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【Application】An introduction to laser cleaning technology and its application in the tire industry
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【Application】An introduction to laser cleaning technology and its application in the tire industry

【Application】An introduction to laser cleaning technology and its application in the tire industry

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(Summary description)Cleaning technology is often required in industrial production, heritage conservation and in the treatment of dental diseases. For example: industrial products in electroplating, phosphating, spraying, welding, packaging and integrated circuit assembly, in order to ensure the quality of the workpiece in the next process, must remove the product surface grease, dust, rust, dirt or residual solvent, binder and other dirt. Due to environmental pollution and poor protection, many cultural artifacts and works of art are gradually being corroded and defaced, in order to restore the old appearance, it is necessary to clean the dirt and rust on the surface of cultural artifacts.

【Application】An introduction to laser cleaning technology and its application in the tire industry

(Summary description)Cleaning technology is often required in industrial production, heritage conservation and in the treatment of dental diseases. For example: industrial products in electroplating, phosphating, spraying, welding, packaging and integrated circuit assembly, in order to ensure the quality of the workpiece in the next process, must remove the product surface grease, dust, rust, dirt or residual solvent, binder and other dirt. Due to environmental pollution and poor protection, many cultural artifacts and works of art are gradually being corroded and defaced, in order to restore the old appearance, it is necessary to clean the dirt and rust on the surface of cultural artifacts.

Information

I. INTRODUCTION

        Cleaning technology is often required in industrial production, heritage conservation and in the treatment of dental diseases. For example: industrial products in electroplating, phosphating, spraying, welding, packaging and integrated circuit assembly, in order to ensure the quality of the workpiece in the next process, must remove the product surface grease, dust, rust, dirt or residual solvent, binder and other dirt. Due to environmental pollution and poor protection, many cultural artifacts and works of art are gradually being corroded and defaced, in order to restore the old appearance, it is necessary to clean the dirt and rust on the surface of cultural artifacts.

        Traditional cleaning methods include mechanical cleaning method, chemical cleaning method and ultrasonic cleaning method, mechanical cleaning method that uses scraping, rubbing, brushing, sand blasting and other mechanical means to remove surface dirt; wet chemical cleaning method is the use of organic cleaning agent, by spraying, pouring, soaking or high-frequency vibration and other measures to remove surface attachment property ultrasonic cleaning method is to be treated parts into the cleaning agent, the use of ultrasonic vibration effect to remove dirt.

        At present the three kinds of cleaning method in our country cleaning market is still dominant, but in environmental protection and high precision under the requirements of its application is subject to great restrictions. Mechanical cleaning method can not meet the requirements of high cleanliness cleaning, easy to damage the surface area of the workpiece to be cleaned and chemical cleaning method is likely to lead to environmental pollution, access to cleanliness is also very limited, especially when the complex composition of dirt, must use a variety of cleaning agent repeatedly cleaned before possible to meet the requirements of surface degreasing. Ultrasonic cleaning method despite the cleaning effect is good, but the cleaning of sub-micron dirt particles can not help, the size of the cleaning tank limits the scope and complexity of the processing parts, and after cleaning the drying of the workpiece is also a major problem.

        In recent years, as people's awareness of environmental protection increased, to the worldwide cleaning industry has brought great challenges to the development of a variety of environmental protection cleaning technology has emerged, laser cleaning technology is one of them.

        The so-called laser cleaning technology refers to the use of high-energy laser beam irradiation of the surface of the workpiece, so that the surface of the dirt, rust or coating occurred instant evaporation or stripping, high-speed and effective removal of cleaning objects surface adhesion or surface coating, so as to achieve a clean process. It is based on the laser and material interaction effect of a new technology, and the traditional mechanical cleaning method, chemical corrosion cleaning, liquid solid strong impact cleaning, high-frequency ultrasonic cleaning and other traditional cleaning methods, compared with the obvious advantages. It is efficient, fast, low cost, the thermal load on the substrate and mechanical load is small, cleaning for non-damage; waste recycling, no environmental pollutants safe and reliable, no harm to operator health certificate can remove a variety of different thickness, different composition of the coating level cleaning process is easy to achieve automated control, remote remote remote cleaning and so on.

Second, the principle and method of laser cleaning

        Lasers are characterized by high directionality, monochromaticity, high coherence and high brightness. By focusing and Q-switching of the lens, the energy can be concentrated to a small spatial and temporal range. In laser cleaning treatments, the following properties of lasers are utilized.

1, laser can achieve a high degree of concentration of energy in time and space, focused laser beam in the focus near the focus can produce thousands of degrees or even tens of thousands of degrees of high temperature, so that instantaneous evaporation of dirt, gasification or decomposition.
2, the laser beam divergence angle is small, good directionality, through the condensation system can make the laser beam gathered into different diameters of the spot. In the laser energy under the same conditions, control of different diameters of the laser beam spot can adjust the laser energy density, so that the fouling is heated and expanded. When the expansion of dirt is greater than the dirt on the adsorption of the substrate, dirt will be separated from the surface of the object.
3, the laser beam can be generated by ultrasonic waves in the solid surface, produce mechanical resonance, so that the dirt broken off.

        Laser cleaning technology is the use of the above-mentioned characteristics of the laser to achieve the purpose of cleaning. According to the substrate material to be cleaned and the optical properties of the dirt to be removed, the laser cleaning mechanism can be divided into two categories.

        One type of cleaning substrate (also known as the matrix) is used to clean the surface attachment (dirt) and the absorption coefficient of a particular wavelength of laser energy is very different. Radiation to the surface of the laser energy is mostly absorbed by the surface attachment, which is heated or vaporized by evaporation, or instantaneous expansion, and the formation of airflow, from the surface of the object, to achieve the purpose of cleaning. The substrate due to the wavelength of the laser absorption energy is very small, will not be damaged. For such laser cleaning, select the appropriate wavelength and control the laser energy size, is the key to achieve safe and efficient cleaning.

        Another class applies to clean the substrate and the surface adhesion of the laser energy absorption coefficient is not much difference, or substrate on the formation of heat coating acidic vapors are more sensitive, or the coating will produce toxic substances after heat cleaning method. This type of method is usually the use of high power and high repetition rate of pulsed laser impact is cleaned surface, so that part of the beam into sound waves. Sound waves hit the lower hard surface, return to the part and laser generated by the incident sound waves interfere, producing high-energy waves, so that the coating explosion occurred in a small area, the coating is pressed into powder, and then removed by the vacuum pump, and the substrate underneath but not damage.


        Analysis from the method, laser cleaning method has 4 kinds: 1, laser dry cleaning method, that is, the use of pulsed laser direct radiation decontamination; 2, laser + liquid film method, that is, the first deposition of a layer of liquid film on the surface of the matrix, and then use laser radiation decontamination; when the laser irradiation on the liquid film, liquid film is dramatically heated, resulting in explosive vaporization, explosive shock waves make the matrix surface of the dirt loose. And with the shock wave fly away from the surface of the processing object, to achieve the purpose of decontamination.3, laser + inert gas method, that is, in the laser radiation at the same time, with an inert gas blown to the surface of the matrix, when the dirt from the surface stripping will be immediately blown away from the surface by the gas, in order to avoid re-contamination of the surface and oxidation; 4, the use of laser so that the dirt loose, and then non-corrosive chemical methods of cleaning. At present, the commonly used is the first 3 methods. The fourth method is applied only to the cleaning of stone cultural relics, and a complete laser cleaning system includes: laser or YAG laser), sample processing station, light guide system, console, auxiliary systems (such as calorimeter, beam profiler and its accessories). For laser + liquid film cleaning methods, liquid film deposition systems are also available. When using laser + inert gas cleaning method, should also include inert gas into and out of the system.

Third, the laser cleaning application status

        High-grade stone artworks of long ages, such as stone sculptures and stone carvings, have become the earliest field of application of laser cleaning technology due to their extremely fine and fragile surface structure. It has been found that the use of laser to remove dirt on the surface of stone cultural relics has its unique advantages, it can be very precise control of the light beam in the complex surface movement, remove dirt without damage to the cultural relics of stone.

        For example, in September 1992, the UNESCO World Cultural Heritage Protection Organization, to commemorate the organization's twentieth anniversary, carried out a repair project on the famous Arminian Cathedral in England. The exquisite marble carvings on the west side of the door of Our Lady of Armin is the key to the project. In a year of the Virgin Mary Gate maintenance project, maintenance personnel with the help of laser, with a laser beam to remove a few millimeters thick layer of black dirt covering the marble carvings on the pattern, the original color of the marble surface reflects, make the exquisite carvings regain its glory.

        Another example: Britain's most important stone carving collection of one of the Innsbrentir stone carving collection by laser cleaning, also got the same effect. People used an electron microscope to observe the surface of the stone carvings after laser cleaning, and found that the structure of the stone did not change after laser cleaning, and the surface that was cleaned was both smooth and flat, without damage. This is with the particle blasting method (sand blasting method) after cleaning the surface is completely different. Micro-particle jet method after cleaning the marble surface structure damage is difficult to avoid, especially for the existing sulfate layer of marble surface. Electron microscope observation also found that, after laser irradiation, the surface of the rock material under the properties of neither degradation, nor change.

        At present, with laser cleaning limestone, marble and other high-grade stone material surface dirt work has become a new very promising business project. In addition to the stone material cleaning, laser cleaning in glass, metal, mold, disk and various microelectronics products have good effect, in the production of automobile tires, tire mold bottom and surrounding pattern every two to three weeks need to clean once, every few months will be the whole mold thoroughly cleaned once. Traditional method is to use chemical soaking or sand blasting cleaning, not only expensive, noise, serious pollution, but also affect the surface quality of the mold.

        In addition, this kind of cleaning method can't realize online cleaning, cleaning before the demolition of the mold and cleaning after the installation of the mold is time-consuming and long, affect the normal operation of the production line. The use of laser technology to clean moulds can realize online cleaning operation. According to the mould surface organic adhesions and rubber structure of the different, cleaning a set of mould only 45-90 minutes (including loading and unloading and cleaning mould parts on both sides). The surface of the mould is not damaged by the laser as it reflects the laser beam. Laser cleaning has a very high flexibility, the user can use this technology instead of other methods in use. At present, foreign countries have used YAG laser in the tire production line to realize the tire mold online cleaning, and has been applied to the industry. When the mold needs to be cleaned, at the end of curing at the same time open the curing machine, the laser mold cleaning system will be moved to the curing machine before the mold cleaning, no need to wait for the mold cooling.

Also note that

        The time required to clean the mold is independent of the temperature of the mold. The operator starts the cleaning process by pressing the head of the laser cleaning system against the mold. During the cleaning process, the laser beam scans the surface of the mold and illuminates it from four different angles, which ensures that all types of molds are cleaned. After cleaning half of the mold, the head of the system is moved to the other half of the mold to clean it. After the mould has been completely cleaned, the cleaning device is moved to another vulcaniser mould to be cleaned. The cleaned vulcanizer is ready for immediate production. In addition to cleaning moulds, industrial applications also include tire marking, removing brake lines and other parts of the coating or flat wire stripping on the wire.

        At present, foreign countries have used YAG laser in the tire production line to achieve the tire mold online cleaning, and has been applied to the industry. If the system is running at full capacity, with the original tire factory cleaning 1500 pairs of moulds a year, can save production time 6000h; tire production can be increased by about 30,000 sets. Not only environmental protection, economic benefits are also considerable.

        Laser cleaning technology application in Europe to promote the application has been several years now, and have products, and our country only just started, mainly laser equipment investment is expensive, universal application there is a certain degree of difficulty, laser cleaning technology and traditional cleaning technology, compared with incomparable advantages. At present, the tire mold high efficiency and low cost cleaning methods urgently need to promote, according to incomplete statistics, China's tire and its products manufacturers thousands, annual output of a million sets of tires above the enterprise also no less than 2000. Annual output in a million sets of tires manufacturers have tens of thousands of sets of moulds, and a set of moulds to use about 3 weeks to clean once. Can see the significance of promoting the application of laser technology cleaning. I believe that in this technology continues to improve on the basis of mass production equipment, with the equipment, laser cleaning technology will play an important role in the tire mold cleaning or other cleaning industry, has very good prospects for development.

Four, laser cleaning benefit analysis

        The following is an example of laser cleaning of tire molds to illustrate the economic benefits of laser cleaning compared to offline blasting and dry ice cleaning equipment. Laser cleaning technology offers significant advantages: it is fast, labour-intensive, non-abrasive, and non-hazardous for the operator.

        However, the initial investment in the equipment is high - $300,000 to $600,000. The plant therefore needs to establish a reasonable payback plan. A typical JET laser system plant can achieve payback in less than 18 months. Short vulcanization downtime, low labor costs, low tooling wear and tear, and low production costs are potential benefits. For example, a machine producing 20,000 tires per day, with 8 curing machines (16 dies) required to be cleaned on average once per day, assuming 3 curing machines are cleaned per shift or 9 curing machines are cleaned twice per day (some plants clean twice) to remove the two halves of the mold from the curing machine for offline cleaning, requires approximately 15h of operation and 10h of downtime, and if the two halves of the mold are cleaned by laser, it requires 0.3h of work and 3h of downtime, so that, after cleaning a vulcanizer can save 14h of work and 7h of downtime. And suppose, only do 10 times cleaning (5 curing machine), 5 times in the mold shop for offline cleaning, using laser cleaning will produce great returns: every day can save 70 hours of operation and 35 small downtime, then according to a year 320 days of working days, an annual increase of 22,400 hours of operation and 1,200 hours of machine time.

        Laser cleaning equipment repair and maintenance costs should also be taken into account, in order to wipe the laser mirror and remove residues deposited on the filter, the unit needs to be serviced 30 min per week, and the main components every 4 weeks for 60 min. Routine maintenance and operation of the laser system every 6 months in accordance with the manufacturer's requirements. Most of the mechanical parts can be used for more than 10 years as well as the laser frame, some laser parts require replacement after about 300h of use. These parts can be replaced on site during routine preventive maintenance. The laser unit plus its one-year warranty is included. Including the replacement of wearing parts and providing typical spare parts, the total operating cost is approximately $4-8 per hour. All units have modems (modems) installed so that the manufacturer can provide remote service.

        Combination of the above factors, overall, the economic benefits of laser cleaning technology is very significant.

V. Summary and outlook

        Laser cleaning technology than the traditional cleaning technology has great advantages in economic efficiency and "green" engineering aspects can bring great benefits to society, the market prospects are quite broad. China's current research in this area is still not enough, if we can use our existing laser technology, the development of supporting laser cleaning equipment, and put it into production, industrialization, is entirely possible. With the decline in the cost of lasers, will make laser cleaning technology gradually to be popularized, which to promote the development of high-tech industry itself is also of great significance.

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