JPH06104917B2 - Continuous electroplating method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electroplating method for producing a product free from flaws by preventing deposition of plating metal on an energizing roll during electroplating of a steel strip.

(Prior Art) Horizontal electroplating equipment has advantages such as smaller voltage loss and smaller strength of energizing rolls than vertical electroplating equipment. Therefore, it has been widely used for galvanizing since ancient times. Has been.

FIG. 1 is a schematic view of a horizontal electroplating apparatus generally used for galvanizing a steel strip. In the horizontal electroplating apparatus, a plurality of electrolytic cells are sequentially arranged, and each electrolytic cell is provided with a pair of anode electrodes corresponding to the top and bottom of the steel strip.
A current-carrying roll 2 and a backup roll 4 are installed in the vicinity of the inlet / outlet side of each tank, where the steel strip 1 is negatively charged and an electrolytic reaction occurs in the plating solution 3 to plate the surface of the steel strip 1. Be seen. In the electroplating apparatus having such a structure, since the energizing roll 2 and the plating solution 3 are in direct contact with each other, the plating metal is deposited and adheres to the energizing roll 2. Energizing roll 2
If the metal plating is attached, it will be caught between the current-carrying roll 2 and the steel strip 1 to cause a flaw on the surface of the steel strip, resulting in a product defect. Further, the electrical contact between the energizing roll and the steel strip 1 becomes incomplete, and the energization is partially hindered, making uniform plating impossible. Therefore, it is essential to prevent or remove the plating metal from the energizing roll 2.

For this purpose, the following methods have been conventionally performed. FIG. 2 shows the energizing roll 2 between the energizing roll 2 and the anode electrode 5.
The reverse electrolysis electrode 6 is attached in the vicinity of, and a reverse electrolysis voltage is applied to electrolytically remove the plating metal attached to the energizing roll 2. Further, FIG. 3 shows the one in which the abrasive 7 is pressed against the rotating energizing roll 2 to remove the plating metal adhered to the energizing roll 2. Further, there is a method disclosed in Japanese Patent Laid-Open No. 1-147089 as a method for detecting the adhesion of plated metal to the energizing roll.

(Problems to be Solved by the Invention) In the above-described method of reverse electrolysis, electrolysis is performed between the current-carrying roll and the reverse electrolysis electrode installed in the vicinity of the current-carrying roll. If so, the portion of the energizing roll where the plating metal is not adhered is directly electrolyzed, and the impurity metal ions are mixed in the plating solution. In addition, the roll life is shortened because the roll is galvanically corroded. On the other hand, in the case of the method of pressing the abrasive to remove the plating metal adhered to the energizing roll, the removed plating metal is mixed into the plating solution to cause a flaw. Also, the surface of the energizing roll is flawed to shorten the roll life. Further, the example shown in Japanese Patent Laid-Open No. 1-147089 only detects the adherence of the plating metal to the energizing roll,
It is not a means to prevent the adhesion of plated metal itself.

As can be understood from the above description, once the plating metal adheres to the current-carrying roll, it causes a problem and must be prevented. Under such circumstances, the present invention provides an electroplating method for preventing the plating metal from adhering to the energizing roll.

(Means for Solving the Problems) The gist of the present invention is to use a horizontal plating cell in a sulfuric acid-based electroplating bath to continuously electroplat a steel strip in a continuous electroplating method, in which the contact linear pressure between the energizing roll and the steel strip is controlled. 20-120kg / c
m, the Fe ³⁺ concentration in the plating solution is 0.2 to 0.6 g / l, which is a continuous electroplating method.

(Operation) The operation of the present invention will be described below.

Conventionally, in order to prevent the plating metal from depositing on the energizing roll, in order to reduce the contact resistance between the energizing roll and the steel strip, there has been a method of increasing the contact linear pressure between the energizing roll and the steel strip as high as possible within the allowable range of equipment specifications. It has been taken. However, when the contact linear pressure is increased, a linear recess is generated along the circumferential direction of the surface of the energizing roll by the end of the steel strip, and the contact resistance between the energizing roll and the steel strip locally decreases in the recessed portion. The plating metal will adhere to that part. For this reason, the upper limit of the contact linear pressure between the energizing roll and the steel strip must be 120 kg / cm to prevent dents.
Need to On the other hand, when the contact linear pressure between the current-carrying roll and the steel strip is too low, the contact resistance between the current-carrying roll and the steel strip increases, and the plating metal deposition on the current-carrying roll becomes violent.
It is necessary to set the lower limit of contact line pressure to 20 kg / cm.

The contact linear pressure between the energizing roll and the steel strip described here can be managed by the pressing force of the backup roll 4 shown in FIG. A pressure cylinder is added to the backup roll to change the pressing force. The contact linear pressure between the energizing roll and the steel strip can be expressed by the following formula.

Contact line pressure (kg / cm) = backup roll pressing force (kg) ÷ steel strip width (cm) The above-mentioned actions are based on the assumption that the surface of the energizing roll is flat. It is difficult to maintain the flatness because the electrolytic corrosion progresses by touching the plating solution with low pH. Electrolytic corrosion on the surface of the current-carrying roll progresses as the Fe ³⁺ concentration in the plating solution increases, so the Fe ³⁺ concentration must be 0.6 g / l or less. Fe ³⁺ is present around 1 g / l in the plating solution due to elution from the steel strip, etc. However, the Fe ³⁺ concentration can be controlled by treating the plating solution with an ion exchange resin. On the other hand, plating metal into the plating solution,
For example, when replenishing Zn, 2e ⁻ generated together with Zn ^{2+ due} to the dissolution of Zn combines with hydrogen ions to generate hydrogen gas, so that the dissolution rate decreases. But then 0.2g
When Fe ³⁺ is present in an amount of at least 1 / l, this iron ion reacts with the electron, so the generation of hydrogen gas is suppressed, the dissolution rate does not decrease, and it is therefore possible to continue plating continuously. Become.

(Example) Current-carrying roll body Ni-Cr-Fe alloy plating solution Zinc sulfate 300 g / l Sodium sulfate 100 g / l pH 1.4 Temperature 50 ° C Current density 150 A / dm ² Contact linear pressure between current-carrying roll and steel strip Also, the Fe ³⁺ concentration in the plating solution was changed and the state of plating metal deposition on the surface of the current-carrying roll and the state of occurrence of flaws on the steel strip were visually inspected. The results are shown in Table 1.

(Effects of the Invention) The present invention is an excellent invention capable of preventing the deposition of plated metal on an energizing roll during electroplating and producing a product free from flaws.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a general horizontal electroplating apparatus, FIG. 2 is a schematic diagram of a horizontal electroplating apparatus equipped with a reverse electrolysis electrode, and FIG. It is a figure which shows an example. 1 ... steel strip, 2 ... energizing roll, 3 ... plating solution, 4 ...
… Backup roll, 5 …… Anode electrode, 6 …… Reverse electrolysis electrode, 7 …… Abrasive material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-59-182997 (JP, A) JP-A-55-122896 (JP, A) JP-A-59-219488 (JP, A)

Claims (1)

[Claims] 1. A continuous electroplating method for electroplating a steel strip using a horizontal plating cell in a sulfuric acid electroplating bath, wherein the contact linear pressure between the energizing roll and the steel strip is 20 to 120 kg / cm, A continuous electroplating method characterized in that the Fe ³⁺ concentration is 0.2 to 0.6 g / l.