CA2119987C - Method for the controlled pre-rolling of thin slabs leaving a continuous casting plant, and relative device - Google Patents
Method for the controlled pre-rolling of thin slabs leaving a continuous casting plant, and relative deviceInfo
- Publication number
- CA2119987C CA2119987C CA002119987A CA2119987A CA2119987C CA 2119987 C CA2119987 C CA 2119987C CA 002119987 A CA002119987 A CA 002119987A CA 2119987 A CA2119987 A CA 2119987A CA 2119987 C CA2119987 C CA 2119987C
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- Prior art keywords
- rolling
- slab
- rolls
- pairs
- control
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
- B22D11/0602—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by a casting wheel and belt, e.g. Properzi-process
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
- B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/12—Accessories for subsequent treating or working cast stock in situ
- B22D11/1206—Accessories for subsequent treating or working cast stock in situ for plastic shaping of strands
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Continuous Casting (AREA)
- Control Of Metal Rolling (AREA)
- Casting Or Compression Moulding Of Plastics Or The Like (AREA)
- Laminated Bodies (AREA)
- Metal Rolling (AREA)
- Manufacture, Treatment Of Glass Fibers (AREA)
- Financial Or Insurance-Related Operations Such As Payment And Settlement (AREA)
Abstract
Method for the controlled pre-rolling of thin slabs (20) leaving a continuous casting plant, whereby the pre-rolling is carried out with a plurality of pairs of rolls (14-16) grouped together in one or more pre-rolling assemblies (10), the first of the pre-rolling assemblies (10) being positioned immediately downstream of foot rolls (12) of a mold (11), at least one displaceable roll (16) being included in the pairs of rolls (14-16), the pairs of rolls (14-16) being associated with pressure transducer means (18) and hydraulic capsule means (17), position transducer means (24) being included, the pressure transducer means (18) and position transducer means (24) can be associated with a data processing unit (21), at least the first of the pairs of rolls (14-16) processing a slab (20) which has just emerged from the mold (11) with a thin solidified skin. The method achieves a pre-rolling with a reduction of the thickness of the slab (20) leaving the last pair of pre-rolling rolls (14-16) by at least 10% so as to eliminate the liquid core and to bring into contact the zones in a two-phase condition in order that the central solidification structure be refined and the central separation be minimized. Device suitable to carry out the controlled pre-rolling of thin slabs according to the above method, which comprises means (25a) to monitor the temperature of the liquid bath in a tundish, means (25b) to monitor the temperature of a slab (20), means (26) to monitor the speed of the slab (20) and means (28) to monitor the inclusion of a liquid cone.
Description
1 "METHOD FOR THE CONTROLLED PRE-ROLLING OF THIN SLABS LEAVING
2 A CONTINUOUS CASTING PLANT, AND RELATIVE DEVICE"
3 * * * * *
4 This invention concerns a method for the controlled pre-rolling of thin slabs leaving a continuous casting plant, 6 and the relative device.
7 To be more exact, this invention concerns a method and 8 relative device for controlled pre-rolling, carried out on 9 thin slabs leaving a mold for the continuous casting of thin slabs, immediately downstream of the foot rolls of that mold 11 and concerns also the device suitable to apply that method.
12 By thin slabs are meant slabs 800 to 2500 mm. wide, or 13 more, and 25 to 90 mm. thick.
14 The invention is applied advantageously, but not only, to slabs having a final thickness between 30 and 60 mm. at the 16 outlet of the continuous casting machine.
17 The invention can also be applied to the continuous 18 casting of billets, whether the billets be round, square, 19 rectangular, etc.
The invention can be applied to straight and curved 21 continuous casting plants.
22 Pre-rolling methods are known whereby a thin slab 23 undergoes a pre-rolling action in a zone distant from the 24 foot rolls.
In the methods of the state of the art disclosed in JP-A-26 130759, US-A-3,891,025, US-A-4,056,140 and US-A-4,134,440 27 the pre-rolling does not give satisfactory results inasmuch 28 as it is performed in a position of the slab such that the 29 liquid core or pool is only seldom still present and the skin of the slab is anyway already thick and is such that it 31 cannot be readily deformed.
32 Moreover, the skin of one side of the slab is connected to 33 the skin of the other side by columnar solidification 1 elements at an intermediate position between the edges; both 2 the edges, which contain a consistent solidified thickness, 3 and also the columnar solidification elements offer a strong 4 resistance to any alteration of the thickness of the slab.
The pre-rolling in the methods of the state of the art, 6 therefore, has only a marginal and very limited effect, 7 which does not give the envisaged results.
8 Moreover, the pre-rolling as carried out in the methods of 9 the state of the art has only the purpose of performing a marginal superficial work, and the real work of reducing the 11 thickness of the slab is entrusted to the rolling train 12 located downstream.
13 Furthermore, in the pre-rolling assemblies of the state of 14 the art only some pairs of rolls are controlled to check the pre-rolling parameters, and these pairs of rolls are 16 controlled in a differentiated or separate manner (see JP-A-17 130759). This has the result that the operating method 18 cannot be conditioned according to specific requirements but 19 is quite random in some ways.
Pre-rolling assemblies are also known which comprise 21 mechanical adjustment systems together with pre-adjustment 22 at the beginning of a casting campaign. These assemblies 23 are associated with pre-rolling rolls in continuous rows or 24 divided into sectors or groups of rolls or else with assemblies of pressure belts.
26 These systems of the state of the art do not make possible 27 excellent adjustments, nor a substantial pre-rolling action 28 of a desired value, nor a continuously controlled travel 29 continuously related to the actual pre-rolling requirements.
They also do not enable processing to be carried out on a 31 zone where the liquid core or pool is still substantial and 32 the surface skin is still of very small values.
33 The state of the art prevents controlled mechanical action ~ 3 ~ - 2 1 1 9 9 8 7 1 to reduce the length of the liquid cone and thus to ensure 2 better quality.
3 Moreover, the state of the art e,ntails considerable 4 limitations with regard to problems linked to the transient conditions of starting and stopping and does not permit an 6 excellent yield of the system.
7 The state of the art does not obviate the flow of liquid 8 material at start-up and the re-flow of the liquid metal at 9 stopping and therefore keeps the reject rate high.
The present applicant has examined, tested and achieved 11 this invention so as to overcome the shortcomings of the 12 state of the art and to provide further advantages.
13 The pre-rolling method according to the invention can be 14 performed advantageously with a pre-rolling assembly of the type disclosed herein and in EP-A-0.539.784.
19 The purpose of this invention is to achieve a controlled pre-rolling or soft reduction of the slab leaving the 21 crystallizer so as to produce a slab of a smaller thickness 22 at the end of the casting machine.
23 The main advantages of the controlled pre-rolling, or soft 24 reduction, or reduction with a liquid core or pool are essentially two; the first advantage is to be able to 26 produce at the outlet of the casting machine a slab of a 27 slender thickness (30-60 mm.) by using a crystallizer having 28 a greater thickness, that is to say, the short side of the 29 lengthwise through passage of the crystallizer has a greater width than the finished thickness of the slab after the 31 controlled pre-rolling.
32 This controlled pre-rolling improves the fluid-dynamic 33 behaviour of the liquid metal in the crystallizer of the A
_ - 4 ~ 21 1 99~ 7 1 mold; it also improves the life of the submerged nozzle 2 assembled on the tundish and improves the behaviour during 3 melting of the powders which are placed above the upper part 4 of the liquid metal in the mold.
The second advantage is the achievement of a refining of 6 the structure of solidification of the metal and the 7 elimination of the central segregation in the slab.
8 In both cases, the soft reduction, if it is to be 9 effective, has to take place with a continuous controlled reduction of the thickness of the slab, and this can be 11 achieved with a substantially conical conformation of the 12 segment of slab undergoing the soft reduction.
13 This conical segment can have a length ranging from about 14 0.8 to 7 meters, preferably 3.8 meters to 6.3 meters; the greater length corresponds to the end of the containing zone 16 produced by the containing rolls included downstream of the 17 crystallizer and after the foot rolls.
18 The length of this segment of reduction of the thickness 19 with a conical development depends on the following metallurgical factors.
21 The solidification takes place in a substantially 22 different manner with different types of steel; steels with 23 a low content of carbon (C less than 0.10%) have a 24 solidification characterised by short columnar grains and the solidification face moves forward in a compact condition 26 without great discontinuities and with a short two-phase 27 zone.
28 Steels with a high carbon content (C greater than 0.70%) 29 have a solidification characterised by long columnar grains and the solidification face moves forward with great 31 discontinuities, creating a grid of large dendrites, among 32 which there remain islands of segregated liquid steel. In 33 this case the two-phase zone is very extensive.
_ 5 21199~ 7 1 The moment when the two faces of solidification (upper 2 side and lower side of the slab) meet is a very critical 3 moment for the definition of the internal quality and, more 4 generally, of the finished quality of the slab.
In fact it is known that owing to the effect of bulging 6 (swelling of the slab between two opposed pairs of 7 containing rolls), an effect of pumping the segregated 8 liquid is created; this bulging effect may be restricted but 9 is never fully eliminated.
When the slab opens owing to the bulging effect, the 11 liquid between the dendrites is sucked back by the cavities 12 between the dendrites towards the centre line of the slab.
13 When the slab closes on passing through the next pair of 14 rolls, the liquid is pumped in the opposite direction from the centre line to the cavities between the dendrites.
16 This alternating pumping effect creates islands of 17 positive and negative segregation at the centre line of the 18 slab.
19 So as to prevent this continuous to-and-fro flow of the segregated liquid, it is necessary to try to close the 21 passages between the dendrites and between one grain and the 22 next grain by means of compacting the structure at the 23 solidification face.
24 This can be achieved by compressing the two halves of the slab against each other by means of a light rolling of the 26 slab producing a substantially conical development of the 27 reduction.
28 Owing to the different extent of the two-phase zone 29 produced in the various types of steel, the compression has to take place in such a way that the two solidification 31 faces penetrate into each other with different degrees 32 according to the type of steel.
33 Steels with a low content of carbon and a short two-phase ~ - 6 - 21199~7 1 zone have to penetrate into each other by a few millimeters 2 to a depth where the solid fraction is consistent (about 90-3 95%) and the small spaces between the dendrites are already 4 practically nil.
Steels with a high content of carbon and a long two-phase 6 zone have to penetrate into each other in a consistent 7 manner to a depth where the solid fraction is less (up to 8 70%) and the spaces between the dendrites are very 9 extensive.
The best solid fraction at the end of the reduction 11 depends, therefore, on the type of steel and can be thus 12 summarised by bearing in mind a variation of the solid 13 fraction upwards or downwards of 2 to 2.5%, depending on 14 metallurgical factors.
15 C content (%) Solid fraction (%) 16< 0.20 95 170.20 - 0.40 90 180.40 - 0.70 80 19> 0.70 70 20 Where soft reduction is carried out, this means that the 21 end of the conical segment of reduction of the thickness of 22 the slab has to take place in a zone where the solid 23 fraction is best for obtaining a good internal quality.
24 Let us assume that it is desired to obtain at the end of the casting machine a slab with a thickness of 30 mm., 26 starting with a short side of 50 mm. of the crystallizer of 27 the mold and assuming also that steel is of a C 70 type.
28 The reduction to be carried out is 20 mm. (50 - 30).
29 Having valuated the profile of solidification of the slab at the current casting conditions, it is necessary to 31 determine at what distance from the level of the meniscus of 32 the liquid metal in the crystallizer of the mold there 33 exists in the slab leaving the crystallizer a solid fraction ~ _ 7 _ 21 1 9~ 8 7 1 of 70% at a distance of 15 mm. from the surface (15 being 2 the half of 30).
3 Let us suppose that this distance from the meniscus is 4 4 meters.
If the crystallizer is 1.2 meters long, the soft reduction 6 has to have a length (Lsr) of:
7 Lsr = 4 minus 1.2 = 2.8 meters 8 and the gradient of reduction (Gsr) has to be:
9 Gsr = (50 minus 30) = 20 mm./2.8 meters = 7.143 mm/m.
that is to say, for each meter of slab outside the 11 crystallizer it is necessary to apply a reduction of 12 thickness of 7.143 mm.
13 The pre-rolling method therefore consists in a model of ON
14 LINE solidification which determines the exact profile of solidification of the slab on the basis of the current 16 casting conditions.
17 This model calculates the length of the pre-rolling - Lsr 18 - that is to say, the position along the machine where a 19 desired solid fraction exists at a depth from the surface equal to the half-thickness of the slab to be produced.
21 Having defined this level, the conical segment of the 22 reduction is adjusted by rolling in such a way as to have a 23 gradient of reduction - Gsr - such as will bring the end of 24 the reduction to the calculated pre-rolling length Lsr.
This result is achieved by reducing in a controlled, 26 desired manner the length of the liquid cone or pool, thus 27 minimizing the occurrence of segregation found in unalloyed 28 steels with a medium-high content of carbon, or alloyed 29 steels with a medium-low content of carbon, or in steels in general which entail the occurrence of segregation.
31 This desired, controlled reduction of the length of the 32 liquid cone enables the mushy zone to be kept in contact 33 eliminating the li~uid phase in such a way as to promote the 1 growth of an equiaxe structure such as that which can be 2 produced with electromagnetic stirring.
3 A further purpose of the pre-rolling method according to 4 the invention is to speed up the formation of crystals and therefore the formation of stable columnar connections 6 between the skin of one side and the skin of the other side 7 of the slab.
8 In the method according to the invention these columnar 9 connections are formed in a compressed environment owing to the pre-rolling action exerted by the pre-rolling assembly, 11 so that these connections are produced already compacted 12 with a typical arrangement.
13 This leads to the advantage that the product leaving the 14 continuous casting plant arrives more compact at the rolling line and with a substantially smaller thickness and better 16 levelled.
17 By carrying out a dynamic control of the length of the 18 liquid cone or pool as a function of the main casting 19 parameters (speed, superheating in the tundish, secondary cooling downstream of the mold and steel grade), the 21 invention also enables the transient periods of starting and 22 stopping (at the end of casting or owing to an accident) to 23 be optimized and the scrap to be reduced.
24 Moreover, the method according to the invention makes possible the casting in a mold of a slab having a section of 26 a greater thickness than the final one with all the 27 advantages in terms of surface quality arising from 28 optimization of the working conditions of the lubricating 29 powder (greater melting surface, regularity of the covering of the powders on the liquid steel), of superheating of the 31 steel and of downflow in the mold (with less turbulence and 32 greater stability of the meniscus), and also makes possible 33 the use of a submerged nozzle having a greater cross-section g 1 and therefore more longlasting.
2 This pre-rolling method enables the outgoing cross-section 3 of the slab to be reduced so as to be able to reach smaller 4 final thicknesses, given an equal number of rolling units.
According to the invention the pre-rolling rolls 6 positioned on the outer curved side of the plant, in the 7 event of continuous curved casting, can be associated with 8 load cells, which control the pressure which those rolls 9 exert on the thin slab.
The pre-rolling rolls positioned on the inner curved side 11 of the plant are associated with a hydraulic capsule, for 12 instance of the type disclosed in EP-0444420, and may also 13 be associated with load cells as an alternative to those 14 envisaged for the rolls on the outer curved side.
A pressure transducer is included on each hydraulic 16 capsule and enables the rolling pressure to be controlled.
17 According to the invention the pairs of rolls are arranged 18 in one or more groups, each group forming a pre-rolling 19 assembly. Each pre-rolling assembly includes a stationary portion and a displaceable portion. This description assumes 21 as an example that the outer curved side contains stationary 22 rolls while the displaceable rolls form the inner curved 23 side, but in practice the two sides can also be inverted.
24 According to a variant the inner and outer curved sides may include a stationary portion and a displaceable portion, 26 which cooperate with a displaceable portion and a stationary 27 portion of the opposite side respectively.
28 According to a first lay-out of the invention each pair of 29 rolls is associated with a single position transducer, which monitors the distance between the opposed rolls.
31 In a second lay-out of the invention each group of pairs 32 of rolls forming a pre-rolling assembly includes two 33 transducers monitoring the position of that assembly, these 211~987 1 transducers being located respectively at the upstream and 2 downstream ends of that pre-rolling assembly and monitoring 3 the distance between the opposed rolls at those positions.
4 According to a variant of this second lay-out each pair of rolls is also associated with a single position transducer.
6 By means of the position transducers it is possible to 7 determine in the pre-rolling assemblies a rolling passage 8 between the pairs of rolls; this passage may have its sides 9 parallel or converging, depending on the particular requirements.
11 Moreover, if each pair of rolls is associated with a 12 single position transducer, it is possible to determine a 13 pre-rolling passage having a lengthwise section of any 14 particular form by positioning each roll of each pair of rolls as required.
16 The whole system is governed by a pre-rolling control and 17 data processing unit, which receives signals from the 18 pressure transducers and position transducers, whether 19 single or belonging to assemblies, and also from monitors of the speed of the slab, from monitors of the secondary 21 cooling parameters and from monitors of the temperature of 22 the cast molten metal and of the temperature of the thin 23 slab leaving the mold.
24 Further temperature monitors may also be included which monitor the temperature of the slab at intermediate 26 positions in the area where the pre-rolling assembly 27 according to the invention is working, and which send 28 signals to the pre-rolling control and data processing unit.
29 Furthermore, a monitor, possibly of a sonar type for instance, may be included to identify the presence or 31 absence of a liquid pool within the slab and thus to ensure 32 correctly the actual closure of the liquid cone or pool in 33 the pre-rolling assembly according to the invention.
1 The control and data processing unit, which may be 2 connected to or form part of other general control and data 3 processing units, processes all these parameters and 4 compares them with the pre-rolling parameters fed into or contained in appropriate internal files and provides the 6 pairs of rolls with optimum adjustment values.
7 The control and data processing unit may also be connected 8 to an auxiliary data collection unit, which, besides 9 recording all the values provided by the monitors, feeds them to a data bank able to display and/or print the 11 progress of the values over a period of time.
12 In this description, by rolls are meant rolls positioned 13 in continuous rows or divided into sectors, or else belts, 14 etc., thus covering any system of the state of the art.
The adjustments which are carried out with the method 16 according to the invention are adjustments of single rolls, 17 or of one assembly of rolls at a time followed by another 18 assembly and so on, or general adjustments of the whole pre-19 rolling assembly. The adjustments may be added algebraically.
21 The pre-rolling method according to the invention enables 22 a reduction of the thickness of the slab by between about 23 10% and 50% to be achieved. This reduction of the thickness 24 is obtained in a travel between 0.8 and 7 meters long, but advantageously between 1.2 and 1.8 meters long.
26 The reduction of the thickness of the slab may be 27 progressive with constant values.
28 According to a variant the reduction of the thickness of 29 the slab is carried out in steps, with a final finishing segment in which the reduction of thickness is progressive.
31 According to a variant means for the secondary cooling of 32 the slab are associated with the pre-rolling assembly 33 according to the invention and consist, for instance, of a ~ - 12 - 21 19~ 7 1 plurality of sprayer nozzles.
2 Both the rate of flow and the delivery pressure of the 3 sprayer nozzles are adjusted advantageously by the data 4 processing and control unit and/or by the general data processing and control unit, thus ensuring a continuous 6 control of the condition of the slab.
7 The regulation of the sprayer nozzles may be governed by 8 possible monitors of the temperature of the slab, these 9 monitors being arranged along the pre-rolling assembly.
According to another variant at least one descaling unit 11 of the type shown in patent application EP-93110927.6 filed 12 in the name of the present applicant, for instance, may be 13 associated with the pre-rolling assembly according to the 14 invention. This descaling unit installed upstream of the first pre-rolling assembly enables thin slabs to be produced 16 with an excellent surface quality as required for special 17 successive processings.
18 According to a variant a plurality of descaling units are 19 included and are placed between the pairs of pre-rolling rolls.
21 According to yet another variant the descaling units are 22 placed between each pair of pre-rolling rolls.
23 According to a further variant and particularly where 24 descaling units are positioned between the pairs of pre-rolling rolls, the rolls are cooled inside to prevent the 26 scale removed from the surface of the thin slabs from 27 adhering to the surface of the roll itself.
28 The attached figures are given as a non-restrictive 29 example and show some preferred lay-outs of the invention as follows:-31 Fig.1 is a diagram of one side of an assembly for the pre-32 rolling of thin slabs produced by continuous curved 33 casting according to the invention;
_ - 13 -1 Figs.2 and 3 show two other possible types of pre-rolling 2 rolls;
3 Figs.4 are diagrams of two possible positions of the pre-4 rolling assembly of Fig.l;
Fig.5 shows the formation of the two-phase zone according 6 to the invention.
7 In the figures the pre-rolling method according to the 8 invention is carried out by at least one pre-rolling 9 assembly 10 consisting of a plurality of pairs of rolls 14-16.
11 Fig.l shows only the first of these pre-rolling assemblies 12 10 in association with foot rolls 12 and a mold 11, which 13 produces a thin slab 20 continuously, a second pre-rolling 14 assembly 10 installed immediately downstream being shown only partly.
16 The first pre-rolling assembly 10 is installed immediately 17 downstream of the mold 11 at a distance of about 0.5 meters.
18 The pairs of rolls 14-16 shown may consist of continuous 19 rows or be divided into sectors 14-16 or into groups of two or more pairs 114-116 or consist of belts 214-216 or be of 21 any other known type.
22 In the example shown the outer curved side 13 of the 23 assembly 10 is the stationary or fixed part or frame, while 24 the inner curved side 22 of the assembly 10 is the displaceable or loose part or frame of the pre-rolling 26 assembly 10.
27 The rolls 14-114 and 214, and the other rolls disclosed in 28 a variant, of the outer curved side 13 may be associated 29 singly or in groups with at least one load cell 15, which sends signals to a control and data processing unit 21 of 31 the pre-rolling device.
32 In the form of embodiment shown in Fig.l the rolls 16-116 33 and 216, and the other rolls disclosed in a variant, of the 211~37 1 inner curved side 22 are associated singly or in groups with 2 at least one hydraulic capsule or cylinder 17.
3 Each hydraulic capsule 17 is controlled by a servovalve 19 4 and is associated with a pressure transducer 18. The servovalves 19 are controlled by the control and data 6 processing unit 21 of the pre-rolling device.
7 In this example each pair of rolls 14-16 is associated 8 with an individual position transducer 24, and each pre-9 rolling assembly 10 is associated with two transducers 124 monitoring the position of the assembly and arranged 11 respectively at the upstream end 124a and downstream end 12 124b of the pre-rolling assembly 10.
13 Where two assembly position transducers 124, namely an 14 upstream position transducer 124a and a downstream position transducer 124b respectively, are associated with the pre-16 rolling assembly 10, it is possible to determine between the 17 pairs of rolls 14-16 a rolling passage with parallel 18 (Fig.4a) or converging (Fig.4b) walls.
19 In this example the assembly position transducers 124 are installed between the stationary outer curved side 13 and 21 the displaceable inner curved side 22 of the pre-rolling 22 assembly 10.
23 According to a variant which is not shown here the 24 assembly position transducers 124 are associated only with the displaceable inner curved side 22 of the pre-rolling 26 assembly 10.
27 Each pressure transducer 18, each individual position 28 transducer 24 and each assembly position transducer 124 send 29 their own signals to the control and data processing unit 21 and possibly receive control and checking signals.
31 The parameters linked to the pre-rolling to be carried out 32 and possibly associated with the type of material cast and 33 with the dimensions of the thin slab 20 are set or _ - 15 - 21 I 998 7 1 introduced in the control and data processing unit 21 at the 2 beginning of a rolling campaign.
3 The control and data processing unit 21 pre-arranges the 4 pairs of rolls 14-16, 114-116, 214-216 and, when casting has started and the starter bar has been withdrawn, controls and 6 adjusts the pairs of rolls 14-16, 114-116, 214-216 one by 7 one so that the desired pre-rolling takes place.
8 So as to regulate and control the pre-rolling in order to 9 achieve a desired, controlled reduction of the thickness of the slab 20, means 25a to monitor the temperature of the 11 cast molten metal and to monitor the temperature of the 12 metal in the tundish, means 25b to monitor the temperature 13 of the thin slab 20 leaving the mold 11 and means 26 to 14 monitor the speed of the slab 20 are associated with the control and data processing unit 21 according to the 16 invention.
17 All these monitoring means 25a, 25b and 26 send their 18 signals to the control and data processing unit 21, thus 19 enabling a dynamic control of the pre-rolling method to be carried out as a function of the speed of the slab 20 and 21 ensuring a more correct management of the transient 22 conditions of starting and stopping.
23 According to a variant a plurality of auxiliary monitors 24 25b of the temperature of the slab 20 may be included and be positioned along the pre-rolling assembly 10 so as to 26 control the development of the temperature of the slab 20 at 27 pre-set points.
28 In this case the control and data processing unit 21 is 29 connected to a general control and data processing unit 121 and to a unit 27 which introduces and collects data.
31 The control and data processing unit 21 and/or the general 32 control and data processing unit 121, which control 33 adjustments, condition on the basis of a governing and ~ - 16 - 21199~7 1 control program set by the machine operator, for instance, 2 the reciprocal positions of the rolls of the pairs of rolls 3 14-16 forming the pre-rolling assembly 10.
4 This control and adjustment system enables the thickness of the slab 20 to be reduced between 10% and 50%.
6 According to a variant means 29 for secondary cooling of 7 the slab 20 are associated with the pre-rolling assembly 10 8 according to the invention and consist in this case of a 9 plurality of sprayer nozzles 30.
Both the rate of flow and the pressure of delivery of 11 these sprayer nozzles 30 are regulated advantageously by the 12 control and data processing unit 21 and/or by the general 13 control and data processing unit 121, thus ensuring a 14 continuous control of the conditions of the slab 20.
The regulation of the sprayer nozzles 30 may be governed 16 by the possible monitors 25b of the temperature of the thin 17 slab 20 which are arranged along the pre-rolling assembly 18 10.
19 According to a variant at least one monitor 28 of a sonar type, for instance, is associated with the pre-rolling 21 assembly 10 according to the invention so as to identify the 22 point of actual closure (kissing point) of the liquid cone 23 within the slab 20. This at least one monitor 28 is 24 connected advantageously to the general control and data processing unit 121 so as to regulate the secondary cooling 26 means 29.
27 To give an example, it is possible with the pre-rolling 28 method according to the invention to reduce the thickness of 29 a slab 20 moving at a casting speed of 4.5 meters per minute from a value of 70-75 mm. to 50 mm. in a travel between 0.8 31 and 2.5 meters long, but advantageously between 1.2 and 1.5 32 meters long.
33 Depending on the program set in the control and data ~ - 17 - 2Il998 7 1 processing unit 21, or 121, the reduction of thickness can 2 be progressive with constant values or be in steps, but 3 advantageously with a final finishing segment in which the 4 reduction is progressive.
In this example a descaling device 23 is fitted downstream 6 of the foot rolls 12 so as to produce a thin slab 20 having 7 an excellent surface quality and has the purpose of removing 8 the layer of oxides formed on the surface of the slab 20 9 immediately upstream of the pre-rolling assembly 10 according to the invention.
11 According to a variant more than one descaling device 23 12 may be included and be installed between one pair of rolls 13 14-16 and the next pair.
14 According to another variant the pairs of rolls 14-16 associated with the descaling devices 23 include means for 16 the internal cooling of the pre-rolling rolls 14-16, for 17 instance by internal circulation of a cooling fluid; the 18 purpose of this is to prevent the scale removed by the 19 descaling devices 23 from the surface of the slab 20 from adhering to the surface of the rolls owing to the high 21 temperature, thus making necessary frequent maintenance and 22 cleaning operations to keep the working surface of the rolls 23 perfectly smooth.
24 Fig.5 shows how the skin 31 increases progressively and how at the same time the two-phase zone 32 too, which forms 26 in a substantial manner owing to the pressure exerted by the 27 pre-rolling assembly 10, is progressively reinforced and is 28 closed before the slab 20 has left the pre-rolling assembly 29 10, so that the cone or pool of the liquid metal 33 remains surrounded within the pre-rolling assembly 10.
7 To be more exact, this invention concerns a method and 8 relative device for controlled pre-rolling, carried out on 9 thin slabs leaving a mold for the continuous casting of thin slabs, immediately downstream of the foot rolls of that mold 11 and concerns also the device suitable to apply that method.
12 By thin slabs are meant slabs 800 to 2500 mm. wide, or 13 more, and 25 to 90 mm. thick.
14 The invention is applied advantageously, but not only, to slabs having a final thickness between 30 and 60 mm. at the 16 outlet of the continuous casting machine.
17 The invention can also be applied to the continuous 18 casting of billets, whether the billets be round, square, 19 rectangular, etc.
The invention can be applied to straight and curved 21 continuous casting plants.
22 Pre-rolling methods are known whereby a thin slab 23 undergoes a pre-rolling action in a zone distant from the 24 foot rolls.
In the methods of the state of the art disclosed in JP-A-26 130759, US-A-3,891,025, US-A-4,056,140 and US-A-4,134,440 27 the pre-rolling does not give satisfactory results inasmuch 28 as it is performed in a position of the slab such that the 29 liquid core or pool is only seldom still present and the skin of the slab is anyway already thick and is such that it 31 cannot be readily deformed.
32 Moreover, the skin of one side of the slab is connected to 33 the skin of the other side by columnar solidification 1 elements at an intermediate position between the edges; both 2 the edges, which contain a consistent solidified thickness, 3 and also the columnar solidification elements offer a strong 4 resistance to any alteration of the thickness of the slab.
The pre-rolling in the methods of the state of the art, 6 therefore, has only a marginal and very limited effect, 7 which does not give the envisaged results.
8 Moreover, the pre-rolling as carried out in the methods of 9 the state of the art has only the purpose of performing a marginal superficial work, and the real work of reducing the 11 thickness of the slab is entrusted to the rolling train 12 located downstream.
13 Furthermore, in the pre-rolling assemblies of the state of 14 the art only some pairs of rolls are controlled to check the pre-rolling parameters, and these pairs of rolls are 16 controlled in a differentiated or separate manner (see JP-A-17 130759). This has the result that the operating method 18 cannot be conditioned according to specific requirements but 19 is quite random in some ways.
Pre-rolling assemblies are also known which comprise 21 mechanical adjustment systems together with pre-adjustment 22 at the beginning of a casting campaign. These assemblies 23 are associated with pre-rolling rolls in continuous rows or 24 divided into sectors or groups of rolls or else with assemblies of pressure belts.
26 These systems of the state of the art do not make possible 27 excellent adjustments, nor a substantial pre-rolling action 28 of a desired value, nor a continuously controlled travel 29 continuously related to the actual pre-rolling requirements.
They also do not enable processing to be carried out on a 31 zone where the liquid core or pool is still substantial and 32 the surface skin is still of very small values.
33 The state of the art prevents controlled mechanical action ~ 3 ~ - 2 1 1 9 9 8 7 1 to reduce the length of the liquid cone and thus to ensure 2 better quality.
3 Moreover, the state of the art e,ntails considerable 4 limitations with regard to problems linked to the transient conditions of starting and stopping and does not permit an 6 excellent yield of the system.
7 The state of the art does not obviate the flow of liquid 8 material at start-up and the re-flow of the liquid metal at 9 stopping and therefore keeps the reject rate high.
The present applicant has examined, tested and achieved 11 this invention so as to overcome the shortcomings of the 12 state of the art and to provide further advantages.
13 The pre-rolling method according to the invention can be 14 performed advantageously with a pre-rolling assembly of the type disclosed herein and in EP-A-0.539.784.
19 The purpose of this invention is to achieve a controlled pre-rolling or soft reduction of the slab leaving the 21 crystallizer so as to produce a slab of a smaller thickness 22 at the end of the casting machine.
23 The main advantages of the controlled pre-rolling, or soft 24 reduction, or reduction with a liquid core or pool are essentially two; the first advantage is to be able to 26 produce at the outlet of the casting machine a slab of a 27 slender thickness (30-60 mm.) by using a crystallizer having 28 a greater thickness, that is to say, the short side of the 29 lengthwise through passage of the crystallizer has a greater width than the finished thickness of the slab after the 31 controlled pre-rolling.
32 This controlled pre-rolling improves the fluid-dynamic 33 behaviour of the liquid metal in the crystallizer of the A
_ - 4 ~ 21 1 99~ 7 1 mold; it also improves the life of the submerged nozzle 2 assembled on the tundish and improves the behaviour during 3 melting of the powders which are placed above the upper part 4 of the liquid metal in the mold.
The second advantage is the achievement of a refining of 6 the structure of solidification of the metal and the 7 elimination of the central segregation in the slab.
8 In both cases, the soft reduction, if it is to be 9 effective, has to take place with a continuous controlled reduction of the thickness of the slab, and this can be 11 achieved with a substantially conical conformation of the 12 segment of slab undergoing the soft reduction.
13 This conical segment can have a length ranging from about 14 0.8 to 7 meters, preferably 3.8 meters to 6.3 meters; the greater length corresponds to the end of the containing zone 16 produced by the containing rolls included downstream of the 17 crystallizer and after the foot rolls.
18 The length of this segment of reduction of the thickness 19 with a conical development depends on the following metallurgical factors.
21 The solidification takes place in a substantially 22 different manner with different types of steel; steels with 23 a low content of carbon (C less than 0.10%) have a 24 solidification characterised by short columnar grains and the solidification face moves forward in a compact condition 26 without great discontinuities and with a short two-phase 27 zone.
28 Steels with a high carbon content (C greater than 0.70%) 29 have a solidification characterised by long columnar grains and the solidification face moves forward with great 31 discontinuities, creating a grid of large dendrites, among 32 which there remain islands of segregated liquid steel. In 33 this case the two-phase zone is very extensive.
_ 5 21199~ 7 1 The moment when the two faces of solidification (upper 2 side and lower side of the slab) meet is a very critical 3 moment for the definition of the internal quality and, more 4 generally, of the finished quality of the slab.
In fact it is known that owing to the effect of bulging 6 (swelling of the slab between two opposed pairs of 7 containing rolls), an effect of pumping the segregated 8 liquid is created; this bulging effect may be restricted but 9 is never fully eliminated.
When the slab opens owing to the bulging effect, the 11 liquid between the dendrites is sucked back by the cavities 12 between the dendrites towards the centre line of the slab.
13 When the slab closes on passing through the next pair of 14 rolls, the liquid is pumped in the opposite direction from the centre line to the cavities between the dendrites.
16 This alternating pumping effect creates islands of 17 positive and negative segregation at the centre line of the 18 slab.
19 So as to prevent this continuous to-and-fro flow of the segregated liquid, it is necessary to try to close the 21 passages between the dendrites and between one grain and the 22 next grain by means of compacting the structure at the 23 solidification face.
24 This can be achieved by compressing the two halves of the slab against each other by means of a light rolling of the 26 slab producing a substantially conical development of the 27 reduction.
28 Owing to the different extent of the two-phase zone 29 produced in the various types of steel, the compression has to take place in such a way that the two solidification 31 faces penetrate into each other with different degrees 32 according to the type of steel.
33 Steels with a low content of carbon and a short two-phase ~ - 6 - 21199~7 1 zone have to penetrate into each other by a few millimeters 2 to a depth where the solid fraction is consistent (about 90-3 95%) and the small spaces between the dendrites are already 4 practically nil.
Steels with a high content of carbon and a long two-phase 6 zone have to penetrate into each other in a consistent 7 manner to a depth where the solid fraction is less (up to 8 70%) and the spaces between the dendrites are very 9 extensive.
The best solid fraction at the end of the reduction 11 depends, therefore, on the type of steel and can be thus 12 summarised by bearing in mind a variation of the solid 13 fraction upwards or downwards of 2 to 2.5%, depending on 14 metallurgical factors.
15 C content (%) Solid fraction (%) 16< 0.20 95 170.20 - 0.40 90 180.40 - 0.70 80 19> 0.70 70 20 Where soft reduction is carried out, this means that the 21 end of the conical segment of reduction of the thickness of 22 the slab has to take place in a zone where the solid 23 fraction is best for obtaining a good internal quality.
24 Let us assume that it is desired to obtain at the end of the casting machine a slab with a thickness of 30 mm., 26 starting with a short side of 50 mm. of the crystallizer of 27 the mold and assuming also that steel is of a C 70 type.
28 The reduction to be carried out is 20 mm. (50 - 30).
29 Having valuated the profile of solidification of the slab at the current casting conditions, it is necessary to 31 determine at what distance from the level of the meniscus of 32 the liquid metal in the crystallizer of the mold there 33 exists in the slab leaving the crystallizer a solid fraction ~ _ 7 _ 21 1 9~ 8 7 1 of 70% at a distance of 15 mm. from the surface (15 being 2 the half of 30).
3 Let us suppose that this distance from the meniscus is 4 4 meters.
If the crystallizer is 1.2 meters long, the soft reduction 6 has to have a length (Lsr) of:
7 Lsr = 4 minus 1.2 = 2.8 meters 8 and the gradient of reduction (Gsr) has to be:
9 Gsr = (50 minus 30) = 20 mm./2.8 meters = 7.143 mm/m.
that is to say, for each meter of slab outside the 11 crystallizer it is necessary to apply a reduction of 12 thickness of 7.143 mm.
13 The pre-rolling method therefore consists in a model of ON
14 LINE solidification which determines the exact profile of solidification of the slab on the basis of the current 16 casting conditions.
17 This model calculates the length of the pre-rolling - Lsr 18 - that is to say, the position along the machine where a 19 desired solid fraction exists at a depth from the surface equal to the half-thickness of the slab to be produced.
21 Having defined this level, the conical segment of the 22 reduction is adjusted by rolling in such a way as to have a 23 gradient of reduction - Gsr - such as will bring the end of 24 the reduction to the calculated pre-rolling length Lsr.
This result is achieved by reducing in a controlled, 26 desired manner the length of the liquid cone or pool, thus 27 minimizing the occurrence of segregation found in unalloyed 28 steels with a medium-high content of carbon, or alloyed 29 steels with a medium-low content of carbon, or in steels in general which entail the occurrence of segregation.
31 This desired, controlled reduction of the length of the 32 liquid cone enables the mushy zone to be kept in contact 33 eliminating the li~uid phase in such a way as to promote the 1 growth of an equiaxe structure such as that which can be 2 produced with electromagnetic stirring.
3 A further purpose of the pre-rolling method according to 4 the invention is to speed up the formation of crystals and therefore the formation of stable columnar connections 6 between the skin of one side and the skin of the other side 7 of the slab.
8 In the method according to the invention these columnar 9 connections are formed in a compressed environment owing to the pre-rolling action exerted by the pre-rolling assembly, 11 so that these connections are produced already compacted 12 with a typical arrangement.
13 This leads to the advantage that the product leaving the 14 continuous casting plant arrives more compact at the rolling line and with a substantially smaller thickness and better 16 levelled.
17 By carrying out a dynamic control of the length of the 18 liquid cone or pool as a function of the main casting 19 parameters (speed, superheating in the tundish, secondary cooling downstream of the mold and steel grade), the 21 invention also enables the transient periods of starting and 22 stopping (at the end of casting or owing to an accident) to 23 be optimized and the scrap to be reduced.
24 Moreover, the method according to the invention makes possible the casting in a mold of a slab having a section of 26 a greater thickness than the final one with all the 27 advantages in terms of surface quality arising from 28 optimization of the working conditions of the lubricating 29 powder (greater melting surface, regularity of the covering of the powders on the liquid steel), of superheating of the 31 steel and of downflow in the mold (with less turbulence and 32 greater stability of the meniscus), and also makes possible 33 the use of a submerged nozzle having a greater cross-section g 1 and therefore more longlasting.
2 This pre-rolling method enables the outgoing cross-section 3 of the slab to be reduced so as to be able to reach smaller 4 final thicknesses, given an equal number of rolling units.
According to the invention the pre-rolling rolls 6 positioned on the outer curved side of the plant, in the 7 event of continuous curved casting, can be associated with 8 load cells, which control the pressure which those rolls 9 exert on the thin slab.
The pre-rolling rolls positioned on the inner curved side 11 of the plant are associated with a hydraulic capsule, for 12 instance of the type disclosed in EP-0444420, and may also 13 be associated with load cells as an alternative to those 14 envisaged for the rolls on the outer curved side.
A pressure transducer is included on each hydraulic 16 capsule and enables the rolling pressure to be controlled.
17 According to the invention the pairs of rolls are arranged 18 in one or more groups, each group forming a pre-rolling 19 assembly. Each pre-rolling assembly includes a stationary portion and a displaceable portion. This description assumes 21 as an example that the outer curved side contains stationary 22 rolls while the displaceable rolls form the inner curved 23 side, but in practice the two sides can also be inverted.
24 According to a variant the inner and outer curved sides may include a stationary portion and a displaceable portion, 26 which cooperate with a displaceable portion and a stationary 27 portion of the opposite side respectively.
28 According to a first lay-out of the invention each pair of 29 rolls is associated with a single position transducer, which monitors the distance between the opposed rolls.
31 In a second lay-out of the invention each group of pairs 32 of rolls forming a pre-rolling assembly includes two 33 transducers monitoring the position of that assembly, these 211~987 1 transducers being located respectively at the upstream and 2 downstream ends of that pre-rolling assembly and monitoring 3 the distance between the opposed rolls at those positions.
4 According to a variant of this second lay-out each pair of rolls is also associated with a single position transducer.
6 By means of the position transducers it is possible to 7 determine in the pre-rolling assemblies a rolling passage 8 between the pairs of rolls; this passage may have its sides 9 parallel or converging, depending on the particular requirements.
11 Moreover, if each pair of rolls is associated with a 12 single position transducer, it is possible to determine a 13 pre-rolling passage having a lengthwise section of any 14 particular form by positioning each roll of each pair of rolls as required.
16 The whole system is governed by a pre-rolling control and 17 data processing unit, which receives signals from the 18 pressure transducers and position transducers, whether 19 single or belonging to assemblies, and also from monitors of the speed of the slab, from monitors of the secondary 21 cooling parameters and from monitors of the temperature of 22 the cast molten metal and of the temperature of the thin 23 slab leaving the mold.
24 Further temperature monitors may also be included which monitor the temperature of the slab at intermediate 26 positions in the area where the pre-rolling assembly 27 according to the invention is working, and which send 28 signals to the pre-rolling control and data processing unit.
29 Furthermore, a monitor, possibly of a sonar type for instance, may be included to identify the presence or 31 absence of a liquid pool within the slab and thus to ensure 32 correctly the actual closure of the liquid cone or pool in 33 the pre-rolling assembly according to the invention.
1 The control and data processing unit, which may be 2 connected to or form part of other general control and data 3 processing units, processes all these parameters and 4 compares them with the pre-rolling parameters fed into or contained in appropriate internal files and provides the 6 pairs of rolls with optimum adjustment values.
7 The control and data processing unit may also be connected 8 to an auxiliary data collection unit, which, besides 9 recording all the values provided by the monitors, feeds them to a data bank able to display and/or print the 11 progress of the values over a period of time.
12 In this description, by rolls are meant rolls positioned 13 in continuous rows or divided into sectors, or else belts, 14 etc., thus covering any system of the state of the art.
The adjustments which are carried out with the method 16 according to the invention are adjustments of single rolls, 17 or of one assembly of rolls at a time followed by another 18 assembly and so on, or general adjustments of the whole pre-19 rolling assembly. The adjustments may be added algebraically.
21 The pre-rolling method according to the invention enables 22 a reduction of the thickness of the slab by between about 23 10% and 50% to be achieved. This reduction of the thickness 24 is obtained in a travel between 0.8 and 7 meters long, but advantageously between 1.2 and 1.8 meters long.
26 The reduction of the thickness of the slab may be 27 progressive with constant values.
28 According to a variant the reduction of the thickness of 29 the slab is carried out in steps, with a final finishing segment in which the reduction of thickness is progressive.
31 According to a variant means for the secondary cooling of 32 the slab are associated with the pre-rolling assembly 33 according to the invention and consist, for instance, of a ~ - 12 - 21 19~ 7 1 plurality of sprayer nozzles.
2 Both the rate of flow and the delivery pressure of the 3 sprayer nozzles are adjusted advantageously by the data 4 processing and control unit and/or by the general data processing and control unit, thus ensuring a continuous 6 control of the condition of the slab.
7 The regulation of the sprayer nozzles may be governed by 8 possible monitors of the temperature of the slab, these 9 monitors being arranged along the pre-rolling assembly.
According to another variant at least one descaling unit 11 of the type shown in patent application EP-93110927.6 filed 12 in the name of the present applicant, for instance, may be 13 associated with the pre-rolling assembly according to the 14 invention. This descaling unit installed upstream of the first pre-rolling assembly enables thin slabs to be produced 16 with an excellent surface quality as required for special 17 successive processings.
18 According to a variant a plurality of descaling units are 19 included and are placed between the pairs of pre-rolling rolls.
21 According to yet another variant the descaling units are 22 placed between each pair of pre-rolling rolls.
23 According to a further variant and particularly where 24 descaling units are positioned between the pairs of pre-rolling rolls, the rolls are cooled inside to prevent the 26 scale removed from the surface of the thin slabs from 27 adhering to the surface of the roll itself.
28 The attached figures are given as a non-restrictive 29 example and show some preferred lay-outs of the invention as follows:-31 Fig.1 is a diagram of one side of an assembly for the pre-32 rolling of thin slabs produced by continuous curved 33 casting according to the invention;
_ - 13 -1 Figs.2 and 3 show two other possible types of pre-rolling 2 rolls;
3 Figs.4 are diagrams of two possible positions of the pre-4 rolling assembly of Fig.l;
Fig.5 shows the formation of the two-phase zone according 6 to the invention.
7 In the figures the pre-rolling method according to the 8 invention is carried out by at least one pre-rolling 9 assembly 10 consisting of a plurality of pairs of rolls 14-16.
11 Fig.l shows only the first of these pre-rolling assemblies 12 10 in association with foot rolls 12 and a mold 11, which 13 produces a thin slab 20 continuously, a second pre-rolling 14 assembly 10 installed immediately downstream being shown only partly.
16 The first pre-rolling assembly 10 is installed immediately 17 downstream of the mold 11 at a distance of about 0.5 meters.
18 The pairs of rolls 14-16 shown may consist of continuous 19 rows or be divided into sectors 14-16 or into groups of two or more pairs 114-116 or consist of belts 214-216 or be of 21 any other known type.
22 In the example shown the outer curved side 13 of the 23 assembly 10 is the stationary or fixed part or frame, while 24 the inner curved side 22 of the assembly 10 is the displaceable or loose part or frame of the pre-rolling 26 assembly 10.
27 The rolls 14-114 and 214, and the other rolls disclosed in 28 a variant, of the outer curved side 13 may be associated 29 singly or in groups with at least one load cell 15, which sends signals to a control and data processing unit 21 of 31 the pre-rolling device.
32 In the form of embodiment shown in Fig.l the rolls 16-116 33 and 216, and the other rolls disclosed in a variant, of the 211~37 1 inner curved side 22 are associated singly or in groups with 2 at least one hydraulic capsule or cylinder 17.
3 Each hydraulic capsule 17 is controlled by a servovalve 19 4 and is associated with a pressure transducer 18. The servovalves 19 are controlled by the control and data 6 processing unit 21 of the pre-rolling device.
7 In this example each pair of rolls 14-16 is associated 8 with an individual position transducer 24, and each pre-9 rolling assembly 10 is associated with two transducers 124 monitoring the position of the assembly and arranged 11 respectively at the upstream end 124a and downstream end 12 124b of the pre-rolling assembly 10.
13 Where two assembly position transducers 124, namely an 14 upstream position transducer 124a and a downstream position transducer 124b respectively, are associated with the pre-16 rolling assembly 10, it is possible to determine between the 17 pairs of rolls 14-16 a rolling passage with parallel 18 (Fig.4a) or converging (Fig.4b) walls.
19 In this example the assembly position transducers 124 are installed between the stationary outer curved side 13 and 21 the displaceable inner curved side 22 of the pre-rolling 22 assembly 10.
23 According to a variant which is not shown here the 24 assembly position transducers 124 are associated only with the displaceable inner curved side 22 of the pre-rolling 26 assembly 10.
27 Each pressure transducer 18, each individual position 28 transducer 24 and each assembly position transducer 124 send 29 their own signals to the control and data processing unit 21 and possibly receive control and checking signals.
31 The parameters linked to the pre-rolling to be carried out 32 and possibly associated with the type of material cast and 33 with the dimensions of the thin slab 20 are set or _ - 15 - 21 I 998 7 1 introduced in the control and data processing unit 21 at the 2 beginning of a rolling campaign.
3 The control and data processing unit 21 pre-arranges the 4 pairs of rolls 14-16, 114-116, 214-216 and, when casting has started and the starter bar has been withdrawn, controls and 6 adjusts the pairs of rolls 14-16, 114-116, 214-216 one by 7 one so that the desired pre-rolling takes place.
8 So as to regulate and control the pre-rolling in order to 9 achieve a desired, controlled reduction of the thickness of the slab 20, means 25a to monitor the temperature of the 11 cast molten metal and to monitor the temperature of the 12 metal in the tundish, means 25b to monitor the temperature 13 of the thin slab 20 leaving the mold 11 and means 26 to 14 monitor the speed of the slab 20 are associated with the control and data processing unit 21 according to the 16 invention.
17 All these monitoring means 25a, 25b and 26 send their 18 signals to the control and data processing unit 21, thus 19 enabling a dynamic control of the pre-rolling method to be carried out as a function of the speed of the slab 20 and 21 ensuring a more correct management of the transient 22 conditions of starting and stopping.
23 According to a variant a plurality of auxiliary monitors 24 25b of the temperature of the slab 20 may be included and be positioned along the pre-rolling assembly 10 so as to 26 control the development of the temperature of the slab 20 at 27 pre-set points.
28 In this case the control and data processing unit 21 is 29 connected to a general control and data processing unit 121 and to a unit 27 which introduces and collects data.
31 The control and data processing unit 21 and/or the general 32 control and data processing unit 121, which control 33 adjustments, condition on the basis of a governing and ~ - 16 - 21199~7 1 control program set by the machine operator, for instance, 2 the reciprocal positions of the rolls of the pairs of rolls 3 14-16 forming the pre-rolling assembly 10.
4 This control and adjustment system enables the thickness of the slab 20 to be reduced between 10% and 50%.
6 According to a variant means 29 for secondary cooling of 7 the slab 20 are associated with the pre-rolling assembly 10 8 according to the invention and consist in this case of a 9 plurality of sprayer nozzles 30.
Both the rate of flow and the pressure of delivery of 11 these sprayer nozzles 30 are regulated advantageously by the 12 control and data processing unit 21 and/or by the general 13 control and data processing unit 121, thus ensuring a 14 continuous control of the conditions of the slab 20.
The regulation of the sprayer nozzles 30 may be governed 16 by the possible monitors 25b of the temperature of the thin 17 slab 20 which are arranged along the pre-rolling assembly 18 10.
19 According to a variant at least one monitor 28 of a sonar type, for instance, is associated with the pre-rolling 21 assembly 10 according to the invention so as to identify the 22 point of actual closure (kissing point) of the liquid cone 23 within the slab 20. This at least one monitor 28 is 24 connected advantageously to the general control and data processing unit 121 so as to regulate the secondary cooling 26 means 29.
27 To give an example, it is possible with the pre-rolling 28 method according to the invention to reduce the thickness of 29 a slab 20 moving at a casting speed of 4.5 meters per minute from a value of 70-75 mm. to 50 mm. in a travel between 0.8 31 and 2.5 meters long, but advantageously between 1.2 and 1.5 32 meters long.
33 Depending on the program set in the control and data ~ - 17 - 2Il998 7 1 processing unit 21, or 121, the reduction of thickness can 2 be progressive with constant values or be in steps, but 3 advantageously with a final finishing segment in which the 4 reduction is progressive.
In this example a descaling device 23 is fitted downstream 6 of the foot rolls 12 so as to produce a thin slab 20 having 7 an excellent surface quality and has the purpose of removing 8 the layer of oxides formed on the surface of the slab 20 9 immediately upstream of the pre-rolling assembly 10 according to the invention.
11 According to a variant more than one descaling device 23 12 may be included and be installed between one pair of rolls 13 14-16 and the next pair.
14 According to another variant the pairs of rolls 14-16 associated with the descaling devices 23 include means for 16 the internal cooling of the pre-rolling rolls 14-16, for 17 instance by internal circulation of a cooling fluid; the 18 purpose of this is to prevent the scale removed by the 19 descaling devices 23 from the surface of the slab 20 from adhering to the surface of the rolls owing to the high 21 temperature, thus making necessary frequent maintenance and 22 cleaning operations to keep the working surface of the rolls 23 perfectly smooth.
24 Fig.5 shows how the skin 31 increases progressively and how at the same time the two-phase zone 32 too, which forms 26 in a substantial manner owing to the pressure exerted by the 27 pre-rolling assembly 10, is progressively reinforced and is 28 closed before the slab 20 has left the pre-rolling assembly 29 10, so that the cone or pool of the liquid metal 33 remains surrounded within the pre-rolling assembly 10.
Claims (28)
1. A method for the controlled pre-rolling of the thin slabs (20) leaving the mould (11) of a continuous casting plant, wherein said pre-rolling is carried out with a plurality of pairs of rolls (14-16) grouped together in one or more pre-rolling assemblies (10), a first one of said pre-rolling assemblies (10) being positioned immediately downstream of said mold (11), each one of said point or rolls (14,16) having at least one displaceable roll (16), said pairs of rolls (14-16) being associated with pressure transducer means (18) and hydraulic capsule means (17), position transducer means (24) being provided, said pressure transducer means (18) and said position transducer means (24) being associated with a control data processing unit (21), at least a first one of said pairs of rolls (14-16) processing a slab (20)which has just left said mold (11) with a thin solidified skin (31), the method being characterised in that said control and data processing unit (21) is further associated with first means (25a) for monitoring the temperature of a liquid bath in a tundish, with second means (26) for monitoring the casting speed and with third means (25b) functionally associated to the temperature of the slab (20) both while the slab (20) leaves said mold (11) and while the slab (20) is at least within said first pre-rolling assembly (10), and in that said control and data processing unit (21) also conditions, on the basis of a governing and control program, the reciprocal positions of said displaceable rolls (16) of at least a part of said pairs of rolls (14-16) so as to achieve a pre-rolling with a reduction of the thickness of the slab (20) leaving the last pair of said pre-rolling rolls (14-16) by at least 10%, whereby eliminating the liquid pool (33) and to bring into contact the zones in a two-phase condition (32) in order that the central solidification structure be refined and the central segregation and porosity be minimized.
2. A pre-rolling method as in claim 1, wherein said control and data processing unit (21) performs a dynamic control of the entire pre-rolling cycle and optimizes the management of the transient periods of start-up and stopping of casting.
3. A pre-rolling method as in claim 1, wherein the reduction of thickness of the slab (20) is achieved in a travel between 0.8 and 7 meters long starting from the outlet of the mold (11).
4. A pre-rolling method as in claim 1, wherein the reduction of thickness of the slab (20) is progressive with constant values.
5. A pre-rolling method as in claim 1, wherein the reduction of thickness of the slab (20) is achieved in steps with a final stage of progressive finishing reduction.
6. A pre-rolling method as in claim 1, wherein the slab (20) undergoes a descaling step at least before entering said first pre-rolling assembly (10).
7. A pre-rolling method as in claim 1, wherein the kissing point of the liquid cone (33) in the advancing slab (20) is controlled with fourth means (28) which monitor the kissing point of the liquid pool, said fourth means (28) being associated with said control and data processing unit (21).
8. A pre-rolling method as in claim 1, wherein the rate of flow of the secondary cooling means (30) is controlled by said control and data processing unit (21) through said third means (25b) which detect the temperature of said slab (22).
9. A device for the controlled pre-rolling of thin slabs (20) leaving the mould (11) of a continuous casting plant, comprising a first plurality of pairs of rolls (14-16) grouped together in one or more pre-rolling assemblies (10), a first one of said pre-rolling assemblies (10) being positioned immediately downstream of said mold (11), each one of said pairs of rolls having at least one displaceable roll (16), said pairs of rolls (14-16)being associated with pressure transducer means (18) and hydraulic capsule means (17), position transducer means (24) being provided, said pressure transducer means (18) and said position transducer means (24) being associated with a control and data processing unit (21), at least a first one of said pairs of rolls (14-16) processing a slab (20) which has just left said mold (11) and has a thin solidified skin (31), the device being characterised in that said control and data processing unit (21) is associated with first means (25a) for monitoring temperature of a liquid bath in a tundish with second means (26) for monitoring the speed of the slab (20) and with third means (25b) functionally associated with the temperature of said slab (2c).
10. A pre-rolling device as in claim 9, wherein individual position transducer means (24) are associated with each one of said pairs of rolls (14-16).
11. A pre-rolling device as in claim 9, wherein transducer means (124-124a-124b) monitoring the position of said first pre-rolling assembly (10) are associated with said plurality of pairs of rolls (14-16).
12. A pre-rolling device as in claim 9, wherein said third means (25b) detect the temperature of said slab (2c).
13. A pre-rolling device as in claim 9, wherein said control and data processing unit (21) is associated with fourth means which control at least a rate of flow of the cooling water of secondary cooling means (30) of the slab (20).
14. A pre-rolling device as in claim 9, wherein said control and data processing unit (21) includes a unit (27) for introducing and collecting data.
15. A pre-rolling device as in claim 9, wherein said pairs of rolls (14-16) are associated with internal cooling means.
16. A pre-rolling device as in claim 9, wherein said first pre-rolling assembly (10) comprises a stationary sector (13) provided adjacent a first major surface of the slab (20) and comprising a second plurality of rolls (14-114-214); and a movable sector (22) provided adjacent a second major surface of the slab (20) and comprising a third plurality of rolls (16-116-216) associated with at least one hydraulic capsule (17) governed by a servovalve (19) for positioning said third rolls (16-116-216) with respect to said second plurality of rolls.
17. A pre-rolling device as in claim 16, wherein said second plurality of rolls (14-114-214) are associated with at least one load cell (15).
18. A pre-rolling device as in claim 17, wherein said hydraulic capsule (17) is associated with transducers indicating pressure (18) and position (24).
19. A pre-rolling device as in claim 18, wherein said load cell (15), said servovalves (19) and said pressure (18) and position (24) transducers are associated with said control and data processing unit (21), and wherein said control and data processing unit (21) comprises means for the insertion/introduction of the pre-rolling parameters (27) and the characteristics of a liquid core (33) of the slab (20).
20. A pre-rolling device as in claim 16, wherein said third plurality of rolls (16) is arranged in groups (116), and wherein each one of said groups (116) is associated with a hydraulic capsule (17) governed by a servovalve (19).
21. A pre-rolling method as in claim 1, wherein at least one of said pre-rolling assembly (10) is controlled so as to achieve a reduction in thickness of the thin slab (20) of about 10% to 50%.
22. A pre-rolling method as in claim 1, wherein at least said first pre-rolling assembly (10) is controlled in such a way that the thin slab (20) leaving said first pre-rolling assembly (10) contains a core (33) which is not completely solidified.
23. A pre-rolling method as in claim 1, wherein a solid fraction of the thin slab (20) leaving said first pre-rolling assembly (10) is about 67.5% to 97.5%.
24. A pre-rolling method as in claim 1, wherein the thin slab (20) leaving said first pre-rolling assembly (10) has a two phase central core (33) whereby the central solidification structure is refined and the central segregation is minimized.
25. A pre-rolling method as in claim 1, wherein said third means detect the temperature of said slab (20).
26. A pre-rolling method as in claim 1, wherein said third means are provided for the secondary cooling of said slab (20).
27. A pre-rolling device as in claim 9, wherein descaling means (23) are provided at least upstream of said pre-rolling assemblies (10).
28. A pre-rolling device as in claim 9, wherein fourth means (28) for detecting the presence of a liquid pool are associated to said control and data processing unit (21).
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ITUD930083A IT1262116B (en) | 1993-05-17 | 1993-05-17 | CONTROLLED PRELAMINATION PROCEDURE FOR THIN SLABS OUT OF CONTINUOUS CASTING AND RELATED DEVICE |
| ITUD93A000083 | 1993-05-17 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2119987A1 CA2119987A1 (en) | 1994-11-18 |
| CA2119987C true CA2119987C (en) | 1999-03-30 |
Family
ID=11421290
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002119987A Expired - Lifetime CA2119987C (en) | 1993-05-17 | 1994-03-25 | Method for the controlled pre-rolling of thin slabs leaving a continuous casting plant, and relative device |
Country Status (13)
| Country | Link |
|---|---|
| EP (1) | EP0625388B1 (en) |
| KR (1) | KR100263779B1 (en) |
| CN (1) | CN1043193C (en) |
| AT (1) | ATE194527T1 (en) |
| BR (1) | BR9401449A (en) |
| CA (1) | CA2119987C (en) |
| DE (1) | DE69425188T2 (en) |
| DK (1) | DK0625388T3 (en) |
| ES (1) | ES2147562T3 (en) |
| IT (1) | IT1262116B (en) |
| PT (1) | PT625388E (en) |
| RU (1) | RU2111083C1 (en) |
| TW (1) | TW276196B (en) |
Families Citing this family (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1280171B1 (en) * | 1995-05-18 | 1998-01-05 | Danieli Off Mecc | VERTICAL CASTING LINE FOR BRAMME |
| ES2128816T3 (en) * | 1995-11-28 | 1999-05-16 | Danieli Off Mecc | METHOD FOR PREVIOUS PASSING BY ROLLERS OF THIN PLATES. |
| DE19817034A1 (en) | 1998-04-17 | 1999-10-21 | Schloemann Siemag Ag | Continuous casting of thin metal slabs |
| JP3355311B2 (en) * | 1999-04-21 | 2002-12-09 | 住友重機械工業株式会社 | Continuous casting method and continuous casting machine for thin slab slab |
| KR100733371B1 (en) * | 2001-07-20 | 2007-06-28 | 주식회사 포스코 | Device for removing the scale of grind machine |
| DE10236367A1 (en) * | 2002-08-08 | 2004-02-19 | Sms Demag Ag | Dynamic control of a casting strand made from steel on both sides of roll segments used in a continuous casting installation comprises using the roll segments in a cold strand, hot strand and/or soft reduction region |
| DE102004010038A1 (en) * | 2004-03-02 | 2005-09-15 | Sms Demag Ag | Driving the safety rolls (7c) of a continuous casting machine useful for casting molten metals, especially molten steels |
| ITMI20051764A1 (en) * | 2005-09-22 | 2007-03-23 | Danieli Off Mecc | PROCESS AND PLANT FOR THE PRODUCTION OF METAL TAPES |
| DE102007004053A1 (en) * | 2007-01-22 | 2008-07-31 | Siemens Ag | Casting plant for casting a cast product and method for guiding a cast material from a casting container of a casting plant |
| DE102007058109A1 (en) * | 2007-12-03 | 2009-06-04 | Sms Demag Ag | Device for controlling or regulating a temperature |
| DE102008014524A1 (en) * | 2007-12-28 | 2009-07-02 | Sms Demag Ag | Continuous casting plant with a device for determining solidification states of a cast strand and method therefor |
| AT506824B1 (en) * | 2008-05-26 | 2013-01-15 | Siemens Vai Metals Tech Gmbh | MORE STRAND CASTING |
| DE102008050393A1 (en) * | 2008-10-02 | 2010-04-08 | Sms Siemag Aktiengesellschaft | Arrangement and method for detecting an operating state of a strand guide |
| WO2010051981A1 (en) * | 2008-11-04 | 2010-05-14 | Sms Siemag Ag | Method and device for controlling the solidification of a cast strand in a strand casting plant in startup of the injection process |
| BRPI1013747B1 (en) * | 2009-05-06 | 2020-10-27 | Primetals Technologies Germany Gmbh | method to manufacture a laminated rolling stock in a rolling mill of a rolling mill and rolling mill |
| CN103212683B (en) * | 2012-01-20 | 2016-06-22 | 钢铁研究总院 | Chamfer type foot roller with inclined rotating shaft |
| CN109158568A (en) * | 2018-10-18 | 2019-01-08 | 武汉中飞扬测控工程有限公司 | A method of it is calculated by gap values between rollers to arc |
| AT524482B1 (en) * | 2020-09-18 | 2022-07-15 | Primetals Technologies Austria GmbH | Continuous casting plant and method for operating the continuous casting plant |
| CN113333472B (en) * | 2021-08-08 | 2021-10-12 | 常州市坚力橡胶有限公司 | Rubber roll and machine tool assembled by same |
| EP4417341A1 (en) * | 2023-02-14 | 2024-08-21 | SMS Concast AG | Method for producing metallic long products and casting and rolling installation for carrying out the method |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3891025A (en) * | 1972-06-29 | 1975-06-24 | Schloemann Siemag Ag | Apparatus for withdrawing a casting and feeding a dummy bar in a continuous casting machine for steel |
| US4134440A (en) * | 1974-09-16 | 1979-01-16 | Nippon Kokan Kabushiki Kaisha | Method of continuously casting steel |
| US4056140A (en) * | 1976-10-20 | 1977-11-01 | United States Steel Corporation | Method and mechanism for controlling forces in a continuous-casting machine |
| JPS6030565A (en) * | 1983-07-21 | 1985-02-16 | O C C:Kk | Method for stabilizing surface shape of ingot with heated casting mold type continuous casting method |
| US4809766A (en) * | 1988-05-26 | 1989-03-07 | Usx Corporation | Continuous caster breakout damage avoidance system |
| DE3822939C1 (en) * | 1988-07-04 | 1989-10-05 | Mannesmann Ag, 4000 Duesseldorf, De | Continuous casting method for the production of slabs with a reduced thickness relative to the cast condition |
| DE3823861A1 (en) * | 1988-07-14 | 1990-01-18 | Thyssen Stahl Ag | METHOD AND SYSTEM FOR PRODUCING A STEEL TAPE THICKNESS THAN 10 MM |
| FR2645461A1 (en) * | 1989-04-06 | 1990-10-12 | Techmetal Promotion | PROCESS AND DEVICE FOR CONTINUOUS CASTING THIN METAL PRODUCTS |
| IT1252847B (en) * | 1991-10-31 | 1995-06-28 | Danieli Off Mecc | CONTROLLED PRE-LAMINATION GROUP FOR THIN SLABS OUT OF CONTINUOUS CASTING |
-
1993
- 1993-05-17 IT ITUD930083A patent/IT1262116B/en active IP Right Grant
-
1994
- 1994-02-25 DE DE69425188T patent/DE69425188T2/en not_active Revoked
- 1994-02-25 PT PT94102876T patent/PT625388E/en unknown
- 1994-02-25 DK DK94102876T patent/DK0625388T3/en active
- 1994-02-25 ES ES94102876T patent/ES2147562T3/en not_active Expired - Lifetime
- 1994-02-25 AT AT94102876T patent/ATE194527T1/en not_active IP Right Cessation
- 1994-02-25 EP EP94102876A patent/EP0625388B1/en not_active Revoked
- 1994-03-25 CA CA002119987A patent/CA2119987C/en not_active Expired - Lifetime
- 1994-03-26 TW TW083102667A patent/TW276196B/zh active
- 1994-03-29 RU RU94010099A patent/RU2111083C1/en active
- 1994-04-08 BR BR9401449A patent/BR9401449A/en not_active IP Right Cessation
- 1994-04-12 KR KR1019940007562A patent/KR100263779B1/en not_active IP Right Cessation
- 1994-04-25 CN CN94104661A patent/CN1043193C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| PT625388E (en) | 2000-12-29 |
| IT1262116B (en) | 1996-06-19 |
| ITUD930083A0 (en) | 1993-05-17 |
| BR9401449A (en) | 1994-12-06 |
| CA2119987A1 (en) | 1994-11-18 |
| DE69425188D1 (en) | 2000-08-17 |
| CN1043193C (en) | 1999-05-05 |
| EP0625388A1 (en) | 1994-11-23 |
| RU2111083C1 (en) | 1998-05-20 |
| DE69425188T2 (en) | 2001-03-22 |
| TW276196B (en) | 1996-05-21 |
| ATE194527T1 (en) | 2000-07-15 |
| EP0625388B1 (en) | 2000-07-12 |
| ES2147562T3 (en) | 2000-09-16 |
| ITUD930083A1 (en) | 1994-11-17 |
| KR100263779B1 (en) | 2000-09-01 |
| DK0625388T3 (en) | 2000-10-30 |
| CN1118719A (en) | 1996-03-20 |
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