Laser Paint Research Articles

Epoxy-paint stripping using TEA CO2 laser: Determination of threshold fluence and the process parameters

It is shown that the threshold fluence for laser paint stripping can be accurately estimated from the heat of gasification and the absorption coefficient of the epoxy-paint. The threshold fluence determined experimentally by stripping of the epoxy-paint on a substrate using a TEA CO2 laser matches closely with the calculated value. The calculated threshold fluence and the measured absorption coefficient of the paint allowed us to determine the epoxy paint thickness that would be removed per pulse at a given laser fluence even without experimental trials. This was used to predict the optimum scan speed required to strip the epoxy-paint of a given thickness using a high average power TEA CO2 laser. Energy Dispersive X-Ray Fluorescence (EDXRF) studies were also carried out on laser paint-stripped concrete substrate to show high efficacy of this modality.

Directional laserlike emission from a dye-doped polymer containing rutile nanoparticles

A novel scheme for generation of laserlike emission from highly scattering media is presented. A high degree of directionality is obtained owing to the excitation of surface plasmons in a silver film. The electromagnetic energy coupled to surface plasmons is transferred to a polymeric disk containing Rhodamine and TiO2 nanospheres placed in close contact with the film. The fluorescence produced in the disk, outcoupled through a prism, displays features of a “laser paint” plus a high directionality.

Removal of embedded contamination in chlorinated rubber coatings using a portable high power diode laser

In this article we report the process characteristics for removing embedded contamination in white chlorinated rubber (CR) coatings from concrete surfaces utilizing a portable 120 W continuous wave diode laser operating at 810 nm wavelength and applying a cylindrical focusing system. Coating layers of 350 μm thickness have been prepared to industrial standards. A contaminant simulant ZrO2 layer was embedded in the coating. The coatings were subsequently removed by the laser with the aid of oxygen process gas. The reflectivity properties of the CR material from the visible to the near infrared wavelengths, as well as their behavior under high temperatures have been examined with a normal incidence reflectance spectrometer. Even though the reflection coefficient of white CR at 810 nm is almost 100%, a drop in reflectivity after a brief period of laser irradiation explains the initiation and the sustaining of the combustion process and the subsequent coating removal. The sizes of the generated airborne particles are measured and interpreted. The removal quality and efficiency dependence on laser parameters are assessed and discussed, together with safety aspects regarding portable laser paint removal process. An attempt is made to interpret the mechanisms involved in the removal process. The remaining surfaces were then analyzed via optical microscopy, by energy dispersive analysis of x rays and total reflectance x-ray fluorescence, to establish the effectiveness of the embedded contaminant simulant removal.

An Experimental Study of Paint-Stripping Using an Excimer Laser

An excimer laser paint stripping process on metallic surfaces has been investigated, applicable to all those situations, such as adhesive bonding or spot welding, where a localised removal of the surface coating on single parts before assembly could be less expensive and better in quality than the ones realised with traditional methods. This process, due to the properties of the UV laser radiation used, is also suitable for paint stripping on already thermal treated metallic surfaces and plastic composites surfaces. The absence of contact of the laser “tool” with the coating and the easy removal of products formed during the process is another important advantage of this method. Treating radioactive or contaminated parts is also possible, keeping the process in a closed chamber. Several kinds of polymer coatings have been tested for paint stripping experiments applied on aluminium and low carbon steel substrates, with different composition, colours, and thicknesses. The results obtained show that high quality surfaces can be obtained using this treatment, but the processing time is long. These characteristics make the method suitable for treatment of small zones when either high surface quality, or absence of contact, is essential.

An Experimental Study of Paint-Stripping Using an Excimer Laser

An excimer laser paint stripping process on metallic surfaces has been investigated, applicable to all those situations, such as adhesive bonding or spot welding, where a localised removal of the surface coating on single parts before assembly could be less expensive and better in quality than the ones realised with traditional methods. This process, due to the properties of the UV laser radiation used, is also suitable for paint stripping on already thermal treated metallic surfaces and plastic composites surfaces. The absence of contact of the laser “tool” with the coating and the easy removal of products formed during the process is another important advantage of this method. Treating radioactive or contaminated parts is also possible, keeping the process in a closed chamber. Several kinds of polymer coatings have been tested for paint stripping experiments applied on aluminium and low carbon steel substrates, with different composition, colours, and thicknesses. The results obtained show that high quality surfaces can be obtained using this treatment, but the processing time is long. These characteristics make the method suitable for treatment of small zones when either high surface quality, or absence of contact, is essential.

Theory of lasing in a multiple-scattering medium.

In several recent experiments, isotropic lasing action was observed in paints that contain rhodamine 640 dye molecules in methanol solution as gain media and titania particles as optical scatterers. These so-called paint-on laser systems are extraordinary because they are highly disordered systems. The microscopic mechanism for laser activity and the coherence properties of light emission in this multiple-light-scattering medium have not yet been elucidated. In this paper we derive the emission intensity properties of a model dye system with excited singlet and triplet electronic energy levels, which is immersed in a multiple-scattering medium with transport mean free path l*. Using physically reasonable estimates for the absorption and emission cross section for the singlet and triplet manifolds, and the singlet-triplet intersystem crossing rate, we solve the nonlinear laser rate equations for the dye molecules. This leads to a diffusion equation for the light intensity in the medium with a nonlinear intensity-dependent gain coefficient. Using this model we are able to account for nearly all of the experimentally observed properties of laser paint reported so far when l*\ensuremath{\gg}${\ensuremath{\lambda}}_{0}$, the emission wavelength. This includes the dependence of the peak intensity of amplified emission on the mean free path l*, the dye concentration \ensuremath{\rho}, and the pump intensity characteristics. Our model recaptures the collapse of the emission linewidth at a specific threshold pump intensity and describes how this threshold intensity varies with l*. In addition, our model predicts a dramatic increase in the peak intensity and a further lowering of the lasing threshold for the strong scattering limit l*\ensuremath{\rightarrow}${\ensuremath{\lambda}}_{0}$. This suggests a striking enhancement of the characteristics of laser paint near the photon localization threshold in a disordered medium. \textcopyright{} 1996 The American Physical Society.

Mechanical behavior of 2024 Al alloy specimen subjected to paint stripping by laser radiation and plasma etching

Paint removal is required in a series of aeronautical procedures such as maintenance and repair. Today's paint stripping processes which are based on application of chemicals and abrasion are inadequate for modern aircraft structures in addition to environmental contamination. several alternative techniques are in progress. However, the aspect of material property degradation when developing novel, alternative paint stripping techniques has not been properly faced up to present. The influence of two novel paint stripping processes on the mechanical properties of the substrate 2024 7351 aluminium alloy has been investigated. The paint stripping processes included laser radiation with excimer, CO 2, TEA-C0 2 and YAG laser sources as well as plasma etching. These processes have been applied for the removal of polyurethane coating which is a typical aeronautical paint system. The results indicated no significant degradation in yield strength and ultimate tensile strength. However a significant degradation in tensile ductility and toughness is observed with the application of all paint stripping processes, the highest degradation being associated with the ultraviolet excimer laser and plasma etching. On the other hand there is a considerable extension in fatigue life, which depends on the paint stripping process and the applied stress amplitude. At high stress there is no appreciable effect while at low stress there is an order of magnitude life extension associated with CO 2 laser paint stripping. At moderate stresses, there is an up to sixfold life extension associated with the excimer laser processing.

Applications industrielles des lasers U.V. au Centre Commun de Recherches Louis-Blériot d'AEROSPATIALE

This paper concerns investigations conducted by AEROSPATIALE (Louis-Bleriot Joint Research Center) on UV radiation-matter interaction and on the potential industrial applications like laser paint stripping, machining of special materials (ceramics, composites,) and the surface annealing of metals.