Cooling section with adjustment of the cooling agent flow by means of pumps

Abstract

The invention relates to a cooling section (2) arranged within a rolling train or upstream or downstream of the rolling train. A hot-rolled product (1) made of metal is cooled by means of the cooling section (2). Application devices (6) of the cooling section (2) are supplied with a respective actual current (F) of a water-based liquid coolant (7) via a respective supply line (8) and a respective pump (10). The respective actual current (F) of the coolant (7) is applied to the hot-rolled product (1) by means of the respective application device (6). The hot-rolled product (1) is transported within the cooling section (2) in a horizontal transport direction (x) during the application of the coolant (7). A controller (11) of the cooling section (2) dynamically ascertains a respective target actuation state (S*) for each pump (10) on the basis of a respective target current (F*) of the coolant (7) to be applied onto the hot-rolled product (1) by means of the respective application device (6) and controls the respective pump (10) in a corresponding manner such that the respective actual current (F) delivered by each pump (10) approximates the respective target current (F*) as much as possible at any time.

Description

field of technology

[0001] The present invention relates to an operating method for a cooling section that is arranged within a rolling mill or is located upstream or downstream of the rolling mill and by means of which a hot rolled metal product is cooled, wherein a respective actual flow of a liquid, water-based coolant is supplied to a number of application devices of the cooling section via a respective supply line and a respective pump, wherein the respective actual flow of the coolant is applied to the hot rolled material by means of the respective application device, wherein the hot rolled material is transported within the cooling section in a horizontal transport direction during the application of the coolant.

[0002] The present invention further relates to a cooling section that is arranged within a rolling mill or is located upstream or downstream of the rolling mill and by means of which a hot rolled metal product is cooled, wherein the cooling section has a number of application devices to which a respective actual flow of a liquid, water-based coolant is supplied via a respective supply line of the cooling section and a respective pump of the cooling section, wherein the respective actual flow of the coolant is applied to the hot rolled material by means of the respective application device, wherein the hot rolled material is transported in a horizontal transport direction in the cooling section during the application of the coolant.

[0003] In the cooling section of a rolling mill, a metallic workpiece is cooled after rolling. The workpiece can be made of steel or aluminum, for example. Depending on requirements, it can be a flat workpiece (strip or heavy plate), a rod-shaped workpiece, or a profile. Precise temperature control in the cooling section is standard practice to achieve desired material properties and maintain them with low temperature variation. Particularly in cooling sections downstream of the rolling mill, several spray bars are installed along the cooling section for this purpose. These spray bars apply a liquid coolant, usually water, to the hot workpiece from above and below to cool it. The amount of water flowing through each spray bar should be adjustable as quickly and precisely as possible. State of the art

[0004] To adjust the amount of water supplied to the spray bar, it is known, for example, to install switching valves or control valves in the supply lines. Switching valves can only be controlled in a purely binary manner. They are therefore either fully open or fully closed. Control valves can be adjusted continuously, so that the amount of water supplied to each spray bar can also be continuously adjusted.

[0005] In the case of control valves, the valves can be designed as butterfly valves or ball valves. Butterfly valves are relatively simple and inexpensive. However, they can only be operated with relatively small pressure differentials, usually a maximum of 1 bar. Otherwise, cavitation occurs, which damages the butterfly valve very quickly. Butterfly valves are therefore particularly unsuitable for intensive cooling. They are also often disadvantageous in laminar flow cooling systems. In particular, they frequently exhibit switching hysteresis. Switching hysteresis means that, with the same control input, the set valve angle varies depending on whether the butterfly valve is moved from a more open or a more closed position to the new position. Ball valves do not have a flap, but rather a perforated ball that rotates within a tube.Depending on the ball's rotational position, a larger or smaller cross-section is provided for the coolant flow. Ball valves can operate with higher pressure differentials up to approximately 3 bar. Hysteresis either does not occur or is negligible. However, ball valves are expensive.

[0006] In another solution, the spray bar is continuously supplied with coolant. However, a controllable deflector plate is present. Depending on the position of the deflector plate, the coolant is either directed towards the rolled material or flows off to the side without contributing to its cooling. With this arrangement, rapid switching operations without pressure surges are possible. However, continuous adjustment of the water flow is not possible. Furthermore, the full coolant flow must be maintained at all times.

[0007] All types of valves, including deflection plates, require appropriate actuators. Pneumatically driven actuators are common. For control valves, a position control system is also needed. This system continuously compares the actual position of the control valve with its target position and adjusts the actual position until a sufficient match with the target position is achieved.

[0008] All these systems share the common requirement of an external coolant supply. The coolant can be drawn from an elevated tank, for example, or transported via a larger pipeline from a more distant pumping station. Combinations of these methods are also possible. For instance, in so-called intensive cooling, the water is often first drawn from an elevated tank. The pressure is then increased to a variable extent using booster pumps, and thus supplied to the intensive cooling system at a correspondingly variable pressure. Usually, several booster pumps are present, all connected in parallel, meaning they all draw coolant from the same reservoir at the inlet and feed it to a common collection point at the outlet. The intensive cooling system is equipped with several spray bars, to which – starting from the booster pumps or...The coolant is supplied individually via a separate supply line to the common collection point. Ball valves are installed in these supply lines, which are controlled to adjust the amount of coolant supplied to each spray bar.

[0009] Several disadvantages arise in the current state of the art. Switching valves produce pressure surges when they close. Therefore, they cannot be closed arbitrarily quickly. Typical switching times are above 1 second, sometimes up to 2 seconds. Control valves and ball valves achieve similar response times. Furthermore, position control is required for every control valve. The achievable accuracy is approximately 1% to 2%. Control valves also produce pressure surges when they close. Therefore, they too cannot be closed arbitrarily quickly. Typical switching times are around 1 second. All valves experience flow losses, which lead to increased wear and energy consumption. Pneumatic actuators are prone to defects, especially with frequent actuation.Furthermore, they require additional energy for the control air, which also needs to be cleaned and dried, and must be supplied, for example, by a separate compressor.

[0010] WO 2010 / 040 614 A2 discloses a descaling device in which a pump is driven by a variable-speed drive. The control of the drive takes into account the operating state of the descaling area and the fill level of a high-pressure accumulator.

[0011] US patent 2008 / 0 035 298 A1 discloses a casting process that utilizes, among other things, a cooling water source comprising a water-cooled coil. The cooling water is supplied to the coil via a pump that can be switched on and off and has a mechanism for controlling the amount of coolant. The liquid is recirculated. The temperature of the cast metal strand is measured and transmitted to a control unit. Based on this temperature, the control unit regulates the cooling water source.

[0012] A process is known from US Patent 2010 / 0218516A1 in which a metal strip is cooled with a liquid coolant during heat treatment in a cooling unit. The metal strip runs vertically from bottom to top. The coolant is pentane or a mixture of pentane and hexane. During the application of the coolant, the metal strip is in a protective gas atmosphere. Depending on the temperature of the metal strip at the inlet and outlet of the cooling unit and the speed of the metal strip, a quantity of coolant is determined to be pumped to the application devices of the cooling unit. The pump is controlled accordingly.

[0013] US Patent 2007 / 0 074 846 A1 discloses a casting process in which the cast strand is passed through a cooling chamber where it is cooled with a liquid cooling medium. The liquid cooling medium is a metal or a molten salt. A circulating pump draws the liquid cooling medium from a reservoir, feeds it into the cooling chamber, and then returns it to the reservoir. The amount of liquid is controlled based on the temperatures at which the liquid cooling medium is supplied to and discharged from the cooling chamber, and also based on the inlet pressure of the cooling chamber.

[0014] US Patent 2009 / 0 314 460 A1 discloses a casting process in which the cast strand is formed using a two-roll casting machine. The rolls are cooled internally with a liquid cooling medium. The liquid cooling medium is a metal or a molten salt. The liquid cooling medium is drawn from a reservoir by a circulating pump, fed to the rolls, and then returned to the reservoir from the cooling chamber.

[0015] US Patent 2012 / 0 298 224 A1 discloses the predictive operation of a pump in a rolling mill with a downstream cooling section. However, this pump does not directly feed application devices that apply the cooling medium to the hot rolled material, but rather only pumps the cooling medium into a reservoir to ensure it is always sufficiently full. The application of the coolant to the rolled material itself is not described in detail.

[0016] From EP 2 898 963 A1, a cooling section is known which is downstream of a rolling mill and by means of which hot rolled metal stock is cooled. This cooling section has a number of application devices, each of which is supplied with a specific flow of a liquid, water-based coolant via a supply line. The respective flow of coolant is applied to the hot rolled stock by means of the respective application device. The hot rolled stock is transported horizontally within the cooling section during the application of the coolant.

[0017] EP 2 767 353 A1 also discloses a cooling section downstream of a rolling mill, used to cool hot rolled metal stock. This cooling section includes several application devices, each supplied with a specific flow of a liquid, water-based coolant via a separate supply line. The coolant flow is then applied to the hot stock by the respective application device. During coolant application, the hot stock is transported horizontally within the cooling section. Valves are integrated into the supply lines, and their opening positions are dynamically controlled by a control unit within the cooling section.A common pump located upstream of the supply lines is set by the control unit according to the total flow to be applied to the rolled material in its entirety by means of the application device. Summary of the invention

[0018] The object of the present invention is to create possibilities by means of which a cooling section with superior operating characteristics can be realized in a simple and reliable manner.

[0019] The problem is solved by an operating method with the features of claim 1. Advantageous embodiments of the operating method are the subject of dependent claims 2 to 7.

[0020] According to the invention, an operating method of the type mentioned at the outset is first designed in such a way that a control device of the cooling section dynamically determines a respective target control state for the respective pump depending on a respective target flow of coolant to be applied to the hot rolled material by means of the respective application device and controls the respective pump accordingly, so that the respective actual flow delivered by the respective pump is always as close as possible to the respective target flow.

[0021] The pump in question – or more precisely, the drive for the pump – is therefore a variable-speed drive. It can, for example, be inverter-controlled. Within the framework of dynamic control, only the pump itself is controlled, not any valve that may be located in the supply line.

[0022] Control or regulation can be implemented as needed. In the case of regulation, the actual flow rate of the liquid coolant is measured at the input or output of the respective pump and fed to the control unit.

[0023] In many cases, the rolled material is a flat product, such as a strip or a heavy plate. In this case, it is possible for the liquid coolant to be applied to the rolled material from both sides using the respective application device. Alternatively, it is possible for the liquid coolant to be applied to the rolled material from only one side, in particular from above or below, using the respective application device. Of course, it is also possible in this case to apply the coolant to the other side of the flat rolled material, so that the flat rolled material is cooled, for example, simultaneously from above and below. In this case, however, two application devices are required, which are controlled separately and, in principle, can also be operated independently of each other. The operating method according to the invention is thus, so to speak, implemented twice in this case.However, both pumps can be controlled uniformly by one and the same control unit. In this case, the control unit can also take into account any interdependencies in cooling, if necessary.

[0024] It is possible for the application device to have several spray nozzles arranged in series in the direction of the rolled material's transport. For example, groups of spray nozzles can be formed within a single spray bar, each supplied with coolant via its own supply line and pump. Alternatively, groups of spray nozzles can be formed that span multiple spray bars and are supplied with coolant via their respective supply lines and pumps. This configuration can be particularly advantageous because it requires fewer pumps than if each spray bar were supplied with coolant via its own supply line and pump.

[0025] In many cases, the application unit has several spray nozzles arranged side by side, perpendicular to the direction of travel of the rolled material. This can be particularly advantageous for flat rolled materials (strip or heavy plate). The application unit can extend across the full width of the rolled material or only a portion of it. In the latter case, several application units are arranged side by side, each supplied with coolant via its own supply line and pump, with the pumps being controlled independently.

[0026] According to the invention, no shut-off device is arranged between the respective pump and the respective application device. Alternatively, it is possible according to the invention to arrange a shut-off device between the respective pump and the respective application device. In this case, however, the shut-off device is either kept fully open permanently during the transport of the rolled material through the cooling section or is actuated, both opening and closing, only when the rotational speed of the respective pump is below a minimum speed. In this case, the respective minimum speed is so low that only a very small actual flow is conveyed. It is also possible according to the invention for the shut-off device to be actuated only manually in order to take the respective application device out of service, for example, for maintenance purposes.

[0027] Furthermore, according to the invention, a return line is arranged parallel to each pump, the return line having a smaller cross-section than the respective supply line. This allows the use of pumps in which, due to their design, a certain minimum coolant flow rate must always be maintained. However, this minimum flow rate is considerably smaller than the maximum possible coolant flow rate. If, in such a case, a quantity of coolant is to be applied to the rolled material that is less than the respective minimum flow rate, it is only necessary to open a valve arranged in the return line accordingly (bypass operation).

[0028] It is also possible for the respective pump to operate in generator mode or with reversed rotation whenever the target current falls below a certain lower limit. This allows for very low actual currents. Furthermore, this prevents an excessively high actual current from flowing through a pump that does not self-lock when the target current is low.

[0029] In a preferred embodiment, a check valve or non-return valve is provided in the respective supply line between the respective pump and the respective application device. This prevents the respective pump from running dry and thus being damaged.

[0030] Preferably, the system provides that the inlet pressure of the liquid coolant is measured upstream of each pump, and that the control unit takes this measured inlet pressure into account when determining the target operating state of each pump. This allows for a more precise determination of the target operating state for each pump.

[0031] It is possible that the pressure of the liquid coolant is measured downstream of each pump and that the control unit takes this measured pressure into account when determining the target operating state of that pump. This leads to an even more precise determination of the target operating state.

[0032] Preferably, the control unit determines the respective target current based on the thermodynamic energy state of the rolled material immediately before it reaches the respective application device. This allows for particularly precise temperature control. The thermodynamic energy state of the rolled material can be known to the control unit, for example, from a previous measurement. Alternatively, it is possible to perform a model-based calculation of the respective thermodynamic energy state based on a known thermodynamic energy state.

[0033] In a cooling section, many application devices are often arranged sequentially. The corresponding actual coolant flows are thus applied sequentially to the hot rolled material by means of the application devices. In this case, the operating method according to the invention is preferably designed in such a way that the control unit determines the respective thermodynamic energy state of the rolled material based on the thermodynamic energy state of the rolled material before the immediately preceding application device, additionally taking into account the target coolant flow or the actual coolant flow that is to be applied or is being applied to the hot rolled material by means of the immediately preceding application device. The calculation of the thermodynamic energy states can therefore be carried out sequentially.

[0034] The problem is further solved by a cooling section with the features of claim 8. Advantageous embodiments of the cooling section are the subject of dependent claims 9 to 14.

[0035] According to the invention, a cooling section of the type mentioned above is initially designed in such a way that the control device is configured to dynamically determine a target control state for the respective pump, depending on the target flow rate of the coolant to be applied to the hot rolled material by means of the respective application device, and controls the respective pump accordingly, so that the actual flow rate delivered by the respective pump is always as close as possible to the respective target flow rate. Furthermore, either no shut-off device is arranged between the respective pump and the respective application device, or a shut-off device is arranged.If a shut-off device is present, the control unit either keeps the shut-off device fully open permanently during the transport of the rolled material through the cooling section, or it only opens and closes the device when the speed of the respective pump falls below a minimum speed. Finally, a return line is arranged parallel to each pump, with the return line having a smaller cross-section than the respective supply line.

[0036] The advantageous designs of the cooling section essentially correspond to those of the operating process. The advantages gained thereby also correspond to the respective corresponding designs of the operating process. Brief description of the drawings

[0037] The properties, features, and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more readily understandable in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings. These show, in schematic representation: FIG 1 a cooling section downstream of a rolling mill, FIG 2 a cooling section upstream of a rolling mill, FIG 3 a cooling section arranged within a rolling mill, FIG 4 a single application device, FIG 5 a timing diagram, FIG 6 a diagram, FIG 7 a section of a supply line with a pump, FIG 8 a diagram, FIG 9 a section of a supply line with a pump, FIG 10 the operation of a control device, FIG 11 spray bars and spray nozzles and FIG 12 spray bars and spray nozzles. Description of the embodiments

[0038] According to FIG 1 A hot rolled metal stock 1 is to be cooled in a cooling section 2. The cooling section 2 is designed according to FIG 1 downstream of a rolling mill. It is shown in FIG 1 Only one rolling stand 3 of the rolling mill, namely the last rolling stand 3 of the rolling mill. However, the rolling mill usually has several rolling stands 3, which the hot rolled material 1 passes through sequentially. In the case of the configuration according to FIG 1 The hot rolled material 1 enters the cooling section 2 immediately after passing through the last rolling stand 3 of the rolling mill. The time interval between rolling in the last rolling stand 3 of the rolling mill and entering the cooling section 2 is on the order of a few seconds.

[0039] Alternatively, cooling section 2 could be configured as shown in FIG 2 It is located upstream of the rolling mill. This is depicted in FIG 2 likewise, only a single rolling stand 4 of the rolling mill, namely the first rolling stand 4 of the rolling mill. However, the rolling mill often exhibits – as in the design according to FIG 1 - several rolling stands 3, which the hot rolled material 1 passes through sequentially one after the other. In the case of the configuration according to FIG 2 The hot rolled material 1 is rolled in the first rolling stand 4 of the rolling mill immediately after exiting the cooling section 2. The time interval between cooling in the cooling section 2 and rolling in the first rolling stand 4 of the rolling mill is on the order of a few minutes. However, it can also be as short as a few seconds.

[0040] Alternatively, cooling section 2 could be configured as shown in FIG 3 They are located within the rolling mill. They are shown in FIG 3 two rolling stands 5 of the rolling mill. In this case, the cooling of the rolled material 1 – more precisely: a section of the rolled material 1 – takes place in the cooling section 2 between the rolling in the two rolling stands 5 of the rolling mill. The time interval between cooling in the cooling section 2 and rolling in the two successive rolling stands 5 of the rolling mill is on the order of a few seconds. According to the illustration in FIG 3 The cooling section 2 is arranged between two consecutive rolling stands 5 of the rolling mill. However, it could also extend over a larger area, so that the cooling section 2 passes through at least one FIG 3 The further rolling mill stand, not shown, is divided into a corresponding number of sections.

[0041] The rolled material 1 consists of metal. For example, the rolled material 1 can be made of steel or aluminum. Other metals are also possible. In the case of steel, the temperature of the rolled material 1 before cooling section 2 is typically between 750 °C and 1,200 °C. In cooling section 2, it is cooled to a lower temperature. In some cases, the lower temperature may be only slightly below the temperature before cooling section 2. However, particularly if cooling section 2 is located downstream of the rolling mill, the rolled material 1 is usually cooled to a significantly lower temperature, for example, between 200 °C and 700 °C.

[0042] The hot rolled material 1 is fed to the cooling section 2 in a horizontal transport direction x. Within the cooling section 2, the hot rolled material 1 does not change its transport direction x. It is therefore transported horizontally throughout the cooling section 2. After leaving the cooling section 2, the rolled material 1 can either maintain or change its transport direction. If the hot rolled material 1 is a strip, it can, for example, be deflected diagonally downwards to feed it to a coiler. If the hot rolled material 1 is a heavy plate, it usually maintains its transport direction x. A roller conveyor that may be required for transporting the hot rolled material 1 is not shown in the FIG.

[0043] Cooling section 2 has a number of application devices 6. A coolant 7 is applied to the rolled material 1 by means of the application devices 6. The coolant 7 is water. Optionally, small amounts (maximum 1% to 2%) of additives may be added to the water. In any case, however, the coolant 7 is a liquid, water-based coolant.

[0044] At a minimum, only one application device 6 is present. In many cases, however, several application devices 6 are present. For example, the application devices can be arranged as shown in FIG 1 The application devices 6 are arranged one after the other. In this case, the application devices 6 sequentially apply their respective portion of the coolant 7 to the rolled stock 1. The term "sequentially" refers in this context to a specific section of the rolled stock 1, as this section sequentially passes through areas in which the individual application devices 6 apply their respective portion of the coolant 7 to the corresponding section of the rolled stock 1. The number of application devices 6 is often in the double digits, sometimes even in the upper double digits. A sequential arrangement is generally implemented, in particular, when the cooling section 2 is downstream of the rolling mill. However, it can also occur in other configurations.

[0045] The application devices 6 are connected to a coolant reservoir 9 via a supply line 8. In this case, the reservoir 9 is the same for all application devices 6. However, there could also be several independent reservoirs 9. A pump 10 is located in each supply line 8. In principle, the pumps 10 can be located at any point within the supply lines 8. In practice, however, it is advantageous if the pumps 10 are located as close as possible to the reservoir 9.

[0046] The following is described – representing all application devices 6 – in conjunction with FIG 4 The operation of one of the application devices 6 is explained in more detail. The other application devices 6 are operated in essentially the same way. However, the specific operating method for each application device 6 can be determined individually. Therefore, while it is possible, it is not necessary to operate the application devices 6 in the same manner.

[0047] The application device 6 receives a current flow rate F of coolant 7 from reservoir 9 via supply line 8 and pump 10. This current flow rate F is applied to the hot rolled material 1 by means of the respective application device 6. The distance between the application device 6 – for example, from spray nozzles – and the rolled material 1 is typically between 20 cm and 200 cm.

[0048] A control unit 11 of the cooling section 2 is aware of a corresponding target flow rate F*, which is to be applied to the hot rolled material 1 by means of the application device 6. The target flow rate F* is generally not constant over time, but variable, i.e., a function of time t. Depending on the target flow rate F* of the coolant 7, the control unit 11 dynamically determines a target control state S* for the pump 10. It controls the pump 10 accordingly. The pump 10 thereby pressurizes the coolant 7 at the pump 10 outlet with an outlet pressure pA. The outlet pressure pA varies according to the target control state S*. However, it is below 10 bar in every operating state. It is usually at a maximum of 6 bar. In every operating state, however, the actual flow rate F delivered by the pump 10 is always approximated to the target flow rate F* as closely as possible.

[0049] The target control state S* can also be easily determined. This will be explained below using a simple example.

[0050] Assume that pump 10 is located in the immediate vicinity of reservoir 9. The supply line 8 has a length 1 and a cross-sectional area A. The pressure at the inlet of pump 10 is subsequently denoted by pE. The pressure in the delivery device 6 is denoted by p0.

[0051] Then the relationship applies first. F = FN ⋅ p 0 pN

[0052] FN is a nominal flow rate that flows from the application device 6 when the coolant 7 in the application device has a nominal pressure pN. The nominal flow rate FN and the nominal pressure pN are defined and determined by the design of the application device 6. They can be determined, for example, by a single measurement of the flow rate that results at a pressure that can be set arbitrarily.

[0053] The following relationship also applies to the actual current F: F ˙ = A ρ ⋅ l pA − p 0 − l ⋅ r ⋅ F 2 with ρ = density of the coolant 7 and r = resistance coefficient for the flow resistance of the coolant 7 in the supply line 8.

[0054] If one now solves equation (1) for the pressure p0 and substitutes it into equation (2), the following equation (3) is obtained: F ˙ = A ρ ⋅ l ⋅ pA − pN FN 2 ⋅ F 2 − l ⋅ r ⋅ F 2

[0055] Equation (3) is now solved for pA: pA = pN FN 2 + l ⋅ r ⋅ F 2 + ρl A ⋅ F ˙

[0056] The actual current F is readily available. For example, it can be measured. The desired time derivative of the actual current F is directly derived from the difference between the target current F* and the actual current F. If necessary, the time derivative of the actual current F can be limited to keep the output pressure pA within permissible limits.

[0057] Thus, the required outlet pressure pA can be easily determined. Using the desired outlet pressure pA and the inlet pressure pE, the corresponding rotational speed n can be determined according to the characteristic curve f of pump 10, which is usually readily known: n = f pA − pE , F

[0058] Furthermore, the actual current F, if it is not measured, can easily be determined using the relationship F = F 0 + ∫ o t F ˙ τ dτ to be determined, where F0 is a suitably chosen constant.

[0059] Furthermore, the actual current F is available to the control unit 11 at all times – either through measurement or calculation according to equation (6). This is necessary to be able to calculate and update the thermodynamic energy state H of the rolled material 1. This will be discussed in more detail later. The only remaining dead time of the application device 6 is the generally very short time that the coolant 7 needs to reach the rolled material 1 – calculated from the point where it exits the application device 6.

[0060] Control or regulation can be implemented as needed. In the case of regulation, the actual current F is measured at the input or output of pump 10 and fed to the control unit 11. If no such measurement takes place, the actual current F is controlled.

[0061] In order to control pump 10 accordingly, pump 10 – more precisely, its drive 12 – must be capable of operating at variable speeds. For example, the drive 12 of pump 10 can be inverter-controlled for this purpose. Such control systems are generally known to experts and therefore do not require further explanation. Pump 10 should preferably be operable within a control range between 0 and a maximum speed. The pump 10's seal should also be designed for low speeds. This is readily achievable, however, as suitable pumps 10 are known to experts.

[0062] To adjust the actual current F to the target current F*, pump 10 is dynamically controlled accordingly, thereby approximating the actual current F to the target current F* as closely as possible. However, unlike the prior art, no valve located in the supply line 8 is controlled. Any such valve, should it be present, remains permanently fully open.

[0063] Within the framework of the operating method according to the invention, it is therefore possible that no shut-off device is arranged between the pump 10 and the application device 6. Alternatively, as shown in the illustration in FIG 4 It is possible that such a shut-off device 13 is arranged between the pump 10 and the application device 6. The shut-off device 13 is in FIG 4 The line is only shown with a dashed line because it may be present, but it is not necessarily present. If the shut-off device 13 is present, it can be operated in two different ways.

[0064] Firstly, it is possible that the shut-off device 13 is kept fully open permanently during the transport of the rolled material 1 through the cooling section 2. This is in FIG 5 This illustrates that the rolled material 1 enters the cooling section 2 at time t1. However, the shut-off device 13 is opened at time t2, before time t1. Similarly, the rolled material 1 exits the cooling section 2 at time t3. Only after time t3 is the shut-off device 13 closed again at time t4. Between times t2 and t4, the shut-off device 13 remains fully open.

[0065] On the other hand, it is possible that the shut-off device 13 is only activated when the speed of the pump 10 is below a minimum speed nmin. This is explained below in conjunction with FIG 6 explained in more detail. According to FIG 6 The speed of pump 10 can vary between 0 and a nominal speed nmax. As long as the speed n remains below a minimum speed nmin, the shut-off device 13 can be actuated. This applies to both opening and closing the shut-off device 13. However, if and as soon as the speed n reaches or exceeds the minimum speed nmin, the shut-off device 13 remains open. In this case, the shut-off device 13 must first be opened at a very low speed n. The application device 6 then operates, during which only the pump 10 is controlled to adjust the actual current F. Only when the speed n falls below the minimum speed nmin again can and may the shut-off device 13 be actuated again.

[0066] Depending on the type of pump 10, the pump 10 must always deliver a minimum flow rate when operating. The minimum flow rate can be greater than the set flow rate F*. To also cover this case, the following applies as shown in FIG 7 It is planned to arrange a return line 14 parallel to the pump 10. However, the return line 14 has a smaller cross-section than the supply line 8. This is because, in particular, the return line 14 only needs to be designed to deliver the minimum flow rate. The supply line 8, on the other hand, needs to be designed to deliver a maximum flow rate, which is greater – usually considerably greater – than the minimum flow rate. Due to the design according to FIG 7 This allows the use of a pump 10 which, due to its design, must always maintain a certain minimum flow rate of coolant 7. However, the minimum flow rate is considerably lower than the maximum possible flow rate of coolant 7. If, in the case of the configuration according to FIG 7 If a quantity of coolant 7 is to be applied to the rolled material 1 that is less than the minimum flow rate, it is only necessary to open a valve 15 located in the return line 14 accordingly (bypass operation). Furthermore, the shut-off device 13 must be present in this case. The shut-off device 13 and the valve 15 must be designed as control valves. However, even in this case, the shut-off device 13 will only close (fully or partially) if the actual flow rate F is below the minimum flow rate. The situation in which the target flow rate F* assumes values ​​below the minimum flow rate occurs very rarely in practice. As a rule – i.e., if the actual flow rate F is above the minimum flow rate – the shut-off device 13 can remain fully open and the bypass valve 15 can remain fully closed.

[0067] According to FIG 8 The target current F* can vary. At higher values, the rotational speed n of pump 10 reaches significant values, so that pump 10 actively pumps the coolant 7. Pump 10 thus consumes energy E. However, if the target current F* decreases, pump 10 may continue to rotate in the same direction as at higher values, but it will operate as a generator. It will therefore supply energy E. For example, this energy E can be fed back into a power grid via the pump 10's drive 12. It is even possible for pump 10 to operate with reversed rotation ("rotational speed n < 0"). In this case, pump 10 continues to consume energy because it is actively attempting to pump the coolant 7 back.

[0068] If the pump 10 is operated with an inverted direction of rotation in certain operating conditions, preferably according to the illustration in FIG 9 A check valve 16 or a check flap is arranged between the pump 10 and the application device 6. The check valve 16 or the check flap can operate purely passively. For example, the check valve 16 or the check flap can be actuated by a slight spring force, so that it is pre-loaded towards the closed position but opens even at a very low pressure. The check valve 16 or the check flap does not need to be actively controlled by the control device 11. The check valve 16 or the check flap, in particular, prevents the supply line 8 between the pump 10 and the application device 6 from running dry when the direction of rotation is reversed. In this case, after the shut-off device 13 has closed, the pump 10 can be switched off as soon as the shut-off device 13 is closed, thus blocking further flow of the coolant 7.Since the shut-off device 13 does not need to slow down the flow of the coolant 7, but only closes when the flow of the coolant 7 has already stopped or is at least substantially stopped, a comparatively simple embodiment of the shut-off device 13 suffices. Furthermore, the shut-off device 13 can have low dynamics, as dynamic adjustments are made by the pump 10. Such a check valve 16 or check flap is also necessary if an application device 6 located above the rolled material 1 is supplied via the pump 10. Otherwise, at zero rotational speed, the coolant 7 would flow backward through the pump 10 into the reservoir 9. This could empty a buffer zone of the application device 6. The buffer zone would then only need to be refilled when the pump 10 is switched on again.This would increase the effective reaction time of the application device 6, which is - of course - not desirable.

[0069] If the coolant 7 is supplied to the pump 10 at no pressure, the pump 10 can have conventional impellers. However, if the coolant 7 has a pre-charge pressure, for example 1 bar, the pump 10 can be designed such that the coolant 7 cannot simply flow through it when the pump 10 is at rest. In this case, the pump 10 must be designed to seal at least to a large extent when at rest. Alternatively, the pump 10 can be designed to operate in reverse. Particularly in the latter case, it is advisable to actuate the shut-off device 13 after reducing the actual flow rate F to 0. The above points, in conjunction with... are particularly relevant in cases where the coolant 7 has a pre-charge pressure. FIG 9 The operating methods explained were useful.

[0070] As already mentioned, it is possible to control pump 10 solely. However, preferably, as shown in the illustration in FIG 4 The inlet pressure pE of the liquid coolant 7 is measured before pump 10 and fed to the control unit 11. In this case, the control unit 11 takes the measured inlet pressure pE into account when determining the target control state of pump 10. Measuring the water level in reservoir 9 is often equivalent to measuring the pressure. If necessary, as also described in FIG 4 As shown, it is also possible to additionally measure the outlet pressure pA downstream of pump 10 and feed it to the control unit 11. In this case, the control unit 11 also takes the measured outlet pressure pA into account when determining the target control state of pump 10.

[0071] It is possible that the target current F* of the control device 11 is specified directly and immediately. Preferably, however, the thermodynamic energy state H of the rolled material 1 immediately before it reaches the application device 6 is known to the control device 11. The thermodynamic energy state H can, in particular, be the enthalpy or the temperature of a respective section of the rolled material 1. In this case, the control device 11 determines the current F* according to the illustration in [reference to figure]. FIG 10 First, the control unit 11 determines the target flow rate F* based on the thermodynamic energy state H, and then, based on the target flow rate F*, the corresponding target control state S*. In particular, it is possible for the control unit 11 to be given a spatial or temporal target profile for the thermodynamic energy state H, which should be maintained as closely as possible. The control unit 11 can therefore determine which thermodynamic energy state H should be present immediately downstream of the application device 6. By comparing this with the actual thermodynamic energy state H immediately upstream of the application device 6, the control unit 11 can then determine the quantity of coolant 7 that must be applied to the corresponding section of the rolled material 1 so that the actual thermodynamic energy state H immediately downstream of the application device 6 corresponds as closely as possible to the desired target state.The required amount of coolant 7, in conjunction with the time required for the corresponding section of the rolled material 1 to pass through the application device 6, defines the target flow rate F*.

[0072] All the procedures described above in connection with one of the application devices 6 and its associated components can be carried out in a completely analogous manner for the other application devices 6. As already mentioned, the procedure is performed for a section of the rolled material 1 in each case.

[0073] The thermodynamic energy state H of the corresponding section of the rolled stock 1 varies from application device 6 to application device 6. In particular, it is changed by each of the application devices 6. For the application device 6 that first applies its share of coolant 7 to the rolled stock 1, the thermodynamic energy state H of the control device 11 can be predetermined as such. For example, as shown in FIG 1 A temperature measuring station 17 is arranged at the inlet of the cooling section 2, by means of which the temperature T is recorded for each section of the rolled material 1. The recorded temperature T is then assigned to the respective section.

[0074] For each section, path tracking is implemented during its passage through the cooling section 2. However, for each subsequent application unit 6 that applies its share of coolant 7, the corresponding thermodynamic energy state H of the rolled stock 1 (or the corresponding section of the rolled stock 1) must be updated. Here, the control unit 11 takes into account, in particular, the thermodynamic energy state H immediately before the immediately preceding application unit 6 and the quantity of coolant 7 that the immediately preceding application unit 6 applies to the rolled stock 1. With regard to the quantity of coolant 7, the control unit 11 can alternatively consider the target flow rate F* or the actual flow rate F of the immediately preceding application unit 6. It thus sequentially determines the thermodynamic energy state H of the rolled stock 1 for each application unit 6.If necessary, the control unit 11 can in this context apply a heat conduction equation and a phase conversion equation and solve them iteratively.

[0075] In many cases, the rolled material 1 is a flat product, such as a strip or a heavy plate. In this case, it is possible for the liquid coolant 7 to be applied to the rolled material 1 from both sides using each individual application device 6. This procedure is often used with a cooling section 2 that is located upstream of or within the rolling mill. However, it can also be used when the cooling section 2 is downstream of the rolling mill. Particularly when the cooling section 2 is downstream of the rolling mill, the liquid coolant 7 is generally applied to the rolled material 1 from only one side using each individual application device 6, specifically from above or below. Of course, it is also possible in this case to apply coolant 7 to both sides of the flat rolled material 1.In this case, however, this is done by means of different application devices 6, each of which has its own pump 10 assigned, whereby the pump 10 is controlled independently of the pumps 10 of the other application devices 6.

[0076] In extreme cases, it is possible that the application devices 6 each have only a single spray nozzle 18. However, as a rule, the application devices 6 each have several spray nozzles 18. The spray nozzles 18 can be arranged as shown in the illustration. FIG 11 The spray nozzles 18 are arranged one after the other in the transport direction x of the rolled material 1. For example, the spray nozzles 18 can be arranged one after the other within a single spray bar 19. Several spray bars 19 arranged one after the other in the transport direction x can also be combined to form a single application unit 6. This applies regardless of whether the respective spray bar 19 as such has several spray nozzles 18 arranged one after the other or not. In any case, it is crucial that each application unit 6 is individually supplied with coolant 7 via its own supply line 8 and its own pump 10, with the pump 10 being individually controlled to adjust the respective actual flow rate F.

[0077] The application devices 6 can be arranged according to the illustration in FIG 12 Furthermore, they often have several spray nozzles 18 arranged side by side transversely to the transport direction x of the rolled material 1. Such a design can be particularly useful for a flat rolled material 1, i.e., a strip or a heavy plate. In this case, the application devices 6 can extend over the full width of the rolled material 1. Alternatively, it is possible for the application devices 6 to extend only over a portion of the width. This is shown purely by way of example in the left part of FIG 12 The figure shows a spray boom 19 which – purely by way of example – is divided in its width into three application units 6. In this case, several application units 6 are arranged side by side, each supplied with coolant 7 via its own supply line 8 and its own pump 10, with the pumps 10 being controlled independently of each other.

[0078] The present invention has many advantages, some of which are listed below.

[0079] Since the supply of coolant 7 is not shut off, there are no pressure surges when the amount of coolant 7 is abruptly reduced. Shutdown is possible within a few tenths of a second (often less than 0.2 s, sometimes even less than 0.1 s). The same applies when increasing the delivered amount of coolant 7. The actual flow rate F of the respective application device 6 can be adjusted accordingly quickly. The drives 12 for the pumps 10 can be controlled very precisely. A typical accuracy of the rotational speed n is in the range of 0.1%. The actual flow rate F for the respective application device 6 can be adjusted with the same or a similar accuracy. Considering the response characteristics of the drives 12, it should most likely be possible to adjust the actual flow rate F with 1% accuracy in less than 0.5 s, possibly even in 0.2 s to 0.3 s.

[0080] If the coolant 7 is supplied to the pumps 10 at the inlet side without pressure, particularly fast response times can be achieved. Here is a numerical example: Assume that the distance of the reservoir 9 from one of the application devices 6, and thus the length of the associated supply line 8, is a typical length of 10 m. Flow velocities in the supply line 8 at maximum flow rate are normally around 3 m / s. If such a volume of fluid is accelerated at a pressure of 2 bar, the acceleration is 20 m / s². With such acceleration, the volume of fluid can be accelerated from 0 to maximum flow rate with a time constant of 150 ms. If the pressure increase by the pump 10 is suddenly reduced to 0, the volume of fluid decreases again to zero with a time constant of 150 ms, since the application device 6 initially opposes the flow with a back pressure of 2 bar.This results in extremely fast response times, which are not even remotely achievable with current technology. The control is even faster if pump 10 not only reduces the pressure increase to zero, but also actively slows down the fluid flow.

[0081] If the coolant 7 is supplied to the pumps 10 – with or without pre-charge pressure – via a common inlet pipe, the pumps 10 are coupled at the inlet. In this case, the acceleration of the effective liquid column in this common pipe must also be taken into account. This can have an impact, especially if many of the pumps 10 are to be started up or shut down simultaneously. In practice, however, this condition rarely occurs, so the resulting problem is tolerable. Furthermore, the problem can be avoided by suitable predictive control of the pumps 10.

[0082] The cooling section 2 according to the invention can be operated with low energy consumption. For example, some of the application devices 6 can be designed as conventional underside intensive cooling beams with a spray height of 20 m, which apply the coolant 7 to the rolled material 1 from below. In this case, the corresponding application device 6 can be operated with a pump 10 with a rated power of 25 kW, assuming a coolant flow rate of 360 m³ / h. This is because 360 ​​m³ / h corresponds to 0.1 m³ / s. A spray height of 20 m corresponds to an operating pressure of 2 bar, or 200 kPa. The mechanical power required to pump such a flow rate F is therefore 0.1 m³ / s x 200 kPa = 20 kW. Even with an efficiency of only 80%, a pump power of 25 kW is thus entirely sufficient. In contrast, prior art intensive cooling systems operate at approximately twice the pressure. Similar figures result for intensive cooling from the top.

[0083] The energy savings are even greater if the respective application device 6 is operated with a smaller volume of water. In conventional intensive cooling, the reduction in water volume is achieved by closing a valve. The pressure (4 bar) is maintained, and the pump 10 often continues to run at its full flow rate. In contrast, in the cooling section 2 according to the invention, the speed n of the pump 10 is simply reduced. With half the water volume, this results in a spray height of only 5 m. Therefore, only half the volume needs to be delivered at a quarter of the spray height. This means that only 1 / 8 of the full power is required, i.e., slightly over 3 kW. In contrast, intensive cooling according to the prior art requires approximately 25 kW.

[0084] Wear on pumps 10 and drives 12 is minimal. Typical service lives for pump bearings are 100,000 hours and more. This allows the pumps 10 to operate continuously for over 11 years without requiring maintenance. The cooling section 2 according to the invention is therefore very reliable and requires virtually no maintenance with regard to the pumps 10 and the drives 12.

[0085] A further advantage is the highly flexible operation of the cooling section 2. In particular, the same application devices 6 can be used and operated as intensive cooling or laminar cooling as required. The usable control range is usually between 5% and 100% of the maximum pumpable coolant quantity.

[0086] Equipping cooling line 2 with the required number of pumps 10 and associated drives 12, including the corresponding drive controls, does require a certain investment. However, this one-time investment is recouped relatively quickly through lower operating costs and increased system availability. Furthermore, the costs are put into perspective when one considers that even a conventional cooling line incurs significant costs when using high-quality ball valves. For example, in a cooling line with 100 upper spray bars 19 and 100 lower spray bars 19, each individually controlled by a ball valve, the cost of the ball valves is approximately £700,000.For the same amount, one could also build a cooling section 2 according to the invention, in which 100 upper spray bars are supplied by 50 pumps 10 and 100 lower spray bars are supplied by 50 lower pumps. Despite the smaller number of individually controllable spray bars 19, superior cooling is still achieved because the spray bars 19 can be controlled with significantly higher dynamics.

[0087] In intensive cooling, the costs for the cooling section 2 according to the invention are of the same order of magnitude as the costs for conventional intensive cooling. For example, with 16 upper and 16 lower spray bars 19, a total of 32 relatively small pumps 10 and the associated drives 12, each with 25 kW, are required, for a total electrical power of 800 kW. In contrast, an investment in a conventional cooling section requires 32 ball valves, 32 pneumatic actuators, 5 booster pumps, each with 400 kW (one pump is a reserve), and 5 correspondingly large frequency converters.

[0088] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples and other variants can be derived by the person skilled in the art without leaving the scope of protection of the invention as defined by the claims. Reference symbol list

[0089] 1. Rolled material 2. Cooling section 3 to 5. Rolling stands 6. Application devices 7. Coolant 8. Supply lines 9. Reservoir 10. Pumps 11. Control device 12. Drives 13. Shut-off device 14. Return line 15. Valve 16. Check valve 17. Temperature measuring station 18. Spray nozzles 19. Spray bar EEnergy FIActual Current F*Target Current FMaximum Current FMinimum Current HThermodynamic Energy State nSpeed nMinimum Speed nMaximum Speed p0 Pressure in the application device pA Output-side pressure pE Input-side pressure S*Control state tTime t1 to t4 Time points xTransport Direction

Claims

1. Method for operating a cooling section (2) which is arranged within a rolling train or upstream or downstream of the rolling train and by means of which a hot-rolled product (1) made of metal is cooled, - wherein a number of application devices (6) of the cooling section (2) are supplied with a respective actual flow (F) of a liquid, water-based coolant (7) via a respective supply line (8) and a respective pump (10), - wherein the respective actual flow (F) of the coolant (7) is applied to the hot-rolled product (1) by means of the respective application device (6), - wherein the hot-rolled product (1) is transported in a horizontal transport direction (x) within the cooling section (2) during the application of the coolant (7), - wherein a controller (11) of the cooling section (2) dynamically determines a respective target control state (S*) for the respective pump (10) on the basis of a respective target flow (F*) of the coolant (7) to be applied to the hot-rolled product (1) by means of the respective application device (6) and controls the respective pump (10) in a corresponding manner such that the respective actual flow (F) delivered by the respective pump (10) is approximated as far as possible to the respective target flow (F*) at any time, characterized in that - either no shutoff device (13) is arranged between the respective pump (10) and the respective application device (6), - or, although a shutoff device (13) is arranged between the respective pump (10) and the respective application device (6), the shutoff device (13) is kept permanently in the fully open state during the transport of the rolled product (1) through the cooling section (2), - or, although a shutoff device (13) is arranged between the respective pump (10) and the respective application device (6), the shutoff device (13) is actuated both in the opening and in the closing direction only when a speed of the respective pump (10) is below a minimum speed, and in that the respective pump (6) is assigned a return line (14) in parallel, and the return line (14) has a smaller cross section than the respective supply line (8).

2. Operating method according to Claim 1, characterized in that the respective pump (10) is operated as a generator or operated with a reverse direction of rotation whenever the respective target flow (F*) falls below a respective lower limit value.

3. Operating method according to Claim 2, characterized in that a check valve (16) or a swing check valve is arranged in the respective supply line (8) between the respective pump (10) and the respective application device (6).

4. Operating method according to any of the preceding claims, characterized in that an inlet-side pressure (pE) of the liquid coolant (7) is sensed upstream of the respective pump (10), and in that the controller (11) takes the sensed inlet-side pressure (pE) into account when determining the respective target control state (S*) of the respective pump (10).

5. Operating method according to any of the preceding claims, characterized in that an outlet-side pressure (pA) of the liquid coolant (7) is sensed downstream of the respective pump (10), and in that the controller (11) takes the sensed outlet-side pressure (pA) into account when determining the respective target control state (S*) of the respective pump (10).

6. Operating method according to any of the preceding claims, characterized in that the controller (11) determines the respective target flow (F*) on the basis of a respective thermodynamic energy state (H) of the rolled product (1) pertaining immediately before the respective application device (6) is reached.

7. Operating method according to any of the preceding claims, characterized - in that the actual flows (F) of the coolant (7) are applied to the hot-rolled product (1) sequentially in succession by means of the application devices (6), and - in that the controller (11) determines the respective thermodynamic energy state (H) of the rolled product (1) from the thermodynamic energy state (H) of the rolled product (1) upstream of the immediately preceding application device (6) while additionally taking into account the target flow (F*) of the coolant (7) or the actual flow (F) of the coolant (7) which is applied or is intended to be applied to the hot-rolled product (1) by means of the immediately preceding application device (6).

8. Cooling section which can be arranged within a rolling train or upstream or downstream of the rolling train and by means of which a hot-rolled product (1) made of metal is cooled, - wherein the cooling section has a number of application devices (6), which are supplied with a respective actual flow (F) of a liquid, water-based coolant (7) via a respective supply line (8) of the cooling section and a respective pump (10) of the curling section, - wherein the respective actual flow (F) of the coolant (7) is applied to the hot-rolled product (1) by means of the respective application device (6), - wherein the hot-rolled product (1) is transported in a horizontal transport direction (x) in the cooling section during the application of the coolant (7), - wherein the cooling section has a controller (11), - wherein the controller (11) is configured such that it dynamically determines a respective target control state (S*) for the respective pump (10) on the basis of a respective target flow (F*) of the coolant (7) to be applied to the hot-rolled product (1) by means of the respective application device (6) and controls the respective pump (10) in a corresponding manner such that the respective actual flow (F) delivered by the respective pump (10) is approximated as far as possible to the respective target flow (F*) at any time, characterized in that - either no shutoff device (13) is arranged between the respective pump (10) and the respective application device (6), - or, although a shutoff device (13) is arranged between the respective pump (10) and the respective application device (6), the shutoff device (13) is kept permanently in the fully open state by the controller (11) during the transport of the rolled product (1) through the cooling section (2), - or, although a shutoff device (13) is arranged between the respective pump (10) and the respective application device (6), the shutoff device (13) is actuated by the controller (11) both in the opening and in the closing direction only when a speed of the respective pump (10) is below a minimum speed, in that the respective pump (6) is assigned a return line (14) in parallel, and the return line (14) has a smaller cross section than the respective supply line (8).

9. Cooling section according to Claim 8, characterized in that the respective pump (10) is controlled by the controller (11) such that it is operated as a generator or operated with a reverse direction of rotation whenever the respective target flow (F*) falls below a respective lower limit value.

10. Cooling section according to Claim 8, characterized in that a check valve (16) or a swing check valve is arranged in the respective supply line (8) between the respective pump (10) and the respective application device (6).

11. Cooling section according to any of Claims 8 to 10, characterized in that means for sensing the inlet-side pressure upstream of the respective pump (10) are provided, in that an inlet-side pressure (pE) of the liquid coolant (7) is sensed upstream of the respective pump (10), and in that the controller (11) takes the sensed inlet-side pressure (pE) into account when determining the respective target control state (S*) of the respective pump (10).

12. Cooling section according to any of Claims 8 to 11, characterized in that means for sensing the outlet-side pressure downstream of the respective pump (10) are provided, in that an outlet-side pressure (pA) of the liquid coolant (7) is sensed downstream of the respective pump (10), and in that the controller (11) takes the sensed outlet-side pressure (pA) into account when determining the respective target control state (S*) of the respective pump (10).

13. Cooling section according to any of Claims 8 to 12, characterized in that the controller (11) determines the respective target flow (F*) on the basis of a respective thermodynamic energy state (H) of the rolled product (1) pertaining immediately before the respective application device (6) is reached.

14. Cooling section according to Claim 13, characterized - in that the actual flows (F) of the coolant (7) are applied to the hot-rolled product (1) sequentially in succession by means of the application devices (6), and - in that the controller (11) determines the respective thermodynamic energy state (H) of the rolled product (1) from the thermodynamic energy state (H) of the rolled product (1) upstream of the immediately preceding application device (6) while additionally taking into account the target flow (F*) of the coolant (7) or the actual flow (F) of the coolant (7) which is applied or is intended to be applied to the hot-rolled product (1) by means of the immediately preceding application device (6).

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