Introduction and Application of Laser Cleaning Technology

The traditional cleaning methods include mechanical cleaning, chemical cleaning and ultrasonic cleaning. Mechanical cleaning uses scraping, wiping, brushing, sandblasting and other mechanical means to remove surface dirt; wet chemical cleaning uses organic cleaning spraying, showering, soaking or high-frequency vibration and other measures to remove the surface adhering property ultrasonic cleaning method is to put the processed parts into the cleaning agent, and use the vibration effect generated by ultrasonic waves to remove the dirt.

At present, these three cleaning methods still dominate the cleaning market, but their applications are greatly limited under the requirements of environmental protection and high precision. The mechanical cleaning method cannot meet the requirements of high cleanliness cleaning, and it is easy to damage the surface area of the workpiece to be cleaned, while the chemical cleaning method is easy to cause environmental pollution, and the cleanliness obtained is also very limited, especially when the dirt composition is complex, it is necessary to choose a variety of cleaning agents repeatedly.

Although the ultrasonic cleaning method has a good cleaning effect, it is powerless to clean the sub-micron dirt particles. The size of the cleaning tank limits the scope and complexity of the processed parts, and the drying of the workpiece after cleaning is also a big problem.

In recent years, with the enhancement of people's awareness of environmental protection, it has brought huge challenges to the development of the cleaning industry around the world. Various cleaning technologies that are conducive to environmental protection have emerged as the times require, and laser cleaning technology is one of them.

The laser cleaning technology refers to the use of high-energy laser beams to irradiate the surface of the workpiece to instantly evaporate or peel off the dirt, rust spots or coatings on the surface, and effectively remove the surface attachments or surface coatings of the cleaning object at high speed, so as to achieve a clean process. . It is a new technology based on the interaction effect of laser and matter. Compared with traditional cleaning methods such as traditional mechanical cleaning method, chemical corrosion cleaning, liquid solid strong impact cleaning, and high-frequency ultrasonic cleaning, it has obvious advantages. It is efficient, fast, low cost, small thermal load and mechanical load on the substrate, non-destructive cleaning; recyclable waste, no environmental pollutants, safe and reliable, does not damage the operator's health certificate, can remove a variety of different thickness, different The sub-cleaning process of the coating of the components is easy to realize automatic control, and realize long-distance remote control cleaning, etc.

Lasers are characterized by high directivity, monochromaticity, high coherence and high brightness. Through the focusing and Q-switching of the lens, the energy can be concentrated into a small spatial and temporal range. In the laser cleaning process, the following characteristics of the laser are mainly used:

1. The laser can achieve a high concentration of energy in time and space, and the focused laser beam can generate a high temperature of several thousand degrees or even tens of thousands of degrees near the focus, causing the dirt to evaporate, vaporize or decompose instantly.

2. The divergence angle of the laser beam is small and the directionality is good. The laser beam can be collected into different diameters of light spots through the light-condensing system. Under the condition of the same laser energy, controlling the laser beam spots of different diameters can adjust the energy density of the laser and make the dirt expand by heat. When the expansion force of the dirt is greater than the adsorption force of the dirt on the substrate, the dirt will be separated from the surface of the object.

3. The laser beam can generate mechanical resonance by generating ultrasonic waves on the solid surface, so that the dirt can be broken and fallen off.

Laser cleaning technology utilizes the characteristics of the above-mentioned lasers to achieve the purpose of cleaning.

• Application status of laser cleaning

Due to its extremely fine and fragile surface structure, high-end stone artworks such as stone carvings and stone carvings have become the earliest fields of application of laser cleaning technology. It has been found that the use of lasers to remove dirt on the surface of stone cultural relics has its unique advantages. It can control the movement of the light beam on complex surfaces very precisely to remove dirt without damaging the cultural relics.

Applications

1. In September 1992, the World Cultural Heritage Protection Organization affiliated to UNESCO implemented the maintenance project of the famous British Yameen Cathedral in order to commemorate the 20th anniversary of the establishment of the organization. The exquisite marble carvings on the Door of Our Lady on the west side of Yameen Cathedral were the key to the project. During the one-year maintenance project of Notre Dame, the maintenance personnel used a laser to remove the black scale layer several millimeters thick covering the marble carving pattern, the original color of the marble surface was reflected, and the exquisite carving was reproduced brilliance.

2. The same effect was obtained after laser cleaning of the stone carving collection in Insbrentier, one of the most important stone carving collections in the UK. People observed the surface of the stone sculpture after laser cleaning with an electron microscope, and found that the structure of the stone after laser cleaning did not change, and the cleaned surface was smooth and flat without damage. This is completely different from a surface cleaned by micro-particle blasting (sandblasting). The damage to the marble surface structure after the micro-particle jet cleaning is unavoidable, especially for the marble surface with the existing sulfate scale layer. Electron microscope observation also found that after laser irradiation, the properties of the subsurface rock materials were neither degraded nor changed.

At present, the work of cleaning the surface dirt of high-grade stone materials such as limestone and marble with laser has become a new and promising business project. In addition to the cleaning of stone materials, laser cleaning has a good effect in the cleaning of glass, metal, molds, magnetic disks and various microelectronic products. In the production of automobile tires, the bottom and surrounding patterns of tire molds are It needs to be cleaned every two to three weeks, and the entire mold needs to be thoroughly cleaned every few months. The traditional method is to use chemical liquid to soak or sandblast cleaning, which is not only expensive, noisy and polluted, but also affects the surface quality of the mold.

In addition, this type of cleaning method cannot realize online cleaning, and the disassembly of the mold before cleaning and the installation of the mold after cleaning take a long time, which affects the normal operation of the production line. Using laser technology to clean molds can realize online cleaning operations. Depending on the amount of organic deposits on the surface of the mold and the structure of the rubber compound, it only takes 45-90 minutes to clean a set of molds (including loading and unloading and cleaning the parts on both sides of the mold). Since the mold surface can reflect the laser beam, the mold surface will not be damaged by the laser. Laser cleaning is highly flexible, and users can use this technology to replace other methods in use. At present, the online cleaning of tire molds has been realized on tire production lines abroad, and it has been applied to the industry. When the mold needs to be cleaned, turn on the vulcanizer at the same time as the vulcanization is over, and move the laser mold cleaning system to the vulcanizer to clean the mold without waiting for the mold to cool.

The application of laser cleaning technology has been promoted and applied in Europe for several years, and there are mature products. At present, a high-efficiency and low-cost cleaning method for tire molds is in urgent need of promotion. A set of molds needs to be cleaned every 3 weeks or so. It can be seen that the promotion and application of laser technology cleaning is of great significance. It is believed that on the basis of the continuous improvement of this technology, with the mass production of equipment, laser cleaning technology will play an important role in mold cleaning and other cleaning industries, and has a good development prospect.