Jul 15, 2019
The principle and method of laser cleaning, laser features high directionality, monochromaticity, high coherence and high brightness. Through the focus and Q-switching of the lens, energy can be concentrated into a small spatial range and time range. In the laser cleaning process, the following characteristics of the laser are mainly utilized:
1. The laser can achieve high concentration of energy in time and space. The focused laser beam can generate several thousand degrees or even tens of thousands of degrees of high temperature near the focus, so that the dirt instantaneously evaporates, vaporizes or decomposes.
2. The divergence angle of the laser beam is small and the directivity is good. The laser beam can be focused into spots of different diameters by the concentrating system. Under the same conditions of laser energy, controlling the laser beam spot of different diameters can adjust the energy density of the laser to cause the dirt to expand. When the expansion force of the dirt is greater than the adsorption force of the dirt on the substrate, the dirt will leave the surface of the object.
3. The laser beam can generate mechanical resonance by generating ultrasonic waves on the solid surface to break and fall off the dirt. The laser cleaning technology utilizes the characteristics of the above laser to achieve the purpose of cleaning. According to the optical properties of the substrate to be cleaned and the dirt to be removed, the laser cleaning mechanism can be divided into two categories: one is to use a cleaning substrate (also called a mother) and a surface attachment (dirt) to a certain wavelength of laser. The absorption coefficient of energy has a large difference. Most of the laser energy radiated to the surface is absorbed by the surface deposits, which is evaporated by heat or vaporization, or instantaneously expanded, and is driven by the formed airflow to separate from the surface of the object for cleaning purposes. The substrate does not suffer damage due to the minimal energy absorption of the laser light at this wavelength. For such laser cleaning, choosing the right wavelength and controlling the laser energy is the key to safe and efficient cleaning. Another type of cleaning method is that the laser energy absorption coefficient of the cleaning substrate and the surface attachment is not much different, or the substrate is sensitive to the acidic vapor formed by the heat of the coating, or the toxic substance is generated after the coating is heated. This type of method usually uses a high power, high repetition rate pulsed laser to impact the surface being cleaned, converting part of the beam into sound waves. After the sound wave hits the lower hard surface, the returned part interferes with the incident acoustic wave generated by the laser, generating a high-energy wave, causing a small-scale explosion of the coating, the coating is pressed into a powder, and then removed by the vacuum pump, and the underlying substrate It will not be damaged.