GB1603161A - Rolling of slabs into hot strip - Google Patents

Description

(54) ROLLING OF SLABS INTO HOT STRIP (71) We, SCHLOEMANN-SIEMAG AKTIENGESELLSCHAFT, of Steinstrasse 13, 4000 Diisseldorf 1, Federal Republic of Germany, a joint stock company organised under the laws of the Federal Republic of Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a rolling mill.

In the rolling of hot strip, slabs are rolled from a thickness of, for example, 200 to 300 millimetres down to a thickness of 40 to 60 millimetres, or even as low as 25 millimetres. Subsequently. the rolled stock then runs into a finishing train in which the hot strip is cooled at one or several places between finishing stands.

Continuous hot strip roughing trains operate with several, for example, six indi vldual stands. Since, during the rolling process, there should be no pressure stresses in the longitudinal direction of the slabs which would upset the material and thereby cause a lateral running out or bending out of the rolled stock, and since tension stresses, which could lead to uncontrolled deformation or even to tearing of the rolled stock, must be avoided, the spacings between the individual stands are frequently such that the slab is not rolled simultaneously in two stands. Consequently, in some hot strip roughing trains, the spacings between the individual stands from the first to the last stand are increased stage-by-stage and can reach 70 metres.

For such roughing trains, therefore, a rolling shed of great length is required and plant expenditure is substantial, as correspondingly long roller beds must be provided for the connection between the individual stands.

Since the investment for such a roughing train and for hot rolling mills is considerable, there is a need to reduce as far as possible the constructional effort of the entire rolling mill plant, i.e. of the rolling shed, the foundations and the rolling train.

To achieve this, it has been proposed to arrange the last two roll stands of a six-stand hot strip roughing train closely together and thereby to save the last roller bed as well as the corresponding part of the foundations and the rolling shed. In practice, the penultimate stand was not provided. As a result, the hot strip roughing train in fact operated in a conventional manner, but with only five individual stands. Thus, in practice no use was made of the envisaged simultaneous rolling of the slabs in the last two stands of this hot strip roughing train, apparently because an impairment of the rolling quality of the roughing strip by the occurrence of pressure and/or tension stresses was feared.

In hot strip finishing trains arranged downstream of the roughing trains, the rotational speed of the individual roll stands is regulated by loop lifters or loop measuring apparatus which are arranged between the stands and form corresponding regulating devices, which effect corrections of the rotational speed of the roll stands in dependence on the increase and decrease in size of the loops.

Due to the loop formation between the roll stands of the hot strip finishing trains, spray cooling is used for cooling and a relatively uniform wetting of the hot strip with the cooling liquid is possible by the jet system used. However, as the hot strip raised by the loop lifters or loop measuring apparatus extends obliquely, a satisfactory cooling effect is not achieved by the spray cooling. The applied cooling liquid runs off at different speeds depending on the size of the formed loops and therefore does not have a constant cooling effect.

Due to the loop lifters or loop measuring apparatus arranged between the individual roll stands in the hot strip finishing trains, a relatively large plant expenditure and spacing of the successive roll stands are necessary, which increase the length of the rolling shed and the foundations for the rolling train.

According to the present invention there is provided a rolling mill comprising a multi-stand continuous hot strip roughing train provided with a plurality of closely spaced roll stands for simultaneously rolling a slab, a multi-stand continuous hot strip finishing train disposed downstream of the roughing train and provided with a further plurality of roll stands for rolling the slab, a liquid bath disposed between at least one pair of successive stands of the finishing train for cooling the slab during movementthereof between the stands of said at least one pair, the stands of said at least one pair being so arranged that, in use, the slab is substantially horizontally suspended therebetween and is moved through the bath exclusively by operation of the stands, and tension regulating means associated with each of the stands of the trains and operative to cause the tension of the slab between the stands to be maintained at a predetermined minimum value.

The roughing train may be in the form of a compact plant of small length, within which all roll stands may have the same spacing of, for example, five to six metres from each other. The plant expenditure on and space requirement of such a roughing train can be reduced without impairment of the rolling quality. An improvement of the rolling quality may even result.

The control of the roll stands to provide minimum tension in the slab allows use, in place of the alternating current synchronous motors normally used for the drive of roll stands, of direct current motors, the armature current of which can be varied to provide regulation of the tension.

For the rolling process, the minimum tension regulation may be such that tension stresses between 0.2 and 0.5 kilograms per square millimetre are generated in the rolled slab between the stands and that the resulting tension moment in the slab remains below 10% of the rolling moment causing the slab deformation at each stand.

A reduction of plant expenditure and consistently good cooling of the rolled slab may be provided by the cooling of the slab, for example by water, between the roll stands of the finishing train while the stands are controlled to maintain minimum tension in the slab. The slab can be held at a low tension stress of 0.2 to 0.5 kilograms per square millimetre (2 to 5 Newtons per square millimetre) between successive stands of the finishing train and guided, lying substantially flat in a horizontal plane, through a water bath, so as to be subJected to laminar cooling. The water bath can be of flat construction and can be augmented by spray cooling in such a manner as to provide continuous maintenance of the water level required for achieving laminar cooling.

By controlling the roll stands of the finishing train to provide minimum tension regulation, not only is the cooling effect improved, but there is also a reduction in plant expenditureKbecause loop lifters and loop measuring apparatus between the individual finishing stands are not needed. This permits closer spacing of the stands, particularly where a cooling zone is not present between adjacent stands.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings in which: - Fig. 1 is a schematic side elevation of a hot strip roughing train in a rolling mill according to the said embodiment, Figs. 2.1 to 2.7 are schematic diagrams showing simplified regulation of minimum tension in a hot strip passing through the roughing train shown in Fig. 1, Figs. 3.1 to 3.7 are schematic diagrams showing detailed regulation of the minimum tension in a hot strip passing through the roughing train shown in Fig. 1 in the first half of the rolling operation.

Figs. 4.1 to 4.7 are diagrams similar to Figs. 3.1 to 3.7 but showing the passage of the strip in the second half of the rolling operation, and Fig. 5 is a schematic elevation of a hot strip finishing train in the rolling mill, the finishing train having a cooling zone between two successive roll stands thereof.

Referring now to the drawings, in Fig. 1 there is shown a hot strip roughing train 10 of a rolling mill, the train comprising six roll stands 1 to 6 disposed at a relatively small spacing of, for example, 5 to 6 metres from one another so as to provide a relatively compact train, preferably without intermediate roller beds.

Due to the relatively short and uniform spacings between the stands 1 to 6, after the first pass of each slab 7, simultaneous rolling of the slab 7 takes place in several successive ones, and possibly even all, of the roll stands, which are driven separately by respective direct current motors 11 to 16 and are coupled with each other at least temporarily by the slab 7.

Since a reduction in cross-section of the slab 7 takes place by the rolling passes in each of the stands 1 to 6 without the slab volume changing, the exit speed of the slab from each of the roll stands 1 to 6 increases by a factor which is dependent on the respective pass reduction AE:AA and on the widening of the rolled stock. The material speed in the roll gap of each roll stand 1 to 6, however, only coincides at the so-called no-slip point with the peripheral speed of the rolls, while the speed VE of the material entering the roll gap differs by the so-called backwash and the speed VA of the material issuing from the roll gap by the so-called precession from the peripheral speed of the rolls.

During the simultaneous rolling of the slab 7 in several successive stands 1 to 6, the rotational speeds of the individual stands must therefore be so matched to one another that, if possible, no pressure stresses and only minimum tension stresses can arise in each section of the slab 7 extending between pairs of roll stands 1, 2; 2, 3; 3, 4; 4, 5; and 5, 6. In order to achieve this, the hot strip roughing train 10 is operated with a minimum tension regulation means 20 in which an individual minimum tension regulator 21 to 26 is associated with each roll stand 1 to 6.

Figs. 2.1 to 2.7 of the drawings show a simplified way of regulating the minimum tension using the tension regulation means 20 associated with the hot strip roughing train 10. On the first pass of the slab 7 in the roll stand 1 (Fig. 2.1) the lever arm al of the stand 1 is determined automatically and stored for the duration of the roll pass. The length of the lever arm al to a6 of each stand corresponds (Fig. 1) to the horizontal spacing of the no-slip point F from the vertical plane passing through the axes of the two rolls of the stand and is determined by the entry cross-section AE and exit cross-section AA of the slab 7 at the stand. The length of the lever arm a1is nearly half the length Ld of the pressed section of the slab 7 in this stand.

As soon as the stand 2 starts to pass the slab (Fig. 2.2) the difference m between the rotational drive moment of the roll pair at the stand 1 and the moment counteracting the rotational drive moment, the counteracting moment being a function of inter alia the length of the lever arm of the roll pair, is continuously determined, compared with a predetermined intended difference value mX, and any detected deviation (i.e. m 7 mX) is translated by the minimum tension regulator 21 associated with the stand 1 into a correction An2x of the rotational drive speed for the stand 2 (and all subsequent stands 3, 4, 5, 6), as is evident from Fig. 2.2 As in the case of the stand 1, the lever arm a2 (Fig. 1) is calculated for the stand 2 and the rotational speed correction an2", which is provided by the minimum tension regulator 21, is stored for the duration of the pass before the opening of the regulating circuit.

The manner in which the regulation is effected after the first pass in stand 3 is shown in Fig. 2.3. Thus, the minimum tension regulator 22, by reason of a determined deviation (m f mX) at the stand 2, resets the rotational speed of stand 3 corresponding to a correction An3x, until the difference m + mx and thereby the longitudinal stress in the slab 7 between the stands 2 and 3 is reduced to the desired amount.

Meanwhile, the lever arm a3 (Fig. 1) can be determined for the stand 3.

This manner in which the regulation is effected is applied to the other stands as shown in Figs. 2.4 to 2.7 until the last stand 6 of the continuous hot strip roughing train 10 has been adapted to the speed of the slab 7, the determined rotational speed relationships being kept constant for the remainder of the pass.

The above-described manner of regulation presupposes that parameters significant in rolling technique, such as rolled stock temperature and input cross-section, do not change too much during the pass, as otherwise precession changes would occur at the individual stands 1 to 6 which could lead to a build-up of undesirable longitudinal stresses.

In these circumstances it is not sufficient to maintain the rotational speed relationships determined in the first pass phase of the slab 7 unchanged up to the end of the slab passage. The longitudinal stresses in the slab 7 must be constantly monitored by regulation during the passage phase.

Figs. 3.1 to 3.7 of the drawing show a detailed manner of regulation by the minimum tension regulation means 20 which makes influencing of the longitudinal stresses during the passage phase of the slab 7 possible.

Figs. 3.1 and 3.2 correspond to Figs. 2.1 and 2.2.

As shown in Figs. 2.1 to 2.7, the rotational speed is so reset by corrections An2x An6x at each stand, when it is just beginning to pass the slab, in the regulation shown in Figs. 3.1 to 3.7 that the deviation represented by m # mx disappears at the respective immediately preceding stand. At the other preceding stands, the difference m is additionally regulated by a respective minimum tension regulator 22,23,24 25 and 26 to a settable intended value mxi - mX6, as shown in Figs. 3.3 to 3.7.

Fig. 3.3, shows that the roll speed at the stand 2 still exceeds the slab speed, while the rotational driving speed of stand 3 has just been matched to the slab speed. Additionally, the minimum tension regulator 21 at the stand 1 holds the difference m to the predetermined intended value mx in that it corrects the rotational driving speed of the stand 1 if necessary, so that this goes over into the passage phase of the operation.

In the case of the first pass of a new slab dimension, the rotational speed settings of the individual drives 11 to 16 show considerable error. In order, therefore, not to worsen the rotational speed relationships between a stand just starting to pass and the following stands, all idling stands in the rolling direction are reset by the same percentage of the rotational speed as the stand just starting to pass must be reset for adaptation to the slab speed. The minimum tension regulation means 20 thus operates according to the principle of forward regulation.

Fig. 3.7 shows the manner of regulating the minimum tension by regulation means 20 after the conclusion of the first pass phase, i.e. the passage phase for all stands 1 to 6. In this stage, for example, the stand 5, penultimate in the rolling direction, of the hot strip roughing train 10 is operated at constant rotational speed and consequently also defines the slab speed. The rotational speeds of all the remaining stands 1 to 4 and 6 are so reset, if necessary, by the minimum tension regulation means 20 that the stress difference at the stands is reduced to the value of the predetermined minimum tension, which for example is between 0.2 to 0.5 kilograms per square millimetre (2 to 5 Newtons per square millimetre).

The manner of regulating the minimum tension by regulation means 20 during the exit phase of the slab 7 is shown in Figs. 4.1 to 4.7 of the drawings. In this case, Fig. 4.1 corresponds to the passage phase for all stands 1 to 6 as shown in Fig. 3.7, whereas the end of the slab 7 has just left the stand 1 in Fig. 4.2. In this case, the stressing of the slab 7 is automatically taken over by the following stand 2, 3, etc., as shown in Figs.

4.2 to 4.4 until the stand 4 disposed before the speed-guiding stand 5, has been reached.

Stands, which are disposed behind the stand 5, take over, on the issue of the slab 7 from the preceding stand, the rotational speed value stored for the last resetting, as shown in Figs. 4.6 to 4.7.

By the above-described operation of the roll stands 1 to 6 of the continuous hot strip roughing train 10, the simultaneous rolling of slabs 7 is realized with a close spacing of the stands, preferably without intermediate roller beds, wherein the minimum tension regulation brings about a high uniformity of the rolled thickness and thereby a high rolling quality when rolling according to the principle of the constant mass flow is utilised. This is possible in a simple manner in that regulation of thickness, during rolling, takes place only on the first stand by the setting devices, while the remaining stands are operated with a constant roll gap.

Fig. 5 shows a hot strip finishing train 30 with six roll stands 31 to 36 in which a cooling zone 37 is provided between the stands 33 and 34. Each of the roll stands 31 to 36 is individually driven by a direct current motor, wherein the rotational speeds of these direct current motors can be influenced through a minimum tension regulation means 40 which comprises a respective minimum tension regulator 41 to 46 for each of the stands 31 to 36.

The construction and operation of such minimum tension regulation means has been described above and is also known from continuous rod and profile steel rolling trains.

The hot strip finishing train 30 is operated with the minimum tension regulation means 40 so that the rolled strip extends in the horizontal plane in the cooling zone 37 between successive finishing stands, in this case the finishing stands 33 and 34, and thereby a highly effective laminar cooling of the strip can be effected in a flat water bath, which in some circumstances can be kept at a suitable liquid level by conventional spray cooling.

WHAT WE CLAIM IS: 1. A rolling mill comprising a multistand continuous hot strip roughing train provided with a plurality of closely spaced roll stands for simultaneously rolling a slab, a multi-stand continuous hot strip finishing train disposed downstream of the roughing train and provided with a further plurality of roll stands for rolling the slab, a liquid bath disposed between at least one pair of successive stands of the finishing train for cooling the slab during movement thereof between the stands of said at least one pair, the stands of said at least one pair being so arranged that, in use, the slab is substantially horizontally suspended therebetween and is moved through the bath exclusively by operation of the stands, and tension regulating means associated with each of the stands of the trains and operative to cause the tension of the slab between the stands to be maintained at a predetermined minimum value.

2. A rolling mill as claimed in claim 1, wherein said value lies between 2 and 5 Newtons per square millimetre.

3. A rolling mill substantially as hereinbefore described with reference to the accompanying c drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. In the case of the first pass of a new slab dimension, the rotational speed settings of the individual drives 11 to 16 show considerable error. In order, therefore, not to worsen the rotational speed relationships between a stand just starting to pass and the following stands, all idling stands in the rolling direction are reset by the same percentage of the rotational speed as the stand just starting to pass must be reset for adaptation to the slab speed. The minimum tension regulation means 20 thus operates according to the principle of forward regulation. Fig. 3.7 shows the manner of regulating the minimum tension by regulation means 20 after the conclusion of the first pass phase, i.e. the passage phase for all stands 1 to 6. In this stage, for example, the stand 5, penultimate in the rolling direction, of the hot strip roughing train 10 is operated at constant rotational speed and consequently also defines the slab speed. The rotational speeds of all the remaining stands 1 to 4 and 6 are so reset, if necessary, by the minimum tension regulation means 20 that the stress difference at the stands is reduced to the value of the predetermined minimum tension, which for example is between 0.2 to 0.5 kilograms per square millimetre (2 to 5 Newtons per square millimetre). The manner of regulating the minimum tension by regulation means 20 during the exit phase of the slab 7 is shown in Figs. 4.1 to 4.7 of the drawings. In this case, Fig. 4.1 corresponds to the passage phase for all stands 1 to 6 as shown in Fig. 3.7, whereas the end of the slab 7 has just left the stand 1 in Fig. 4.2. In this case, the stressing of the slab 7 is automatically taken over by the following stand 2, 3, etc., as shown in Figs. 4.2 to 4.4 until the stand 4 disposed before the speed-guiding stand 5, has been reached. Stands, which are disposed behind the stand 5, take over, on the issue of the slab 7 from the preceding stand, the rotational speed value stored for the last resetting, as shown in Figs. 4.6 to 4.7. By the above-described operation of the roll stands 1 to 6 of the continuous hot strip roughing train 10, the simultaneous rolling of slabs 7 is realized with a close spacing of the stands, preferably without intermediate roller beds, wherein the minimum tension regulation brings about a high uniformity of the rolled thickness and thereby a high rolling quality when rolling according to the principle of the constant mass flow is utilised. This is possible in a simple manner in that regulation of thickness, during rolling, takes place only on the first stand by the setting devices, while the remaining stands are operated with a constant roll gap. Fig. 5 shows a hot strip finishing train 30 with six roll stands 31 to 36 in which a cooling zone 37 is provided between the stands 33 and 34. Each of the roll stands 31 to 36 is individually driven by a direct current motor, wherein the rotational speeds of these direct current motors can be influenced through a minimum tension regulation means 40 which comprises a respective minimum tension regulator 41 to 46 for each of the stands 31 to 36. The construction and operation of such minimum tension regulation means has been described above and is also known from continuous rod and profile steel rolling trains. The hot strip finishing train 30 is operated with the minimum tension regulation means 40 so that the rolled strip extends in the horizontal plane in the cooling zone 37 between successive finishing stands, in this case the finishing stands 33 and 34, and thereby a highly effective laminar cooling of the strip can be effected in a flat water bath, which in some circumstances can be kept at a suitable liquid level by conventional spray cooling. WHAT WE CLAIM IS:

1. A rolling mill comprising a multistand continuous hot strip roughing train provided with a plurality of closely spaced roll stands for simultaneously rolling a slab, a multi-stand continuous hot strip finishing train disposed downstream of the roughing train and provided with a further plurality of roll stands for rolling the slab, a liquid bath disposed between at least one pair of successive stands of the finishing train for cooling the slab during movement thereof between the stands of said at least one pair, the stands of said at least one pair being so arranged that, in use, the slab is substantially horizontally suspended therebetween and is moved through the bath exclusively by operation of the stands, and tension regulating means associated with each of the stands of the trains and operative to cause the tension of the slab between the stands to be maintained at a predetermined minimum value.

2. A rolling mill as claimed in claim 1, wherein said value lies between 2 and 5 Newtons per square millimetre.

3. A rolling mill substantially as hereinbefore described with reference to the accompanying c drawings.