[Haichuan Corrosion Prevention Knowledge] Surface treatment of steel components – Differences and applications of sandblasting, shot blasting, and bead blasting

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Surface treatment of steel components is a crucial process for ensuring their corrosion resistance, coating adhesion, and structural mechanical properties. Sandblasting, shot blasting, and bead blasting are the three most widely used mechanical impact-based surface treatment methods in the industrial sector. All three use high-speed particles to impact the workpiece surface in order to clean and strengthen it, but they differ in terms of power source, processing medium, process effectiveness, applicable scenarios, cost, and surface quality. Let’s start with sandblasting. Sandblasting is a surface cleaning and texturing process that uses compressed air or high-pressure air to propel angular abrasives such as river sand or metal ore sand at high speed against the surface of steel components. The principle involves using the edges of the abrasives to cut and impact the surface, thereby removing contaminants such as oxide scale, rust, oil, and old coatings from the component ； The surface has its natural metallic color, featuring a dull and rough texture without luster, with diffused light reflection and no shine. Shot blasting also uses compressed air or high-pressure air as a power source to shoot spherical particles such as steel balls, cast iron balls, glass balls, and ceramic balls; it is a combined process of surface cleaning and surface strengthening. High-speed impact on the spherical pellets causes slight plastic indentation on their surface, without any destructive damage ； The excess energy is converted into surface cold work hardening, resulting in residual compressive stress that enhances the component’s fatigue and stress-corrosion resistance. After treatment, the surface retains its natural metallic color, with a uniform matte finish; light is partially refracted, giving it a delicate texture. Shot blasting is an efficient batch cleaning process in which centrifugal force generated by a high-speed rotating flywheel is used to propel steel sand/steel pellets at high speed to impact the surface of the workpiece. Centrifugal projection delivers high energy and fast speed, enabling effective removal of thick oxide scales, rust, and molding sand ； It can simultaneously achieve mild surface strengthening, making it suitable for large-scale continuous production. Surface finish: natural metal color, uniform roughness, no obvious cutting marks, and good overall consistency. Below is a table outlining the core features and key differences among the three major rust removal processes. The surface treatment methods suitable for different types of steel components vary slightly among these three processes. 1. Sandblasting is suitable for steel components whose primary requirement is pre-treatment prior to painting, such as bridge girders, storage tanks, pipelines, ship segments, and building steel structures ； Or steel components with complex structures, numerous welds, and on-site operation and maintenance requirements. 2. Shot blasting is suitable for precision/ load-bearing steel components that require surface strengthening and fatigue resistance, such as gears, bearings, springs, aircraft landing gear, and key shafts in construction machinery ； Small, irregular-shaped, thin-walled steel components. 3. Shot blasting is suitable for steel components with simple shapes and produced in large quantities on a standardized basis, such as H-beams, steel plates, raw materials for steel structure factories that require continuous pre-treatment, steel pipes, profiles, and castings/forgings ； Steel components that require efficient removal of thick scale/mold sand. It should be noted here that the rust removal grades for these three types of processes are divided into 4 levels: SA1, SA2, SA2.5, and SA3. 1.Sa1: Light cleaning, only removing loose rust and oxidized scale; the lowest grade. 2.Sa2: Thorough cleaning, most dirt removed; a small number of uniform defects are allowed; suitable for general industrial use. 3.Sa2.5: Very thorough cleaning (near-white level), with only slight spot-like/striped discolorations remaining; mandatory standard for high-corrosion resistance applications (bridges, petrochemical industries, offshore engineering). 4.Sa3: Clean apparent grade, with no visible contaminants and a uniform metallic color; the highest grade. Generally, a standard project meets the SA2.5 standard; as for the cleanliness levels of the three methods, shot blasting is ≥ sandblasting > blast cleaning. In terms of cost, as well as treatment effectiveness, shot blasting is superior to blast cleaning and sandblasting; however, shot blasting also provides the best treatment results and features a high degree of automation ； For components produced in bulk, the cost of shot blasting is actually the lowest, due to high efficiency.