There are four objects of action in the laser cleaning process, namely:
1) Attachments
The laser causes the attachment to heat and expand, and when the expansion force is greater than the attraction between the attachment and the substrate, the attachment falls off; or the laser directly evaporates, gasifies, decomposes, ablates or burns the attachment.
2) Gas in the attachment layer
The laser makes the ambient gas in the deposit layer into plasma, and impacts the deposit to make it peel off.
3) Matrix
The laser causes the substrate to generate thermoelastic waves, breaking and falling off the attachments.
4) Pre-coated liquid film
The laser acts on the pre-coated liquid film, causing the liquid film to explode and boil, and the energy is transferred to the surface attachments, causing them to shatter and detach.
The first three are called "dry" cleaning, which are most widely used in the industry. For many common attachments such as paint and rubber, it can be effectively removed by selecting appropriate lasers and process parameters. The fourth is called "wet" cleaning, and the liquid film plays an auxiliary role in removing some difficult-to-remove attachments. Although the method produces waste liquid, compared with the traditional chemical cleaning method, the amount of waste liquid produced is small and the harm is less. For the flammable, corrosive or toxic dirt in the petrochemical industry, in order to avoid the burning or diffusion of pollutants during laser cleaning, "wet" cleaning can be used, that is, the appropriate liquid film can be used to flame-retardant or absorb pollutants, and can also be used according to needs. Useful components are extracted from waste liquid to save raw materials. High power, high repetition rate pulsed lasers can also be used for "dry" cleaning, converting part of the beam into sound waves. The reflected sound wave and the incident sound wave interfere with each other to generate high-energy waves, and the explosion impact in a small area turns the dirt layer into powder, which is removed with a vacuum device to avoid the spread of pollutants.
