US3316160A

US3316160A - Process for electrolytic chromium-plating steel strips without a bluish tint while using two or more plating tanks

Info

Publication number: US3316160A
Application number: US300589A
Authority: US
Inventors: Uchida Hiromu; Yanabu Osamu; Hada Takashi; Adachi Takeo; Jun Tsujimoto
Original assignee: Fuji Iron and Steel Co Ltd
Current assignee: Fuji Iron and Steel Co Ltd
Priority date: 1962-08-16
Filing date: 1963-08-07
Publication date: 1967-04-25
Anticipated expiration: 1984-04-25
Also published as: DE1267052B; GB991310A; BE635457A

Description

Aprll 1967 HIROMU UCHIDA ETAL 3, 0

PROCESS FOR ELECTROLYTIC CHROMIUM-PLATING STEEL STRIPS WITHOUT A BLUISH TINT WHILE USING TWO OR MORE PLATING TANKS Filed Aug. 7, 1963 3 Sheets-Sheet 1 k) g L 31 L. a; Q Q a {Q I\ & *w

1 N VEN TORS BY 74/(50 ADACH/ umv TSUJ/MOTO April 1967 HIROMU UCHIDA ETAL 3,316,160

PROCESS FOR ELECTROLYTIC CHROMIUMPLATING STEEL STRIPS WITHOUT A BLUISH TINT WHILE USING TWO OR MORE PLATING TANKS Filed Aug. 7, 1963 3 Sheets-Sheet 2 A M Q;

JUN W 9 April 25, 1967 IROMU UCHIDA ETAL 3,316,160 PROCESS FOR ELECTROLYTIC CHROMIUM-PLATING STEEL WITHOUT A STRIPS BLUISH TINT WHILE USING TWO OR MORE PLATING TANKS Filed Aug. 7, 1963 3 Sheets-Sheet 5 Y NABU BY 741645! #404 A Tram/5w.

United States Patent 3,316,160 PROCESS FOR ELECTROLYTIC CHROMIUM-PLAT- ING STEEL STRIPS WITHOUT A BLUISH TINT WHILE USING TWO OR MORE PLATING TANKS Hiromu Uchida, Osamu Yanabu, Takashi Hada, Takeo Adachi and Jun Tsujimoto, all of Hyogo-ken, Japan, assignors to Fuji Iron & Steel Co., Ltd., Tokyo, Japan Filed Aug. 7, 1963, Ser. No. 300,589 Claims priority, application Japan, Aug. 16, 1962, 37/155,474; Dec. 3, 1962, 37/54,480 8 Claims. (Cl. 204-28) This invention relates to a process for producing electrolytic chromium-plated steel strips using more than two plating paths or plating tanks and, more particularly, to an economical and advantageous process of this type in Which the electrolytic chromium-plated steel strip is produced without a bluish tint.

In the usual case, when a steel strip or wire is electrolytically plated with chromium using only one plating tank, plating having a lustrous silvery white color is obtained easily. However, when the number of plating tanks is increased to two or more, and if the plating in and after the second tank is effected using the same procedure as in the first plating tank, the surface of the steel strip will become bluish and lusterless. In turn, this will interfere with the color quality of paint coated thereon, thus lowering the value of the plated steel strip as saleable merchandise. The same phenomenon occurs using only one plating tank, if the plating paths are increased to two or more.

The cause of the plated surface becoming bluish, when plating is effected using two or more plating tanks or paths, is not clear. However, it has been surmised that a film of a complex chromium oxide is produced at the surface of the steel strip as it emerges from the first tank and may be the cause of this phenomenon.

As a result of experiments in an attempt to solve the problem of the bluish tint, the invention process has been developed and by this process chromium-plated steel strips without a bluish tint may be easily and advantageously obtained even when there are two or more plating tanks, or two or more plating paths in a single tank. The essence of the present invention resides in using certain specific treatment conditions within successive tanks or paths as cept the first tank or path.

More specifically, in accordance with the present invention, electrolytically chromium-plated steel, without the bluish tint, is provided by moving the steel strip through more than two tanks or paths, and in each of the plating tanks or paths after the first, imparting to the steel strip a cathodic treatment under low current density succeeded by chromium plating in the same path or tank.

For example, to remove the film causing the bluish tint, the present invention may rely upon the known Surgeant bath for the chromium plating process. In this case the cathodic treatment is effected by maintaining the steel strip negative with a current density of about 0.1-l0 a./dm. for 0.01 to 3 seconds. The eificiency of removing the said bluish tint will be insufiicient if the current density is greater than about a./dm. or less than 0.1 a./dm.

In accordance with the invention it has been found that, when such cathodic treatment and chromium plating are effected successively within the same plating tank, or along the same plating path, an electrolytic chromiumplated steel without the bluish tint may be obtained even if there are two or more plating tanks used or two or more plating paths, and the steel strip obtained will have a 2 lustrous silvery white color such as is obtained by using only one plating tank or path.

The present invention is applicable to plating using vertical type or tanks of a horizontal When using vertical tanks, plating is effected in each tank during the downward path of the strip or wire and, after the latter passes over the sink roll, in the upwith low current density before the plating. An electrolytically chromium-plated steel strip without a bluish tint may thus be obtained advantageously by using more than two plating tanks.

When the of small holes. In this case the steel strip or wire may be provided with a preliminary plating of a thin layer of. copper, nickel or alloys thereof.

The present invention is based upon the discovery that plating tank,

path in each path after the first plating path.

A feature of the invention plating tanks, in each tank after the first the downward manner as mentioned above.

The material used for the shielding plate or plates must be dielectric and corrosion resistant, such as, for example, vinyl chloride or the like.

For an understanding of the principles of the invention the following description of typical embodiments thereof, as illustrated in the accompanyin drawings and in accordance with the examples given hereinafter.

In the drawings:

FIG. 1 is a somewhat schematic and diagrammatic side elevational view illustrating the practice of the present invention using vertical plating tanks;

FIG. '2 is a somewhat schematic and diagrammatic side elevation illustrating the practice of the invention using horizontal plating tanks;

FIG. 3a is a partial elevational view illustrating one of the shielding plates or members in association with the strip to be treated;

FIG. 3b is a sectional view taken on the line AA of FIG. 3a; and

FIG. 3c is a sectional view taken FIG. 3a.

Referring to FIG. 1, the steel strip or wire is led from an uncoiler roll 1 through pinch rolls 2, a welder 3, and a driving and tensioning roll assembly 4, the strip being led into an electrolytic degreasing tank 5. From tank 5 the strip is led through a water tank 6, where the strip is washed, an electrolytic pickling tank 7 and a waterwashing tank 8 where the strip is again washed. The strip is then led into the first plating tank 9. In tank 9, electrolytic chromium plating is effected in a downward path 10 and an upward path 11.

In accordance with the invention, the steel strip is then led into a second plating tank 12 which is provided with the aforementioned shielding means A positioned so as to cover the upper portion of the downward path 13. Within the portion of the path covered by the shielding tank A, the strip is given a cathodic treatment which is effected by the relatively small electric current flowing through the small holes in the shielding plate. In the same tank, and after passing over the sink roll, the strip is electrolytically chromium-plated in the upward path 14.

The treatment given to the strip in tank 12 is repeated in each of the tanks '15, 16 and .17, utilizing shielding plates or casings B, C and D corresponding to the plate or casing A.

The steel strip or wire emerging from the tank 17 is then passed through a washing tank 18, a chemical treating tank 19, and a hot Water washing tank 20. The strip is then sprayed with oil in an emulsion-oiling tank 21 and coated with a predetermined amount of oil film by means of the squeezing rolls 22. The steel strip is then dried in drying furnace 23 and coiled on a coiling roll 25 after passing through tensioning and driving roll assembly 24.

In the schematically illustrated electrical supply for the apparatus, components 26 and 27 are D.C. sources for the electrolytic degreasing and electrolytic pickling. D.C. sources 28 through 32 are used for each of the

plating tanks

9, 12, 1'5, 1 6 and 17, respectively.

FIG. 2 illustrates the invention as used with horizontal plating tanks. In this case the steel strip or wire is led from the uncoiler means 33 into an electrolytic degreasing tank 37 after passing through pinch rolls 34, welder and a tension and driving roll assembly 36. Leaving tank 37, the strip is passed through a brush scrubber 38, an electrolytic pickling tank 39, a brush scrubber 40, and over an electric potential applying conductor roll 41 into the first plating tank 43. Roll 41 is connected to the negative terminal of D.C. source 66. In tank 43 electrolytic plating is effected by means of an electrode 42, connected to the positive terminal of source 66.

The strip of wire is then led into the second plating tank 46 over a conductor roll 44 connected to the negative terminal of source 67. However, in tank 46, cathodic treatment using a very small current is effected at the entrance portion to the electrode 45 by means of a shielding plate A which may be the same as previously described. After passing through the electrode 45, the strip is electrolytically plated in the usual manner. Electrode 45 is connected to the positive terminal of D.C. source 67.

In each of the succeeding plating tanks 49 to 52 and 55 cathodic treatments followed by electroplating are effected in the same manner as mentioned for tanks 46. In advance of entering each of the succeeding tanks 49, 52 or 55, the strip or wire passes over a

conductor roll

47, 50 or 53, respectively, connected to the negative terminal of a D.C. source 68, 69 and 70, respectively. (Electrodes 48, 51 and 54 are provided in the respective tanks 49, 52 and 55, and are connected to the respective positive terminals of the sources 68, 69 and 70. In each case, the shielding dielectric and corrosion resistant plates B, C and D are positioned to enclose the strip as the strip enters the electrodes 48, 51 and 54, respectively.

On leaving tank 55, the strip of wire passes over the on the line B-B of roll 56, which is connected to the negative terminal of the D.C. source 66, and then into a washing tank 57 after which the strip passes through a chemical treating tank 58 and a hot water washing tank 59 before it is sprayed with oil in the emulsion oiling tank 60 and coated with a predetermined thickness of oil film by means of pressure roll 52. The steel strip is then dried in the drying furnace 63 and coiled on a recoiler 65 after passing through the driving and tensioning roll assembly 64.

The D.C. current sources for the degreasing tank 37 and the pickling tank 39 are illustrated at 71 and 72.

Referring to FIGS. 3a, 3b and 3c, the construction of the shielding plate A may be seen. Each shielding plate A, which is also representative of the shielding plates B, C and D, is a fiat rectangle in cross-section and has a substantial lateral and longitudinal extent with respect to the strip S. One wide surface or wall of each plate or casing A is imperforate, while the opposite parallel surface is formed with the very small perforations 73. These very small perforations greatly decrease the current flow to the strip S, while the latter is passing through the shielding plate A.

The following specific examples are given to illustrate how the invention may be applied in practice:

Example I A steel strip having 0.25 mm. thickness is electrolytically degreased at 30 C. in a degreasing solution containing 5% caustic soda and 3% sodium silicate, with a current density of 40 a./dm. for two seconds. It is then washed by water and is electrolytically pickled in a 5% solution of sulfuric acid with a current density of 20 a./dm. for two seconds. It is washed with water again, and while keeping the temperature of the chromium plating electrolyte, which contains 250 g./l. of chromic acid anhydride and 2.5 g./l. of sulfuric acid, at 45 C.', it is chromium plated for two seconds in the first plating tank (the vertical type) with a current density of 30 a./dm. The strip is then subjected to cathodic treatment in the downward path of the second plating tank (the vertical type) with a current density of 3 a./dm. for 0.5 second, and to plating in the upward path with a current density of 30 a./dm. for one second.

In the third, fourth and fifth plating tanks (the vertical type) the plating is effected in the same manner as in the second plating tank. Chromium coating of 0.05 micron thickness, having a lustrous silver white color, is thus made on the steel strip.

The steel strip is then washed by water and dipped in a 1% chromic acid water solution at 50 C. for two seconds and after being washed by hot water, it is oiled by an emulsion-Oiler and is coiled on the recoiler.

Example 11 A steel strip having 0.25 mm. thickness, which has been subjected to electrolytic degreasing and electrolytic picking in the same manner as Example I, is plated in the first plating tank (vertical type) with a current density of 40 a./dm. for one second in each of the downward path and the upward path, while keeping the temperature of the chromium plating electrolyte, containing 200 g./l. of chromic acid anhydride and 2 g./l. of sulfuric acid, at 50 C. The strip is then subjected to cathodic treatment in the downward path of the second plating tank, with a current density of 5 a./dm. for 0.2 second, and then plated, with a current density of 40 a./dm. for one second, in the upward path.

In the third, fourth and fifth plating tanks, the plating is effected in the same manner as in the second plating tank, and thus chromium coating of about 0.06 micron thickness, having a lustrous silver white color, is obtained on the steel strip.

Example 111 A steel strip having 0.25 mm. thickness, which has been subjected to electrolytic degreasing and electrolytic pickling in the same manner as Example I, is plated in the first plating tank (vertical type) with a current density of 30 a./dm. for one second, in both the downward path and the upward path, while keeping the temperature of the chromium plating electrolyte, which contains 200 g./l. of chromic acid anhydride and 2.0 g./l. of sulfuric acid, at 50 C.

The strip is then subjected to cathodic treatment in the downward path of the second plating tank with a low current density of about 5 a./dm. restricted by means of the shielding plate, for about 0.1 second and then plated, with a current density of about 30 a./dm. for about 0.9 second. In the upward path the plating is effected, without any shielding plate, at a current density of 30 a./dm. for about one second.

In the third, fourth and fifth plating tanks the plating acid, at 50 C. It is then subjected to cathodic treatment in the second plating tank (the horizontal type) with a low current density of about 1 a./dm. by passing through a shielding plate having small holes, on the inlet side of the electrode, for about 0.3 second, and then plated with a current density of 30 a./dm. after leaving the shielding plate, for about 1.2 seconds.

In the third, fourth and fifth plating tanks (the horizontal type) cathodic treatment is effected by using shielding plates on the inlet side of the electrode. Plating is then effected in the same manner as in the second plating tank, and thus chromium coating of 0.05 micron thickness, having a lustrous silver white color, is obtained on the steel strip.

1. A process for obtaining an electrolytic chromiumplated steel strip or Wire having a lustrous chrorninum coating, characterized by the absence of a bluish tint, comprising the steps of passing the steel strip or wire through more than two plating paths; in the second path and in each succeeding path the second path, initially at a low current density of 0.1 to a/dm. thereafter, in each plating path, chromium-plating the steel strip or Wire; and intermediate each plating path withdrawing the steel strip or wire from the plating solution.

2. A process for obtaining an electrolytically chromiupon the steel strip or wire to a value which is only a minor fraction of the current density effective during the plating operation; thereafter, in the second path and in each of the succeeding paths, subjecting the steel strip or wire to an electrolytic chromium-plating at normal current density; and intermediate each plating path withdrawing the steel strip or wire from the plating solution.

3. A process for electrolytically chromium-plating steel strip or wire to obtain a lustrous coating characterized by the absence of a bluish tint, comprising the steps of passing the steel strip or wire along more than two horizontal plating paths each having an activating electrode disposed therealong; in the second path and in each path succeeding the second path, in advance of the: steel strip orwire passing the activating electrode, passing the steel strip or wire through shielding means formed with a preselected number of very small apertures to reduce the currentflow to the strip or wire to a value which is only a minor fracplating action; in the activating electrode, a normal chromium plating current flow; and, intermediate each plating path, withdrawing the steel strip or wire from the solution.

4. A process for obtaining an electrolytically chromium-plated steel strip having a lustrous chromium coating characterized by the absence of a bluish tint, comprising or wire through more each tank succeeding the second tank, chromium-plating the steel strip or wire; and intermediate each plating path withdrawing the steel strip or wire from the plating solution.

5. A process for obtaining an electrolytically chromium-plated steel strip or wire having a lustrous chromium the absence small value which is only a minor fraction of the normal plating current density; and in the upward section of the second tank and of each tank succeeding the second tank chromium-plating a steel strip or wire with a current density of a normal value.

for electrolytically chromium-plating a electrode; in the the second tank, in advance of the steel strip or wire passing the activating electrode, shielding the plating operation; in the second tank, and in each tank succeeding the second tank, as the steel strip or wire passes the activating electrode, subjecting the steel strip or wire to the normal current density of the plating; and intermediate each plating path withdrawing the steel strip or wire from the plating solution.

7. A process for electrolytically chromium-plating steel ond path and in each path succeeding the second path initially subjecting the steel strip or wire to a cathodic treatment using a low current density of 0.01 to 10 a/dm. in the succeeding portion of the second path and of each 5 path succeeding the second path, subjecting the steel strip or wire to normal chromium-plating density; and intermediate each plating path withdrawing the steel strip or wire from the plating solution.

8. In the process claimed in claim 7, in the initial portion of the second path and of each path succeeding the second path, shielding the steel strip or wire by passing it through shielding means formed with a preselected number of very small perforations to reduce the current density during the cathodic treatment to said low value.

8 References Cited by the Examiner UNITED STATES PATENTS 1,794,973 3/ 1931 McBride 204-428 2,266,330 12/1941 Nachtman 204-28 2,619,454 11/ 1952 Zapponi 204-211 FOREIGN PATENTS 727,789 4/1955 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner.

JOHN H. MACK, Examiner. T. TUFARIELLO, Assistant Examiner.

Claims

1. A PROCESS FOR OBTAINING AN ELECTROLYTIC CHROMIUMPLATE STEEL STRIP OR WIRE HAVING A LUSTROUS CHROMINUM COATING, CHARACTERIZED BY THE ABSENCE OF A BLUISH TINT, COMPRISING THE STEPS OF PASSING THE STEEL STRIP OR WIRE THROUGH MORE THAN TWO PLATING PATHS; IN THE SECOND PATH AND IN EACH SUCCEEDING PATH THE SECOND PATH, INITIALLY SUBJECTING THE STEEL STRIP OR WIRE TO A CATHODIC TREATMENT AT A LOW CURRENT DENSITY OF 0.1 TO 10 A/DM.2; THEREAFTER, IN EACH PLATING PATH, CHROMIUM-PLATING THE STEEL STRIP OR WIRE; AND INTERMEDIATE EACH PLATING PATH WITHDRAWING THE STEEL STRIP OR WIRE FROM THE PLATING SOLUTION.