EP3086889B1 - Hot rolling method, hot rolling mill and computer programm for carrying out such method - Google Patents

Description

The invention relates to the hot rolling of metallurgical products. More specifically, it relates to a method of controlling at least one parameter of the hot rolling process.

In the following text we will take the example of hot rolling steel strips but the invention is applicable to hot rolling other metallurgical products, including aluminum or its alloys.

• coulée continue d'une brame d'épaisseur allant de 200 à 260 mm;
• réchauffage de la brame à une température d'environ 1100-1200°C;
• passage de la brame dans un laminoir dégrossisseur comportant une cage réversible unique ou une pluralité de cages indépendantes (par exemple au nombre de cinq) disposées les unes à la file des autres, de manière à obtenir une bande ayant une épaisseur de 30 à 50 mm environ;
• passage de la bande dans un laminoir finisseur comportant une pluralité de cages (par exemple au nombre de six ou sept) dans lesquelles la bande est simultanément présente, de manière à lui conférer une épaisseur de 1,5 à 10 mm environ, puis mise de la bande sous forme d'une bobine.

Usually, hot-rolled steel strips are manufactured according to the following scheme:

• continuous casting of a slab of thickness ranging from 200 to 260 mm;
• reheating of the slab at a temperature of about 1100-1200 ° C;
• passage of the slab in a roughing mill comprising a single reversible cage or a plurality of independent cages (for example five in number) arranged one in line with the others, so as to obtain a strip having a thickness of 30 to 50 mm about;
• passage of the strip in a finishing mill comprising a plurality of cages (for example six or seven) in which the strip is simultaneously present, so as to give it a thickness of about 1.5 to 10 mm, then the tape in the form of a coil.

The hot-rolled strip thus obtained can then be subjected to heat or mechanical treatments which will give it its final properties, or undergo a cold rolling which will further reduce its thickness before the completion of the final heat or mechanical treatments.

During the hot rolling of steel strips, in each cage of the finishing train, the steel strip is subjected to a specific thermal and mechanical path (reduction, temperature) which is influenced by the friction between the working rolls and the band in the gap between the rollers. This path has a major influence on the quality of the band (surface appearance and metallurgical properties).

It is therefore essential to be able to control and control the friction in the air gap of the rollers (or cylinders). Too high a coefficient of friction leads to excessive energy consumption, rapid degradation of the rollers and surface defects on the belt. On the other hand, a coefficient of friction that is too low causes slippage and guiding problems of the strip as well as problems of engagement thereof in the cage.

The regulation of the coefficient of friction is in particular ensured by the lubrication process.

At present, lubrication is generally carried out at each roll stand by injecting an emulsion composed of water and a lubricating fluid, usually oil, onto the cylinder at the gap, see for example the document US Patent 3605473 .

The need for efficient lubrication is further increased with the rolling of the new grades of steel THR (Very High Strength, generally between 450 and 900 MPa) or UHR (Ultra High Strength, generally greater than 900 MPa) and / or new formats, for example band thicknesses less than 3mm. In fact, these steels such as USIBOR® or Dual Phase steels are naturally harder and require the application of a greater rolling force, which reduces the capacity of the rolling mill. These steels may also have a surface composition such that it has less scale which usually acts as the first lubricating element.

Moreover, in current rolling processes, in order to avoid the risk of non-engagement of the strip in the air gap of the rolls linked to a coefficient of friction that is too high, the injection of lubricating emulsion is deactivated during the rolling of the beginning of the roll. gang. In the same way to prevent the next strip refuses to engage due to the presence of lubricating emulsion on the cylinders, the lubricating emulsion injection is deactivated during the rolling of the tail of the previous strip. These two portions which are therefore rolled without lubricant must be removed because not having the required thickness, which represents a loss of several meters of tape (from 5 to 10 meters of tape per cage) and therefore a significant loss in terms of loss of productivity.

In order to ensure efficient lubrication and consequently regulate the coefficient of friction so as to avoid rolling incidents such as slippage or non-engagement of the strip, many solutions have been proposed.

The document JP-A-2008264828 discloses a hot rolling method in which the working rolls are coated with a coating layer of specific composition to ensure a certain coefficient of friction value.

The document JP-A-2005146094 discloses a hot rolling method wherein slip of the strip would be avoided by using a lubricating oil of particular composition.

However, these solutions do not allow to regulate the coefficient of friction continuously during rolling. In fact, the coefficient of friction depends inter alia on the nature of the material constituting the strip to be rolled, the state of the working rolls (roughness, degradation, scale, etc.), the rolling speed and the percentage of reduction. to reach. Thus, the lubrication efficiency can be very different between the beginning and the end of a rolling campaign, and even from one train to another and from one cage to another in the same train. However, the two solutions proposed do not make it possible to take into account the variations of these parameters during the process.

JPH-A-1156410 discloses a method in which the clamping force of the applied rolling rolls would be measured by sensor, then the amount of lubricating oil injected would be adjusted so that the measured rolling force is equal to a target value. .

This solution aims to adjust the coefficient of friction during the process but does not take into account all the parameters on which the coefficient of friction depends, which makes it inefficient. In addition this solution involves significant risks of instabilities of the rolling process, such as. variations in speed or traction, if the amount of lubricant to be supplied to achieve the required force is important.

The object of the invention is therefore to provide a rolling method in which the coefficient of friction is reliably and effectively controlled during production in order to avoid rolling incidents and to obtain optimum performance. The object of the invention is also preferably to provide a method reducing the instabilities of the rolling process and allowing lubrication over the entire length of the strip.

For this purpose the invention firstly relates to a control method according to claim 1.

This control method may also include the features of claims 2 to 7, singly or in combination.

The invention also relates to a rolling method according to claim 8.

This rolling method may also include the features of claims 9 to 13, taken alone or in combination.

The invention also relates to a hot rolling mill according to claim 14.

This mill may also include the features of claim 15.

The invention also relates to a computer program product according to claim 16.

Other characteristics and advantages of the invention will appear on reading the description which follows.

• La figure 1 représente un laminoir à deux cages équipées d'un mode de réalisation d'un dispositif de régulation selon l'invention,
• La figure 2 représente les différentes variables utilisées dans un mode de réalisation d'un procédé de régulation selon l'invention
• La figure 3 représente un schéma de régulation selon un premier mode de réalisation de l'invention
• La figure 4 représente un schéma de régulation selon un second mode de réalisation de l'invention
• La figure 5 représente le début d'injection d'huile et le couple moteur en fonction du temps lors d'un essai utilisant un procédé de régulation selon l'invention
• La figure 6 représente l'épaisseur de la bande laminée en sortie de cage en fonction du temps lors d'un essai utilisant un procédé de régulation selon l'invention

In order to illustrate the invention, tests have been carried out and will be described by way of nonlimiting examples, in particular with reference to the figures which represent:

• The figure 1 represents a rolling mill with two cages equipped with an embodiment of a regulating device according to the invention,
• The figure 2 represents the different variables used in one embodiment of a regulation method according to the invention
• The figure 3 represents a control scheme according to a first embodiment of the invention
• The figure 4 represents a control scheme according to a second embodiment of the invention
• The figure 5 represents the start of oil injection and the engine torque as a function of time during a test using a control method according to the invention
• The figure 6 represents the thickness of the rolled strip at the exit of the cage as a function of time during a test using a control method according to the invention

The figure 1 shows a metal strip B during rolling in a rolling mill comprising two cages 1, 2 in which the band B is simultaneously under the influence, for example a finishing mill for the hot rolling of the steel strips. Rolling mills of this type generally have 5, 6 or 7 cages. Each of the cages 1, 2 comprises, conventionally, two working rolls 1a, 1a 'and 2a, 2a' and two support rolls 1b, 1b 'and 2b, 2b'. Each cage is activated by a motor torque C ₁ , C ₂ (not shown). The distance between the two working cylinders, respectively 1a -1a 'and 2a-2a' is called the air gap S (not shown) and is adjusted by means of clamping screws 7.

The lubrication of the cylinders is ensured at each of the cages by an injection device 3, such as for example projection nozzles for projecting an emulsion of oil and water.

According to one embodiment of the invention, a speed measuring device 4 is disposed at the exit of the first cage in the running direction of the strip, this device 4 makes it possible to measure the speed of the strip at the exit of the strip. cage v _output . This device may be, for example, an optical measuring device such as a laser velocimeter. This measurement of the speed makes it possible to calculate in real time the forward sliding (FWS for ForWard Slip ratio in English) from the following formula: $$\mathrm{FWS}=\frac{\left|v_{\mathit{exit}}-v_{\mathit{cage}}\right|}{v_{\mathit{cage}}}$$

• v_sortie est la vitesse de la bande en sortie de la cage, par exemple mesurée à l'aide du dispositif 4.
• v_cage est la vitesse linéaire des cylindres de travail calculée selon la formule suivante : $${\mathrm{v}}_{\mathrm{cage}}=\mathrm{\omega R}$$
  
  R étant le rayon du cylindre de travail et ω la vitesse angulaire des cylindres de travail mesurée par exemple par un générateur à Impulsion)

In which :

• v _output is the speed of the band leaving the cage, for example measured using device 4.
• v _cage is the linear speed of the working rolls calculated according to the following formula: $${\mathrm{v}}_{\mathrm{cage}}=\mathrm{\omega R}$$
  
  R being the radius of the working cylinder and ω the angular speed of the working cylinders measured for example by a pulse generator)

The v- _output and v- _cage speeds can be expressed in any speed unit, provided they are both expressed in that same unit. In the same way the unit in which the angular velocity ω is expressed must be coherent with that of v _cage .

Still according to one embodiment of the invention a device 5 for measuring force to measure in real time the clamping force F of the working rolls is also provided at each cage. These devices, well known to those skilled in the art, may for example be strain gauges installed on the cage uprights or under the clamping screws 7.

The measured tightening force F and the speed of the output band C _output are transmitted to a processing unit 6 which can then, according to these measurements and other parameters previously recorded, send instructions by example to the lubricating emulsion injection nozzles 3 or to the clamping screws 7.

A processing unit 6 for implementing a first embodiment of the regulation method according to the invention is described below with reference to FIG. figure 3 .

The speed of the output band of the _exit v-cage and the angular velocity of the work rolls ω are measured in line and their values are sent to a first computer 8. This first computer 8 comprises at least one internal memory on which the value of the radius R of the working rolls is stored, which makes it possible to calculate the linear speed of the working rolls v _cage and then the value of the slip ratio. forward FWS according to formula 1.

The calculated value FWS is then transmitted to a second computer 9 which also receives as input the value of the clamping force F measured in real time by the sensor 5. This second computer comprises at least one internal memory on which are stored the parameters P ₁ . These parameters P ₁ depend on the model chosen for the calculation of the _real coefficient of friction μ.

Various simplified models can be adapted to obtain the calculation of the _actual coefficient of friction μ from the values of forward sliding ratio FWS and clamping force F. These models are known in their generality but not in their particular application as as described in the invention.

As an example we will describe below the use for the purposes of the invention Orowan model, but other models known to those skilled in the art may be used, such as the model of SIMS or Bland & Ford. The general theory of each of these three models is described for example in E.Orowan, Proceedings of the Institute of Mechanical Engineers, June 1943, vol.150, No. 1,140-167 for the Orowan model , RB Sims, Proceedings of the Institute of Mechanical Engineers, June 1954, vo1.168, No. 1 191-200 for the Sims Model , " The Calculation of Roll and Torque Force in Cold Strip Rolling with Tensions, "DR Bland and H. Ford, Proceedings of the Institute of Mechanical Engineers, June 1948, vol.149, p.144, for the Bland & Ford model .

To calculate in real time the _actual friction coefficient μ using the model Orowan P ₁ parameters are input thicknesses e _input and output an _output of the band, σ _entry input and output tractions σ _output of the band, these parameters being in the present example fixed at the beginning of rolling but can also be estimated or measured in real time. These parameters are illustrated in figure 2 .

From these data, the second computer 9 thus calculates the _real coefficient of friction μ given to a processor 10. The computation time of _real μ is less than or equal to 100 ms and preferably less than or equal to 50 ms.

The input data processor 10 are _real μ, a target value of _target friction coefficient μ determined from graphs or modeling, depending on the steel grade of the rolled strip, the number of kilometers strips laminated on the installation in question, the wear of the rollers, the type of oil used, etc. as well as a parameter α ₀ . This parameter is the initial value of the process parameter α which will be used to regulate the _real coefficient of friction μ.

This parameter may be, for example, the _oil injection rate Q of the lubricating oil. The initial value can be determined for example using charts or by modeling.

The value of the _actual μ friction coefficient is then compared with the target value of friction coefficient μ _target. If the absolute value of the difference between these two values | μ _target - μ _real | is greater than a predetermined value Δ, a new value of the parameter α _n is then calculated and then applied so that the value of the _real coefficient of friction μ is reduced to a value closer to the target value μ _target , in order to avoid a refusal of commitment and slip of the band if μ _real < _target + Δ Δ or premature wear of the work rolls and surface defects in the opposite case. For example, it will be possible to reduce or increase the _oil injection flow rate of the lubricating oil. It is preferable to keep the flow of water in the emulsion constant for thermal considerations of cylinder cooling and smooth operation to ensure that the injected emulsion covers a large part of the cylinder.

The time elapsing between the measurement of the strip exit speed v _output and receiving the setpoint α _n is less than or equal to 500 ms and preferably less than or equal to 150 ms.

This succession of measurements, calculations and regulations can thus be repeated until the end of the rolling of the band in question and until the end of the rolling campaign.

The figure 4 represents a control scheme according to a second embodiment of the invention.

The difference with the first embodiment previously described and illustrated in figure 3 is that the values FWS and _real μ calculated respectively by the computers 8 and 9 are transmitted to a second processor 11. The input data of this second processor are FWS, _real μ and a set of parameters P ₂ . These parameters P ₂ depend on the model chosen for calculating the _real coefficient of friction μ.

If is used as in the previous embodiment the Orowan model parameters P ₂ are the input thicknesses e _input and output an _output of the band, the input traction σ _input and output _output σ of the strip, the radius R of the rollers, these parameters being in the present example set at the beginning of rolling, but can also be estimated or measured in real time. P2 also includes the milling module M of the mill stand considered. This module, generally expressed in t / mm, characterizes the elastic deformation of the cage related to the rolling force.

From this data the processor calculates for example the value of rolling force F 'which should be applied to obtain the thickness e _output

Indeed the new value of the parameter α can generate modifications on other parameters and thus create problems for example of under thickness at the exit of the cage.

Dans laquelle :

• F' est la valeur de la force de laminage calculée par le processeur 11.
• F est la valeur de la force de laminage mesurée par le capteur 5.
• M est le module de cédage de la cage considérée

Indeed if one changes the oil flow Q injected _oil is varied the _actual coefficient of friction μ and consequently the force F applied by the roller on the strip. This then results in a change in the thickness e _output of the strip at the exit of the cage, as illustrated in FIG. figure 5 . It is therefore possible to obtain non-compliant cage exit thicknesses. If this problem arises one can then use the same model as that used to calculate _real μ but in opposite direction. In the present case of the Orowan model, the input parameters of thickness e _input , e _output , traction σ _input , σ _output , diameter D, the _desired coefficient of friction μ, and the slip ratio are taken up. calculated FWS and thus obtain the force F 'to be applied on the band, and the necessary variation of the air gap ΔS according to formula 3 below and then corrects the clamping screw positions 7 which define the air gap. $$\mathrm{\Delta }S\equiv \frac{F\text{'}-F}{M}$$

In which :

• F 'is the value of the rolling force calculated by the processor 11.
• F is the value of the rolling force measured by the sensor 5.
• M is the caging module of the cage considered

The units of these three quantities must be coherent with each other and may for example be in Newton for the forces F and F 'and in N / mm for the curing module M.

We can use this same principle of calculation by inverted model to control other parameters of the rolling process such as the upstream and downstream tractions of the cage σ _input , σ _output to avoid disturbances of the speed of the output band rolling.

The treatment units described above with reference to Figures 3 and 4 contain different elements such as computers or processors but one could consider a single processor for performing the various calculation operations and instructions, or any other possible configuration for calculation steps and instructions.

Trial

A hot rolling method according to the invention was made with a Drawn and Wall Ironed (DWI) steel strip, the lubricating oil used being a commercial standard oil.

The results are illustrated in figures 5 and 6 .

As illustrated in figure 5 , the injection rate Q _oil is zero during the rolling of the tape head. This is voluntary this test being mainly devoted to the lubrication of the tail of tape.

On the other hand, it is found that the oil injection rate Q _oil has been regulated until the end of the rolling of the strip, which means that the tail of the strip has it was also rolled in the presence of lubricant, which was not the case in the prior art.

The figure 6 represents the thickness of the strip at the output of the cage e _output as a function of the rolling time. There is a drop of this thickness e _output after 10 seconds, this decrease corresponds to what has been explained above. The modification of the injected oil flow rate Q _oil causes a change in the force F applied and in this case a significant decrease in the thickness e _exit of the strip at the exit of the cage. Thanks to the regulation illustrated in figure 4 a new clamping force F 'is calculated and the air gap S modified accordingly in order to obtain a thickness of output e _output according to the expectations of the customer. The increase and the maintenance of the thickness e _output are visible on this figure 6 .

No slippage or refusal of engagement of the next strip occurred during this test, which means that the coefficient of friction has been reliably and effectively controlled. In addition, the tape tail could be rolled in the presence of lubricant without affecting the rolling of the next strip.

Claims (16)

1. A method for regulating at least one of the parameters (α) of a method for hot rolling a metal semi-finished product in at least one rolling mill housing comprising at least two work cylinders,
   the regulating method comprising the following steps:

   - calculating a forward slippage ratio (FWS) using the following equation: $$\mathit{FWS}=\frac{\left|v_{\mathit{sortie}}-v_{\mathit{cage}}\right|}{v_{\mathit{cage}}}$$

   

   where v_sortie is the speed of the semi-finished product upon leaving said housing and v_cage is the linear speed of the work cylinders;

   - calculating an estimate of a friction coefficient (µ_réel) based on a measured value of the clamping force (F) of said work cylinders in the housing and the forward slippage ratio (FWS) previously calculated; and

   - regulating at least one of the parameters (α) from the calculated estimate of the friction coefficient (µ_réel).
2. The regulating method according to claim 1, wherein:

   - during the step for calculating the estimate of the friction coefficient (µ_réel), a target value of the friction coefficient (µ_cible) is predetermined, and the friction coefficient (µ_réel) is calculated in real time;

   - during the regulating step, if |µ_cible = µ_réel | is greater than a predetermined value (Δ), the corresponding method parameter (α) is adjusted such that |µ_cible = µ_réel | becomes less than or equal to the predetermined value (Δ).
3. The rolling method according to claim 1 or 2, wherein before calculating the forward slippage ratio (FWS), the speed (v_sortie) of the semi-finished product leaving the housing is measured, and the time between said measurement of (v_sortie) and the calculation of the friction coefficient (µ_réel) is less than or equal to 100 ms.
4. The rolling method according to claim 3, wherein the time between the measurement of v_sortie and the calculation of µ_réel is less than or equal to 50 ms.
5. The rolling method according to one of the preceding claims, wherein the time between the measurement of v_sortie and the regulation of at least one of the parameters of the hot rolling method (α) is less than or equal to 500 ms.
6. The regulating method according to any one of the preceding claims, comprising a correction step, after the step for regulating at least one of the α parameters of the method, that consists of regulating the clamping force F based on calculated forward slippage ratio (FWS) and friction coefficient (µ_réel) values.
7. The regulating method according to any one of the preceding claims, comprising a correction step, after the step for regulating at least one of the α parameters of the method, that consists of regulating the entry (σ_entrée) and exit (σ_sortie) attractions of the band based on the calculated values of the forward slippage ratio (FWS) and friction coefficient (σ_réel).
8. A method for hot rolling a metal semi-finished product in at least one rolling mill housing comprising at least two work cylinders in which at least one of the α parameters of the method is regulated using a regulating method according to any one of the preceding claims.
9. The hot rolling method according to claim 8, wherein a lubricating emulsion made up of oil and water is injected at the clearance of the work cylinders and wherein at least one of the method parameters α is the injection flow rate of said oil (Q_huile).
10. The rolling method according to one of claims 8 or 9, wherein the rolled metal semi-finished product is a strip of aluminum.
11. The rolling method according to one of claims 8 or 9, wherein the rolled metal semi-finished product is a strip of steel.
12. The rolling method according to claim 11, wherein the rolled steel strip is a high-strength or ultra-high-strength steel strip.
13. The rolling method according to claim 11 or 12, wherein the rolled steel strip has a thickness at the end of the rolling of less than or equal to 3 mm.
14. A hot rolling mill comprising means for carrying out the rolling method according to any one of claims 8 to 11.
15. The hot rolling mill according to claim 14, wherein the speed of the semi-finished product v_sortie leaving the rolling mill housing is measured using a laser velocimeter.
16. A computer program product including software instructions which, when implemented by a computer, carry out the regulating method according to any one of claims 1 to 7.

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