Method and apparatus for optically coupling an element analysis system and a laser to liquid metal in a melting vessel

• US 4,995,723 A
• Filed: 09/29/1989
• Issued: 02/26/1991
• Est. Priority Date: 10/03/1988
• Status: Expired due to Fees

• Current Assignee: Ferrotron Elektronik GmbH (Minerals Technologies Incorporated)
• Original Assignee: Fried. Krupp Gesellschaft mit beschrankter Haftung
• Inventors: Nick, Klaus-Peter, Carlhoff, Christoph, Lorenzen, Claus-Jurgen
• Primary Examiner(s): McGraw, Vincent P.
• Application Number:
  US07/414,387
• Time in Patent Office: 515 Days
• Field of Search: 356/317, 356/318
• US Class Current: 356/318
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0208 using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
• CPC Class Codes: G01J 3/0218 using optical fibers
• CPC Class Codes: G01J 3/0237 Adjustable, e.g. focussing
• CPC Class Codes: G01J 3/443 Emission spectrometry
• CPC Class Codes: G01N 2021/695 Molten metals
• CPC Class Codes: G01N 21/718 Laser microanalysis, i.e. with formation of sample plasma

Abstract

A method of analyzing elements of a metal melt contained in a melting vessel comprises the following steps: introducing an inert gas at a temperature in excess of 300° C. laterally into a tube passing through a lateral wall of the melting vessel and opening thereinto; generating a laser beam; passing the laser beam through an adjustable first lens system; reflecting the laser beam by a mirror into the tube; guiding the laser beam through a quartz window which closes the tube; generating a plasma in the tube by focusing the laser beam by the adjustable first lens system onto the surface of the metal melt in the tube; guiding the light generated by the plasma through the quartz window to an adjustable second lens system; coupling the light by the adjustable second lens system with an optical waveguide; and introducing the light by the optical waveguide into a spectrometer.

Claims

1. A method of analyzing elements of a metal melt contained in a melting vessel, comprising the following steps:

(a) introducing an inert gas at a temperature in excess of 300°

C. laterally into a tube passing through a lateral wall of the melting vessel and opening thereinto;

(b) generating a laser beam;

(c) passing the laser beam through an adjustable first lens system;

(d) reflecting the laser beam by a mirror into said tube through a quartz window closing said tube;

(e) generating a plasma in said tube by focusing the laser beam by said adjustable first lens system onto the surface of the metal melt in said tube by the condition that the relation of the intensities Me_I /Me_II is a minimum;

(f) guiding the light generated by the plasma through said quartz window to an adjustable second lens system;

(g) coupling the light by said second lens system with an optical waveguide so that the plasma is focused on the input end of the waveguide; and

(h) introducing the light by the optical waveguide into a spectrometer.

2. A method as defined in claim 1, wherein said inert gas is argon.

3. A method as defined in claim 2, wherein said temperature is in excess of 500°

C.

4. A method as defined in claim 1, further comprising the step of varying said adjustable first and second lens systems upon changes of wall thickness of the melting vessel, such that the laser beam continues to be focused on said surface of the metal melt and the generated plasma is focused continuously on the input end of the waveguide.

5. An apparatus for the emission spectrum analysis of a metal melt contained in a melting vessel, comprising

(a) a housing;

(b) a tube connected to said housing and extending therefrom and being adapted to pass through a wall of the melting vessel;

the tube having an open end for communicating with the metal melt, whereby a surface of the metal melt is exposed in the tube;

(c) a quartz window closing said tube at a distance from said open end;

(d) a gas intake nipple provided in said tube between said open end and said quartz window for introducing an inert gas into the tube;

(e) a laser beam generator accommodated in the housing;

(f) a mirror supported in said housing and oriented for reflecting a laser beam, emitted by the laser beam generator, into said tube through said quartz window;

(g) an adjustable first lens system arranged in the path of the laser beam for focusing the laser beam on the surface of the metal melt to generate a plasma thereon;

(h) a spectrometer situated externally of said housing;

(i) an optical waveguide extending from the housing to the spectrometer; and

(j) an adjustable second lens system for directing light, emitted by the plasma and passing through the quartz window, into the optical waveguide for introduction therefrom into said spectrometer.

6. An apparatus as defined in claim 5, wherein said tube has two consecutive length portions of unlike diameter;

the length portion closer to the housing having the greater diameter.

7. An apparatus as defined in claim 6, wherein the length portion of smaller diameter is ceramic and the length portion of greater diameter is metal.