EP0266564B1 - Strip casting installation with a following multiple stand continuous rolling mill - Google Patents

Abstract

A process and apparatus for making hot-rolled steel strip from a striplike continuously cast starting material uses successive processing steps in which the striplike cast starting material after solidification is brought to the hot rolling temperature and fed to a multi-stand rolling mill for rolling to the finished rolled product. A continuous casting unit supplies the multi-stand rolling mill. The rolling to the finished rolled product occurs continuously in three or four roll stands to achieve the largest possible reduction per pass. The first two roll stands operate with an approximately maximum rolling moment and a large working roll diameter.

Description

The invention relates to a method and a plant for the production of hot-rolled steel strip from a strip-shaped, continuously cast starting material in successive working steps, the strip-like starting material being brought to a hot rolling temperature after solidification and being introduced into a multi-stand rolling mill for rolling out into finished strip.

Attempts have been made earlier to continuously roll raw material emerging from continuous casting plants. The difficulties that arise, however, arise above all because the maximum casting speed at which the casting strand leaves the continuous casting installation is much lower than the lowest possible rolling speed of a conventional rolling mill comprising, for example, seven roll stands.

The strip-shaped primary material cast as a strand generally has a thickness in the range between 25 and 60 mm. For example, assuming a casting speed of about 0.13 m / s with an average strip thickness of 40 mm and assuming that the strip is to be rolled down to 2 mm, this means a twenty-fold change. In continuous operation, provided that the casting speed is equal to the entry speed into the first stand, a tandem mill with seven stands would result in an exit speed of 2.67 m / s after the last stand. The minimum exit speed at a final rolling thickness of 2 mm is approximately 10 m / s, because at lower speeds an excessive decrease in temperature makes rolling impossible. So far, two approaches have been taken to solve these problems. One way envisaged that a multi-stand continuous line would be replaced by a high-forming machine (for example a planetary rolling mill), which works at a low entry speed into the roll stand and with which a high pass reduction can be achieved (see Berg- und Hüttenmännchen Monthly Bulletin, 107th year, page 149). With such a very expensive special construction, however, no satisfactory results have so far been achieved, since in particular no homogeneous rolling quality can be produced.

A method known from German Offenlegungsschrift DE-A-32 41 745 according to the preamble of claim 1 or a system according to the preamble of claim 5 provides for problem solving that the band-shaped casting strand is wound into a bundle and unwound again after heating a rolling mill for rolling out to final cross sections. The rolling mill is designed as a Steckel rolling mill or a finishing stand group of a hot strip rolling mill. The disadvantage of this known system is primarily the high investment costs for a multi-stand tandem mill, the cost of which is well over DM 100 million. Such high costs can only be borne if the Konti-Straße is fully utilized; therefore it is also proposed in the cited publication to arrange a multi-core continuous casting installation in front of the continuous road. However, this increases the total effort and the output of the entire system, which is not required in many applications.

It is therefore an object of the present invention to provide a process for producing hot-rolled steel strip and a strip caster with a downstream hot strip rolling mill, with which the disadvantages mentioned can be avoided and the difficulties eliminated and with which even with smaller production quantities, economically, i.e. can be used at high capacity and in particular only low investment costs are required.

The object is achieved for the method according to the invention by the features of claim 1. In this way, the investment costs for the continuous road can even be considerably reduced, while at the same time adapting the technologically given rolling speed to the casting speed.

The professional world was previously of the opinion that this path was not feasible, since it was feared that with a reduction in the number of stands and an increase in the decrease per stitch, the technological boundary conditions would no longer be met. These are essentially the maximum transferable torque, the maximum transferable rolling force (line load between the support roller and work roll as well as the stand design) and the gripping angle in the roll gap. As a result of the higher stitch decrease and the lower heat losses with a reduced number of stands, however, the rolling speed can now be greatly reduced (from approx. 10-11 to 4-6 m / s) according to the invention, which results in a reduction in the total drive power and a reduction in system wear , ie a reduction in costs on the electrical and mechanical side.

According to the invention it is provided that the first two stands work with approximately maximum rolling moment and large work roll diameter. The work rolls are driven. The increase in the gripping angle due to a larger decrease is compensated for by the enlargement of the work roll diameter and by the lowering of the rolling speed, since it is known that the gripping capacity also decreasing rolling speed increases.

In a further embodiment of the invention, in the third and / or fourth stand, the drive takes place via the support rollers. Such a mode of operation is particularly useful with very small end cross sections of less than 2 mm.

It is advantageously provided that the primary material is temporarily stored before being introduced into the rolling mill. In this way, the technologically given different speeds of the strip caster and the hot strip mill can be optimally adapted. Such a buffer store can be designed both as a storage furnace with transverse displacement of the strip lengths or as a continuous furnace and correspondingly longer.

The method for rolling narrow finished strips between 1000 to 2000 mm, preferably 1350 mm wide and with great success for rolling finished strips of low strength is used particularly expediently and advantageously.

For a strip caster with a downstream multi-stand continuous rolling mill, the object is achieved by the features of claim 5. All work rolls of the rolling mill are advantageously provided with their own drive. Furthermore, the work rolls of the first two stands can be provided with a drive and the third and / or fourth stand can be provided with a support roll drive, in particular if the smallest final thicknesses are to be rolled.

Further advantages of the invention result from the following explanation of several exemplary embodiments schematically illustrated in the drawings.

• Fig. 1 eine Prinzipskizze eines Ansführungsbeispiels der erfindungsgemäßen Anlage in Seitenansicht,
• Fig. 2a-d Prinzipdiagramme für den Walzbetrieb in vier Gerüsten nach dem Ausführungsbeispiel des erfindungs gemäßen Verfahren,
• Fig. 3 Walzdiagramm für die Stichabnahme im ersten Gerüst,
• Fig. 4 Walzdiagramm für die Stichabnahme im zweiten Gerüst,
• Fig. 5 Walzdiagramm für die Stichabnahme im dritten und letzten Gerüst.

Show it:

• 1 is a schematic diagram of an exemplary embodiment of the system according to the invention in side view,
• 2a-d principle diagrams for the rolling operation in four stands according to the embodiment of the inventive method,
• 3 rolling diagram for the stitch acceptance in the first stand,
• 4 roll diagram for the stitch acceptance in the second stand,
• Fig. 5 rolling diagram for the stitch acceptance in the third and last stand.

In FIG. 1, (1) denotes a strip or continuous caster, which is followed by a cross-cutting device (2), for example a flame cutting machine or scissors, for separating the cast strip (3) and leaving the strip caster (1) into sections of the same length . The individual partial lengths of the strip (3) are then temporarily stored in a storage and heating device (4), for example a roller hearth furnace, and brought to a homogeneous hot rolling temperature of approximately 1050 to 1100 degrees Celsius. A partial length (5) leaving the furnace (4) is descaled in a known manner and possibly also brought to a new pre-strip length (not shown). The partial strip (5) is then finished rolled in a rolling train (6) consisting of three (or four) stands (6 ', 6 ", 6) from the initial cross section to the final roll thickness. After leaving the last rolling stand (6) of the rolling train (6) with an outlet temperature of approximately 860 degrees Celsius, the finished strip (7) passes through the cooling section (8) in order to be subsequently wound up by the underfloor reel (9) at a temperature of approximately 560 degrees Celsius.

Figures 2a to 2d schematically show the pass reductions and rolling parameters in four stands, the thickness decrease "ie" of the rolling stock in mm being shown on the abscissa and the sum of the effective rolling moment "Ma" in kNm being shown on the ordinate.

In FIG. 2a an initial thickness of the strip material of 50 mm is assumed for the first stand. The maximum transferable rolling moment (10) with a certain work roll diameter (13 - 17) intersects the curves (11, 12) as a horizontal line, whereby the curve (11) the rolling moment limit with backup roll drive with a coefficient of friction of u = 0.15 and the curve ( 12) indicates the rolling torque limit for work roll drive. The lines of the same work roll diameter (13-17) rise, for example, from bottom to top in the range from 400 to 800 mm. Taking advantage of an almost maximum rolling torque for a certain and relatively large work roll diameter (between lines 15 and 16) with work roll drive (12), the working point (18) for the first stand can be chosen so that the thickness decrease is, for example, 26 mm, so that a remaining thickness after the first framework of 50-26 = 24 mm remains, which is introduced into the second framework. The related thickness or stitch reduction reaches a value of 52%.

In FIG. 2b, the reference numbers (23-27) in turn indicate increasing work roll diameters as a function of the rolling torque and reduction in thickness. Utilizing the maximum transferable rolling moment (20), the working point (28) in the permissible range above the line for the maximum transferable rolling moment with work roll drive (22), but outside the permissibility for, results in the second stand with preferably the same work roll diameter (between 25 and 26) Back-up roller drive (21) with a reduction in thickness of, for example, 12 mm, so that from 24 to 12 a residual thickness = 12 mm remains, corresponding to a related stitch reduction of 50%. The permissible field of work between the lines (22) and (20) is delimited to the right by the line of the maximum gripping angle (29) at the highest stitch decreases.

In FIG. 2c, the reference numbers (33-37) in turn indicate increasing work roll diameters as a function of the rolling moment and the decrease in thickness. The set decrease in thickness here is, for example, 6 mm with a remaining thickness of 6 mm, corresponding to a related decrease in height of 50%. The selected working point (38) lies far below the maximum transferable rolling torque in the permissible range of the rolling torque line for backup roller drive (31), so that the work rollers can either be driven themselves (32) or indirectly via the backup rollers (31).

In FIG. 2d, the same increasing work roll diameters are also shown with reference numbers (43-47) depending on the rolling moment and the reduction in thickness. The desired decrease in thickness is, for example, 3 mm with a final thickness of 3 mm, corresponding to a related decrease in height of again 50%. The selected working point (48) is, as in Fig. 2c, far below the maximum transferable rolling torque in the permissible range of the rolling torque lines (41, 42) for work and backup roll drive, so that the work rolls here, as in the third stand, optionally have their own drive own (42) or driven by the support rollers (41).

In FIG. 3, operating values for the pass reduction in a first of three stands are shown as a working diagram, the decrease in thickness "ie" of the rolling stock in mm being indicated on the abscissa and the sum of the effective rolling moment "Ma" in kNm being shown on the ordinate. With the reference numbers (53 - 57) the work roll diameter increases from 400 to 800 mm. Taking advantage of the maximum transferable rolling torque of 1700 kNm (50), the working point (58) in the permissible range above the line for the maximum transferable rolling torque with work roll drive (52) results for a work roll diameter of 710 mm (between 56 and 57), outside the permissibility for back-up roller drive (51), with a thickness reduction of 19 mm, so that from an input thickness of 41 mm - 19 a residual thickness = 22 mm remains, corresponding to a related stitch reduction of 46.34%. The permissible working field between lines (52) and (50) is not limited by the line of the maximum gripping angle (59).

In FIG. 4, the reference numerals (63-67) in turn indicate increasing work roll diameters as a function of the rolling moment and the decrease in thickness. Using a maximum transferable rolling moment of 1700 kNm (60), the working point (68) in the permissible range above the line for the maximum transferable rolling moment results in the second stand with preferably the same work roll diameter as in the first stand of 710 mm (between 66 and 67) with work roll drive (62) but outside the permissibility for backup roll drive (61) with a decrease in thickness of 14 mm, so that from 22 - 14 a remaining thickness = 8 mm remains, corresponding to a related stitch decrease of 63.64%. The permissible working area between lines (62) and (60) is limited in the case of high stitch decreases to the right by the line of the maximum gripping angle (69).

In FIG. 5, the numbers (73-77) denote the lines of increasing work roll diameters from 400 to 800 mm. The set decrease in thickness is, for example, 4 mm to achieve a remaining thickness of 4 mm, corresponding to a related decrease in height of 50%. The selected working point (78) is 900 kNm with a 4 mm decrease in thickness, far below the maximum transferable rolling torque in the permissible range of the rolling torque line for back-up roll drive (not shown) and work roll drive (72).

The measures according to the invention are not limited to the exemplary embodiment shown in the drawing figures. For example, without departing from the scope of the invention, work rolls with different roll geometries can be arranged in the individual stands to optimize the individual deformation states, for example in particular in the last stands so-called bottle rolls that can be displaced relative to one another for continuous change of the roll gap on the roll wear. The respective structural design is left to the person skilled in the art to adapt to the later use of the device.

Claims (5)

1. Method of manufacturing hot-rolled steel strip from a strip-shaped continuously cast starting material in successive working steps, wherein the strip-shaped starting material is brought to hot-rolling temperature after hardening and is introduced into a multistand continuous roll train (6) for rolling out to finished strip, wherein narrow finished strips of between 1000 and 2000 millimetres in width are rolled, characterised thereby that the rolling out into finished strip takes place in three or four horizontal roll stands (6, 6", 6"'), wherein at least in the first two stands (6', 6") for the attainment of highest possible roll pass reductions with use of an approximately maximum rolling moment the operation is with a relatively large working roll diameter of between 400 and 800 millimetres at the rolling moment limit with working roll drive and with a rolling speed strongly reduced to 4 to 6 metres per second.

2. Method according to claim 1, characterised thereby that the drive by way of the working rolls takes place for all stands.

3. Method according to claim, characterised thereby that finished strips of lower tensile strength are rolled.

4. Method according to one or more of the claims 1 to 3, characterised thereby that the starting material is intermediately stored before introduction into the roll train.

5. Strip casting plant (1) with multi-stand continuous rolling mill (6) arranged thereafter for the manufacture of hot-rolled steel strip from a strip-shaped continuously cast starting material in successive working steps, wherein the strip-shaped starting material is brought to hot-rolling temperature after hardening and is introduced into the rolling mill (6) for rolling out to finished strip, wherein narrow finished strips of between 1000 and 2000 millimetres in width are rolled, for the performance of the method according to one or more of the preceding claims, wherein the rolling mill (6) consists of three (6', 6", 6"') or four roll stands, characterised thereby that all working rolls of the rolling mill (6) have the same roll diameter of between 400 and 800 millimetres and that working rolls (6', 6") with working roll drive are provided at least in the case of the first two stands.

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