The root cause of peeling during shot blasting lies in an imbalance between material properties and process parameters. Defects in the gating/runner system of mold design are the underlying trigger, while synergistic optimization of process parameters is the key to resolution. Analysis should integrate factors including materials, molds, equipment, processes, grinding, shot pellets, parameters, and environment.
Alloy compositions with Silicon (Si) ≥11.5%, Iron (Fe) ≥1.2%, Magnesium (Mg) ≥0.3%, Manganese (Mn) ≥0.5%, or Zinc (Zn) ≥1.2% tend to cause peeling. Copper (Cu) ≤1.5% reduces surface strength and hardness, leading to dents, deformation, peeling, or wrinkling under shot blasting impact. A return material ratio ≥50% also makes slag removal and degassing during melting extremely difficult, resulting in deviations in product appearance and mechanical properties.
Unreasonable mold design—such as turbulent flow during casting (causing porosity), poor mold temperature control (leading to hot spots, shrinkage cavities, or cold shuts), inadequate gas venting (resulting in shallow surface porosity at part ends)—easily triggers peeling. Obstructed filling pressure increases force transmission resistance, causing product looseness, substandard mechanical properties, and a higher risk of peeling or deformation.
Issues like unreliable platen clamping, stuck injection plungers, failed vacuum systems, or malfunctioning spot cooling systems can all directly lead to peeling during shot blasting.
Improper holding furnace temperature (≤640°C) causes silicon segregation. If mold temperature is also low, or if the release agent is excessively diluted, spraying time is too long, or air blowing fails to dry the surface, aluminum melt fluidity decreases. This produces loose surface defects (cold shuts, flow marks, pitting, porosity) that severely increase peeling risk.
Incomplete removal of flash/excess material from blanks makes peeling likely after shot blasting. Over-grinding removes the blank’s dense surface layer, causing peeling under shot blasting impact.
Inconsistent pellet diameters or pellets exceeding the set size increase blasting force, making parts prone to peeling.
Excessively high blasting speed or overly long duration damages the part’s dense layer, leading to peeling.
Poor ventilation, limited air permeability, or high temperatures in the shot blasting environment soften the part surface, causing peeling.
When using release agents, focus on dilution ratio and spraying parameters (angle, direction, atomization, distance, time). Excessive spraying time can create loose surface defects (cold shuts, flow marks, pitting, porosity) that risk peeling. Inadequate spraying at hot spots leads to shrinkage cavities or oxide scale delamination—also increasing peeling risk.
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