METHOD AND APPARATUS FOR PRODUCING FLAT METAL PRODUCTS

Abstract

Method for the production of flat metal products, in particular coils of strip, in endless and/or semi-endless mode, in which a metal product is continuously fed to a rolling mill consisting overall of at least 4 stands. The rolling stands are, in sequence, roughing stands, and finishing stands. It is provided to perform a flying gauge change of the metal product exiting from the rolling mill.

Claims

1. A method for the production of flat metal products, in particular coils of strip, in endless and/or semi-endless mode, in which a metal product is continuously fed to a rolling mill consisting overall of at least 4 stands, in which the rolling stands are, in sequence, roughing stands (18a, 18b, 18c), and finishing stands (21a, 21b, 21c, 21d, 21e), wherein it is provided to perform a flying gauge change, namely a change of thickness without interrupting the rolling process, of the metal product exiting from the rolling mill, wherein at least the rotation speed of the rollers of the first stand (18a) of the rolling mill and their gap are not modified during the flying gauge change of the strip.

2. The method as in claim 1, wherein the flying gauge change is applied without modifying the speed of the material fed to the rolling mill.

3. The method as in claim 1, wherein the transition from the current thickness to the subsequent thickness occurs by applying a new set-up of parameters, for example gap between the rollers, speed of the rollers and inter-stand tension, to all the rolling stands involved in the flying gauge change.

4. The method as in claim 3, wherein the application of the new set-up of gap between the rollers, speed of the rollers and inter-stand tension to the stands involved in the flying gauge change occurs in the following manner: a first step in which the new target thickness and a new speed cone, that is, the rotation speed reference for the work rollers of the rolling stands, are applied, and a second step in which a new inter-stand tension is applied by means of loopers or tensioners.

5. The method as in claim 4, wherein when the section of strip affected by the thickness change reaches a specific stand (n.sup.th stand), the gap of that stand is modified from the current gap to a new gap calculated to produce the subsequent thickness with the current inter-stand tension, and the speed of the stand is increased, or decreased, as a function of the new thickness in order to maintain the mass-flow (thickness×speed) constant.

6. The method as in claim 5, wherein inter-stand tension is modified only when the section involved in the thickness change reaches the subsequent stand (n+1.sup.th) and simultaneously with the change of the inter-stand tension the gap and the speed of the n.sup.th stand are adjusted completing the transition to the new set-up for the n.sup.th stand.

7. The method as in claim 3, wherein the transition from the current thickness to the subsequent thickness occurs by applying a new set-up to the rolling stands involved, and the application of the new set-up occurs simultaneously for all the stands involved.

8. The method as in claim 7, wherein if the stands involved in the flying gauge change are more than two, the set-up variation is applied in sequence in the first stands and simultaneously in the last two or more stands.

9. The method as in claim 3, wherein all the variations from the old to the new set-up are conducted in a ramped manner.

10. The method as in claim 1, wherein the number of stands involved in the flying gauge change, starting from the last stand (21e) of the finishing stand, is obtained taking into account the distribution of the rolling force of each stand, so that the new distribution of forces due to the thickness change does not cause the value of the rolling force of any stand whatsoever to exit from an acceptable tolerance range.

11. The method as in claim 10, wherein in the event the new distribution of rolling forces due to the flying change determines the exit from an acceptable tolerance range, then at least a new rolling stand located upstream of those already provided will be involved in the thickness change process.

12. An apparatus for the continuous production of flat metal products, comprising at least one continuous casting machine (11) having a mold (12), a rolling mill comprising roughing rolling stands (18a, 18b, 18c) and finishing rolling stands, (21a, 21b, 21c, 21d and 21e), a high-speed flying shear (23) for cutting the strip to size, to be used in endless and/or semi-endless rolling in order to divide the strip, engaged with the winding reels, into coils of the desired weight; and a pair of winding reels, (24a, 24b), wherein there is a control system suitable to apply the method for flying gauge change as in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0106] These and other characteristics of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

[0107] FIG. 1 schematically shows an example of an apparatus for producing flat metal products in accordance with some characteristics of the present invention;

[0108] FIGS. 2-6 schematically represent graphs of embodiments of the flying gauge change method applicable in the method for producing flat metal products in accordance with some characteristics of the present invention;

[0109] FIG. 7 shows a table relating to an example of parameter changes in the passage from one thickness to another;

[0110] FIGS. 8-11 show example graphs of the criteria for identifying the stands involved in the thickness change.

[0111] To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can conveniently be incorporated into other embodiments without further clarifications.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

[0112] We will now refer in detail to the various embodiments of the present invention, of which one or more examples are shown in the attached drawings. Each example is supplied by way of illustration of the invention and shall not be understood as a limitation thereof. For example, the characteristics shown or described insomuch as they are part of one embodiment can be adopted on, or in association with, other embodiments to produce another embodiment. It is understood that the present invention shall include all such modifications and variants.

[0113] FIG. 1 shows, as a whole, and schematically, an example of an apparatus 10 for the production of flat metal products in which the flying gauge change method described hereafter in detail can be applied. It is understood that the representation of FIG. 1 is only an example to facilitate the understanding of the invention, which is completely non-binding for the application of the concepts presented below.

[0114] It is also understood that not all the components shown are necessary and essential for the correct functioning of the apparatus.

[0115] For example, the apparatus 10 comprises a control system suitable to receive the instructions relating to the cards relating to a determinate casting process, as well as relating to determinate flying gauge changes of the final product to be made, and to adjust the work parameters of all the rolling stands as a result of the flying gauge change as above.

[0116] In general, the apparatus 10 comprises, as constituent elements: [0117] a continuous casting machine 11 having an ingot mold 12; [0118] a possible first descaling device 13; [0119] a pendulum shear 14; [0120] a tunnel furnace 15, which can have at least one laterally mobile end module 115a-115b, [0121] an oxyacetylene cutting device 16; [0122] a possible second descaling device 113; [0123] a possible vertical or edge-trimmer stand 17; [0124] a third descaling device 213; [0125] three roughing rolling stands 18a, 18b, 18c; [0126] a crop shear 19 to crop the head and tail ends of the bars in order to facilitate their entrance into the first stand of the finishing mill; it can also be used in the event of an emergency shearing in the event of blockages in the finishing mill in endless mode; [0127] a modular induction rapid heating device 20; [0128] an intensive cooling system (not shown) located downstream of the rapid heating device to be used in case there is a need to carry out a thermomechanical rolling process or a ferritic field rolling process in the finishing mill; [0129] a fourth descaling device 313; [0130] a finishing rolling mill, comprising in this case five stands, respectively 21a, 21b, 21c, 21d and 21e; [0131] laminar cooling showers 22; [0132] a high-speed flying shear 23 to shear the strip to size, to divide the strip into coils of the desired weight, when it is directly engaged with the winding reels; and [0133] a pair of winding reels, respectively first 24a and second 24b.

[0134] The casting and rolling process carried out by the apparatus 10 can occur in endless, semi-endless and coil-to-coil modes.

[0135] FIGS. 2-6 represent graphs which represent, by varying the specific parameters indicated, modes for the flying change of the final thickness of the strip of the type applicable in the apparatus 10 described above, in particular in the endless and/or semi-endless modes indicated above.

[0136] In a first embodiment, shown in FIG. 2, only the finishing stands 21a-21e, indicated as F1-F5, are involved in the thickness change that occurs in the two-step mode.

[0137] As can be seen from the graphs, observing the lines traced from top to bottom, when it is necessary to modify on the fly the final thickness of a strip being rolled, a set-point of the new thickness is identified in the first finishing stand F1. In this case, the new thickness is smaller than the previous thickness (thickness reduction).

[0138] In the first step, the new gap between the rolling rollers, corresponding to the new thickness, of the first finishing stand F1 is set, and the speed of the rollers of the same stand F1 is increased simultaneously until it reaches the new set-point. The second step provides the application of the new set of inter-stand tension, in this case the tension of the strip is increased.

[0139] All the successive stands F2-F5 progressively adjust their speed both in relation to each speed change of the previous stand, and also in relation to the moment in which the final end of the transition segment reaches the stand itself. As can be seen in the trend of the last line, the speed at which the material is fed, in this case the casting speed, remains constant, as well as the speed of all the stands upstream of the stand F1, that is, of all the roughing stands.

[0140] In a second embodiment, shown in FIG. 3, only the finishing stands 21a-21e, indicated as F1-F5, are involved in the thickness change which occurs, however, contrary to what observed previously, in simultaneous mode.

[0141] As can be observed, the adjustment of the speed of all the stands F1-F5 occurs in the same instant, while the thickness adapts sequentially, stand by stand, from the preceding value to the final target value.

[0142] The speed at which the material is fed, in this case the casting speed, remains constant, as well as the speed of all the stands upstream of the stand F1, that is, of all the roughing stands.

[0143] In another embodiment, shown in FIG. 4, some of the roughing stands are also involved, in this case the stands 18b, 18c downstream of the first stand 18a. The roughing stands 18a-18c are indicated in the graphs as H0-H2.

[0144] According to the invention, as can be observed, the speed of the first stand H0 is not modified, as is the case for the other work parameters of the same stand H0. The first stand involved in the thickness change is the (second) stand H1 and the rotation speed of the rolling rollers is adjusted in two steps. The same applies to the (third) stand H2.

[0145] The speed at which the material is fed, in this case the casting speed, remains constant, as does the speed of the first roughing stand H0.

[0146] FIG. 5 shows, in greater detail, the first embodiment of the two-step thickness change for the single stand (n.sup.th); in particular, it is possible to observe when the new inter-stand tension set-ups and the new profile and flatness set-ups are actuated.

[0147] FIG. 6 shows, in greater detail, the second embodiment of the simultaneous thickness change for the single stand (n.sup.th); in particular, it is possible to observe how all the set-ups are actuated simultaneously: the application of the new force set-up (in this case an increase of the compression/reduction, the penultimate line of the graph) entails the simultaneous application of the new gap set-up (that is, of thickness reduction); simultaneously, the set-ups for the inter-stand tension and for the profile and flatness actuators are also modified.

[0148] The new speed set-up is calculated starting from the previous set-up with the aim of keeping the mass-flow unchanged.

[0149] In particular, the formula for calculating the new set-up can thus be expressed:

subsequent roller speed=(current roller speed)*(thickness in stand(n.sup.th)−subsequent)/(thickness in stand(n.sup.th)−current).

[0150] FIG. 7 (Table 1) shows, by way of example only, an example of a variation of the set-up of parameters, from a current set-up to a subsequent set-up, in the event of a change from a final thickness of the strip of about 3 mm to a final thickness of the strip of about 2.3 mm.

[0151] As can be observed, in this case only the finishing stands F1-F5 are affected by the change of set-up of parameters. The reduction in the final thickness of the strip is accompanied by an increase in the speed of the rollers of the stands, as well as an increase in the compression force. The inter-stand tension also increases in relation to the thickness reduction to be obtained.

[0152] FIGS. 8 to 11 describe the modes in which another embodiment of the invention provides to calculate the number of stands involved in the flying gauge change (FGC). In particular, we take for example the case where it is not necessary to change the thickness of the transfer bar and the finishing mill comprises 5 finishing stands, with reference to the lay-out of FIG. 1.

[0153] A typical distribution of the rolling force on the various stands is shown in FIG. 8.

[0154] The central continuous line represents the distribution of reference forces, while the two dashed lines above and below indicate the upper and lower tolerance range, within which the rolling force can vary without compromising the quality of the finished product. Let us assume that the final thickness of the strip is changed using FGC, and in particular that a reduction thereof is actuated.

[0155] Keeping constant the thickness of the bar (transfer bar) entering the first rolling stand of the finishing mill, the overall rolling force (that is, the sum of the individual rolling forces on the 5 stands) will have to increase. As can be observed in FIG. 9, the effective rolling force in the last two stands increases, but remains within the acceptable upper tolerance range. Consequently, the thickness change can be taken on by the last two stands of the finishing mill, without involving other stands upstream.

[0156] If, on the other hand, the new distribution of forces causes the rolling force in even just one of the stands to exit from the acceptable tolerance, as shown in FIG. 10, then the FGC cannot be taken on the last two stands alone, but at least one further stand upstream has to be involved.

[0157] FIG. 11 shows how the new distribution of forces on the finishing mill leads to a trend similar to the initial one of FIG. 8, but with a greater force value in all the stands, that is, the curve of the forces in all 5 finishing stands has the same trend but with an increased value compared to the beginning.

[0158] It is clear that modifications and/or additions of parts may be made to the apparatus 10 and method for the production of strip as described heretofore, without departing from the field and scope of the present invention.