Ⅰ- Acid Pickling
1.- Definition of Acid-Pickling: Acids are used to remove iron oxide scale chemically at a certain concentration, temperature, and speed, which is called pickling.
2.- Acid-Pickling classification: According to the type of acid, it is divided into sulfuric acid pickling, hydrochloric acid pickling, nitric acid pickling, and hydrofluoric acid pickling. Different media must be selected for pickling based on the material of the steel, such as pickling carbon steel with sulfuric acid and hydrochloric acid, or pickling stainless steel with a mixture of nitric acid and hydrofluoric acid.
According to the shape of steel, it is divided into wire pickling, forging pickling, steel plate pickling, strip pickling, etc.
According to the type of pickling equipment, it is divided into tank pickling, semi continuous pickling, fully continuous pickling, and tower pickling.
3.- The principle of acid pickling: Acid pickling is the process of removing iron oxide scales from metal surfaces using chemical methods, hence it is also called chemical acid pickling. Iron oxide scales (Fe203, Fe304, Fe0) formed on the surface of steel pipes are basic oxide that are insoluble in water. When they are immersed in acid solution or sprayed with acid solution on the surface, these basic oxide can undergo a series of chemical changes with acid.
Due to the loose, porous, and cracked nature of the oxide scale on the surface of carbon structural steel or low alloy steel, coupled with the repeated bending of the oxide scale along with the strip steel during straightening, tension straightening, and transportation on the pickling line, these pore cracks further increase and expand. Therefore, the acid solution reacts with the oxide scale chemically and also reacts with the steel substrate iron through cracks and pores. That is to say, at the beginning of acid washing, three chemical reactions between iron oxide scale and metal iron and acid solution are carried out simultaneously Iron oxide scales undergo a chemical reaction with acid and are dissolved (dissolution) Metal iron reacts with acid to generate hydrogen gas, which mechanically peels off the oxide scale (mechanical peeling effect) The generated atomic hydrogen reduces iron oxides to ferrous oxides that are prone to acid reactions, and then reacts with acids to be removed (reduction).
Ⅱ-Passivation/Inactivation/Deactivation
1.- Passivation principle: The passivation mechanism can be explained by thin film theory, which suggests that passivation is due to the interaction between metals and oxidizing substances, generating a very thin, dense, well covered, and firmly adsorbed passivation film on the metal surface. This layer of film exists as an independent phase, usually a compound of oxidized metals. It plays a role in completely separating the metal from the corrosive medium, preventing the metal from coming into contact with the corrosive medium, thereby basically stopping the dissolution of the metal and forming a passive state to achieve anti-corrosion effect.
2.- Advantages of passivation:
1) Compared with traditional physical sealing methods, passivation treatment has the characteristic of absolutely not increasing the thickness of the workpiece and changing the color, improving the precision and added value of the product, making operation more convenient;
2) Due to the non reactive nature of the passivation process, the passivation agent can be repeatedly added and used, resulting in a longer lifespan and more economical cost.
3) Passivation promotes the formation of oxygen molecular structure passivation film on the metal surface, which is compact and stable in performance, and has self repairing effect in the air at the same time. Therefore, compared with the traditional method of coating antirust oil, the passivation film formed by passivation is more stable and corrosion resistant. Most of the charge effects in the oxide layer are directly or indirectly related to the process of thermal oxidation. In the temperature range of 800-1250 ℃, the thermal oxidation process using dry oxygen, wet oxygen, or water vapor has three continuous stages. Firstly, the oxygen in the environmental atmosphere enters the generated oxide layer, and then the oxygen diffuses internally through silicon dioxide. When it reaches the Si02-Si interface, it reacts with silicon to form new silicon dioxide. In this way, the continuous process of oxygen entry diffusion reaction occurs, causing the silicon near the interface to continuously convert into silica, and the oxide layer grows towards the interior of the silicon wafer at a certain rate.
Ⅲ- Phosphating
Phosphating treatment is a chemical reaction that forms a layer of film (phosphating film) on the surface. The phosphating treatment process is mainly used on metal surfaces, with the aim of providing a protective film to isolate the metal from air and prevent corrosion; It can also be used as a primer for some products before painting. With this layer of phosphating film, it can improve the adhesion and corrosion resistance of the paint layer, improve decorative properties, and make the metal surface look more beautiful. It can also play a lubricating role in some metal cold working processes.
After phosphating treatment, the workpiece will not oxidize or rust for a long time, so the application of phosphating treatment is very extensive and is also a commonly used metal surface treatment process. It is increasingly used in industries such as automobiles, ships, and mechanical manufacturing.
1.- Classification and application of phosphating
Usually, a surface treatment will present a different color, but phosphating treatment can be based on actual needs by using different phosphating agents to present different colors. This is why we often see phosphating treatment in gray, color, or black.
Iron phosphating: after phosphating, the surface will show rainbow color and blue, so it is also called color phosphorus. The phosphating solution mainly uses molybdate as raw material, which will form a rainbow color phosphating film on the surface of steel materials, and is also mainly used to paint the bottom layer, so as to achieve the corrosion resistance of the workpiece and improve the adhesion of the surface coating.
JINBAICHENG is a leading steel pipe factory in China, We can produce and supply seamless steel pipe, welded pipe, ssaw pipe, gi pipe with the surface of Acid-Pickling, Passivation, and Phosphating. We provide custom-tailor service and will give you the best solution for your projects. Contact us for best price: https://www.sdjbcmetal.com/steel-pipe-series/ email: jinbaichengmetal@gmail.com or WhatsApp at https://wa.me/18854809715
Post time: Jul-12-2023