With the higher and higher requirements for the precision of high-grade stone cleaning and the increasing awareness of human environmental protection, laser cleaning technology is being recognized and developed as a new cleaning method. Laser cleaning technology mainly uses laser beams to remove attachments on the surface to be cleaned at high speed. It saves time, effort, and water, and is safe, reliable, widely applicable, and easy to control automatically. Especially for stone carvings, stone carvings, fine stone structures such as various corners, and old-fashioned stone artifacts and other high-grade stone cleaning, the advantages of laser cleaning technology are unmatched by many traditional cleaning techniques. Therefore, it can be said that laser cleaning is a major advancement in cleaning technology, and the promotion and application of laser cleaning technology will surely make the stone cleaning industry even more powerful. From the surface of the object; Third, the dirt molecules will be vaporized, vaporized or decomposed instantaneously. Laser cleaning technology is the use of the laser pulse vibration, the thermal expansion of the particles and the molecular light decomposition or phase change of three kinds of role or their combined effect to overcome the binding force between the surface of the dirt and the substrate material, so that it is off the surface of the object to achieve The purpose of cleaning.
According to the analysis of the optical properties of the cleaned matrix material and the contaminants, the laser cleaning mechanism can be further divided into two categories: one is the difference in the absorption coefficient of the laser energy at a certain wavelength due to the adhesion of the substrate material and the surface dirt, so that the laser The energy is fully absorbed by the attached dirt, so that it is thermally expanded or vaporized and volatilized, and the vaporized stream formed by vaporization drives away from the matrix material to achieve the purpose of cleaning. The requirement is that the absorption coefficient of the laser energy of the matrix material is small.
The combined forces of dirt and stone surfaces are mainly physical and weak chemical forces. Weak chemical forces include hydrogen bonds and the bond energy formed by charge transfer. Physical forces include van der Waals forces (including electrostatic, induced and dispersive), and capillary forces. The reason that stone is harder to clean than other surface materials is due to the existence of a large number of micro-pores in natural stone. The capillary force of micro-pores not only enhances the various binding forces between the dirt and the stone, but also causes the enveloping effect of each. It is difficult for the cleaning force to work.
Laser is a kind of light radiation with good monochromaticity and directionality. The combination of mirrors can focus the beam and concentrate the beam in a small area or area. The laser beam can produce at least three aspects: First, it will produce mechanical resonance on the solid surface to make the surface layer or condensate break off; second, it will expand the surface layer to overcome the adsorption of the substrate material on the dirt particles. It will not be damaged, so the key to achieving safe and efficient cleaning is to choose the right laser wavelength and control the moderate energy density. The other type is that the absorption coefficient of the laser beam between the substrate substance and the surface attachment substance is not greatly different, or the cleaning of the surface attachment substance when producing toxic substances is usually performed by pulse laser shock of higher frequency and power. On the surface, some of the light beams are converted into sound waves. The sound waves return after hitting the hard surface of the lower middle layer. The returned part interferes with the human-generated sound waves generated by the laser, thereby generating high-energy resonant waves, causing tiny cracks in the scale layer, causing smashing, and it is easy to crush. Detach from the substrate surface.
For the cleaning of the surface of the stone, the above mechanisms are often used in combination. The frequency of laser light pulses (0.5 to 30 pulses per second) and amplitude (8 to 25 ns) are usually based on the condition of the treated stone and dirt, allowing the dirt material to properly absorb light energy. The pulse laser's repetitive frequency impact can loosen the coke scale in the stone surface and micropores. When the impact force of the laser is greater than the adsorption force of the substrate to the dirt particles, the dirt particles will break away from the substrate to achieve the purpose of cleaning. When the laser photon energy is greater than that of the (adhesion layer) fouling molecules, the photodecomposition and photo-exfoliation effects of the lasers exert their effects one after the other. For example, the KrF excimer laser photon energy is 5 eV, which is greater than the organic contaminants OO, HH, OH, CC, The bond energy of CH and NH and other chemical bonds, the role of the laser can destroy part of the chemical bond, decompose the organic matter, which can clean organic oil. When the laser beam energy density further increases, some inorganic dirt. For example, salts containing K, Na, and inorganic substances generated by photodecomposition by organic soils can be thermally expanded by the laser to generate thermal peeling (ie, photo-stripping) to separate from the surface of the substrate. In order to fully utilize various functions of the laser and enhance the cleaning effect of the laser, the surface of the substrate to be cleaned is artificially coated with some water or a mixed liquid of water and methanol or ethanol in advance. When the laser light is irradiated on the liquid film, the liquid film will be explosively vaporized due to rapid heating, and the impact of the explosion will loosen the dirt on the surface of the substrate and fly away from the surface of the substrate with the shock wave to achieve the purpose of decontamination. In this method, although the vibration of the dirt particles and the thermal expansion of the particles also exist, the effect of the explosive shock wave is dominant. This method is also called laser+liquid film method. The thickness of the liquid film covering the surface of the substrate is generally 10/m. .