1.With the rapid development of science and technology, laser technology has been increasingly used in various fields of people's production and life. From the supermarket bar codes, laser printers to laser beauty, treatment of myopia, and has become familiar. The cutting, drilling and welding of laser equipment for industrial production are also known to many people. However, people are still not familiar with and understand the application of laser equipment in the cleaning industry. Laser cleaning technology is a new type of cleaning technology that has been rapidly developed in the past 10 years. It has gradually replaced traditional cleaning processes in many fields with its own advantages and irreplaceability. Why can laser equipment be cleaned below? What can be used for cleaning? How effective is the cleaning efficiency? Make a brief introduction.
2. Laser and cleaning
The traditional cleaning industry has a variety of cleaning methods, mostly using chemical agents and mechanical methods for cleaning. Under the increasingly stringent environmental protection regulations in China, and people’s growing awareness of environmental protection and safety, the types of chemicals that can be used in industrial production and cleaning will become less and less. How to find a cleaner and non-invasive cleaning method is a problem we have to consider. Laser cleaning is characterized by non-abrasive, non-contact, non-thermal effects and objects suitable for various materials, and is considered to be the most reliable and most effective solution. At the same time, laser cleaning can solve problems that cannot be solved using traditional cleaning methods. For example, when the surface of the workpiece has sub-micron-sized contaminant particles, these particles tend to stick tightly, and conventional cleaning methods cannot remove it. Cleaning with nano-lasers on the surface of the workpiece is very effective. In addition, since the laser is used to clean the workpiece without contact, it is safe to clean the precise workpiece or its fine parts, and its accuracy can be ensured. Therefore, laser cleaning has unique advantages in the cleaning industry.
Why can laser be used for cleaning? Why is it not harmful to the object being cleaned? First understand the nature of the laser. In simple terms, the laser is no different from the light (visibly and invisible light) that goes along with us, but the laser uses the resonant cavity to concentrate the light in the same direction and has a simpler wavelength, coordination, etc. The performance is better, so theoretically all the wavelengths of light can be used to form the laser, but in fact it is limited by the few media that can be excited, so laser sources that can produce stable and suitable for industrial production are quite limited. Probably widely used are Nd:YAG lasers, CO2 lasers, and excimer lasers. Since Nd:YAG lasers can be more suitable for industrial applications via optical fiber transmission, they are also used in laser cleaning.
3. The advantages of laser surface cleaning
Compared with traditional cleaning methods such as mechanical friction cleaning, chemical corrosion cleaning, liquid solid strong impact cleaning, and high-frequency ultrasonic cleaning, laser cleaning has obvious advantages.
3.1 Laser cleaning is a "green" cleaning method. It does not require the use of any chemicals or cleaning fluids. The cleaned waste is basically solid powder, small in size, easy to store, recyclable, and can be easily cleaned by chemical cleaning. Environmental pollution problems brought by 3.2. Traditional cleaning methods are often contact cleaning. There is mechanical force on the surface of the cleaning object. The surface of the damaged object or the cleaning medium adheres to the surface of the object to be cleaned and cannot be removed. Sub-pollution, non-abrasive and non-contact laser cleaning to solve these problems; 3.3 laser can be transmitted through the optical fiber, and robots and robots to facilitate, to achieve long-distance operation, can clean the traditional method is not easy to reach the site, This can be used in some dangerous places to ensure the safety of personnel; 3.4 Laser cleaning can remove various types of contaminants on the surface of various materials to achieve the cleanliness that conventional cleaning cannot achieve. Moreover, it can also selectively clean the contaminants on the surface of the material without damaging the surface of the material. 3.5 Laser cleaning has high efficiency and saves time. 3.6 Although the laser cleaning system is higher in the previous one-time investment, it is cleaned. The system can be used stably for a long time, and the running cost is low. Take the LASERLASTE of Quantel as an example, the operating cost per hour is only about 1 Euro, and more importantly, it can be easily automated.
The principle of laser surface cleaning
The pulsed Nd:YAG laser cleaning process relies on the characteristics of the light pulses generated by the laser, based on the photophysical response caused by the interaction between the high-intensity beam, the short-pulse laser, and the contamination layer. The physical principle can be summarized as follows:
a) The laser beam emitted by the laser is absorbed by the contamination layer on the surface to be treated. b) Absorption of large energy forms a rapidly expanding plasma (highly ionized unstable gas), generating shock waves. c) Shockwaves contaminate and remove contaminants. d) The width of the light pulse must be short enough to avoid heat build-up that can damage the treated surface. e) Experiments show that when an oxide is present on the metal surface, plasma is generated on the metal surface.
The plasma is generated only when the energy density is above the threshold, which depends on the contaminant layer or oxide layer removed. This threshold effect is very important for the effective cleaning of the base 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 ensure effective cleaning of the substrate material, laser parameters must be adjusted according to the conditions so that the energy density of the light pulse is strictly between two thresholds.
Each laser pulse removes a certain thickness of the contamination layer. If the contamination layer is thick, multiple pulses are required for cleaning. The number of pulses needed to clean the surface depends on the degree of surface contamination. An important result produced by the two thresholds is the self-control of cleaning. Light pulses with an energy density above a first threshold will always remove contaminants until the substrate material is reached. However, because its energy density is lower than the damage threshold of the base material, the base is not damaged.
5. Practical application of laser cleaning
Laser cleaning can be used not only to clean organic contaminants, but also to clean inorganic materials, including metal corrosion, metal particles, and dust. The following describes some practical applications. These technologies have been very mature and have been widely used.
5.1 mold cleaning:
Every year, tire manufacturers in the world manufacture hundreds of millions of tires, and the tire molds in the production process must be quickly and reliably cleaned to save downtime. Conventional cleaning methods include sandblasting, ultrasonic or carbon dioxide cleaning, but these methods usually have to be cooled in a hot mold for several hours, then moved to the cleaning equipment for cleaning, cleaning takes a long time, and easy to damage the accuracy of the mold Chemical solvents and noise can also cause problems such as safety and environmental protection. The use of laser cleaning methods, because the laser can be transmitted using optical fiber, so it is very flexible in use; because the laser cleaning method can be used to connect the optical fiber to the blind corner of the die or difficult to clean the parts to be cleaned, so easy to use; due to rubber and Without gasification, no toxic gas will be produced, which will affect the safety of the working environment. The technology of laser cleaning tire molds has been widely adopted in the tire industry in Europe and America. Although the initial investment cost is high, the benefits obtained in saving standby time, avoiding mold damage, working safety, and saving raw materials can be quickly recovered. According to the LASERLASTE laser cleaning system of Quantel Corporation, the cleaning test conducted on the production line of Shanghai Shuangqin Trucking Tire Co., Ltd. showed that the mold of a large-sized truck tire can be cleaned online in only 2 hours. Compared with conventional cleaning methods, the economic benefits are obvious.
The anti-adhesive elastic film layer on food industry moulds needs to be replaced regularly to ensure hygiene. The use of laser cleaning without chemicals is also particularly suitable for this application.
5.2 Weapon Equipment Cleaning:
Laser cleaning technology is widely used in weapon maintenance. The use of laser cleaning system can remove rust and pollutants efficiently and quickly, and can select cleaning sites to achieve automatic cleaning. The use of laser cleaning not only has a higher degree of cleanliness than the chemical cleaning process, but also has little damage to the surface of the object. Quantel's LASERLASTE can also form a dense oxide protective film or molten metal layer on the surface of metal objects by setting different parameters to improve surface strength and corrosion resistance. The laser-eliminated waste does not substantially pollute the environment and can also be operated remotely, effectively reducing health damage to operators.
5.3 removal of aircraft paint:
The European laser cleaning system has long been used in the aviation industry. The surface of the aircraft will be repainted after a certain period of time, but the original paint must be completely removed before painting. The traditional method of mechanical removal of paint is likely to cause damage to the metal surface of the aircraft, causing hidden dangers to safe flight. If multiple laser cleaning systems are used, the paint on the surface of an A320 Airbus can be completely removed within two days without damaging the metal surface.
5.4 Cleaning of external walls of buildings:
With the rapid development of China's economy, more and more skyscrapers have been set up, and the problem of cleaning the external walls of buildings has become increasingly prominent. LASERLASTE laser cleaning system provides good cleaning of external walls of buildings through optical fibers up to 70 meters in length. The solution is that it can effectively clean various pollutants on various kinds of stone, metal and glass, and is much more efficient than conventional cleaning. It can also remove dark spots and stains on various types of stone in buildings. LASERLASTE laser cleaning system Cleaning experiments on buildings and stone monuments at Shaolin Temple in Songshan Mountain indicate that the use of laser cleaning is very effective in protecting the appearance of ancient buildings.
5.5 Cleaning in the Electronic Industry
The electronics industry uses lasers to remove oxides: The electronics industry needs high-precision decontamination, which is particularly suitable for laser deoxidation. Before the board is soldered, the component pins must be completely de-oxidized to ensure optimal electrical contact. The pins must not be damaged during the decontamination process. Laser cleaning can meet the requirements of use, and the efficiency is very high. Only one laser beam is needed for one pin.
5.6 Precision De-Ester Cleaning in the Precision Machinery Industry:
The precision machinery industry often needs to remove the esters and mineral oils used for lubrication and anti-corrosion on the parts, usually by chemical methods, while the chemical cleaning often still has residues. Laser deesterification can completely remove the esters and mineral oil without damaging the surface of the parts. The removal of contaminants is accomplished by shock waves. The explosive vaporization of thin oxide layers on the surface of the part creates shock waves that cause the removal of dirt rather than mechanical interaction. The material is completely deesterified for use in the cleaning of aerospace industrial machinery parts. Oil ester removal in the machining of mechanical parts can also be cleaned by laser.
5.7 Reactor reactor pipe cleaning:
The laser cleaning system is also used for the cleaning of pipelines in reactors of nuclear power plants. It uses optical fiber to introduce a high-power laser beam into the reactor and directly removes radioactive dust. The cleaned material is easy to clean. And because it is a long-distance operation, staff safety can be ensured.
In summary, laser cleaning plays an important role in many fields, such as automobile manufacturing, semiconductor wafer cleaning, precision parts processing and manufacturing, military equipment cleaning, building exterior wall cleaning, cultural relics protection, circuit board cleaning, and precision parts. Processing, manufacturing, liquid crystal display cleaning, chewing gum remnants and other areas can play an important role.
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