EP0466570A1 - Reversible rolling method - Google Patents

Abstract

The subject of the invention is a method for rolling a flat product (5) by means of successive passes in a reversing rolling mill, alternately in one direction and then in the other. According to the invention, the product (5) having a substantially uniform thickness (eo) in the unprocessed state, the rolls (2, 2'), for the first starting pass (P1), are given a spacing (e1) which is less than (eo), determining an angle of attack (A1) which is small enough to prevent an engagement refusal and, during this first pass (P1), the spacing between the rolls (2, 2') is reduced to a value (e2) such that the total reduction in thickness (eo - e2) remains compatible with the maximum power and force of the rolling mill, then, for the second pass (P2), the work rolls (2, 2') are given a spacing (e3) such that the angle of attack (A2) is small enough to avoid an engagement refusal and, during this second pass (P2), the spacing between the rolls is reduced to a value (e4) which is compatible with the maximum power and force of the rolling mill, and so on. The invention applies especially to the rolling of metal sheets. <IMAGE>

Description

The invention relates to a method of rolling a flat product in a reversible rolling mill. The invention applies in particular to the hot rolling of aluminum but can also be used for other non-ferrous metals and, even, under certain conditions, for ferrous metals such as steel.

It is known that hot rolling can advantageously be carried out in a reversible manner in a rolling mill comprising a single cage associated with means for controlling the passage of the laminated product, alternately in one direction then in the other.

In general, the rolling mill comprises, in a quarto arrangement, two working rolls associated with two support rolls. Intermediate cyclinders can also be interposed between the support cylinders and the working cylinders in a so-called sexto assembly. The set of cylinders is placed between the two uprights of a rigid cage. Each cylinder is carried by two chocks slidably mounted in windows provided on the two uprights of the cage and a clamping force is applied between the two support cylinders which determines the rolling of the product, for example by means of two jacks mounted on the cage and bearing, respectively, on the two chocks of a support cylinder, the other being blocked.

The means for controlling the passage of the product between the working rolls, alternately in one direction and then in the other, may consist, for example, of two roller tables placed on either side of the cage. Before rolling, the product is reheated in an oven placed next to the cage.

Such reversible rolling mills can be used, for example, as trimmers in a band train or in sheet metal from aluminum or steel.

The rolling is carried out from a blank such as a bloom or a slab having a significant thickness. This can, for example, be 600 mm in the case of aluminum and 250 mm in the case of steel.

In this type of rolling mill, rolling is carried out by successive passes in one direction and then in the other, performing, with each pass, a reduction in thickness, the relative importance of which depends on the characteristics of the product such as the material of the metal. , its temperature and its thickness.

Generally, in a rolling process, the product has, at the entry of the cage, a thickness greater than the spacing of the working rolls which therefore tend to crush it by producing a certain reduction in thickness . The metal is thus applied to a circular sector of each cylinder lying between two horizontal planes corresponding to the external face of the product respectively at the inlet and at the outlet of the rolling mill. The pinching of the product between the two cylinders determines its progress, at least one of the cylinders being driven in rotation. A certain pinching of the product is necessary to allow its entrainment.

It is possible to define, at the entrance to the rolling mill, an angle of attack A corresponding to the dihedral limited by the external face of the product and the plane tangent to the cylinder of the level where the latter comes into contact with the product. The value of the angle of attack is therefore a function of the diameter of the cylinder and of the reduction in thickness produced, that is to say of the difference between the thickness of the product before it enters the rolling mill and the width of the air gap existing between the two working rolls.

During rolling, thanks to the friction which is exerted between the working rolls and the product on the surface of the two cylindrical sectors, the drive is carried out without difficulty insofar as the reduction in thickness is compatible with the torque and the force that can be exerted on the cylinders. On the other hand, when the product is engaged, the friction is exerted only on the two lateral edges which come into contact respectively with the two cylinders and it is understood that the engagement cannot occur if the angle A is too important.

Given the lubrication conditions, the diameter of the working rolls which must remain fairly reduced and their surface condition, it is therefore necessary to limit the reduction in thickness produced on each pass to avoid a "refusal of engagement". Generally, the reduction in thickness thus limited for geometrical reasons is less than that which could theoretically have been achieved given the available rolling power and this results in an increase in the number of passes required and, consequently, a decrease in the productivity of the rolling mill.

Furthermore, to avoid shocks, the speed of rotation of the rolls is reduced when the product is introduced and then accelerated, after engagement, to come to the normal rolling speed. This results in a sudden increase in dynamic loads and the torque which can cause overheating and even breakage of the mechanism due to inertia.

The object of the invention is to remedy all of these drawbacks as much as possible by means of a new process which makes it possible, with each pass, to achieve the optimal reduction in thickness, while avoiding shocks and refusals of engagement. .

According to the invention, the product having a substantially uniform gross thickness e₀, the working cylinder is given, for the first start pass P₁, a spacing e₁ less than e₂ determining an angle of attack A₁ sufficiently reduced to avoid refusal of engagement and, after engagement, the spacing of the rolls is reduced to a value e₂ such that the total reduction in thickness e₀ - e₂ remains compatible with the power and the maximum force of the rolling mill, then, for the second pass P₂, the working cylinders are given a spacing e₃ such that the difference e₂ - e₃ determines an angle of attack A₂ sufficiently reduced to avoid a refusal of engagement and, after the engagement of the product, the spacing of the cylinders up to a value e₄ determined so that the total reduction in thickness e₁ - e₄ is as large as possible while remaining compatible with the maximum power and force of the rolling mill and so on, the spacing of the working rolls being first adjusted, at the start of each pass P _n , to a value e _2n-1 determining an angle of attack A _n sufficiently reduced to avoid a refusal of engagement, then decreased after engagement of the product to a value e _2n determining a total reduction in thickness e _2n-3 - e _2n optimal and remaining compatible with the maximum power and force of the rolling mill.

The thickness reduction is thus continued in two stages for each pass, as long as the thickness at the end of a pass risks determining a refusal of engagement for a reduction in the spacing of the working rolls on the next pass compatible with the rolling power and the rolling is then terminated in a normal manner.

The adjustment at each pass of the spacing of the cylinders will be carried out automatically by means of an automatic regulation system of the clamping force associated with a mathematical model programmed so as to calculate, at each pass, the reduction in thickness at perform in two stages, depending on the available torque, taking into account the mechanical and dimensional characteristics of the rolling mill and the product and the nature of the rolled metal.

To this end, the mathematical model is programmed so as to calculate, as a function of the foreseeable state of the product on each pass, taking into account the thickness reached in the previous pass and the number of passes previously carried out, the maximum reduction d possible thickness and tightening of the cylinders necessary for training without risk of refusal of engagement and that, at each pass P _n , the product to be laminated having, over most of its length, a thickness e _2n-2 and, on its tail, a thickness e _2n-3 corresponding to the engagement in the previous pass P _n-1 , the mathematical model determines, first of all, by taking into account the foreseeable physical and dimensional characteristics of the product during said pass P _n and capacities of the rolling mill, the rolling thickness e _2n during said pass P _n making it possible to obtain a maximum thickness reduction e _2n-3 - e _2n remaining compatible with the available power and the possible effort, and the spacing e _2n-1 of the cylinders allowing the introduction of the head of the strip without refusal of engagement, and the regulation system controls the introduction of the strip by adjusting the spacing of the cylinders to the engagement value e _2n-1 and, after the engagement of the head of the strip, controls the tightening of the cylinders to the calculated spacing e _2n and the change to speed rolling, the spacing e _2n of the rollers being maintained until the end of said pass P _n .

The invention will be better understood from the following description of a particular embodiment given by way of example, with reference to the accompanying drawings.

Figure 1 shows schematically, in elevation, a quarto rolling mill.

Figure 2 shows the rolling process during the first pass, in two successive diagrams 2a, 2b.

Figure 2 shows the rolling process during the second pass, in two successive diagrams 2a, 2b.

Figure 4 shows the process during a pass P _n .

Figure 5 is a flow diagram of the regulatory process.

In Figure 1, there is shown schematically a conventional quarto type rolling mill comprising a cage 1 consisting of two spaced apart uprights 11 provided with windows 13 and between which are placed four cylinders, respectively two working cylinders 2 and 2 ′ and two cylinders d 'support 3 and 3 ′. Each cylinder is carried at its ends by bearings mounted in chocks, respectively 21, 21 ′, 31, 31 ′, which slide along vertical guide faces 12 formed along the windows 13. As is well known, the chocks 21, 21 ′, working cylinders 2, 2 ′, are guided along the lateral faces of two hydraulic blocks 14, 14 ′, fixed on the faces 12, 12 ′, of each window 13 and in which are housed jacks making it possible to exert on the chocks 21, 21 ′, efforts of bending of the working rolls 2, 2 ′.

The cage is also provided with means for clamping the cylinders capable of clamping under load, for example hydraulic cylinders 4, which bear on each side on the chocks 31 of the support cylinder 3, the chocks 31 ′ of the other support cylinder 3 ′ resting on fixed stops. The jacks 4 thus exert, in the vertical plane P passing through the axes of the cylinders, a clamping force which determines a bringing together of the two working cylinders 2, 2 ′.

The rolling technique, which has been used since the beginnings of the steel industry, has been continuously improved, but particularly in recent years. Of course, this technique is suitable for different working conditions, in particular the nature of the metal and the dimensions of the product to be laminated, in particular the thickness that one wishes to obtain. However, the arrangement which we have just described is found in most rolling mills which can differ in the number and dimensions of the rolls as well as in the various ancillary devices.

For example, to ensure good flatness of the rolled product while avoiding defects which result from the deformation of the rolls and from a non-uniform distribution of the stresses, various arrangements can be used such as the bending of the cylinders, already mentioned, or the adjustment of the profile of the support cylinders.

As indicated, the invention applies especially to a hot rolling mill of the reversible type used for the operation called "roughing". In such a rolling mill, the product 5 passes between the working rolls 2, 2 ′, alternately in one direction then in the other, that is to say with reference to FIG. 1, from left to right then from right to left and so on, the thickness reduction being carried out progressively by successive passes. For this purpose, the cage 1 can be placed between two roller tables of the conventional type and which have therefore not been shown in the drawing.

In general, the operation of the whole rolling mill and of the related devices is controlled and controlled by a regulation system 6 associated with a computer 60, which performs an automatic adjustment of the thickness of the product during rolling while taking account for all the mechanical and dimensional characteristics of the rolling mill.

The regulation system 6 uses known means which need not be described in detail. This is why FIG. 1 only shows, by way of example, an installation of this type equipped with a regulation system 6, 60, making it possible to adjust the hydraulic flow rate of supply to the jack at its inlet 41 according to the indications given by a measuring device 61 which is associated with the chock 31 of the support cylinder 3 and makes it possible to measure the position of the axis of the cylinder cylinder 3, and the assembly thus constitutes a digital loop for regulating the tightening position as a function of a spacing of the cylinders displayed on the input 62 of the regulation system 6.

In the present case, the automatic regulation system 6 is associated, in addition, with a mathematical model 63 programmed so as to adjust the clamping force applied to the support cylinders as a function of the dimensions of the product, as well as the nature and condition of the metal, to effect an optimal thickness reduction corresponding to the possibilities of the rolling mill.

Figure 2 schematically illustrates the rolling process during the first pass P, called start.

Of course, the thickness reductions are exaggerated to facilitate understanding of the drawing.

In diagram 2a, to the left of Figure 2, there is shown the end 50 of product 5 which comes into contact with the working rolls 2, 2 ′. The product 5 has a gross thickness e₀ and the air gap, limited by the generators 20, 20 ′, of the cylinders 2, 2 ′, lying in the clamping plane, has a width e₁. Also shown is the angle of attack A₁ which corresponds to the dihedral between each lateral face 51 of the product 5 and the tangent plane T at the point of contact of the edge 52 with the cylinder 2. It can be seen that the value of l angle of attack A₁ is a function of the ratio between the diameter d of the cylinder and the arrow a which is equal to half the reduction in thickness r₁ = e _o - e₁.

The mathematical model 63 associated with the regulation system 6 is programmed so as to calculate, with each pass, the maximum possible reduction in thickness compatible with the available power and the possible effort, taking into account, on the one hand, the characteristics of the rolling mill which determine its working capacity and its possible deformations and, on the other hand, the physical and dimensional characteristics of the product.

Indeed, the effort to be exerted to determine a certain reduction in thickness depends on the nature of the metal and its thickness, but also on its temperature which rises during rolling. Thanks to its self-adaptation, the mathematical model 63 will be able to predict, for each pass and according to the operations already carried out, the state of the metal and the maximum reduction in thickness possible without risk of excessive stress on the rolling mill.

In addition, the risk of refusal of engagement depends on the thickness of the metal, its condition and the lubrication conditions. The model 63 can therefore also provide, according to the passes, the spacing of the cylinders determining a sufficient pinch for the entrainment of the product without risk of refusal of engagement.

To automatically adjust the cylinder spacing and the clamping force during each pass, the mathematical model 63 displays on input 62 of the regulator 6, first of all, the first clamping position setpoint making it possible to guarantee good engagement of the strip, taking into account the diameter of the cylinders and, then, during the pass, the thickness setpoint making it possible to obtain the optimal reduction calculated previously.

In Figure 5, a schematic flow diagram of the regulatory process is shown.

The mathematical model 63 is associated with the computer 60 which has in memory all the characteristics of the rolling mill 1 which must be taken into account to determine the reduction in thickness.

Before starting the rolling of a determined product, in an initialization step 1, all the specific parameters of the product to be laminated, and corresponding, in particular, to the nature of the metal, are displayed on an input 64 of the mathematical model 63 the initial dimensions, the target dimensions and the temperature measured before the operation.

The product is then introduced into the rolling mill. In a step 2, the mathematical model 63 determines, on the one hand, the maximum possible thickness reduction allowing, from the gross thickness e₀, to obtain an optimal thickness e₂ and, on the other hand, the spacing e₁ of the cylinders which guarantees good engagement of the product 5, taking into account the gross thickness e₀ and the diameters d of the cylinders 2, as well as the lubrication conditions.

This engagement is carried out at reduced speed with pinching of the product 5, the thickness of which is reduced to e1 between the cylinders 2, 2 ′.

As soon as the product is engaged, the regulating device 6 controls the tightening of the rolls up to the spacing e₂ calculated previously and then the transition to rolling speed.

The rolling continues as normal, the thickness e₂ being regulated by the system 6. On leaving the rolling mill, the product therefore has, over most of its length and up to its downstream end 54, a thickness e₂, excluding the head 50 which has a greater thickness e₁.

The first start pass P1 which, as indicated by an arrow in Figure 2, was carried out from left to right, is then completed, product 5 being on the right of cylinders 2 and 2 ′.

The second rolling pass P2 is then carried out according to the process indicated in FIG. 3, that is to say from right to left.

The part of the product 5 which now comes into contact with the cylinders 2, 2 ′, is then its end 54 of thickness e₂.

As before, the mathematical model 63 first of all determines, in a step 3, the optimum thickness e₄ that can be obtained, which corresponds to the maximum reduction in thickness possible compatible with the capacities of the rolling mill, taking into account since the tail of the product is thicker, the reduction to be made is equal to e₁ - e₄. Then, in a step 4, the mathematical model determines the spacing e₃ which it is necessary to give to the cylinders to allow the introduction of the product without refusal of engagement, taking into account the thickness of the product and its temperature predictable at this time.

The product 5 then engages between the cylinders 2 and 2 ′, taking the thickness e₃. As soon as the engagement is ensured, the regulation system 6 controls the tightening of the rolls at the spacing e₄ and the transition to rolling speed.

The rolled product at the end of this second pass P₂ therefore has a thickness e₄ on most of its length 56 and a head 55 of thickness e₃.

There is thus carried out, at each pass P _n , a thickness reduction in two stages.

As indicated, one can determine, by experience, the foreseeable state of the product, in particular its temperature, after a certain number of passes and thus program the mathematical model 63 so that it determines, with each pass P _n and depending on the thickness e _2n-2 reached on the previous pass P _n-1 , the maximum reduction in thickness e _2n-3 - e _2n that it can make without exceeding the capacity of the rolling mill and the spacing e _{2n -1} to be given to the cylinders to avoid a refusal of engagement.

The process described above for the second pass P₂ can therefore be repeated on each pass until the ratio between the diameter d of the working rolls which remains substantially fixed and the thickness of the product which decreases with each pass is such that, by immediately carrying out the maximum thickness reduction compatible with the rolling power, there is no risk of a refusal of engagement.

Since the target thickness is (e), it is possible to define in advance the thickness e + x from which the refusal of engagement is no longer to be feared. Thus, at the end of each pass P _n , in a step 6 of the process, the thickness reached e _2n is compared with the parameter e + x and, as soon as it becomes less than this parameter, the process described above is stopped and the rolling continues normally, in a step 7, until the desired thickness (e) is obtained.

It can be seen that, at each pass P _n , the total reduction in thickness e _2n-3 - e _2n is higher than that which had to be respected before to avoid a refusal of engagement. The total number of passes will thus be significantly reduced.

Of course, the invention is not limited to the details of the embodiment which has just been described by way of simple example and which could give rise to variants. In particular, the system has been described in the context of a quarto rolling mill, but it is applicable in the same way to a duo or a sexto or to any other type of rolling mill.

Likewise, other regulation systems could be devised to determine the minimum number of rolling passes compatible with the power of the rolling mill.

The reference signs, inserted after the technical characteristics mentioned in the claims, have the sole purpose of facilitating the understanding of the latter and in no way limit their scope.

Claims (4)

Method for rolling a flat product (5) in a reversible rolling mill comprising at least two working rolls (2, 2 ′), with parallel axes superimposed along a clamping plane P inside a cage (1) , means for controlling the passage of the product between the cylinders (2, 2 ′), in one direction then in the other, and so on alternately, by successive passes and means (4) (6) for automatic adjustment of the clamping position of the rolls during the rolling of the product (5), characterized in that, the product (5) having a rough thickness (e₀) substantially uniform, the working roll is given, for the first start pass ( P₁), a spacing (e₁) less than (e₂) determining an angle of attack (A₁) sufficiently reduced to avoid a refusal of engagement and, after engagement, the spacing of the cylinders is reduced to a value (e₂) such that the total reduction in thickness (e₀ - e₂) remains compatible with c the maximum power and force of the rolling mill then, for the second pass (P₂), the working rolls are given a spacing (e₃) such that the difference (e₂ - e₃) determines a fairly reduced angle of attack (A₂) to avoid a refusal of engagement and, after the engagement of the product, the spacing of the cylinders is reduced to a value (e₄) determined so that the total reduction in thickness (e₁ - e₄) is as great as possible while remaining compatible with the maximum power and force of the rolling mill and so on, the spacing of the working rolls being first adjusted, at the start of each pass (P _n ), to a value (e _2n-1 ) determining an angle of attack (A _n ) sufficiently reduced to avoid a refusal of engagement, then, after the engagement of the product decreased to a value (e _2n ) determining a total reduction in thickness (e _2n-3 - e _2n ) optimal and remaining compatible with the maximum power and force of the rolling mill. Laminating method according to claim 1, characterized in that the thickness reduction is thus continued in two stages for each pass until the thickness (e _2n ) reached at the end of a pass ( P _n ) no longer risks determining a refusal of engagement for a reduction in the spacing of the working rolls on the next pass (P _{n + 1} ) compatible with the maximum power and force of the rolling mill and that one finishes then rolling in the normal way. Laminating process according to either of Claims 1 and 2, characterized in that the spacing of the rolls (2, 2 ′) is adjusted with each pass by means of a system (6, 60) for automatic regulation of the clamping force associated with a mathematical model (63) programmed so as to calculate, with each pass, the reduction in thickness to be carried out in two stages, depending on the effort and the possible rolling power and taking into account mechanical and dimensional characteristics of the rolling mill and of the product and the nature of the rolled metal. Laminating method according to claim 3, characterized in that the mathematical model (63) is programmed so as to calculate, as a function of the foreseeable state of the product on each pass, taking into account the thicknesses reached in the previous pass and the number of passes previously made, the maximum possible thickness reduction and the tightening of the cylinders necessary for the drive without risk of refusal engagement and that, at each pass (P _n ), the product to be laminated having, over most of its length, a thickness (e _2n-2 ) and, on its tail, a thickness (e _2n-3 ) corresponding to the engagement in the previous pass (P _n-1 ), the mathematical model (63) first determines, taking into account the foreseeable physical and dimensional characteristics of the product during said pass (P _n ) and capacities of the rolling mill, the rolling thickness (e _2n ) during said pass (P _n ) making it possible to obtain a maximum thickness reduction (e _2n-3 - e _2n ) compatible with the available power and the force possible, and the spacing (e _2n-1 ) of the cylinders allowing the introduction of the head of the strip without refusal of engagement, then the regulation system (6) controls the introduction of the strip (5) by adjusting the spacing of the cylinders at the engagement value (e _2n-1 ) and, after the engagement of the tape head, controls the tightening cylinders at the calculated spacing (e _2n ) and the transition to rolling speed, the thickness (e _2n ) of the strip being maintained until the end of the pass (P _n ).

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