P-Laser / Basics

Laser cleaning basics:

1) Principles of LASER CLEANING

The illustration above shows the effects of laser cleaning. The grey layer on top op the base material is the contamination. This layer will absorb the laser energy very well, whereas the base material (steel, aluminum, wood, plastics...) will reflect most of the energy. 

The laser is short pulsed, this means that the laser beam is comparable to small bullets of light, shooting at a very high frequency ! 

When a bullet hits the absorbing layer, two things can happen:

Crimp effect:

  • The base material stays cold, while the absorbing layer heats up. The heat-expansion difference will cause the contaminant to crimp off the base material.

Evaporation:

  • The contaminant heats up fast, a plasma is created around the working area. This will cause evaporation

Lasers with different power levels :

  • Low power lasers, show a very peak oriented laser profile. When the light bullet hits the surface it will be able to remove contamination even in very small cracks of the material (in depth).
  • High power lasers, have a flat peak, making sure the heat is equal over the light bullet surface. This prevents the base metal from getting damages and makes sure that higher cleaning speeds (bigger surface/min) can be achieved.
No base-metal damage:
 
  • The fact that the contamination is evaporated and the fact that the base metal is able to distribute the heat that it absorbed in its much bigger volume and spread immediately results in NO DAMAGE TO THE BASE METAL.
  • Although Surface Treatment is also possible with power lasers: next side effects are Possible but with proposer control of the process parameters and setting this will be avoided: surface melt- surface hardening- surface roughening, surface oxidation, surface visual outlook.

 2) Safety

Risk:

  • Class 4 Laser: Direct radiation of laser light into eye is harmful without recovery. Skin will get burnt. Diffuse and scattered radiation is harmful at a distance above 6m.
  • Class 3 Laser : Direct radiation of laser light into eye is harmful without recovery. Diffuse and scattered radiation is not harmful. 
  • Invisible IR light reflection : Reflected light could be harmful !
  • Reflection of substrate, Roughness of substrate (scattering) 

Prevention

  • Wear special IR protective glasses
  • Inform workers 
  • Trained personnel (certified) (1 day)
  • Enclosed laser system (possible with fixed installation)
  • No trespassing barrier
  • No direct radiation may be visible! (because it is infra red)
  • Wear protective clothing
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