How to Select Steel Shots for Rust Removal Based on Workpiece Characteristics (Part 1)

　　Among the many manufacturing processes, rust removal of steel structures is a critical step in ensuring product quality and service life. As an important rust removal consumable, the appropriate selection of steel shot is crucial. Different workpieces have varying materials and complex, variable surface conditions, requiring the appropriate steel shot to achieve optimal rust removal while avoiding damage to the workpiece.

　　I. Workpiece Material

　　• Carbon Steel Workpieces

　　Carbon steel is a widely used basic material in industry. It has varying carbon contents, ranging from low-carbon steel to high-carbon steel. For low-carbon steel workpieces, such as common lightweight steel components used in construction, the hardness is relatively low and the toughness is relatively good. In these cases, cast steel shot with a moderate hardness, typically between 40 and 50 Rockwell hardness (HRC), can be selected. This type of steel shot effectively breaks up rust on the workpiece surface. Its toughness makes it difficult to break, allowing for multiple reuse and reducing costs. The impact force removes rust without leaving deep indentations on the workpiece surface, ensuring dimensional accuracy.

　　High-carbon steel workpieces, such as some mechanical parts made of tool steel, are hard due to their high carbon content. Using ordinary hardness steel shot will not only result in ineffective rust removal, but the shot itself will also be easily worn and broken. High-hardness reinforced steel shot, with an HRC of 55-65, should be selected to provide sufficient impact force to penetrate the tough oxide layer and achieve deep rust removal. However, careful control of shot parameters is crucial to prevent microcracks and other damage to the high-carbon steel workpiece, which could affect its mechanical properties.

　　• Stainless Steel Workpieces

　　Stainless steel is known for its excellent corrosion resistance, but it can still rust under certain conditions. Stainless steel workpieces typically have a smooth surface and require a very high surface finish to maintain both aesthetic appeal and corrosion resistance. For these workpieces, stainless steel cut wire shot is ideal. This shot is similar in material to the stainless steel workpiece, offering good chemical compatibility and preventing the risk of galvanic corrosion between the dissimilar metals. Its particle size is generally fine, ranging from 0.2 to 0.8mm. It can precisely polish even tiny rust spots on workpiece surfaces, preserving the original surface finish to the greatest extent possible while removing rust. This method meets the stringent appearance and hygiene standards for stainless steel workpieces in food processing equipment, medical devices, and other applications.

　　• Non-ferrous Metal Alloy Workpieces

　　Non-ferrous metal alloys such as aluminum and copper are widely used in aerospace, electronics, and electrical applications. Aluminum alloy workpieces are lightweight and strong, but their surface oxide films have unique properties. When processing aluminum alloys, it is important to use aluminum or ceramic shot with a low hardness and soft material, approximately 20-30 HRC. This soft steel shot gently removes the loose oxide layer on the aluminum alloy surface, preventing scratches on the aluminum substrate and safeguarding its structural integrity and subsequent surface treatment. For example, when removing rust from aluminum alloy blades in aircraft engines, precise selection of soft steel shot is crucial to ensuring the blade's aerodynamic performance is not compromised.

　　Copper alloy workpieces are suitable for copper-based alloy shot or natural abrasives such as garnet sand (specially processed into pellets) due to copper's relatively soft texture and good conductivity. Garnet sand is chemically stable, does not react with copper, and has a uniform particle size. It can remove copper rust while maintaining the copper alloy workpiece's pristine color and unique texture. It is suitable for rust removal of copper components used in cultural relic restoration and high-end handicraft manufacturing.