AU2003271666B2

AU2003271666B2 - Method and device for descaling and/or cleaning a metal casting

Info

Publication number: AU2003271666B2
Application number: AU2003271666A
Authority: AU
Inventors: Bodo Block; Rolf Brisberger; Klaus Frommann; Hans Georg Hartung
Original assignee: SMS Demag AG
Current assignee: SMS Siemag AG
Priority date: 2002-11-09
Filing date: 2003-09-30
Publication date: 2009-03-12
Anticipated expiration: 2023-09-30
Also published as: TW200408466A; WO2004044257A1; EP1558779A1; AU2003271666A1; EP1558779B1; CN100471981C; DE10252178A1; PL374974A1; KR101010580B1; US20060108034A1; JP4431045B2; BR0315719A; PL207871B1; KR20050084976A; CA2505152C; MY138080A; RU2005117797A; JP2006505411A; DE50311018D1; ATE419407T1

Abstract

Process for descaling and/or for cleaning a metal strand, especially a hot-rolled strip made from normal steel or a stainless steel, comprises feeding the strand (1) in the conveying direction (R) through a device (2) for plasma descaling and/or plasma cleaning. The metal strand has a high degree of planarity before it enters the device. An Independent claim is also included for a device for descaling and/or for cleaning a metal strand, especially a hot-rolled strip made from normal steel or a stainless steel.

Description

la METHOD AND DEVICE FOR DESCALING AND/OR CLEANING A METAL

CASTING

The invention relates to a method and device for descaling s and/or cleaning a metal casting. In one aspect, the present invention relates to a method and a device for descaling and/or cleaning a hot-rolled strip made of normal steel or of stainless steel.

A method from a related class is known from JP 03207518 A.

For subsequent processing, for example by cold-rolling, for a metallic coating or the direct finishing to a final product the hot-rolled strip must have a descaled surface.

Thus, the scales originating from hot-rolling and during the following cooling must be completely removed. In the afore-mentioned method, this is achieved by means of a pickling process, wherein the scales made of various ferrous oxides (FeO, Fe 3 0 4 Fe 2 0 3 or in the case of stainless steel of ferrous metals rich in chromium are dissolved depending on the quality of the steel by means of various acids (for example, hydrochloric acid, sulphuric acid, nitric acid or mixed acid) at high temperatures in a chemical reaction with the acid. Prior to pickling normal steel requires an additional mechanical treatment by means of stretcher-and-roller levelling in order to break open the scales and to allow a quicker permeation of the acid into the scale layer. For stainless, austenitic and ferritic steels which are substantially more difficult to pickle, an annealing and a mechanical pre-descaling of the strip precedes the pickling process in order to attain the best possible strip surface for pickling. Following descaling the steel strip must be rinsed, dried and if necessary oiled in order to prevent oxidation.

The pickling of steel strip is performed in continuous lines whose process section may exhibit a very sizable length depending on the speed of the conveyance. Such production lines thus require high investments. The pickling process further necessitates a very large amount of energy and high expenditures for the disposal of waste water and the regeneration of hydrochloricacid which is usually used for normal steel.

Therefore, there are various approaches in the state-of-theart which effect the descaling of metal castings without the deployment of acids.

Hitherto known developments are usually based on a mechanical removal of the scales (for example, Ischiclean method, APOmethod). Such methods however are not suited for the industrial descaling of broad steel strip with respect to the efficiency and quality of the descaled surface. For this reason, acids are still deployed for descaling such strips.

The disadvantages relating to efficiency and environmental pollution therefore have been tolerated up to now.

Newer approaches for the descaling of metal casting employ plasma technology. This method is already described in the afore-mentioned JP 03207518 A as well as in WO 00/56949 Al, WO 01/00337 Al, RU 2153025 C1 and RU 2139151 Cl. In the plasmadescaling technology disclosed therein the material to be descaled passes between special electrodes which are located in a vacuum chamber. The descaling results by means of the

I

-3plasma generated between the steels strip and the Selectrodes, wherein a metallic bright surface without residue is produced. Plasma technology thus represents an O efficient, high-quality and environmentally friendly option for descaling and cleaning steel surfaces. It can

\O

ND be deployed for normal steel as well as for stainless, ID austenitic and ferritic steel. A special pre-treatment is not required.

M The mentioned state-of-the-art is primarily applied to the descaling of wire and pipes. The advantage in this regard is a relatively simple guidance of the electrodes which is possible based on the geometry of the material to be descaled, so that an efficient descaling can be effected.

In the case of descaling steel strip, however it appears that the method disclosed in the mentioned literature does not lead to a practical outcome, that steel strip treated in such a manner cannot be descaled with the required quality, at least when it exhibits a certain width.

JP 07275920 A indeed discloses a method of this sort, wherein a set of bending rollers is arranged before the plasma-descaling chamber by means which the strip entering the chamber is treated. However, the strip evenness achieved thereby does not suffice to attain the intended quality of descaling.

According to one aspect of the invention there is provided a method for descaling and/or cleaning of a metal casting, wherein the metal casting is guided in a direction of conveyance through a device inside which it is subjected to a plasma descaling and/or plasma cleaning, wherein before the device for plasma descaling and/or plasma cleaning, in the direction of conveyance, the metal 4 casting which is subjected to a stretcher levelling or a stretcher-and-roller levelling process which imparts a high degree of flatness to the metal casting.

Thus, embodiments of the invention may provide for descaling and/or cleaning of a metal casting where it is possible to efficiently and effectively descale even wide metal castings over their entire width with consistent quality by means of plasma technology, wherein the io economical as well as ecological advantages of this method should be utilizable.

The stretcher levelling process or a stretcher-and-roller levelling process may exert a tensile force on the metal casting to such an extent that the degree of flatness of the metal casting entering the device for plasma descaling and/or plasma cleaning is so high that the casting can pass through the device as flat sheet metal. The result of descaling and/or cleaning is thereby improved dramatically, so that the finished metal strip exhibits a high quality.

During the levelling process the tensile force may be selected such that a tensile stress arises in the metal casting which corresponds to at least 10% of the yield point of the metal casting material.

The method can be carried out on continuously conveyed metal casting; however, it is also possible to convey the metal casting through the descaling and/or cleaning machine in a discontinuous manner, with a varying speed. The last-mentioned case is particularly interesting for smaller lines.

An especially high quality of the finished metal casting can be achieved if the surface of the metal casting is inspected after the device for plasma descaling and/or O plasma cleaning; in this case it is intended that the speed with which the metal casting is conveyed through the Sdevice for plasma descaling and/or plasma cleaning is specified in a closed-loop control in dependence on the inspection, such that the desired quality of descaling and/or cleaning is attained. Explicitly this means that

\O

ND if the quality of descaling and/or cleaning is still unsatisfactory, the speed of the metal casting conveyed through the device for plasma descaling and/or plasma cleaning will be decreased, such that the plasma has a longer time to act on the metal casting. This makes it possible to adapt the quality of the descaling and/or cleaning process to special demands.

In one embodiment, the descaling and/or cleaning of the metal casting can be directly followed by a coating of the casting with liquid metal, in particular a hot galvanizing. Known coating techniques can be applied.

One possibility results in the metal casting being guided through a boiler which is filled with liquid coating metal, wherein a deflection of the metal casting takes place in the boiler.

Alternatively, the CVGL-method (Continuous Vertical Galvanizing Line) can also be deployed, by means which the metal casting is guided from the bottom through a boiler which is filled with liquid metal, wherein the coating metal is retained in the boiler by means of an electromagnetic closure. Following descaling and/or cleaning and prior to coating with liquid metal the metal casting may be heated, for example by means of induction heating.

The cold-rolling of the metal casting can be advantageously carried out immediately following the descaling and/or cleaning of the metal casting.

-6- O According to a second aspect of the invention there is 3 provided the method according to one of claims 1 to 8, Swherein the metal casting following descaling and/or cleaning is cold-rolled.

An S-roll stand may be used as a stretching device.

\O

Embodiments of the device enable the metal casting to be kept very flat when passing through the plasma device which increases the quality of the descaling and/or Scleaning.

The device for plasma descaling and/or cleaning can exhibit a treatment chamber under vacuum in which a number is of modularly built electrodes are arranged in the direction of conveyance of the metal casting. In this regard the individual electrodes can be designed to be switched on or off independently of one another in dependence on the degree of scaling and/or degree of contamination of the surface of the metal casting as well as in dependence on the speed with which the metal casting passes through the plasma device. In this regard, as many electrodes can be switched on for descaling and/or cleaning as are necessary to achieve the desired result.

In one embodiment inspection means for inspecting the surface of the metal casting may be arranged in the direction of conveyance behind the device for plasma descaling and/or plasma cleaning; These are connected with control means, wherein these control means set the speed with which the metal casting is conveyed through the device in dependence on the inspection, so that the desired descaling and/or cleaning quality of the metal casting is achieved.

As previously illustrated, the descaling and/or cleaning line according to an embodiment of the present invention 7 can be advantageously deployed in combination with additional treatment devices. Means for coating the metal casting with liquid metal, particularly for hot galvanizing can be arranged in the direction of conveyance s behind the device for plasma descaling and/or plasma cleaning. These means can exhibit a boiler for liquid metal and at least one deflection roller integrated therein. Alternatively, the means for coating may exhibit a boiler and under the boiler electromagnetic means for i0 retaining the liquid metal in the boiler. Means for heating the metal casting, in particular induction heating means can be arranged in the direction of conveyance behind the device for plasma descaling and/or plasma cleaning and in the direction of conveyance before the means for coating the metal casting.

As an alternative to or in addition to the coating means, means for rolling the metal casting can be arranged behind the device for plasma descaling and/or plasma cleaning in the direction of conveyance; this can be multiple stand cold rolling tandem mill A continuous operation of the entire line is aided by the fact that a strip storage is arranged in the direction of conveyance before the device for plasma descaling and/or plasma cleaning.

High productivity may be facilitated if means for trimming the metal casting (trimming shears) are arranged in the direction of conveyance behind the device for plasma descaling and/or plasma cleaning.

The productivity of the line is also further improved by the fact that means for oiling the metal casting are arranged in the direction of conveyance behind the device for plasma descaling and/or plasma cleaning.

8 An overall highly productive line for the processing metal casting, preferably for hot-rolled strip made of normal steel or of stainless steel, is the result which guarantees an economical and ecological descaling and/or cleaning of the metal casting and which has proven effective particularly in combination with subsequent/downstream treatment devices.

The described technology is believed to provide great io advantages especially compared with pickling with respect to environmental protection, energy conservation and quality. In addition, the investment costs for such lines are considerably less than for known descaling and/or cleaning lines.

Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, wherein: Fig.l schematically shows a device for descaling and for subsequent hot galvanizing of a metal casting, Fig.2 schmeatically shows a device for descaling and for subsequent rolling of the metal casting and, Fig.3 schematically shows a device for descaling a metal casting.

Fig.l schematically shows a device with which a metal casting 1 can first be descaled and subsequently hot galvanized. The metal casting 1 enters the line with a predetermined speed of conveyance v in the direction of conveyance R and is initially guided between two S-roll stands 5 and 6 which exert a tensile force F on the metal casting 1. A means 4 for stretcher levelling the metal casting 1 is arranged between both S-roll stands 5, 6.

This means 4 is a stretcher-and-roller levelling machine.

A schematic outline shows that the metal casting 1 is bent or stretcher levelled by means of adjustable rolls under 8a high tension by the tensile force F in the stretcher-androller levelling machine 4, so that the metal casting 1 exhibits a high degree of flatness upon leaving the stretcher-and-roller levelling machine 4.

Following the stretcher-and-roller levelling machine 4 the metal casting 1 is conveyed to the device 2 for plasma descaling and/or cleaning. This device 2 exhibits a treatment chamber 8 which is kept under vacuum. Locks 19 and 20 are each located at the entrance and the exit of the metal casting 1 into and out of the treatment chamber.

An S-roll stand 7 is also arranged in the direction of conveyance behind the device 2; in interaction with S-roll stand 6 it is possible to keep the metal casting 1 under tension (tensile force F) while passing through the device 2, ensuring that the metal casting 1 runs through the device 2 with a high degree of flatness. This is required for attaining a good result with respect to descaling and/or cleaning.

As seen in Fig. i, a number of electrodes 9 are arranged in the treatment chamber 8 which are required in order to produce the plasma with which the surface of the metal casting 1 is descaled or cleaned. Details relating to this process can be found in the afore-mentioned literature.

Several electrodes 9 are arranged successively in the direction of conveyance R as can be seen in in Fig. i. These can allbe activited simultaneously for descaling and/or cleaning, in other words, powered with electrical energy. It is however also possible to selectively switch the individual modularly built electrodes 9, so that only a number of electrodes which is necessary for effecting the desired descaling and/or cleaning outcome is activated.

An inspection means 10 is arranged in the direction of conveyance R behind the device 2 for plasma descaling and/or plasma cleaning which is able to inspect the surface of the metal casting 1 and relay the result of the inspection to the control means 11. Depending on the desired quality of descaling and/or cleaning, the control means 11 can be programmed such that it affects the power unit of the entire device, not illustrated herein, in a way that the speed of conveyance v is influenced so that the result of descaling and/or cleaning corresponds to the desired specifications.

If the quality of descaling and/or cleaning is not sufficient, the control means 11 can lower the speed of the conveyance v; the surface of the metal casting is thereby exposed to the plasma for a longer time, whereby the result of descaling and/or cleaning is improved. If the quality is already excessively high and not required, the control means 11 can effect an increase in the speed of conveyance v, so that although the quality of the descaling and/or cleaning is reduced, the productivity of the overall line however is increased.

As additionally seen in Fig. I, an induction heating means 14 which can heat the metal casting 1 is located in the direction of the conveyance R behind the device 2 for plasma descaling and/or plasma cleaning. In particular, this can be an induction-heated annealing furnace with a protective gas atmosphere with which it is possible to heat the metal casting 1 to a temperature of approximately 500 0 C within a very short time. Afterwards the metal casting 1 is conveyed in a protective atmosphere and by means of a blowpipe, not shown herein, to a boiler 3 with liquid coating metal. A deflection roll 13 is arranged in the boiler 3 which deflects the metal casting 1 after coating with the liquid coating metal vertically to the top. The induction heating means 14, the boiler 3 and the deflection roll 13 comprise the schematically illustrated means 12 for coating the metal casting 1.

An alternative embodiment of the line can be seen in Fig. 2.

The difference to Fig. 1 resides in the fact that in Fig. 2 means 15 for rolling the descaled and/or cleaned metal casting 1 are arranged downstream of the device 2 for plasma descaling and/or plasma cleaning. In this case the means represent a multiple stand cold-rolling tandem mill, on which the metal casting 1 is rolled to the desired final thickness.

A device is outlined in Fig. 3 which solely serves the descaling of the metal casting i, but which can also be combined with downstream devices such as those solutions shown in Figs. i and 2.

The metal casting 1 is fed in a coiled state from a reel 21 to a welding machine 22 where the metal casting 1 is welded together with the previous metal casting. Prior to welding the strip ends are cut with shears 23 in order to enable flawless welding.

The metal casting 1 is then conveyed to a stretcher levelling machine or a stretcher-and-roller levelling machine 4 in which the casting 1 can be levelled by bending and the application of a tensile force such that it exhibits an optimal flatness prior to entering the device 2 for plasma descaling and/or plasma cleaning. The metal casting initially passes the lock 19 whereupon it is then situated in the treatment chamber 8 which is under vacuum. The vacuum is generated by a vacuum pump 24. Descaling and/or cleaning is carried out in the treatment chamber 8 by means of the plasma located between the electrodes 9 and the metal casting 1. The number of electrodes 9 depends on the strip speed v in order to guarantee the required dwell time of the metal casting 1 in the plasma.

Following the complete descaling and/or adequate cleaning the metal casting 1 passes through the vacuum lock 20 to the Sroll stand 7 which as already mentioned produces, in interaction with the S-roll stand 6, the a high enough strip tension to enable the most horizontal strip passage possible.

Support rolls 25 are arranged between the electrodes 9 which prevent the sagging of the metal casting 1 within longer treatment chambers 8 and at higher strip speeds v.

The exact width of the metal casting can be attained by means of trimming shears 17.

If necessary, the metal casting i is electrostatically oiled by means of the oiling machine 18 in order to protect the surface of the metal casting from corrosion. The metal casting 1 is separated with shears 26 before kicking off the finished coil. It is also possible to work with two reels 21 and 27 each located in the inlet and in the outlet, respectively in order to attain the shortest possible coil changing times.

A continuous strip passage in the process section of the line is made possible with strip storage 16 and strip storage 28.

A discontinuous operation without strip storage is possible for lines with low output, wherein the line is stopped while the coil is changed. Contrary to pickling, this is possible for plasma descaling without losses in output.

In the above description, both descaling and cleaning of a metal casting have been mentioned side by side. Plasma technology namely has turned out to be suitable not only for descaling but also very good for the cleaning of organic and inorganic substances oil) from metallic surfaces.

Cold-rolled oiled steel strip for example prior to a metal coating must pass through special alkaline and electrolytic cleaning tanks followed by rinsing and in part also by brushing in order to attain the required metallic bright surface. The lines already mentioned also deploy chemical substances for this purpose which raise the environmental 13 C concerns previously stated. The application of plasma f technology for the cleaning of metal casting also yields CI great advantages in this regard.

As already mentioned above, great economic advantages result when coupling the line outlined in Fig.3 with

\O

IND downstream treatment devices according to Figs.l and 2.

\O

The intermediate storage of descaled and/or cleaned strip C-i can be omitted, so that both production and quality 0 io improvements can be effected. The strip storage 28 (see SFig.3) behind the device 2 for plasma descaling and/or c-i plasma cleaning has special importance in this regard.

The descaled and preferably already trimmed strip can then continuously enter the successive device (hot galvanizing, cold-rolling tandem mill) under constant strip tension without intermediate storage.

Following the successive device, in particular behind the cold-rolling tandem mill, the finished strip can be alternately recoiled with two reels and separated with shears.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, 13a i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

List of Reference Numbers 1 Metal casting 2 Device tor plasma descaling and/or plasma cleaning 3 Boiler with liquid coating metal 4 Means tor levelling the metal casting (stretcher levelling machine, stretcher-and-roller levelling machine) Stretching device (S-roll stand) 6 Stretching device (S-roll stand) /7 Stretching device (S-roll stand) 8 Treatment chamber 9 Electrodes Inspection means 11 Control means 12 Means tor coating the metal casting 13 Detlection roll 14 Means tor heating the metal casting (induction heating means) Means for rolling the metal casting 16 Strip storage 17 Means for trimming the metal casting (trimming shears) T18 Means tor oiling the metal casting (oiling machine) 19 Lock Lock 21 Reel 22 Welding machine 23 Shears 24 vacuum pump Support roll 26 Shears 27 Reel 28 Strip storage R Direction ot conveyance v Speed ot conveyance F Tensile torce

Claims

2. A method for descaling and/or cleaning of a metal casting, wherein the metal casting is guided in a direction of conveyance through a device inside which it is subjected to a plasma descaling and/or plasma cleaning, wherein before the device for plasma descaling and/or plasma cleaning in the direction of conveyance, the metal casting is subjected to a stretcher levelling or a stretcher-and-roller levelling process which imparts a high degree of flatness to the metal casting, wherein after the device for plasma descaling and/or plasma cleaning an inspection of the surface of the metal casting is performed, wherein the speed with which the metal casting is guided through the device for plasma descaling and/or plasma cleaning is specified in the closed-loop control in dependence on the inspection, such that the desired quality of descaling and/or cleaning is attained.
3. The method according to claim 1 or 2, wherein a tensile force is exerted such that a tensile stress arises in the metal casting which corresponds to at least 10% of the yield point of the metal casting 16 material.
4. The method according to any one of claims 1 to 3 wherein the metal casting is continuously guided s through the device for plasma descaling and/or plasma D cleaning. \O \O The method according to any one of claims 1 to 3 wherein the metal casting is discontinuously guided M 10 through the device for plasma descaling and/or plasma Scleaning.
6. The method according to one of claims 3 to 5 wherein after the device for plasma descaling and/or plasma cleaning an inspection of the surface of the metal casting is performed, wherein the speed with which the metal casting is guided through the device for plasma descaling and/or plasma cleaning is specified in the closed-loop control dependent on the inspection, such that the desired quality of descaling and/or cleaning is attained
7. The method according to one of claims 1 to 6, wherein the metal casting with liquid metal comprising coating the following the descaling and/or cleaning.
8. The method according to claim 7, wherein the metal casting after descaling and/or cleaning and prior to coating with liquid metal is subjected to heating.
9. The method according to one of claims 1 to 8, wherein the metal casting following descaling and/or cleaning is cold-rolled.
10. The method according to any one of claims 1 to 9 wherein the metal casting is a hot-rolled strip made of normal steel or of stainless steel. 17
11. The method according to claim 7 or 8 wherein the coating comprises hot galvanizing.
12. The method according to claim 8 wherein the heating comprises induction heating.
13. A device for descaling and/or cleaning of a metal casting, particularly a hot-rolled strip made of normal steel or of stainless steel wherein the device is configured to guide the metal casting in a direction of conveyance and to subject the metal casting to plasma descaling and/or plasma cleaning, the device comprising means which are arranged before the device for plasma descaling and/or plasma cleaning in the direction of conveyance and which impart a high degree of flatness to the metal casting, wherein before and/or behind the means at least one stretching device is arranged for producing a tensile force in the metal casting.
14. A device for descaling and/or cleaning of a metal casting, wherein the device is configured to guide the metal casting in a direction of conveyance and to subject the metal casting to plasma descaling and/or plasma cleaning, the device comprising means which are arranged before the device for plasma descaling and/or plasma cleaning in the direction of conveyance and which impart a high degree of flatness to the metal casting, wherein before and/or behind the means at least one stretching device is arranged for producing a tensile force in the metal casting, wherein inspection means for inspecting the surface of the metal casting are arranged behind the device for plasma descaling and/or plasma cleaning in the direction of conveyance, which are connected with control means, wherein the control means set the 18 speed with which the metal casting is conveyed through the device for plasma descaling and/or plasma cleaning, dependent on the inspection.
15. The device according to claim 13 or 14 wherein the device for plasma descaling and/or plasma cleaning comprises a treatment chamber under vacuum inside which a number of modularly built electrodes are arranged in the direction of conveyance of the metal io casting.
16. The device according to claim 15, wherein the individual electrodes can be switched on or off independently of one another in dependence on the degree of scaling and/or degree of contamination of the surface of the metal casting as well as in dependence on the speed with which the metal casting passes through the plasma device for plasma descaling and/or plasma cleaning.
17. The device according to claim 15 or 16 wherein inspection means for inspecting the surface of the metal casting are arranged behind the device for plasma descaling and/or plasma cleaning in the direction of conveyance, which are connected with control means, wherein the control means set the speed with which the metal casting is conveyed through the device for plasma descaling and/or plasma cleaning, dependent on the inspection for attaining the desired descaling and/or cleaning quality of the metal casting.
18. The device according to one of claims 13 to 17, wherein means for coating the metal casting with liquid metal, in particular for hot galvanizing are arranged behind the device for plasma descaling and/or plasma cleaning in the direction of 19 Cq conveyance.
19. The device according to one of claims 13 to 18, wherein means for cold-rolling the metal casting are arranged behind the device for plasma descaling Sand/or plasma cleaning in the direction of conveyance. CI 20. A method for descaling and/or cleaning of a metal casting substantially as hereinbefore described and with reference to the accompanying drawings.
21. A device substantially as hereinbefore described and with reference to the accompanying drawings.