- №1. General principles of cold galvanizing
- №2. Nature of cold galvanizing
- No. 3. Advantages and disadvantages of cold galvanizing
- №4. How is cold galvanizing done?
- №5. Where can I use cold galvanizing?
- №6. Compositions for cold galvanizing
Metal products for all their strength have one significant drawback - they easily rust. In the production environment, steel products are protected against corrosion by hot dip galvanizing. This is quite a complex and expensive process, besides, it is not designed to protect large-sized structures. In everyday life, to protect against the rust of the roof, fence, visor, car and other structures is best use the cold galvanizing of metal, which is carried out with the help of special zinc-containing compositions. The process of coating is maximally simple, and the method of cold galvanizing for a number of reasons can be called universal. Understand the technology, compositions and find out how zinc "armor" works.
№1. General principles of cold galvanizing
Hot-dip galvanizing protects the metal from corrosion for the next 40-50 years, and no additional measures are required. Technologically difficult and costly process at home replaced cold zincing, which allows Get a quality protective coating with minimal effort, but it will have to periodically update.
The process of cold galvanizing resembles simple stainingmetal structures, only instead of conventional paints use zinc-filled paints (CNC). They contain not less than 94% zinc, the rest - binders. TsNK should not be confused with zinc-containing paints: in them the share of zinc is lower, and the density of the composition is always less, kg / l.
Due to the simplicity of the work, the metal is cold-galvanized not only in industrial conditions, but also in the home to protect structures of any size and geometry.
№2. Nature of cold galvanizing
To better understand the features and advantages of the method, it is necessary to recall the school chemistry course.The process of protection of iron-containing alloys with zincis possible due to the unique physico-chemical properties of this element. Zinc very easily enters into chemical reactions with different types of substances, and when interacting with water it forms practically insoluble hydroxide, which covers the metal surface and prevents further interaction zinc and water. Similarly, by the way, aluminum behaves.
If the zinc layer is covered with a steel structure, then zinc in air will eventually oxidize. The reaction product is zinc oxide, which does not react with water and forms a strong film on the surface of the structure. Everything, on this further passage of the reaction is impossible, since zinc oxide and zinc hydrogen carbonate (formed in a smaller amount) are inert with respect to water. itbarrier protection. It is worth noting that iron also reacts with water to form oxides, which we call rust, but these compounds do not form a continuous dense film, passing moisture into the interior of the metal and provoking the development corrosion.
In addition to barrier protection, zinc also provides an electrochemical. We recall the electrochemical series of metal stresses, in which zinc precedes iron. This means that zinc is chemically more active and in the zinc / iron pair will react first. In the presence of atmospheric moisture, an electrochemical reaction may occur to form zinc carbonate. This compound is also insoluble in water and stops further development of the corrosion process.
The principle of "working" of the zinc coating remains the same, in spite ofmethod of its application:
- hot-dip galvanizing;
- electrolytic galvanizing;
- diffuse galvanizing;
- gas-dynamic zinc-plating;
- cold galvanizing.
Immediately after the protection of metal structures by the method of cold galvanizing, mainly electrochemical protection: while the coating has not yet reached maximum strength, moisture particles can penetrate through it and reach become. At this point, an electrochemical pair of zinc / iron is formed. In the future, the protection is built according to the barrier type, but if the integrity of the paint is broken and the moisture penetrates the structure, then the electrochemical protection is activated again.
No. 3. Advantages and disadvantages of cold galvanizing
Cold galvanizing of metal is simple, reliable and one of the most popular ways to protect it. In everyday life, technology has become widespread, as it hasa lot of advantages:
- the compositions used are characterized by good adhesion both to the base and to the decorative paint materials, so the structure can be easily painted in the required color;
- coating can be applied to a product of any size and any geometry, and if it is already installed and operated, it should not be dismantled - all work can be done on site;
- The surface preparation before cold galvanizing is relatively simple;
- metal parts protected by this method are easily welded together;
- simplicity of coating, no special skills and tools are needed. For painting use spray guns, paint rollers and ordinary brushes;
- You can do the work practically in any weather (the permissible temperature is -20... + 400С);
- low financial and time costs.
The main disadvantage of cold galvanizing- low resistance of the coating to mechanical damage. Simply put, paint can simply be scratched, exposing the steel structure. On the other hand, updating the coverage is not so difficult and expensive, so the minus can not be called very significant.
№4. How is cold galvanizing done?
The method of cold galvanizing is the application of formulations with a zinc content on the metal surface. The technology and application procedure depends on the type of composition, but most often materials are used whose characteristics are prescribed inGOST 9.305-84. The same document permits the use of compounds for cold-galvanizing on any structures, except for steel with increased strength and magnesium alloys.
The process of applying the composition (about the most popular we'll talk further) is preceded by carefulmetal surface preparation:
- removal of any kind of contamination, salts, cracks;
- abrasive surface treatment (abrasive blasting or hydrodynamic method) to give the necessary roughness (provides better adhesion) and remove old rust;
- drying of the structure;
- manual cleaning from splashes, burrs and sharp corners;
- dedusting by air.
If there are grease spots on the metal, the surface must be degreased. The standards require a thorough check of the level of dedusting, degreasing and roughness, for which special tools are needed. If it is a question of protecting a responsible design, it is better not to neglect it.
This completes the preparation and beginsdirectly cold galvanizing. Produced at a surface temperature above the dew point by three degrees or more, and the air temperature recommended by the manufacturer. To apply paint advise with the help ofspecial equipment(pneumatic, paint chambers, etc.) in several layers, each new layer is applied after the previous one has dried. To handle some places, you can use a brush and a roller. The coating is allowed to dry, then leveled. On it in the subsequent it is possible to put usual paint. It is advisable to check the quality of the coating after application of the CEC and its drying, using special devices that measure the thickness of the protective film.
To determine the dew point, you should use a hygrometer, thermometer, psychrometer or devices that allow measuring both temperature and humidity. The readings of the instruments are compared with the table and it is determined whether it is possible to carry out the procedure of cold galvanizing of the metal.
№5. Where can I use cold galvanizing?
Galvanized cold is suitable for any steel, except for high-strength and alloy with an increased content of magnesium. Requirements for size, weight, shape, thickness of products do not exist. The method is suitable for already manufactured and installed products (including large metal structures). You do not need to remove them.
Galvanizing can be used both in production and in the maintenance and repair of infrastructure elements (for example, pipelines, tanks and towers), and in ordinary life for structures such as:
- fences and gates, gates;
- garages made of metal;
- bottom and other body parts of cars;
- various tanks and reservoirs;
- trolleys, agricultural and construction tools.
№6. Compositions for cold galvanizing
According to the standards, the CEC should contain at least 94% of zinc with a particle size of 12-15 μm or 88% of zinc with particles of 3-5 μm. The higher the zinc content, the better the anticorrosive properties, and the smaller the particles, the better the adhesion. There are manycold galvanizing compounds, but we will focus on the most popular:
- "Galvanol"- composition based on pure electrolytic zinc and with a small content of binding components, domestic development. The composition provides excellent adhesion and can be applied even to rusted structures, if the rust on them is well held. It is applied quickly and easily, can be used at temperatures from -30 to + 500C, as well as with high humidity. The composition is resistant to salt solutions and alcohol, and the finished coating is resistant to abrasion and impact, has good adhesion to paints. Available ready for use, can be applied by brush, roller, spray, aerosol can. The scope of application is the widest;
- CinotanIt is used as an independent agent against corrosion and in combination with other compounds. Can be used in any climatic conditions, often used in industry to protect structures located in salt water or polluted atmosphere. The structure is covered with fences, tanks for oil products, power transmission lines, pipes, automobile structures, etc. It is used by the giants of domestic industry;
- "Cinconol"- polyurethane primer with a high content of zinc, very elastic, resistant to high temperatures, salt water, oils, oils and alkalis;
- "Cinol"- a composition comprising zinc particles of different fractions with a size of 4 to 20 μm or more, is applied in a thickness of 100-120 μm, dries in 1 hour, has a high resistance to water;
- CECcontains zinc powder and ethyl silicate, is well suited for high-alloy and ordinary steels;
- Master AK-100Excellent for car bodywork;
- UR-100 Liquid Zincproduce on the basis of zinc powder with a particle size of 3-5 microns, is inexpensive;
- Zinga- composition for cold galvanizing of metal from the Belgian company Zinga Metall. The manufacturer uses zinc powder 3-5 microns and claims unique properties of its product, which explains the high cost, almost equivalent to hot galvanizing.
It is important that the treated product is not subjected to a permanent mechanical attack - in this case, the coating will not last very long.
Cold galvanizing is suitable for all products that need to be protected from corrosion. Despite the fact that such a coating can be damaged, like ordinary paint, it works efficiently and excludes the appearance of rust stains, and even simplifies the staining: the paint on the zinc layer is kept better than on the ordinary metal.
More details on the method of cold galvanizing you will find out on http://spektrlkm.ru/jidkiy_cink