Sweep Blasting - Hot Dip Galvanizing

This method of surface preparation is appropriate before applying, good top quality paint topcoats over galvanizing.

Particularly in circumstances where good wet adhesion or semi immersion of the combined system is intended light sweep blasting can provide maximum topcoat adhesion over galvanizing.

To achieve a successful result it must be understood that blast standards for preparing steel are totally inappropriate for galvanizing where the outer free zinc layer requires very little impact or scouring action to promote adequate surface roughness.

The Following Criteria Should be Observed

  • Blast pressure 40 p.s.i maximum
  • Abrasive Grade 0.2 - 0.5mm (clean ilmenite)
  • Angle of blasting to surface 45 angle
  • Distance from surface 300-400 mm
  • Nozzle type min 10mm of venturi type

These controls will ensure that the severity of blasting does not damage the galvanized surface and should remove only 10 µm of surface zinc.

If operators with good experience in sweep blasting are unavailable, it is wise to begin with a greater distance between the nozzle and the surface to be sweep blasted until standards for the work have been established.

Source: Galvanizers Association of Australia

For more information on this source please visit Galvanizers Association of Australia

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