Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/46—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting
  • B21B1/463—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting in a continuous process, i.e. the cast not being cut before rolling
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/46—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B13/00—Metal-rolling stands, i.e. an assembly composed of a stand frame, rolls, and accessories
  • B21B13/22—Metal-rolling stands, i.e. an assembly composed of a stand frame, rolls, and accessories for rolling metal immediately subsequent to continuous casting, i.e. in-line rolling of steel
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B2265/00—Forming parameters
  • B21B2265/14—Reduction rate
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
  • B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
  • B21B45/0203—Cooling
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
  • B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
  • B21B45/0203—Cooling
  • B21B45/0209—Cooling devices, e.g. using gaseous coolants
  • B21B45/0215—Cooling devices, e.g. using gaseous coolants using liquid coolants, e.g. for sections, for tubes
  • B21B45/0218—Cooling devices, e.g. using gaseous coolants using liquid coolants, e.g. for sections, for tubes for strips, sheets, or plates

Definitions

• the present invention concerns a plant and a process for the continuous or batch production of hot rolled strips and plates, in a wide size range with high plant productivity and cost effectiveness and high product quality.
• EP 1558408 the so-called "cast-rolling" technology is used which unites the continuous casting of a thin slab with liquid core reduction (LCR) to a first roughing rolling step through a high-reduction mill (HRM) or roughing mill that achieves an intermediate product which, after a heating phase in an induction heater and subsequent descaling, is further processed in a second phase of finishing rolling.
• LCR liquid core reduction
• HRM high-reduction mill
• EP 1868748 teaches some improvements from the point of view of plant compactness and energy saving, providing that the continuous casting is directly connected with a rolling step in a single manufacturing step without solution of continuity. In practice there are no longer two separate rolling steps, roughing and finishing, but a single rolling step and the distance between the outlet of the continuous casting and the first stand of the rolling mill will not be greater than 50 m in order to limit the temperature losses of the slab.
• EP 1868748 also provides the production of plates only with "endless" mode and using the same cooling system used for coils, a solution which has proved to be not optimal for the production of plates since the "endless" mode works better for coils and the optimal cooling parameters for plates are significantly different from those for coils.
• the cast slab has a maximum thickness of 50 mm prior to the liquid core reduction that takes it to 40 mm and it undergoes a maximum thickness reduction of 3 mm performed by the pinch rolls located just downstream from the casting machine.
• a roughing mill is arranged just downstream from the casting machine to perform a slab thickness reduction up to 70%, but in case of problems along the subsequent rolling line said thickness reduction can temporarily be reduced down to zero.
• the aim of the present invention is therefore to provide a solution for the production of continuously hot rolled strips or plates with strip thickness from 0,6 mm to 12 mm and plate thickness from 12 mm to 50 mm or in any case half of whatever may be the slab thickness at the exit of the continuous caster with liquid core reduction, said thickness having a minimum value of 80 mm, with maximum width at least 2100 mm or whatever may be the maximum mould width foreseen, with plate and strip quality the same or better, lower energy consumption, lower impact on the environment, higher productivity and flexibility compared with the afore-mentioned prior art.
• a minimum- reduction rolling stand (so-called "kiss pass” stand) which allows to achieve: • optimisation of the crystalline structure of the slab, by recrystallizing the coarse grains which make up the slab surface at the exit of the continuous caster, in order to obtain smaller grains which tend to detach from each other less easily in the subsequent rolling step,
• a plant according to the present invention conventionally includes a continuous caster 1 followed at a certain distance by an induction heater 2, with a pendulum shear 3 therebetween, and then a rolling mill 4 followed by a rotary shear 5 and a run out table with a cooling device 6 and a pusher or pusher/piler 7 for plates and finally a high-speed shear 8 before the down coilers 9.
• caster 1 includes a mould followed by a curved liquid core reduction section to produce a slab with a minimum thickness of 80 mm, e.g. 100 mm x 2100 mm, at a casting speed up to 9 m/min. Said slab is then heated by the induction heater 2, comprising four coils in the illustrated example, prior to entering the finishing rolling mill 4, comprising up to seven stands as in the illustrated example, in which the slab undergoes a progressive thickness reduction with decreasing reduction rates, e.g. 58%; 52%; 47%; 43%; 40%; 35%; 30% and work rolls of larger diameter in the initial stands (e.g. the first two in the illustrated example).
• the induction heater 2 comprising four coils in the illustrated example, prior to entering the finishing rolling mill 4, comprising up to seven stands as in the illustrated example, in which the slab undergoes a progressive thickness reduction with decreasing reduction rates, e.g. 58%; 52%; 47%; 43%; 40%; 35%; 30% and work rolls of larger diameter in the initial stands (e
• the finishing rolling mill 4 may also include, at any position after the first two stands, cooling and/or heating devices (e.g. gas or induction heaters) located between the rolling stands so as to be able to better control the rolling conditions by adapting the temperature of the material being rolled to its specific characteristics and needs.
• cooling and/or heating devices e.g. gas or induction heaters
• the resulting strip is then cooled by the cooling device 6 and finally coiled by the down coilers 9 and cut by the high speed shear 8 when the coil has reached the intended weight.
• the slab is then cut into plates by the rotary shear 5 and said plates are moved out of the line by the pusher or pusher/piler 7, possibly after having been cooled in the first section of the cooling device 6.
• a first novel aspect of the present invention resides in the presence of a so-called "kiss pass" stand 10 between the continuous caster 1 and the pendulum shear 3, said stand 10 performing a thickness reduction of only about 10%, and in any case not more than 20%), therefore starting from a minimum reduction of about 8 mm, that has a metallurgical rather than a mechanical purpose.
• this minimum reduction is aimed at the optimisation of the crystalline structure of the slab surface by recrystallizing the coarse grains coming out of the caster in order to obtain smaller grains which are less prone to detach from each other in the actual rolling step carried out in the rolling mill 4.
• the plant also preferably includes, between caster 1 and stand 10, an additional induction heater 11, comprising two coils in the illustrated example, and a descaler 12 so as to: a) avoid the ductility draft temperature ranges, b) keep segregating elements in solution, and c) improve the result of the "kiss pass" reduction (similarly, a further descaler 13 preferably precedes the rolling mill 4).
• the presence in the cast alloy of low-melting elements e.g. copper and tin as in the steel produced from scrap in an EAF
• low-melting elements e.g. copper and tin as in the steel produced from scrap in an EAF
• the recomposition and refining of these grains achieved through this "light" reduction pass provides the double advantage of being able to: a) apply a higher reduction rate in the subsequent first actual reduction step without breaking the material at the surface, and b) obtaining strips/plates of the same high quality even using cheaper and lower-quality scrap, i.e. scrap containing higher concentrations of impurities such as copper and tin.
• the "kiss pass" stand 10 preferably includes working cylinders of smaller diameter with respect to the first stand in the rolling mill 4, since it must apply a minimum reduction while cooling the slab as little as possible, whereby a smaller arc of contact is sufficient and preferable with the advantage that tension stresses at the surface of the rolled stock are minimized.
• Another advantage obtained by arranging the "kiss pass" stand 10 between the continuous caster 1 and the pendulum shear 3, as mentioned above, is the creation of a "mechanical filter” between said two components so as to avoid any disturbance in caster 1 when the slab is cut by shear 3 in case of emergency if there is a cobble in the portion of plant downstream from shear 3.
• a second novel aspect of the present invention resides in the presence of an edger 14, i.e. a narrow face vertical rolling stand, that is preferably positioned immediately upstream from the "kiss pass" stand 10 and preferably preceded by an induction edge heater 15, i.e. a heater with C-shaped coils that heat only the edges of the slab.
• edger 14 could also be arranged immediately upstream from the rolling mill 4 together with its corresponding induction edge heater 15 that could be arranged adjacent to the induction heater 2 on any side thereof.
• edger 14 allows to recrystallize the slab edges, which are the coldest parts and therefore those most sensitive to the formation of cracks, to shape them for minimizing the tension stresses in the subsequent rolling step and to improve the width tolerances. Moreover, edger 14 can reduce the slab width on each side by up to 50 mm whereby a narrower strip/plate can be obtained without any intervention on the mould and thus without reducing the plant productivity.
• a third novel aspect of the present invention resides in the presence, between the "kiss pass" stand 10 and the induction heater 2, of an interconnecting furnace 16 suitable to allow the introduction/removal and the controlled advancement of slabs S.
• an interconnecting furnace 16 suitable to allow the introduction/removal and the controlled advancement of slabs S.
• a typical example is a gas-heated roller hearth furnace or walking beam furnace, usually about 30 m long, but other equivalent types of furnace can obviously be used.
• Said furnace 16 is immediately preceded by an additional pendulum shear 17 so that, as previously mentioned, the present plant not only makes possible to evacuate through a piler 18 re-usable slabs in the case of unavailability of the rolling mill 4, but also to select between the "endless” and “batch/combined” operating modes, as well as to load into the interconnecting furnace 16 (through a loading station 19) slabs at ambient temperature that have been bought on the market.
• the furnace 16 also acts as a buffer to hold and then subsequently load to the rolling line the hot slabs produced and stored in the furnace because of a cobble in the rolling mill 4, once the latter is available again.
• the "kiss pass” stand 10 is located between the continuous caster 1 and the additional pendulum shear 17 therefore it acts as a "mechanical filter", as mentioned above, also between said two components so as to avoid any disturbance in caster 1 when the slab is cut by shear 17 to select the "batch/combined" mode.
• the "kiss pass" stand 10 can be used as a first rolling pass upstream from furnace 16 exactly because it performs a thickness reduction of about 10%, and not more than 20% in any case. Such a reduction is much smaller than the thickness reduction in a roughing mill or in the first stand of a finishing rolling mill according to the prior art, which is in the order of 50-70%), that would result in an unacceptable length of furnace 16.
• the furnace must be sized to hold a slab of a weight corresponding to the weight of a finished coil of strip or a stack of plates to be produced in a batch production cycle, whereby an excessively thinned slab would have an unacceptable length to obtain the required weight.
• a fourth novel aspect of the present invention resides in the fact that the cooling device 6 may include a first cooling section capable of performing an ultra-fast cooling of the plates that corresponds to a quenching thereof. A subsequent tempering at a later working step will provide plates having a higher quality with respect to those produced with prior art plants whose cooling sections are only optimized for strips.
• a plate-specific cooling device 20 may be arranged offline such that the plates removed by the pusher or pusher/piler 7 undergo a multi-stage high-pressure cooling, i.e. each intense cooling stage is followed by an interval in which the temperature of the plate has the time to become substantially homogeneous prior to the successive cooling.
• the cooling device 20 may be followed by a tempering furnace 21, a further controlled cooling 22, a skin pass stand 23 and a roller leveller 24 for a complete treatment of the plates (either cooled in the specific cooling device 20 or in the above-mentioned ultra-fast cooling section of the cooling device 6).
• Another possibility is to provide a cooling device 6 that can be easily adjusted to a plate-specific setting, and in such a case it is obvious that the pusher/piler 7 or an additional pusher/piler 7' would be located between the cooling device 6 and coilers 9. In this way the cooling device 6 can be properly used for the cooling of both high- quality strips and high-quality plates.
• the above-described plant according to the present invention is therefore suitable for producing both high-quality strips and high-quality plates, either in "endless” mode with no solution of continuity of the slab between caster 1 and rolling mill 4 (i.e. the entry speed of the rolling mill 4 is linked to the casting speed through the speed increase in the kiss pass stand), or in "batch/combined” mode with the slab that enters the rolling mill 4 which is disconnected from the slab in caster 1.
• such a plant can use as starting material also slabs coming from the interconnecting furnace 16, either loaded at ambient temperature through the loading station 19 or held at high temperature in furnace 16 itself when used as a buffer.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Metal Rolling (AREA)
• Continuous Casting (AREA)

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Citations (7)

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• 2017
  • 2017-04-10 IT IT102017000039423A patent/IT201700039423A1/it unknown
• 2018
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  • 2018-04-09 JP JP2020504467A patent/JP7095071B2/ja active Active
  • 2018-04-09 RU RU2019135817A patent/RU2752592C2/ru active
  • 2018-04-09 EP EP19208335.0A patent/EP3632582B1/en active Active
  • 2018-04-09 ES ES19208335T patent/ES2887184T3/es active Active
  • 2018-04-09 ES ES18718524T patent/ES2866154T3/es active Active
  • 2018-04-09 KR KR1020197033306A patent/KR102435246B1/ko active IP Right Grant
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