I. Introduction.
Steel formwork, also known as box board, template. Steel formwork in the construction industry a tool commonly used materials. Alternative to steel formwork for concrete construction wooden springboard not only easy to use, construction speed, quality, and cost-effective high.
Since direct contact of steel formwork and concrete, will produce the so-called electrochemical corrosion,glue stick reducing the template accuracy of project quality.
In the past, anti-corrosion steel template to use more spray or brush paint, many ills. For example, the template with the Ministry of negative gluten plate welding is not easy painting, the film looks bad, its adhesion, impact and other technical indicators are low, and workers in labor-intensive, slow construction, paint waste.
Wuhan Iron and Steel Plant 1979 trial electrophoretic coating of metal structures of steel template to be successful. 1980 built the first domestic steel formwork electrophoretic coating production lines. This production line has not only greatly improved product quality, and production has increased year by year, has now reached an annual output of 5000t, glue gun social and economic good.
Second, the basic principles of electrophoretic coating of steel formwork.
The so-called electrophoretic coating is to be coated (steel template) immersion in water-soluble coating as the anode (anode electrophoresis), a separate one with its corresponding cathode, DC pass between two poles, the current generated by the physical and chemical effects so that uniform coating was painted on the coating in a coating technology.
Electrophoresis electrophoresis paint coating must be used, electrophoresis paint is often known as water-soluble coating, electrophoresis paint with distilled water by a certain percentage must be diluted before use.
Electrophoretic coating generally consists of four simultaneous processes:
1, electrophoresis: the role of the electric field, positive and negative charged colloidal particles to the negative, positive direction, also known as swimming.
2, the electrolysis: the electrode redox reaction, respectively, but the formation of the electrode oxidation and reduction phenomena.
3, electrodeposition: the role of the electrophoresis, go to the anode of charged colloidal particles near the table in the template body emit electrons and the state was insoluble precipitate, precipitation phenomena, when the film formation.
4, the electro-osmotic: the electric field, the solid phase does not move, while the liquid mobile phenomenon. Electroosmosis moisture content within the film coating was gradually discharged, the final form of the current will not pass without hardly over, moisture content is very low, very high density film resistors.
5, iron oxide red epoxy electrocoating example: epoxy resin coating system of the electrophoresis, butanol, ethanolamine, talc, red iron composition, electrophoresis paint mixed with distilled water, the role of the electric field, ie separated into positively charged cations and negatively charged anion, and a series of complex physical and chemical colloid chemistry, the electrochemical process of change.
Third, the technological process.
1, the steel formwork electrophoretic coating process.
Oil, water will rust → → → washing → drying → electrophoresis on a knee flush → drying → packing → trademark → jet factory.
2, a description of the process.
, Rust: The Combo method, that is, degreasing, descaling step, the solution from the factory with.
Floods came, and washing: its purpose is to remove the template surface acid residues. Washing, the best use of regular water.
Electrophoresis painting: This is the purpose and core technology. Electrophoresis tank current, voltage, solid component content, PH value, temperature, speed, and electrophoresis electrophoresis tank proper use of additional equipment, is to determine the key to the success of electrophoretic paint.
Drying: steel formwork must be dried after the electrophoretic paint. Operating temperature drying box 160-180 ℃, baking time was 30min.
Major equipment required for electrophoretic coating. Various sink, electrophoresis tank, channel drying box, mechanical transmission system, electrical control systems, liquid paint and paint equipment, such as conductivity meter, such as adhesion tester.
3, quality inspection and control.
(1) paint concentration.
Electrophoretic paint mixed with distilled water, its concentration should be 10% -15% too high concentration of poor film leveling, easy to orange peel and other defects. Concentration is too low, the film thinning, prone to pin holes.
(2) voltage.
Electrophoresis voltage of 60V should generally be controlled at around. Voltage increases, deposits increased, the film becomes rough, the formation of orange peel, the voltage is too low, the film is very book, or even swimming is not painted.
(3) PH value.
PH value of the general 8-9 liquid paint can be satisfied when the film. PH value is too low, the electrophoresis tank with pulse current density is reduced, resulting in no local paint template to form a painted face, PH value is too high will cause the wet film then dissolves to book the film changes, affecting coating quality. Adjust the PH value of the bath has a variety of methods, we chose to cover the cathode method. Cathode cathode cover is mounted on a canvas bag, the bags supported by wire frame, the bag filled with distilled water. Electrophoresis, the amine cation and the paint solution positively charged impurity ions (such as water in the Ca2 +, Mg2 +) can enter the cathode through the canvas hood, and the cathode discharge. Replace the hood of distilled water, impurities can be removed.
(4) electrophoresis time.
Electrophoresis coating thickness generally increases with increasing electrophoresis time, however, when the electrophoresis time reaches a certain point, the film thickness is no longer increasing, the reason is that when the film reaches a certain thickness of the insulation produced. Therefore, electrophoresis time by the Director to make the film thickness is not feasible, and because of increased power consumption in the economy does not pay. Electrophoresis time can generally 3min.
(5) conductivity.
Electrophoretic paint the working fluid conductivity, electrical conductivity is usually expressed. Low conductivity liquid paint, the film is not easy to form; conductivity is too high, resulting in the appearance of rough film. For the same coating, the conductivity of the liquid paint paint the most influential factor is the presence of impurity ions in solution. Therefore, by controlling the impurity content must be to maintain normal electrical conductivity. Electrophoretic Coating of steel formwork part of the performance in Table 1.
Fourth, the conclusion.
Electrophoretic coating and the use of water-based paint, marking paint industry, a major step forward.
Electrophoretic coating speed of construction, to achieve continuous operation of mechanization and automation, reducing labor intensity, the film uniformity, strong adhesion and easy coating on the general approach to painting or coating the bad parts, as mentioned earlier in the welding rib joints, etc. can be smooth, and smooth film. Paint up to 90% -95% utilization, as electrophoretic coating is water as a solvent, with non-flammable, non-toxic, easy operation. After electrophoresis, the film after drying, with excellent adhesion, corrosion resistance, its corrosion resistance, weather resistance and other properties are better than ordinary paint and general construction methods. Wuhan Iron and Steel metal structure factory production license electrophoresis template, selling more than twenty provinces, municipalities, autonomous regions and municipalities. 1991-1993 only 10 months, the steel formwork electrophoresis to a value of 2.77 million yuan, profits and taxes 24 million.