Man conquered nature when he learned to process metals. Iron alloy products with various components have transformed the world beyond recognition. The main disadvantage of metal products has always been the property of oxidation, especially in the presence of water. Rust greatly reduces the life of any metal. For millennia, metal processing technologies have evolved. Improved rust protection techniques.
In the 21st century, the widespread use of metal has greatly supplanted polymer and composite materials. But even in this case, the problem of rust is not a thing of the past.
What is rust?
Iron, used as the main component of many metal alloys, has high chemical activity in combination with the presence of carbon and salts dissolved in water. The resulting iron oxides coat the metal with a thin layer. Subsequently, they react with oxygen and water, the metal is completely destroyed, and rust is formed.
In addition, rust refers to hydroxides formed under the influence of carbon dioxide or sulfur dioxide. The latter components are almost always present in water. Unlike oxides, they do not densely coat the main body of the metal, but form a thin film that exfoliates from the bulk. This opens the way for external exposure to aggressive environments.
While iron is present surrounded by oxygen, water, carbon dioxide and sulfur dioxide, the process cannot be stopped.
Why paint is needed
A significant role in the protection against corrosion is played by paints for metal. The chemical composition is selected so that they form a stable film on the surface. Due to adhesion, the substance penetrates the structure of the material and practically becomes one with it. The outer layer forms a thin film that is not exposed to an aggressive environment. Thus, the paint plays not so much the role of a decorative coating, but serves as a protective mechanism against metal corrosion.
From the foregoing, it is seen that adhesion and resistance to external influences are important indicators of the quality of paint on metal. Among which stand out:
- Fire safety.
- Chemical resistance.
- Non-UV exposure.
- The number of freeze-thaw cycles without losing their properties.
- Shock resistance, including vibration resistance.
Depending on the chemical composition, all paints can be divided into several groups.
Epoxy enamel
To create heat-resistant paints for metal, epoxy resins are often used as a base. The ability of the resin to create a durable film on the surface is very much appreciated. Such a base is practically not subject to chemical influences and has high fire safety indicators. Due to various additives, a certain viscosity is achieved, which makes the painted surface resistant to vibration. It is not by chance that such compositions are widely used in the automotive industry.
As a base material, you can consider the “Epostat” primer-enamel. The main advantage of this enamel is its high drying speed and resistance to temperature extremes. It is almost not exposed to oil-containing products, salt and fresh water.
The main disadvantages of paints for metal based on epoxy resins are their high cost and complexity in use.
Oil paints
Relatively cheap option for protection against rust are paints for metal based on drying oil. The main advantage of this coating is a high degree of protection of the metal from environmental influences. Water cannot penetrate through such a layer. In addition, manufacturers produce a wide range of colors for such coatings. This property makes them popular as paints for metal for outdoor applications.
As an example, we can cite the high-quality Lakra trademark with a product line that meets all the requirements of painting work.
The property of the material to form an impermeable film plays a bad joke with it. Simultaneously with protection against aggressive media, gas exchange is blocked by the mass of the structure. This leads to peeling and bloating, which reduces the life of the coating and requires regular paint repairs.
Alkyd coatings
Alkyd based coatings are widely used. Usually white alcohol is the solvent. The high volatility of this substance speeds up the drying process of the surface. A mixture of solvent, alkyd, pigments with various additives and neutral gas made it possible to create a new paint tool - paint on metal in cans.
A wide variety of color shades and ease of use of such aerosols made them attractive for many works. It turns out a uniform coating of the surface and deep filling of all its pores.
Surfaces coated in this way do not lose their qualities for a very long time. The price remains affordable for the ordinary consumer. One of the leaders in this market is the Hamerayt brand.
Acrylic Powders
The development of petrochemicals has allowed the development and production of materials with previously unknown properties. This is how polymer-based paints were born. Due to the fact that the solvent is ordinary water, such materials are very widely used. The staining process was greatly simplified, and the quality of work increased.
Polymer powders made it possible to create new surface treatment technologies. Under the influence of high temperature, powder paint on metal lays, forming a perfectly smooth surface, very reminiscent of enamel. The polymerization process allows you to create highly decorative surfaces with very good protection of the bulk of the metal. The consumption of the coloring composition remains minimal per unit surface. The main disadvantage of such technologies is the availability of specialized equipment.
Hammer surfaces
Hammer paints for metal are classified not by the chemical composition of the substance, but by the presence of special additives. The composition itself can have any filler - epoxy, acrylic or alkyd. More importantly, what additives are used to give the hammer effect. Most often used are small fractions of glass and aluminum powder. The surface covered with such a composition has very interesting decorative qualities, reminiscent of hand stamping with a hammer. Defects of the painted surface are lost.
An example is the Dali trademark. Such enamels fit well on a rusty surface and ensure the safety of the metal up to 8 years. Often based on them create flame retardants. An interesting side effect: surfaces acquire a dirt-repellent property.
Enamel primer
As already noted, one of the main characteristics of high-quality surface treatment is adhesion. When it comes to treating a new surface, almost all paints have good setting properties. Another thing is the painting of old metal or objects operating in difficult conditions.
In these conditions, it is customary to use primers for surface pretreatment. Such enamels have high adhesion. The finish coating already lays well on the pre-prepared area with better quality characteristics for resistance to external influences.
The main qualities of primers are:
- The formation of a film that prevents the penetration of water and air.
- Slowing down the corrosion process, which is achieved by additives that slow down chemical processes.
- Phosphoric acid, which is part of enamels, reacts with metal and rust. Iron phosphate is formed, which prevents the further corrosion process from developing.
- High adhesion allows the composition to penetrate even into the galvanized layer.
- Due to the inclusion of metallic microparticles on the surface, a tread is formed.
- It is useful to use such primers in high humidity.
A brief review does not allow a comparative analysis of various types of metal surface treatment. The main purpose of this article is to give a concept of the variety of protective paints for metal.