Traditional cleaning industrial equipment 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, low thermal effects and objects suitable for various materials. It is considered to be the most reliable and effective solution.
In the surface contamination of the workpiece, the binding between the attachment on the workpiece surface and the surface is mainly due to the existence of the following kinds of forces: covalent bonds, double dipoles, capillary action, hydrogen bonds, adsorption forces, and electrostatic forces. Among them, capillary force, adsorption force and electrostatic force are the most difficult to destroy. Laser cleaning technology is to overcome these forces.
These adsorption forces are much larger than gravity (some orders of magnitude), and are related to the particle diameter d. The adsorption force shows a slow linear decay tendency as the particle radius decreases, and the particle mass m is proportional to the cubic of the diameter. According to Newton's law, F=ma, when the particle size becomes smaller, the acceleration provided by the adsorption force increases rapidly. Therefore, the smaller the size of the particles, the greater the acceleration needed to remove them, which is why conventional cleaning technology is difficult to remove the surface attachments of small diameter objects.
Due to the complex composition and structure of the surface attachments, the mechanism of laser interaction with them is also different. The most commonly used theoretical models for this explanation are the following:
1, phosgenation/light decomposition
The laser generated by the laser can achieve high concentration of energy through the focusing of the optical system. The focused laser beam can generate high temperatures of several thousand degrees or even tens of thousands of degrees in the vicinity of the focal point, and instantaneously vaporize or decompose the attachments on the surface of the object.
2, light stripping
By the action of the laser, the attachment on the surface of the object is thermally expanded. When the expansion force of the attachment on the surface of the object is greater than the adsorption force between the attachment and the substrate, the attachment on the surface of the object will be detached from the surface of the object.
3, optical vibration
A pulsed laser with a higher frequency and power is used to strike the surface of an object and an ultrasonic wave is generated on the surface of the object. The ultrasonic wave returns after hitting the hard surface of the lower middle layer and interferes with the incident sound wave, thereby generating a high-energy resonant wave, which causes microscopic cracking and crushing of the dirt. From the surface of the matrix material, this cleaning method can be used when the absorption coefficient of the laser beam between the object and the surface attachment is not very different, or when toxic substances are generated after the surface attachment material is heated.
At present, there is no uniform standard for the structure of laser cleaning equipment, which needs to be determined based on factors such as the actual cleaning method, the type of substrate and dirt, and the effect of cleaning requirements. However, they are still roughly the same in some basic structures. It mainly includes lasers, mobile platforms, real-time monitoring systems, semi-automatic control operating systems, and other auxiliary systems.