CN113272084A

CN113272084A - Method for producing a metal strip and production plant for implementing said method

Info

Publication number: CN113272084A
Application number: CN201980080882.8A
Authority: CN
Inventors: 詹皮耶特罗·本尼迪蒂; 保罗·博比奇
Original assignee: Danieli Machinery Co ltd
Current assignee: Danieli Machinery Co ltd; Danieli and C Officine Meccaniche SpA
Priority date: 2018-10-08
Filing date: 2019-09-25
Publication date: 2021-08-17
Also published as: KR20210102877A; IT201800009259A1; KR20230084614A; US20220001442A1; KR102591941B1; EP3863781A1; US20230330740A1; CN116511247A; WO2020075205A1; RU2768955C1

Abstract

A method of producing a metal strip (N), the method comprising: casting a cast product (P) by means of a casting machine (11) equipped with a crystallizer (15a) to obtain a slab (B), and hot rolling said slab (B) in a rolling station (19) to obtain a metal strip (N). During casting, the casting machine (11) exerts an action of reducing the thickness of the cast product (P) leaving the crystallizer (15 a).

Description

Method for producing a metal strip and production plant for implementing said method

Technical Field

The invention relates to a method for producing a metal strip and to a production plant for carrying out said method.

In particular, the method of the invention enables to define a mode for obtaining a metal strip and a constructive layout of a plant for producing hot-rolled metal strips.

Background

In the steel industry, plants for producing metal strip are well known, these plants generally comprising: a mould configured for casting slabs (slabs), extraction means for extracting the slabs from the mould, and a rolling line downstream of the extraction means, the rolling line being configured to reduce the overall thickness of the slabs until a metal strip of the desired thickness is obtained.

It is known, at least in terms of productivity of the plant and thickness of the strip, to suitably adjust the dimensions of the whole plant to the required parameters, according to the thickness of the metal strip to be obtained and the overall productivity required by the plant.

With respect to these requirements, it is known to provide customers with "endless" type equipment, semi-continuous type equipment, such as: a "coil to coil" and/or a "semi-endless" or "endless" and semi-continuous combination device.

Headless type equipment is used to provide the cast product and clamp the cast product directly from the die to the mill pass line, except that the product being worked does not need to be cut prior to final bending.

Semi-continuous plants downstream of the casting or roughing stands (roughing stands) cut the cast product to size and treat it in a heating and/or maintenance furnace, which can also act as an accumulation buffer for the cast product, if necessary, for example in the case of interruption of the downstream rolling due to minor accidents or planned roll changes.

If the cast product is cut to length downstream of the casting or roughing mill in order to obtain a coil (coil) at the end of the rolling process, the process is called roll-to-roll. On the other hand, if the cast product is cut to length downstream of the caster or roughing stand in order to obtain a plurality of coils (typically between 2 and 5) at the end of the rolling process, the process is called semi-endless.

It is known that, by suitable expedients, it is possible to operate the semi-continuous type plant also in headless mode, thus obtaining the advantages of this solution.

The type of application device and the number of required components are generally chosen according to the experience of the person skilled in the art, for example: the number of rolling stations, or the number of roughing stands selected and how many roughing stands and how many finishing stands (finishing stands) are used.

However, such scale, i.e. the preparation of the strip production plant, sometimes fails to achieve an effective compromise between the investment (also called capital expenditure) required for the plant construction and the operational transformation cost (also called operational expenditure). Therefore, in some cases, the construction investment cost of the production facility is too high compared to the income, and thus the production facility provided is too large with respect to the productivity requested by the customer, or the production facility is too small, and thus the productivity requested by the customer cannot be achieved.

However, some known methods and apparatuses for producing metal strip have the above-mentioned problems, such as: the above problems are encountered in documents WO 92/00815A 1, JP S62248542A and WO 02/40201A 2.

It is therefore an object of the present invention to provide a production plant of the correct dimensions according to the needs of the customers who use the hot-manufacturing process of metal strips (for example steel), so as to optimize the productivity of the strip production plant with the smallest possible number of strips, while maintaining the maximum casting speed associated with various steels.

Another object of the present invention is to provide an apparatus for producing hot-rolled metal strip which requires only a limited investment (capital expenditure) and has a lower operating transition cost (operating expenditure) than an apparatus producing the same strip thickness.

Another object of the present invention is to provide an apparatus and a corresponding method perfected for producing hot-rolled metal strip that can selectively vary the thickness of the cast slab with respect to the final thickness of said strip.

Another object of the present invention is to provide a method for producing a metal strip which makes it possible to obtain a plant having extreme flexibility and which can be adapted to specific customer requirements.

Another object of the invention is to provide an apparatus for producing a metal strip that is competitive in the market.

The inventors have devised, tested and practiced the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

Disclosure of Invention

The invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with the above object, the present invention provides a method of producing a metal strip, the method comprising: casting a cast product through a casting machine equipped with a crystallizer to obtain a slab, and hot rolling said slab in a rolling station to obtain metal strips having different strip thicknesses.

During casting, the caster exerts an effect of reducing the thickness of the cast product exiting the crystallizer.

According to one aspect of the invention, the method provides that the casting machine is selectively set up, in each case as a function of the strip thickness, so as to exert a varying degree of reduction in thickness on the cast product.

In particular, in the case of equal dimensions of the crystallisers, the method comprises: at least a first step of producing a first strip having a first thickness, wherein said caster applies a first reduction (first thinning) to said cast product, and a second step of producing a second strip having a second thickness, said second thickness being less than said first thickness, wherein said caster applies a second reduction to said cast product, said second reduction being different from said first reduction, said reduction being defined as the difference between the thickness of said cast product exiting said crystallizer and the thickness of said slab exiting said caster, said difference being correlated with the thickness of said cast product exiting said crystallizer.

This solution enables the adjustment of the relationship between the thickness of the slab leaving the caster and the final strip thickness, in order to improve the efficiency of the strip production plant and the quality of the strip produced.

In particular, in some applications of the invention, it is also possible to reduce the number of rolling stands of the rolling station by at least one unit, but at the same productivity as known plants. This determines the economic and efficiency advantages of the overall production facility.

The effect of reducing the thickness of the strip produced each time is partly in the casting machine and partly in the rolling station, thus increasing the efficiency and increasing the quality of the strip produced.

If the number of rolling stands of the rolling station is substantially the same as that of the known plant at the same production rate, it is in any case possible to reduce the number of rolling compressors, since the reduction of the part thickness is carried out directly by the casting machine and not only at the rolling station, as in the prior art.

This expedient makes it possible to obtain energy savings due to the reduction of the compression pressure on the slab being rolled, and to obtain a higher quality strip, since for example the profile and flatness of the strip are improved and the risk of leaving scratches on the surface of the strip is reduced.

Furthermore, the invention makes it possible to reduce maintenance interventions at least in the rolling stations.

Drawings

These and other features of the invention will become apparent from the following description of some embodiments thereof, given by way of non-limiting example with reference to the accompanying drawings, in which:

figures 1 to 9 show some possible embodiments of an apparatus for producing a metal strip for carrying out a method of the invention;

FIG. 10 graphically illustrates curves determined relative to the thickness H of the cast product exiting from the crystallizer, the curves illustrating the reduction imparted to the cast product by the caster as a function of the thickness of the strip;

FIG. 11 shows a plurality of curves determined by the thickness H of the cast product leaving the crystallizer, said curves showing the development of the reduction in the drawing unit as a function of the strip thickness;

FIG. 12 illustrates criteria for selecting a rolling mode;

figure 13 graphically illustrates further criteria for selecting a rolling mode, said criteria relating to strip thickness and capacity of plant architecture applied to one and/or other rolling modes;

FIGS. 14 and 15 are graphs graphically illustrating the relationship of nominal slab thickness (nominal slab thickness) to equipment productivity and casting speed; FIGS. 14 and 15 both indicate a casting operation of 7200 hours/year;

FIG. 16 is a graph graphically illustrating the correlation of the thickness ratio to the number of rolling stations required;

fig. 17-22 illustrate two exemplary embodiments for implementing the teachings of the present invention.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It should be understood that elements and features of one embodiment may be readily incorporated into other embodiments without further recitation.

Detailed Description

Reference will now be made in detail to the various embodiments of the invention, one or more examples of which are illustrated in the figures. Each example is provided by way of illustration of the invention and should not be construed as a limitation of the invention. For example, features illustrated or described in connection with one embodiment can be employed on or in conjunction with other embodiments to yield yet a further embodiment, as long as the features are part of one embodiment. It is to be understood that the invention is intended to embrace all such modifications and variations.

Embodiments of the present invention relate to a metal strip N produced in a production plant 10.

Fig. 2 to 9 show a plurality of possible configurations of a plant 10 for producing strip material, said plant 10 implementing the principles of the present invention.

In particular, in the following, reference will be made to fig. 1, which shows a plurality of operating members arranged reciprocally along a working line. These components shown in fig. 1 may be combined with each other to obtain one or more configurations for producing strip material, as then shown in fig. 2-9. For this purpose, the variant embodiments of the production device 10 shown in fig. 2 to 9 refer to the components of the device described with reference to fig. 1.

Said plant 10 for producing a strip N comprises at least one casting machine 11 in which liquid metal is cast in the solid state to obtain a slab B.

According to one aspect of the invention, the production plant 10 further comprises a rolling station 19 located downstream of the casting machine 11, and the rolling station 19 is configured to hot-roll the slab B to obtain a strip N.

The casting machine 11 includes at least one mold 15 equipped with a crystallizer 15a, and a cast product P passing through the entire casting machine 11 is formed in the crystallizer 15 a.

Said crystallizer 15a may comprise at least two wide plates facing each other and spaced apart, at least in a terminal section, by a determined value substantially corresponding to the thickness H of the cast product P exiting from said crystallizer 15 a.

Moreover, the plates of said crystallizer 15a have a width determined with respect to the width of the strip N to be obtained.

At the outlet of the crystallizer 15a, the cast product P has a solidified shell or skin, which enables the liquid metal to be contained even outside the crystallizer 15 a.

According to some solutions of the invention, the casting machine 11 can have thickness reducing means located downstream of the crystallizer, providing that in each case, as a function of the strip thickness, thickness reducing means are selectively provided to exert a variable degree of thickness reduction on the cast product P leaving the crystallizer 15 a.

The thickness reduction device may comprise a pre-rolling device having a plurality of rolls (rollers) and/or roll units (roll units), such as: of the stretch type described below.

According to some embodiments, the casting machine 11 comprises a pre-rolling device 16 with a plurality of rollers, hereinafter also referred to as roller units, the pre-rolling device 16 being located downstream of the mould 15 and configured to reduce the thickness of the cast product P exiting from the crystallizer 15a, while its core is still liquid or partially liquid.

According to some embodiments of the invention, the roll unit 16 has a plurality of rolls grouped into segments opposite each other and aligned along the casting axis.

The plurality of rolls are selectively moved toward and away from each other to exert a selective effect of reducing the thickness of the cast product.

An adjusting device 17 of a known type, for example hydraulic cylinders, is associated with said plurality of sectors, so as to move said plurality of rollers of said roller unit 16 towards or away from each other and to reduce the thickness of the cast product P exiting from said crystallizer 15 a.

The overall reduction in thickness undergone by the cast product P leaving the crystallizer 15a in the roll unit 16 is liquid core reduction, so that no lengthening of the material occurs.

The blank 16 leaving the roller unit 16 is fully cured and has a blank thickness SB 1.

The slab thickness SB1 obtained at the end of the liquid core pre-rolling affects the productivity of the casting machine 11 and therefore of the whole plant.

The compression performed by the roller unit 16 makes it possible to join the two half-shells in a joint (also called "contact point" (KP)) in which the cast product is completely solidified. Said KP is also considered as the terminal vertex of the liquid cone (liquid cone), which originates from the meniscus of the liquid metal in the crystallizer 15 a.

According to one aspect of the invention, the position of KP can be varied along the longitudinal extension of the roll unit 16, so as to intervene in the intensity of liquid core thickness reduction and secondary cooling intensity obtained by adjusting the segments of the roll unit 16. The position of KP is also a function of casting speed. The thickness of the cast product corresponding to KP is equal to the slab thickness SB1 leaving the roll unit 16.

According to one aspect of the invention, the slab thickness SB1 is selectively set according to the final thickness of the strip N, in particular according to the product combination produced by the plant, as will be explained more clearly hereinafter.

According to possible solutions, various known types of cooling devices (also called secondary cooling) can be associated with the roller unit 16 and configured to cool the outer surface of the slab, determining its further solidification. The cooling device may comprise a plurality of nozzles for delivering atomized water or water mixed with air (air mist). The effect of the cooling means also has an influence on the location of KP.

According to some embodiments, the caster 11 comprises a stretching unit 18 located downstream of the roller unit 16 and configured to stretch the slab B towards the rolling station 19.

The stretching unit 18 includes a plurality of pairs of stretching rollers, and the number of the plurality of pairs of stretching rollers includes 1 to 6 stretching rollers.

The rollers of each pair are disposed on opposite sides of the blank B to be stretched.

According to some embodiments, the stretching unit 18 may also be configured to roll the slab B therethrough.

By way of example, each pair of rollers or at least one of them may be associated with moving means, for example hydraulic cylinders of known type (not shown), for moving the rollers closer to or further from each other and determining a predetermined compression action on the fully solidified slab B, as described hereinafter.

According to a possible solution, the stretching unit 18 may comprise a first stretching device 18a located immediately downstream of the roller unit 16, in other words in a vertical section of the casting machine 11. According to one possible solution (possibly in combination with the previous one), the drawing unit 18 may comprise a second drawing device 18b located directly downstream of the bending section of the casting machine 11.

The presence of the first stretching means 18a is only provided in the case of vertical casting.

The presence of the second stretching means 18b is provided in the case of vertical-bending casting.

The first stretching device 18a and/or the second stretching device 18b may comprise a plurality of pairs of rollers, the number of rollers being between 1 and 3.

As mentioned above, the rolls of the drawing unit 18 are configured to perform a slight liquid core reduction on the slab B of thickness SB1, so that a real rolling determines the elongation of the material, although of a smaller amplitude. The rolling of the drawing unit 18, although light, causes a further reduction in the thickness of the slab B, which has a further thickness SB2 less than SB1, so as to reach a thinner thickness in the rolling stations 19 located downstream. Since the drawing unit 18 is located at the end of the casting machine 11, the thickness SB2 of the slab B leaving the drawing unit 18 corresponds to the thickness of the slab B leaving the casting machine.

The drawing unit 18, together with the Rolling unit and the crystallizer 15a, form an integral part of the casting machine 11, and can be defined as a "Rolling Caster" due to the Rolling action performed by the rolls.

The rolling continuous caster 11 is a caster that can perform casting of a product and rolling of a partially liquid core and a partially solid core.

The cast product P exiting from the crystallizer 15a in the casting machine 11 undergoes a reduction in overall thickness, partly liquid core and partly solid core.

According to one aspect of the invention, the profile of the reduction in thickness of the casting machine 11 can be advantageously adjusted between liquid and solid cores, according to specific production requirements.

According to a possible embodiment, the rolling station 19 comprises a roughing unit 12 configured to roll the slab B.

The roughing unit 12 may have one or more roughing stations 20.

According to a further embodiment of the invention, the rolling station 19 comprises a finishing unit (finishing unit)13, the finishing unit 13 being configured to roll a slab B and to process the slab B to its final dimensions, i.e. to define a metal strip N.

The finishing rolling unit 13 is located downstream of the rough rolling unit 12.

The finishing unit 13 may also comprise one or more finishing stations 21, each finishing station 21 being configured to roll and define the thickness SN of the strip.

According to a possible solution, a shear 26 is provided immediately downstream of the roughing unit 12, said shear 26 being configured to cut the rolled slab B and defining a bar, also called transfer bar in the section, to be subjected to a subsequent rolling to obtain the strip N.

The apparatus 10 may include at least one induction heating device, in this case one, two or three

induction heating devices

22, 23 and 34 and is configured to heat the slab B.

According to one possible solution, the plant 10 comprises a first induction heating device 22 located downstream of the casting machine 11, in this case upstream of the roughing unit 12, and configured to restore the temperature of the slab before it is introduced into the rolling station 19.

According to a possible solution, the plant 10 comprises a second induction heating device 23 located upstream of the finishing unit 13, for example between the roughing unit 12 and the finishing unit 13, and configured to increase the temperature of the bar between its introduction into the finishing unit 13.

According to a possible solution, the second induction heating device 23 is located directly downstream of the roughing unit 12.

According to a further solution, the plant 10 comprises a third induction heating device 34 arranged between the two finishing stations 21, and the third induction heating device 34 is configured to restore the temperature of the bars during finishing.

According to a further embodiment, the production plant 10 may comprise at least one heating and/or maintenance unit, in which case the two heating and/or

maintenance units

32 and 33 are configured to heat or maintain the temperature of the bar segments.

The heating and/or

maintenance units

32 and 33 may comprise heating and/or maintenance tunnel ovens which may act as accumulation buffers (accumulation buffers) for the bars when the rolling process is interrupted by an accident or a programmed roll change, thereby avoiding material and energy losses, in particular avoiding casting interruptions.

According to a possible solution, the production plant 10 comprises a first heating and/or maintenance unit 32 located immediately upstream of the rolling station 19.

According to a further embodiment, the production plant 10 comprises a second heating and/or maintenance unit 33 located between the roughing unit 12 and the finishing unit 13.

According to this embodiment, it is advantageous to provide the production plant 10 with a shearing member 35, said shearing member 35 being arranged between said casting machine 11 and said rolling station 19 and being configured to cut said slab B produced by said casting machine 11 into a plurality of segments. In case of emergency, or in case of need for maintenance (for example: replacement of rolls in the rolling station 19), said plurality of segments can then be stored and maintained at the temperature inside said first heating and/or maintenance unit 32.

According to some embodiments, the production plant 10 comprises an intermediate winding/unwinding device 29 arranged between the shears 26 and the finishing unit 13, and the intermediate winding/unwinding device 29 is configured to wind the bars cut by the shears 26 and to provide the previously wound and cut bars to the finishing unit 13.

According to a possible embodiment, the apparatus may comprise a second heating and/or maintenance unit 33 and an intermediate winding/unwinding device 29 downstream with respect to the heating unit 32.

For example, the intermediate winding/unwinding device 29 can be of the type described in the international application WO-A-2011/080300 in the name of the applicant.

According to some solutions, the intermediate winding/unwinding device 29 comprises a first unit 30 and a second unit 31, the first unit 30 and the second unit 31 alternately winding the bars received from the roughing unit 12 and unwinding the previously wound bars in order to feed them to the finishing unit 13.

In particular, when one of the two

units

30, 31 winds a bar, the

other unit

31, 30 unwinds another rough rolled bar and supplies it downstream. Such intermediate winding/unwinding devices 29 are also able to define a temporary accumulation buffer to compensate for the different operating speeds of the casting machine 11 and of the finishing unit 13. In this way, the intermediate winding/unwinding device 29 is able to absorb (abs) the downtime of the rolling mill, to perform small-scale maintenance or programmed roll replacements, or to handle small accidents/blockages, without having to interrupt the casting process and therefore without causing production losses and without having an impact on the upstream steelworks.

According to a possible solution, said intermediate winding/unwinding device 29 may comprise heating means (not shown) to heat or maintain the temperature of the bars inside.

According to a further solution of the invention, the plant 10 may comprise a cutting member 28 arranged between the roughing unit 12 and the finishing unit 13, and the cutting member 28 is configured to cut the head or tail end of the bar supplied by the roughing unit 12, in this case supplied by the intermediate winding/unwinding device 29, and sent to the finishing unit 13.

According to a further solution, a cooling unit 24 is provided between the rolling station 19 and the final winding unit 14, said cooling unit 24 being configured to cool the strip N exiting from the rolling station 19 and to allow the collection of the strip N in the final winding unit 14.

According to a further embodiment of the invention, the plant 10 comprises a final winding unit 14 of the web material N.

The final winding unit 14 may comprise winding members 25, said winding members 25 being adapted to wind the strip material N into coils (coils).

According to some embodiments, the plant 10 comprises a cutting device 27 located upstream of the final winding unit 14, said cutting device 27 being configured to cut the strip material N to suitable dimensions once a predetermined weight of the coils of strip material N is reached. The cutting device 27 may be located between the cooling unit 24 and the final winding unit 14.

With reference to fig. 2, fig. 2 shows a variant embodiment of a production plant 10, said production plant 10 comprising, in succession, the casting machine 11, the shearing member 35, the first induction heating device 22 and/or the first heating and/or maintenance unit 32, the finishing unit 13, the cooling unit 24 and the final winding unit 14 as defined above.

With reference to fig. 3, fig. 3 shows a further variant embodiment of the production plant, the production plant 10 of fig. 3 providing, in addition to the components provided by the production plant 10 of fig. 2, the rolling station 19 comprising the rough rolling unit 12, the second induction heating device 23, the second heating and/or maintenance unit 33, and the cutting member 28 upstream of the finishing rolling unit 13.

With reference to fig. 4, fig. 4 shows a further variant embodiment of the production plant 10, the production plant 10 comprising, in succession, the casting machine 11, the roughing unit, the shears 26, the second induction heating device 23, the intermediate winding/unwinding device 29, the cutting member 28, the finishing unit 13, the cooling unit 24 and the final winding unit 14, as defined above.

With reference to fig. 5, the production plant 10 comprises, in succession, the casting machine 11 as defined above, the rolling station 19 provided with the roughing unit 12, the shear 26, the second induction heating device 23, the second heating and/or maintenance unit 33, the finishing unit 13, the cooling unit 24 and the final winding unit 14.

The production facility 10 described with reference to fig. 2-5 may be selectively configured to operate in a roll-to-roll mode with the production facility 10.

With reference to fig. 6, the production plant 10 comprises, in succession, the casting machine 11 as defined above, the rolling station 19 provided with the shearing member 35, the second induction heating device 23, the second heating and/or maintenance unit 33, the finishing unit 13, the cooling unit 24, the cutting device 27 and the final winding unit 14.

The production facility 10 described with reference to fig. 6 may be configured to operate in a roll-to-roll or semi-endless mode.

With reference to fig. 7, the production plant 10 comprises, arranged in succession, the casting machine 11 as defined above, the rolling station 19 provided with the roughing unit 12, the shearing machine 26, the second induction heating device 23, the finishing unit 13, the third induction heating device 34 arranged between a plurality of finishing stations 21, the cooling unit 24, the cutting device 27 and the final winding unit 14.

The production facility 10 described with reference to fig. 7 may be configured to operate in a headless mode.

With reference to fig. 8, the production plant 10 comprises, arranged in succession, the casting machine 11 as defined above, the rolling station 19 provided with the roughing unit 12, the shears 26, the second induction heating device 23, the intermediate winding/unwinding device 29, the cutting member 28, the finishing unit 13, the third induction heating device 34 arranged between a plurality of finishing stations 21, the cooling unit 24, the cutting device 27 and the final winding unit 14.

The production facility 10 described with reference to fig. 8 may be configured to operate in a roll-to-roll or headless mode.

With reference to fig. 9, the production plant 10 comprises, arranged in succession, the casting machine 11 as defined above, the rolling station 19 provided with the shearing members 35, the first induction heating device 22, the first heating and/or maintenance unit 32, the roughing unit 12, the shears 26, the second induction heating device 23, the finishing unit 13, the third induction heating device 34 arranged between a plurality of finishing stations 21, the cooling unit 24, the cutting device 27 and the final winding unit 14.

The production facility 10 described with reference to fig. 9 may be configured to operate in a roll-to-roll or semi-endless or endless mode.

The embodiments of the plant 10 described with reference to fig. 2 to 9 define a series of examples of production plant architecture, with which the end user can select, in an optimized manner, the production rate, the product combination and the type of steel to be produced, also known as "steel grades".

According to one aspect of the invention, a method of producing a metal strip N comprises: casting a cast product P by at least the casting machine 11 to obtain a slab B, and hot rolling the slab B in the rolling station 19 to obtain a metal strip N.

According to one aspect of the invention, during casting, the casting machine 11 exerts an action of reducing the thickness of the cast product P leaving the crystallizer 15 a.

According to another aspect of the invention, for each thickness dimension of the strip N produced, the casting machine 11 is selectively set to exert a different action to reduce the thickness of the cast product P exiting from the crystallizer 15 a.

In particular, in each case the thickness of the slab B produced by the caster 11 is adjusted at least as a function of the final thickness of the strip N to be obtained and of the type or combination of products possibly to be obtained.

This solution makes it possible to reduce the compression exerted in said rolling station 19, thus reducing the rolling power required, reducing the wear of the rolling rolls and, in some cases, also the number of at least one rolling stand with respect to known plants having the same overall productivity.

By way of example only, the same size crystallizer 15a may be provided, the method comprising a first step of producing a first strip having a first thickness SN ', wherein the caster 11 applies a first reduction TAU a' to the cast product P exiting the crystallizer 15a, and a second step of producing a second strip having a second thickness SN ", which is less than the first thickness SN ', wherein the caster 11 applies a second reduction TAU a", which is different from the first reduction TAU a', to the cast product P exiting the crystallizer 15 a.

According to one solution, said first reduction ratio TAU a' is smaller than said second reduction ratio TAU a ".

The reduction ratio TAU is defined as the difference between the thickness H of the cast product P exiting the crystallizer 15a and the thickness SB2 of the slab exiting the caster 11, which is associated with the thickness H of the cast product P exiting the crystallizer 15 a.

According to a possible solution of the invention, the inventors have determined that the casting machine 11 is selectively set to exert an action of reducing the thickness of the cast product P, said action being defined by the formula:

TAUA＝K·A·H^-1·e^a·SN

wherein:

k is a variable parameter between 0.8 and 1.1;

a is a factor approximately equal to 4689;

h is the thickness of the cast product P exiting from the crystallizer 15a, i.e. the thickness of the crystallizer 15 a;

a is a coefficient equal to-0.37;

SN is the thickness of the strip obtained at the end of rolling.

The TAU a derived from the formula is a percentage value, and by way of example only, the TAU a may typically be a value between 2% and 75%.

Fig. 10 shows some examples of curves determined in relation to the thickness H of the cast product P, which show the development of TAU a in relation to the strip thickness SN.

This formula enables to optimize the setting of the casting machine 11 in relation to the thickness of the crystallizer 15a and the strip thickness SN, so as to achieve an efficient operation of the whole production plant, as described above.

According to a possible solution of the invention, the casting machine 11 is configured to apply:

(i) the action of reducing the thickness of the cast product P by liquid core pre-rolling using a roll unit 16, referred to as the reduction ratio TAU 1;

(ii) the action of reducing the thickness of the cast product P by using the action of the drawing unit 18, referred to in the drawing unit as the reduction ratio TAU 2.

The thickness reduction via the stretching unit 18 is optional.

Therefore, the reduction ratio TAU a is given by a combination of the reduction ratios TAU1 and TAU 2.

The reduction ratio TAU1 in the roll unit is defined as the difference between the thickness H of the cast product P exiting the crystallizer 15a and the thickness SB1 of the slab exiting the roll unit 16, which is associated with the thickness H of the cast product P exiting the crystallizer 15 a.

The reduction ratio TAU2 in the stretching unit is defined as the difference between the thickness SB1 of the blank leaving the roller unit 16 and the thickness SB2 of the blank leaving the stretching unit 18, which is correlated to the thickness SB1 of the blank leaving the roller unit 16.

According to a possible solution of the invention, the applicant has determined that the drawing unit 18 is selectively set to exert on the solid cast product P an action of reducing the thickness SB1, said action being defined by the formula:

TAU2＝Q·(-B·H^b·lnSN+C·H^c)

wherein:

q is a variable parameter between 0.8 and 1.1;

b is a first coefficient equal to 10928;

h is the thickness of the cast product P leaving the crystallizer 15a as defined above;

b is a second coefficient equal to-1.659;

SN is the thickness of the strip;

c is a third coefficient equal to 10648;

c is a fourth coefficient equal to-1.596.

According to a possible solution, the solid reduction of the thickness of the cast product P is suitable for strips having a thickness SN between 0.6 mm and 3.5 mm. In fact, for strip thicknesses SN of these dimensions, the action of liquid core reduction is relatively high in order to reduce the starting slab to the maximum from the outset, so that the further action of solid core reduction of thickness exerted by the drawing unit 18, in combination with the action of liquid core reduction, is advantageous.

Furthermore, the solid core rolling action exerted by the drawing unit 18 enables an increase in the productivity of the strip, thus being particularly advantageous for thin strip thicknesses.

Fig. 11 shows an example of a plurality of curves determined from the thickness H of the cast product P leaving the crystallizer, said curves showing the development of TAU2 as a function of the strip thickness SN.

The reduction ratio of the rough rolling unit 12 is referred to as TAU3 and is defined as the difference between the thickness SB2 of the slab B upstream of the rough rolling unit 12 and the thickness of the slab B downstream of the rough rolling unit 12, which is associated with the thickness SB2 of the slab B upstream of the rough rolling unit 12.

The reduction ratio at the finishing unit 21 is called TAU4 and is defined as the difference between the thickness of the slab B upstream of the finishing unit 21 and the obtained strip thickness SN, which is correlated to the thickness of the slab B upstream of the finishing unit 21.

The total reduction of the rolling station 19 is defined as tau ub and as the difference between the slab thickness SB2 exiting from said casting machine 11 and the strip thickness N obtained, correlated with the slab thickness SB2 provided by the casting machine 11. The total reduction ratio TAUB of the rolling station 19 can also be defined as the combination of the reduction ratios TAU3 and TAU4 of the roughing unit 12 and the finishing unit 13.

According to a further aspect of the invention, a method of producing a metal strip comprises providing by a customer design data comprising at least:

productivity PR, for example: annual production rate of production facility 10;

a series of thicknesses RS and average widths LN of the strip that said production plant 10 must produce;

the respective profile of the production rate as a function of the thickness of the strip N produced;

the types of products that can be cast with a casting machine, i.e. the steel grades mentioned above;

the respective distribution of the production rates in relation to the type of castable product;

the above set of parameters defines the so-called "product mix" of the plant, i.e. the kind of product that the production plant 10 will have to produce, and its dimensions are determined according to said kind in order to achieve the object of the invention.

The thickness range RS is provided to determine the minimum thickness SMN and the maximum thickness SMAX of the strip material obtainable.

In some embodiments of the invention, the rolling method provides for determining the type of optimal rolling mode for slab B according to the product mix required by the customer.

The rolling mode of the slab B is selected from modes of no head, semi-no head and coil to coil (coil to coil).

Fig. 12 shows a diagram of criteria for selecting one of the above rolling modes, at least as a function of the strip thickness SN and the castable steel grade.

In general, in order to enable the production plant 10 to use a plurality of operating modes, the rolling mode carried out in each case will be determined by optimizing the operating conditions of the plant, on the basis of economic assessments (process energy consumption and production) and the quality required of the final product (dimensional tolerances and mechanical characteristics of the strip).

By way of example only, it may be provided that if a thinner thickness is prevalent in the product mix (excluding special types of steel, e.g. peritectic steel that are difficult to cast and require low casting speeds), the headless rolling mode is selected and therefore one of the various plant layouts shown in fig. 7, 8 or 9 may be selected.

If thinner thicknesses are prevalent in the product assembly and a particular type of steel is to be cast, roll-to-roll and semi-endless rolling modes are generally chosen, so one of the plant layouts shown in fig. 6 and 9 can be chosen. Both roll-to-roll and semi-endless rolling modes are capable of casting special steel at low speeds, so the casting process is not limited by the rolling process. The semi-headless mode is suitable for thin and ultra-thin thicknesses of the web material N, for example, between 0.8 mm and 1.4 mm. For strip thicknesses greater than 1.4 mm, a roll-to-roll mode is preferred.

Figure 13 shows in graphical form further criteria for selecting the rolling mode, which criteria are related to the thickness of the strip and the capacity of the layout of the plant to select one and/or other of the various rolling modes described above.

By way of example only, with reference to fig. 13, if the constructive layout of fig. 2 to 5 is selected, the apparatus operates in a roll-to-roll mode for strip having a thickness between about 1.2 mm and about 12 mm, if the constructive layout of fig. 9 is selected, the apparatus operates in a headless mode for strip having a thickness between about 0.6 mm and about 1 mm, in a semi-headless mode for strip having a thickness between about 1 mm and about 2 mm, and in a roll-to-roll mode for strip having a thickness between about 2 mm and about 12 mm.

According to a further solution, the production method is used to set a casting speed VC selected from a value between 4.5 and 6 meters/minute.

In particular, for the types of steel that are difficult to cast (e.g., API, peritectic steel, and Cowden steel), it is advantageous to set a lower casting speed, such as: the casting speed was between 4.5 m/min and 5 m/min. For easier casting steels, for example: low carbon, medium carbon, HSLA, DP, CP, HC, MnB steels, set higher casting speeds, for example: the casting speed was between 5 m/min and 6 m/min.

In the same way, the choice of casting speed VC can also be defined in relation to the chosen rolling mode, i.e. with a relatively low casting speed for the roll-to-roll and semi-endless mode and a higher casting speed for the endless mode.

The production method is then used to determine the value of the nominal slab thickness SBN, which is related to the casting speed VC and to the average strip width LN, so that the production rate PR can be reached.

The nominal slab thickness SBN, which corresponds to the average of the slab thicknesses (variable) weighted (average) under the liquid core pressure of the production per hour, can also be interpreted as the constant thickness of the equivalent slab (equivalent slab) for the same overall production of a given product combination.

According to a possible solution, the nominal slab thickness SBN is defined by the following formula:

SBN PR/operation time/(VC LN PS)

Here and in the following description and claims, the operating time refers to the running time, i.e. the running time of the device in the calendar year (minus the production interruption time due to maintenance, accidents, etc.).

Wherein PS is the specific gravity of the steel, usually about 7.8kg/dm³。

With reference to fig. 14 and 15, the relationship between the nominal slab thickness SBN and the annual productivity PR of the plant and the casting speed VC is shown graphically.

In particular, fig. 14 refers to a blank width of about 1300 mm, while fig. 15 refers to a blank thickness of about 1400 mm.

According to one possible embodiment of the invention, the method comprises: the thickness H of the cast product P leaving the crystallizer 15a is determined, i.e. the distance between the plates of the crystallizer 15a is determined in correspondence with the outlet portion of the latter. This thickness H of the cast product P is the thickness that the customer defines for the entire product combination.

In a possible embodiment of the invention, the thickness H of the cast product P leaving the crystallizer 15a is between 10 mm and 15 mm greater than the nominal slab thickness SBN.

The method is then provided for determining a thickness ratio RSP applied by the rolling station 19 and calculated as the ratio between the values of the plurality of slab thicknesses SB2 entering the rolling station 19, the minimum thickness SMIN of the strip material N being obtainable when working a strip material N of minimum thickness SMIN.

When processing the strip N of minimum width SMIN, the value of the slab thickness SB2 entering the rolling station 19 is calculated as the thickness H of the cast product P exiting the crystallizer 15a minus the maximum reduction imposed by the caster. According to one possible solution, the maximum reduction caused by the casting machine 11 is at least equal to 31 mm or more.

Subsequently, the method is used to determine the number of rolling stands of the rolling station 19 related to the thickness ratio.

When the thickness ratio is between 4 and 12, four rolling stands are provided.

When the thickness ratio is between 12 and 21, five rolling stands are provided.

When the thickness ratio is between 21 and 52, six rolling stands are provided.

When the thickness ratio is between 52 and 110, seven rolling stands are provided.

The relationship between the number of rolling stands and the thickness ratio is shown in the graph of fig. 16.

The number of rolling stands of the rolling station 19 is the sum of the number of finishing rolling stations 21 and the number of roughing rolling stations 20.

Subsequently, the method is provided for setting a mode for distributing liquid core pressure and solid core pressure (solid core reduction) in the casting machine 11 by the roller unit 16 and the drawing unit 18 on the slab B exiting from the crystallizer 15a with respect to the final thickness of the strip N.

This pattern of thickness reduction, which distributes the cast product P, can be determined by the TAU a and TAU2 formulas defined above.

According to a further possible solution, the casting machine 11 can be set to perform a reduction in thickness of the cast product P equal to 5 mm for a strip thickness equal to the maximum thickness SMAX and between 25 and 31 mm for a strip thickness equal to the minimum thickness SMIN.

According to one possible solution, the roller unit 16 can perform a maximum hydrocore pressure RCLMAX of about 25 mm. According to one possible solution, the roller unit 16 can perform a minimum hydrocore pressure RCLMIN of about 5 mm. This reduction gives the cast metal product P a higher quality.

According to one solution of the invention, the stretching unit 18 can perform a maximum solid reduction of at least 7 mm, while the minimum reduction is 0.

In particular, each pair of rollers of the stretching unit 18 can achieve a compression between 0.5 mm and 1.5 mm, when required.

According to various possible embodiments of the method, if a production mode of the reel-to-reel type is set and a winding/unwinding device 29 is used, the number of roughing stations 20 is determined so as to provide bars having a thickness comprised between 8 and 25 mm when entering the winding/unwinding device 29. A thickness of the bars of less than 8 mm would lead to problems of conveying and introducing the bars into the winding/unwinding device, whereas a thickness of the bars of more than 25 mm would lead to difficulties of handling and/or sizing, possibly generating surface defects on the bars themselves.

According to a further possible embodiment of the method, if a production mode of the reel-to-reel type has been set and a heating unit 33 is used, the number of roughing stations 20 can be determined so as to provide bars with a thickness greater than or equal to 30 mm when entering the heating unit. Dimensions smaller than these thickness values require the use of very long heating units, which are difficult to manage and uneconomical.

According to one possible solution, the number of finishing stations 21 is at least 2.

Example (c):

with reference to fig. 17 to 22, examples of two embodiments of the teachings of the present invention will now be described.

In particular, with reference to figures 17 to 19, in the first case, the productivity PR is about 1.1 metric tonnes/year, the thickness range RS is between 1.2 mm and 8 mm, and the desired average width LN of the strip is about 1300 mm.

With reference to figures 20 to 22, on the other hand, in the second case, the productivity PR is about 1.4 tonnes/year, the thickness range RS is between 0.8 mm and 3 mm, and the desired average width LN of the strip is about 1400 mm.

With reference to the tables shown in fig. 17 and 20, a comparison of productivity versus distribution of product combinations in the case of traditional casting and casting with reduced thickness can be observed in at least the last four columns on the right according to the teachings of the present invention.

The product mix and annual output values (see

columns

11 and 12 of the table) are parameters required by the customer and are set according to the requirements of the customer for using the equipment.

Meanwhile, referring to the tables shown in fig. 17 and 20, it can be observed that in the sixth column, the slab thickness SB2 exiting from the casting machine 11 is not a constant value as the strip thickness changes, but a value that decreases as the strip thickness decreases. In conventional or known techniques, on the other hand, the slab thickness SBN leaving the caster is always the same as the varying thickness of the strip, as shown in the second column from the left. Fig. 18 and 21 also graphically illustrate this consideration.

This variation of the thickness of the slab with respect to the thickness of the final strip is obtained by the fact that: the casting machine 11 applies a liquid core reduction RCL of a thickness to the cast product, as shown in the third column of the table of fig. 17 and 20.

The table also shows the thickness reductions performed by means of the drawing unit 18 (column five), the roughing unit 12 (column seven) and the finishing unit 13 (column ninth), and how these operations are distributed according to the final strip thickness to be obtained.

On the other hand, in the case of known conventional casting and in the case of casting with variable thickness reduction according to the invention, fig. 19 and 22 graphically illustrate the relationship between the distribution of the hourly productivity (route productivity) of the plant and the strip thickness to be obtained.

In particular, in fig. 19 and 22, it should be noted that in the case of the known traditional casting, the hourly production rate remains constant for any strip thickness to be obtained, whereas in the case of said casting according to the invention, the hourly production rate varies with respect to said strip thickness to be obtained.

From the analysis of fig. 19 and 22 it can be observed that the present invention has a lower productivity for low strip thickness values compared to the conventional solution and a higher productivity for high strip thickness values compared to the conventional solution. Overall, however, the annual productivity of the plant is equal in the case of traditional casting and of casting according to the invention, and in the solution according to the invention, the above-mentioned advantages are obtained compared with known solutions.

With reference to the first case illustrated in fig. 17 to 19, we will now describe a mode of selection of the type of equipment and of the number of rolling stands of the rolling station 19.

In particular, according to the range of variable strip thicknesses between 1.2 and 8 mm and the diagram of fig. 12, it is advantageous to use a layout of the plant that enables a roll-to-roll rolling mode.

Then, a casting speed set at about 5.5 m/min is provided, corresponding to a nominal slab thickness SBN of about 45 mm, for an average strip width LN of 1300 mm and a productivity of 1.1 metric tons/year, as shown in fig. 14.

From the SBN value, it is possible to determine the thickness H of the cast product P, said thickness being from 10 to 15 mm greater than the nominal slab SBN, in this case the nominal slab SBN being equal to 55 mm, as shown in the table in fig. 17.

The nominal slab SBN is then provided to determine the thickness reduction to be applied by the rolling station 19.

When a minimum thickness is to be worked, the slab thickness SB2 entering the rolling station 19 is 24 mm.

The rolling station 19 therefore has a thickness ratio RSP of 24/1.2 to 20.

Referring to fig. 16, it can be observed that the number of frames is equal to 5, corresponding to this thickness ratio.

On the other hand, with reference to conventional casting, the conventional thickness ratio is given by the ratio between the nominal slab thickness SBN and the minimum thickness SMIN of the strip, in this case 45/1.2-37.5. Referring to fig. 16, the number of frames equal to 6 corresponds to this thickness ratio. From this example it can be observed how the number of rolling stands can be reduced by one unit with respect to the traditional production model, with the same annual productivity of the plant.

With reference to the second case illustrated in fig. 20 to 22, we will now describe another mode of selecting the type of plant and the number of rolling stands of the rolling station 19.

In particular, according to the variable strip thickness range between 0.8 mm and 3.0 mm and the diagram of fig. 12, it is advantageous to use a layout of the plant that enables the endless rolling mode.

A casting speed of about 6.0 m/min, an average width LN for 1400 mm and a production rate of 1.4 metric tons/year, corresponding to a target scale slab thickness of about 50 mm, can then be set, as can be seen from the diagram of fig. 15.

From this SBN value, the thickness H of the cast product P can be determined, said thickness being from 10 mm to 15 mm greater than the nominal slab SBN, in this case the nominal slab SBN being equal to 65 mm, as shown in the table in fig. 20.

When a minimum thickness is machined, the slab thickness SB2 entering the rolling station 19 is 34 mm.

The thickness ratio RSP of the rolling station 19 is therefore 34/0.8-42.5.

Referring to fig. 16, it can be observed that the number of frames is equal to 6, corresponding to this thickness ratio.

On the other hand, with reference to conventional casting, the conventional thickness ratio is given by the ratio between the nominal slab thickness SBN and the minimum thickness SMIN of the strip, in this case 50/0.8-62.5. Referring to fig. 16, the number of frames equal to 7 corresponds to this thickness ratio. From this example it can be observed how the number of rolling stands can be reduced by one unit with respect to the traditional production model, with the same annual productivity of the plant.

Clearly, modifications and/or additions of parts may be made to the method for producing metal strip and to the production plant for carrying out the method as described heretofore, without departing from the field and scope of the present invention.

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

In the following claims, references made between parentheses are intended for the sole purpose of facilitating reading and they should not be construed as limiting the claim area.

Claims

1. A method of producing a metal strip (N), the method comprising: -casting a cast product (P) through a casting machine (11) equipped with a crystallizer (15a) to obtain a slab (B), and-hot rolling said slab (B) in a rolling station (19) to obtain metal strips (N) having different strip thicknesses (SN), wherein during casting said casting machine (11) exerts an effect of reducing the thickness of said cast product (P) exiting said crystallizer (15a), characterized in that: -the casting machine (11) is selectively set, as a function of the strip thickness (SN), to exert different actions to reduce the thickness of the cast product (P), i.e. at least a first step of producing a first strip having a first thickness (SN ') given a crystallizer (15a) of the same size, wherein the casting machine (11) exerts a first reduction (TAU A') on the cast product (P), and at least a second step of producing a second strip having a second thickness (SN ') less than the first thickness (SN'), wherein the casting machine (11) exerts a second reduction (TAU A ") on the cast product (P), said second reduction (TAU A ') being different from the first reduction (TAU A'), the reduction ratio is defined as the difference between the thickness (H) of the cast product (P) leaving the crystallizer (15a) and the thickness (SB2) of the slab leaving the casting machine (11), said difference being correlated to the thickness (H) of the cast product (P) leaving the crystallizer (15 a).

2. The method of claim 1, wherein: the first reduction ratio (TAU A ') is less than the second reduction ratio (TAU A').

3. The method of any of the preceding claims, wherein: the casting machine (11) is selectively set to exert an action of reducing the thickness of the cast product (P) leaving the crystallizer (15a), said action being defined by the formula:

TAUA＝K·A·H^-1·e^a·SN

wherein:

k is a variable parameter between 0.8 and 1.1;

a is a factor approximately equal to 4689;

h is the thickness of the cast product (P) exiting from the crystallizer (15 a);

a is a coefficient equal to-0.37;

SN is the thickness of the strip obtained at the end of rolling.

4. The method of any of the preceding claims, wherein: the casting machine (11) comprises a pre-rolling device (16), the pre-rolling device (16) having a plurality of rolls exerting, through pre-rolling with liquid core, an effect of reducing the thickness of the cast product (P) leaving the crystallizer (15 a).

5. The method of claim 4, wherein: the pre-rolling device (16) with rolls has opposite rolls between which the cast product (P) passes and which are selectively moved towards and away from each other so as to exert a selective liquid core reduction action on the thickness of the cast product (P).

6. The method of claim 4 or 5, wherein: the casting machine (11) comprises a drawing unit (18), said drawing unit (18) exerting an effect of reducing the thickness of the cast product (P) leaving the pre-rolling device (16) with the rolls, by solid-core rolling of the cast product (P).

7. The method of claim 6, wherein: the drawing unit (18) is selectively set to exert an effect of reducing the thickness on the solid cast product (P), the effect being defined by the formula:

TAU2＝Q·(-B·H^b·lnSN+C·H^c)

wherein:

q is a variable parameter between 0.8 and 1.1;

b is a first coefficient equal to 10928;

h is the thickness of the cast product (P) leaving the crystallizer (15 a);

b is a second coefficient equal to-1.659;

SN is the thickness of the strip;

c is a third coefficient equal to 10648;

c is a fourth coefficient equal to-1.596.

8. The method of claim 6 or 7, wherein: the reduction of the thickness of the solid cast product (P) is suitable for strip thicknesses (SN) between 0.6 mm and 3.5 mm.

9. The method of any of the preceding claims, wherein: the method comprises determining the thickness (H) of the cast product leaving the crystallizer (15a), said thickness being a number between 10 mm and 15 mm greater than the thickness (SBN) of a nominal slab, said nominal slab thickness (SBN) being defined by the formula SBN PR/operating time/(VC LN PS), where PR is the production rate of the plant, VC is a casting speed chosen between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific gravity of the steel.

10. The method of any of the preceding claims, wherein: the method comprises determining a thickness Ratio (RSP) applied by the rolling station (19), calculated as the ratio between the value of the thickness (SB2) of the slab entering the rolling station (19) and the value of the minimum thickness (SMIN) of the strip material (N) when working the minimum thickness (SMIN) of the strip material (N).

11. The method of claim 10, wherein: the method comprises the following steps: -determining the number of rolling stands of said rolling station (19), wherein:

when the thickness ratio is between 4 and 12, four rolling stands are provided;

when the thickness ratio is between 12 and 21, five rolling stands are provided;

when the thickness ratio is between 21 and 52, six rolling stands are provided;

12. An apparatus for producing metal strips (N), comprising a casting machine (11) with a crystallizer (15a), said casting machine (11) being configured to cast a cast product (P) to obtain a slab (B), and a rolling station (19) of said slab (B) to obtain metal strips (N) having different strip thicknesses (SN), wherein during casting said casting machine (11) is configured to exert an effect of reducing the thickness of said cast product (P) exiting said crystallizer (15a), characterized in that: -said casting machine (11) is selectively configured to exert different actions to reduce the thickness of the cast product (P) when the strip thickness (SN) varies, so as to exert, given a crystallizer (15a) of the same size, at least a first step of producing a first strip having a first thickness (SN '), wherein said casting machine (11) exerts a first reduction ratio (TAU A') on the cast product (P), and a second step of producing a second strip having a second thickness (SN ') less than said first thickness (SN'), wherein said casting machine (11) exerts a second reduction ratio (TAU A ") on the cast product (P), said second reduction ratio (TAU A ') being different from said first reduction ratio (TAU A'), the reduction ratio is defined as the difference between the thickness (H) of the cast product (P) leaving the crystallizer (15a) and the thickness (SB2) of the slab leaving the casting machine (11), said difference being correlated to the thickness (H) of the cast product (P) leaving the crystallizer (15 a).