FR2780502A1 - Measuring flatness of product produced as band, particularly applicable to process control in steel mills - Google Patents

Abstract

Stresses in a band of steel (2) passing over a roller (1) are measured by helically displaced sensors (13) under a thin skin. At the band edges a width (l) which does not cover a measuring zone (A) completely may be compensated provided it exceeds 50-60% of the measuring width (A). Where this is not achieved the roller is moved axially in sliding guides by a jack for a distance of half the measuring width (A/2) frequently making compensation possible.

Description

The subject of the invention is a method and a device for determining

  the distribution of stresses on a strip product, in particular to identify flatness defects. In strip product processing installations and, more particularly, in metal strip rolling installations, it is necessary to correct flatness defects which may be due, for example, to a non-uniform distribution of the stresses applied on the strip, during rolling. In particular, as the rolling forces are exerted on the ends of the support rolls, these tend to bend and, consequently, to produce greater crushing at the edges. The elongation thus produced is therefore slightly greater on the sides than in the central part. During rolling, the strip is tensioned, in particular in so-called tandem installations comprising several successive cages and the edges or edges of the strip tend to be less taut than the central part, the longitudinal fibers of which have been less elongated. When the tension is removed, in particular when the strip is cut into plates, the tensions are balanced and there are flatness defects such as undulations at the edges and

pockets in the central part.

  These faults can be corrected by various known means. For example, to compensate for the bending effect of the cylinders, we can give the support cylinders

  of the rolling mill, a curved profile, possibly variable.

  More recently, it has been proposed to act more precisely on the distribution of the stresses, for example by exerting cambering forces on the ends of the working cylinders or else by using a support cylinder with a rotating envelope comprising a mounted cylindrical envelope. rotatable around and fixed on a fixed shaft by means of a plurality of shoes, the radial positions and pressures of which can be adjusted individually so as to

  modify the distribution of constraints.

  It is also possible to modify the profile of the cylinders by carrying out watering divided by adjacent zones so as to slightly modify, by thermal effect, the

diameter of each section.

  Finally, in a sexto type rolling mill, the working rolls or the

intermediate cylinders.

  In all cases, it is necessary, in order to correct faults, to know their position and, for this purpose, a measurement device is generally used consisting of a roller rotating around an axis perpendicular to the longitudinal axis of travel and mounted as a deflector so that the strip under tension is applied to a certain angular sector of the roller. A variation in the longitudinal tensions over the width of the strip results in a corresponding variation in the pressure applied to the corresponding areas of the roller. This consists of a plurality of adjacent measurement zones arranged one beside the other over its entire length and each provided with a measurement means sensitive to the pressure applied by the strip on the corresponding zone. The roller is associated with a computer having software intended to develop, from the measurements made on all of the zones, a flatness curve which is an image of the variation of the stresses in the strip and therefore makes it possible to control the associated means. to the rolling mill to make the necessary corrections, for example by split watering or by bending the rolls. French Patent No. 2,468,878 describes, for example, a measuring roller made up of a cylindrical body in which cavities are closed radially closed by a thin envelope which covers the cylindrical body. Inside each cavity is housed a sensor having a feeler applied against the part of the envelope closing the cavity and which can deform slightly under the effect of the stresses applied by the strip on the corresponding zone of the roller. Such a provision is well known and does not

  not require a detailed description.

  Other means can be used to measure the distribution of stresses by adjacent zones, French patent N 2,468,878 having been cited as a simple

example.

  Generally speaking, therefore, a flatness measuring roller comprises a plurality of adjacent measuring zones which each deliver a signal proportional to the longitudinal tension in the corresponding edge of the strip, the signals being processed so as to provide a image of the flatness of the strip after removal of the traction. Furthermore, the rolling installations are designed to produce strips of different widths, within a determined range. Of course, the flatness measuring roller, which remains in place in the installation, cannot be modified and the width of the measurement zones does not necessarily correspond to the width of the strip applied to the roller. This is, however, centered relative to the axis of travel of the strip which passes, either through the center of a measurement area or at the interface between two adjacent areas. The strip therefore comprises a central part which completely covers an entire number of measurement zones and, on each side, an end zone called the edge, which only partially covers the measurement zone.

corresponding measure.

  The measurement is therefore distorted on the banks and it may be necessary to eliminate the signals corresponding to the end zones, taking into account only the signals corresponding to completely covered measurement zones.

by the band.

  For some time, to exploit the signal given by the sensors on the banks, that is to say in a partially covered area, it has been proposed to program the computer associated with the roller so as to compensate for the values delivered on the two banks, taking into account the proportion of the

measurement covered by the tape.

  In practice, however, for the signal to be significant, the end zone must be covered over a minimum part, generally 50% or%, of its width. Therefore, if it is desired to produce strips of any width, according to the needs of the clientele, there is a significant proportion of the widths for which the compensation of the partial overlap is not possible, which requires the elimination of the shores

  for measuring the stress distribution.

  This is all the more annoying as the variation in traction is very rapid on the edges of the strip because of the pinching phenomenon between the rolls, called the edge effect, which increases over a width of 25 mm to 35 mm. from the edge. A bad taking into account of the value on shore or not taking into account this value can therefore lead to a bad adjustment of the means of correction of the

distribution of constraints.

  Of course, to reduce the influence of banks not taken into account, it is possible to consider reducing the width of the measurement zones, but this leads to multiplying the number

  sensors or roller segments.

  The subject of the invention is therefore a particular arrangement which makes it possible to solve the problem of the banks without excessively complicating the production of the measuring roller. The invention therefore relates to a method for determining a stress distribution on a strip product under tension and running along a longitudinal axis, in which the strip is applied, during running, on an angular sector of a roll. meter rotatably mounted about an axis perpendicular to the longitudinal axis of travel and comprising a plurality of adjacent measurement zones arranged one beside the other along the length of the roll and each covering a section of the roll having a width elementary A, each measuring zone being provided with means for measuring the application pressure on said zone of a corresponding part, of the moving strip, said strip having a width L = LI + 21 comprising a central part of width L1 = n A equal to an integer n of measurement zones and two banks on which the application pressure can be measured by compensation if the width (1) of the bank is at least s equal to a minimum measurable width a = SA, S being a coefficient less than 1, In accordance with the invention, in cases where the edge width (1) is less than the minimum measurable width (a), a relative axial offset of

  roll relative to the strip, over a half-width of zone A / 2, so as to give the edges a new width (1 ') increased by a half-width A / 2 compared to the width of the initial bank (25 1), the proportion of non-measurable edge widths being reduced by 0.5.

  In this way, when the width of the strip can vary between n A and (n +) lA, n being an integer number of covered areas, the roller is placed in one or the other of these two centering positions according to the band width. In a first position, the measurement is carried out with edge compensation for all bandwidths (L) such that: (n + S) A <L <(n + 1) A

  and, in a second position offset by half a

  zone width, the measurement is carried out with edge compensation for all bandwidths (L) such that: (n - 1/2 + S) A <L <(n + 1/2) A so that the edges are eliminated only for two width ranges, respectively, a first range for which: n A <L <(n - 1/2 + S) A and a second range for which: (n + 1/2) A. L <(n + S) A. Thus, thanks to the arrangements according to the invention, the proportion of width of strips for which the edges

  must be eliminated is no more than 2 (S - 1/2).

  The invention also covers an improved measuring device for implementing the method. According to the invention, such a device comprises a measuring roller mounted to slide parallel to itself, on its support, and associated with means for controlling the axial sliding and with means for locking the roller in two positions for centering the zones of measurement with respect to the longitudinal axis of travel, respectively a first position for which the travel axis passes through the center of a measurement area, the strip covering an odd number of areas and a second position, offset by half zone width compared to the first, for which the longitudinal axis of travel passes over the junction between two adjacent measurement zones, the strip covering an even number

zones.

  But the invention will be better understood by the

  following description of a particular embodiment, given by way of example, with reference to the accompanying drawings

  in which: Figure 1 is a schematic view, in cross section, of a flatness measuring roller.

  Figure 2 is a front view, partially broken away, of the roller.

  Figure 3 is a perspective view of the assembly

of a roller according to the invention.

  Figure 4 and Figure 5 schematically show the measurement of a strip in two positions of the roller. Figure 6 is a diagram showing the ranges of

  width measurable and not measurable.

  In Figure 1, there is shown very schematically a flatness measuring roller 1, mounted

  rotatable around an axis 10 and on which a band 2 passes.

  The roller is mounted in a deflector so that the strip 2, which is put under tension, is applied to a

angular sector x of the roller 1.

  In the embodiment shown by way of example in the figures, the measuring roller 1 is of the type described in French patent N 2,468,878, and therefore consists of a cylindrical body 11 covered with a thin envelope 12 and inside which are placed sensors 13 housed in cavities 14 formed radially in the body 11 and distributed over the entire length of the

roller 1.

  Each cavity 14 is closed by a part of the casing 12 against which a sensor sensor 13 is applied which therefore records the variations in the pressure of application of the corresponding part of the strip 2 on the roller. In this way, each sensor can cover an area of width A of the roller corresponding to a slice

longitudinal of the strip.

  In the embodiment given by way of example and which corresponds to the device of French patent N 2,468,878, the sensors are arranged in a helix along the roll so that two adjacent sensors 13, 13 ′ are angularly and axially offset relative to each other. In this way, although each sensor is placed in a cavity, the measurement zones can overlap each other. The roller 1 therefore comprises a series of adjacent measurement zones 15 arranged one beside the other over the entire length of the roller L. The roller 1 is mounted to rotate around its axis 10 on two trunnions 30 rotating in bearings 3 being supported on a fixed frame B. As indicated, other known arrangements can be used. For example, the roll may consist of adjacent segments which can move slightly relative to each other, in a radial direction, depending on the pressure of application of the strip, each segment being associated with means of radial position measurement with respect to the axis of rotation of the

roll of each segment.

  The strip 2 whose flatness is to be checked has a width L which can vary over a certain range according to the capacity of the rolling mill and according to the

customer needs.

  The elementary measurement width A, which depends on the arrangement of the sensors 13 inside the roller cannot, of course, be modified as a function of the width L of the strip. This therefore comprises, as shown in FIG. 1, a central part 21 of width L1 which covers an integer n of zones 15 of width A and, on each side, an edge 22 of width (1) which therefore covers a part

  only from the end zone 15a.

  In the example shown in Figure 2, the edge 22 covers almost the entire end region 15a. It is therefore possible, for the determination of the stress applied by the edge of the strip 2, to take into account the measurement carried out by the corresponding sensor. The information processing system associated with the measuring roller 1 can indeed make the desired correction to the measurement, taking into account the proportion of the width A covered by

shore 22.

  However, such compensation is only possible if the edge 22 covers a minimum width (a) which corresponds to a determined proportion S of the measurement width A. We can therefore write: a = SA, S being is a coefficient

less than 1.

  In practice, we know that a measurement zone gives a usable signal from 50% or 60% overlap, S

  being equal, therefore to 0.5 or 0.6.

  As a result, it has hitherto been possible to take into account only the measurements carried out on banks 22 of width (1) between a and A, for each range of widths between n A and (n + 1) A, i.e. for a proportion of 100 (1-S)% of the possible bandwidths. For all other widths, i.e. for a proportion greater than half of the possible bandwidths, it was necessary to eliminate the measurement

carried out on the banks.

  As will be seen, the invention makes it possible, on the contrary, to very substantially increase the proportion of bandwidths for which it is possible to

take into account the shores.

  According to the invention, the device comprises means for axially moving the roller 1 with locking in two determined positions axially spaced apart by a

  distance corresponding to an elementary half-width A / 2.

  To this end, as shown in FIG. 3, the two support bearings 3 of the measuring roller 1 are fixed respectively on two plates 32 connected by a cross member 33 so as to form a drawer, the plates 32 being mounted to slide, parallel to the axis 10 of the roller 1, on slides 34 fixed to the fixed frame B. Locking devices such as pins 35 make it possible to removably fix the plates 32 in two offset positions

axially half-width A / 2.

  The axial movement of the roller 1 can be controlled by a jack 36 or a screw-nut system actuated by a motor. The locking devices 35 which cooperate, for example, with orifices provided on the slide 34, are arranged so that the median plane P of the strip 2, parallel to the longitudinal axis of travel passes, in a first position of the roller , through the center of a measurement zone 15 and, in a second position, coincides with the junction plane between two adjacent measurement zones. These two positions of the roller have been shown

  schematically in Figures 4 and 5.

  In the case of FIG. 4, the scroll axis passes through the center of a median measurement zone 15c and the central part 21 of the strip 2 therefore covers a number

integer, odd, of zones 15.

  As indicated, the width L of the strip 2 does not usually correspond to an integer number of zones and therefore comprises, on its sides, two edges 22a 22b which partially cover the extreme measurement zones 15a, 15b

over a width (1).

  In the example shown, this width (1) is less than the minimum measurement width (a) and it follows that the measurements made on the two banks 22a,

  22b cannot be taken into account for the processing of the information transmitted by the various sensors.

  In this case, by means of the jack 36, an axial displacement of the assembly of the roller 1 relative to the roller 2 is determined over a length equal to a half-width A / 2. On25 is then in the position shown in FIG. 5 for which the median plane P passes over the junction between two adjacent zones 15c, 15'c. The central part 21 ′ of the strip 2 then covers a whole number (n-l) of zones 15 and the two edges 22 ′ a, 22 ′ b have a width (1 ′) increased by half a width. So we have: L = L'1 + 21 ', with L'il = (n-l) A

1 '= 1 + A / 2

  The edges thus having a width increased by A / 2 become measurable in the majority of cases, as shown in FIG. 6 which indicates, in three successive diagrams, the measurement possibilities, the ranges not

measurable being hatched.

  FIG. 6a, which corresponds to the arrangement of FIG. 4, shows that, for bandwidths greater than L1 = n A, n being an integer, the measurement on the banks can be used if the width (1) of the bank 22 is greater than a = SA, that is to say for the widths of bands between (n + S) A and (n + 1) A. On the other hand, for the bands having a width between n A and ( n + S) A, the measurement on the banks does not

  should not normally be taken into account.

  FIG. 6b corresponds to the arrangement of FIG. 5, that is to say after shifting of the roller 1 by a half-width A / 2 to the right. In this position of the roller, it is possible to take into account the edges for all the strip widths between (n-0.5 + S) A and (n + 0.5) A. On the other hand, the measurement on the shores must be

  eliminated for bandwidths between (n-

  0.5) A and (n-0.5 + S) A. However, part of this interval was covered by the measurements carried out in the first position of the roller, corresponding to FIG. 6a, which makes it possible to take into account the edges for the widths between (n-1 + S) A and n A. Therefore, as shown in Figure 6c, over an interval of width A on either side of the position nA, it is ie for the widths between (n - 0.5) A and (n + 0.5) A, there are only two ranges of widths for which the edges are not measurable, respectively a first range for the widths included between (n-0.5) A and (n-1 + S) A and a second range for the widths between n A and (n-0.5 + S) A, the width of each range being equal to ( S - 0.5) A.35 Thus, for each range 4 of edge widths between n A and (n + 1) A, a range 41 is defined, corresponding to a proportion (1-S) of the widths, for which measurement can be performed in this pre first position and a range 42, corresponding to a proportion S of the bandwidths, most of which will allow measurement in the second position offset from the roll. Indeed, to the first range 41 of measurable widths, the offset of the roller makes it possible to add a new range 43 having a width: [(n + 0.5) - (n-0.5 + S)] A = ( 1-S) A

  i.e. the same width as zone 41.

  Consequently, the percentage of correctly measured bandwidths is doubled thanks to the offset of the roller, the percentage of unmeasured widths being reduced to 2. (S-0.5), which corresponds to ranges 44, 45 on

Figure 6c.

  For example, if a roller is used which defines adjacent measurement areas having a width A of 50 mm and which must be 60% covered to deliver a reliable signal, in the first position of the roller, the entire width of strips are taken into account in% of cases, the minimum edge width for taking

  account of the measurement being 50.0.6 = 30mm.

  Thanks to the offset of the roller, the edges can be taken into account in 2.100 (1-S)%, i.e. 80%

  cases, the maximum edge width not taken into account for each of the zones 44, 45 being 50. (0.6-0.5) = 5mm.

  In general, the two predetermined positions are calibrated during the installation of the roller so as to have an even number of measurement zones under the width of the strip for a first position and,

  respectively, an odd number for the second position.

  The displacement will intervene, if necessary, when changing the width of the strip, between two coils for a discontinuous installation and scrolling at speed

  reduced tape travel for continuous installations.

  The displacement device is provided so that the duration of the displacement does not exceed one second. During this time the measurement will be rendered inoperative and the regulations

  will be frozen on the last calculated values.

  Software implemented in the computer associated with the measuring roller is provided to take into account the change in the number of sensors and especially the change in symmetry resulting from the change in parity of the number of sensors under the strip. This software is intended to develop, from the measurements made on all the sensors, a flatness curve by carrying the calculated values on a graph displayed on the operator's desk, the abscissae of the points of this graph being fixed relative to to the geometry of the rolling stand, ie also with respect to the median plane P of the strip centered in running in the stand

of rolling mill.

  In the case shown in FIGS. 4 and 5, a central measurement zone 15c is centered in the median plane of the strip in the first position of the roller and the interface between two adjacent zones 15c, 15b is centered in the same plane in the second offset position. Of course this arrangement depends on the parity of the number (n)

  of fully covered areas and could be reversed.

  In fact, the choice of the position of the measuring roller according to the width of the strip will automatically cause centering, in the median plane P, either of a central zone or of the interface between two adjacent zones. In general, if we call (p) the number of fully covered areas placed on the same side of the median plane P of band 2, we have: n = 2p if n is even n = 2p + 1 if n is odd It can be established that a central zone 15c will be centered in the median plane of the band for the bandwidths L such that: 2p A + 2A (S-0.5) <L <(2p + 1) A + 2A (S-0.5) And the interface between two adjacent zones will be centered on the median plane P for the bandwidths L such that: (2p + l) A + 2A (S-0.5) <L <( 2p + 2) A + 2A (S-0.5) The software will calculate the position selected when changing the width. Then, during the running of the strip and during the measurement period, it will conventionally carry out the compensation of the partially covered areas as a function of the width of the strip and of its possible offset, which

  must be measured and entered into the calculator.

  Of course, the invention is not limited to the details of the embodiment which has just been described in

title of simple example.

  In particular, as indicated, the invention does not apply only to rollers comprising sensors placed in radial housings but to any flatness measuring roller defining a series of adjacent measurement zones of the same width A. Furthermore, it is simpler to move the roller axially with respect to a fixed strip, but the invention could also be implemented by transverse displacement of the axis of travel of the strip,

the measuring roller remaining fixed.

  The reference signs inserted after the technical characteristics mentioned in the

  claims are intended only to facilitate the

  understanding of them and in no way limit them

the scope.

Claims (4)

  1. Method for determining a stress distribution on a tensioned strip product traveling along a longitudinal axis, in which the strip is applied, during running, on an angular sector of a measuring roller rotatably mounted around of an axis perpendicular to the longitudinal axis of travel and comprising a plurality of adjacent measurement zones arranged one beside the other along the length of the roll and each covering a section of the roll having an elementary width A, each measurement zone being provided with means for measuring the application pressure on said zone of a corresponding part, of the moving strip, said strip having a width L = L1 + 21 comprising a central part of width L1 = n A equal to an integer n of measurement zones and two edges on which the application pressure can be measured by compensation if the width (1) of the edge (1) is at least equal to a width r minimum measurable a = SA, S being a coefficient less than 1, characterized in that, in cases where the edge width (1) is less than the minimum measurable width (a), a relative axial offset of the roll relative to the strip, over a half-width of zone A / 2, so as to give the edges a new width (1 ′) increased by a half-width of zone A / 2 compared to the width of edge initial (1), the proportion of widths of   non-measurable strands thus being reduced by 0.5.   2. Method according to claim 1, characterized in that, the measuring roller being in a first position, the measurement is carried out with edge compensation for all the bandwidths L such that (n + S) A <L <( n + 1) A, n being an integer number of measurement areas completely covered by the strip and that, in a second position offset by half a width A / 2, the measurement is carried out with edge compensation for all widths of bands (L) such that: (n - 1/2 + S) A, L <(n + 1/2) A so that the edges are eliminated only for two ranges of widths respectively: n A <L < (n - 1/2 + S) A and (n + 1/2) A <L <(n + S) A 3. Method according to claim 1, characterized in that the choice of the first position of the roller and of the second offset position is carried out as a function of the parity of the number (n) of zones entirely covered by the strip with: n = 2p if n is even n = 2p + 1 if n is odd It can be established that a central zone 15c will be centered in the median plane of the band for the bandwidths L such that: 2p A + 2A (S-0, 5) <L <(2p + l) A + 2A (S-0.5) And the interface between two adjacent zones will be centered on the median plane P for the bandwidths L such that: (2p + l) A + 2A (S-0.5) <L <(2p + 2) A + 2A (S-0.5) 4. Device for measuring the distribution of stresses on a strip product under tension and running along a longitudinal axis, comprising a measuring roller mounted to rotate on a fixed support, around an axis perpendicular to the longitudinal running axis and to which the strip is applied, said roller comprising a plurality of adjacent measurement zones arranged one beside the other along the length of the roller and each covering an elementary width (A), each measurement zone being provided with means for measuring the application pressure on said zone of a corresponding part of the moving strip, said strip comprising a central part of width Lo = n A equal to an integer (n) of measuring zones and two edges of width (1), the measurement of the application pressure of an edge being taken into account only if the edge width (1) is at least equal to a minimum width a = SA corresponding to a given proportion (100s)% of the width of a measurement zone, characterized in that the measuring roller is slidably mounted, parallel to itself, on its support and is associated with means for controlling the axial sliding and with means locking the roller in two centering positions of the measurement zones with respect to the longitudinal travel axis, respectively a first position for which the travel axis passes through the center of a measurement zone, the strip covering an odd number of zones and a second position, offset by a half-width of zone A / 2 relative to the first, for which the longitudinal axis of travel passes over the junction between two adjacent measurement zones, the strip covering an even number of areas.