MXPA98000554A - Deflecting metal with a laser device that has a very short drive duration and average power a - Google Patents
Deflecting metal with a laser device that has a very short drive duration and average power aInfo
- Publication number
- MXPA98000554A MXPA98000554A MXPA/A/1998/000554A MX9800554A MXPA98000554A MX PA98000554 A MXPA98000554 A MX PA98000554A MX 9800554 A MX9800554 A MX 9800554A MX PA98000554 A MXPA98000554 A MX PA98000554A
- Authority
- MX
- Mexico
- Prior art keywords
- radiation
- laser
- oxide
- optical element
- lens
- Prior art date
Links
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 97
- 239000002184 metal Substances 0.000 title claims abstract description 97
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- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims abstract description 21
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- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 4
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- 150000007513 acids Chemical class 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- -1 ferrous metals Chemical class 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 229910001220 stainless steel Inorganic materials 0.000 description 3
- 239000010935 stainless steel Substances 0.000 description 3
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- PFNQVRZLDWYSCW-UHFFFAOYSA-N (fluoren-9-ylideneamino) n-naphthalen-1-ylcarbamate Chemical compound C12=CC=CC=C2C2=CC=CC=C2C1=NOC(=O)NC1=CC=CC2=CC=CC=C12 PFNQVRZLDWYSCW-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 239000004743 Polypropylene Substances 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
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- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 2
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910000599 Cr alloy Inorganic materials 0.000 description 1
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 1
- 229910000677 High-carbon steel Inorganic materials 0.000 description 1
- 229910000990 Ni alloy Inorganic materials 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- UAIXRPCCYXNJMQ-RZIPZOSSSA-N buprenorphine hydrochlorie Chemical compound [Cl-].C([C@]12[C@H]3OC=4C(O)=CC=C(C2=4)C[C@@H]2[C@]11CC[C@]3([C@H](C1)[C@](C)(O)C(C)(C)C)OC)C[NH+]2CC1CC1 UAIXRPCCYXNJMQ-RZIPZOSSSA-N 0.000 description 1
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 description 1
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Abstract
The present invention relates to an apparatus for removing oxide from a metal strip surface, characterized in that it comprises: a laser for producing electromagnetic radiation having a very short pulse width, a very high pulse repetition rate and a very high average power , at least one optical element for focusing the radiation on an incident beam having a surface power density of at least about 5 MW / cm2 at a point of contact with the metal strip and a sealed interaction chamber for removing strip oxide metal, the chamber contains a non-oxidizing gas and a slotted inlet to receive a moving metal strip that has a surface covered with a rust, a grooved outlet for the passage of the metal strip that has rust removed from the surface, at least one elongated window to receive the radiation in the camera, with which the radiation can be crossed transversally and complet amente through the surface cover oxide to remove peroxide by vaporization
Description
DES INCRUSTATION OF METAL WITH A LASER DEVICE THAT HAS A -D RACIO-N OF -IMPULSOS.MUY SHORT AND A HIGH AVERAGE POWER
FIELD OF THE INVENTION
This invention relates to a process and apparatus for using electromagnetic radiation to remove rust from a metal. More specifically, the invention includes using a pulsed or pulse laser to produce electromagnetic radiation having very short pulse width or duration, a very high pulse repetition ratio and a high average power, to descaling the metal by vaporization of molecular layers of the oxide, with each impulse.
-ANTECJ3.DE. TES OF THE INVENTION
One of the most environmentally intensive operations in the metal fabrication industry is the acid-wet pickling of a metal such as steel to remove the rust or scale that forms
REF: 26603 during hot processing, such as forging, lamination for band, hot, or annealing. The techniques to remove these incrustations have changed little since the beginning of the century. The majority of steel strips of electric furnace and low carbon steel are decanted by hydrochloric acid at belt speeds of approximately 250 m / min. Stainless steel has incrustations or scales that adhere more strongly can require the blasting csn shot or roller leveling, to lose or break the scale, before pickling with acid. In addition, stainless steel pickling requires more aggressive acids such as hydrofluoric, sulfuric, or nitric acid, and requires longer immersion times, resulting in, for the belt, process line speeds of approximately 30-100. m / min The main motivation to improve or eliminate this type of scale removal process are the investment costs and the costs of disposing, in a safe way for the environment, the acids associated with pickling. The annual cost associated with a single production line could be as great as 8 million dollars, only for the disposal of dangerous acids. A major disadvantage of the chemical processes of descaling are the environmental problems related to the disposal of chemicals used in pickling. The use of lasers to eliminate or help eliminate the incrustation of steel is known. For example, US Patent No. 4,063,063 relates to a process for descaling metallic products by irradiating a metal surface with a C02 laser beam of sufficient intensity to produce a rapid and intense local heating of an oxide film. The laser described in this patent can have a beam power of up to 10 KW. However, subsequent work has revealed that it is not possible to completely eliminate the oxide scale using pulse C02 or continuous wave lasers, at process line speeds comparable to those achieved by acid etching. Only an expensive and irrational number of laser beams could achieve comparable pickling speeds. The patent application _j apone s a 2 -197588 is r-e. fJ was a- a- method for- alimi-nar-incrustation or rust of the steel. The incrustation or rust, which is on the steel, is irradiated with a laser beam that is in a region of wavelengths of the UV, in the electromagnetic spectrum, such as an excimer laser beam that has a wavelength of 100. -400 nm for a duration of the impulses less than or equal to 200 nsec, will cause the fine break of the incrustation or rust. Since the power of an excimer laser is limited to approximately 300 Watts and a pulse repetition ratio of less than 1 KHz, it would also be necessary to have an expensive and reasonably large number of excimer laser beams to strip the steel at reasonable speeds On the line. The laser beams of C02, Nd: YAG, and excimer represent the industrial laser rays of high average power, - more common, through the wavelength range that goes from the extreme infrared (C02 to 10.6 microns) to the near infrared (Nd: YAG a 1064 microns) to the ultraviolet excimer (XeCl at 0.308 microns, KrF at 0.248 microns, and ArF at 0.193 microns). In order to obtain high incrustation speeds it is necessary to use very high power laser beams. Many of the commercially available laser slots L of high average power, for example, greater than 1 KW, operate in a continuous wave (OC) mode. The continuous wave operation presents problems for the elimination of incrustation, due to the absorption of the incident-e laser beam by the column of plasma generated by the elementary components removed. This is caused by the residence times, relative-J-aj-r g-o-s .a-sod -o-s can. e.l pj-r-ocje-s-a-dO with continuous wave laser. This has been confirmed by the work carried out by Schluter, et al., Described in an article entitled Austenitic Steels Descaling by Laser Radiation, Proc. ICALEO 94, Orlando, Fia., 17-20, 1994. This same article presents data that show that, even the C02 pulsed lasers, are inefficient in the removal of the oxide because the pulse duration is long enough for The incoming laser beam interacts with the plasma column created in such a way that the energy of the incoming laser is a-bsorbed through the plane and so does not remove additional rust. The net result is a low rate of incrustion. Wehner et al. Describes in an article entitled "Wear of Oxide Layers on Metallic Surfaces by Laser Radiation Excimer, Proc. ECLAT 90, V2, PP. 917, that short pulses, for example 10-250 nanoseconds, of an excimer laser, are more efficient in removing oxide layers but these lasers are only available at a low average power, for example less than 250 W, and low repetition rates, that is, less than 1 KHz. A simple "good eye" estimate of the applicant, based on exceeding the vaporization heat of the oxide layer, reveals that to remove an aluminum oxide layer 5 microns thick, on one side of an aluminum surface with 1 m width, moving at 31 m / min requires an average laser power of 100 KW, although a 45 KW C02 laser is commercially available , in Trans Tec / Convergent Energy, it operates in a continuous wave mode, so even if two of these 45KW lasers are used to cover an aluminum surface 1 m wide, the desired descaling speed will not be achieved , due to problems of ab plasma sorption associated with continuous-wave lasers or with long-duration impulse lasers, just mentioned. It is only possible to obtain this type of energy from excimer lasers of short duration of impulses, by using a large number, for example 400, of lasers, each one treating a small fraction of the desired material in its full width. In this way, conventional industrial lasers are not suitable for the economical elimination of steel oxide casings. A major disadvantage of these laser descaling processes, of the prior art, is that it was not possible to completely remove the scale from a strip or strip of steel traveling at a high speed. Alternatively, the low speeds of the bands, required for the complete elimination of the incrustation, by means of conventional laser technology, does not economically justify the use of this type of scale removal. Accordingly, there is still a need for a process for the descaling of metal oxide, which does not require the use of an acid that causes a waste problem to the environment. There is still a need for a descaling process, where a band of oxidized metal, traveling at high speed, does not have to receive a pre-treatment of shot blasting, to lose the incrustation, to ensure the complete elimination of the oxide. It needs a laser process that can economically eliminate the scale layer, to achieve this, the laser must have a high average power, so that it can eliminate rust at speeds in the line, comparable to those achieved. with acid etching, conventional, without requiring the use of an acid and / or chorrao with grana-Lia, to help in the elimination of metal oxide from the metal band Another need is for the laser to be efficient in the elimination The laser must have a very short pulse duration, it must have a high repetition rate and it must have a wavelength that can be selected to give a minimum amount of laser photons. the highest rate of scale removal Another need is that the investment and operating costs of the laser be reasonable to justify the economics of the process.
BRIEF DESCRIPTION OF THE INVENTION
A principal object of the invention is to provide a process and apparatus for using laser radiation in the removal of surface oxide from a metal, with a minimum input energy per volume of oxide (scale) the imine. Another object of the invention is to provide a descaling process and apparatus, capable of completely removing an oxide film from a metal. Another object is to provide a deburring process and apparatus, capable of completely removing an oxide film from a strip or strip of metal, traveling at high speed (eg, greater than 30 m / min). Still, other objects of the invention include providing a descaling process and apparatus, which eliminates the need for chemicals, which eliminates the need for chemical waste, shot blasting, from the oxide film, and eliminates the need for pickling line with acid, large and costy. This invention relates to a process and apparatus for using laser radiation to remove oxide scale from a metal. The process includes using electromagnetic radiation that has a very short pulse duration, a very high pulse repetition rate and a very high average power. The average radiation is passed through at least one optical element to focus the radiation on an incident beam having a surface power density of about 5 MW / cm2 at the point of contact with the metal surface. The focused radiation beam extends transversely and completely, through the surface of the metal, covered with the oxide, to eliminate the oxide by vaporization, by means of one or more laser pulses, thus forming a free surface of rust
Another feature of the invention is the aforementioned laser radiation, which has a photo-wavelength of photo-nfi-s, which is found in the ultraviolet range. Another feature of the invention is with respect to the optical element, mentioned above, ei which is a lens, u_n -e-spe j -o-, or a combination thereof. Another feature of the invention is the optical element, mentioned above, which is a combination of aligned elementa-S. ~
Another feature of the invention is the aforementioned element, which includes means for dividing the radiation beam into a plurality of subrajyos or focused secondary rays, each of which has a lower power than the original beam that is produced by the laser. Another feature of the invention is the aforementioned element, which includes means for the homogenization of each secondary beam, to provide a relatively uniform spatial power distribution, through the focused beam. Another feature of the invention is the homogenization means, mentioned above, which includes an optical fiber and a lens for focusing the radiation beam at one end of the fiber. Another characteristic of the invention is the aforementioned homogenization means, which includes a linear divergent lens having a short radius at the apex. Another characteristic of the invention is the secondary ray, mentioned above, which is focused on in at least one line that extends transversely across the full width of the metal surface or that is focused in the form of a luminous spot that is traversed across the entire width of the surface of the metal. of the invention is the secondary beam, mentioned above, which makes contact with the surface of the metal, with an acute angle of 1-0-75 °. Another characteristic of the invention includes the additional step of collecting the oxide vaporized in the form of a powder. Another feature of the invention includes the additional step of protecting the point of contact of the surface of the metal and of the surface -b-e-of-oxide-with a ga-s -oxidant. Another feature of the invention is the duration of the laser pulse, which is less than
100 PS. Another feature of the invention is the repetition rate of the laser pulses, which is at least 1 Hz. Another feature of the invention is the average power of the laser, which is at least 1 KW. Another feature of the invention is the metal, mentioned above, which is an annealed or hot rolled strip, traveling at a consistent speed with a pulse repetition rate of the laser beam. Another feature of the invention is the metal, mentioned above, which consists of a band traveling at a speed of at least 1 m / min. The apparatus includes a laser capable of producing electromagnetic radiation having a very short pulse duration, a very high pulse repetition rate and a beam power surface density of at least about 5 MW / cm2, at least one optical element for focus the radiation in the form of an incident ray and a sealed interaction chamber for the treatment of a metal band in motion, covered with oxide, where the chamber contains a non-oxidizing gas to remove oxide residue and to protect the surface of the band, so cleaned. The chamber also includes a slotted inlet to receive the rust-covered strip, a slotted outlet for passage of a cleaned strip, at least one elongated window for receiving the radiation beam within the chamber, and means for removing the oxide vapari-zada-, of X? camera-. Another feature of the invention is the laser radiation mentioned above, which has a wavelength of the photons, in the ultraviolet range. Another feature of the invention is the chamber, mentioned above, which includes an outlet duct to remove from the chamber the non-oxidizing gas charged with vaporized oxide residues, a filter to remove the residue as a powder, from the gas, and a return duct to return the clean gas to the chamber. Another feature of the invention is the aforementioned chamber, which includes a blower to send clean gas back to the return duct. Another feature of the invention is the camera, mentioned above, which includes a nozzle to direct the gas towards the chamber. Another feature of the invention is the aforementioned optical element, which includes at least one lens, a mirror or a combination thereof. Another feature of the invention is the optical element, mentioned above, which consists of a plurality of aligned elements. Another feature of the invention is the optical element, mentioned above, which includes a means for dividing the radiation beam into a plurality of focused secondary rays and the camera includes a corresponding number of windows, each window for receiving one of the secondary rays. of radiation. Another feature of the invention is the optical element, mentioned above, which includes means for homogenizing the radiation, to provide a relatively uniform spatial distribution of power through the focused beam. Another feature of the invention is the optical element, mentioned above, which includes homogenization means having a linear divergent lens with an acute radius at an apex. Another feature of the invention is the aforementioned optical elastomer, which includes means for homogenization having a lens and an optical fiber of stepped index, and the lens is used to focus the ray of r-di-cC-i. -ó - at an extreme of 1.a. fiber. Another feature of the invention is the radiation beam, mentioned above, which is focused in the form of a line. A principal advantage of the invention includes the removal of the pickling with acid in a humid way, to eliminate the incrustation of the metal. Another advantage of the invention is to provide a descaling process which vaporizes the oxide, so that the oxide residue can be easily collected for disposal. Other advantages include a laser process for removing scale, faster than other laser removal methods, known, due to the combination of a laser with high average power, high repetition speed d "and impulses, very short duration of impulses, and the ability to select an optimal laser wavelength All these laser properties can be obtained from a free-electron laser with high average power The objectives, characteristics and advantages of the invention, above, thus like other additional ones, they will become clear when considering the detailed description and the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of an optical system for providing a focused line, for the descaling of a metal band, of the invention,
"Figure 2 is a schematic view of a generic ray homogenizer of the invention,
Figure 3 is a schematic view of a staggered Index fiber, used in the homogenizer of Figure 2,
Figure 4A is a perspective view of an optical system of the invention, to focus the radiation in the form of a line having a uniform intensity,
Figure 4B shows a graphical representation of the distribution of the intensity of the radiation of Figure 4A, along the length of the projected line,
Figure 5 is a perspective view of another embodiment of the invention, which illustrates a laser system for descaling a metal strip,
Figure 6 is a perspective, detailed view of a chamber for the elimination of vaporized scale, of the invention,
Figure 7 is a perspective view of the detailed area around the reaction zone of the beam, of Figure 6, illustrating the eviction of the vaporized scale residue ", by means of an inert gas,
Figure 8 is a side view of the reaction zone of Figure 6,
Figure 9 is a perspective view of another embodiment of the invention, illustrating an optical system of mirrors for focusing the radiulation in a line to descale the metal band of the invention,
Figure 1AA is a perspective view of another embodiment of an optical system for laser embedding, of the invention, illustrating a network scanning system, with refractive lenses of flat field, to focus laser radiation in the form of a luminous stain, to eliminate the incrustation of the metal band.
Figure 10B is a perspective view of yet another embodiment of an optical laser descaling system of the invention, illustrating a network scanning system, with 'telecentric' reflecting mirrors to focus the laser radiation in the form of a luminous stain, to eliminate the incrustation of a metal strip, and
Figure 10C illustrates, in detail, the focused, incident elliptical luminous spot of Figure 1 OB.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention relates to the use of a laser to remove rust, for example, scale or scales, from a metal such as a steel strip or strip. The process includes using electromagnetic radiation that has a very short pulse duration, a very high pulse repetition rate and a high speed in.ar--g.La pram.ed _.- LQ, and has to pass to. beam or beam of radiation through a series of aligned optical elements, such as cylindrical lenses, mirrors, or a combination thereof, to focus the beam in the form of a light spot projected transversely, and completely through a band of metal in movement. Alternatively, the radiation can first pass through a medium for homogenization, to form a beam of radiation having uniform intensity, and then the homogenized beam can be passed through the aligned optical elements to focus the beam on the beam. form of a straight line projected trans-seeing, completely through a moving metal band, a power density per surface area, at the point of contact incident by laser radiation with the surface of the band, covered with oxide, it is at least 5 MW / cm2 Depending on the average power of the laser beam, the beam can be divided into a series of lower power secondary rays, each focusing on a line or spot whose length / diameter is smaller The entire width of the band should be sufficient, however, there should be a sufficient number of beam splitters and optical cylindrical focusing elements or scanning optical elements. n luminous spot, so that the entire width of the band is covered by this series of secondary rays focused, transversely contiguous, in such a way that the surface covered by the oxide, along this section in width is completely descaled by molecular layers of the vaporized oxide, during each impulse of the radiation. Each division of a ray of radiation, in secondary rays, reduces the power of the original main beam, in a ratio of the inverse of the number of secondary rays. A sealed device removes residues of vaporized oxide, so that the particles do not settle again on the descaling, clean surface. The apparatus contains a protective non-oxidizing gas, for example helium or argon, which blows through the reaction zone of the focused beam or of the contact surface with the beam, to remove the vaporized metal oxide particles. There is also a vacuum outlet duct from the descaling chamber, which removes the inert gas that transports the vaporized waste through a filter where the waste is deposited in the form of a powder, for eventual disposal. The inert gas can then be recirculated to the chamber. The angle of incidence of the focused, striking laser beam is preferably not perpendicular to the surface of the band, but is a somewhat acute angle to decrease the interaction and possible absorption of incoming laser radiation by the beam column, created by the vaporized residues The elimination of the entire thickness of the oxide layer is achieved by supplying many pulses of laser radiation at the same location of the focused beam Each impulse vaporizes a layer of molecular oxide until the layer is reached This is controlled by the residence time of the lightning at each location, which is determined by the pulse repetition rate and the speed of the surface of the band moving through the length of the focused laser beam. The depth of the removed oxide can also be controlled by adjusting the total average power of the laser, through variable attenuators and, for a veil pulse repetition, fixed, the energy released in each impulse. The laser of the invention has unique properties that allow the elimination of metal oxide (scale), at an economically attractive speed, with a minimum number of lasers.Las laser produces electromagnetic radiation having a very short pulse duration, for example, less than 1 nanosecond, a very high pulse repetition rate, for example greater than 1 million pulses per second, and a high average power, for example 1-1000 KW average power. Laser is a free electron laser (LEL) .An additional advantage of the free electron laser is that it can be tuned to work within a wide range of wavelengths in the near, visible UV, and in the part of the near IR Since it is believed that the shorter wavelengths, for example, in the UV part of the spectrum, will be absorbed more efficiently by the scale layer and this leads to Therefore, at higher descaling rates, the free electron laser of the invention will be operated so that the radiation has a wavelength of photons that is in the ultraviolet range. However, it is also believed that the laser can be operated at d-wavelengths belonging to the visible, near IR, and intermediate regions of the IR, of the electromagnetic spectrum, and also obtain efficient removal of the scale. For a free electron laser to work, it requires an electron beam accelerator. A lot of electrons are injected into the accelerator. One accepted method is to use a low average power laser, such as the one described by Benson et al in an article titled Development of a Laser Powered by Photoelectric Cathode, Ready for an Accelerator, in CEBAF, Process Particle Accelerator Conference, 1995, Dallas, Texas, incorporated herein as a reference, to impact on an objective material and thereby release electrons. This method of photoelectric cathode generates large amounts of electrons that are then accelerated by several RF modules, superconductors, up to speeds very close to the speed of light. These groups of electrons with relativistic energy travel through a "corrugator" section consisting of fixed magnetic fields, directed in an alternating manner, each of which exerts a Lorentz force pependicular to the direction of travel of the group of electrons The next magnetic field found in the "inverter" exerts a field that is positively directed to the one preceding it, so that the electron group now suffers a Lorentz force perpendicular to the direction of travel but at a 180 degree direction. the one just found. Thus, the trajectory of the electron group "waves" back and forth, along its primary direction of travel through the "inverter". Since the electron is a charged particle, the transverse accelerations that the electron groups suffer as they pass through the inverter, cause the emission of electromagnetic radiation. This radiation is amplified by mirrors that are placed appropriately in the direction of travel of the electron group. This radiation gives origin to the real laser beam, created by groups of electrons that travel freely _ and that are accelerated transversely. For an industrial device to be attractive, it must be possible to have a continuous production of these groups of electrons, in such a way that an average laser power is obtained. Each group of electrons that pass through each magnet of the "inverter" gives rise to a pulse of laser radiation. The more electrons there are in the group, the greater the energy per laser pulse emitted; and the more lasers there are, the higher the pulse repetition rate will be, and hence the higher the average power of the laser. Thus, a key to having a laser with high average power is to have a high, average electron beam current. This means that the laser photocathode generates as many electrons in each group as possible, at a high repetition rate as possible. If this is done on a continuous basis, then an average high power laser with a high pulse repetition rate will occur. Although a number of free electron lasers have been built around the world, none produce high average power or none is capable of long-term operation. An LEL laser with 100 KW average, in continuous operation, will allow the deain-crus-taci? -a- with Lásar sa to perform at economically attractive speeds. The embedding layer is removed by vaporizing molecular layers of oxide with each pulse. By vaporization it is understood that the laser pulse supplies sufficient energy to raise the temperature of the oxide to the vaporization temperature, while exceeding the heat of fusion and then the heat of vaporization of the oxide. It will also be understood that the removal of the scale, by vaporization, may also include the removal of the oxide by an explosive shock wave, a gaseous release of the bound oxygen, to blow the oxide layer and remove it from the metal substrate, or any other mechanism that benefits from the very short pulse duration and the high power produced by this type of laser. A potential advantage of the very short pulse duration and high pulse power is that a shockwave mechanism or some other mechanism, for example, the gaseous release of oxygen bound to the oxide, may allow a speed of incrus higher than that which can be predBclx by -simply thermal considerations only. An LEL laser, of the type used in this invention, is constructed in the Thomas Jefferson National Accelerator Facility (LAB Jefferson). The laser is described in a review report of the Department of Energy, entitled Lasers of Free Electrons for Industry, Volume I, May 1995, incorporated herein by reference. The Jefferson LAB is located in Newport News, Virginia and is operated by DOE by the Southeast University Research Association (SURA). Two key features of this laser, unlike any other LEL, is continuous operation and high average power. These characteristics are essential to use that laser for any continuous high-speed industrial process, such as laser descaling. For this invention, it will be understood that a very short pulse duration is understood as a duration of less than 1 nanosecond, preferably with a pulse duration of less than 100 picoseconds, more preferably less than 10 second peaks, most preferably less than 6 picoseconds. A pulse duration as short as 1 femtosecond may be possible. This very short pulse duration is a key feature required to provide efficient removal of the scale. The ability to vaporize any material with laser radiation is dependent on the supply of a sufficiently high surface area power density, that is, greater than about 5 million watts / cm2 (5 MW / cm2). The impulse power is calculated by dividing the impulse energy by the duration of the impulse. The power density per surface area is determined by dividing the power of the pulse between the laser spot area of the focused laser. Thus, the shorter the pulse duration, the lower the pulse energy required to achieve sufficient surface power density and cause vaporization. Of course, the amount of material vaporized per pulse is determined by the total energy in each laser pulse. For example, if there are only 33.3 microjoules of energy in a single pulse, obtained from a 1 KW LEL laser, which operates at a repetition rate of 30 million pulses per second-D
(30 MHz), 100 thousand pulses may be needed to remove a 5 micron thick layer of iron oxide over a surface area of 2 cm2. However, because the repetition rate is so high, this area of 2 cm2 will be disincrusted to the depth of 5 microns in 1/30 of a second. As the average laser power becomes higher, there will be more energy in each pulse, so that each pulse can now vaporize a larger volume of oxide, thereby increasing the overall rate of scale removal. If the average laser power is increased to 100 KW, it may be possible to descale a surface area of 200 cm2, at the same depth of 5 microns, in the same time of 1/30 of a second. Another key benefit obtained by the very short pulse duration is the ability to efficiently remove an oxide layer, with the energy of the impulse, before there is enough time for a plasma column to develop, which will absorb a significant portion of the incoming laser pulse, thereby reducing the speed at which the incrustation of the surface is removed. The molecular layers of the oxide are removed in a picosecond time frame and then blown and removed with an inert gas before the next laser pulse arrives to remove the next molecular layers of the oxide. This allows all the average laser power to be used in rust removal, without loss of energy, due to the interaction of the beam with the plasma. This is a key advantage over continuous wave laser (OC) operation. The pulse duration is in the range of 1 femtosecond to 100 picoseconds. For this invention, it will be understood that a very high pulse repetition rate means a speed of at least 1 KHz, a speed of 1 MHz (one million pulses per second) being desired. Preferably, a pulse frequency, greater than 10 MHz, is recommended, because the energy per pulse will be limited by the number of electrons in each group passing through the free electrons laser inverter. More preferably, the pulse repetition rate is at least 30 MHz and in the most preferred form at least 40 MHz and could possibly be used up to 1 GHz (1 billion pulses per second). average power in the laser beam because it determines the rate of descaling Calculations show that approximately 100 KW of laser beam power is required to descaling at an economical speed, thus the pulse repetition rate multiplied by the energy per impulse is equal to the average power of the laser beam, for example, if the energy per pulse is 3.33 milijoules (0.00333 joules), then the speed of repetition of impulses would be 30 MHz, so that the total power of the If the energy per impulse could be increased to 3.33 joules by injecting a much larger number of electrons in each group that circulates in the electron accelerator, then the The pulse repetition rate can be lowered to 30 KHz, obtaining an average global beam power of 100 KW. For this invention, high power means an average power of at least 1 KW. Preferably, the power is greater than 1 KW, more preferably at least 10 KW and most preferably at least 100 KW. A power of 100 KW is desired to make laser removal of the oxide layer an attractive economic process. Although a lower average laser power will also remove the oxide layer, this results in a slow removal rate, which requires a large number of lasers to obtain a high removal rate. For this invention, metal means any metal that can be oxidized during hot processing, such as hot forging., hot rolling, annealing and the like. These metals may include ferrous materials such as low carbon steel, steel with an average content of carbon and high carbon steel, nickel alloy steel, chromium alloy steel, stainless steel, electric furnace steel and metals non-ferrous metals such as nickel, aluminum, copper, titanium and alloys thereof. The metal may be a cast metal or it may be in a rough condition such as a continuous band, sheet, paper, bar, ingot, plate, wire, cast articles, etc. For ferrous metals, the metal oxide or scale will be predominantly iron oxide With reference to Figure 1, the reference numeral 20 denotes electromagnetic radiation in the form of pulses, which impinges on one or more optical elements such as a first diverging spherical lens 22. Although pulsed radiation 20 is illustrated as having a square cross-section, it will be understood that this original non-focused beam may have other cross-sectional shapes such as a rectangle, a circle, an ellipse, and the like.As will be discussed further below, it is important that the beam of radiation 20 has a uniform distribution of intensity through the extension of the beam, then a ray of radiation is passed n divergent electromagnetic radiation 24 through a first cylindrical lens 26 for collimating or aligning the beam 24 in the shape of a collimated beam 28, in a vertical x-direction 48. The vertically collimated beam 28 then passes through a second cylindrical lens 30. to collimate the beam in one direction and horizontal 5-0 and produce the beam 32. The beam 32 now collimates in both directions, horizontal and vertical, by means of the ascending collimator created by the combination of the lenses 22, 26, and 30. Through the judicious choice of focal lengths and spacings, of these three lenses, it is possible to independently adjust the horizontal size and the horizontal collimation degree, and the vertical size and the vertical collimation degree of the beam 32 coming out of the element 30. The beam 32 then passes through a third cylindrical lens 34 to focus beam 32 an an incident ray 36 focused as a straight line 38 projected transversely, completely through a dirty surface and rust cover, of a metal strip 40 having a travel direction as indicated by the arrow 42. The incident ray 36 cleans the surface 44 of the strip, forming a surface 46 without rust. The length of the transversely focused line 38 can have any desired value that is limited by the physical, transverse length of the aligned optical elements 30 and 34 and by the choice of the focal lengths and spacings of the aligned optical elements 22, 26, and 30. Preferably, the web 40 travels in a vertical gravitational direction. Figure 1 illustrates the removal of the scale, only from one side of the band 40. Normally, a metal band will have incrustation on the other sides, so both sides need to be cleaned. It will be understood that one side of the band can be cleaned with a laser optical system, such as the one illustrated in Figure 1, the band could be wound into the shape of a roll and then the roll could be passed back through the system. cleaning, to clean the other side of the band. Alternatively, two laser optical systems, such as those illustrated in FIG. 1, can be placed to clean both sides of the band, simultaneously, with the radiation of a system striking a surface of the band, and the radiation of the other if s-topic affecting the other surface of the band. Another important feature of the invention is that the length of the focused laser line has a 'uniform intensity' distribution across its length. This will ensure that all the oxide thickness is removed uniformly, along the length of the focused line. There are a number of methods that can be used to achieve this uniform removal, depending on what type of optical system is used. Figure 2 shows a generic ray homogenizer. A full power laser beam 56 may have a Gaussian distribution 58 (TEM0o), donut mode (TEMoi), or some other spatial power distribution with a higher order mode. The function of a beam homogenizer 60 is to transform the beam 56 into a beam 62 having a uniform energy intensity distribution through the spatial extent of the beam. This is a 64 square or top hat distribution. One way to achieve this is to focus the beam on a step-in-step optical fiber. Figure 3 illustrates an original collimated beam 56 of a laser 54, which is focused by a lens 66 at the end of a stepped index optical wave 68. Multiple internal reflections occur when the beam is propagates along the length of the fiber, they overlap each other, resulting in a uniform, spatial distribution of power 70, which leaves the fiber. At the fiber exit another lens 72 is placed to re-collimate the beam. If the original laser beam 56 of free electrons is divided by the ray splitters, into secondary rays of reasonable power, for example, of no more than 10 KW each, then each secondary beam could be focused on a fiber, to achieve a distribution spatial power, uniform. However, the free electron laser can be tuned through a fairly large wavelength range. A reasonably valued fiber, with low attenuation, is only practical if the laser wavelength is in the near UV, in the visible, and in the part of the near IR, of the spectrum, 16. Preferably, the radiation has a length of photon wave that is in the ultraviolet range. Figure 4A illustrates a preferred method for homogenizing a laser radiation beam, which uses an in-line projection. This optical system uses a specially designed 7 ~ 4 linear diverging lens, which has the appearance of a prism, with a relatively sharp radius at the apex. A lens like. { that is described in U.S. Patent No. 4,826,299, incorporated herein by reference. This expands the laser beam 20 in only one direction in such a way that a triangular prism of laser radiation 76 is formed, which has a uniform intensity distribution along its transverse direction and 50. The length 86 of the line it increases linearly in the direction and as the radiation diverges away from the lens in a z-direction 52. An intensity distribution 82 along the length of the line is not perfectly uniform, but has some variation 84 as illustrated in Figure 4B. An additional, convex, cylindrical lens 78 is illuminated by the projected laser line 80 such that the laser beam sharply focuses on line 38 on the surface of the oxide layer to be removed. The diverging lens design 74 should include the incident diameter of the laser beam. The projector lens of the line must be made of an appropriate material based on the wavelength of the laser radiation that will pass through it. This is to avoid the absorption of laser radiation as it is refracted by the projector lens. For example, if the wavelength of the free electron laser was tuned to 1 micron in the near-infrared part of the spectrum, then molten silica or BK7 can be used to build the laser line projector. This material must also be coated with antireflection material, for the wavelength of the laser. If the laser wavelength was in the range of 2-7 microns in the mid-infrared, then calcium fluoride could be used, magnesium fluoride, zinc sulphide, or zinc selenide, for the projection lens of the laser line. The final focusing lens 78 will also be made of the same material and will also be coated with a material against reflection, to minimize the absorptive and reflective losses of the laser, respectively. The width of the focused laser line is controlled by the focal length of this final cylindrical lens 78. The length of the laser line is determined by knowing how far the projector lens 74 is from the line, from the surface of the metal, covered with oxide, end. replacing by a combination of a plane, rectangular, long mirror 168, for redirecting the laser radiation line and a concave, cylindrical, final focus mirror 170, such as that shown in Figure 10B. refractive, the full power of a laser beam, for example, 100 KW, can be divided into a plurality of secondary rays, Figure 5 illustrates a pair of secondary rays covering the total width of the metal band 40 where each ray covers Half of the width of the band It will be understood that this concept can be extended to include any number of secondary rays, for example, if the beam is divided into ten secondary rays, each secondary ray will descaling one tenth of the width of the band. e the metal band. The embodiment of Figure 5 includes a sealed interaction chamber 90 having a sealed inlet for receiving the band 40, a sejed outlet 92, and a pair of sealed windows 93 that allow the rays 36 to pass into the chamber. The chamber 90 also includes an outlet conduit 94 for driving the scale debris, removed, to a filter unit 96, a supply conduit 98, a blower 100 for circulating a non-oxidizing gas through a conduit 102 for the return of the gas, to an outlet or vent 104 within the chamber 90. The gas is recirculated by the blower 100 to collect the scale debris, which is deposited on a filter, and is returned to the chamber 90. Each ray secondary 20 will be passed through one of the ascending, anamorphic collimators (lenses 22, 26, 30) described above in figure 1 or by the mirrors described in detail in figure 9 and then focused by the cylindrical lens 34 ( or a concave mirror). Figures 6-8 illustrate more detailed views of a reaction zone at a location adjacent to the point of incidence of the laser beam 36 and the metal surface 44 within the chamber 90. The chamber 90 contains a non-oxidizing gas 108, such as helium or argon, supplied from a reservoir 110. This inert gas medium is used to protect the reaction zone and to transport vaporized oxide particles 118 away from the interaction chamber. The incident ray 36 is shown as a wave front, rectangular, convergent, focused on the surface 44 of a mobile, metal band. Preferably, the spoke 36 strikes at a certain angle that is not perpendicular, that is, bucked, on the surface 44 of the strip. By acute it will be understood a preferred angle that is in the range of 10 to 75 °, measured from the normal to the surface of the metal. A more preferred range is from 25 to 60 ° and the most preferred angle is 30 °. It is known that a plasma column 112 created by the vaporized residues has its maximum intensity in a direction perpendicular to the surface of the band. By orienting the direction of the focused, incident radiation away from a direction normal to the surface, it is believed that there will be less absorption of incoming incident beam 36 by the created plasma 112. This will produce a greater efficiency in removing the oxide layer. Above the column 112 and just beyond the front of the wave, rectangular, focusing, de-i ray 36, is mounted a nozzle 114 for gras, similar to a long slot, to direct the inert gas 108 over the created plasma 112. An important feature of this invention is to surround the created plasma column, as well as to clean the surface 46 of the metal, with the non-oxidizing atmosphere, to prevent again oxidation of the surface 46 of the metal, clean. By maintaining sufficient pressure in the oxidizing gas, around the column and the surface of the metal, clean, and by keeping the chamber sealed and isolated from the environment, the atmosphere of the environment, ie oxygen, can be kept away from the area of laser interaction, immediately adjacent to the plasma column. The nozzle 114 extends along the entire length of the focused line 38. An exhaust outlet or vent 116, in the conduit 94, is located on the opposite side of the chamber, from where the incident ray 36 enters and withdraws the inert gas charged with particles 118 of the waste oxide, to the outlet duct 94. The duct 94 and. the nozzle 114 for the gas are preferably mounted on the inlet side of the chamber, i.e. adjoining the dirty surface 44 of the strip. This minimizes the amount of waste that could otherwise settle on the cleaned metal strip, which again contaminates the newly descalmed surface 46. In contrast, the particles 118 of the residue would fall on the untreated surface 44 and would pass back to the incident ray 36 where they would vaporize again. The waste oxide (scale) particles 118 are drawn to the inlet side of the chamber, as indicated by the direction of the arrow 180 to be deposited on a filter 106 located within the filter unit 96 that removes the particles of the residue with micron size. This would be especially true if the band 40 traveled in a vertical direction such that gravity tended to cause the particles to fall away from the band, toward the exit or venting 116. The filter unit 36 may also include a vibratory mechanism such that the particles of the waste can be deposited in a collection container or container (not shown) located under the filter. The inert gas 108 is removed "through the filter 106 and is recirculated by the blower 100 and re-enters the vacuum chamber 90 through the nozzle 114 to collect more residue 118. The gas reservoir 110 injects periodically, gas fresh inert 108, in the return duct 102 to replenish any amount of gas, lost A pressure gauge 120, located in the nozzle, inspects the gas pressure and is used to control a solenoid valve 122 which is located on the The gas reservoir shows the flow pattern of the inert gas 108 and particles 118 of the waste, which are collected by this flow, and how the particles are transported towards the exhaust vent 116. The same nozzle and exhaust system can be used with the scanned light spot system, as described in Figure 1 OA and 10B.In this case, the focused line is now the width of the scanned field through which the focused light spot is scanned. The important feature of the invention is illustrated in Figure 8. Figure 8 illustrates the importance of preventing the ambient atmosphere from entering chamber 90. In addition to maintaining a protective atmosphere 108 within chamber 90, it is also important to properly seal the chamber . For example, even if the cylindrical lens 34 could be placed outside or inside the chamber 90, preferably the lens 34 is mounted inside the window 93, whereby a seal is formed. An inlet 91 (FIG. 6) for receiving the strip 40 and the outlet 92 are both preferably sealed with a flexible material 178t as the polypropylene. By orienting the nozzle 114 for the gas, towards the surface 44 of the metal, at a certain angle with respect to the component of the gas velocity, towards the exhaust vent 116, the inert gas, charged with the particles 118 of the waste oxide, is directed towards the exhaust duct 94. By placing the duct 94 and the nozzle 114 for the gas, on the inlet side of the exhaust. the chamber that is above the surface 44 of the dirty band will prevent any residue from re-settling on the clean metal strip, and re-contaminating the newly descalmed surface 46. The width of the focused line 38, in the direction 42 of the movement of the metal, will be determined by the focal length of the lens 3 ^ for final focus, by the degree of ascending collimation achieved, and by the divergence of the ray 20 incident on the first lens 22 of the anamorphic upward collimator. It would be possible to control this width of the focused line 38 through the given interval ap r-ax Lmadamanta Q.L mm up to a few centimeters. The actual value will depend on the length of the focused line and the energy per impulse. For example, if with an original beam 14, of 100 KW, of the laser 54, is divided into 10 secondary rays of 10 KW each, it is desired to descaling a metal band of 1 meter wide, then each of the 10 lines focused will be 10 cm long and will be focused on a width of approximately 2 mm for each one. If the laser is operating at a repetition rate of 30 MHz and a pulse duration of 2 second peaks, each pulse in each of the 10 KW secondary rays will have an energy of 333 microjoules and will have a focused surface power density, of approximately 83 MW / cm2. An important feature of this invention is that the surface power density (watts / cm2) is sufficient to cause the vaporization of the oxide which is found on the metal band. This requirement is fundamental for this invention, in the determination of the length and width of the focused line, in such a way that the laser energy. per unit time, by impulse released on this line, meet this criterion to give rise to a surface power density of at least 5 MW / cm2. With these considerations in mind, the length of the line focused transverse to the direction of the direction of travel of the metal, can be as small as 1 mm and a width of 2 m, and the width of the focused line can be 0.1. mm to 10 cm, as long as the previous restrictions of surface power density are maintained. For example, with a system in reflective mode, such as the one shown in Figure 9, the length of the laser line, with a laser beam with average energy of 100 KW would be 1 m extending completely through the entire width of the metal band and the width of the focused line 38 is 2 mm. With an impulse energy of 3.33 millijoules and a duration of impulses of 2 picoseguns, the same surface density-d of power is obtained, per impulse, mentioned, of 83 MW / cm2 mentioned above, which is obtained for each one of the sections of 10 cm long, focused by a system of refractive lenses. Thus, the same capacity can be obtained to descale the entire metallic surface, by means of a single optical system that focuses all 100 KW, or 10 subsystems that each approach 10 KW, or even 100 subsystems that each approach 1 KW. The details of how this system is used depend on other aspects such as the comparative cost and the availability of the optical components. The oxide layer will vaporize and be removed from the total surface area of the metal strip, forming the clean, substantially rust-free metal surface 46, without further mechanical or chemical assistance. For example, pretreatment such as shot blasting or roller leveling, will not be required to break or detach the scale or scale, prior to laser treatment, and a small, surface treatment will be necessary, if needed., such as a pickling with acid immersion, to dissolve remaining amounts of the scale, after the laser treatment. The descaling process of this invention would have significant environmental advantages because it will no longer be required to dispose of toxic liquors from pickling. The surface 44 of the metal moves under the focused line 38 at a speed ratio that is consistent with the pulse repetition rate and with the pulse energy necessary to remove the oxide thickness, completely in. to the base metal. Given that the metal band moves continuously in a vertical direction, at line speeds, of at least 10 m / min, preferably at least 30 m / min and possibly at speeds as large as a few hundred meters per minute, the high speed of repetition of impulses, for example 30 MHz-. sLgnLLLca- qua mLLtLpLas L-mpuLsaa will collide against the same site. This is necessary since a single pulse does not contain enough energy to completely remove the scale layer. Each pulse removes a number of molecular layers in such a way that a large number of pulses are required in the same location to completely eliminate the scale layer of the base metal. Although it is possible to make the optical combination of the lens or mirror large enough to cover the width of the widest metal band, for example, about two meters, which probably requires descaling, there are additional considerations that suggest multiple combinations of lenses or mirrors that can be a better method. With an optical system of mirrors it is possible to cover approximately a section of 1 m wide, as a single set of mirrors. An optical element of mirrors is typically capable of accepting a higher power density on the reflecting surface, than a refractive element. The refractor elements have some degree of absorption of the radiation which causes the heating up to a high temperature. When the average power is greater than 10 KW, the heating of the optical element can be a significant effect depending on the diameter of the beam. The dimensionally large refractor elements are also more expensive than their reflective counterparts, especially if the chosen wavelength requires a more expensive refractor material, for example, zinc selenide. It will be understood that the invention can also use a combination of flat, convex and concave beams to focus the laser radiation on a transverse line. Figure 9 illustrates another embodiment of the invention which uses a combination of convex, flat and concave mirrors, used to focus the laser radiation on a line. The original incident laser beam 20 hits the surface of a convex mirror 124 that diverges the beam, both in the x direction 48 and in the y direction, to produce the divergent beam 24. The diverging beam 24 is intercepted afterwards. by a concave, cylindrical mirror, 126, which acts to collimate the beam in the direction and produce the beam 32. The collimated beam 32 now has a rectangular shape whose cross-sectional dimensions are controlled by the focal lengths and spacings of the mirrors 124 , 126, and 128. The length in the direction of this section. trans-aversaL, ractajx.gui.a., - sa datarmln-a through the desired width of the metal band 40 treated by this optical system. If there are going to be multiple optical systems to cover the entire width of the surface of the band, then the length of the optical system will be only a fraction of the entire width. The beam 32 is then reflected by a rectangular planar mirror 130, towards a cylindrical concave eector 132 of long end focus, having the same length as the desired final focused line 38. A method can also be used for the supply of optical scanning rays with focused light spot, to remove the oxide layer (scale). An optical system based on refraction, for this embodiment, is illustrated in Figure 10A. The full-power laser beam 56 can be divided into the secondary rays 57 of a smaller and much more manageable power, and each secondary beam is scanned over some fraction of the total width of the metal band. Then a ray 57 is passed through an ascending collimator 134 which increases the diameter of the beam and decreases the divergence of the beam. (If the laser produces a large diameter beam with low divergence, it may be necessary to collide the beam in a downward direction, to reduce the diameter of the beam to a more manageable size.) A beam diameter of an LEL laser may be several centimeters, with a divergence limited by diffraction in such a way that descending collimation may be necessary). The beam 136 collimated upwardly (or downwardly collimated) is passed through a pair of mirrors 138 and 140 directing a beam 142, at the appropriate angle, towards a scanning mechanism 144 which may be a rotating polygon or a rocking mirror 146. A beam 148 is then passed through a flat-field focusing lens 150, which focuses the collimated beam 148 to a desired luminous spot size 154 on the surface of the metal strip 40 to be descaled. One advantage of the focused, scanned luminous spot system is that it does not require that the intensity distribution through the incoming laser beam be spatially uniform that is, it will not be required from the homogenizer 60. Another advantage is that the scanning mechanism allows that the focused light spot is scanned transversely through the surface 40 covered with the oxide in such a way that the attached scale layer is removed by one or more pulses of laser radiation at each point, along the scan line 182 as customized that the metal band 40 continuously passes through the focused laser light spot with transverse scanning. A disadvantage over the projected and focused laser line, illustrated in FIG. 4A, is that it adds more optical surfaces for additional loss of laser energy and has a moving mechanical element. As an alternative, the flat field focusing lens 150, of FIG. 10A, could be replaced with a pre-scan focusing lens, positioned forward of the oscillating mirror 146. The pre-scan focusing lens will be moved back and forth. in the direction of beam propagation, in synchronization with the scanning speed of the mirror, to keep the spot focused, on the flat metal surface. Figure 10B illustrates yet another embodiment of the invention, for an optical scanning light spot system, using mirrors with a focusing lens, to provide a telecentric scanning system, to maintain a uniform luminous spot size, over the width of the exploration field. The laser beam 136 impinges on a lens 156 placed in front of the revolving scanning polygon 146 to redirect a beam 158. A convergent beam 159 is directed towards a long rectangular flat mirror 160, which extends over a large portion. of the desired exploration field. The mirror 160 redirects a scanned beam 162 towards a curved parabolic mirror 164 that extends across the width of the scanned field. This curved mirror redirects a convergent beam 166 in such a way that it impinges on the surface, at the same angle, without taking into account where the beam is focused through the scanning field. The beam is focused to the same size as the light spot through the entire length of the scanning field. This system has the advantage over the refractory system illustrated in Figure 10A that most of the optical elements are mirrors that do not have the absorption losses of the refractory elements. This is advantageous due to the high energy requirements needed for a laser descaling system in an economical way in production. A rectangular mirror 168 can be addedplane, long, to direct the focused radiation, towards a mirror 170 of concave, cylindrical, long focus, to converge the radiation into a converging beam 172 to provide additional compression, of the focused luminous spot, in the direction 42 travel of the band. A cylindrical, converging, full-width lens 34 could be used instead of the mirrors. 168 and 170, to focus the beam and produce a smaller dimension of the descending grid. This will result in an elliptical luminous spot 174 focused with the longitudinal direction of the luminous spot focused in the scanning direction 176 as illustrated in greater detail in Figure 10C.
Example
An example will be provided to demonstrate the feasibility of the invention. An estimate of the amount of energy, and the projected processing speed of the metal band, necessary to vaporize an aluminum oxide with a thickness of 5 microns, that is AI2O3, in an aluminum band can be made. It is assumed that this oxide layer has a density of 4 g / cm 3, a melting temperature of 2,050 ° C, a vaporization temperature of 2,980 ° C, a heat of fusion of 255 cal / g, a heat of vaporization of 1,138 cal / g, and a heat capacity of 0.32 cal / g / ° C. The source from which this data was obtained is the Laser Institute of America Handbook: Guide for Material Processing by Lasers, 2a. Edition, 1978, pp. 9-3, incorporated herein by reference. For this example, it will be assumed that a projected laser line system, such as that illustrated in Figure 4, will be used to focus the laser radiation in the form of a line. It will also be assumed that there will be ten of these systems, oriented side by side, to descaling a whole band 1 meter wide. It is also assumed that a LEL laser of 100 KW, produces a beam divided into 10 secondary rays of 10 • KW of laser radiation each, and that these secondary rays are then focused ", each, in a line of 10 cm long 2 mm wide Assuming that there is an inlay layer 5 microns wide, and a focused line 10 cm long by 2 mm wide, the volume of aluminum oxide to be vaporized is V = (0.0005) cm) (10 cm) (0.2 cm) = 0.001 cm3 The energy needed to vaporize this volume is E = (4 g / cm3) (0.001 cm3) (0.32 cal / g / ° C) (2, 960 ° C) + 255 cal / g + 1,138 cal / g) (4,184 J / cal) = 39.2 joules If each of the ten secondary rays supplies 10 KW of average power, the energy per pulse at a repetition rate of 30 MHz is of 333 microjoules per pulse, so the number of pulses required to supply these 39.2 joules of energy is N = 39.2 J / (0.000333 J / impulse) = 117, 720 pulses. Lightning, at this point, to release 117,720 pulses of the 30 MHz laser beam is T = (117,720 impulse s / s) = 0.00392 s. To determine the speed of the line, necessary to eliminate this layer of 5 microns in thickness, an aluminum band is required in which the oxide layer can only move the width of the focused laser line, that is, 2 mm, to the once it has to supply all the 117,720 impulses. As well as the speed of the line is V = 0.002 m / 0.00392 s) (60 s / min) = 30.6 m / min. Thus, if there were ten of these rays, of 10 KW each, focused in the form of a line of 10 cm of transversal length, and each one was oriented in the contiguous form in the transversal width, as illustrated in fiche 5, then an aluminum band with a total width of 1 m could be removed by an oxide layer 5 microns thick, on one side, at a speed of 30.6 m / min. It could be noted that the rust removal rate may be higher, due to other scaling removal mechanisms, that may be taking place, due to the short pulse duration and the high surface power density. However, by this calculation, based simply on a thermal vaporization mechanism, it would require a LEL laser, of 200 KW, to descale both sides of this band of aluminum with a meter of width, at a speed of 30.6 m / min. It will be understood that various modifications can be made to the invention, without departing from the spirit and scope thereof. Therefore, the limits of the invention should be determined from the appended claims. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:
Claims (58)
1. A method for removing or removing oxide from a surface of a metal, characterized in that it comprises: using a laser beam to produce electromagnetic radiation having a very short pulse duration or width, a very high pulse repetition rate and a very high average power high, produce the radiation, ac-er pass the radiation through at least one optical element to focus the radiation in the form of an incident beam having a surface power density of at least about 5 MW / cm2 at a point of contact with the surface of the metal, and make the ray of radiation pass, focused, transversely, completely through the surface of the metal covered with the oxide, to remove or eliminate the oxide by vaporization, through the interaction of one or more laser pulses, thereby forming a surface without rust.
2. The method according to claim 1 is that the metal is a hot-rolled or annealed strip or strip, traveling at a consistent speed with a pulse repetition rate of the lightning. er.
3. The method according to claim 1, characterized in that the metal is a band traveling in a vertical direction, at a speed of at least 10 m / min.
4. The method according to claim 1, characterized in that the duration of the laser pulse is less than a nano second.
5. The method according to claim 4, characterized in that the duration of the laser pulse is less than 100 peak seconds.
6. The method according to claim 4, characterized in that the duration of the laser pulse is less than 10 seconds.
7. The method according to claim 4, characterized in that the laser pulse has a width or duration of about 1 femtoseconds to 6 peaks seconds.
8. The method according to claim 1, characterized in that the repetition rate of the pulse J-As-er e-s d-a at least 1 KHz.
The method according to claim 8, characterized in that the repetition rate of the -i-mpulsa XAS axis is 1-40 MHz.
10. The method according to claim 8, characterized in that the repetition rate dal i p-ulsQ -laser is 40 MHz at 1 GHz.
11. The method according to claim 1, characterized in that the average power of the laser is at least 1 KW.
12. The method according to claim 1, characterized in that the average power of the laser is at least 10 K.
13. The method according to the rei indication 1, characterized in that the average power of the laser is at least 10-0 KW.
14. The method according to claim 1, characterized in that the surface power per unit area, per laser pulse supplied to the surface of the oxide layer, is at least 10 x 106 watts / cm2.
15. The method according to claim 1, sarasterized because the radiation has a wavelength of photons that is in the range or range of ultraviolet.
16. The method according to claim 1, characterized in that the optical element is a lens.
17. The method according to claim 1, characterized in that the optical element is a mirror.
18. The method of conformance with the rei indication 1, sarasterized in that the optical element includes a combination of a-1 minus a lens and of at least one mirror.
19. The method according to claim 18, characterized in that the optical elements are aligned.
20. The method according to claim 1, characterized in that the optical element includes a means for dividing the radiation beam into a plurality of focused secondary rays, and each secondary beam has a lower power than that of the beam originating from the laser.
21. The method according to claim 1, characterized in that the optical element includes a means for the homogenization of the radiation, in order to provide a relatively uniform spatial distribution of power through the focused beam.
22. The method according to claim 21, characterized in that the means for homogenization includes a linear divergent lens having a sharp radius at the apex.
23. The method according to claim 21, characterized in that the means for homogenization includes a lens and a stepped index optical fiber, and the lens is used to focus the radiation beam at one end of the fiber.
24. The method according to the indication rei 20, characterized in that each secondary beam is passed through a means for homogenization, to provide a relatively uniform spatial distribution of power through each secondary beam.
25. the method according to claim 21, characterized in that the radiation beam is focused on at least one distribution line. It gives uniform power, which extends transversely across the full width of the metal surface.
26. The method according to claim 1, characterized in that the radiation beam is focused in the form of a light spot, the method includes the additional step of running the light spot through the entire width of the metal surface , whereby the oxide is removed or removed, due to one or more. impulses of radiation.
27. The method according to claim 1, characterized in that the radiation beam makes contact with the metal surface at an acute angle.
28. The method according to claim 2 1, ac achoxy because the angle is 10-75 °.
29. The method according to claim 27, characterized in that it is 25-60 °.
30. The method according to claim 1, characterized in that it includes the additional step of gathering the vaporized oxide in the form of a powder.
31. The method according to claim 1, characterized in that it includes the additional steps of protecting the contact point and the oxide-free surface, and expelling the oxide residue with a non-oxidizing gas.
32. The method according to claim 1, characterized in that it includes the additional steps of gathering the vaporized oxide, with a non-oxidizing atmosphere, separating the oxide residue, from the non-oxidizing gas, in the form of a powder, and recirculating the non-oxidizing gas. oxidant, cleaned, towards the point of contact with the metal surface.
33. The method according to claim 16, characterized in that the optical element is a combination of lenses to the beam, a first optical element is a divergent spherical lens, a second optical element is a cylindrical lens to collimate or vertically align the beam, a The third optical element is a cylindrical lens for horizontally collimating the beam, and a fourth optical element is a cylindrical lens for focusing the beam in the form of a narrow line.
34. The method according to claim 17, characterized in that the optical element is a combination of elements to the unfilled, a first optical element consisting of a convex, divergent, circular mirror, a second optical element consisting of a concave mirror, cylindrical, to vertically collimate the beam, a third optical element consisting of a concave, cylindrical mirror to horizontally collimate the beam, a fourth optical element consisting of a plane mirror, to redirect or redirect the beam, and a fifth optical element which consists of a concave mirror, cylindrical, to focus e-1 ray in the form of a narrow line.
35. The method according to claim 18, characterized in that the combination includes, a first optical element consisting of a lens for collimation, a second element consisting of at least one addressing mirror, for orienting the collimated beam, and a means for explore the imam ray imado.
36. The method according to claim 35, characterized in that the collimation lens is an ascending collimation lens or a descending collimation lens.
37. The method according to claim 35, characterized in that the optical element further includes a scanning lens, with a flat field, and the scanning means includes a rotating mirror for repetitively scanning the collimated beam at lt > long of a flat field lens entrance pupil.
38. The method according to claim 18, characterized in that the combination is a telecentric system that includes a rotating mirror to explore the beam, a parabolic mirror to redirect the scanned beam, with the same angle, towards the surface, no matter where the lightning is focused on the surface, through the field of exploration.
39. The method according to claim 38, characterized in that the combination includes a focusing lens positioned forward of the rotating axis.
40. The method according to claim 38, characterized in that the combination includes a reversing mirror, which follows the parabolic mirror.
41. A method for removing rust from a surface of a metal strip or strip, characterized by comprising: using a laser to produce electromagnetic radiation having a pulse duration or width of less than 10 picoseconds, a pulse repetition rate of at least 10 MHz and an average power greater than 10 KW, producing the radiation, passing the laser radiation through at least one optical element to focus the radiation in the form of an incident beam having a surface power density of at least about 10 MW / Cm2 at a point of contact with the surface of the band, the optical element includes a means for the homogenization of the radiation and at least one between a converging lens, cylindrical, long, or a concave, cylindrical, long mirror, to focus the ray in the form of at least one straight line, passing the band through the focused radiation line, transversally and in full Through the surface covered with the oxide, to remove the oxide by vaporization, by interacting one or more of the spatially elongated laser pulses, thereby forming a surface without rust.
42. An apparatus for removing rust from a surface of a metal strip or strip, characterized in that it comprises: a laser for producing electromagnetic radiation having a very short pulse duration or width, a very high pulse repetition rate and a very high average power high, at least one optical element for focusing the radiation in the incident beam shape having a surface power density of at least about 5-MW / cm2 at a contact point of the metal band and a sealed interaction chamber for removing the oxide from the metal strip, the chamber contains a non-oxidizing gas and a slotted inlet to receive a moving metal strip that has a surface. covered with an oxide, a slotted outlet for the passage of the metal strip to which the oxide has been removed from the surface, at least one elongated window to receive the radiation in the chamber whereby the radiation can be Pass through the surface covered with the oxide transversely and completely, to remove the oxide by vaporization.
43. The apparatus according to claim 42, characterized in that it includes an exhaust or outlet to remove the gas containing the vaporized oxide residue, from the chamber, a filter to remove the residue, in the form of a powder, from the gas. and a return duct to return the cleaned gas to the chamber.
44. The apparatus according to claim 43, sarasterized because it includes a blower used to return the cleaned gas, through the return conduit.
45. The apparatus according to claim 42, characterized in that it includes a nozzle to direct the gas towards the chamber, _ above and adjacent to a plasma column, formed in a reaction zone.
46. The apparatus according to claim 45, characterized in that the nozzle is positioned at a certain angle towards the strip or strip, in a direction towards the exit direction of the metal band, from the chamber.
47. The apparatus according to claim 46, characterized in that an outlet vent is placed on the side of the chamber where the entrance for the band is located.
48. The apparatus according to claim 42, characterized in that the optical element includes at least one of the following: a lens, a mirror or a combination of the same.
49. The apparatus according to the rei indication 42, characterized in that the optical element is a plurality of elements to the unfilled.
50. The apparatus according to claim 42, characterized in that the optical element is a lens placed inside a window.
51. The apparatus according to claim 42, characterized in that the optical element includes a means for dividing the radiation beam into a plurality of focused secondary rays and the camera includes a corresponding number of windows, and each window serves to receive one of the secondary rays.
52. The apparatus according to claim 42, characterized in that the optical element includes a means for the homogenization of the radiation, to provide a relatively uniform spatial distribution of power through the focused beam.
53. The apparatus according to claim 52, characterized in that the means for homogenization includes a linear divergent lens having a sharp radius at the apex.
54. The apparatus according to claim 52, characterized in that the means for homogenization includes a lens and a stepped index optical fiber, and the lens serves to focus the radiation beam at one end of the fiber.
55. The method according to claim 42, characterized in that the radiation has a wavelength of photons that is in the range or range of the ultraviolet.
56. The apparatus according to claim 4-2, characterized in that the radiation beam is focused in the form of a line.
57. The apparatus according to claim 42, characterized in that the optical element includes a flat field focus lens, for focusing the radiation in the form of a luminous spot, a means for tracing the luminous spot of radiation, transversely along the length of the width of the window, to completely traverse the surface of the band, whereby the oxide is removed by one or more pulses of the radiation, as XB.Jbanda continuously passes through the chamber.
58. An apparatus for removing rust from a surface of a metal strip or strip, characterized in that it comprises: a laser device for producing electromagnetic radiation having a very short pulse duration or width, a very high pulse repetition rate and an average power very high, a plurality of aligned optical elements, to focus the radiation in the form of an incident beam having a surface power density of at least about 10 MW / Cm2 at a point of contact with the metal band, an interaction camera sealed to remove rust from the metal band and a splitter to split the radiation into secondary rays, the chamber contains a non-oxidizing gas and a slotted inlet to receive a moving metal strip, which has a surface covered with an oxide, a slotted out for the passage of a strip of metal that has been eliminated the oxide of the surface, an elongated window to receive r each secondary ray of radiation, in the chamber, whereby the secondary rays of the radiation can be passed completely and transversely through the surface covered with the oxide, to remove the oxide by vaporization. SUMMARY OF THE INVENTION The present invention relates to a process and apparatus for using laser radiation in the removal of an * oxide layer (scale) from a strip or strip of steel (40) hot rolled or annealed, by means of vaporization, which travels in a vertical gravitational direction, at a speed of at least 10 m / min. The process includes using electromagnetic radiation from a high power laser such as a free electron laser, whose radiation has a surface power density of at least about 5 MW / cm2 at a point of contact with the surface of the strip or band. of metal. The radiation is passed through an optical system of aligned lenses or mirrors, to focus the radiation in the form of a straight line projecting transversely and completely through the band. The radiation has a pulse width or duration less than 100 picoseconds, a pulse repetition rate greater than 10 MHz, and a high average power of at least 10 KW. A radiation beam (56) is passed through a homogenizer (60) having a linear divergent lens (-74) to spread the radiation in a linear, transverse direction. The radiation is passed through a cylindrical convergent lens (78) or a long cylindrical mirror (132), and is focused in the shape of a straight line beam (36) projected completely across the bandwidth, removing the oxide by vaporization, by interacting with one or more of the spatially elongated laser pulses, thereby forming a surface without oxide. A sealed interaction chamber (90) contains a non-oxidizing gas (108), a slotted inlet (91) to receive the rusted band, a slotted outlet (92) for the passage of the strip thus cleaned, at least one elongated window (93) for receiving the radiation in the chamber, an outlet or exhaust duct (94) for removing the non-oxidizing gas charged with oxide debris, from the chamber, and a filter (106) to remove the oxide dust, of gas. The non-oxidizing gas is directed or sent to the chamber, at a point just • on top of a plasma column (102) and just behind the radiation beam (36) focused, incident, through a nozzle (114) for gas, long slot type. By keeping the chamber sealed from the ambient atmosphere and by maintaining a sufficient amount of non-oxidizing gas, adjacent to the area of interaction with the plasma and the metal surface, cleaned, it can be prevented that the cleaned steel surface will be return to oxidize.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08695930 | 1996-08-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| MXPA98000554A true MXPA98000554A (en) | 1999-10-14 |
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