METHOD FOR REVAMPING A PLANT FOR PRODUCING FLAT ROLLED PRODUCTS

Abstract

A method for revamping a starting rolling plant, for producing a final strip starting from a slab having a determinate starting thickness, including: at least one heating furnace configured to heat at least the slab to a determinate starting temperature; at least one reversible roughing stand configured to subject the slab to one or more rolling passes in order to obtain an intermediate rolled product; and a rolling train disposed operatively in line with the roughing stand, including at least one pre-finishing stand and a plurality of finishing stands and configured to reduce the thickness of the intermediate rolled product, until the final strip having a determinate final thickness is obtained.

Claims

1. A method for revamping an existing rolling plant, for producing a final strip starting from a slab having a determinate starting thickness, comprising: at least one heating furnace configured to heat at least said slab to a determinate starting temperature; at least one reversible roughing stand configured to subject said slab to one or more rolling passes in order to obtain an intermediate rolled product; a compact rolling train disposed operatively in line with said at least one roughing stand, comprising a plurality of finishing stands located in line with each other and configured to reduce the thickness of said intermediate rolled product until said final strip having a determinate final thickness is obtained; wherein in order to obtain a revamped plant, the method provides to operate on said existing plant by carrying out at least one step of modifying said rolling train, in which at least one initial stand of said rolling train is moved away from the remaining stands located downstream of it and brought closer to the roughing stand, thus dividing the rolling train into a pre-finishing unit and a finishing unit, wherein said pre-finishing unit is positioned at a minimum distance from said roughing stand such that the intermediate rolled product is not operatively engaged with both respective stands simultaneously, and at least one step of installing a rapid heating device, consisting of selectively activatable elements, between said pre-finishing unit and said finishing unit, in order to heat said pre-finished rolled product, at exit from said pre-finishing unit, so that the temperature of said final strip (P) in correspondence with the outlet of the last stand of said finishing unit is higher than at least 830? C., even for a minimum thickness of less than 1.2 mm.

2. The method as in claim 1, wherein in said modification step said rolling train is divided in such a way that said pre-finishing unit has a number of stands comprised between one and two and said finishing unit has a number of stands comprised between five and six.

3. The method as in claim 2, wherein said pre-finishing unit comprises two stands and said finishing unit comprises five stands.

4. The method as in claim 1, wherein said at least one roughing stand is configured to define said intermediate rolled product having a thickness comprised between about 45 mm and about 80 mm, wherein said pre-finishing unit is configured to define said pre-finished rolled product having a thickness comprised between about 10 mm and about 50 mm, and wherein said finishing unit is configured to define said final strip having a determinate final thickness comprised between about 1 mm and about 26 mm.

5. The method as in claim 1, wherein it provides to position third descaling means between said rapid heating device and said finishing unit.

6. The method as in claim 1, wherein it provides to position a cutting machine in a condition interposed between said pre-finishing unit and said rapid heating device.

7. The method as in claim 1, wherein said determinate starting temperature of said slab is lower than or equal to 1200? C.

Description

DESCRIPTION OF THE DRAWINGS

[0068] These and other aspects, characteristics and advantages 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:

[0069] FIGS. 1 and 2 are schematic representations of two types of HSM plants for producing flat rolled products, in accordance with the prior art;

[0070] FIGS. 3 and 4 are graphic representations of the relation between rolling speed and outlet temperature of rolled products of different thicknesses, in accordance with the prior art;

[0071] FIGS. 5 and 6 are schematic representations of the corresponding HSM plants shown in FIGS. 1 and 2, after having been subjected to the method for revamping a plant for producing flat rolled products, in accordance with the present invention;

[0072] FIGS. 7 and 8 are graphic representations of the relation between rolling speed and outlet temperature of rolled products of different thicknesses, of a revamped HSM plant for producing flat rolled products, in accordance with the present invention.

[0073] We must clarify that in the present description the phraseology and terminology used, as well as the figures in the attached drawings also as described, have the sole function of better illustrating and explaining the present invention, their function being to provide a non-limiting example of the invention itself, since the scope of protection is defined by the claims.

[0074] 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 be conveniently combined or incorporated into other embodiments without further clarifications.

DESCRIPTION OF SOME EMBODIMENTS OF THE PRESENT INVENTION

[0075] With reference to FIGS. 5 and 6, these show two types of HSM plants 10, each obtained from the revamping of corresponding starting operating HSM plants 100, according to the method of the present invention.

[0076] The plants 10 are revamped with respect to the starting plants 100, for rolling a flat rolled product, for example a final strip P, with a thickness comprised between about 0.9 mm and about 26 mm wound to form a reel, or coil, starting from slabs 50 having a starting thickness comprised between about 150 mm and about 350 mm.

[0077] Both the starting plant 100 as well as the revamped plant 10 comprise one or more gas heating furnaces 16, for example of the type known in the sector with the term walking beam, configured to receive and heat to a determinate starting temperature at least one slab 50, supplied even at ambient temperature.

[0078] In the solutions with the revamped plant 10, at exit from the gas furnace 16 the slab 50 has a temperature comprised between about 1100-1150? C. and about 1200? C., instead of the original 1200? C.-1250? C. The outlet temperature of the slab at exit from the heating furnaces is therefore 50-150? C. lower than the original one, with consequent benefits in terms of gas consumption, and corresponding costs, atmosphere emissions and scale formation, thanks to the shorter residence time in the furnace.

[0079] A warehouse 40 can also be part of the plant 10, which cooperates with the gas heating furnace 16 and is configured to store the slabs 50, for example coming from another production site or from another production area of the same factory. The warehouse 40 allows to selectively feed at least one slab 50 to the gas heating furnace 16, according to desired feeding sequences and timings.

[0080] In the original type of plant 100 shown in FIG. 1, and in the corresponding revamped plant 10 of FIG. 3, downstream of the gas heating furnace 16 there are disposed, in sequence, a first water descaling device 20, a vertical or edging stand 21 and a reversible roughing stand 23 which is configured to subject the slab 50 to a determinate number of passes and reduce its thickness until an intermediate rolled product 51 is obtained.

[0081] In the original type of plant 100 shown in FIG. 2, and in the corresponding revamped plant 10 of FIG. 4, downstream of the gas furnace 16, in addition to the descaling device 20, there are provided two reversible roughing stands 23 with corresponding vertical stands 21.

[0082] The reversible roughing stands are equipped with descaling means mounted on board and forming an integral part of the stands themselves, which are disposed both on the inlet side and also on the outlet side of each stand (not shown in the drawings).

[0083] The corresponding layout described heretofore between the original plant 100 and the corresponding revamped plant 10, whether of the type with one or two roughing stands 23, highlights the advantageous characteristic of the revamping method according to the present invention, whereby most of the plant remains intact as originally installed, to the advantage of costs, timings and the impact of the revamping intervention.

[0084] With the revamped plant 10, the intermediate rolled product 51 obtained at exit from the roughing stand/s 23 has a thickness comprised between about 45 mm and about 80 mm, instead of the original 35 mm-45 mm. By way of example only, at the end of the required roughing passes, the intermediate rolled product 51 has a temperature which ranges from about 1020? C. to about 1120? C.

[0085] At this point, in order to carry out the revamping of both types of plant 100 shown in FIGS. 1 and 2, the drum shear 27 is removed, and the descaler 24 and two stands of the compact rolling train 25 are disassembled.

[0086] The descaler 24 and the two stands are displaced toward the reversible stands 23 at a determinate distance D therefrom, so that the intermediate rolled product 51 is never operatively engaged with both types of stand simultaneously.

[0087] In this way, the compact rolling train 25 is divided into two macro rolling units, a pre-finishing unit 26 and a finishing unit 31, which are deliberately distanced from each other by a predetermined distance d.

[0088] The stands of the finishing unit 31 substantially maintain their original installation position, without impacting the revamping intervention.

[0089] The revamped rolling train is configured to progressively reduce the thickness of the intermediate rolled product 51 in order to obtain the final strip P with a minimum thickness equal to 0.9-1.2 mm.

[0090] In the solution according to the present invention, a pre-finished rolled product 52 exits from the two pre-finishing stands 26 having a thickness comprised between about 10 mm and about 50 mm.

[0091] According to the invention, downstream of the pre-finishing unit 26 there is disposed, in this specific case, the same drum shear 27, after possible reconditioning, to trim the heads and tails of the pre-finished rolled product 52, in order to facilitate its entry into the stands of the finishing unit 31 and to reduce the chances of cobble, especially for the production of final strips having a thickness smaller than 3.0 mm.

[0092] However, it is not excluded that, according to one variant, the shear 94 can be replaced with an alternative cutting machine, having a different size and functionality from the drum shear 27 originally provided in the plant 100.

[0093] The method according to the present invention also comprises positioning a rapid heating device 28 interposed between the pre-finishing unit 26 and the finishing unit 31 of the revamped rolling train.

[0094] Preferably, the rapid heating device 28 comprises, for example, an induction furnace disposed downstream of the flying shear 27 and consisting of elements that can be activated selectively, even independently of each other.

[0095] The rapid heating device 28 is configured to heat, selectively and in an adjustable manner, the pre-finished rolled product 52 before it enters the finishing stands 31.

[0096] The temperature to which the pre-finished rolled product is heated is selected, among other parameters, at least as a function of its thickness and the final thickness of the final strip P, so that the latter has an optimum temperature of at least 830? C. at the outlet of the finishing unit 31, and in particular at the outlet of the last finishing stand.

[0097] By way of example only, the temperature to which the pre-finished rolled product 52 is heated, that is, the temperature it has at exit from the rapid heating device 28, reaches a value advantageously comprised between about 1000? C. and about 1100? C., or in any case a temperature such that, also as a function of the operating and product parameters, the temperature of the final strip at exit from the last finishing stand 31 is higher than at least 830? C.

[0098] This allows to reduce the value of the rolling mass flow MF.sub.L required to obtain the above mentioned optimum temperature of at least 830? C., for example comprised between 830? C. and 900? C., at the outlet of the last stand of the finishing unit 31.

[0099] The reduction of the rolling mass flow MF.sub.L allows both to carry out the rolling with a reduced rolling speed V.sub.L, preferably lower than 12 m/s, and at the same time to reach the optimum temperature of at least 830? C. at the outlet of the continuous rolling train 25 even for the tail of the final strip P, eliminating the need for speed up as a tool for reaching the target temperature. An example of this embodiment is schematized graphically in FIG. 7.

[0100] Advantageously, in the absence of speed-up, the rolling speed V.sub.L in the finishing stands 31 is substantially constant and allows both to keep the temperature of the final strip P between its head and tail constant, and also to choose the most suitable temperature control (for example thermomechanical treatment) as a function of the steel grade and the use of the final strip P.

[0101] Another advantage of not performing the speed-up consists in the fact that it allows a high control of both the final shape of the final strip P, for example crown and flatness thereof, which will therefore be advantageously uniform along the entire length of the coil, and also of the mechanical properties of the final strip P which will be advantageously constant and uniform along the entire length of the coil.

[0102] This last advantage, which cannot be achieved with plants of the prior art, is of considerable importance, particularly for quality productions such as, for example, final strips P intended for molding.

[0103] According to some embodiments, it may be necessary to resort to speed-up in order to be able to increase the productivity of the line when very thin thicknesses are produced, or to achieve very high productivity with other thicknesses. An example of this embodiment is schematized graphically in FIG. 8.

[0104] In addition to the original plant 100, downstream of the rapid heating device 28 and upstream of the finishing unit 31 there is also disposed a third water descaling device 29, which has the function of further cleaning the surface of the pre-finished rolled product of scale before entering the finishing stands.

[0105] Therefore, the scale that has formed on the surface of the pre-finished product is removed, thus avoiding qualitative defects on the rolled strip, such as imprinted scale for example.

[0106] Downstream of the finishing unit 31, the cooling device 33 and the showers 34 of the original plant 100 are kept, to cool the strip P.

[0107] Furthermore, at the outlet of the showers 34 the two winding reels 36, 38 are kept, to wind the strip P into coils for its subsequent storage and shipment.

[0108] It is clear that modifications and/or additions of parts may be made to the method for revamping a plant for producing flat rolled products as described heretofore, without departing from the field and scope of the present invention, as defined by the claims.

[0109] It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of method for revamping a plant for producing flat rolled products, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

[0110] In the following claims, the sole purpose of the references in brackets is to facilitate their reading and they must not be considered as restrictive factors with regard to the field of protection defined by the same claims.