Study On Laser Cleaning Of Particles On The Surface Of High Boric Acid Glass

High boric acid glass is needed to realize its light transmission function in special nuclear reactor window,high-rise building outer wall,automobile windshield,steel manufacturing enterprise control workshop and other applications.However,in the process of using glass,it is easy to stick particle pollutants,and the removal of particle pollutants is mainly done by human,so the operation efficiency and cost are relatively high.And in some cases,it is dangerous,especially the window of nuclear reactor can not be completed manually.The laser cleaning technology is to use the direct or indirect interaction between the laser and the material to remove the pollutants from the surface of the object to be cleaned.Compared with the traditional cleaning,laser cleaning has the advantages of good stability,no mechanical contact,wide application range and positioning cleaning.In this paper,the positive and negative surfaces of high boric acid glass are cleaned dry and wet to master the laser cleaning mechanism of glass and provide theoretical and experimental basis for laser cleaning of glass.The main conclusions are as follows:（1）When the pulse width is 10～100ns,the main peeling mechanism of dry cleaning is the thermal expansion of particles.When the pulse width is 240 ns,the peeling mechanism is the impact force formed by the shock wave generated by the thermal explosion of particles.When the pulse width is 10～100ns,the peeling mechanism of front and back wet cleaning is the stress wave generated by bubble nucleation,and the position of stress wave is different.The front wet cleaning mainly occurs in the middle and upper surface of the liquid film.From the cleaning effect,the position of bubble generation is in the middle,and the back wet bubble mainly occurs on the contact surface.When the pulse width is 240 ns,the bubble generation speed is limited,at this time,the bubble surface will collapse and collapse,resulting in cavitation phenomenon,which will generate the sound wave amplitude in the form of wave to form a lateral cleaning force.（2）Through the comparison of four cleaning methods,it can be concluded that the opposite wet cleaning has the best effect.The dry cleaning needs high energy and is easy to cause damage to the glass surface.In dry cleaning,the minimum cleaning power density is 0.12×10⁶W/cm²,and the minimum damage power density is5.72×10⁶W/cm².It is easy to form the phenomenon of"dust accumulation"when cleaning the fine particles.This phenomenon is mainly caused by the lap ratio and is inevitable.Dry cleaning will increase the cleaning process if it has the selectivity to the type of particles.The reason why the front wet cleaning can reduce the probability of damage is that the liquid film hinders the expansion of laser heating materials,and there is no dust accumulation phenomenon when cleaning small particles.When the power density increases to the maximum,it is easy to form"plume effect"which will damage the substrate.At this time,the lowest damage power density is3.82×10⁶W/cm²,and the lowest cleaning power density is 0.119×10⁶W/cm².In this case,the damage threshold and the cleaning threshold are the same as those of the negative wet type.（3）Through the optimization of the back wet cleaning parameters,when the power density is 4.77×10⁶W/cm²,the scanning speed is 1500mm/s,the pulse width is130ns,the longitudinal and transverse overlap rate is 50%,and the cleaning effect is the best when the scanning times are 15.In the same case,the power and scanning times needed for cleaning Si O₂particles are less,and the cleaning effect for oil and ink is better.