KR20000011280A - Process and a plant for producing an electrolytically coated, hot-rolled strip - Google Patents

Abstract

PURPOSE: The aim is to provide a manufacturing method of electrolytic coated hot rolled steel strip that the method is characterized by combining of pickling part and coating part containing electrolytic pickling cell. CONSTITUTION: Non-treated hot rolled steel strip is supplied into chemical pickling part(2) consisted with two pickling chambers(3,4). Fresh acid(5) is added into the pickling part which is strip outlet. Used acid(6) is exhausted from steel strip inlet and is brought to acid cleaning step. Waste pickling solution(8) is brought to recycling apparatus. After chemical pickling(2), steel strip is cleaned in cleaning part to remove remaining acid of steel strip. The steel strip is supplied into electrolytic cell(10) to be coated. Coated steel strip(11) leaves the apparatus and winded. Electrolyte(12) is supplied from electrolytic part(13). Iron sulfuric compound or iron chloride compound solution(14) produced from pickling process can be used after through acid cleaning step(7) and Zn is supplemented.

Description

PROCESS AND A PLANT FOR PRODUCING AN ELECTROLYTICALLY COATED, HOT-ROLLED STRIP

In the manufacture of steel products, coatings are often applied to the final product. The main purpose in the above is to protect the product against corrosion. Coatings containing zinc or zinc alloys represent a significant part in the field for this purpose, but tin or chromium coatings also play an important part in the packaging plate part.

In continuous coating of steel strips, two processes in particular are of considerable importance:

Hot galvanizing and electrolytic galvanizing (coating)

In both cases, cold rolled steel was used as the initial material. The cold rolled steel strip, starting from a thick material of a typical hot rolled steel strip with 1.5 to 5 mm, was run in a cold rolling mill and rolled to a final thickness of 0.3 to 2 mm.

Before the hot rolled steel strip is cold rolled, the scale formed by the surface layer of other iron oxides at a typical thickness of about 5-20 μm in hot rolling must be removed. This can usually be done by decomposing the layer in an inorganic acid such as sulfuric acid or hydrochloric acid. The process is known as pickling and is performed in a batch-type or continuous pickling apparatus. One shape of this process is described, for example, in AT 399,537.

The purpose is to combine the individual steps in the manufacture of the strip to save cost and improve product quality for the required device. For example, in the current state of the art, the pickling and cold rolling processes are combined with each other.

On the other hand, DE-PS 1 960 6305 C1 (Mannesmann) describes a means for carrying out the hot rolling and pickling process in one apparatus. In the cold rolling process described, the material curing and the above effects have to be countered in the continuous annealing process.

The annealing process is carried out in a batch operation in a hood-type furnace or continuously in a through-type furnace. In hot galvanizing, the annealing and coating processes are combined into a single strip treatment apparatus, where the annealing process is first made and then the strips are covered with a zinc layer by being precipitated into the molten zinc in a further step.

Another means for depositing zinc and other metals on a steel strip is the electrolytic process. In this case, the strip is usually annealed and the cold rolled strip is pulled through an electrolytic bath containing dissolved metal ions. The strip is connected to the cathode of the rectifier (cathode) by suitable means, and the metal anode connected to the anode of the rectifier is mounted opposite the strip. By applying an electric current between the electrodes, metal ions are deposited on the steel strip in the form of metal.

For example, a process of this type is described in AT 373,922. Another process is particularly suitable for depositing zinc alloy from chloride electrodes since the anode region is separated from the cathode region by the diaphragm described in EP 580 730 (SIKEL).

In the past years, the manufacturing process for hot rolled steel has made significant progress and it has made it possible to manufacture thin and thin steel strips directly in the hot rolled process. As a result, the hot rolled steel strip can be used in many applications previously opposed for cold rolled steel sheets. However, this means that a corrosion protection layer should be applied to the hot rolled steel strip. Therefore, JP 91258210 proposes to supply a descaling hot rolled steel strip in a drying process and then to the hot galvanizing process. However, the process has some disadvantages because the dry scale removal process is expensive and there is no further point through the combination of an annealing and hot galvanizing process which has the advantage for cold rolled steel since there is no need to anneal the hot rolled steel. Has

The invention is characterized in that in one line, hot rolled steel strips are continuously supplied to the chemical pickling portion and then to the coating portion with the electrolytic cell.

Further preferred developments of the present invention are characterized in that the strip is cleaned between pickling and electrolytic coating.

An advantageous form of the invention is characterized by hydrochloric acid used as pickling and chloride electrolyte as coating, but sulfuric acid can also be used as sulfide electrolyte as pickling and coating.

Further advantageous developments of the invention are characterized by ferrous solutions formed in pickling used as coatings.

The advantageous shape of the invention is characterized by a solution draining out of the cell used as the pickling solution at one or more stages of the pickling process.

The invention also relates to an apparatus for producing an electrolytically coated hot rolled steel strip. It is characterized by a chemical pickling portion coupled to one line with a coating portion comprising an electrolytic cell, wherein the chemical pickling portion can be separated from the electrolytic cell in a cleaning step.

An advantage of the method is that both processes can be carried out at relatively low temperatures of 50 to 90 ° C. in aqueous solution. As a result, there is no need to heat the entire size of the strip to a temperature of 300 to 500 ° C., resulting in substantial energy savings. In conventional manufacturing processes for electrolytically coated steel strips, this requires simply pickling the steel strips in the acid as a preliminary treatment at all times and mainly requires that the coating layer is well adhered to the substrate. . In addition, the prior art requires degreasing because the strip is oiled to prevent any corrosion during intermediate storage. The process steps can also be omitted because the pickling and coating in the process according to the invention occur continuously in the middle, possibly separated by a cleaning step. This reduces the amount of harmful emissions produced and results in chemical savings. The iron sulfide or iron chloride solution produced during pickling is subjected to a cleaning process as described in AT 400.042 as an iron source in an alloy coating, for example an electrolyte for depositing a zinc iron alloy, and then partially in any process. Can be used. A process for applying this form of coating in chloride electrolytes is described, for example, in AT 397.663.

In the following, the invention has been described on the basis of an in-drawing drawing of a device according to the invention.

1 shows a device according to the invention.

The untreated hot rolled steel strip 1 is supplied to the chemical pickling portion 2 which constitutes, for example, two pickling bathtubs 3 and 4. Fresh acid (5) was added to the pickling section (2) which is the outlet of the strip. Although the pickling process is shown here with one pickling agent, however, other acids may also be used in each pickling bath 3, 4. The spent acid 6 is discharged from the steel strip inlet and brought to the acid rinse step 7. The waste pickling liquid 8 is brought to the acid regeneration apparatus so that it can be used again in the acid bath as fresh acid. After chemical pickling (2), the strip is washed in the cleaning section (9) to remove any acid adhering to the strip and immediately fed to the electrolytic cell (10) for coating, followed by coated strip (11). ) Leaves the device and is wound up.

The electrolyte 12 is supplied from the dissolving portion 13 in which the electrolyte is prepared. The iron sulfide or iron chloride solution 14 produced in the pickling process can be used after proceeding through the acid washing step 7 and supplemented with zinc 15.

Example

Test device for electrolytic coating of metal steel strip, mainly compose the following device −

De-winder, degreasing device, pickling equipment, galvanic cell, cleaning unit,

Dryer, Ash Winder

A thin, descaled coil of hot rolled steel strip was used with a steel strip width of 300 mm and a thickness of 1 mm. Degreasing apparatus was not used.

Exam 1:

The hot rolled steel strip was treated in a pickling section with a sulfuric acid solution containing 20% H ₂ SO ₄ at a temperature of 90 ° C. At the end of the pickling portion, the strip was simply cleaned. In a vertical device, the galvanic cell is equipped with an insoluble titanium anode coated with IrO. The cell contains a zinc sulfide electrolyte having a pH-value of 1.5 and a temperature of 55 ° C. Each of the four anodes (two on the top and bottom side of the strip) is supplied with 3000A.

At a strip speed of 30 m / min, a layer of zinc of approximately 2 μm was applied. After leaving the cell, the strip was washed and then dried. The product has a shiny silvery white surface.

In the next test, the coating showed good adhesion to the surface.

Exam 2:

In this test, the strip was pickled at a temperature of 80 ° C. and using hydrochloric acid at a concentration of 16%. The strip was introduced into the galvanic cell without any previous cleaning. The cells are fitted with soluble zinc anodes in the form of a strip. The electrolyte is a zinc chloride solution with a pH-value of 3. A pure zinc layer was deposited despite containing approximately 5 g / l iron. The surface is brighter than coated with a sulfide electrolyte. The coating was evaluated to adhere very well. In addition, metallographic investigations indicated that the pickling process was completed, and no residual scale was detected.

Trial 3:

In this test. The solution from the pickling section was to be operated with hydrochloric acid and was roughly composed of 100 g / l Fe, 60 g / l HCl, 190 g / l of total chloride and contained granular zinc and fed through the dissolution section.

After the dissolution process, the balance of hydrochloric acid was consumed in the mixed zinc. The solution provided is analyzed as follows: Fe 100 g / l, Zn 54 g / l, chloride 190 g / l. The solution was used as electrolyte in the galvanic section. The cell is fitted with insoluble anodes and diaphragms. By applying electric current, the zinc and iron layers are then deposited on the steel strip. The analysis of iron content in this layer is between 11 and 13%.

After the test, the solution from the galvanic cell is fed to the pickling section. The free acid formed in the galvanic electrical portion can be used to dissolve the scale.

As described above, the present invention relates to a process and apparatus for producing an electrolytically coated hot rolled steel strip, which can be omitted since the process steps occur continuously in the middle separated into a cleaning step to enable pickling and coating. Reduce the amount of harmful emissions released and achieve chemical savings.

Claims (8)

A hot rolled steel strip is a process for producing an electrolytically coated hot rolled steel strip, all through one line, continuously supplied to the chemical pickling portion and then to the coating portion having an electrolytic cell. The process of claim 1 wherein the strip is cleaned between pickling and an electrolytic coating. 3. Process according to claim 1 or 2, wherein hydrochloric acid is used as pickling agent and chloride electrolyte is used as coating agent. 3. Process according to claim 1 or 2, wherein sulfuric acid is used as pickling agent and sulfide electrolyte is used as coating agent. 5. Process according to any one of the preceding claims, wherein the ferrous solution is formed in pickling used as a coating agent. The process according to any one of claims 1 to 5, wherein the solution draining out of the cell is used as the pickling solution in at least one step of the pickling process. Apparatus for producing an electrolytically coated hot rolled strip characterized in that the chemical pickling portion (2) is joined in one line with a coating portion comprising an electrolytic cell (10). 8. Apparatus according to claim 7, wherein the chemical pickling portion (2) is separated from the electrolytic cell (10) by a cleaning step.