How to Select Steel Shots for Rust Removal Based on Workpiece Characteristics (Part 2)

　　Workpiece Surface Condition

　　• Lightly Rusted Surface

　　When the workpiece surface has only a thin layer of loose rust, such as steel that has been stored for a short time and in a low-humidity environment, the focus is on accurate and non-destructive rust removal. In this case, choose steel shot with a smaller grit size, such as 0.4-0.6mm ordinary cast steel shot. Smaller grit sizes provide a relatively gentle impact force per unit area, allowing for precise "wiping" of loose rust without excessively cutting the workpiece surface, preserving the workpiece's original flatness. Combined with a lower shot velocity, this ensures effective rust removal while reducing dust generation and optimizing the workshop environment. This is commonly used for pre-treatment of precision mechanical parts indoors.

　　• Moderately Rusted Surface

　　Moderately rusted surfaces indicate a thick layer of rust, possibly with localized pits. For this type of workpiece, steel shot with a stronger impact force is required. Reinforced steel shot with a grit size of 0.8-1.2mm can be used, and the shot intensity can be appropriately increased. Reinforced steel shot has a higher hardness and can quickly break through thick rust layers. Its appropriately increased particle size allows for more even energy distribution during impact, effectively filling the gaps left by impact indentations. This results in a relatively smooth surface after rust removal, paving the way for subsequent painting and other processes. This is commonly used in the rust removal and renovation of large outdoor steel structures, such as billboards and bridge beams.

　　• Severely Rusted and Corroded Surfaces

　　For workpieces exposed to severe corrosion for extended periods, such as steel structures at seaside docks, the surface rust is thick, pits are deep, and even portions of the metal substrate may have been eroded. In these cases, a single particle size steel shot is insufficient, requiring a mixed particle size shot mix. For example, a combination of large-particle, high-hardness steel shot (1.0-1.5mm) and small- and medium-particle steel shot (0.6-0.8mm) is used in a specific ratio. The large-particle steel shot is used to break through thick rust layers and knock off large corrosion products, while the small- and medium-particle steel shot provides follow-up refinement, polishing the bottoms and edges of pits, gradually restoring the surface to a smooth finish. At the same time, chemical pretreatment can be combined with acidic solutions to moderately dissolve stubborn rust stains, followed by steel shot removal, effectively tackling the challenging problem of heavy rust.

　　In short, in the field of steel structure rust removal, scientifically selecting steel shot based on the workpiece material and surface condition is no easy task, requiring comprehensive consideration of multiple physical and chemical factors. Every precise selection effectively safeguards workpiece quality, production costs, and the smoothness of subsequent processes, helping the manufacturing industry continuously advance in precision technology.