EP0049425B1 - Method and device for the rolling of strips, free of stress - Google Patents

Description

The invention relates to a method for rolling tension-free rolled strip by thermally influencing the diameter of the rolls by regulating their axial temperature distribution by applying a cooling, lubricating and / or cleaning liquid to the rolls, depending on behind the last stand in the transverse direction of the strip lying zones determined partial tensile stresses amount, pressure or temperature of the liquid can be changed by supplying at least the rolling stand arranged in front of the measuring point of the partial tensile stresses preferably adjustable in the application width per zone two liquids of different temperatures, the partial amounts of which can be regulated depending on the partial tensile force determined are, as well as an arrangement for performing the method.

It has been shown that when cold-rolled strip is rolled, at least low thicknesses, cross-flow of the material no longer occurs and practically only an extension corresponding to the reduction in thickness takes place. Rolling out excessively in the transverse direction of the rolled strip adversely affects the flatness of the rolled strip due to bending of the strip occurring in these zones, while zones of insufficient thickness decrease are under tension. To achieve a flat strip, it is therefore necessary to roll out this strip so that there are no tensions after it emerges from the last stand.

To create a uniformly strong roll gap, it is known to camber rolls in such a way that a flat roll gap, delimited by parallel surface lines, results under load. However, such a crowning can only compensate for a defined load condition. The additionally provided roll deflection can only make a correction to adapt certain symmetrical load cases. To achieve a largely free tension during rolling. For this reason, aluminum sheets were proposed in the ASEA brochure AV 83-102 T (October 1971) to introduce an automatic thermal crown control, in which a measuring roller, which detects the tension of the strip occurring behind the frame, is arranged as a sensor, via control devices acts on control valves, which are arranged upstream of all the nozzles arranged in a zone for dispensing a lubricant or coolant. A special print C No. 931 of the Archives for the Iron and Steel Works, published for the first time in May 1972, explains that to correct the flatness error, a targeted thermal change in the roll diameter and thus the roll gap at the place of such flatness error could be considered. Possible measures include changing the quantity, pressure and temperature of the coolant. When cold rolling broad strips, three- or five-zone cooling systems are often used for this, and in aluminum rolling mills, cooling that is even more finely divided is common.

Difficulties have been encountered in transferring the experience gained from rolling aluminum to strips of other metals, preferably steel. Minimum lubrication is a prerequisite for achieving long service life of the roller surfaces and for achieving the desired flawless strip surface, and in a number of cases, e.g. when valving relatively hard strips, certain requirements must also be placed on the coolant and lubricant temperature. Furthermore, the zone-by-zone heating of rollers to achieve a predetermined thermal crowning had given the expert the experience that such thermal changes in diameter could only be achieved over long periods of time. Even the proposal of DE-OS 29 08 641, which comes from aluminum rolling mill technology, was not well received by experts, although the recommended mixture of coolants of two different temperatures resulted in larger temperature differences between the liquid and the roll and thus an increased heat transfer. A disadvantage of observing the teaching given there is that the consumption of liquid to be cooled more is relatively high and that the control valves equipped with mixing valves require a lot of production and maintenance.

The invention has for its object to provide a method of the type mentioned and an arrangement for its implementation, in which short control times can be achieved with low creation, maintenance and operating costs, and which are applicable to all working conditions under which in cold rolling stands used in the steel industry work.

This object is achieved by the features listed in claims 1 and 6. It turns out to be advantageous here that the required basic amount of the liquid can be predetermined in each case, so that a perfect basic cooling and a completely sufficient lubrication are ensured and even in the case of the use of cleaning liquids their optimal effect is ensured. In particular, it is possible to adjust the basic lubrication, basic cooling or basic quantity of the cleaning liquid so that the liquid in question can be supplied at a temperature which can be adjusted to an optimal lubricating effect, for example viscosity, droplet size and the like, as well as optimal cleaning properties. Effective cooling is only introduced in addition, so that the consumption of more chilled liquid is reduced to a minimum. Furthermore, the structure is relatively simple, since expensive mixing valves are dispensed with and simple control valves or even simple shut-off valves can replace them.

Developments in basic teaching are characterized in the subclaims.

• Figur 1 perspektivisch die Walzen eines Quartogerüstes mit ihnen zugeordneten Kühlbalken und nachgeordneter Bandspannungs- Meßwalze, und
• Figur 2 symbolisch eine Anordnung zur Speisung der Kühlbalken.

The features of the invention are described in detail with reference to the following description of an exemplary embodiment in conjunction with a drawing representing the same. They show:

• Figure 1 is a perspective view of the rolls of a four-high stand with their associated cooling beams and downstream belt tension measuring roll, and
• Figure 2 symbolically an arrangement for feeding the chilled beams.

1 is a perspective view of a cold-rolled strip 1 made of steel, which is guided between the work rolls 2 and 3 of a four-high cold stand, not shown, which are supported by support rolls 4 and 5. The emerging cold rolled strip 1 runs with a small wrap angle around a strip tension measuring roller 6, which is able to detect the respective strip tension in axially successive jacket zones. The measured values obtained are dissipated via the slip ring system 7.

The rollers 2 to 5 are assigned cooling bars 8 to 13 which are equipped with nozzles for dispensing liquid. The division of these nozzles is adapted to that of the zones of the belt tension measuring roller 6, and in the exemplary embodiment the cooling bars each have 52 mm two nozzles which can be fed with liquid jointly and separately from the others. Here, the cooling beams 8 and 9 are assigned to the support rollers 4 and 5, and they are subjected to a constant liquid flow in an adjustable width and intensity in order to achieve a predetermined basic lubrication and cooling. In the same way, the cooling beams 10 and 11 of the work rolls 2 and 3 are subjected to an adjustable width and intensity. The cooling beams 12 and 13 arranged upstream of the roll gap are subjected to a liquid whose temperature is lower than that supplied to the cooling beams 8 to 11, and their intensity is regulated in dependence on the tensile stresses determined for the zone in question in such a way that the Differences in tensile stresses in the different zones can be brought towards zero.

The feeding of the nozzles is explained in detail on the basis of the Sylbold representation in FIG. 2.

In the proposal of FIG. 2, the supply with liquid takes place from two separate reservoirs 14 and 15, one of which contains liquid of the commonly used temperature, for example 45 °, while the reservoir 15 contains liquid whose temperature is lower than that of the liquid of the 14th example. the temperature in the reservoir 15 can be 25 ° C. The reservoirs are filled in the usual way by returning liquid, and under certain circumstances the reservoir 15 can be filled from the reservoir 14 via a cooler.

The supply of the chilled beams takes place via the reservoirs 14 and 15 downstream feed pumps 16 and 17, the delivery head of which can be set independently of consumption by downstream pressure relief valves 18 and 19. Filters 20 and 21 can be arranged after the pressure relief valves, which filters can be bypassed in the event of clogging. In the area of the feed pump 17, a cooler 22 is additionally shown, which may be able to effect additional cooling.

The feed pump 16 is followed by a plurality of valves 23 connected in parallel, the number of which corresponds to the number of zones of the chilled beams 8 to 11. In the illustration, only the first two and the last of the valves 23 are taken into account, and the corresponding downstream zones of the chilled beams 8 to 11 are fed in parallel. - If necessary, however, it is possible, for example, to double the number of valves 23 and to feed the corresponding zones of the cooling beams 8 and 9 and 10 and 11 in parallel, or to quadruple the number of valves and each of the corresponding zones of the cooling beams to keep separately adjustable. With the selected bale width there are 31 zones, so that accordingly 31, 62 or 124 valves 23 would have to be provided.

The liquid discharged from the feed pump 17 is fed to a similar group of control valves 24, each of which feeds a zone of the cooling beams 12 and 13. Here, too, it is assumed in the illustration that 31 valves are to be provided in accordance with the selected number of zones, of which only the two outermost are shown, and of which the one shown on the right feeds the corresponding outer zone of the cooling beams 12 and 13 in parallel. Here, too, it is possible to individually control the corresponding zones of the chilled beams by doubling the control valves.

The belt tension measuring roller 6 acts as an encoder for the control devices 26. The sensor systems of the individual zones, in the exemplary embodiment 31, are connected to corresponding inputs of the control device 26 via the wires of a measuring line 25. The outputs of the individual regulators of the regulating device act via the cores of the actuating line 27 on the regulating valves 24 provided as actuators. In order to achieve a fast, effective regulating process, a fixed value regulation can be provided. However, it has proven useful to form an average from the signals of the sensor systems of the individual zones, which serves as a guide variable for slave controllers, so that the deviations in the partial belt tension within the zones are regulated against their mean value towards zero. When designing the individual controllers, make sure that the sensors provided as sensors of the controlled system are arranged after the roll gap by approx. 1000 to 2000 mm, so that the controlled system is not only affected by the thermal inertia of the respective zone of the roll shell Use of liquid at a lower temperature and thus the increase in the temperature difference when the load is reduced is stressed, but in addition the running times become noticeably noticeable, due to the migration of the liquid-affected points of a roll into the roll gap and of the cold rolling strip emerging from the roll gap up to Tape tension measuring roller 6 result. Especially with larger selected temperature differences, the control characteristic is to be designed in such a way that the build-up of control vibrations is avoided.

The invention shows ways of obtaining effective thermal crowning control by using a second liquid of lower temperature, which also takes effect relatively quickly and is therefore able to compensate for short-term voltage fluctuations. It has proven to be advantageous here that both the control device and the valves controlling the additional liquid flow as actuators have a relatively simple structure and thus enable an inexpensive system. The display device usually provided for tension distribution in the transverse direction of the belt is also appropriately taken into account here, but is not shown in the exemplary embodiment to simplify the illustration. The regulation can also be favorably influenced by the fact that 28 disturbance variables and 29 reference variables can be introduced via inputs. The setting of the valves 23 can be carried out manually or controlled manually. Not only can the basic cooling be adapted to the respective working conditions; the nozzles lying outside the width of the respectively rolled strip can be switched off, and the ones lying in the edge areas of the respective rolling program can be acted on in such a way that a favorable thermal setting of the crowning also results in the transition area to the unloaded roll shell. In addition, for example in the case of stands having six rolls, zone deactivation can prevent the application of liquid to the side of their end face or in their position area in the case of axially displaced rolls.

It has also been shown to be advantageous that the basic lubrication can be effected at the temperature recognized as advantageous, so that the viscosity of the oil used or emulsified can be set as optimally as the droplet size in emulsions. Vegetable or animal fats can also be used at the appropriate temperature. When using cleaning fluids, the temperature can also be set here in such a way that an optimal cleaning effect and thus extensive use of the cleaning fluid are achieved: the basic lubrication or cleaning has only a minor influence on the respective roller temperature; Rather, this is determined by the controllable addition of the low-temperature liquid, and here it is possible to make do with relatively little additional, colder liquid by using the higher temperature difference, supported by the application of the rollers over a larger circumferential area, so that result in cheaper operating costs.

The arrangement chosen in the recommended exemplary embodiment can be varied in many ways; for example, it is possible, as already mentioned, to arrange separate valves in front of the nozzles of a zone of the cooling beams and to dispense with zones of different cooling beams of the same type operating in parallel. A simple and maintenance-friendly supply of the liquids can be achieved by the cooling beams being equipped with one or more liquid connections acting in parallel and the valves, carried by the cooling beams, being arranged directly upstream of the nozzles. They can be partially or completely embedded in the chilled beams. Strong current and thus pressure fluctuations that occur when the valves are switched can be reduced by adding additional pressure control valves upstream of the valves at a short distance or via short lines, or else the pressure control valves 18 and 19 shown in FIG. 2 to the valves 23 and control valves 24 directly upstream. A further reduction of pressure changes occurring during switch-on and switch-off processes can be achieved by the pressure accumulators 30 and 31 being arranged upstream of the valves 23 and control valves 24, likewise via short lines and thus small liquid masses to be accelerated.

For the sake of simplifying the return of the liquid, it can be taken over into one of the reservoirs, for example reservoir 14, and brought to the intended upper operating temperature in the cooler arranged upstream or in it. In particular in the case of a cooler arranged upstream of a pressure control valve, in contrast to the illustration in FIG. 2, the liquid of the lower temperature can be obtained by a simple cooler. However, it has proven useful to transfer the liquid to be used at low temperature into a reservoir 15 from the reservoir 14, the further cooling required being able to be carried out by an interposed and / or a cooler built into this reservoir and, if appropriate, according to FIG Reservoir still cooler can be subordinated, which, however, expediently a pressure control valve are arranged upstream, so that an approximately constant liquid flow results in clear cooling conditions.

It has also proven useful, if appropriate, to also include a scaffold that is upstream of the regulated system and to equip its work rolls with chilled beams that are controlled to be controlled by liquid at a lower temperature. The larger distance to the measuring roller can be taken into account here by making the control characteristic flatter, i. that is, the respective triggered differences in the liquid flows are smaller and / or the liquid is supplied at a temperature which, including the limits, lies between the first and second temperature.

A simple control and in particular a simple and therefore low-maintenance and inexpensive design of the control valves result if no analog control is carried out, but the controllers work according to the two-point or three-point principle. For example, when the liquid flows of the individual nozzles are switched on and off in pulses, the switch-on duration and / or the switch-on pauses can be varied such that the different cooling effects to be regulated result. On the other hand, it is possible to regulate a base current in a corresponding manner and, if a limit value is exceeded, at which the base cooling runs constantly, to additionally generate stronger current pulses. The effects of current fluctuations can be kept relatively low by different switch-on and switch-off times of the individual regulators, and, as noted, pressure regulating valves and / or pressure accumulators can be arranged directly in front of the valves 23 and / or regulating valves 24 to compensate for them as far as possible.

When designing the control device, an average value of the individual zone measurements can be determined, which can be used as the setpoint of the control variable. However, it is also possible to arbitrarily specify a target value or to form it from the reel train: The only thing that is important is that the tensions in the individual zones are guided against a common mean value, so that after the reel train has ended, there are no tensions that deform the rolled strip.

In all of these cases, effective thermal control of the roller crowning can be achieved with little production effort and thus allow the rolling of tension-free and thus flat rolled strip without it being necessary to move the basic lubrication or cleaning to a temperature range which is recognized as unfavorable for the functions .

Claims (20)

1. Method for the rolling of stress-free rolled strip through thermal influencing of the diameter of the rolls by means of regulation of their axial temperature distribution through acting on the rolls with a cooling, lubricating and/or cleaning liquid, wherein quantity, pressure or temperature of the liquid is altered in dependence on partial tension stresses determined in zones lying in transverse direction of the strip behind the last stand in that two liquids of different temperatures, the partial quantities of which are regulable in dependence on the determined partial tension force, for each zone are conducted, preferably settable in their width of impingement, to at least the roll stand arranged upstream of the place of measurement of the partial tension stresses, characterised thereby, that a first liquid, which is kept at a first temperature, is conducted at settable constant quantity flow to the rolls and that the quantity flow of the second liquid, which displays a lower temperature and is conducted additionally to at least the working rolls (2, 3), is regulable zone by zone in dependence on the determined partial tension stress.

2. Method according to claim 1, characterised thereby, that the regulation takes place in analog manner.

3. Method according to claim 1, characterised by a two-position regulation with pulse-like on- phases.

4. Method according to one of the claims 1 to 3, characterised thereby, that the rolls (2 to 5) of at least the last stand of a train are acted on at the strip intake side.

5. Method according to one of the claims 1 to 4, characterised thereby, that the impingement, which is regulable zone by zone, by the liquid of lower temperature is effected at a greater angular spacing from the roll gap than that of the region, in which the liquid of the first, higher temperature is supplied.

6. Arrangement for the performance of the method according to claims 1 to 5 with at least one roll stand, the rolls of which are associated with nozzles arranged in cooling beams and chargeable with liquid and downstream of which is arranged a transmitter which detects the strip stresses in zones of the cold strip and acts on regulating devices, downstream of which valves are arranged as setting members, characterised thereby, that cooling beams (8 to 11), the nozzles of which are feedable settably portion by portion by way of valves (23) from a first reservoir (14) containing liquid of a first temperature, are associated with the rolls (2 to 5) and that at least one respective further cooling beam (12, 13), the nozzles of which are chargeable zone by zone with a liquid of lower temperature by way of regulating valves (24) arranged downstream of the regulating devices (26), are associated with each of working rolls (3, 4).

7. Arrangement according to claims 1 to 6, characterised thereby, that the portion-wise division of the nozzles of the cooling beams (10, 11) corresponds to the zone-wise division of the nozzles of the cooling beams (12 and 13).

8. Arrangement according to one of the claims 1 to 7, characterised thereby, that the cooling beams (8 to 13) of the stand last in running direction of the strip are arranged at its intake side

9. Arrangement according to one of the claims 1 to 8, characterised thereby, that the cooling beams (12, 13), which are charged by the liquid of lower temperature, are arranged at a greater angular spacing from the roll gap formed between the working rolls (2, 3) than those (10, 11) chargeable by the liquid of higher temperature.

10. Arrangement according to one of the claims 1 to 9, characterised thereby, that two or three cooling beams (12, 13) of regulable throughflow quantity of the liquid of lower temperature are respectively associated with each of the working rolls (2, 3).

11. Arrangement according to one of the claims 1 to 10, characterised thereby, that the valves (23) and/or the regulating valves (24) are arranged at and/or in the cooling beams (8 to 13).

12. Arrangement according to one of the claims 1 to 11, characterised thereby, that the regulators of the regulating device (26) are effective on the two-position or three-position principle of regulation.

13. Arrangement according to one of the claims 1 to 12, characterised thereby, that pressure- regulating valves (18, 19) are arranged at small spacing upstream of the valves (23) or the regulating devices (24).

14. Arrangement according to one of the claims 1 to 13, characterised thereby, that pressure storage devices (30, 31) are associated at the input side by way of short ducts with the valves (23) or the regulating devices (24).

15. Arrangement according to one of the claims 1 to 14, characterised thereby, that the return flow of the liquid is taken up by the reservoir (14) and the liquid to be cooled to lower temperature is taken from this.

16. Arrangement according to claim 15, characterised thereby, that the withdrawn liquid is conducted through a cooler.

17. Arrangement according to claim 15 or 16, characterised thereby, that the withdrawn liquid is conducted through a second reservoir (15).

18. Arrangement according to claim 17, characterised thereby, that the reservoir (15) displays a cooling device.

19. Arrangement according to one of the claims 1 to 18, characterised thereby, that also working rolls of the penultimate stand arranged upstream of the transmitter (6) detecting the strip stresses display at least one cooling beam regulably chargeable with the liquid of lower temperature.

20. Arrangement according to claim 19, characterised thereby, that the liquid regulation of the cooling of the working rolls of the stand is effected with a flatter characteristic and/or more strongly damped than that of the working rolls (2, 3) arranged directly upstream of the transmitter (6).

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