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Principle and classification of laser cleaning
Traditional cleaning industrial equipment has a variety of cleaning methods, mostly using chemical and mechanical methods. With the increasingly stringent requirements of China's environmental protection laws and regulations and the increasing awareness of environmental protection and safety, there will be fewer and fewer types of chemicals that can be used in industrial production cleaning. How to find a cleaner and non-destructive cleaning method is a problem that people must consider. Laser cleaning has the cleaning characteristics of no grinding, non-contact, low heat effect and suitable for objects of various materials. It is considered to be the most reliable and effective solution.
In the product surface pollutants, the combination between the product surface adhesion and the surface is mainly due to the following forces: covalent bond, double dipole, capillary action, hydrogen bond, adsorption and electrostatic force. Among them, capillary force, adsorption and electrostatic force are difficult to destroy, and laser cleaning technology also needs to solve these forces. This kind of adsorptivity is much larger than gravity (several orders of magnitude) and is related to particle diameter D. the adsorptivity shows a slow linear attenuation trend with the decrease of particle radius, while the cubic positive ratio of particle mass m to diameter is f = ma according to Newton's law. When the particle size becomes smaller, the acceleration given by adsorptivity increases rapidly. Therefore, the smaller the size of particles, the greater the acceleration required to remove them, which is why it is difficult for conventional cleaning technology to remove the surface adhesion of objects with small diameter. Due to the complex composition and structure of the surface adhesion of the object, the mechanism of laser action is also different. The most commonly used theoretical models to explain this are as follows:
1. The laser caused by phosgenation / photodegradation laser can achieve high concentration of energy through the concentration of optical system. The focused laser beam can cause a high temperature of thousands or even tens of thousands of degrees near the focus, making the adhesion on the surface of the object vaporize or decompose instantly.
2. Light stripping expands the surface adhesion of the object by heating according to the action of laser. When the expansion force of the surface adhesion of the object is greater than its adsorption with the substrate, the surface adhesion of the object will be separated from the surface of the object.
3. Light vibration uses high-frequency and high-power pulsed laser to impact the surface of the object, causing ultrasonic waves on the surface of the object. The ultrasonic waves return after impacting the hard surface of the middle and lower layers, interfere with the incident sound waves, and then cause high-energy resonance waves, causing micro explosion, crushing and separation of the dirt from the surface of the matrix material, This kind of cleaning method can be selected when there is little difference in the absorption coefficient of the laser beam between the object and the surface adhesive, or when the surface adhesive will cause toxic substances after heating.
At present, there is no unified standard for the structure of laser cleaning equipment, which needs to be determined according to the actual cleaning methods, types of substrates and dirt, cleaning effect and other factors. However, they are roughly the same in some basic structures, mainly including lasers, mobile platforms, real-time monitoring systems Semi / automatic control operating system and other auxiliary systems.