Laser Cleaning
Continuous-wave diode sources for thermal cleaning of porous surfaces
The most widespread form of laser cleaning uses short pulses to remove the surface layer by ablation. On very rough or porous materials, such as brick, concrete, stone or ceramics, paint penetrates the pores and ablation cannot remove it. In these cases thermal cleaning with a continuous-wave diode laser works better: the coating absorbs the radiation, degrades and detaches, while the temperature-resistant substrate remains intact if the irradiance and exposure time are right.
Paint and graffiti removal
Continuous-wave diode lasers have removed graffiti in six colors from quarry stone without damaging the substrate, at an irradiance of 800 W/cm², a speed of 10 mm/s and two passes. The continuous regime gave better results than the modulated one [1]. Chlorinated rubber coatings 0.3 mm thick have also been removed from concrete with a 120 W diode at 810 nm, at around 0.5 m²/h and with very little waste [2].
In tests carried out with the Laser Centre of the Universidad Politécnica de Madrid (UPM), we have removed spray paint from different substrates with a 940 nm fiber-coupled diode module, using a strongly defocused beam and overlapping lines at 800 mm/min [3]:
| Substrate | Power (CW) | Result |
|---|---|---|
| Brick | 60–90 W | Insufficient cleaning: the paint dries |
| Brick | 120 W | Complete cleaning without damaging the brick |
| Brick | 207 W | Surface vitrification |
| Very rough concrete tile | 200–300 W | Complete cleaning, with a slight color change |
| Ceramic tile | 292 W | Complete cleaning |
| Ceramic tile | 488 W | Breakage by thermal shock |
The process window depends on the substrate: below it the paint is not removed, and above it the material is damaged. For each application the irradiance, speed and overlap must be tuned and, for materials sensitive to thermal shock, the temperature must be controlled.
Our sources
We design and manufacture near-infrared fiber-coupled diode bars, with powers of up to hundreds of watts, for integration into cleaning heads.
References
1. Penide J, Quintero F, Riveiro A, et al. Removal of graffiti from quarry stone by high power diode laser. Opt Lasers Eng. 2013;51(4):364–370. doi:10.1016/j.optlaseng.2012.12.002
2. Schmidt MJJ, Li L, Spencer JT. Removal of chlorinated rubber coatings from concrete surfaces using a 120-W high power diode laser. Surf Coat Technol. 2001;141(1):40–47. doi:10.1016/S0257-8972(01)01161-6
3. Centro Láser UPM. Pruebas para la validación de sistemas láser desarrollados por Monocrom. Procesos láser industriales. Informe técnico, junio de 2024.
Need to clean difficult surfaces?
Tell us about the substrate, the type of coating, the area to be treated and the throughput you need, and we will work with you to define the most suitable configuration. We develop custom solutions for equipment manufacturers and integrators.
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