AU618850B2

AU618850B2 - Process and plant for pickling highly refined steel strip

Info

Publication number: AU618850B2
Application number: AU44313/89A
Authority: AU
Inventors: Wilhelm Hofkirchner; Erich Mahr; Gerald Dr. Maresch
Original assignee: Andritz AG
Current assignee: Andritz AG
Priority date: 1988-11-15
Filing date: 1989-11-02
Publication date: 1992-01-09
Anticipated expiration: 2009-11-02
Also published as: AT394734B; KR960002121B1; JPH02185988A; ES2048867T3; EP0369984B1; FI895408A0; DE58904565D1; KR900008064A; EP0369984A1; FI89511B; JP2926342B2; FI89511C; AU4431389A; ZA898671B; ATA279988A; BR8905794A

Description

AUSTRALIA 6 8 PATENTS ACT 1952 Form COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: I Lapsed: Published: K Priority: Related Art: i TO BE COMPLETED BY APPLICANT Name of Applicant: MASCHINENFABRIK ANDRITZ ACTIENGESELLSCHAFT Address of Applicant: STATTEGGERSTRASSE 18 A-8045 GRAZ-ANDRITZ

AUSTRIA

Actual Inventor: Address for Service: GRIFFITH HACK CO., 601 St. Kilda Road, Melbourne, Victoria 3004, Australia.

i Complete Specification for the invention entitled: SPROCESS AND PLANT FOR PICKLING HIGHLY REFINED STEEL STRIP.

The following statement is a full description of this invention including the best method of performing it known to me:- CZ c Si I KOHLER9.AUS The invention relates to a process and to a plant for pickling steel strip.

According to conventional processes, hot and cold strip of steel is treated in continuous annealing and pickling lines.

In this procedure the belt in coiled form is unwound off an uncoiling hasp and connected to the end of a preceding coil in a welding machine. In order to avoid stoppages in the plant and resultant over-pickling of the preceding belt the 'o o strip is withdrawn during the stationary period of the belt 10 in the uncoiling section from a strip store means. The 0 0 0o0Oo1 incoming strip is first annealed in an annealing oven, 0 0 cooled with air and water, whereafter the scale is removed in a pickling plant. A large variety of methods for pickling a hot or cold strip have found acceptance in the industry, the best known method being pickling with neutral electrolyte followed by mixed acid post-treatment. In this context mixed acid denotes a mixture of nitric and oo° hydrofluoric acid. After rinsing the strip is dried and 0recoiled. The resulting welding seams are cut out in this process, resulting once again in a coil of approximately the Oo': same length as when entering the plant. This process suffers 00o a from drawbacks amongst which primarily a high plant investment and labour input as well as large space requirements are to be mentioned.

As compared with the use of other pickling processes, particularly in relation to the passage of the strip through Sthe plant a general technical misconception existed that the conventional material might cause damage to the strip. In particular it was feared that the brick linings of pickling vessels might result in scratching or similar impairment of the strip, this in particular when pickling highly refined steel strip.

On the other hand materials are needed for lining the pickling plant capable of withstanding the chemical attack by the treatment chemicals as well as the mechanical wear and tear. Mechanical linings of brick and ceramics, although resistant to chemical attacks, frequently result in damage to the surface of the pickled product or are themselves not capable of readily withstanding mechanical wear and tear.

There accordingly exists a need for a process avoiding the aforesaid drawbacks and for an apparatus for carrying out the process wherein the risk of damage to the pickled products is reduced to a minimum.

Accordingly, the present invention provides a process for pickling steel strip, wherein a stainless steel strip is delivered to the pickling plant in the form of a coil and is uncoilded by an uncoiling hasp and is advanced through a treatment line comprising at least one preliminary descaling unit, at least one pickling vat with at least one pickling section, which has a lining of acid and abrasion resistant material such as PVC, carbon bricks, graphite filled and or aluminium oxide filled polyester resin, and a rinsing unit, and after rinsing the strip is either clamped to a recoiling hasp and is recoiled and drawn solely by said hasp or in cooperation with driven treatment rolls through the treatment plant, or, alternatively, the strip is cut into stainless steel sheets by the transverse parting unit.

Preferably the belt passes through a plurality of pickling sections comprising different pickling media.

In the course thereof the strip may be treated in at least one section with sulphuric acid and in a subsequent section with a mixture of nitric and hydrofluoric acid.

The concentration of the sulphuric acid amounts to 3 F i FI*l~ II~ UIP U4-ii*b ll~- 250-600 g/l, preferably 300-450 g/l. The temperature of this pickling acid may be 60-95, preferably 70-90°C.

In the case of the mixed acid, the concentration of the nitric acid may be 100-250 g/l, preferably 100-200 g/l and of the hydrofluoric acid 10-100, preferably 20-80 g/l, calculated as total available hydrofluoric acid. In this context the temperature of the mixed acid may be 40-70, preferably 40-65°C.

For carrying out the process according to the invention, a plant is proposed using at least one uncoiling hasp, one guide means, at least one pickling section, one rinsing plant and one rewinding hasp and respectively or a transverse parting plant, the pickling vessel according to the invention comprising a support structure of steel, glass fibre reinforced syntheric resin or polypropylene and a lining of acid- and abrasion-resistant material comprising PVC, carbon bricks, graphite filled and/or aluminium oxide filled polyester resin.

According to a further feature of the invention, at least two pickling vats, each comprising at least one pickling section are provided, a wash brushing machine being provided between the pickling vats.

Further details of the invention will be further explained with reference to the drawing in which a working example of the relevant plant is illustrated. There is shown in diagrammatic manner in Fig. i, a perspective view of the plant including the most important facilities, Fig. 2, a longitudinal section of the plant in the region between the end of a pickling section and the beginning of 4 the next following pickling section, Fig. 3, a longitudinal section through the ends of two pickling vats including the wash brushing machine therebetween, Fig. 4, a longitudinal section through the countercurrent rinsing plant and Fig. 5, a longitudinal section through the bottom of the pickling vessel.

The plant illustrated in Fig. 1 comprises essentially an 1Ouncoiling hasp 1, a straightening machine 2, a mechanical predescaling plant, e.g. an abrasive blaster 3, two elongate flat pickling vats 4 with a wash brushing machine therebetween, a countercurrent rinsing plant 7, a drier 8 and a recoiling hasp 9. Between the uncoiling hasp 1 and the straightening machine 2, a pusher 10 composed of two superimposed rolls as well as two mutually opposing guide rolls 11 are provided.

Between the straightening machine 2 and the abrasive blaster 3 two guillotines 12, 13 as well as two pushers 14 are the latter in turn comprising two superimposed rolls.

Between the drier 8 and the recoiler hasp 9 a strip guide means 11' composed of two mutually opposing guide rolls, one on each side of the strip 14 to be pickled, is provided, followed by a reverse traction assembly 18 formed by two superimposed rolls.

At least one of the pickling vats 4 comprises at least two successive pickling sections 6, between which the strip 14 passes between two squeegee rolls 15 (Fig. 2) of which the i y~ch-r~ I uppermost is driven and contributes to the advance of the strip 14. The pickling vat 4, respectively each of the pickling sections 6 is provided with a sectionally liftable lid 16 on the inlet as well as the outlet side with a sloping bottom region 17 forming a weir for the pickling acid contained in the vat 4, respectively in the pickling section 6. The geometry of these bottom regions 17 is such that the region on the inlet side slopes downwardly in the direction of travel of the strip, whilst the region on the outlet side slopes upwardly. Thus, the region on th(. outlet sides with a corresponding region of the lid 16 forms a funnel 19 for guiding between the squeegee rolls 15 the beginning of the strip which is inclined to rise upright.

The pickling vat, respectively the pickling section 6 itself is constructed of a carrying structure and a lining of acid and abrasion resisting material. The carrying structure is composed of steel with a lining of chlorinated PVC, respectively of glass fibre reinforced plastics or pure plastics such as e.g. polypropylene. This is followed by a layer of carbon bricks and for the uppermost layer polyester resin filled with aluminium oxide, respectively graphite, is used.

The amount of filler may be between 10 and 100% by mass in the case of aluminium oxide, preferably between 20 and by mass. If graphite is used as the filler, the values are between 50 to 400, preferably between 80 to 200% by mass.

This combination of polyester resin matrix and filler results in a material which on the one hand is adequately resistant to the chemical and mechanical wear and tear of the pickling operation but which cannot damage the high quality steel strip.

The countercurrent rinsing plant 7, as shown in Fig. 4, 6 L, r'

I

I~ u- r~a~ i comprises a wash brushing machine 5' and both upstream and downstream each a rinsing plant 20, respectively 20'. On the feed as well as the discharge side each rinsing plant, respectively between rinsing plants 20, respectively 20' and the wash brushing machine superimposed squeegee rolls similar to those between the pickling sections 6, are provided, of which at least the upper one is driven. In the rinsing plants 20, 20' lower and upper spray pipes 21, respectively 22 are provided between which the strip 14 to be treated passes in the direction of the arrow A. The bottom of the rinsing plant 20, 20' is formed by panels 23 similar to or equal to the lining of the pickling vats 4 and each sloping upwards in the direction of movement A of the strip 14. The lower spray pipes 21 are accommodated between the panels 23 and below their upper surface in order to be protected against damage from the strip 14, particularly when the strip end is introduced.

In addition the lower spray pipes 21 also take care of the formation of a water film between the underside of the belt and the lining material, so that the strip slides on this water film and has no or only light contact with the bottom of the vat. This similarly contributes to the avoidance of mechanical damage both to the pickled product as well as to the plant itself.

For guiding the strip 14 to the squeegee rolls 15, a funnel 24 formed in the present case by a bottom and a lid panel is provided similar to that associated with the pickling sections 6.

The wash brushing machine 5' provided between the rinsing plants 20, 20' successively comprises two pairs of superimposed rolls, namely a support roll 25 and a brush roll 26, viewed in the direction of travel of the strip 14, the support roll 25 in the case of the first pair of rolls It being lowermost and in the second pair uppermost, and the lower roll in relation to the upper one being staggered in the direction of travel of the strip 14. In order to avoid damage to the brush rolls 26 when inserting the start of the strip, the first brush roll is raisable and the second one is lowerable. Also for the same purpose each of the upper ones of the two squeegee rolls can be raised. Between the two rolls 25, 26 as well as between the first pair of rolls and the preceding squeegee roll pair 15 and the second roll pair and the subsequent squeegee roll pair 15 and the second roll pair and the subsequent squeegee roll pair 15 a funnel 27, respectively 28, respectively 29 is provided in each case, corresponding to the funnel 24.

In the present working example a second squeegee roll pair is provided on the exit side of the second rinsing plant downstream of the squeegee roll pair 15, a funnel being positioned between the two squeegee roll pairs corresponding to the funnel 24.

The rinsing proceeds as a countercurrent cascade rinsing procedure in which the rinsing medium from the third cascade passes into the second cascade from where it passes into the first cascade, i.e. into the wash brushing machine From the latter the rinsing medium passes to the preceding cascade of the rinsing plant 20 and from there to the wash brushing machine 5 located between the two pickling vats 4.

The spent rinsing, respectively washing medium drains into a collecting vessel which is not illustrated, from where it is optionally recycled to the rinsing and washing process by way of a treatment plant.

The wash brushing machine 5 located between the pickling vats 4 correspond to the above described wash brushing machine equal components being denoted in Fig. 3 with the same reference symbols.

The process according to the invention proceeds, to the extent not yet described above, in such a manner that at the start of the treatment of a coil held on the uncoiling hasp 1, the latter is driven at least until the start of the strip has reached the pusher means 10 and has been gripped thereby. For centering the strip the uncoiled hasp 1 may be adjustable transversely to the travelling path of the strip. The pusher means 10 then pushes the strip 14 forward in the direction of the arrow A. The strip guide means 11 lateral malalignment of the strip. The guillotine 12 service the front end of the strip which, if the strip is received from the rolling mill, is tongue-shaped. The guillotine 13 then trims the edges of the strip front end obliquely so that the strip front end is given a conical taper to promote the guidance of the strip. The strip front end thus receives a trapezium configuration, it being advantageous if the upper side of the trapezium, respectively the end of the strip has a width at least half that of the strip and the angle between the direction of and the trapezium size amounts to between 10 and preferably 30 and 60 0

C.

In the pickling vats 4, respectively the pickling sections 6, the dame pickling medium or different media may be used.

In this context the pickling medium is introduced into the pickling vat 4, respectively the pickling section 6 on that side where the strip exits and is discharged at the strip entry side, thereby flowing counter to the movement of the strip 14. The circulation of the pickling medium in the pickling vat, respectively in the pickling section proceeds least once and at the most 20 times, preferably 5 to times per hour.

After leaving the countercurrent rinsing pla 7 and the drier 8, the strip 14 is guided by the la t •'leys or rolls of a strip guide means 11' to the recoil hasp 9, whilst the strip 14 is braked by two superposed rolls of a reverse traction aggregate 18 in order for the windings of the recoiling hasp 9 being tightly wound.

It stands to reason that further treatment steps such as e.g. cold rolling, longitudinal or transverse parting, respectively grinding of the strip in the same plant are feasible and can be installed. An optional cross cutting plant which cuts the pickled finished product into sheets, can take the place of the recoiling hasp 9. A longitudinal parting plant which divides the strip into narrower strips as well as a grinding plant is to be provided upstream of the recoiling hasp 9. In order to avoid over pickling of that part of the strip which is inside the pickling vat, a means is provided by which in the event of the strip being stationary, the pickling vat is drained rapidly and flooded with water. More particularly for the pickling of ferritic high quality steel strip with mixed acid, the latter may be cooled by means of externally fitted heat exchangers.

Finally the recoil hasp may be preceded by a rolling mill for reducing the strip thickness.

In order to avoid the escape of vapours or dust from the individual treatment plants, air or vapour may be sucked off from there by ventilation means.

As shown in Fig. 5, the lining material may be composed of sheets having a sawtooth configuration in the direction of travel of the strip and which are laid by means of an acidresistant cement. In that figure, 27 denotes the synthetic resin blocks which are of sawtooth-like configuration in the direction of strip travel, 28 denoting the carbon bricks there below and 29 the support structure.

The claims which follow are to be considered an integral L1-r i part of the present disclosure. Reference numbers (directed to the drawings) shown in the claims serve to facilitate the correlation of integers of the claims with illustrated features of the preferred embodiment(s), but are not intended to restrict in any way the language of the claims to what is shown in the drawings, unless "he contrary is clearly apparent from the context.

11

Claims

1. A process for pickling steel strip, wherein a stainless steel strip is delivered to the pickling plant in the form of a coil and is uncoilded by an uncoiling hasp and is advanced through a treatment line comprising at least one preliminary descaling unit, at least one pickling vat with at least one pickling section, which has a lining of acid and abrasion resistant material such as PVC, carbon bricks, graphite filled and or aluminium oxide filled polyester resin, and a rinsing unit, and after rinsing the strip is either clamped to a recoiling hasp and is recoiled and drawn solely by said hasp or in cooperation with driven treatment rolls through the treatment plant, or, alternatively, the S strip is cut into stainless steel sheets by t-e 015 transverse parting unit. 00 0 oo o o o0s00 0 14 0 0 0 0 0i~ 0o0 oooooo 00. 00 0.0~0 0 0 000 011 0 4004 *4' 5

2. Process according to claim 1, wherein the strip is treated in a plurality of pickling vats, each comprising a plurality of pickling sections, and in at least one pickling section thereof a mixture of nitric and hydrofluoric acid is used.

3. Process according to claim 1, wherein the strip is treated in a medium in which sulphuric acid is 5 present in a concentration ranging from 250 to 600 g/l.

4. Process according to claim 3, wherein the 2 concentration ranges from 300 to 450 g/l. Process according to claim 2, wherein the strip prior to its treatment with mixed acid is treated with 3 sulphuric acid. Process according to any one of the preceding claims, wherein the temperature of the pickling acid is 3 in the range of 60 to 95 0 C. 12 S7. Process according to claim 6, wherein the 2 temperature is in the range from 70 to 90 0 C.

8. Process according to claim 2, wherein the temperature of the mixed acid is in the range from 30 to the concentration of the nitric acid is in the range from 100 to 260 g/l, and that of the hydrofluoric acid from 10 to 100 g/l, calculated as total available hydrofluoric acid.

9. Process according to claim 8, wherein the temperature of the mixed acid is in the range from 40 to 0 C, the concentration of nitric acid is in the range from 100 to 200 g/l and that of the hydrofluoric acid is in the range from 20 to 80 g/l. Process according to claim 1, wherein the front end of the strip being inserted into the plant is trimmed to a trapezium configuration, the two corners of the front edge of the strip being trimmed at an angle in the range from 300 to 450 measured from the side edges of the strip, and the length of the front edge after trimming of the corners amounting to at least half of the strip width.

11. Process according to claim 1, wherein the strip after treatment in at least one pickling vat and prior to treatment in a subsequent pickling vat is treated in a wash brushing machine and after pickling in a countercurrent cascade rinsing unit, the washing water fed to the wash brushing machines being withdrawn from the countercurrent cascade rinsing unit.

12. Process according to claim 1, wherein the pickling medium mixed acid when pickling ferritic stainless steel strip i- cooled by means of externally 4 fitted heat exchanger means. 13 AiL I

13. Process according to claim 1, wherein, when the strip is stationary, the pickling tanks are rapidly 3 drained and flooded with water.

14. Plant for carrying out the process according to claim 1, comprising at least one uncoiling hasp with strip guide means, a preliminary descaling unit, at least one pickling vat with at least one pickling section, a rinsing plant as well as a recoiling hasp and/or a transverse parting plant, wherein the at least one enses=pE pickling vat Aa- a supporting structure of steel, glass fibre reinforced synthetic resin or polypropylene and a lining of acid and abrasion resistant material, comprising PVC, carbon bricks, graphite filled and/or aluminium oxide polyester resin. Plant according to claim 4, wherein the lining on its surface facing the stainless steel strip comprises a layer of polyester resin filled with A1 2 0 3 wherein the 4 content of A1 2 0 3 is in the range from 10 to 100 mass

16. Plant according to claim 15, wherein the content 2 of Al 2 0 3 is in the range from 20 to 50 mass

17. Plant according to claim 14, wherein the uppermost layer of the lining is composed of graphite filled polyester resin, the proportion of graphite is in 4 the range from 50 to 400 mass

18. Plant according to claim 17, wherein the proportion of graphite is in the range from 80 to 200 3 mass

19. Plant according to any one of claims 14 to 18, wherein the lining material is composed of panels of sawtooth-shaped configuration in the direction of strip 4 travel and laid down with an acid resistant cement. 14 r; rr" Plant according to any one of claims 14 to 19, wherein between at least two pickling vats a wash brushing machine and following onto the last pickling vat a countercurrent cascade rinsing installation comprising a wash brushing machine as well as one rinsing plant each on the entry and exit side thereof is provided, the same lining material as in the pickling vats being provided in at least one of the rinsing plants and or in at least one of the wash brushing machines.

21. Plant according to claim 14, wherein the uncoiling hasp is adjustable transversely to the strip o0 a 3 travelling direction. o 22. Plant according to claim 20, wherein the rinsing plants are provided with upper and lower spray pipes, of which the lower spray pipes are fitted between bottom lining panels and reused beneath the upper surface of said panels.

23. Plant according to claim 20, wherein the wash brushing machines comprise two successive roller pairs 0°0 having superposed rolls of which the upper roll of the first and the lower roll of the second roll pair take the form of brush rolls and the other roll serves as support roll.

24. Plant according to claim 23, wherein the lower roll of each pair of rolls is staggered in relation to the upper roll in the direction of travel of the strip and between the two pairs of rolls a guide funnel having a V-shaped taper in the direction of travel of the strip is provided, composed of the lining panels. Plant according to claim 23, wherein the brush roller of the first roller pair is adapted to be lifted 3 free and that of the second pair of rolls is adapted to A L 4 I__i 4 be lowered free.

26. Plant according to claim 23, wherein the brushes are composed of synthetic resin to which adheres an 3 abrasive material, such as e.g. silicon carbide or A120 3

27. Plant according to claim 14, wherein the recoiling hasp or the transversed cutting plant is 3 preceded by a rolling mill.

28. Plant according to claim 14, wherein upstream of the recoiling hasp a longitudinal parting plant or a 3 grinding plant is installed.

29. Plant according to any one of claims 14 to 28, Swherein of the various pairs of rolls in each case only 3 one roll is driven. Plant according to claim 29, wherein in each case 2 the driven roll is the upper roll.

31. Plant substantially as described with reference 2 to or as illustrated in the accompanying drawings.

32. Process as claimed in claim 1, substantially as 2 hereinbefore described. DATED THIS 20TH DAY OF JUNE 1991 MASCHINENFABRIK ANDRITZ ACTIENGESELLSCHAFT By Its Patent Attorneys: GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia. 16 2 f