WO2013053507A1

WO2013053507A1 - Rolling apparatus

Info

Publication number: WO2013053507A1
Application number: PCT/EP2012/063464
Authority: WO
Inventors: Peter Christoforou
Original assignee: Siemens Vai Metals Technologies Ltd.
Priority date: 2011-10-12
Filing date: 2012-07-10
Publication date: 2013-04-18
Also published as: GB2495512A; GB2495512B; GB201117588D0

Abstract

Rolling apparatus, the apparatus comprising a pair of work rolls (5, 6) adapted to receive in a nip (4) between the work rolls, an article (3) to be rolled; an internal cooling source provided within one or more of the work rolls; and an external cooling source provided outside one or more of the work rolls; wherein the internal cooling source is adapted to provide a first cooling fluid (30) within the work roll; wherein the external cooling source is adapted to provide a second cooling fluid (10) at the surface (7) of the work roll; and wherein the first and second cooling fluids are different.

Description

ROLLING APPARATUS

This invention relates to rolling apparatus, in particular for hot or cold rolling of metal sheet, strip or slabs.

In the field of metal rolling, whether of continuous sheets, or strips or slabs in a reversing mill, a lot of heat is generated in the rolling process and it is necessary for the work rolls to be cooled in operation. Conventionally, this has been done by applying a stream of liquid to the outer surface of the work rolls. The choice of liquid depends upon the application. For example, when rolling steel, water or a mixture of water and a lubricant can be used to provide the cooling. A water and lubricant mixture can also be used when hot rolling aluminium. However, water is not suitable for cold rolling aluminium because the water tends to mark the surface of the aluminium. One solution to this marking issue has been to roll the aluminium in such a way with respect to speed and load, etc., that the aluminium is above 100°C as it exits the work rolls, to dry off any water to prevent staining, but since the strip temperature has to be in excess of 100°C, this is not practical for all grades of aluminium.. Instead, the normal cooling liquid for aluminium cold rolling is kerosene. Amongst the disadvantages of using kerosene are the fire risk and complicated liquid recycling infrastructure required to prevent environmental damage, as well as keeping the area well ventilated to prevent build up of toxic emissions.

Another reason for applying cooling to the work rolls is to be able to control the profile and flatness of the material as it exits the work rolls. In order to control the profile, the distribution of cooling across the width has to be changed by changing the amount of coolant applied across the width, for example as described in GB 1434477. As described in our earlier patent application, publication no. WO2010/070310, temperature control for profile may be carried out by applying cryogenic fluid to one or more zones of the surface of the work roll and also applying heat to some of the zones.

The use of a cryogen, which is liquid only at very low temperatures, typically below 110 K, such as nitrogen, carbon dioxide, argon and oxygen has advantages over the use of kerosene because the cryogen is generally inert with respect to the material being rolled and less combustible. However, the disadvantage of using cryogenic fluids is that the fluid turns gaseous and is lost, whereas kerosene or water/lubricant mixtures can be re-circulated.. In accordance with a first aspect of the present invention, a rolling apparatus comprises a pair of work rolls adapted to receive in a nip between the work rolls, an article to be rolled; an internal cooling source provided within one or more of the work rolls; and an external cooling source provided outside one or more of the work rolls; wherein the internal cooling source is adapted to provide a first cooling fluid within the work roll; wherein the external cooling source is adapted to provide a second cooling fluid at the surface of the work roll; and wherein the first and second cooling fluids are different.

Preferably, the first cooling fluid comprises water.

Preferably, the second cooling fluid comprises a cryogenic fluid.

Preferably, the cryogenic fluid comprises one of nitrogen, carbon dioxide, argon, helium and oxygen.

The work roll may be provided with a single hollow cooling tube along its longitudinal axis, or a spiral tube, but preferably the work roll comprises a plurality of cooling tubes arranged longitudinally within the work roll.

Cooling fluid may be supplied to and extracted from each of the plurality of tubes, but preferably the plurality of cooling tubes are hollow and coupled to adjacent tubes at their ends to form a circuit, the circuit being provided with an input and an output to allow a continuous flow of cooling liquid.

This reduces the number of connections and supply pipes, simplifying roll change.

Preferably, the external cooling source further comprises a plurality of outlets and a flow control mechanism to control flow to each outlet.

This allows the external cooling to be adjustable for distribution across the width, enabling modification of the profile by use of a different amount of cooling at different positions across the work roll.

Preferably, the internal cooling source further comprises a flow control mechanism.

Preferably, the flow control mechanism further comprises a controller.

In accordance with a second aspect of the present invention, a method of cooling rolling apparatus comprises supplying a first cooling fluid within one or more of a pair of work rolls; and supplying a second cooling fluid to the surface of the one or more of the pair of work rolls; wherein the first and second cooling fluids are different. In accordance with a third aspect of the present invention, a method of controlling a profile of a material to be rolled in a rolling apparatus comprising a pair of work rolls comprises cooling the rolling apparatus according to the method of the second aspect; and rolling the material between the pair of work rolls, whereby the profile of the material is adapted to the modified profile of the work rolls.

The second cooling fluid modifies the profile of the work roll, so that when it is used to roll the material, the material takes up the modified profile of the work roll, the first cooling fluid comprises water.

Preferably, the second cooling fluid comprises a cryogenic fluid.

Preferably, the distribution of the second cooling fluid across the width is adjustable.

The apparatus and method of the present invention provide internal cooling of work rolls using one medium, in combination with external cooling of the work rolls, using another medium. This allows the higher cost cryogenic fluid to be used for the external fine temperature control and low cost coolant, such as water, to be used for the internal cooling of the work roll.

An example of rolling apparatus and a method of cooling the rolling apparatus according to the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates an example of rolling apparatus according to the present invention;

Figure 2 illustrates in more detail a work roll in the apparatus of the present invention;

Figure 3 shows alternative implementations of the work roll of Fig.2; and,

Figure 4 is a flow diagram of an example of a method of controlling the profile of a material to be rolled in accordance with the present invention.

Fig. l illustrates a simplified example of part of a rolling mill incorporating rolling apparatus 1 according to the present invention. In this part of the mill there is an entry side roller table 2a for supplying the material 3 to be rolled, typically thin sheet or strips of aluminium, to a nip 4 between a pair of work rolls 5, 6. Rolling of the material 3 takes place on surfaces 7 of the work rolls 5, 6 remote from their ends. The material is then moved out of the nip 4 on an exit side roller table 2b. One or both of the work rolls are supplied with an internal coolant 30 and an external coolant from an external coolant source 10. The supply of coolant may be regulated by a controller 12.

Fig.2 illustrates in more detail how the internal coolant 30 is supplied to the work rolls. In this example, as can be seen in Fig. 3a too, a hollow pipe or tube 13a is provided within a bore 13b in the work roll 5, the bore and the tube being aligned with an axis of rotation 14 of the work roll. Typically, both work rolls 5, 6 are cooled internally, but for convenience, only one is shown in the figure. Cooling fluid 30, in this example water, is supplied from one end of the work roll 5, 6, via a conventional rotary joint 8 and flows as indicated by arrows 15. The other end, the drive end 9, is connected to a drive mechanism (not shown) by which the work rolls are driven.

In order to control the profile of the material 3, the external surface 7 of the work rolls is cooled by application of a cooling medium 16, preferably, a cryogen, to the work roll surface from the external coolant source 10. The preferred cryogen for cooling aluminium during rolling is nitrogen, which is extracted from the atmosphere and liquefied. There is no need for any recycling or collection of nitrogen gas, so it is preferable to, for example, carbon dioxide, for which there are controls on the amount exhausted to the atmosphere.

Typically, the current practice is that the roll temperatures are around 70 °C and the coolant temperature, when using kerosene is about 40 °C. In the case of a cryogenic fluid e.g. liquid nitrogen, then the spray temperature is much colder and once the cryogenic fluids are sprayed onto the roll they become gaseous, so it is not possible to simply re-circulate them, as is done with with kerosene or water. Therefore, with cryogenic fluids it is advantageous to minimise the quantity of fluid that is used. The internal cooling of the roll with water 30 removes some of the heat, so less cryogenic fluid is required than if all of the cooling was by cryogenic fluid.

The cryogen is sprayed onto the surface through a spray nozzle from a supply, under control of the controller. The spray nozzles may be arranged, for example as described in WO2010/070310, to spray different zones, so that more or less cooling is applied at the different zones across the width of the work roll surface, leading to different profile effects. As well as determining the zones to be sprayed, the controller may modify the amount of spray applied in any zone by controlling the extent of opening of a valve (not shown). There may be a valve per zone, or per spray nozzle according to the degree of fine control which is actually required. As the cooling spray is applied during the rolling process, in some cases the material being rolled will also be cooled by the spray which comes into contact with it. Use of such a low

temperature cooling medium means that the medium evaporates on contact with the material, so it does not mark the surface in the way which water does, although care must be taken as condensation or ice formation may occur.

For example, there might be problems if water or ice form due to the cold, so for aluminium rolling, the material is less likely to be sprayed and to avoid this, the roll can be sprayed within a shroud as in co-pending patent application no.

PCT/EP2012/000688, where a shield is placed around a coolant delivery nozzle, with an opening towards the work roll. If the material is hot enough to evaporate any water from condensation due to the cold, or is not susceptible to damage from water, then spraying the material is not a problem.

A temperature sensor, or flatness sensor, sometimes referred to as a shapemeter, or both types of sensor may provide feedback to the controller 12, so that the amount of coolant, or its position can be altered in response. In aluminium rolling, the primary controller is a flatness sensor and control system which alters the spray pattern across the width of the material to optimise the flatness. There may also be a temperature sensor or a series of temperature sensors.

An alternative embodiment is illustrated in Fig.3b, showing a plurality of cooling tubes 13b, arranged around the work roll, just beneath the surface. Each of these cooling tubes may take a similar form to the tube of Fig.3a, so that water can circulate within each individual tube, although they may have a smaller diameter than tube 13a. Alternatively, the bores 13b may be coupled to an adjacent bore by pipes at alternate ends, so that cooling fluid can enter one of the bores and circulate through all of the bores before exiting from the final one of the bores. This reduces the number of external connections to the work roll, simplifying roll changes. Another design which achieves this is shown in Fig.3c, where a continuous spiral tube 13c is wound around the inside of the work roll, with a central return tube 16 aligned with the axis 14 for the water to exit. Again, only two connections are required, an entry and exit.

Fig.4 is a flow diagram showing an example of the steps in controlling the total cooling power and the profile of the work rolls and hence the profile and flatness of the material being rolled. At step 20 an initial estimate of the total cooling power required is made based on the material that is going to be rolled, the reduction required, the rolling speed etc. At step 21 an initial estimate of the external sprays cooling distribution which is required to achieve the target flatness is made based on

information such as the ground and thermal profiles of the rolls, the width of the material to be rolled, the predicted rolling load etc. At this step the total external spray flow is kept to the minimum possible flow which is compatible with achieving the required cooling distribution. At step 22 the system checks whether the total cooling power required minus the cooling power due to the flatness / profile control sprays is greater than the maximum available internal cooling power. If it is greater than the maximum available internal cooling power then the system goes to step 23 and sets the internal cooling to maximum. At step 25 the system then increases the total flow from the external sprays, whilst maintaining the required cooling distribution for profile / flatness control, in order to achieve the required total cooling power. If at step 22 the total cooling power required minus the cooling due to the external sprays is less than the maximum possible with the internal cooling then the internal cooling power is reduced - for example by reducing the internal cooling flow - at step 24 to achieve the required total cooling power. At step 26 the required cooling distribution for profile / flatness control is updated based on feedback from a flatness sensor and other measurements at 27. At step 28 the total cooling power required is updated based on measurements of the rolling power and/or speed and/or roll temperatures and/or strip temperature 29. Step 31 checks whether rolling has finished. If rolling has not finished then the system goes back to step 22 and repeats the calculations based on the updated information from steps 26 and 28.

The present invention addresses the problem of making economic the use of cryogenic fluids for both cooling and flatness control of a work roll that is used for rolling of thin sheet or strip material, in particular aluminium. The large amount of heat generated during the rolling process needs to be extracted from the work rolls. The cryogenic cooling sprays used for flatness control, as described in

WO2010/070310, are perfectly able to extract large amounts of heat, but it is more economical to remove some of the heat by using internal cooling of the roll and thus to reduce the quantity of cryogenic fluid required. Although, there may not be a large cost differential between using kerosene with its expensive filtration and re-circulation system and using liquid nitrogen cooling, kerosene is less safe due to its propensity to catch fire, so a safer system is desirable. The problem does not arise with steel rolling, where water, with or without a lubricant, can be sprayed onto the work rolls to cool them, so although there is no technical objection to using external cryogenic cooling for steel rolling, it would not make economic sense to do so.

The invention introduces an internal cooling system in the work roll, preferably using water as the cooling medium, which is used to extract some of the heat from the work roll and reduces the work roll temperature. The invention controls the profile of the metal being rolled by the application of coolant spray externally. The shape of the roll may be modified by varying the external cooling at different sections and consequently, the shape of the rolled metal will be modified accordingly. The cryogen spray will also extract further heat from the roll, but it is not its main function, so the quantities required are reduced. It is desirable to minimise the quantity of cryogenic fluid required but there will be some spraying of cryogenic fluid in order to control the flatness. If internal cooling is not sufficient on its own to keep the roll cool, then the cryogenic sprays are used to do the remaining cooling, plus the flatness control;

whereas if internal cooling is sufficient to keep the roll at the required temperature without the external sprays, then the internal cooling flow may be reduced to ensure that cryogenic sprays for flatness control did not over cool the roll.

This control of the internal cooling flow may be done using a flow control mechanism, such as a flow control valve or similar. The controller can then adapt the internal cooling flow using the flow control mechanism. Hence for operation of the internal cooling and external cooling together i.e. if the total cooling power required is greater than the internal cooling can achieve on its own then the internal cooling is set to maximum and the external cooling makes up the difference and also provides the cooling for the profile / flatness control. If the total cooling power required is less than the internal cooling can achieve then the internal cooling is reduced so that the overall cooling power is that which is required including the required external cooling for achieving profile / flatness control. This allows both the required total cooling and the profile / flatness control with the minimum external cooling flow, but prevents over- cooling of the roll.

The distribution of the internal cooling fluid across the width of the work roll could be controlled and varied to have a different effect in different parts of the work roll. For example, by modifying the example of Fig.3c to have a supply tube and a return tube within the work roll, parallel with the axis 14, the tubes being connected by valves to a series of hollow hoops each with a radius centred on the axis 14 , the hoops being arranged at intervals across the width of the work roll, then the amount of flow to each hoop could be separately controlled and so influence the temperature of the work roll in the vicinity of each hoop.

Claims

1. Rolling apparatus, the apparatus comprising a pair of work rolls adapted to receive in a nip between the work rolls, an article to be rolled; an internal cooling source provided within one or more of the work rolls; and an external cooling source provided outside one or more of the work rolls; wherein the internal cooling source is adapted to provide a first cooling fluid within the work roll; wherein the external cooling source is adapted to provide a second cooling fluid at the surface of the work roll; and wherein the first and second cooling fluids are different.

2. Apparatus according to claim 1, wherein the first cooling fluid comprises water.

3. Apparatus according to claim 1 or claim 2, wherein the second cooling fluid comprises a cryogenic fluid.

4. Apparatus according to claim 3, wherein the cryogenic fluid comprises one of nitrogen, carbon dioxide, argon, helium and oxygen.

5. Apparatus according to any preceding claim, wherein the work roll comprises a plurality of cooling tubes arranged longitudinally within the work roll.

6. Apparatus according to claim 5, wherein the plurality of cooling tubes are hollow and coupled to adjacent tubes at their ends to form a circuit, the circuit being provided with an input and an output to allow a continuous flow of cooling liquid.

7. Apparatus according to any preceding claim, wherein the external cooling source further comprises a plurality of outlets and a flow control mechanism to control flow to each outlet.

8. Apparatus according to any preceding claim, wherein the internal cooling source further comprises a flow control mechanism.

9. Apparatus according to claim 7 or claim 8, wherein the flow control mechanism further comprises a controller.

10. A method of cooling rolling apparatus, the method comprising supplying a first cooling fluid within one or more of a pair of work rolls; and supplying a second cooling fluid to the surface of the one or more of the pair of work rolls; wherein the first and second cooling fluids are different.

11. A method of controlling a profile of a material to be rolled in a rolling apparatus comprising a pair of work rolls; the method comprising cooling the rolling apparatus according to the method of claim 10; the method further comprising rolling the material between the pair of work rolls, whereby the profile of the material is adapted to the modified profile of the work rolls.

12. A method according to claim 10 or 11, wherein the first cooling fluid comprises water.

13. A method according to any of claims 10 to 12, wherein the second cooling fluid comprises a cryogenic fluid.

14. A method according to any of claims 10 to 13, wherein the distribution of the second cooling fluid across the width is adjustable.