Descaling metal with a laser having a very short pulse width and

Details Descaling metal with a laser having a very short pulse width and Descaling metal with a laser having a very short pulse width and

1997-11-17

1999-09-07

Alexander, Lyle A.

Cleaning and liquid contact with solids

Processes

Including application of electrical radiant or wave energy...

134 21, B08B 700

Patent

active

059481722

ABSTRACT:
The invention relates to an apparatus for using laser radiation to remove an oxide layer (scale) by vaporization from a hot rolled or annealed steel strip (40) traveling in a gravitationally vertical direction at a speed of at least 10 m/min. The apparatus includes a high power laser such as a free electron laser and a sealed interaction chamber (90) containing a non-oxidizing gas (108). The electromagnetic radiation from the laser has a surface power density of at least about 5 MW/cm.sup.2 at a point of contact with the metal strip surface. The radiation is passed through an optical system of aligned lenses or mirrors for focusing the radiation into a straight line projected transversely completely across the strip. The radiation has a pulse width 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 diverging lens (74) for spreading the radiation in a linear transverse direction. The radiation is passed through a cylindrical convergent lens (78) or a long cylindrical mirror (132) and focused into a straight line beam (36) projected completely across the width of the strip. The oxidized strip passes into the sealed chamber through a slotted entry (91) and exits the sealed chamber through a slotted exit (92). The sealed chamber includes at least one elongated window (93) for receiving the radiation, an exhaust duct (94) for removing the non-oxidizing gas ladened with oxide debris from the chamber and a filter (106) for removing oxide powder from the gas. The non-oxidizing gas is directed into the chamber at a point just above a plasma plume (112) and just beyond incident focused radiation beam (36) through a long slot-like gas nozzle (114). By keeping the chamber sealed from the ambient atmosphere and maintaining sufficient non-oxidizing gas adjacent to the plasma interaction zone and the cleaned metal surface, reoxidation of the cleaned steel surface can be prevented.

REFERENCES:
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patent: 4826299 (1989-05-01), Powell
patent: 5151134 (1992-09-01), Boquillon et al.
Benson et al, "Development Of An Accelerator Ready Photo Cathode Drive Laser At CEBAF", presented at the Process Particle Accelerator Conference, 1995, Dallas.
Schulter et al, "Descaling of Austenitic Steels by Laser Radiation", Proc. ICALEO 94, Orlando, Fla., Oct. 17-20, 1994.
Weher et al, "Ablation of Oxide Layers on Metallic Surfaces by Excimer Laser Radiation", Proc., ECLAT 90, vol. 2, pp. 917, 1990.
"Free Electron Lasers For Industry", vol. I and II, May 1995, Department Of Energy.
"Solvent Substitution", The First Annual International Workshop On Solvent Substitution, Dec. 4-7, 1990, Phoenix, Arizona.

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