Rust removal on metal surfaces
Rust removal of metal surfaces is an essential step in metal protection and processing. Its core task is to remove rust products from the metal surface, restoring the metal’s original properties and paving the way for subsequent processing. Metals are highly susceptible to oxidation in humid, oxygen-rich environments, forming rust (primarily composed of iron oxide). This rust not only affects the appearance of metal products but also gradually erodes the metal matrix, reducing structural strength and shortening its service life. For example, severe rust on large metal structures such as bridges and pipelines can cause safety accidents. Rust on the metal components of precision instruments can also affect their accuracy and proper operation. Therefore, timely and effective rust removal is crucial to ensuring the safety, reliability, and durability of metal products.
There are many different methods for removing rust from metal surfaces, and the appropriate method can be selected based on the degree of rust, the metal material, and subsequent process requirements. Mechanical rust removal is a widely used traditional method, including sandblasting, shot blasting, and grinding. Sandblasting uses high-speed abrasives (such as quartz sand and steel shot) to impact the metal surface, removing rust. It is suitable for large-area rust removal and can simultaneously increase surface roughness to enhance coating adhesion. Shot blasting uses a high-speed rotating impeller to project projectiles onto the workpiece surface, achieving high rust removal efficiency and commonly used for batch processing of small and medium-sized workpieces. Grinding rust removal uses tools such as sandpaper and grinding wheels for manual or mechanical grinding, and is suitable for treating localized rust or precision parts. Mechanical rust removal is simple to operate and relatively low in cost, but it may cause some mechanical damage to the metal surface, so the intensity of the treatment must be controlled.
Chemical rust removal is a method of using chemical solutions such as acid and alkali to react with rust, converting it into soluble substances and removing it. Commonly used acid rust removers include hydrochloric acid, sulfuric acid, phosphoric acid, etc. Among them, hydrochloric acid has a fast rust removal speed and is suitable for a variety of metals, but it is highly volatile and requires protection; sulfuric acid has a significant rust removal effect at high temperatures and is often used for steel products, but it is highly corrosive to amphoteric metals such as aluminum and zinc; phosphoric acid will form a protective film on the metal surface after rust removal and is suitable for occasions with higher requirements, such as automotive parts, medical equipment, etc. Chemical rust removal can handle workpieces with complex shapes and remove rust more thoroughly, but the solution concentration, temperature and treatment time must be strictly controlled to avoid excessive corrosion of the metal matrix. At the same time, the waste liquid must be properly handled to prevent environmental pollution.
Electrochemical rust removal, based on chemical rust removal, accelerates the rust removal process by applying an electric field. It is divided into anodic and cathodic rust removal. In anodic rust removal, the workpiece acts as the anode, and an oxidation reaction occurs on the surface under the action of an electric current, dissolving and stripping away the rust. In cathodic rust removal, the workpiece acts as the cathode, generating hydrogen on the surface. The mechanical stripping effect of hydrogen removes the rust, while also reducing corrosion of the metal substrate. Electrochemical rust removal is highly efficient and effective, making it particularly suitable for precision parts and complex structural components. However, it requires specialized power supply equipment and electrolytic cells, which are relatively expensive. Furthermore, during operation, it is important to carefully control parameters such as current density and electrolysis time.
The quality of metal surface rust removal directly affects the effectiveness of subsequent processes, so strict quality inspections are necessary. Common inspection methods include appearance inspection, rust residue detection, and surface roughness measurement. Appearance inspection mainly observes whether there is residual rust, spots, etc. on the surface; rust residue detection can use chemical analysis or instrumental analysis to determine the content of surface rust products; surface roughness measurement ensures that the surface state after rust removal meets the requirements of subsequent coating, electroplating and other processes. In addition, the metal surface after rust removal is prone to rust again and requires timely anti-rust treatment, such as coating with anti-rust oil and phosphating treatment. With the deepening of environmental protection concepts, new environmentally friendly rust removal technologies such as laser rust removal and ultrasonic rust removal are gradually emerging. These technologies have the advantages of being pollution-free, highly efficient, and causing little damage to the metal substrate, and represent the future development direction of metal surface rust removal technology.
