Study Of Continuous Co₂ Laser Cleaning Of Rust From Iron Substrate

Removal of contaminant is a hard and arduous work. There are some shortcomings in the traditional cleaning methods. Laser cleaning is a kind of technique which by using laser irradiation to clean the dirty site in a series of complicated physical and chemical processes, and make contaminants ejecte from the surface. For its own unique merits, Laser cleaning technology has become a major research area in recent years.The purpose of this thesis is by using CW-CO2 laser which is very few reported with different intensity and speed to scan the surface of rust on iron substrate, by analyzing the heat distribution, to search interactional relations among optical power, scanning speed and other physical parameter in derusting and to find a better solution based on the dirt and substrate in the actual laser decontamination process in future.The prime tasks as follows:1. The mechanism of continuous CO2 laser cleaning of rust from iron substrate is discussed in this thesis. According to the results of this experiment. The writer thinks the effect of light and heat play the most important role in laser derusting. According to a tremendous difference between rust and iron in absorption coefficient (rust absorption coefficient is about 0.7, but iron only 0.035). In this experiment, the laser effects with rust at once, morn than 60% of irradiation laser energy will be absorbed by rust, only 10% laser can arrive at iron substrate, almost 10% transmission is reflected by iron body and is absorbed by rust again. At a very short period(in this experiment the longest derusting time is 0.3s) rust temperature can reach its boiling point(about 3000K), going with rapid nitrogen flows the surface of sample, some rust which does not reach the boiling point can fly off surface due to thermal expansion.2. By using software of Mathematica and ANSYS finite element, the writer analyzes the internal temperature distribution in various lays of the rust and iron substrate, especial relations between the surface temperature and the parameters of laser, building a model about laser removal-rust. According to heat conduction formula, thinking over actual process of laser removal-rust, the writer taking full account of the performance parameters which changes with the temperature, basing on finite element analysis software established temperature-heat transfer model, acquiring the curves of temperature with time, thermal conductivity depth and laser energy density.