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How should the surface of castings be treated after shot blasting?
release time:
2026-07-31
Although shot blasting removes impurities such as scale and adhering sand from c
Although shot blasting removes impurities such as scale and adhering sand from castings, subsequent treatments are typically required to further enhance their performance and appearance. Common post-blasting surface treatment methods fall into the following categories:
I. Heat Treatment
Purpose: To eliminate residual tensile stresses generated during the shot blasting process, and to enhance hardness, toughness, and corrosion resistance.
Applicability: Castings requiring superior mechanical properties (e.g., high-manganese steel and alloy castings).
Methods: Annealing, Quenching + Tempering, Water Toughening (applicable to high-manganese steel), etc.
II. Chemical Treatment
Objective: To enhance corrosion resistance and aesthetic appeal, and to provide a suitable substrate for painting.
Common Methods:
Chromate Treatment: Forms a dense, colored film layer, thereby enhancing corrosion resistance and paint film adhesion.
Phosphating/Passivation: Creates a protective conversion coating; commonly applied to steel components.
Acid Pickling: Removes trace oxides and improves surface finish (environmental regulations must be observed).
III. Mechanical Treatment
Objective: To correct minor indentations or surface irregularities resulting from shot blasting, and to enhance surface finish.
Methods:
Grinding or Polishing: Utilizing grinding wheels, grinding machines, or brush rollers to further smooth the surface.
Sandblasting (if specific roughness is required): Employed in applications requiring decorative finishes or high surface adhesion.
IV. Coating Treatment
Objective: To enhance properties such as wear resistance, corrosion resistance, and decorative appeal.
Common Methods:
Electrostatic Spraying / Dip Coating: Forms a uniform paint film, enhancing both aesthetics and protection.
Electrophoretic Painting: Suitable for die-cast parts with complex geometries; offers strong adhesion.
Electroplating or Electroless Plating: Improves electrical conductivity, wear resistance, or chemical resistance.
V. Special Considerations
If peeling or flaking occurs following shot blasting, potential causes may include:
Defects inherent in the casting itself, such as cold shuts or porosity;
Excessive shot velocity, prolonged blasting duration, or the presence of impurities in the steel shot;
Improper fixturing resulting in collisions.
In such instances, it is necessary to optimize the shot blasting process parameters or replace the steel shot with a compliant batch.
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