5. Einfluss des Druckluftstrahlens auf die Werkstückoberfläche

Abrasive blasting, that’s the cleaning of surfaces during which a granular material is thrown on a surface at a high speed in order to remove paint residues, scale, sand and other contaminations. The result is called cleanness.

During the blasting process the background (the surface of the workpiece) is also deformed, this deformation (roughness height) can show very low, but also high roughness. But the structural shape can also be influenced.

We make a difference between

Cleanness ----  e.g. SA (2 ½ )
Roughness ---- Ra – Rt – Rz –Rmax., etc.
Structural shape ---- number of peaks per measuring length,
steepness of the peaks, etc.

Energy is transferred to the steel grain during the blasting process. This energy is influenced by:

     the amount of air of the compressor
     the generated pressure
     the nozzle diameter
     the abrasive   shape of the grain

  • specific weight
  • size of the grain
  • hardness of the grain

     the impact angle
     the distance nozzle – surface

The kinetic energy that is transferred to the abrasive breaks down into

     kinetic energy of the rebounding grain      deformation energy of the grain      deformation energy of the surface (only this one does      the cleaning work)

The rate of distribution depends on the following as regards these kinds of energy:

     the hardness of the surface to be blasted      the impact angle of the blasting grain      the physical properties of the blasting grain like:           hardness           size           specific weight           elasticity During the blasting process contaminations are removed from the surface and at the same time this surface is prepared for new coating.

It is the task of abrasive blasting to remove contaminations from the surface. These ones can consist of different materials like for instance:

  • scale
  • rust
  • built-ups of sand (foundries)
  • welding residues
  • old paint coats, etc.

The required energy to clean a coated surface depends on the old coats to be removed, i.e. their

  • composition
  • hardness
  • thickness/toughness
  • condition