How does pickling and phosphating of steel plates improve the performance and durability of the shell of a 1100℃ box-type resistance furnace?

During the operation of a box-type resistance furnace, the shell needs to withstand the test of various complex environmental factors. When running at high temperature, the heat in the furnace will be conducted outward, so that the shell is in a relatively high temperature environment; at the same time, there are often corrosive gases and humid air in the industrial production environment. Ordinary untreated steel plates are very easy to rust in such an environment, which in turn affects the structural strength and sealing of the furnace body and shortens the service life of the equipment. Therefore, effective surface treatment of steel plates has become a necessary measure to ensure the long-term and stable operation of box-type resistance furnaces.
Pickling treatment is the first step in the surface treatment of steel plates. During the processing and storage of steel plates, a layer of oxide scale will form on the surface, and its main components include iron oxides, such as ferric oxide and ferric oxide. These oxide scales will not only affect the adhesion between the coating and the steel plate, but also reduce the mechanical properties of the steel plate to a certain extent. During the pickling process, the steel plate is immersed in an acidic solution. Commonly used acids include hydrochloric acid and sulfuric acid. Hydrochloric acid reacts chemically with the oxide scale on the surface of the steel plate. For example, the reaction of ferric oxide with hydrochloric acid generates water-soluble ferric chloride and water. Ferric oxide reacts with hydrochloric acid to generate ferrous chloride, ferric chloride and water. Sulfuric acid can also react similarly with the oxide scale to dissolve and remove it. Through pickling, the oxide scale on the surface of the steel plate is completely removed, exposing a clean metal matrix, laying the foundation for subsequent treatment.
After the pickling is completed to remove the oxide scale, there are still microscopic impurities and defects on the surface of the steel plate. At the same time, the exposed metal surface is highly active and easily oxidized again in the air. At this time, phosphating treatment plays an important role. Phosphating treatment is to form a phosphate conversion film on the surface of the steel plate through a chemical reaction in a solution containing phosphate. The phosphating solution usually contains dihydrogen phosphate, accelerators and other ingredients. Under appropriate temperature and acidity conditions, dihydrogen phosphate reacts with iron on the surface of the steel plate. Iron reacts with dihydrogen phosphate to form ferrous phosphate precipitation, while releasing hydrogen. During the reaction, phosphate ions in the solution further react with metal ions to form a variety of phosphate crystals, such as zinc phosphate and iron phosphate. These crystals are intertwined to form a dense porous phosphate conversion film on the surface of the steel plate.
This phosphate conversion film is of great significance in many aspects to the performance improvement of the box-type resistance furnace shell. From the perspective of improving the adhesion of the coating, the porous structure of the phosphate conversion film provides a good mechanical anchor point for the coating. When subsequent surface spraying (such as electrostatic spraying) is performed, the coating particles can fill these pores to form an "anchoring" effect, which significantly enhances the bonding force between the coating and the steel plate. Compared with the steel plate that has not been phosphated, the coating that has been sprayed after phosphating has better adhesion test results (such as the cross-grid test), and the coating is not prone to peeling and peeling, thereby ensuring the integrity of the box-type resistance furnace shell coating, so that it can resist the erosion of the external environment for a long time.
In terms of enhancing corrosion resistance, the phosphate conversion film itself has a certain chemical stability and can isolate the steel plate from contact with external corrosive media. Although the phosphate conversion film is a porous structure, the substances filled in the pores and the chemical properties of the film itself can effectively prevent moisture, oxygen and corrosive gases from penetrating into the surface of the steel plate. When external moisture and oxygen try to contact the steel plate, they will be hindered by the phosphate conversion film, slowing down the electrochemical corrosion of the steel plate. Even if the coating is partially damaged during use, the phosphate conversion film can inhibit the corrosion expansion of the damaged area to a certain extent, avoid the rapid expansion of the corrosion area, and thus extend the corrosion resistance life of the box-type resistance furnace shell.
From the perspective of mechanical properties, the pickling and phosphating process will not have a negative impact on the mechanical properties of the steel plate matrix, but can optimize its surface properties to a certain extent. After removing the oxide scale, the surface of the steel plate is smoother and smoother, and the microscopic defects are reduced. In the subsequent processing (such as bending and welding), stress concentration can be reduced and the processing quality can be improved. The presence of phosphate conversion film, although the film layer is relatively thin, can form a uniform protective layer on the surface of the steel plate, which can reduce the scratches and wear on the surface of the steel plate during transportation and installation to a certain extent, and maintain the integrity and beauty of the shell surface.
In addition, the pickling and phosphating process has good process stability and repeatability. In industrial production, by accurately controlling the solution concentration, temperature, treatment time and other parameters during the pickling and phosphating process, it can be ensured that each steel plate used to make the shell of the box-type resistance furnace obtains a surface treatment effect of consistent quality. This stability enables the box-type resistance furnace shell to ensure a high yield rate during the production process, reducing material waste and increased production costs caused by unqualified surface treatment. At the same time, standardized processing technology also facilitates production management and quality control, providing reliable guarantees for large-scale production.
In actual applications, the box-type resistance furnace shell made of steel plates treated with pickling and phosphating has shown good performance in different usage scenarios. During long-term operation in a high-temperature environment, the shell coating will not fall off easily due to factors such as thermal expansion and contraction, and will always maintain its protective effect on the shell; in a humid industrial environment, it can effectively resist water vapor erosion and prevent the steel plate from rusting; in an environment containing corrosive gases such as acids and alkalis, the phosphate conversion film and the coating work together to provide reliable protection for the shell.