Method and device for measuring a chemical composition of a liquid metal suitable for coating a steel strip

1. A device for measuring a chemical composition of a metal melt suitable for coating a steel strip, the device comprising:

a first cavity containing the metal melt;

a measuring instrument for measuring the chemical composition of the metal melt by measuring a direct measurement surface of the metal melt;

a temperature regulator disposed in a vicinity of the direct measurement surface so as to isolate mainly iron-based impurities from a sample of the metal melt reaching the direct measurement surface; and

a circulation circuit, the direct measurement surface being disposed on said circulation circuit for the metal melt of said first cavity, said circulation circuit having a circulation intake disposed at a height level of said first cavity such that most impurities, including a top dross and a bottom dross, are kept away from said circulation circuit.

2. The device as claimed in claim 1 , wherein said first cavity is a coating pot and said circulation circuit has a loop disposed externally to said coating pot.

3. The device according to claim 2 , wherein said circulation circuit has a bypass in a form of a vertical riser of a height at least greater than a melt level in said first cavity and the direct measurement surface is defined by the melt level in said vertical riser.

4. The device according to claim 3 , further comprising a vertical downpipe, said vertical riser is connected to said vertical downpipe terminating in said circulation circuit.

5. The device according to claim 4 , wherein each of said downpipe and said vertical riser has a valve to temporarily block off the metal melt in a bypass.

6. The device according to claim 5 , wherein at least one of said valves is subject to a defined blocking delay to ensure sufficient isolation of the impurities from the direct measurement surface, following which a measuring phase is initiated.

7. The device according to claim 4 , wherein said vertical downpipe has a melt overflow intake.

8. The device according to claim 4 , wherein said temperature regulator is disposed on a least one part subjacent to the direct measurement surface.

9. The device according to claim 4 , further comprising an induction heater selected from the group consisting of a single-phase AC system producing only a moderate mixing of the metal melt and a polyphase AC system producing a significant mixing of the metal melt, said temperature regulator is disposed on a least one part subjacent to said direct measurement surface and to said induction heater.

10. The device according to claim 1 , wherein said circulation circuit has a metal melt circulating channel inside or at least attached to said first cavity, said circulating channel being ideally configured for induction heating of the molten metal.

11. The device according to claim 1 , further comprising:

a second cavity being a coating pot, said first cavity is at least one metal alloy melting pot for preparing the metal melt, said melting pot connected to said second cavity; and

a metal melt conduit disposed between said first and second cavities, said circulation circuit connected to said metal melt conduit.

12. The device according to claim 1 , further comprising a baffle device, and, in said first cavity, a metal melt intake by said circulation circuit is preceded by said baffle device for catching at least compounds floating on the surface of a molten bath sampled in said first cavity.

13. The device according to claim 1 , further comprising a measurement chamber, an inert gas is applied to the direct measurement surface of the metal melt to protect it from oxidation reactions, a gas circulation flowrate of which ensures leakproof scavenging between said measurement chamber containing the direct measurement surface and said measuring instrument.

14. The device according to claim 1 , further comprising a window of a material transparent to an ablation laser beam and to plasma radiation and disposed between said measuring instrument and the direct measurement surface so as to form a leakproof measurement chamber.

15. The device according to claim 1 , wherein said measuring instrument is a spectral analysis device performing laser ablation of the direct measurement surface.

16. The device according to claim 1 , further comprising a measurement chamber and the direct measurement surface is disposed in said measurement chamber made of materials that are unreactive with the metal melt.

17. The device according to claim 16 , wherein said material of said measurement chamber is selected from the group consisting of an austenitic stainless steel, a ceramic and a ceramic-coated metal.

18. The device according to claim 1 , wherein the circulation circuit includes a pump for sampling the metal melt at least at its intake.

19. The device according to claim 18 , wherein said circulation circuit includes a pump having pumping properties coupled with isolation of impurities.

20. The device according to claim 19 , wherein said pump is selected from the group consisting of an electromagnetic pump and a pump equipped with an overflow stage.

21. The device according to claim 18 , wherein said pump is selected from the group consisting of electromagnetic pumps, mechanical pumps, centrifugal type pumps, pneumatic pumps and Venturi effect pump priming pumps.

22. The device according to claim 1 , wherein said circulation circuit has at least one sampling intake capable of being dipped through a molten metal surface.