Method for plating a moving metal strip and coated metal strip produced thereby

Patent metadata

Field	Value
Publication number	US-10422049-B2
Application number	US-201515308017-A
Country	US
Kind code	B2
Filing date	May 21, 2015
Priority date	May 21, 2014
Publication date	Sep 24, 2019
Grant date	Sep 24, 2019

Abstract

A method for producing a steel substrate coated with a chromium metal-chromium oxide (Cr—CrOx) coating layer in a continuous high speed plating line, operating at a line speed (v1) of at least 100 m·min −1 , wherein one or both sides of the electrically conductive substrate in the form of a strip, moving through the line, is coated with a chromium metal-chromium oxide (Cr—CrOx) coating layer from a single electrolyte by using a plating process. A coated steel substrate and a packaging made thereof.

First claim

The invention claimed is:

1. A method for producing a steel strip-coated with a mixed chromium metal-chromium oxide (Cr—CrOx) coating layer, comprising:
transporting a moving steel strip through a plating line with a velocity v1 of at least 100 m·min −1 , the plating line containing a single electrolyte solution comprising trivalent chromium and the single electrolyte solution moving with a velocity v2;
wherein the single electrolyte solution is free of chloride ions, is free of a buffering agent and free of boric acid;
wherein the single electrolyte solution consists of an aqueous solution of chromium (III) sulphate, sodium sulphate as a conductivity enhancing salt and sodium formate as a chelating agent, unavoidable impurities and optionally sulphuric acid to adjust the pH, and optionally a thickening agent,
forming the mixed chromium metal-chromium oxide (Cr—CrOx) coating layer upon one or both sides of the steel strip, the Cr—CrOx coating layer being formed in a plating process from the single electrolyte solution in the plating line;
wherein the steel strip acts as a cathode,
reducing H + to H 2 (g) at an interface between the steel strip and the single electrolyte solution to increase the pH at the interface between the steel strip and the single electrolyte solution and drive Cr—CrOx deposition for forming the mixed chromium metal-chromium oxide (Cr—CrOx) coating layer; and
using the sodium sulfate in a sufficient concentration for increasing a kinematic viscosity of the single electrolyte solution to be 1·10 −6 m 2 ·s −1 (1.0 cSt) to 1·10 −5 m 2 ·s −1 when measured at 50° C. and reduce diffusion flux of H + ions to the interface between the steel strip and the single electrolyte solution, wherein the sodium sulphate concentration is between 100 and 320 g·l −1 ,
wherein reducing the diffusion flux of H + ions reduces current density at the interface to deposit Cr—CrOx.

2. The method according to claim 1 , wherein the kinematic viscosity is increased by using sodium sulphate as the conductivity enhancing salt at concentration from 150 to 250 g·l −1 .

3. The method according to claim 1 , wherein the kinematic viscosity is increased by using the conductivity enhancing salt in a concentration for the kinematic viscosity to be 1.75·10 −6 m 2 ·s −1 (1.0 cSt) to 1·10 −5 m 2 ·s −1 when measured at 50° C.

4. The method according to claim 1 , wherein the single electrolyte solution has a pH at 25° C. of between 2.5 and 3.5, wherein the kinematic viscosity is increased by using sodium sulphate as the conductivity enhancing salt at concentration from greater than 100 to at most 250 g·l −1 for the kinematic viscosity to be 1.22·10 −6 m 2 ·s −1 to 1.89·10 −6 m 2 ·s −1 when measured at 50° C.

5. The method according to claim 1 , further comprising increasing the kinematic viscosity by using the thickening agent and chromium in the single electrolyte solution is solely from chromium (III) sulphate.

6. The method according to claim 4 , wherein the steel strip velocity v1 is 500 to 900 m·min −1 , further comprising increasing the kinematic viscosity by transporting the steel strip and the single electrolyte solution through the plating line in a concurrent flow arrangement, wherein the steel strip and the single electrolyte solution move through the plating line in the concurrent flow arrangement at a ratio of v1/v2 of 0.25-4.

7. The method according to claim 1 , wherein the steel strip velocity v1 is 500 to 900 m·min −1 , further comprising increasing the kinematic viscosity by transporting the steel strip and the single electrolyte solution through the plating line in a concurrent flow arrangement, wherein the steel strip and the single electrolyte solution move through the plating line in the concurrent flow arrangement at a ratio of v1/v2 of between 0.1 and 10.

8. The method according to claim 1 , wherein a plurality (>1) of Cr—CrOx coating layers are deposited onto one or both sides of the steel strip, wherein each layer is deposited in a single step in subsequent plating cells, in subsequent passes through the same plating line, or in subsequent passes through subsequent plating lines.

9. The method according to claim 1 , wherein the single electrolyte solution has a pH at 25° C. of between 2.5 and 3.5, and wherein the unavoidable impurities are selected from the group consisting of dissolved steel strip, and an impurity in one or more chemicals included in the single electrolyte solution, the sodium sulfate at a concentration between 100 and 320 g·l −1 .

10. The method according to claim 1 , wherein the steel strip, prior to being coated with the Cr—CrOx coating layer is one of:
as-deposited tinplate, -or flow-melted tinplate;
tinplate that is diffusion annealed with an iron-tin alloy consisting of at least 80% of FeSn (50 at. % iron and 50 at. % tin);
single-reduced cold-rolled full-hard blackplate, or double-reduced cold-rolled full-hard blackplate;
cold-rolled and recrystallisation annealed blackplate;
cold-rolled and recovery annealed blackplate;
wherein the steel strip is intended for use in packaging applications after coating with the Cr—CrOx coating.

11. The method according to claim 1 , wherein the thickening agent comprises a polysaccharide, wherein the kinematic viscosity is increased by using the polysaccharide and wherein the chromium in the single electrolyte solution is solely from chromium (III) sulphate.

12. The method according to claim 1 , wherein the single-electrolyte solution having a pH at 25° C. of between 2.5 and 3.1, and wherein the unavoidable impurities are selected from the group consisting of dissolved steel strip, and an impurity in one or more chemicals included in the single electrolyte solution, wherein said sodium sulfate is at a concentration between 100 and 320 g·l −1 .

13. The method according to claim 1 , the single electrolyte solution having a pH at 25° C. of between 2.7 and 3.1, and wherein the unavoidable impurities are selected from the group consisting of dissolved steel strip, and an impurity in one or more chemicals included in the single electrolyte solution, wherein said sodium sulfate is at a concentration from 150 to less than 320 g·l −1 .

14. The method according to claim 1 , wherein the steel strip and the single electrolyte solution move through the plating line in a concurrent flow arrangement.

15. The method according to claim 1 , wherein the steel strip and the single electrolyte solution move through the plating line in a concurrent flow arrangement at a ratio of v1/v2 of between 0.1 and 10.

16. The method according to claim 4 , wherein the single electrolyte solution has a pH at 25° C. of between 2.7 and 3.5.

17. The method according to claim 16 , wherein the single electrolyte solution has a pH at 25° C. of between 2.7 and 3.1, wherein the kinematic viscosity is increased by using sodium sulphate as the conductivity enhancing salt at concentration from 150 to 250 g·l −1 for the kinematic viscosity to be 1.30·10 −6 m 2 ·s −1 to 1.89·10 −6 m 2 ·s −1 when measured at 50° C. and wherein the sodium formate is at concentration between 30 and 80 g·l −1 .

Assignees

• Tata Steel Ijmuiden Bv

Inventors

• Wijenberg Jacques Hubert Olga Joseph
• Link Jeroen Martijn

Classifications

• C25D9/08

  by cathodic processes · CPC title

• C25D3/06 Primary

  from solutions of trivalent chromium · CPC title

• C25D7/0621 Primary

  In horizontal cells · CPC title

• C25D9/10 Primary

  on iron or steel · CPC title

• C25D3/56

  of alloys · CPC title