First, the principle of laser cleaning Industrial pipelines are used in the tubular facilities of oil, chemical and other enterprises, including pipes, valves, pipe fittings and so on. Pipes are widely used in the industrial field, and attention must be paid to the removal of dirt inside the pipes when using pipes. After high-pressure water cleaning or pig technology treatment, passivation treatment is also required. After the passivation operation is completed, the pipeline can be kept from oxidation for a long time. Industrial cleaning is sometimes required to keep the equipment running. The final passivation operation is critical and requires passivation immediately after the previous operation is completed to slow the corrosion of the pipe.
The laser has high brightness, high directivity, high monochromaticity and high coherence, which is unmatched by ordinary light sources. With the high brightness of the laser, after focusing by the lens, it can generate tens of millions of degrees or even tens of thousands of degrees of temperature near the focus. The high directivity of the laser allows the laser to be efficiently transported over long distances. The laser's monochromaticity is extremely high and the wavelength is single, which is good for focusing and wavelength selection.
Laser cleaning can be divided into two categories according to its cleaning mechanism. It uses a clean substrate (also called a mother) and a surface attachment (dirt) to have a very different absorption coefficient for a certain wavelength of laser energy. . The laser energy radiated to the surface is mostly absorbed by the surface deposits, so that it is heated or vaporized to evaporate, or instantaneously expands, and is driven by the vapor stream formed on the surface to separate from the surface of the object for cleaning purposes. The substrate is not damaged by the absorption of laser light at this wavelength. For this type of laser cleaning, choosing the right wavelength and controlling the laser energy is the key to safe and efficient cleaning. The other type is a cleaning method that is not sensitive to the difference in laser energy absorption coefficient between the cleaning substrate and the surface attachment, or that the substrate is sensitive to the acidic vapor formed by the coating, or the toxic substance is generated after the coating is heated. . This type of method usually uses a high power, high repetition rate pulsed laser to impact the surface being cleaned, and converts part of the beam into sound waves. After the sound wave hits the lower hard surface, the near portion and the incident sound wave generated by the laser are slightly exploded, the coating is pulverized, pressed into a powder, and then removed by the vacuum pump, and the underlying substrate is not damaged.
Compared with traditional cleaning methods such as laser cleaning, mechanical friction cleaning, liquid solid impact cleaning, and high-frequency ultrasonic cleaning, laser cleaning has obvious advantages. It is efficient, fast, low cost, low heat load and mechanical load on the substrate, cleaning is non-injury; waste can be recycled, no environmental pollution; safe and reliable, does not damage the health of operators; multi-functional, can remove various differences Thickness, different composition of the coating; easy to achieve automatic control of the cleaning process, remote remote cleaning.
Second, the method of laser cleaning
From the method analysis, the laser cleaning method has four kinds of 1 laser dry cleaning methods, that is, direct pulse radiation decontamination using pulsed laser; 2 laser + liquid film method, that is, first depositing a liquid film on the surface of the substrate, and then decontaminating with laser radiation; 3 laser + inert gas method, that is, while irradiating the laser, the inert gas is blown to the surface of the substrate, and when the dirt is peeled off from the surface, it will be immediately blown off the surface by the gas to avoid the surface being re-contaminated and oxidized; After the dirt is loosened, it is cleaned by non-corrosive chemical methods. Currently, the first three methods are commonly used. The fourth method is only found in the cleaning of stone artifacts.
Third, the application of laser cleaning
Stone carvings and stone carvings, such as the high-grade stone art, have become the earliest applications of laser cleaning technology due to their extremely fine and fragile surface structure. It has been found that the use of lasers to remove dirt from the surface of stone artifacts has its unique advantages. It can very accurately control the movement of the beam on complex surfaces, removing dirt without damaging the artifact stone. For example, in September 1992, the World Cultural Heritage Protection Organization organized by the United Nations Textbook Organization commemorated the 20th anniversary of the organization and repaired the very famous English Amiens Cathedral. The beautiful marble of the Virgin Mary on the west side of Amiens Cathedral Engraving is the key to engineering. In the one-year maintenance project of the Notre Dame, the maintenance personnel used the laser to remove the black scale layer covering the marble engraving pattern by a few millimeters thick. The original color of the marble surface was reflected, which made the exquisite carving reappear. Glorious. For example, the stone carvings of Insbrentier, one of the most important stone carving collections in the UK, have been laser-cleaned and have the same effect. Figure 1 shows Austrian cultural relics cleaning the stone carvings on the St. Stephen's Cathedral in the mid-14th century with a YAG laser with articulated arms.
The surface of the stone after laser cleaning was observed with an electron microscope. It was found that the structure of the stone after laser cleaning did not change, and the surface to be cleaned was smooth and flat without damage. This is completely different from the surface cleaned by the microparticle spray method (blasting method).
Damage to the surface structure of the marble after microparticle spray cleaning is inevitable, especially for marble surfaces with existing sulfate scales. Observation by electron microscopy also revealed that the properties of the underlying rock material were neither degraded nor altered after laser irradiation. At present, the work of cleaning the lime with laser, the surface of high-grade stone materials such as marble has become a new promising business project. In addition to the cleaning of stone materials, laser cleaning has a good effect in the cleaning of glass, quartz, metal, mold, teeth, chips, electrodes, magnetic heads, magnetic disks and various microelectronic products. application.
Fourth, laser cleaning benefit analysis
In addition, the industry also uses lasers to periodically clean the mold to ensure the quality of the product. The following is an example of laser cleaning of the tire mold to illustrate the economic benefits of laser cleaning compared with offline blast cleaning and dry ice cleaning equipment. The laser cleaning technology has obvious advantages, rapid cleaning, low labor intensity, no wear and no danger to the operator. However, the initial investment in equipment is relatively high, reaching $300,000 to $600,000. Therefore, the factory needs to establish a cash return plan. A typical JET laser system plant can achieve investment recovery within 18 months. Shorter vulcanization downtime, low labor costs, less mold wear and lower production costs are potential benefits. For example, a machine with a daily output of 20,000 tires is required to be cleaned once a day by 8 vulcanizers (16 modules). It is assumed that 3 vulcanizers are cleaned per shift or 9 vulcanizers are cleaned every day (some factories clean twice) Remove the two molds from the friendship game machine for offline cleaning. It takes about 15 hours of operation and 10 hours of downtime. If the two half molds are cleaned by laser, 03h operation and 3h downtime are required. Cleaning a vulcanizer saves 14 hours of operation and 7 hours of downtime. It is also assumed that only 10 cleanings (5 sets of friendship sulfur machines) and 5 times of offline cleaning in the mold shop will result in huge returns with 70 hours of operation and 35 hours of downtime per day. A working day of 320 days a year can increase the number of operations by 22,400 hours and 11,200 hours per year.
The cost of repair and maintenance of the laser cleaning equipment should also be taken into account. To clean the laser mirror and remove the residue deposited on the filter, the device should be maintained for 30 minutes per week, and the main components should be repaired for 60 minutes every 4 weeks. . The unit is routinely maintained and the laser system is operated every 6 months according to the manufacturer's requirements. Most mechanical components have the same lifetime as the laser frame for more than 10 years, and some laser components require replacement after approximately 3000 hours of use. These parts can be replaced in the field during routine preventive maintenance. The laser unit plus its one-year warranty, including the replacement of consumables and the provision of typical spare parts, ultimately cost about $4 to $8 per hour. All devices are equipped with a Modem (modulator) so that the manufacturer can provide remote services.
Based on the above factors, the overall economic benefits of laser cleaning technology are very significant.
Laser processing and cutting processes have been around for many years, but laser cleaning of the surface is a relatively young technology. Although this process removes all organic materials (such as chewing gum removal), its use in industrial cleaning has only recently begun. It is believed that with the development of lasers and the continuous improvement of laser cleaning technology, more and more applications will be obtained in various cleaning fields.