CN1387467A - Production of thin steel strip - Google Patents

Abstract

A twin roll caster (11) produces thin steel strip (12) which passes in a transit path (10) across guide table (13) to a pinch roll stand (14). After exiting pinch roll stand (14) the strip passes through rolling mill (15) comprising two roll stands (16) in which it is hot rolled to reduce its thickness. The rolled strip passes to run-out table (17) on which it may be force cooled by water jets (18). The already rolled strip is then descaled in a descaler (19) comprising upper and lower water jet nozzles (61,62) which removes scale from both the upper and lower surfaces of the strip. The descaled strip is passed through a pinch roll stand (20) to a coiler (50).

Description

Production of thin steel strip

Technical field

The invention relates to the production of thin steel strips, and the invention is particularly applicable to the production of steel strips which are hot rolled to final gauge or thickness by continuous casting and on-line.

Background technique

Steel strip produced by continuous thin slab casting or by twin roll strip casting can be hot rolled in-line to reduce the strip to final gauge.

In a twin roll caster, molten metal is introduced between a pair of counter-rotating horizontal casting rolls, which are cooled so that the metal skin solidifies on the moving roll surfaces and pools at the nip between the rolls To produce a solidified strip product that is conveyed down the nip between the rolls. The term "nip" is used herein to mean the area where the rolls are closest together. The molten metal can be poured from the ladle into a smaller container from which the molten metal flows through a metal supply nozzle located above the nip in order to direct the molten metal into the nip between the individual rolls so that it is just between the rolls Above the nip is formed a pool of molten metal supported on the casting surface of each roll and extending along the length of the nip. This molten pool is generally confined between side plates or dams which remain in sliding engagement with the ends of the rods, thereby preventing the ends of the molten pool from overflowing, alternatives such as electromagnetic baffles have also been proposed.

When steel strip is cast in a twin roll caster, the steel strip leaves the nip at very high temperatures around 1400°C and if exposed to air it suffers from very rapid scaling due to oxidation at such high temperatures . Therefore, it has previously been proposed to install descaling equipment in order to descale the steel strip before it enters the in-line rolling mill. On the other hand, it has been proposed to shelter the freshly cast strip in a casing containing a non-oxidizing environment until it enters the in-line rolling mill, thereby reducing scale and avoiding the need to remove scale before hot rolling. This proposal is described in U.S. Patent 5,762,126, according to which the cast steel strip is passed through a sealed enclosure from which oxygen is extracted by initial oxidation of the strip passing through the enclosure, after which, the The continuous oxidation of the steel strips of the casing keeps the oxygen content in the sealed casing below the ambient, thereby controlling the thickness of the scales on the steel strips coming out of the casing. By means of this arrangement it is possible to leave the shell with a scale of not more than 10 microns and to feed the strip to the hot rolling mill.

According to previous proposals as described in US Patent 5,762,126, the steel strip leaving the hot rolling mill is subjected to water cooling and then coiled. With this step, the strip may require subsequent descaling or pickling prior to some end uses. We have now confirmed that if the hot-rolled strip is descaled before coiling at a temperature in the range of 900°C to 600°C, the descale rate will be very low. The steel strip can be coiled with only very little scale on the order of 1 to 2 microns thick and will obviously not develop further scale. The coils formed can be sent directly to the end user for various uses, such as for the production of cable reels and any painted steel strip products. Among other uses, they will allow pickling to proceed more quickly than material that has not been descaled just prior to coiling.

Contents of invention

According to the present invention, there is provided a method of producing steel strip, comprising:

continuous cast steel strip;

guiding the strip through a casing containing an environment which prevents the oxidation of the strip surface and consequently the formation of scale;

Conveying the strip through a rolling mill where the strip is rolled as it is produced;

passing the rolled strip through a descaling machine to remove scale from the strip as it exits the rolling mill; and

The rolled and dephosphorized steel strip is conveyed to the coiler.

The steel strip may pass outside the casing before passing through the rolling mill.

Additionally, the rolling mill may be located within the housing so that the steel strip passes through the rolling mill before leaving the housing.

Preferably, the steel strip is continuously cast by supporting a pool of molten steel on a pair of chilled casting rolls forming a nip between them, and the solidified steel strip is formed by rolling the casting rolls in opposite directions to each other. The solidified steel strip is produced by moving down from the nip.

The environment within the enclosure may consist of an inert or reducing gas, or it may be an environment containing a lower level of oxygen than the environment surrounding the enclosure.

Preferably, the environment in the enclosure is created by sealing the enclosure to limit the ingress of an oxygen-containing atmosphere, allowing the steel strip to oxidize within the enclosure during the initial stages of casting, thereby removing oxygen from the sealed enclosure and causing the enclosure to have a lower oxygen content than the environment surrounding the enclosure, after which the oxygen content in the enclosure is maintained below the ambient by continuous oxidation of the steel strip passing through the enclosure, by This controls the thickness of the scale formed on the strip.

Preferably, the rolling mill hot-rolls the steel strip at a temperature in the range of 750 to 1250°C.

The present invention also provides a device for producing steel strip, comprising:

Continuous casting machines for continuous casting of steel strip;

a strip guide that guides the strip away from the caster through the transport path;

an oxidation inhibition enclosure enclosing the steel belt throughout said transport path to control scale formation on the steel belt;

Rolling mills operable to roll steel strip as it is produced;

Descalers operable to remove scale from the strip as it leaves the rolling mill;

A coiler that receives rolled and descaled steel strip.

Preferably, the continuous casting machine includes:

a pair of generally horizontal casting rolls forming a nip between them;

metal feed means for feeding molten metal into the nip between the casting rolls to form a pool of molten metal supported on the casting rolls;

means for cooling the casting rolls; and means for rotating the casting rolls in opposite directions to each other, thereby casting the strip and conveying the strip down from the nip.

Description of drawings

In order to more fully explain the present invention, specific embodiments will be described in detail with reference to the figures. In the attached picture:

Figure 1 is a vertical cross-sectional view through a steel strip casting and rolling facility constructed and operated in accordance with the present invention;

Figure 2 shows the main components of the twin roll caster included in the plant;

Figure 3 is a vertical cross-sectional view through a portion of a twin roll casting machine;

Figure 4 is a cross-sectional view through the end of the casting machine;

Fig. 5 is a cross-sectional view on line 5-5 in Fig. 4;

Figure 6 is a cross-sectional view on line 6-6 of Figure 4; and

Figure 7 is a schematic illustration of a portion of an improved apparatus constructed and operative in accordance with the present invention.

Detailed ways

The casting and rolling plant as shown includes a twin roll caster generally indicated at 11 which produces cast steel strip 12 which passes along a transport path 10 through a guide table 13 to a pinch roll stand 14 . Immediately after leaving the pinch roll stand 14, the steel strip runs into a hot rolling mill 15 comprising a roll stand 16 in which the steel strip is hot rolled to reduce its thickness. The steel strip thus rolled leaves the rolling mill and runs to an output table 17 where it is forcibly cooled by water jets 18 . According to the invention, the strip then passes through a deskinner 19 before passing between the pinch rolls 20A of the pinch roll stand 20 to the coiler 50 .

Twin roll caster 11 includes a main frame 21 supporting a pair of parallel casting rolls 22 having casting surfaces 22A. During a casting operation, molten metal is fed from a ladle through a refractory ladle outlet screen to a tundish 25 and from there through metal feed nozzles 26 into a nip 27 between casting rolls 22 . The hot metal thus conveyed into the nip 27 forms a molten pool above the nip and this molten pool is confined at the ends of the rolls by a pair of side closed weirs or plates 28 which are closed by a pair of pushers. 31 is applied to the stepped end of the roller, the pusher 31 comprising a hydraulic cylinder unit 32 connected to the side plate holder 28A. The upper surface of the molten pool 30 (commonly referred to as the meniscus) may be raised above the lower end of the feed nozzle so that the lower end of the feed nozzle is submerged in this molten pool.

The casting rolls 22 are water cooled so that the skins solidify on the moving roll surfaces and come together at the nip 27 between the rolls to produce solidified steel strip 12 from which the steel strip 12 is conveyed downward.

Shorter lengths of defective strip are produced as casting conditions stabilize at the start of the casting operation. After the continuous casting has stabilized, the casting rolls move apart slightly and then come together again to break this front end of the strip in the manner described in Australian Patent Application 27036/92, thereby forming a flat front end of the subsequently cast strip. The defective material falls into a scrap bin 33 located below the casting machine, at which point a swinging baffle 34, generally hanging from a pivot 35 to the side of the casting machine exit, swings past the casting machine exit to guide the flat end of the casting belt onto the guide table 13 which feeds the casting strip onto the pinch roll stand 14 . The baffle 34 is then retracted to its hanging position to allow the steel belt 12 to hang in a loop under the casting machine before running to the guide table 13 where it engages a series of guide rollers 36 .

The twin roll casting machine may be of the type shown and described in granted Australian Patents 631728 and 637548 and US Patents 5,184,668 and 5,277,243, to which reference may be made for suitable details of construction which do not form part of the present invention. part.

The apparatus is fabricated and assembled to form a single large-scale enclosure, generally designated 37, which defines a sealed space 38 enclosing within it the The steel strip 12 is fed to the conveying path of the entrance nip 39 of the roller bracket 14 .

The enclosure 37 is formed from a plurality of individual wall sections which fit together by various sealing joints to form a continuous enclosure wall. These wall portions include a wall portion 41 formed on a twin roll caster to enclose the casting rolls and a wall portion 42 extending downwardly below the wall portion 41, which is above the scrap bin 33 when the scrap bin is in its working position. The edges are joined so that the waste bin 33 becomes part of the cabinet. The waste bin and enclosure wall portion 42 may be connected by a seal 43 which may be passed through a ceramic fiber fitting into a groove in the upper edge of the waste bin and engaging a planar gasket 44 fitted to the lower end of the wall portion 42 rope formed. The scrap bin 33 can be mounted to a carriage 45 fitted with wheels 46 running on rails 47, whereby the scrap bin can be moved to a scrap discharge position after the casting operation. When the waste bin is in the operative position, the jack unit 40 is operable to lift the waste bin from the bracket 45 whereby the waste bin is pushed upwardly against the housing wall portion 42 and compresses the seal 43 . After the casting operation, the jack unit 40 is released to lower the scrap box onto the carriage 45 so that it can be moved to the scrap discharge position.

The casing 37 also includes a wall portion 48 disposed about the guide table 13 and connected to the frame 49 of the pinch roller 14, the pinch roller support including a pair of pinch rollers 14A against which the casing slides. The sealing device 60 seals. The strip then exits the casing 38 by passing between a pair of pinch rolls 14A, and it immediately passes into the hot rolling mill 15 . The space between the pinch rolls 14 and the entry to the rolling mill should be as small as possible in order to control the generation of scale before entering the rolling mill.

Most of the enclosure walls may be lined with refractory bricks, while the waste bin 33 may be lined with refractory bricks or a castable refractory lining.

The casing wall portion 41 surrounding the casting rolls is formed with side plates 51 provided with recesses 52 shaped to tightly receive the side closure plates 28 when pressed against the ends of the casting rolls by the jack unit 32 Side Closure Panel Holder 28A. The interface between the side plate retainer 28A and the cabinet side wall portion 51 is sealed by a sliding seal 53 to maintain the cabinet seal. The sealing means 53 may be in the form of a ceramic fiber rope.

The jack unit 32 extends outwardly through the housing wall portion 41 and at these locations the housing is sealed by a sealing plate 54 fitted to the jack unit so that when the jack unit is actuated to The seal plate 54 engages the casing wall portion 41 when the side plates are pressed against the ends of the casting rolls. The pusher 31 also moves the refractory slide 55, which is moved by the actuation of the jack unit 32, to close the slot 56 in the top of the cabinet through which the slide was initially inserted into the cabinet and into the holder 28A , to be applied to casting rolls. The top of the cabinet is closed by the tundish, side plate holder 28A and slide plate 55 when the cylinder unit is actuated to apply the side closure plates to the casting rolls. Prior to casting operations, the entire casing 37 is sealed in this manner to create a sealed space 38 thereby limiting the supply of oxygen to the strip 12 as it travels from the casting rolls to the pinch roll stand 14 . Initially, the steel belt will absorb all the oxygen from the cabinet space 38 to form a thicker scale on the steel belt. However, the sealing of the space 38 controls the intake of oxygen-containing atmosphere below the amount of oxygen that the steel belt can absorb, so that, during the initial start-up phase, the oxygen content in the cabinet space 38 will remain depleted, thus limiting the use. Oxygen utilization rate for steel strip oxidation. In this manner, scale formation is controlled without the need for a continuous supply of reducing or non-oxidizing gas into the enclosure space 38 . In order to avoid thicker scales during the start-up phase, the casing space can be ventilated just before the casting starts, so as to reduce the initial oxygen concentration in the casing and reduce the time for the oxygen concentration to stabilize due to the Oxidation of the steel strip of the shell causes oxygen to react with the scaled shell to stabilize it. The casing can be conveniently vented with nitrogen, and it has been found that reducing the initial oxygen content to a concentration between 5% and 10% will limit the scale of the steel strip leaving the casing to about 10 microns to 17 microns, even at The same is true during the initial startup phase.

In a typical caster setup, the temperature of the steel strip traveling from the caster will be on the order of 1400°C, while the temperature of the steel strip fed to the rolling mill is about 1200°C. The width of the steel strip is in the range of 0.9m to 2.0m, and the thickness is in the range of 0.7mm to 2.0mm. The speed of the steel belt is about 1.0m/s. It has been found that for strip produced under these conditions it is possible to control the leakage of air into the enclosure space 38 to such an extent that the scale growth on the strip exiting the enclosure space 38 is limited to With a thickness of less than 5 microns, this equates to an average oxygen concentration of 2% in the enclosure space. The volume of the enclosure space 38 is not particularly important since all the oxygen will be quickly absorbed by the strip during the initial start-up of the casting operation, and subsequent scale formation is determined only by the rate of leakage of atmosphere into the enclosure space through the seals of. Preferably the leakage rate is controlled so that the scale thickness at the mill entry is in the range of 1 micron to 5 microns. Experimental studies have shown that the steel strip needs some scale on its surface to prevent welding and sticking during hot rolling. Specifically, the study suggests that a minimum scale thickness of 0.5 micron to around 1 micron is required to ensure satisfactory rolling. An upper limit of about 8 microns (preferably 5 microns) is desirable to avoid "rolled-in scale" defects on the strip surface after rolling and to ensure the thickness of the scale on the final product Not greater than the thickness of scales on traditional hot-rolled steel strips.

After leaving the hot rolling mill, the steel strip travels to the run-off table 17 where it can be forcibly cooled by water jets 18 . According to the invention, the strip passes through a descaler 19 before being wound onto a coiler 20 . The descaling machine 19 can be a conventional structure, which generally includes upper and lower water jet nozzles 61, 62, which are supplied with water by a pressure pump through corresponding water jet branch pipes 63, 64, so as to generate water that is guided to the upper and lower surfaces of the steel strip. water jets 65, 66 to remove scales from the surface.

In a typical plant producing steel strip around 1300mm to 1700mm wide, there is a row of 15 to 20 upper nozzles 61 and a corresponding row of 15 to 20 lower nozzles 62 spaced across the strip. Typically, the nozzles have a spray angle of about 50° to 55° and are spaced to produce fan-shaped jets with an overlap of about 10mm. They can be positioned at intervals of 60 to 70mm and can be manipulated to operate between A nozzle flow rate of about 60 L/min is generated at a pressure of 10 MPa.

The water jets of the descaler further reduce the temperature of the strip before it cools down. Typically, the strip is descaled at a temperature of 750°C and coiled at a temperature of about 600°C. Under such circumstances, the steel strip in the coil will typically only have a scale of 1 to 2 microns thick, and as the steel strip cools to ambient temperature, the scale will obviously no longer develop. This is a clear advance and has led to the fact that for many applications, such as for the production of cable reels and any painted product, the slightly scaled steel strip can be used directly as raw material without further treatment, thus eliminating the need for pickling or The cost of pretreatment, which is generally required for strip formed by conventional processes. For more demanding applications, slightly scaled strip can be pickled faster than strip that is not immediately descaled before coiling.

FIG. 7 illustrates a modification by which the casing 37 extends to the closed rolling mill 15 so that the strip is rolled before it leaves the casing space 38 . In this case the strip leaves the casing through the last mill stand 16, the rolls of which also function as sealing casings, so that separate sealing pinch rollers are not required.

It has been found that, in order to avoid excessive scale formation, the steel strip should preferably leave the casing 37 at a temperature not exceeding 925°C, so that, with the configuration shown in Figs. °C range, while in the plant constructed as shown in Figure 7, the strip is hot rolled at temperatures throughout the range of 750 to 1250 °C.

Although the preferred embodiment of the invention employs a twin-roll steel strip caster, which is not limiting of the invention in its broadest sense, the twin-roll caster may be replaced by a conventional continuous thin slab caster which produces 120 to 50 mm range A raw slab or strip of thickness that can be rolled in a hot rolling set to a final thickness ranging from 16.0 to 7.0 mm.

Claims (14)

1. method of producing steel band comprises:

Continuous casting steel strip;

The guiding steel band is by casing, and casing comprises the environment that stops the steel strip surface oxidation and stop firecoat to form thereupon;

Sent rolling mill with steel band, in rolling mill, steel band is rolled along with its production;

The steel band that is rolled is passed the skin machine of scaling, thereby remove firecoat from it along with steel band leaves rolling mill; And

To be rolled and the steel band of the skin of scaling is sent to coiler.

2. the method for claim 1 is characterized in that, hot rolled strip under the temperature of rolling mill in 750 to 1250 ℃ of scopes.

3. method as claimed in claim 1 or 2 is characterized in that steel band passed from described casing before passing rolling mill.

4. method as claimed in claim 1 or 2 is characterized in that rolling mill is arranged in the casing, thereby steel band passed through rolling mill before leaving casing.

5. method according to any one of claims 1 to 4, it is characterized in that, steel band casts continuously by the casting roller upper support molten metal pool in a pair of cooling, this forms roll gap to the casting roller between them, and the steel band that solidifies is produced by rotate the casting roller on direction opposite each other, and the steel band that solidifies thus moves down from roll gap.

6. as each described method in the claim 1 to 5, it is characterized in that the environment in described casing is formed by inert gas or reducing gas.

7. as each described method in the claim 1 to 5, it is characterized in that the environment in described casing is the environment that comprises the oxygen that is lower than the concentration in the environment of casing.

8. method as claimed in claim 7, it is characterized in that, environment in the casing is by following formation, promptly, sealed enclosure enters with the restriction oxygenated atmosphere, make steel band oxidation in casing in the casting starting stage, from the casing of sealing, remove oxygen thus, and cause casing to have being lower than around the oxygen content of the environment of casing, the continuous oxidation of the steel band by passing sealed enclosure subsequently, oxygen content in the sealed enclosure remained be lower than surrounding environment, control the thickness of formed firecoat on the steel band thus.

9. as each described method in the claim 1 to 8, it is characterized in that steel band leaves casing being lower than under 925 ℃ the temperature.

10. as each described method in the claim 1 to 9, it is characterized in that, steel band approximate horizontal ground is by the skin machine of scaling, and firecoat is removed by water jet in the skin machine of scaling, and water jet is directed on the upper and lower surface of steel band so that get on except that firecoat from two surfaces.

11. a device that is used to produce steel band comprises:

The continuous casting machine that is used for continuous casting steel strip;

The guiding steel band passes through the strip guide means away from the transmission path of casting machine;

The steel band that sealing runs through described transmission path suppresses casing with the oxidation that the firecoat on the control steel band forms;

Can handle rolling mill with rolling steel band along with the production of steel band;

Can handle to leave rolling mill along with steel band and remove the skin machine of scaling of the firecoat of steel band; And

Reception is rolled and the coiler of the steel band of the skin of scaling.

12. device as claimed in claim 11 is characterized in that, rolling mill is positioned at the outside of described casing, thereby receives the steel band leave behind the casing.

13. device as claimed in claim 12 is characterized in that rolling mill is positioned within the casing, thus before steel band leaves casing the rolling steel band.

14., it is characterized in that continuous casting machine comprises as each described device in the claim 11 to 13:

The casting roller of a pair of approximate horizontal forms roll gap between them;

With the metal feedway of feeding molten metal in the roll gap of casting between the roller, to be formed on the molten metal pool of casting roller upper support;

The device of cooling casting roller; And the device that on direction opposite each other, rotates the casting roller, cast described steel band thus, and described steel band is transmitted downwards from roll gap.

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