EP1917113A1

EP1917113A1 - Inspection method

Info

Publication number: EP1917113A1
Application number: EP06794198A
Authority: EP
Inventors: Jean Perret
Original assignee: Siemens VAI Metals Technologies SAS
Current assignee: Clecim SAS
Priority date: 2005-07-22
Filing date: 2006-07-21
Publication date: 2008-05-07
Anticipated expiration: 2026-07-21
Also published as: WO2007010148A1; EP1917113B1; FR2888763A1; CN101227985A; DE602006012689D1; BRPI0613609A2; US7980109B2; CN101227985B; FR2888763B1; ES2339279T3; US20080165351A1

Abstract

The invention concerns a method for inspecting a strip in a reversible rolling device (1, 3, 5) comprising a cage arranged between two winding/unwinding devices (12, 13) having each a mandrel. The rolling is performed in several passes until the desired thickness is obtained over the entire length of a useful part included between two service lengths maintained wound on each of the mandrels. The invention is characterized in that at the end of the last pass between a winder/unwinder placed upstream of the cage (3, 5) in the rolling direction and acting as unwinding device, and a downstream winder/unwinder acting as winding device, the upstream service length is completely unwound from the unwinding device, then subjected to a rolling pass; the strip is then cut in the vicinity of its useful part to release, at its rear end in the direction of the last pass, a length of inspection part of which corresponds to the upstream service length rolled once.

Description

INSPECTION METHOD

The invention relates to rolling mills. More particularly, the subject of the invention is a method and an installation for inspecting the quality of a sheet metal strip after rolling.

It is known that, at the end of the rolling, the laminated sheet metal strip may have certain appearance defects which may be due, for example, to a slight variation in thickness in the transverse direction, resulting from the deformation and the wear of the rolls and / or the ceding of the cage, or marks left by the working rolls, some defects may also be due to the support rolls or to the cage itself.

These defects of appearance are reproduced on each face, in the longitudinal direction of rolling, with a period corresponding to the development, in this direction, of the circumference of the working rolls.

However, it is increasingly necessary to deliver sheets having a surface quality and, in general, an aspect as perfect as possible. For this, it is necessary to check the surface condition of the sheet metal strip after the rolling, in particular, to observe the marks left periodically on the strip by the passage between the working rolls. In a known manner, it is possible, for example, to take a section of the strip of sheet metal coming out of the rolling mill, in order to inspect both faces. The inspection is carried out on a strip length, the so-called inspection length making it possible to observe the marks or impressions left by the rolls of the rolling mill, and the length of inspection therefore corresponds to the largest period of the marks of the different rolls. In a tandem mill with several cages, the inspection length corresponds to the period of the marks produced in cage 1a upstream, from which band undergoes the greatest elongation by passing into the following cages.

In known manner, the inspection can be done in a particular installation where are made some reels to inspect, after their production by the rolling mill. The inspection facility includes an inspection and a horizontal table for unrolling a length of product corresponding to the length of inspection, on which the operator can perform the observation, the tracking, the layout or any another operation to take into account the marks on both sides of the sample used for the inspection.

Such an inspection facility is expensive to produce and also to operate. Indeed, it is necessary to remove a reel from the produced batch, to convey it towards the inspection facility, then to inspect it before continuing its routing. However, the rolling mill continues to produce during the inspection of a rolled strip sample, and the detection of a large defect then results in the rolled sheet strips produced in the gap being subsequently discarded.

It is possible to avoid this disadvantage in continuous rolling installations comprising several successive cages operating in tandem, the rolled strip being wound into a reel after the exit of the last stand. In this case, in fact, the winding installation usually comprises at least two cores operating alternately, for example on a carousel-type winder, and the band is cut in flight, at the end of the winding on a mandrel, to continue winding on another mandrel. Two successive cuts can then be made which are spaced so as to take an inspection length, which is then conveyed to an inspection table by means of switching and drive systems. This length of inspection has undergone all rolling stages, as the rest of the band and its surface condition is therefore well representative of that of the band.

Such a method is, however, not applicable to a reversible rolling installation comprising at least one rolling stand disposed between two winder / unwinder devices between which the band alternately circulates in one direction and in the other, each winding device / unwinder serving, according to the direction of rolling, of the winder downstream of the rolling stand and uncoiler upstream.

Indeed, the rolling is not continuous, it is not useful to have a carousel winder, with cutting theft of the tape.

In addition, depending on the number of passes, the downstream coiler, at the end of the last pass, can be placed on one side or the other of the rolling mill.

In this case, usually, the length of inspection is simply taken on the band at the end of the last pass, on one side or the other of the rolling mill. Of course, this inspection length must then be rejected. Or ₁ in the reverse rolling, it is already necessary to discard a substantial length of the tape.

Indeed, to allow a traction of the strip, during rolling, in one direction or the other, it is necessary that a certain length of strip that can be called "service length" is wound into several turns on each mandrel.

In some cases, this length of service used to tension the strip, consists of an extension welded to each end of the strip. This can then be rolled practically over its entire length, but the welding of the two extensions and their removal takes a certain time and decreases the productivity of the installation. When the coil is of great length, it seems It is preferable to sacrifice at each end of the strip a service length which is not rolled to the desired thickness and must therefore be discarded.

Usually, such a reversible rolling plant comprises, in addition to the two devices winder / unwinder, a so-called "first pass" unwinder capable of taking coils wound on themselves and without traction. A coil being placed on the first pass unroller, the product is unwound from it, in a first direction of travel, by passing his head in the cage to engage on the device winder / unwinder placed of the other side of the cage and thus serving, of coiler. The product is then wound almost completely on this winder until its end, forming the tail of the strip, leaves the unroller, this first pass being made, therefore, without rolling.

It is then back to engage the tail of the band on the second winder / unwinder device placed on the same side as the first pass rewinder and on which said end is fixed and then wound in superimposed turns. However, the winder / unwinder placed upstream of the mill, is braked so the band, driven by the rotation of the rolls, is energized, which allows to start the rolling which is, therefore, carried out in the opposite direction the first direction of scrolling during this second pass.

The running of the strip is, however, stopped before the end of the unwinding so as to leave, on the mandrel of the uncoiler, upstream of the cage, a minimum wound length corresponding to the number of turns required to maintain tension in the strip and which will be called "service length".

The rolling can then be done alternately in., One way and the other between the two winders / unwinders that serve, alternately, winder and uncoiler, but, to maintain each pass the tension necessary for rolling, it is necessary to keep on each mandrel a length of service that is not laminated. At the end of the last pass, it is necessary to eliminate the length of service at the tail of the tape and which does not have the required qualities. Similarly, the service length at the head of the strip and wound inside the coil, should be eliminated at the end of the course of the latter.

A rolled coil is therefore laminated to the desired thickness only on a central useful portion framed by two non-rolled service lengths, which represent a loss called "put to the mile". As indicated above, this inspection loss usually has to be added to the length of inspection which is taken from the useful part of the strip having the required qualities. Such an inspection process therefore increases the feathering.

The object of the invention is to overcome these drawbacks in a reversible rolling mill by means of a new method allowing an on-line inspection while maintaining a high production yield, the rejected length not exceeding the two lengths of service which must remain wound. on each mandrel and therefore do not have the required thickness.

The invention also covers a rolling installation for implementing the method.

The invention therefore applies, in a general manner, to a reversible rolling installation, comprising at least one rolling stand disposed between two reel / unwinder devices each having a mandrel on which a service length of the strip is wound. in several turns for the tensioning of the strip, the rolling being carried out in several passes with maintenance of the winding, on each mandrel, of the length of service, the strip being laminated to the desired thickness on a useful part lying between the two lengths of service.

According to the invention, at the end of the last rolling pass between a winder / unwinder positioned upstream of the cage, in the rolling direction and serving as a uncoiler, and a downstream winder / unwinder serving as winder, the length of upstream service is completely unrolled from the upstream uncoiler and is subjected to at least one rolling pass, the strip then being cut near the end of its useful part, so as to release, at its rear end in the direction of the last passes, a length at least equal to a necessary inspection length, at least a portion of which corresponds to the upstream service length which has been laminated at least once and thus gives an image of the appearance defects of the useful part.

As indicated above, the roll to be rolled is often first laid on a simple unwinder placed on one side of the rolling mill and from which the strip is unwound to pass into the rolling mill and attach to the reel / unwinder placed the other side.

In the case where the last reversible pass is an even pass, the band goes to the side of the unwinder. It is advantageous, at the end of the rolling of the upstream service length, that the rear end thereof is kept tight between the working rolls and that the direction of rotation of said rolls is reversed so as to return back a strip length sufficient to take an inspection length separated from the strip by the cutting thereof upstream of the cage, in the direction of the last pass, said length taken being placed on an inspection table and the band is returned in the direction of the last pass to completely wind on the downstream winder. In this case, the inspection length is rolled twice, first in the direction of the last pass and then in the opposite direction, before being cut and sent to the inspection table which is placed on the opposite side to the unroller, compared to the rolling mill.

On the other hand, in the case where the last reversible pass is an odd pass, the downstream coil on which the strip is wound is placed on the same side of the rolling mill as the inspection table. The strip can then be cut at a distance from its rear end corresponding to the desired inspection length, this inspection length being laminated once and sent directly to the inspection table placed on the same side of the rolling mill.

The invention thus makes it possible to take from the strip an inspection length of which at least the greater part corresponds to one of the two lengths of service which remains wound on the mandrels of each of the reels / unwinders, this length of service passing at least once between the rolls of the mill, which is sufficient to give an image of possible defects produced by said rolls on the useful length of the strip.

Thanks to the invention, the inspection length is therefore not taken from the useful part but from the tail of the strip, which in any case should have been discarded since it had not been laminated to the thickness. required.

In general, the invention applies to any reversible mill comprising at least one cage placed between two winder / unwinder devices, but it is particularly advantageous in the case of a reversible rolling mill with two rolling stands apart. one in the other because, in this case, the feathering is increased by the fact that the length of the tape included at the end of each pass, between the two cages has been rolled only once in the cage upstream and is therefore not at the required thickness. The length to be discarded then comprises the remaining service length wound on the mandrel to which is added the distance between the two cages and the total length to be rejected is normally greater than the length of inspection required, which can, thus, be easily removed from the tail of the rolled strip at least once at the last pass.

The invention thus makes it possible to carry out an online inspection without taking an inspection length on the useful part of the strip and, consequently, to keep a high production yield.

Furthermore, the implementation of the method can be done at a reduced cost and on existing reversible rolling mills since cutting, routing and inspection means are used which, in any case, were necessary.

The invention also covers an improved rolling mill installation for implementing the method according to the invention. But other features and advantages of the invention will appear in the following description of a particular embodiment of the invention, given solely for illustrative and non-limiting purposes, with reference to the accompanying drawings, in which: FIG. 1 is a schematic representation of a reversible rolling plant according to the invention for carrying out the inspection method according to the invention; - Figures 2a to 2j are schematic views of the mill of Figure 1 in different steps of the method according to the invention.

FIG. 1 represents a rolling mill with two reversible cages, in which the rolling mill 1 comprises two rolling stands 3 and 5 spaced apart from one another and placed between two winder / unwinder devices, respectively 12 and 13. The rolling mill 1 is a rolling mill reversible for rolling a strip of sheet metal in both directions of scrolling ie from right to left in a first direction of travel and from left to right in the opposite direction. In the embodiment shown in the figures, the rolling mill 1 is, in addition, associated with a first-pass unroller 1 1 adapted to receive a coil 21.

This coil 21 is constituted by a sheet metal strip having an initial thickness that it is desired to reduce by rolling to obtain a sheet metal strip having a required final thickness. The sheet metal strip is wound on itself to form the coil 21 and is first placed on the unroller 1 1 which has no mandrel. Means 31 make it possible to grip the head of the sheet metal strip and to guide it to pass between the rolls of the two stands 3 and 5 while proceeding to the left, the head of the band being fixed on the reel / unwinder 12 placed on the second side of the mill 1 and which then serves as a winder for winding the sheet metal strip. It scrolls from the right to the. left in this first scrolling pass which is carried out without rolling until complete unwinding of the band whose rear end, forming the tail, remains tight between the working rolls of the two stands 3 and 5, as shown schematically in Figure 2d. As usual, a second reel / unwinder upstream called second rewinder second pass 13 is disposed between the first unwinder 1 1 and the input of the rolling mill 1. The direction of rotation of the working rolls of the two stands 3 and 5 is then reversed to scroll the band from left to right in a second pass.

The right end of the band, which became the head thereof, is engaged on the mandrel of the winder / unwinder 13 which then operates in second pass winder (Figure 2e). The upstream winder / unwinder 12 which operates uncoiler, is braked so as to tension the strip driven by the cylinders of the two stands 5 and 3. The rolling can start at this second pass. The rolling is then carried out alternately in the first direction of travel from the right to the left, for the odd passes, and in the second direction, from left to right, for the even passes, the number of passes depending on the conditions of the rolling and the final thickness required.

However, to allow the tensioning of the band, a length of service remains wound on the reel / unwinder 13 serving uncoiler for odd passes and the reel / unwinder 12 serving uncoiler for even passes.

In a known manner, an upstream decontamination device 31 of the strip and upstream cutting shears 32 are located just upstream of the rolling mill 1, in the first direction of travel. Similarly, the upstream cage 3 comprises presses 33 making it possible to engage the leading end of the strip to be rolled between the roll trains of the upstream cage 3.

Preferably, the stands 3 and 5 are of the quarto type, that is to say that they respectively comprise two working cylinders 30, 50 of small radius and two retaining cylinders 39, 59 of large radius.

FIG. 1 has been simplified for the sake of clarity, but the rolling mill 1 also comprises all known rolling means, such as means for cooling the rolls, measuring the tension of the strip, cooling the strip or holding it, as well as deflection cylinders 45 for guiding the band.

The downstream casing 5 is identical to the upstream casing 3, except that the decontamination device 51 and the band engagement presses 53 are arranged in downstream of the second cage 5, to allow the operation of the rolling mill in the opposite direction.

A switching device 60 guides the strip first to an overhead conveyor and then to an inspection conveyor constituting the inspection table 62.

Possibly air conveyors and inspection are joined by an intermediate conveyor passage. When the sheet is on the inspection table 62, the actual inspection step is performed by a qualified person with the necessary means.

Downstream of the inspection table 62, the rolling installation comprises a tumbler type turning device 65 for returning the sample to inspect it on its other side. At the end of the inspection step, as will be described below with reference to Figures 2, the inspected sample is rejected in a bucket 69, if necessary after being cut into pieces by means of downstream shears 68.

Moreover, the coils 11, 13 and 12 are carried by jacks allowing their loading and unloading. The entire installation is based on concrete foundations. A metal frame allows to maintain and support the various components of the installation.

Each of FIGS. 2a to 2j shows schematically the rolling plant of FIG. 1, the reference numerals having been taken over to indicate the same constituent elements. In the example shown, the upstream 3 and downstream 5 cages (in the first direction of travel) are of the quarto type comprising two working cylinders and two support cylinders but could be of any other type. The first winder passes 12 and the second winder passes 13 are schematized with their mandrel unlike the first pass unroller 1 1 which does not. The coils 21, 22 and 23 are shown at different stages of the inspection process according to the invention. In FIG. 2a, a rolling sheet metal coil 21 is disposed on the first-pass unrolling device 11 and then unrolled. The leading end 101 corresponding to the front end of the sheet metal strip 100 is engaged between the working rolls of the upstream stand 3. Once the band 100 is engaged, the working rolls of the upstream stand 3 are used to to apply. a friction force for driving the band 100. The leading end 101 then moves in a first direction of travel towards the downstream cage 5 as indicated by the arrow, that is to say from right to left.

In Fig. 2b, the leading end 101, after engagement between the rolls of the second stand 5, has been conventionally fixed to the mandrel of the first pass winder 12. The work rolls of stands 3 and 5 are tight. on the web and rotated to control the unwinding of the sheet metal strip 100 which, at the same time, is wrapped around the mandrel of the first pass winder 12 (Fig. 2c). During this first pass, the coil 21 is unwound while the coil 22 is wound. The first unrolling pass 1 1 does not have a mandrel, it is impossible to apply a voltage on the band 100 during the first pass. Consequently, the desired reduction rate can not be achieved during this first scrolling pass. Figure 2d shows schematically the end of the first pass. The spool 21 is completely unwound and the sheet metal strip 100 is wrapped around the mandrel of the first spooler 12 forming a spool 22. The first pass ends when the tail end 102 of the strip 100 is near the spool. upstream cage 3. It is advantageous not to disengage the tail end 102 at the end of the first pass. By disengagement, it is meant that the tail end 102 goes beyond the downstream cage 5. The first pass is stopped at least when the tail end 102 is between the cages. Of preferably, the first pass is stopped when the tail end 102 is still upstream of the upstream cage 3.

The direction of operation of the mill 1 is then reversed so as to control the scrolling of the sheet metal strip 100 in the opposite direction indicated by the arrow shown in FIG. 2e. In a first step, the working rolls of cages 3 and 5 are simply tightened to control the movement of web 100 from left to right until its front end 102 can be fixed to the mandrel of the machine. second pass winder 13.

It is then possible to start the second pass, illustrated by FIG. 2f, the strip 100 taking place from the coil 22 which thus functions as a de-borer but can be braked so as to put the strip under tension and carry out the rolling between the rolls of the two stands 5 and 3, the spacing between the rolls being adjusted to achieve a suitable reduction ratio. The strip is wound to form a coil 23 on the reel / unwinder 13 serving as a winder. It is then possible to carry out the rolling in successive passes between the two winders, first pass 12 and second pass 13, which are equipped with the necessary means allowing the application of a torque on their respective mandrels in order to keep the sheet metal strip 100 under tension. . Significant reduction rates can be achieved in the second pass.

The number N of passes of the rolling cycle depends on the reduction rate to be achieved in order to obtain the desired final thickness. However, as indicated above, only the useful central portion of the strip is laminated to this thickness, the two lengths of service which must remain wound on the mandrels of the two reels / unwinders 12, 13 not being rolled at each pass. According to the invention, the inspection will be carried out on a section taken on one of these two lengths of service which should, in any case, be rejected. It must, however, that this section is an image of the useful part to present the same aspect and, in particular, the same marks and imprints of the cylinders.

For this purpose, as shown schematically in FIG. 2g, at the end of the last pass which, in the example shown, is an even pass, the rolling is continued between the rolls of the two stands 5 and 3, until the rear end 101, in this second running direction of the strip, is released from the mandrel of the uncoiler 12 and comes close to the cage 5.

The band thus remaining clamped between the rolls of the two stands 5 and 3, the direction of rotation of said rolls is reversed so as to restart the band in the first direction of movement, that is to say from right to left , in Figure 2h.

The scrolling, from right to left, is continued until the tail end 101 of the strip, which is the front end in this first direction of travel, is at a distance from the shear 32, placed upstream of the first cage 3, at least equal to the required length of inspection. In practice, this inspection length is generally slightly greater than the service length and the band can then be cut by the shear 32, as indicated in FIG. 2h, along a line situated in the useful part. of the band but near its rear end. This useful part can therefore be wound completely on the winder 13 to form the coil 23, only the head forming the first turns wound on the mandrel, should be rejected since it corresponds to the non-rolled service length (Figure 2i).

The remaining part 105. the band, which has remained tight between the cylinders of cages 3 and 5, is driven to the left, that is to say in the first direction of travel and directed by a switch to the inspection table 62 shown in Figure 1.

This section 105 corresponding, at least for the most part, to the length of service, is passed twice between the working cylinders, respectively in the first direction of travel, from left to right, in FIG. the second direction of scrolling, from right to left, in Figures 2h, 2i. In addition, even if the rear end 101 has been released from the uncoiler 12, the band has remained energized, in one direction or the other, between the two stands 5 and 3. This part 105 therefore undergoes, when its passage between the cylinders, the same marks as the useful part of the band, these marks reproducing identically to each pass. The sampled section 105 therefore has the same appearance as the strip, which makes it possible to check the quality of the latter.

In FIG. 2j, the sample 105 is positioned on the inspection table where the actual inspection takes place, possibly on both sides by inverting the sample 105. In parallel, the coil 23 is removed from the installation. rolling and fed to, for example, another facility for further processing. Similarly, during the inspection of the sample 105, a new coil 21 'consisting of a new sheet metal strip 100.' The rolling mill is loaded onto the first-pass unroller 11 and its leading end 101 'is engaged in the mill 1 so as to prepare the next rolling cycle.

The inspection method according to the invention therefore takes advantage of the fact that the non-rolled service length, which must be rejected in any case, is used as an inspection sample because it comprises the marks and impressions of the rolls. Indeed, although not rolled to the right thickness, the unlaminated length passes between the cylinders which leave their marks on both sides. The length of the inspection shall be chosen so as to include at least one period of each of the marks of the rolling mill roll trains. Thus, the inspection length comprises at least the non-rolled length, but can also be greater if the period of one of the roll trains requires it.

The invention thus makes it possible to inspect the quality of rolling on-line by minimizing the losses of rolled material to the desired thickness, since the inspection is carried out on a part of the sheet that should have been discarded, whatever happens. not being the right thickness. In addition, the inspection operation does not consume time. Indeed, as shown in Figure 2j, when the rolling inspection of a first cycle takes place, the next rolling cycle can be prepared by engaging for example the leading end 101 'of the next coil 21'. The handling of the coil 23 produced is also done synchronously with the inspection step. In addition, the implementation of the inspection method as described above does not require or few modifications of existing facilities.

Other alternative embodiments of the method according to the invention as well as the rolling installation are possible. For example, shears may be located upstream or downstream of the rolling mill, possibly between the stands of the rolling mill. In the case where shears are disposed only downstream of the mill 1, once the inspection sample has been separated from the remainder of the sheet metal strip 100, the mill can no longer serve as a means of driving the sheet. sample to the inspection table. It would then be necessary to have own drive means capable of moving the sample on the inspection table.

In this case, however, if an odd number of passes is required, the inspection table may be located downstream of the rolling mill 1 in the first direction of scrolling, and will inspect, a sample corresponding to the service length wound on the reel / unwinder 13 and, lying in line in the first direction of travel. In this case, indeed, the inspection table can be placed on the same side as the winder 12 on which the band is wound. If there is a shear between the second cage 5 and the winder 12, the latter can cut the strip at a distance from its rear end 102 at least equal to the required inspection length. The strip can then be wound completely on the reel 12 and its rear part, which constitutes the inspection length, remains tight between the rolls of the stands 5 and 3 which drive it to the left, in the first direction of travel so that to point it towards the inspection table. In this case, the inspection section only passes once between the rolls of the two stands 5 and 3, but this passage is sufficient for the rolls to print and the inspection length has a representative appearance of that of the useful part of the band.

As indicated above, since two reversible cages are used spaced from each other, the inspection length remains tight between the two cages, even after cutting the strip. The method according to the invention is, however, applicable to a rolling mill comprising a single reversible cage. In this case, after being released from the uncoiler, the rear portion of the strip is no longer energized but the passage between the working cylinders which remain tight on the strip, allows to print the same marks on the two faces thereof, the inspection length taken from the rear end of the strip and constituting the length of service, having the same appearance as the useful part of the strip.

Although the invention has been described with reference to a particular embodiment, it is in no way limited to this embodiment. It includes all the technical equivalents of the means described as well as their combinations which come within the scope of the invention.

Claims

1. A method of inspecting a rolled strip in a reversible rolling mill comprising at least one roll stand (3,5) disposed between two winder / unwinder devices (12, 13) each having a mandrel on which a length of service of the strip is wound in several turns for the tensioning of the strip, the rolling being carried out in several passes until the desired thickness is obtained over the entire length of a useful part between two lengths of service maintained wound at each pass on each of the mandrels, characterized in that at the end of the last rolling pass between a winder / unwinder (12) placed upstream of the cage in the rolling direction and serving as a uncoiler, and a downstream reel / unwinder (13) serving as a winder, the upstream service length is completely unrolled from the upstream uncoiler and is subjected to at least one rolling pass, the web being then cut off -in the vicinity of the end of its useful part, so as to release, at its rear end in the direction of the last pass, a length at least equal to an inspection length (105) required, at least a portion of which corresponds to to the upstream service length which has been laminated at least once and thus gives an image of the appearance defects of the useful part.

2. Method according to claim 1, characterized in that, at the end of the rolling of the upstream service length, the rear end thereof is held tight between the working rolls and the direction of rotation of said rolls is then inverted to return a sufficient length of tape back to take an inspection length (105) separated from the tape by cutting it upstream of the cage, in the direction of the last pass, said length removed being placed on a table and the strip being returned in the direction of the last pass to completely wind on the downstream winder (13).

3. Method according to claim 1, characterized in that, at the end of the last rolling pass, the strip

(100) is cut downstream of the rolling mill (1) at a distance from its rear end corresponding to the inspection length (105) and is then completely wound on the downstream winder (13) leaving an inspection length laminated once which is sent to the inspection means.

4. Method according to one of claims 1 to 3, characterized in that, the rolling plant comprising a reversible mill having at least one cage (2, 3) operable for odd passes in a first direction of rolling and for even passes in a reverse direction, said method comprises the steps of

- (a) from a reel (21) placed on a first side of the rolling mill, the strip is unwound in a first direction of travel passing through the open cage and (b) a first end of the head of the strip is attached to a winder-unwinder (12) placed on a second side of the rolling mill and operating in a winder; - (c) during this first pass, the band is clamped between two work rolls of the cage which are rotated in the first direction of travel for the winding of the band on the winder of the second side of the cage , (d) until a second end, at the tail of the strip

(102), arrives near the cage;

- (e) the direction of rotation of the rolls is reversed to control the running of the web in the opposite direction and said second end of the web is attached to a winder-unwinder (13) placed on the first side of the rolling mill;

- The strip is wound on said winder-unwinder (13) of the first side which operates in a winder, the rewinder-rewinder (12) of the second side operating uncoiler and, when a first service length is wound in several turns on said first-side winder, the web is tensioned so as to laminate the web during this second pass (f);

the running of the strip is stopped so as to maintain a second service length wound in several turns on the retractor-rewinder (12) of the second side; - The direction of travel is still reversed, the reel / unwinder (12) of the second side then operating in a rewinder for a third pass with rolling of the strip in the first direction of travel; the rolling is carried out in a plurality of passes, alternately odd in the first direction of travel and pairs in the opposite direction, a length of service being kept wound at each end of the strip on each of the unwinding reels,

after the end of the last rolling pass between a uncoiler placed upstream of the rolling mill and a downstream coiler, the rolling is continued during the latter pass, until the upstream service length placed at the tail band, in the direction of the latter pass, is released from the uncoiler (12) upstream and is laminated at least once (g),

- (i) the strip is cut at a distance from its rear end at least equal to an inspection length (105) at least a portion of which corresponds to said upstream service length rolled at least once,

- (j) the inspection length is sent to inspection means, - the tape is wound completely on the downstream winder (13).

5. Method according to claim 4, characterized in that it comprises, after a first rolling of the upstream service length, the following steps: - (g) stopping the rolling before passage of the rear end (101) of the web (100) and holding it tight between the work rolls;

- (h) inversion of the direction of rotation of said rollers for returning the strip upstream, - (i) cutting the strip at a distance from its rear end, in the direction of the last pass, at least equal to one inspection length (105),

- (j) complete winding of the remaining band on the downstream winder (13), in the direction of the last pass, - sending the inspection length to inspection means.

6. Method according to any one of the preceding claims, characterized in that, after the step of releasing an end (101) and before the step of unrolling an inspection length (105), said released end n is not completely disengaged from said rolling mill (1).

A method according to any one of the preceding claims, characterized in that said step of unrolling an inspection length (105) is performed using said rolling mill (1) as a tape drive means (100). ) of sheet metal.

8. Method according to any one of the preceding claims, characterized in that said inspection length (105) is brought to an inspection table (62) associated with the rolling mill (1).

9. A method according to claim 8, characterized in that for inspection of both sides of the inspection length (105), the latter is returned by means of a drum (65) placed at one end of said table d inspection (62).

A method as claimed in any one of the preceding claims, characterized in that the step of inspecting said inspection length (105) and the step of discarding the inspection length are performed in parallel with the step rewinding the web (100) on the rewinder (13) of the last pass.

11. Method according to any one of the preceding claims, characterized in that it comprises an additional step of positioning a reel (21) of the strip to be rolled on said uncoiling rewinder (11), and in that the step of positioning a roll to be rolled and the step of engaging the leading end (101 ') for a new rolling cycle are performed in parallel with the step of inspecting the inspection length (105) and the step of discarding the inspection length of the previous rolling cycle.

12. Method according to any one of the preceding claims, characterized in that said inspection length (105) is at least equal to a length making it possible to observe at least one period of the marks left by the roll trains equipping said rolling mill. (1).

Method according to one of the preceding claims, characterized in that the rolling installation is provided with shears (32), and in that the step of cutting said inspection length (105) is carried out when at the step of unrolling an inspection length, the distance between said released end and said shears is equal to the required inspection length.

14. Method according to one of the preceding claims, characterized in that it applies to a reversible mill (1 1) having two rolling stands (2, 3) spaced from one another, the set of two cages being placed between two devices winder / unwinder (12, 13) alternately serving dewinder and winder.