Polishing method of stainless steel pipe

Posted by zora li on October 27th, 2022

seamless steel pipes are widely used because of their high corrosion resistance and decorative properties, especially in the popularization and promotion of medical equipment, food industry utensils, tableware, kitchen utensils, etc. Stainless steel utensils should be resistant to corrosion, have a smooth appearance, and the surface of the utensils should not be attached to toxic substances to the human body. Therefore, the surface treatment requirement for the production of such equipment is to completely remove the harmful substances on the surface.

Oxidation Causes
After the stainless steel pipe is hot processed, machined or placed for a certain period of time, a layer of black or gray oxide will be formed on the surface, the main components are Cr2O3, NiO and extremely insoluble FeO, Cr2O3. There are many reports on the removal of stainless steel pipes and the finishing of lighting fixtures. As a mature surface treatment method, stainless steel pipe polishing has been widely used, and polishing can further improve the corrosion resistance and brightening effect of stainless steel.

chemical polishing
Chemical polishing is a common surface treatment process for stainless steel. Compared with the electrochemical polishing process, the biggest advantage is that no DC power supply and special fixtures are required, and complex parts can be polished with high productivity. In terms of functionality, chemical polishing, in addition to the physical and chemical cleanliness of the surface, also removes the mechanical damage layer and stress layer on the stainless steel surface to obtain the mechanical cleanliness of the surface, which is conducive to preventing local corrosion of the mechanical strength of the parts and prolonging the service life of the parts . There have been patents on chemical polishing of stainless steel since the early 1940s, and so far, many formulations have been disclosed, but people are still very difficult in practice. Due to the wide variety of stainless steel and the different corrosion laws of different grades of stainless steel, the same solution cannot be used, so there are many types of seamless carbon steel pipe chemical polishing solutions.

The basic components of chemical polishing liquid include etchant, oxidant and water. The etchant is the main ingredient, and if the stainless steel is dissolved in the solution, it cannot be polished. Oxidants and additives can inhibit this process and make the reaction proceed in a direction favorable for polishing. Water adjusts the concentration of the solution to facilitate diffusion of the reaction products. Whether the chemical polishing of stainless steel can be carried out smoothly depends on the reasonable combination of the above components.

Electrolytic polishing
Electrolytic polishing of stainless steel is to hang stainless steel products on the anode and conduct anode electrolysis in electrolytic polishing solution. Electropolishing is a special anode process. During the whole process of anodic electropolishing, two conflicting processes are simultaneously carried out on the surface of stainless steel products, namely the continuous formation and dissolution of oxide film on the metal surface. However, the chemical film on the surface of stainless steel products is different from the passivation state of the concave surface, and due to the dissolution of the anode, the concentration of metal salts in the anode area continues to increase, forming a high resistivity and thick mucosal layer on the surface of stainless steel products. The thickness of the mucous membrane on the surface of the product is different, and the current distribution on the anode microsurface is uneven. Under the current density, the micro-convex dissolves faster, so that the burrs or micro-convex on the product surface first dissolve and level at the beginning; the concave dent has a small current density, and the dissolution is also slow. Due to the different current density distributions, the product surface continued to film and dissolve at different rates. There are two reverse processes on the anode surface at the same time, film formation and dissolution. The passive film is continuously formed and dissolved, so that the surface of the stainless steel product is smooth, and the appearance of high smooth and glossy is achieved, which can satisfy the polishing of the surface stainless steel product.

Read more ：Passivation treatment of seamless steel pipe