Blasting differences: Al‑alloy, carbon steel, castings

Sandblasting is a surface‑treatment process that propels abrasives onto workpiece surfaces at high speed via compressed air or centrifugal force to achieve cleaning, roughening and texturing through impact and cutting. Due to distinct material properties and surface defects, aluminum‑alloy, carbon‑steel and casting workpieces require different sandblasting parameters in abrasive selection, operating pressure, processing objectives and finished surface performance.

Aluminum Alloy

Aluminum alloy has low Brinell hardness (30‑120 HB) and forms compact yet weakly‑bonded surface oxide films. Sandblasting aims to prevent abrasive embedment and surface damage. Medium‑hard, easily‑removable abrasives such as glass beads, fine alumina powder or plastic grit are adopted; hard steel grit is forbidden as embedded particles impair subsequent anodizing and coating quality. Operating pressure is kept at 0.2‑0.4 MPa, since excessive pressure causes workpiece deformation or over‑rough surfaces. The finished surface presents uniform fine matte texture with oxide films removed. Surface roughness Ra ranges 0.8‑3.2 μm. Serving as key pre‑treatment for auto‑parts and aerospace components, it greatly improves coating adhesion for anodizing and electrophoretic painting.

Carbon Steel

Carbon steel features higher hardness (120‑200 HB) and heavy, tightly‑adhered scale and rust. Sandblasting focuses on efficient rust and scale removal. Hard angular abrasives including quartz sand and steel grit cut off corrosion layers under 0.4‑0.6 MPa working pressure. The resulting uniform rough metallic surface reaches Ra 3.2‑12.5 μm for enhanced anti‑corrosion coating adhesion. Freshly blasted carbon‑steel surfaces are chemically active and prone to re‑rusting, so primer must be applied within 4 hours. This process is widely used for steel structures, pipelines, bridges and storage tanks.

Castings

Cast iron and cast‑steel castings have inhomogeneous material structure, usually with residual molding sand, gate‑riser flash and blowholes. Sandblasting mainly removes contaminants and produces uniform surface roughening. For hard cast‑steel parts, brown fused alumina or steel grit is used. For cast iron containing graphite, moderately angular abrasives such as copper slag or garnet sand are selected to avoid graphite damage and surface porosity. Pressure ranges 0.3‑0.5 MPa: lower values for thin‑wall castings against deformation, higher values for thorough cleaning of thick‑wall pieces. Treated surfaces are free of residual sand with smoothed flash marks and Ra 1.6‑6.3 μm. It serves as pre‑treatment for machining reference and painting for pump‑valve, construction‑machinery and engine‑block castings.

To sum up, process differences derive from material characteristics: aluminum‑alloy sandblasting pursues low‑stress damage‑free cleaning‑roughening; carbon‑steel targets high‑efficiency rust‑scale removal; castings emphasize residual contaminant clearance on complex surfaces. Proper parameter matching avoids defects and boosts product quality. These indispensable pre‑treatment technologies satisfy diverse industrial surface‑processing requirements.