The traditional industrial cleaning methods mainly include high-pressure water, chemical reagents, ultrasonic waves, and mechanical polishing. However, these cleaning methods have problems such as damage to the substrate, poor working environment, pollution, partial cleaning, and high cleaning costs. With the intensification of environmental pollution, scholars from various countries are actively developing energy-saving, environmentally friendly and efficient new cleaning technologies. Because laser cleaning technology has multiple advantages such as low damage to substrate materials, high cleaning accuracy, zero emissions and no pollution, it is gradually being valued and favored by academia and industry. There is no doubt that the application of laser cleaning technology to the cleaning of dirt on metal surfaces has very broad prospects.
Development history and current status of laser cleaning technologyIn the 1960s, the famous physicist Schawlow first proposed the concept of laser cleaning, and then applied the technology to the repair and maintenance of ancient books. Laser cleaning has a wide range of decontamination, from thick rust layers to fine particles on the surface of objects, including the cleaning of cultural relics, the removal of rubber dirt on the surface of tire molds, the removal of silicone oil contaminants on the surface of gold films, and the microelectronics industry. High precision cleaning. Laser cleaning technology really began in 2004, and began to invest a lot of manpower and material resources to strengthen the research on laser cleaning technology. In the past decade, with the development of advanced lasers, from inefficient and bulky carbon dioxide lasers to light and compact fiber lasers; from continuous output lasers to short pulse lasers with nanoseconds or even picoseconds and femtoseconds; from visible light output To the output of long-wave infrared light and short-wave ultraviolet light… lasers have developed by leaps and bounds in terms of energy output, wavelength range, or laser quality and energy conversion efficiency.
The development of lasers has naturally promoted the rapid development of laser cleaning technology. Laser cleaning technology has achieved fruitful results in theory and application. The principle of laser cleaning technologyThe process of pulsed laser cleaning depends on the characteristics of the light pulses generated by the laser and is based on the photophysical reaction caused by the interaction between the high-intensity light beam, the short-pulse laser and the contamination layer.
The physical principle can be summarized as follows (Figure 1)
- A) The beam emitted by the laser is absorbed by the pollution layer on the surface to be treated;
- B) Absorption of large energy forms a rapidly expanding plasma (highly ionized unstable gas), which generates shock waves;
- C) Shock wave turns pollutants into fragments and is eliminated;
- D) The width of the light pulse must be short enough to avoid heat accumulation that would damage the treated surface;
- (E) Experiments show that when there is oxide on the metal surface, plasma is generated on the metal surface.
Plasma is only generated when the energy density is above the threshold, which depends on the contaminated layer or oxide layer being removed. This threshold effect is very important for effective cleaning while ensuring the safety of the substrate material. There is a second threshold for the appearance of plasma. If the energy density exceeds this threshold, the base material will be destroyed. In order to carry out effective cleaning under the premise of ensuring the safety of the substrate material, the laser parameters must be adjusted according to the situation, so that the energy density of the light pulse is strictly between two thresholds.