DE102009054266A1 - Electrolytically descaling and/or pickling cold-rolled and annealed metal strips, comprises guiding the metal strip in a conveying direction through a straightening unit for removing flatness error - Google Patents

Abstract

The method for electrolytically descaling and/or pickling cold-rolled and annealed metal strips (1), comprises guiding the metal strip in a conveying direction through straightening unit for removing flatness error, and subsequently and continuously guiding the metal strip in the conveying direction through a device for electrolytically descaling and/or pickling. The metal strip is stretch-bend directed for removing the flatness error and is subsequently descaled and/or pickled. The metal strip is horizontally guided by the deflection rollers into the device for electrolytically descaling. The method for electrolytically descaling and/or pickling cold-rolled and annealed metal strips (1), comprises guiding the metal strip in a conveying direction through a straightening unit for removing flatness error, and subsequently and continuously guiding the metal strip in the conveying direction through a device for electrolytically descaling and/or pickling. The metal strip is stretch-bend directed for removing the flatness error and is subsequently descaled and/or pickled. The metal strip is horizontally guided by the deflection rollers into the device for electrolytically descaling and/or pickling. The deflection rollers stretch the metal strip. An electrolyte is introduced between the metal strip and the electrodes (5) by using nozzles into the device for electrolytically descaling and/or pickling. A specific strip tension of greater than 15 N/mm 2>amounts to metal strip cross-section. The electrolyte temperature is 70-85[deg] C, where sodium sulfate concentration in the electrolyte is 150-200 g/l. A current density related to the anode is 5-15 A/dm 2>. An independent claim is included for a device for electrolytically descaling and/or pickling cold-rolled and annealed metal strips.

Description

The invention relates to a method and an apparatus for descaling and / or pickling a metal strip. In particular, the invention relates to electrolytic descaling and / or pickling of a cold-rolled and annealed metal strip after removal of flatness defects. Cold rolled metal strips are so-called cold strips. Cold strips contain stainless steel, nickel alloys and titanium. The invention relates to a continuous process. In this case, the electric current is conducted indirectly by means of an electrically conductive electrolyte through the metal strip.

For the further processing of a metallic coating by cold rolling, a scale-free surface must be present. The tinder must therefore be completely removed. This is done in known methods by a pickling process. Here, the various of the iron oxides, FeO, Fe ₃ O _4, Fe ₂ O _3, or in stainless steels, chromium-rich iron oxides existing scale depending on the steel quality by means of various acids, such as hydrochloric acid, sulfuric acid, nitric acid or mixed acid, at elevated temperatures by chemical Reaction solved.

The pickling is carried out according to the prior art in continuous strip pickling plants for cold-rolled and annealed stainless steel in two process steps.

In the first process step, the electrolytic pickling takes place in a chemically neutral electrolyte. The tension is applied indirectly to the metal strip. There are no contact points between the power source and the metal strip. The electrodes, anodes and cathodes are arranged horizontally and lapped by the electrolyte. The distance between the electrodes and the metal strip is more than 60 mm.

In the second process step, complete chemical etching takes place in an aqueous acid or an acid mixture. This process step is often carried out in an annealing and pickling line. As a result, the Glühzunder is removed immediately after the emergence.

Out DE 11 2007 000 641 T5 is a continuous rolling mill having means for joining a plurality of hot rolling coils, correcting the deformation of the bonded hot rolling coils with a scaffold, removing the surface scale of the hot rolling coils by passing the hot rolling coils through a pickling plant and continuously rolling the hot rolling coils with at least two rolling mills.

Out JP 6128774 A For example, an apparatus and a method for pickling a steel sheet are known. In order to increase the speed of the steel sheet in a pickling vessel and the production capacity, hydrochloric acid is dropped or sprayed onto the steel sheet before immersion in the pickling vessel.

Out JP 62211394 A For example, a method for pickling a hot-rolled steel sheet is known. In order to shorten the pickling time and to accelerate the treatment of a coil, a vessel with a molten salt is provided in front of a pickling vessel. The hot-rolled steel sheet is cooled or heated in this vessel to a certain temperature. Then the steel sheet is subjected to the pickling treatment.

Out JP 61279311 A For example, a method for pickling a hot-rolled steel sheet is known. In order to remarkably increase the speed of pickling and descaling a hot rolled steel sheet with a high temperature coil, the hot rolled steel sheet is worked to smoothen the surface thereof and then the hot rolled steel sheet is pickled and simultaneously treated with ultrasonic waves.

Out JP 4120287 A For example, a method for pickling a steel strip is known. To increase the effect of the pickling without causing insufficient pickling in the vicinity of the side edges of the steel strip or without excessive pickling in the middle area by excess pickling, pulling is applied to the side edges of the steel strip and the steel strip is pickled with sulfuric acid and then with hydrochloric acid.

Out JP 2001047121 A is the production of austenitic stainless steel sheets with excellent polishability known. In order to avoid a surface grinding process in a mechanical pre-descaling treatment during hot rolling of a steel sheet, the mechanical pre-descaling treatment is performed at a certain temperature. The pickling is carried out in a mixed aqueous solution having a certain concentration of nitric acid and hydrofluoric acid.

Out JP 5177238 A For example, a method for descaling hot rolled steel strip is known. In order to effectively decalcify a hot-rolled steel strip to which tension is applied during rolling, water is sprayed onto the steel strip under high pressure and acidic liquid is distributed on the steel strip.

From the EP 1 558 779 a method and an apparatus for descaling and / or cleaning a hot-rolled metal strand of normal steel or stainless steel is known in which the metal strand is guided in the conveying direction through a device in which it is subjected to plasma descaling and / or plasma cleaning, wherein the metal strand in the conveying direction before the device for plasma descaling and / or plasma cleaning is subjected to a process that gives the metal strand a high degree of planarity.

In the descaling of cold rolled metal strip, it has been found that the methods disclosed in the cited documents do not lead to any useful result, since the correspondingly treated metal strip, at least if it has a certain width, can not be descaled to the required quality.

The present invention is therefore based on the object to provide an economical and environmentally friendly process for the electrolytic pickling of a cold-rolled and annealed metal strip, with which it is possible to effectively stain wide metal strips over their entire width extension in constant quality.

A further object of the present invention is to provide a device for descaling and / or pickling a cold-rolled and annealed metal strip.

• a) das Metallband in Förderrichtung durch eine Richteinheit zur Beseitigung von Planheitsfehlern geführt wird und
• b) anschließend das Metallband in Förderrichtung durch eine Vorrichtung zum elektrolytischen Entzundern und/oder Beizen geführt wird.

The present invention is achieved by a method for electrolytic descaling and / or pickling of a cold-rolled and annealed metal strip, wherein

• a) the metal strip is guided in the conveying direction by a straightening unit for the removal of flatness errors and
• b) then the metal strip is guided in the conveying direction through a device for electrolytic descaling and / or pickling.

In the method according to the invention, a straightening unit or straightening machine, therefore a stretch bending device, is prefixed to the pickling vessel in order to eliminate band form errors. The use of a straightening unit is possible without producing surface defects on the metal strip. The metal strip has a chromite layer after annealing, which is very ductile. This ductile layer can not be torn even when using bending cassettes or rollers. It can be used all types of straightening units that work by train, pressure or train and bend.

By the stretch bending device, a flatness of the metal strip is produced, whereby it is achieved that the distance of the anodes and cathodes to the metal strip can be reduced to preferably less than 30 mm. The smaller this distance, the lower the voltage drop and the power consumption. The flatness of the metal strip is necessary for such a small distance of the metal strip to the anodes and cathodes. The metal strip can pass through the device for descaling and / or pickling as a flat sheet. The result of the descaling and / or pickling is substantially improved, so that the manufactured metal strip has a high quality.

Through the use of straightening units, it is possible according to the invention to use electrolytic pickling tanks which have a better pickling effect and require a lower energy requirement.

It has proven to be advantageous to adjust the tensile force in the straightening process so that a tensile stress occurs in the metal strip, which corresponds to at least 10% of the yield strength of the material of the metal strip.

The method can preferably be operated with continuously passing metal strip. However, it is also possible to carry the metal strip discontinuously, ie at a non-constant speed, through the descaling and / or pickling plant. The latter case is especially interesting for small plants.

In the pickling vessel, the metal strip is held by counter rolls on tension. This additionally ensures that the distance of the anodes and cathodes is reduced to the metal strip to about 10 mm to 30 mm.

A high specific strip tension> 15 N / mm ² strip cross-section is necessary in order to keep the slack of the metal strip and thus the risk of contact of the metal strip with the electrodes low.

Further reducing the distance of the anodes and cathodes to the metal strip can be further achieved by injecting at least one electrolyte so as to hydraulically stabilize the metal strip between the electrodes. The electrolyte for pickling a metal surface may contain sodium sulfate, sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, or mixtures thereof. However, it is also possible to use aqueous solutions of neutral conducting salts.

The electrolyte temperature is from 50 ° C to 90 ° C, preferably from 70 ° C to 85 ° C. The Na ₂ SO ₄ concentration in the electrolyte is from 150 g / l to 200 g / l, preferably 180. The current density relative to the anode is from 2 A / dm ² to 20 A / dm ² , preferably 5 A / dm ² to 15 A / dm ² .

• a) mindestens eine Vorrichtung zum elektrolytischen Entzundern und/oder Beizen aufweist, durch die das Metallband in Förderrichtung geführt wird und in der das Metallband elektrolytisch entzundert und/oder gebeizt wird, wobei
• b) mindestens eine Richteinheit vorhanden ist, die in Förderrichtung vor der Vorrichtung zum elektrolytischen Entzundern und/oder Beizen angeordnet ist und mit der Planheitsfehler im Metallband beseitigt werden.

The present invention is further achieved by an apparatus for electrolytic descaling and / or pickling of a cold-rolled and annealed metal strip, which

• a) at least one device for electrolytic descaling and / or pickling, through which the metal strip is guided in the conveying direction and in which the metal strip is electrolytically descaled and / or pickled, wherein
• b) at least one straightening unit is provided, which is arranged in the conveying direction before the apparatus for electrolytic descaling and / or pickling and are eliminated with the flatness error in the metal strip.

This straightening unit consists of at least one stretch straightening or stretch bending device. The straightening unit can be designed as a stretching unit, bending unit or a combination thereof. Furthermore, at least one clamping device for generating a tensile force in the metal strip is arranged in front of and behind the straightening unit. As tensioning device, the S-roller stand has proven itself.

The metal strip runs into the treatment chamber of the descaling and / or pickling device at an angle of <5 ° and is held in tension in the treatment chamber by counter-rolls. The electrodes can be set to a much lower level than before. That means a considerable energy saving.

Another advantage of the present invention is that the electrodes are horizontally installed and removed through a lateral opening in the pickling tank. A fixture in the masonry ensures good positioning of the electrodes. The electrodes do not need to be routed over the edge of the lid as usual.

Since the electrodes are no longer guided over the edge of the lid, the pickling container cover can be effectively sealed by a circumferential gutter. As a result, the inventive method is economical and environmentally friendly.

In the treatment chamber, a number of modularly constructed electrodes are arranged in the conveying direction of the metal strand. It can be provided that the individual electrodes depending on the degree of scaling and / or the degree of contamination of the surface of the metal strip and in dependence on the speed at which the metal strip passes the pickling device, independently switched on and off. It is possible to switch on just as many electrodes during descaling and / or pickling that a desired result is achieved.

The apparatus for electrolytic descaling and / or pickling has nozzles in the treatment chamber with which the electrolyte is introduced into the treatment tank.

In the drawings, embodiments of the invention are shown.

Show it:

1 schematically a device for descaling and / or pickling a metal strip,

2 the cross section along the line AA 'in 1 through a pickling tank and

3 the cross section through a straightening unit, shown enlarged.

Out 1 schematically a device is sketched, with a cold-rolled and annealed metal strip 1 descaled and / or pickled. The metal band 1 enters the system with a specified conveying speed in conveying direction R and is fed via an S-pulley stand 3.1 guided and then in a stretch bending device (stretch bending straightening machine) 2 introduced. Behind the stretch bender 2 there is a second S-roll stand 3.2 , The S-roll stands 3.1 and 3.2 practice on the metal band 1 a tensile force F off. The stretch bending device 2 between the S-roll stands 3.1 and 3.2 serves to straighten the metal band 1 , Accordingly, the cold strip to be treated passes through 1 a stretch bender 2 working under train. The S-roller scaffolding 31 , and 3.2 build up or down train F The stretch bending device 2 can be operated dry and wet.

In 1 and in 3 is schematically indicated that the metal strip 1 in the stretch bending device 2 By rolling W under high tension by the tensile force F is bent and directed so that the metal strip 1 has a high degree of planarity, after it the stretch bending leveler 2 leaves.

Following the stretch bending straightener 2 becomes the metal band 1 the pickling vessel 10 supplied for descaling and / or pickling. This pickling vessel 10 has a treatment chamber 11 on.

In 1 is shown as the metal band 1 in the treatment chamber 11 running. The metal band 1 preferably runs at an angle of <5 ° in the treatment chamber 11 and is there by counter-rolls 4.1 and 4.2 kept on tension. The slack of the metal band 1 is in the treatment chamber 11 reduced to a few millimeters. Due to the low sag of the metal strip 1 the distance between the electrodes decreases 5 and the metal band 1 , By reducing the distance, the electrodes can 5 be set at a much lower level than before. The voltage drop decreases and thereby the power consumption. That means a considerable energy saving. In the treatment chamber 11 are at the entrance nozzles 12 attached with which the electrolyte E is introduced into the treatment tank. The electrolyte E is through the nozzles 12 so injected that the process tank is hydraulically sealed. The device 10 for electrolytic descaling and / or pickling has a circumferential gutter 8th on, with the lid 9 is sealed.

In 2 is a cross section through the pickling vessel 10 along the line AA 'shown. It is shown that the electrodes 5 through a side opening 6 in the pickling tank 10 horizontally can be installed and removed. A cradle in the brickwork 7 ensures good positioning of the electrodes 5 , The electrodes 5 do not need to be guided as usual over the edge of the lid. The device according to the invention allows a simpler and more economical production of the electrodes 5 , You can see the electrolyte E. The tank bottom 13 has a passion. Through the nozzles 12 the electrolyte E is fed. During the dressing, mud forms on the bottom of the tank 13 settles. The deposited mud is on the sloping tank bottom 13 moved down and removed from the container. Because the electrodes 5 no longer need to be guided over the edge of the lid, the pickling container cover 9 through a circumferential gully 8th be effectively sealed.

In the treatment chamber 11 is a number of electrodes 5 arranged, which are required to the surface of the metal strip 1 to desalt and / or to stain. In the conveying direction R are several electrodes 5 arranged one behind the other. These can all be activated simultaneously for descaling and / or pickling, therefore be supplied with electrical energy. However, it is also possible, the individual module-like electrodes 5 Optionally switch so that only such a number of electrodes 5 is activated, as is necessary to achieve a desired Entzunderungs- and / or Beizingsgebnis.

Depending on the desired quality of descaling and / or pickling, the conveying speed v of the metal strip 1 be set so that the result of the descaling and / or the pickling corresponds to a desired specification. If the quality of the descaling and / or pickling is insufficient, the conveying speed v can be reduced, as a result of which the surface of the metal strip 1 a longer exposure time in the pickling tank 10 is exposed and the Entzunderungs- and / or Beizgebnis improves.

The advantages of the present invention will be demonstrated by comparing the following example with the comparative example.

example

The pickling of a cold-rolled and annealed metal strip 1 was carried out in a device according to the invention, as in 1 to 3 will be shown. The individual device components are summarized in Table 1 below. The metal band 1 had a width of 1600 mm. The metal band 1 had a strip tension of 15 N / mm ² metal strip cross-section. The metal band 1 was about S-role stall 3.1 and then through a stretch bender 2 and finally about S-role status 3.2 guided. The metal band 1 had a good flatness afterwards. There were so-called humps from the metal band 1 away. With the stretch bending device 2 became the metal band 1 stretched by 1% to 2% over the extension, bending and elongation. After that, the metal band became 1 in the pickling tank 10 with the treatment chamber 11 guided. The pickling tank 10 was 10 meters long, 2 meters wide and 1 meter high. The treatment chamber 11 dismissed counter-rolls 4 on top of the metal band 1 added extra tension and support. The counter-rolls 4 had a diameter of 300 mm. The electrodes 5 were plates. The anode was made of steel. The cathode was made of steel and coated with lead. The electrolyte temperature was 80 ° C. The Na ₂ SO ₄ concentration in the electrolyte E was 150 g / l. The current density relative to the anode was 10 A / dm ² . The distance of the electrodes 5 from the metal band 1 could due to the low sag of the metal strip 1 be set to <30 mm. Because the metal band 1 through the stretch bender 2 was just made, the pickling tank could 10 with a small distance of the electrodes 5 from the metal band 1 be driven through.

Comparative example

The procedure was carried out as in Example 1, with the difference that no stretch-bending machine 2 has been used. The metal band 1 was about two s-roll stands 3.1 and 3.2 and then into the pickling tank 10 guided. It was necessary that the electrodes 5 a distance to the metal band 1 of 150 mm had to have contact with the metal band 1 and thus to avoid a short circuit. The power consumption was 40% higher than by the method according to the invention in Example 1.

The following Table 1 summarizes the devices according to Example and Comparative Example. Table 1 example Comparative example S-roll stand 3.1 S-roll stand 3.1 Stretch-bending machine 2 S-roll stand 3.2 S-roll stand 3.2 pickling tank 10 pickling tank 10

The power consumption was 40% lower in the inventive method than in the comparative example according to the prior art. This result was unexpected and surprising to the skilled person.

LIST OF REFERENCE NUMBERS

1

Metal Band / cold strip

2

Straightener / stretch bending straightener / stretch bender

3.1

Gantry / S-roll stand

3.2

Gantry / S-roll stand

4.1

Counter rollers / guide rollers

4.2

Counter rollers / guide rollers

5

electrodes

6

Opening in the pickling tank

7

masonry

8th

circumferential gully

9

Beizbehälterdeckel

10

Pickling tank / pickling vessel / pickling tank / device for descaling and / or pickling

11

treatment chamber

12

jet

13

tank bottom

e

electrolyte

F

traction

R

conveying direction

W

roller

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 112007000641 T5 [0006]
• JP 6128774 A [0007]
• JP 62211394 A [0008]
• JP 61279311 A [0009]
• JP 4120287A [0010]
• JP 2001047121A [0011]
• JP 5177238 A [0012]
• EP 1558779 [0013]

Claims (22)

Process for the electrolytic descaling and / or pickling of a cold-rolled and annealed metal strip ( 1 ), where a) the metal strip ( 1 ) in the conveying direction (R) by a straightening unit ( 2 ) is led to the removal of flatness defects and b) subsequently the metal strip ( 1 ) in the conveying direction (R) by a device ( 10 ) for electrolytic descaling and / or pickling is performed. Method according to claim 1, wherein the metal strip ( 1 ) is stretch bend-rectified to eliminate flatness defects and subsequently electrolytically descaled and / or pickled. Method according to claim 1 or 2, wherein the metal strip ( 1 ) continuously through the device ( 10 ) for electrolytic descaling and / or pickling is performed. Method according to one of claims 1 to 3, wherein in the device ( 10 ) for electrolytic descaling and / or pickling the metal strip ( 1 ) horizontally via pulleys ( 4.1 . 4.2 ), the metal strip ( 1 ) tighten. Method according to one of claims 1 to 4, wherein in the device ( 10 ) for electrolytic descaling and / or pickling at least one electrolyte between metal strip ( 1 ) and electrodes ( 5 ) by means of nozzles ( 12 ) is introduced. Method according to one of claims 1 to 5, wherein the specific strip tension is> 15 N / mm ² metal strip cross-section. A process according to any one of claims 1 to 6, wherein the electrolyte temperature is from 50 ° C to 90 ° C. The method of claim 7, wherein the electrolyte temperature is preferably from 70 ° C to 85 ° C. Method according to one of claims 1 to 8, wherein the Na ₂ SO ₄ concentration in the electrolyte of 150 g / l to 200 g / l. A method according to any one of claims 1 to 9, wherein the current density relative to the anode is from 2 A / dm ² to 20 A / dm ² . A method according to claim 11, wherein the current density of 5 A / dm referred to the anode is ² to 15 A / dm ² . Device for the electrolytic descaling and / or pickling of a cold-rolled and annealed metal strip ( 1 ), which a) at least one device ( 10 ) for electrolytic descaling and / or pickling, through which the metal strip ( 1 ) is guided in the conveying direction (R) and in which the metal strip ( 1 ) is descaled and / or pickled electrolytically, b) at least one leveling unit ( 2 ), which in the conveying direction (R) in front of the device ( 10 ) is arranged for electrolytic descaling and / or pickling and with the flatness defect in the metal strip ( 1 ) be eliminated. Apparatus according to claim 13, wherein the straightening unit ( 2 ) a stretch bending device ( 2 ). Apparatus according to claim 13 or 14, wherein before and / or behind the straightening unit ( 2 ) at least one tensioning device ( 3.1 . 3.2 ) for generating a tensile force (F) in the metal strip ( 1 ) is arranged. Device according to one of claims 13 to 15, wherein the device ( 10 ) for electrolytic descaling and / or pickling a treatment chamber ( 11 ), in which in the conveying direction (R) of the metal strip ( 1 ) a number of modularly constructed electrodes ( 5 ) is arranged. Device according to claim 16, wherein the individual electrodes ( 5 ) depending on the degree of scaling and / or the degree of contamination of the surface of the metal strip ( 1 ) as well as depending from the speed with which the metal strip ( 1 ) the device ( 10 ) for the electrolytic descaling and / or pickling, independently switched on and off. Device according to one of claims 13 to 17, wherein the device ( 10 ) for electrolytic descaling and / or pickling in the treatment chamber ( 11 ) horizontal pulleys ( 4.1 . 4.2 ) at different heights, the metal strip ( 1 ) tighten. Device according to one of claims 13 to 18, wherein the device ( 10 ) for electrolytic descaling and / or pickling in the treatment chamber ( 11 ) Nozzles ( 12 ), with which at least one electrolyte between metal strip ( 1 ) and electrodes ( 5 ) is introduced. Device according to one of claims 13 to 19, wherein the device ( 10 ) for electrolytic descaling and / or pickling in the treatment chamber ( 11 ) at least one opening ( 6 ), through which the electrodes ( 5 ) horizontally installed and removed. Device according to one of claims 13 to 20, wherein the device ( 10 ) for electrolytic descaling and / or pickling a circumferential gutter ( 8th ), with which the lid ( 9 ) is sealed. Device according to one of claims 13 to 21, wherein the device ( 10 ) for electrolytic descaling and / or pickling electrodes ( 5 ), which are formed as blocks or plates. Use of a device according to one of claims 13 to 22 for the electrolytic descaling and / or pickling of a cold-rolled and annealed metal strip ( 1 ) after correction of flatness errors.

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