Study On Process Parameters Of Laser Cleaning Contamination Layer On Surface Of Ceramic Artifacts

Ceramic artifacts are an important part of China's historical and cultural heritage,a reflection of China's broad and profound culture,and a wisdom crystallization of Chinese people.The unearthed ceramic artifacts will be eroded by various substances in nature for hundreds or thousands of years,and it is difficult to clean up the contamination covering on them.Therefore,the cleaning,protection and restoration of the unearthed ceramic artifacts are particularly important.Laser cleaning,a new surface cleaning technology,has become one of the core cleaning technologies in the cultural relics protection for its advantages of no mechanical contact,no basement damage,selective cleaning,green environmental protection,high safety,wide application,low cost and so on.The related research in this field abroad has a history of more than 20 years.However,it starts relatively late in China and the research on laser cleaning technology applied in ceramic artifacts protection is even less.Under this background,the combination of laser cleaning technology and ceramic artifacts protection is necessary,and the process parameters of laser cleaning contamination on the surface of ceramic artifacts are studied in this paper,including the selection of cleaning methods and the optimization of cleaning parameters.Firstly,the layer-by-layer ablation cleaning method and thermal stress cleaning method are compared in the experiment.It is found that the efficiency of thermal stress cleaning method is much higher than that of layer-by-layer ablation cleaning method,and the basement temperature by thermal stress cleaning method is lower.Simultaneously,there is no damage found after thermal stress cleaning.Therefore,the thermal stress cleaning method is chosen.Then,the parameter for evaluating the thermal stress cleaning effect is determined in the experiment,and the influence of laser power,scanning speed,laser repetition rate and pulse duration on the cleaning effect is discussed.It is found that laser power and scanning speed are the two key parameters determining the cleaning effect,and the multiple changes of laser repetition rate and pulse duration have little influence on the cleaning effect for high repetition nanosecond pulsed laser.After that,the upper and lower limit curves of cleaning threshold related to the laser power and scanning speed are measured in the experiment.Finally,a cleaning model of quasi-three dimensional double-layer structure is constructed.Based on the heat conduction equation,equilibrium equation,geometric equation and generalized Hooke's law,the temperature field and stress field distribution of the model are simulated under the initial and boundary conditions determined by the actual environment.It is considered in the simulation that the produce of cleaning effect should need two points:firstly,the maximum peeling stress at the contact surface is greater than the adhesion stress;secondly,the radial length of peeling stress greater than the adhesion stress is larger than the selected step distance in the cleaning process.On this foundation,the reason why the laser repetition rate and pulse duration have little influence on the cleaning effect is explained quantitatively,and a group of lower limit cleaning thresholds related to laser power and scanning speed is obtained in the simulation,which is consistent with the experiment.