20w UV Laser Marking Source for cleaning steel surface paint

Achievement introduction: Scholars from Harbin Institute of Technology used an environmentally friendly nano-ultraviolet (UV) laser to innovatively apply laser cleaning to the paint on the surface of AH36 steel. The possibility of using this UV laser for cleaning was innovatively proposed and experimentally verified, and further verification was carried out using a theoretical model. The surface quality after laser cleaning was characterized. Its mechanical properties, such as surface microhardness, tensile strength and flexural strength, were characterized. The results show that laser cleaning has very significant advantages as a means of replacing traditional paint removal in marine engineering.

1. Background introduction

Surface cleaning has received much attention over the past few decades, especially in the fields of aerospace, marine engineering, microelectronics, and medicine. The pollutants on the surface of living organisms are nothing more than the presence of oxides, paints, polymers, coatings, microorganisms and particulates on the surface. Ships cruising in the sea are of great concern because they are mainly subject to severe corrosion caused by seawater. For this reason, ships often have to remove the surface paint layer after a period of service, and at the same time carry out the maintenance process of new paint. In particular, it is important to note that each of the above process operations consumes billions of dollars in annual budgets. Therefore, the removal of paint from the surface of the substrate for re-coating and thereby extending the life of the vessel is critical. Looking at previous studies, traditional surface cleaning methods, including mechanical and chemical cleaning methods, are currently the most common methods. However, the problem with these means is that they either pollute the air and water, or generate secondary polluting waste. Based on this consideration, laser cleaning technology, as an emerging surface cleaning technology, is considered to be the most advanced technology to replace traditional cleaning technology, because laser cleaning technology is considered to be more environmentally friendly and does not require contact the surface of the object being cleaned. Depending on the (including but not limited to) excellent plasticity and strength, high mechanical properties and accompanying light weight of AH36 steel, AH36 steel is widely used in marine engineering. However, it should be emphasized that the service life of this steel is strongly affected by the marine environment in which it is used, and a large number of highly corrosive ions and microorganisms existing in the marine environment will act synergistically to accelerate the surface degradation of the steel substrate. Peeling of the coating. Immediately afterwards, the inner layer of the steel matrix surface will also begin to continue to fail when exposed to the harsh ocean. Therefore, surface cleaning becomes necessary as it allows the removal of surface damaged paint and contaminated substrate surfaces. There has been a lot of work on laser cleaning paint. Back in 1974, J.A. Fox pioneered the use of Q-switched lasers for paint removal. It has been reported that the paint layer on the surface can be effectively removed under intense laser photon-induced stress. In addition, K.Liu and F.Garmire et al. used different types of lasers and different pulse widths for depainting. It has been reported that Nd:YAG lasers with Q-switched mode are more effective in removing paint than other lasers, such as CO2 lasers, excimer lasers, and CW lasers. Chen et al.'s study also pointed out that the use of laser cleaning, compared with the traditional cleaning technology, overcomes the main shortcomings, such as secondary pollution.

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However, current laser cleaning, mainly nanosecond lasers in the infrared band, usually exploits thermally induced defects, which means that recast layers and heat-affected zones are formed on the surface of the object. On the other hand, UV lasers may avoid these problems because UV lasers rely on photon energy and the corresponding breakdown of molecular bonds. To the authors' knowledge, there have been no studies using UV lasers to remove paint layers. More importantly, the influence of the corresponding process parameters on the cleaning effect is also unclear. In this study, scholars from Harbin Institute of Technology used UV lasers for the first time to carry out research on removing paint, and changed the laser energy to carry out research. Further, the cleaned samples were tested in metallography, scanning electron microscope and optical profile measurement, as well as mechanical properties.

2. Laser cleaning mechanism

In this experiment, the ultraviolet laser produced by Huari, a unit of Jiangsu Laser Alliance, was used. The mechanism of action is: it is generally believed that in the process of laser cleaning, the photochemical interaction, that is, the energy of the photons emitted by the UV laser, is much greater than the energy of the molecular bonding inside the material, which in turn further destroys the molecules. bonding.

3. Experimental results

Based on the innovative use of nanosecond UV laser to laser peel the paint layer on the AH36 substrate. This innovative experiment has theoretically and practically demonstrated the feasibility and effectiveness of UV laser cleaning of AH36 steel surface paint, as well as the basic interaction mechanism of UV laser, such as photothermal and photochemical interactions. A thermodynamic model was established to describe the relationship between temperature and laser energy, and the results showed that the threshold value for laser cleaning was 4.65 J/cm exp(2) which was very close to the theoretical value (the theoretical value was 5 J/cm exp( 2)). At the same time, the existence of this difference is discussed. The surface morphology, chemical composition, and mechanical properties before and after laser cleaning were also evaluated in detail by SEM, EDS, optical profiler, and mechanical property testing methods. After SEM testing, there are some typical wrinkled shapes, pits and circular microstructures on the surface under different laser energy input conditions. Regarding the mechanical properties, it should be mentioned that the removal of paint by UV laser can significantly improve the surface microhardness, tensile strength and flexural strength. This is attributed to the rapid melting and solidification experienced during surface cleaning with UV lasers, resulting in a microstructure of round and wrinkled morphology, along with a high density of dislocations. Therefore, this advanced UV-nanosecond laser cleaning technology is not only environmentally friendly, but also can significantly improve the mechanical properties of parts after laser cleaning. It can be expected that this promising method will be used for large-scale depainting of marine engineering surfaces and its application in marine engineering and other industrial fields in the future.