cleaner that is followed by a thorough water rinse. Depending on the base material, a light oxidation treatment is also necessary to make the coating work. The best results can only be achieved if the coating is the right thickness and the appropriate chemical is used. The most important step is to select the appropriate product and follow the manufacturer’s instructions. The resulting coating is both aesthetically pleasing and functional. The most successful applications often incorporate multiple conversion coatings in various combinations to meet the needs of the application.

Article source: https://article-realm.com/article/Finance/41572-Chemical-Conversion-Coating.html

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