WO2014016120A1

WO2014016120A1 - Method of rolling metal plate

Info

Publication number: WO2014016120A1
Application number: PCT/EP2013/064565
Authority: WO
Inventors: Joseph Lee
Original assignee: Siemens Plc
Priority date: 2012-07-23
Filing date: 2013-07-10
Publication date: 2014-01-30
Also published as: GB2504269B; GB201213011D0; GB2504269A

Abstract

A method of rolling a metal mother plate (10), the method comprising defining one or more longitudinal thickness profiles; allocating (40) a defined profile to each of two or more sub-sections of the mother plate; rolling (43) the mother plate with the allocated profiles in each sub-section; after rolling, measuring (49) thickness of the plate at a plurality of measurement points (31) along the mother plate; correlating (51) measured thickness with expected thickness from the allocated thickness profile at the measurement points; and deriving (52) cutting positions on the mother plate between the sub-sections based on the result of the correlation.

Description

METHOD OF ROLLING METAL PLATE

This invention relates to a method of rolling a metal plate.

The production of longitudinally profiled plates, also known as taper plates, is a well established process. For example, the paper Steel Plates for Bridge Use and their Application Technologies in JFE Technical Report No.2 describes the use of longitudinally profiled plates for bridge applications and it also describes various different profiles including simple linear tapers, convex and concave profiles and a profile with a two step thickness change. The paper Steel Products for Shipbuilding in JFE Technical Report No.2 describes the use of longitudinally profiled plates in shipbuilding and also describes various profiles. The brochure from Dillinger Hutte GTS titled 'Longitudinally Profiled Plates (LP-Plates)' also describes various applications of longitudinally profiled plates and on page 3 it illustrates the various profiles that Dillinger produce.

The process of rolling a longitudinally profiled plate starts with a single slab which is rolled into a single rolled plate which is known as a mother plate. During the process of rolling the mother plate, a predetermined longitudinal thickness profile is applied to the mother plate. In general, several passes through the rolling mill are necessary in order to achieve the desired final thickness and longitudinal profile and the profile is gradually imparted to the mother plate during the course of several passes. As the mother plate is gradually reduced in thickness and the longitudinal profile is imparted to it, the control system for the mill keeps track of the thickness versus length profile of the plate and the current position of the plate in the mill in order to synchronize the movements of the mill thickness control system with the position of the plate. Plate mills are generally reversing mills and so each pass is executed in the opposite direction through the mill compared to the previous pass and hence the control system also takes this into account.

In many cases the longitudinally profiled mother plate becomes a single final plate which is shipped to the customer. The mother plate will generally be side- trimmed and trimmed at each end in order to obtain the required final plate width and length, but essentially the whole of the mother plate becomes a single final plate.

However, in some cases, the longitudinally profiled mother plate may be divided into two daughter plates. JP07148501 describes dividing a longitudinally profiled plate into two separate daughter plates with different thickness. JP2008238262 describes a similar process of dividing a longitudinally profiled plate into two daughter plates with different thickness and also describes scrapping the part in between the two different thicknesses. The reason for rolling a slab into a longitudinally profiled plate with two different thicknesses and then cutting it into two separate plates is simply to improve the productivity of the mill. For example if the mill has an order for just two plates of the same grade of material and a similar width, but with different thicknesses then it is more efficient to roll one slab with a longitudinal profile and to cut the mother plate into two separate daughter plates than it is to roll two separate smaller slabs. The rolling time is reduced compared to rolling two small slabs and the yield losses from trimming the ends of the mother plates are also reduced.

In the conventional longitudinal rolling process the rate of change of thickness with length which is known as the slope of the profile only changes sign from positive slope to negative slope or from negative slope to positive slope at most once along the length of the mother plate. In some cases the slope goes to zero (i.e. there is constant thickness) several times as in profiles G and I in the Dillinger document, but it still only changes from positive slope to negative slope or vice versa once.

Also the shearing of longitudinally profiled plates has conventionally only been done to divide a single mother plate into two daughter plates with different thicknesses from each other, but where each daughter plate has constant thickness along its length.

In accordance with a first aspect of the present invention, a method of rolling a metal mother plate comprises defining one or more longitudinal thickness profiles; allocating a defined profile to each of two or more sub-sections of the mother plate; rolling the mother plate with the allocated profiles in each sub-section; after rolling, measuring thickness of the plate at a plurality of measurement points along the mother plate; correlating measured thickness with expected thickness from the allocated thickness profile at the measurement points; and deriving cutting positions on the mother plate between the sub-sections based on the result of the correlation.

By measuring the thickness at measurement points on the plate and correlating this with the expected thickness at those points, it is possible to estimate where to cut between each sub-section, so that the cut sub-sections have the expected profile. In one embodiment, the defined profile includes a change of slope from positive slope to negative slope or from negative slope to positive slope.

Alternatively, the allocated profile of each sub-section includes a positive slope or a negative slope, such that the longitudinal thickness profile of the mother plate changes slope at least twice along the length of the mother plate.

Preferably, at least two different profiles are defined and allocated.

Preferably, the method further comprises repeating the allocated plate thickness profiles cyclically along the full length of the plate.

Measurement points may be distributed along the length of the mother plate, set for only a single sub-section, or set between each sub-section to which a profile has been allocated, but preferably the measurement points are distributed in

regions including at least a part of adjacent profiles.

In certain profiles, there may be clear maxima or minima between adjacent profiles, so that using partial data from adjacent profiles gives a more accurate estimate of the cutting point than using all the data from a single profile.

Preferably, the method further comprises tracking passage of the measurement points through a thickness measure in a thickness measuring device.

Preferably, passage of a measurement point is tracked by sensing speed of the plate through the thickness measuring device, in combination with head end position information on entry to the thickness measuring device.

Preferably, the method further comprises applying temperature compensation to a thickness measured at the or each measurement point.

The mother plate may be rolled with directly adjacent profiles and cut between these, but to allow for deviations between expected and measured thickness at different points along the plate, preferably cutting sections are rolled between each sub-section and the cutting position within the cutting section is modified according to the result of the correlation between measured and expected thickness for each profile adjacent to that cutting section.

Preferably, the method further comprises, for each cutting section, determining a tail cut position at the end of one sub-section; a head cut position at the beginning of the next sub-section; and a scrap portion between adjacent tail and head cut positions.

Preferably, the method further comprises marking each derived cutting position. Preferably, the method further comprises cutting the rolled mother plate at the derived cutting positions.

Preferably, the method further comprising determining arrival of each of the cutting positions of the plate at a cutting location of a shear and shearing the plate as each cutting position arrives.

Preferably, arrival of each cutting position of the plate is determined by means of measuring rollers, laser sensors, or mechanical stops.

In accordance with a second aspect of the present invention, a method of rolling a metal plate comprises defining a longitudinal plate thickness profile, the profile changing in slope from positive slope to negative slope or from negative slope to positive slope at least twice along the length of the plate; and rolling the plate with the defined profile.

Preferably, the method further comprising defining and allocating at least two different longitudinal thickness profiles, each profile including a region with a positive slope or a negative slope; and rolling sub-sections of the plate with the allocated profiles.

Preferably, the method further comprising cutting the plate into the rolled subsections.

An example of a method of rolling a metal plate and a rolled metal plate in accordance with the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates an example of a rolling mill in which the method of the present invention can be applied, showing the rolling of the first part of the longitudinal profile.

Figure 2 illustrates the rolling mill of Fig.1 , after the plate has been rolled with a profile having a number of changes in the slope;

Figure 3 illustrates use of a cutter to cut the plate into daughter plates after rolling;

Figures 4a, b and c illustrate examples of plates rolled in accordance with the present invention;

Figures 5 a, b and c are graphs illustrating further detail of the correlation method of the present invention; and, Figure 6 is a flow diagram of an example of a method of rolling according to the present invention.

The present invention addresses the problem of producing a mother plate in which the slope of the longitudinal thickness profile changes sign more than once along the length of the mother plate. It also address the problem of obtaining multiple daughter plates from a single mother plate where each daughter plate has a longitudinal thickness profile. The longitudinal thickness profiles of the multiple daughter plates may be the same as each other or may be different. This is done by rolling partial lengths, sub-sections, of the mother plate with a desired profile and then cutting the rolled mother plate between the sub-sections. Conventional rolling methods were not able to roll multiple profiles or to accurately distinguish between adjacent profiles in order to cut the plate at the required position. The change of sign of the slope of the profile includes any regions with constant thickness (i.e. zero slope) so that for example a change from positive slope to zero slope and then to negative slope counts as one change of sign of the slope.

There are a number of advantages in the method of the present invention. A first advantage of this method is that the mother plate can be rolled in such a way as to allow it to be cut into two or more daughter plates each of which has a longitudinal profile, rather than simply a different constant thickness. Each daughter plate can either have the same longitudinal profile or a different longitudinal profile. This is particularly advantageous where the change in thickness required takes place in a length which is significantly shorter than the typical length of a mother plate which is usually between 20 metres and 50 metres long. For example, when making tubular sections for structures, it can be advantageous to have a thicker wall in the plane where the highest loads occur and a thinner wall at 90 degrees to this plane. If the tubular sections are made from plates then the plate requires the change from thick to thin to take place in a length corresponding to only a quarter of the tube circumference. Since tubular sections for structures usually have diameters of only a few metres then the length over which the thickness has to change is clearly much less than the typical length of a mother plate. Whilst it might be possible to roll a very small mother plate and to use the conventional longitudinal profiling method to produce a single daughter plate it is far more efficient to roll a mother plate with multiple thickness profiles along its length and then to shear this mother plate into multiple daughter plates each of which has a longitudinal profile.

A second advantage of this method is that it allows a rolled plate to be produced which has multiple points along its length where the thickness is greater than the average thickness. It is well known that one way to stiffen a thin plate is to weld or otherwise attach ribs to it. The ribs make the second moment of area of the section much greater than that of the plate on its own and hence provide greater bending stiffness without significantly adding to the total weight and cost. The method of the invention allows a mother plate to be rolled where there are multiple thicker parts along its length and these thicker parts stiffen the plate in the same way as ribs without significantly adding to the overall weight of the plate. The mother plate which is rolled in this way might become a single final plate or it might be cut into two or more daughter plates each of which has multiple thicker parts along its length. Of course the method is not limited to producing plates with multiple thicker parts along the length. It could also be used to produce plates with multiple points along the length which are thinner than the average thickness. For example if the plate required channels or grooves in it then these could be rolled in instead of being machined during a later process.

One of the difficulties with producing multiple profiles within the length of a single mother plate and then dividing this mother plate into daughter plates each with a longitudinal profile is in determining the best position to make the cuts. During rolling there are errors in the tracking of the length of the plate and there are also errors in controlling the thickness. Another problem is that the thickness measurement on most plate mills is some distance away from the mill itself. An additional problem is that the shear-line on most plate mills is usually quite separate from the rolling mill itself.

JP2008238262 relies on the encoder at the rolling mill itself to track the change in thickness and to use this to determine the correct shearing position, but on most mills this is not practical.

To solve the problem of errors in the thickness control and errors in the tracking the method of the invention measures the thickness profile along the length of the plate and may use a correlation type algorithm to determine the best cutting positions.

Figs. 1 and 2 illustrate an example of apparatus 1 for carrying out the method of the present invention. In the example of Fig.1, upper and lower work rolls 2, 3 of a pair of work rolls are mounted relative to a rolling line 4. The work rolls are supported in a rolling mill housing (not shown) in such a way that the work rolls 2, 3 can be moved towards or away from one another by screws 54, or hydraulic cylinders 15, in order to change the gap between them and hence the thickness of the rolled material. A nip 9 is formed between the work rolls and the plate 8 is guided into the nip. Moving the work rolls 2, 3 towards or away from one another changes the size of the nip 9 and allows the thickness of the rolled plate 10 emerging from the nip to be varied. Roller tables 11 , 12 on an entry side and an exit side of the work rolls support and guide the plate to be rolled.

Movement of the work rolls is under control of a mill automation controller 5 which is also coupled to roll speed sensors 6a and 6b and a rolling load sensor 7.

Typically, the rolling load sensor 7 detects the presence of the plate when it enters the rolling mill and the roll speed sensors 6, together with the known roll diameters and forward slip compensation, are used to calculate the length of the plate which has been rolled. The controller calculates a preset thickness versus length profile and it uses the calculated length of the plate which has been rolled to determine the required thickness at each point and hence the correct movements of the hydraulic cylinders 15 and/or the screws 54 during the rolling of the plate.

In general the apparatus cannot achieve the required final plate thickness and longitudinal profile in a single pass through the rolls and therefore the plate is passed several times through the apparatus. Each time the plate passes through the apparatus the overall thickness is reduced and the longitudinal profile gets closer to the final desired profile. Commonly plate mills are reversing mills and each successive pass is in the opposite direction to the previous pass. The controller 5 takes the reversals into account when it calculates the required preset thickness versus length profile for each pass.

The apparatus may include additional sensors, for example hot metal detectors or laser speed measurement devices, but the basic principle is the same. The apparatus may also include thickness measurement devices at the entry side and/or the exit side of the mill to improve the thickness control.

After the plate 10 has finished rolling the thickness of the plate versus its length is measured. In the example shown in Figure 2 the thickness measurement 16 takes place downstream from the rolling mill, but in the same line 4 as the rolling mill. However, it is also possible to do the thickness measurement in a separate line from the rolling mill. For example the thickness measurement could be done in the line where the shearing of the plate is carried out.

In order to obtain an accurate thickness versus length measurement the position of the plate 10 has to be accurately tracked through the thickness measurement device 16. As illustrated in Figure 2 this is usually done by speed sensors such as 17a, 17b, 17c which measure the speed of the rollers 12 on which the plate 10 is transported through the thickness gauge 16. Alternative methods for tracking the position of the plate accurately include laser speed measurement devices, or measuring rolls. In addition to measuring the speed of the plate accurately it is important to start the tracking of the plate position at a precise position relative to the head end of the plate 13. This can be done using a hot metal detector, or a cold metal detector depending on the location of the thickness measurement device, or by means such as light curtains, or similar devices, or from the thickness measurement device itself. If the thickness gauge 16 is closer to the rolling mill than the length of the plate then tail end of the plate 14 could be still being rolled when the head end 13 reaches the thickness gauge 16. In this case the tracking system can use the mill speed sensor 6 as well as the roller speed sensors 17. If the plate thickness is measured whilst the plate is still hot, as would normally be the case if the measurement is done in the same line as the rolling mill, then the thickness measurements require compensation for the plate temperature as per normal practise. Because the plate thickness varies along the length of the plate the temperature will also vary along the length and the temperature compensation needs to take this into account.

Thickness data at measurement points is sent back to the controller 5, for example the measurement points may be for thickness measured at points a fixed distance from the head 13 of the plate, measured at predetermined time intervals after the head is detected, or measured substantially continuously until the sensors detect the passage of the tail 14 of the rolled plate 10 past the sensor 16.

Further along the line, or in a separate line, a cutter 18, also controlled by the controller 5, is arranged so that the rolled mother plate 10 can be cut into daughter plates with their rolled profiles as illustrated in Figure 3. The cutter 18 is typically a shear, but it may also be a plasma cutter, or water jet cutter, or any other type of cutting device. Accurate tracking of the mother plate through the cutter 18 is required in order to make the cuts at the required positions. Typically the plate 10 is moved through the shear 18 by pinch rolls 19a and 19b whose rotation is controlled by the controller 5. The position of the plate within the shear can be measured using measuring rollers 20a and/or 20b. Alternative well known methods for positioning the plate accurately within the shear include laser sensors and adjustable mechanical stops.

The rolled plate may have the same profile repeated in each sub-section, or two or more sub-sections may have different profiles. Examples of how the rolled plate can have different longitudinal thickness profiles in different sub-sections of its length are shown in Fig.4. The example profiles in Fig.4 have a single change in slope within each sub-section for ease of illustration, but the method of the present invention can also be applied to profiles having multiple changes in slope within each sub-section, allowing more complex rolled plates to be created. Fig.4a illustrates a plate having multiple profiles 28a, 28b, 28c within one plate 10. However, the rolled plate 10 still needs to be divided up after rolling. Fig.4b shows an example for obtaining multiple daughter plates of varying profile from one mother plate. Each daughter plate is represented by the sub-sections 25, 26, 27 in the plate 10, which in this example have three different profiles, but the method is equally applicable to the case where there are two different profiles which alternate between sub-sections along the length of the plate 10, multiple profiles which are repeated cyclically along the length of the plate, or a single repeated profile. Between each plate, cutting positions 21 are shown. Fig.4c shows sub-sections 25, 26, 27 with a similar set of profiles to Fig.4b, but in this case, rolled with safety regions 29 between each different sub-section with a head and tail cut line 23, 24 at each end of the safety region. During the cutting process, the excess material between the tail and head cut lines, which formed the safety regions, is scrapped. In Fig 4c the safety regions are of constant thickness, but this is not a necessary requirement; the safety regions could be continuations of the adjacent profiles at each side.

The method of the present invention will be explained in more detail with reference to the graphs of Fig.5 and flow diagram of Fig.6. Before starting a rolling process for a plate, configuration of the required profiles for the sub-sections of the plate needs to be carried out. This configuration is set in the mill automation controller. The profiles may be chosen from pre-stored profiles in the controller or may be downloaded to the controller specifically for that plate to be rolled. For each plate to be rolled, a minimum of two sub-sections are rolled and the profile to be applied in each sub-section of the plate is chosen. The profiles for each sub-section may be the same or different. One way in which each profile may be defined is in terms of multiple positions a known distance along the plate from the head and the

corresponding thickness of the plate at that position. This gives a reference thickness profile 30 which may include several positions having the same thickness 33. The reference thickness profile 30 may include reference head and tail cutting positions 34 and 35.

Once the profiles have been set 40 and rolling is to begin, a plate is supplied 41 to the entry side of the work rolls via the roller table, the head end of the plate is detected 42 and rolling begins 43 in order to apply the chosen profiles to the plate. As the tail end of the rolled plate exits the work rolls 44 the controller checks whether this is the last pass 46. If it is not the last pass then the process 42, 43, 44 and 45 is repeated until the rolling of the last pass has been completed and rolling stops 46. After rolling is completed the plate is transported to the thickness gauge 47 and the head end of the plate is detected 48 and the plate is moved through the thickness gauge whilst the thickness is measured and the position of the thickness measurement is tracked 49. It should be noted that if the thickness gauge is positioned close to the rolling mill then it is possible that the measurement steps 47, 48, 48 might be started whilst the tail end of the rolled plate is still being rolled so that step 45 simply determines that the last pass is being rolled and step 46 is skipped. The detection and thickness measurement may be in the same or separate devices. Whilst the thickness is being measured, the detector also monitors 50 whether the tail end of the rolled plate has arrived in which case the thickness measurement stops.

The measured thickness at the thickness measurement points 31 may be stored on detection 50 of the tail end of the rolled plate. The controller 5 applies a best fit profile 32 to the measured points 31 to obtain the measured thickness fitted curve, then compares this best fit profile with the reference thickness profile 30. Figure 5b illustrates how, if the rolled plate was cut at the original target head and tail cutting positions 34 and 35, then there would be large errors between the reference profile 30 and the measured profile 32. Therefore the controller uses a mathematical method such as correlation, or least squares to adjust the cutting points 52 in order to get the optimum fit between the target profile and the actual profile as illustrated in Figure 5c. In Figure 5c the position of the cuts 34 and 35 is offset by length 36 relative to the original target positions. The resulting final plate thickness profile versus length in 5c is much closer to the target thickness profile versus length than it is if the cutting positions are not adjusted as in 5b. The calculation of the cutting offsets 52 may use simple correlation, or least squares methods, or may use other optimisation methods for example including a cost function. These more sophisticated methods may, for example, penalise errors where the plate is thinner than the target thickness more heavily than errors where it is thicker than the target.

For simplicity the diagrams in Figure 5 illustrate the calculation of the cutting offset 52 for the simple case of a profile with only one change in the sign of the slope. The same principle is equally applicable to a profile with multiple changes in slope such as that illustrated in Figure 4b. In the case of a profile with multiple changes in slope, such as that illustrated in Figure 4c where there are safety regions 29 between each of the sub-sections 25, 26 and 27, the calculation 52 may determine a separate offset for each of the sub-sections such that, provided that the required offset does not exceed the safety length 29, each sub-section is optimised separately.

Fig.4 illustrates example profiles which the mill automation controller may use with multi-point setups to produce several different thickness profiles within one mother plate as described above and, if required, provide areas of excess material between different profiles to allow easier division, such as shown in Fig.4c. Using profile recognition allows the correlation of the measured thickness profile to allow accurate and automatic division of the different sub-sections into daughter plates.

A straight measurement of thickness at certain points might work for some profiles, however it is feasible that there would be multiple positions that have the same expected thickness and this could result in errors in cutting in certain circumstances.

From the determined variation 51 between the required profile and the measured profile for this first profile, a general variation in what is rolled can be estimated and cutting offsets can be calculated 52 for each sub-section and its associated profile, so that the cuts are applied at the correct position on the "as rolled" plate. The plate is then cut 53 into the sub-sections at the calculated position, each sub-section have the required rolled profile.

Although rolling of profiles for the specific plate ceases 46 after the tail of the rolled plate has been detected, the system may be set up for multiple plates and operate nearly continuously by changing the rolling profile configuration to that required for the next plate before the next plate is detected at the entry side of the work rolls.

Alternatively, if the next plate is to be rolled with the same set of profiles, no change is required.

One method of determining the actual rolled profile has been described above, but there are a variety of methods that can be used to establish the actual rolled profile to allow division in the correct place. A shear pinch roll position transducer would be suitable for larger changes in profile, or a thickness gauge, such as x-ray or gamma type can be used which is suitable for all thickness ranges and gives high accuracy. Using pinch roll thickness measurement allows the thickness profile of the plate to be measured using existing equipment on shears, provided that the shear is equipped with a position transducer. The x-ray or gamma ray thickness gauge allows more accurate measurement of the thickness profile, particularly for small changes in thickness than a shear pinch roll position transducer.

Another option is that only the rolling profile is controlled by the mill automation controller and manual measurement using micrometers and hand marking of the cutting point is carried out. Although manual measurement using micrometers is a less accurate method, for lower throughputs, this method of establishing the divide position may be appropriate. For the automated measures, the profile recognition described above is appropriate. The thickness profile is correlated with the target profile and the correlation is used to assist in selecting the correct point of division by shearing. Accurate tracking of the plate from the measurement point to the dividing point in the shear is required. This can be done, for example using laser measurement devices, which are used on shears to provide accurate length measurement for tracking the plate. A laser measurement device allows accurate tracking of the divide position. For plates thicker than the shear can cut, when using automated methods and profile recognition, a paint marker, or a stamp marker can be used to mark the division point for offline flame cutting.

There are a number of advantages of the present invention. Rolling multiple profile steps in a single mother plate allows complex weight saving sections of varying thickness profile for multiple applications to be created. For example, certain structures require reinforcement on only part of their surface and a profile can be rolled, so that the finished construction has thicker sections where the reinforcement is required, but not elsewhere Mother plates for rolling tend to have standard sizes, but not all applications require the full size, so dividing up the mother plate with multiple profiles into multiple daughter plates each with their own profiles increases

productivity and energy efficiency for the production of longitudinal thickness profiled plates. Rather than rolling the successive profiles directly abutting one another, there is an option to use excess material between daughter plates of varying thickness, giving a safety margin for division of the plate into its sub-section.

Claims

1. A method of rolling a metal mother plate, the method comprising defining one or more longitudinal thickness profiles; allocating a defined profile to each of two or more sub-sections of the mother plate; rolling the mother plate with the allocated profiles in each sub-section; after rolling, measuring thickness of the plate at a plurality of measurement points along the mother plate; correlating measured thickness with expected thickness from the allocated thickness profile at the measurement points; and deriving cutting positions on the mother plate between the sub-sections based on the result of the correlation.

2. A method according to claim 1, wherein the defined profile includes a change of slope from positive slope to negative slope or from negative slope to positive slope.

3. A method according to claim 1, wherein the allocated profile of each subsection includes a positive slope or a negative slope, such that the longitudinal thickness profile of the mother plate changes slope at least twice along the length of the mother plate.

4. A method according to any of claims 1 to 3, wherein at least two different profiles are defined and allocated.

5. A method according to any preceding claim, further comprising repeating the allocated plate thickness profiles cyclically along the full length of the plate.

6. A method according to any preceding claim, wherein the measurement points are distributed in regions including at least a part of adjacent profiles.

7. A method according to any preceding claim, further comprising tracking passage of the measurement points through a thickness measure in a thickness measuring device.

8. A method according to claim 7, wherein passage of a measurement point is tracked by sensing speed of the plate through the thickness measuring device, in combination with head end position information on entry to the thickness measuring device.

9. A method according to any preceding claim, further comprising applying temperature compensation to a thickness measured at the or each measurement point.

10. A method according to any preceding claim, wherein cutting sections are rolled between each sub-section and the cutting position within the cutting section is modified according to the result of the correlation between measured and expected thickness for each profile adjacent to that cutting section.

11. A method according to claim 10, further comprising, for each cutting section, determining a tail cut position at the end of one sub-section; a head cut position at the beginning of the next sub-section; and a scrap portion between adjacent tail and head cut positions.

12. A method according to any preceding claim, further comprising marking each derived cutting position.

13. A method according to any preceding claim, further comprising cutting the rolled mother plate at the derived cutting positions.

14. A method according to claim 13, the method further comprising determining arrival of each of the cutting positions of the plate at a cutting location of a shear and shearing the plate as each cutting position arrives.

15. A method according to claim 14, wherein arrival of each cutting position of the plate is determined by means of measuring rollers, laser sensors, or mechanical stops.

16. A method of rolling a metal plate, the method comprising defining a longitudinal plate thickness profile, the profile changing in slope from positive slope to negative slope or from negative slope to positive slope at least twice along the length of the plate; and rolling the plate with the defined profile.

17. A method according to claim 16, the method further comprising defining and allocating at least two different longitudinal thickness profiles, each profile including a region with a positive slope or a negative slope; and rolling sub-sections of the plate with the allocated profiles.

18. A method according to claim 17, the method further comprising cutting the plate into the rolled sub-sections.