Method for rolling a product to be rolled

Abstract

The invention relates to a method for rolling a product to be rolled (3), wherein the product to be rolled (3) is fed through a rolling gap (11) between two working rollers (9, 10) of a roll stand (1) and a cooling lubricant is introduced into a contact zone (15, 16), in which a contact surface (17, 18) of the product to be rolled (3) lies against a working roller (9, 10), in order to lubricate the contact zone (15, 16). Furthermore, a lubrication demand of the contact zone (15, 16) is determined in accordance with at least one process parameter of the rolling process and an additional lubricant is applied to the contact surface (17, 18) of the product to be rolled (3) before the rolling gap (11) at a specified application distance (D) if a cooling lubricant amount (C) presently introduced into the contact zone (15, 16) does not cover the lubrication demand. The application distance (D) is sized in such a way that adhesion of the additional lubricant to the contact surface (17, 18) is increased and the lubricating effect in the contact zone (15, 16) is improved in comparison with application immediately before the rolling gap (11). In addition, the lubricant amount (C) introduced into the contact zone (15, 16) is reduced if additional lubricant is applied to the contact surface (17, 18).

Description

[0001] The invention relates to a method for rolling, in particular for cold rolling, a rolling stock, in which the rolling stock is guided through a roll gap between two work rolls of a rolling stand and a contact zone in which a contact surface of the rolling stock rests against a work roll is lubricated.

[0002] The rolled stock is a metallic rolled strip that is pulled through the roll gap by the rotating work rolls to reduce its thickness. Lubricating a contact zone where the rolled stock is in contact with a work roll reduces the friction between the rolled stock and the work roll. To reduce the temperature and wear of the work rolls, the work rolls are usually cooled. Various methods and devices are known for lubricating contact zones where a rolled stock is in contact with work rolls.

[0003] EP 2 651 577 B1 discloses a method for applying a lubricant during the rolling of a metallic rolled strip, which is guided through a roll gap between two work rolls. A mixture of the lubricant and a carrier gas is generated in an atomization device, and the mixture is applied to the surface of at least one work roll and / or to the surface of the rolled strip using spray nozzles.

[0004] WO 2013 / 029886 A1 discloses an operating method for a reversing rolling mill with at least one reversing rolling stand for rolling a rolling stock and a coiler for coiling the rolling stock after a rolling pass. A rolling oil application device arranged between the at least one reversing rolling stand and the coiler applies exclusively rolling oil, without water as a carrier medium, to the rolling stock.

[0005] WO 00 / 64605 A1 discloses a rolling arrangement with at least one rolling stand for rolling a metal strip and a lubrication device assigned to the rolling stand for applying a quantity of lubricant to the metal strip distributed across the width of the metal strip. The lubrication device has a basic lubrication device and an additional lubrication device, wherein the quantity and distribution of the lubricant to be applied by the basic lubrication device is constant during a pass and the quantity and / or distribution of the lubricant to be applied by the additional lubrication device is adjustable. Downstream of the rolling stand, a lubrication curve is determined across the width of the metal strip using a lubrication curve detection device and used to adjust the quantity and / or distribution of the lubricant and / or at least one rolling parameter.

[0006] EP 1 750 864 B2 discloses a method and a device for cooling and / or lubricating rolls and / or rolled stock. A cooling medium is applied to the rolls from several nozzles / rows of nozzles, and a base oil is applied to the rolled stock in front of the roll gap for lubrication. The cooling medium is applied to the rolls separately from the base oil, and only the base oil is applied directly to the rolled stock across its entire width, without water as a carrier medium, in a very small amount compared to the usual amount.

[0007] EP 0 794 023 A2 discloses a rolling mill and a method for cold rolling a rolling stock, in which rolling oil is introduced between the rolling stock and the work rolls immediately before a roll gap and cooling water is applied to the work rolls.

[0008] WO 2013 / 120750 A1 discloses a device and a method for lubricating the rolls of a rolling stand, wherein a mixture of water and oil is produced by means of a mixing and spraying device and this mixture is sprayed onto at least one of the rolls of the rolling stand and / or onto the surface of the rolling stock.

[0009] JP H01 218710 A discloses a generic method for lubricating and cooling a rolled product in a rolling stand, in which coolant is applied to the rolls on the outlet side and a lubricant on the inlet side and in which, if required, additional lubricant can be sprayed onto the rolled strip in front of the rolling stand.

[0010] According to WO2007 / 025682 A1, lubricant is applied to the work rolls on the inlet side of a rolling stand or directly to the top and bottom surfaces of the rolled strip to achieve better strip qualities through a more stable rolling process, particularly through friction adjustment in the roll gap. The total amount of lubricant applied is controlled by a computer model based on process data, so that only as much lubricant is applied as is needed during the rolling process.

[0011] The invention is based on the object of providing an improved method for rolling a rolling stock, in which the rolling stock is guided through a roll gap between two work rolls of a rolling stand and contact zones in which the rolling stock is in contact with the work rolls are lubricated.

[0012] The object is achieved according to the invention by the features of claim 1.

[0013] Advantageous embodiments of the invention are the subject of the subclaims.

[0014] In the method according to the invention for rolling a rolled stock, the rolled stock is guided in a rolling direction through a roll gap between two work rolls of a rolling stand, and a cooling lubricant is introduced into a contact zone in which a contact surface of the rolled stock rests against a work roll to lubricate the contact zone. Furthermore, a lubrication requirement of the contact zone is determined as a function of at least one process parameter of the rolling process, and an additional lubricant is applied to the contact surface of the rolled stock upstream of the roll gap at a predetermined application distance from the roll gap with respect to the rolling direction if the amount of cooling lubricant currently introduced into the contact zone does not cover the lubrication requirement.

[0015] The process therefore advantageously enables the use of an additional lubricant, if required, in addition to a cooling lubricant to lubricate a contact zone between the rolling stock and a work roll when the applied cooling lubricant quantity is insufficient. The additional lubrication reduces the roll gap friction between the rolling stock and the work roll in the contact zone and thus advantageously enables energy savings due to lower required drive power for the work roll. Improved lubrication by means of the additional lubricant also makes it possible to roll higher-strength rolled stock with acceptable pass reduction, since the rolling of higher-strength rolled stock results in increased rolling forces and therefore a greater lubrication requirement. This advantageously expands the product range that can be produced with the rolling stand.By selecting the additive lubricant based on the product and / or process, production flexibility can be further increased. Applying the additive lubricant as needed also enables lubrication independent of cooling.

[0016] Because the additive lubricant is applied to the rolling stock at a specified application distance upstream of the roll gap, the additive lubricant remains in contact with the rolling stock until it reaches the roll gap. This long exposure time advantageously improves the lubricating effect (the so-called plate-out) of the additive lubricant in the contact zone compared to applying the additive lubricant to the rolling stock immediately upstream of the roll gap.

[0017] The invention provides that the amount of cooling lubricant introduced into the contact zone is reduced when additional lubricant is applied to the contact surface. This takes into account that additional lubricant can be washed away by the cooling lubricant. Therefore, it is advisable to reduce the amount of cooling lubricant when additional lubricant is applied in order to prevent or reduce this washing effect of the cooling lubricant.

[0018] The use of supplementary lubrication also increases the surface cleanliness of the rolled stock, i.e., reduces the iron abrasion remaining on the rolled stock after rolling. Therefore, supplementary lubrication can also be advantageously used in the production of rolled stock with increased requirements for surface cleanliness.

[0019] One embodiment of the invention provides that the amount of additional lubricant applied to the contact surface of the rolling stock is adjusted depending on the lubrication requirement determined for the contact zone. This allows the amount of additional lubricant used to be advantageously adapted to the lubrication requirement, ensuring, on the one hand, sufficient lubrication of the contact zone at all times, while, on the other hand, avoiding an excessive amount of additional lubricant, which would cause the work roll to slip on the rolling stock.

[0020] A further embodiment of the invention provides that a rolling stock speed of the rolling stock and / or a compressive strength of the rolling stock and / or a roughness of the rolling stock and / or a relative speed between the contact surface of the rolling stock at a reference location and the surface of the work roll and / or a thickness of the rolling stock and / or a viscosity of the cooling lubricant is or are used as process parameters for determining the lubrication requirement.

[0021] Using the rolling stock speed as a process parameter for determining lubrication requirements is particularly advantageous because the roll gap friction between the rolling stock and the work rolls, and thus the lubrication requirement, are highly dependent on the rolling stock speed. Roll gap friction also depends significantly on the compressive strength and roughness of the rolling stock, which is why these material properties of the rolling stock are also advantageous as process parameters for determining lubrication requirements. Furthermore, taking these material properties of the rolling stock into account enables product-specific lubrication of the contact zone, which is particularly advantageous.

[0022] The relative speed between the contact surface of the rolling stock and the surface of the work roll depends on the location at which the speed of the contact surface is observed, since the thickness of the rolling stock changes in the contact zone and the contact surface therefore moves slower upstream of the roll gap and faster downstream of the roll gap than the surface of the work roll. Therefore, the relative speed between the contact surface of the rolling stock and the surface of the work roll must be related to a reference location that is fixed with respect to the roll gap. This relative speed is a measure of the relative movement of the contact surface to the work roll in the contact zone. This relative movement leads to plastic deformation of the surface microstructure of the rolling stock and thereby influences the distribution of the additional lubricant adhering in depressions of the contact surface, which in turn influences the roll gap friction.Therefore, the relative speed between the contact surface of the rolling stock at a reference point and the surface of the work roll is also suitable as a process parameter for determining the lubrication requirement.

[0023] The relative speed between the contact surface of the rolling stock and the surface of the work roll at a reference location can be calculated, for example, from an instantaneous angular velocity and a radius of the work roll, a distance of the reference location from the roll gap, the thicknesses of the rolling stock in front of and behind the roll gap, and a rolling stock speed in front of or behind the roll gap. See, for example, equation (3.13) on page 113 in H. Hoffmann, R. Neugebauer, and G. Spur (eds.), "Handbuch Umformen" (Handbook of Forming), 2nd edition, Carl Hanser Verlag, 2012, ISBN 978-3-446-42778-5. The relative speed between the contact surface of the rolling stock and the surface of the work roll at a reference location can thus be determined, at least approximately, from the aforementioned variables, which can be easily determined by measurements and are usually recorded anyway.

[0024] Taking the above-mentioned process parameters into account when determining the lubrication requirement therefore makes it possible, in particular, to reduce the required drive power for the work rolls by means of additional lubrication adapted to the process parameters, to roll rolling stock with high compressive strength or to increase the overall throughput of the rolling process by increasing the rolling stock speed and / or reducing rolling interruptions due to insufficient lubrication.

[0025] A further embodiment of the invention provides that the amount of cooling lubricant introduced into the contact zone is adjusted depending on the at least one process parameter of the rolling process. By also adjusting the amount of cooling lubricant depending on the at least one process parameter, it can be taken into account, in particular, that the additional lubrication reduces roll gap friction, which also reduces the heating of the work rolls and thus the cooling requirement, thus allowing the amount of cooling lubricant used to be reduced accordingly.

[0026] Furthermore, the invention provides for the use of a pure lubricant, such as a rolling oil, as the additional lubricant. This gives the additional lubricant a greater lubricating effect than the cooling lubricant, so that even a relatively small amount of additional lubricant significantly increases the lubrication of the contact zone.

[0027] Further embodiments of the invention provide for the additional lubricant to be applied to the rolling stock by spraying, and / or for the additional lubricant to be applied evenly across the entire rolling stock width to the contact surface of the rolling stock. These embodiments of the invention advantageously enable a uniform distribution of the additional lubricant in the contact zone.

[0028] A further embodiment of the invention provides for the additional lubricant to be applied to the rolling stock using an additional lubrication device that is independent of a cooling lubricant device for introducing the cooling lubricant into the contact zone. This embodiment of the invention thus provides for a separation of the systems for applying the cooling lubricant and the additional lubricant. This advantageously enables a flexible configuration of the entire cooling and lubrication complex for a rolling stand, as well as easy retrofitting of existing systems without having to make changes to their cooling lubricant devices for introducing a cooling lubricant.

[0029] A further embodiment of the invention provides that the lubrication requirement of the contact zone is determined before the start of the rolling process and / or during the rolling process. Determining the lubrication requirement before the start of the rolling process enables lubrication of the contact zone adapted to the at least one process parameter right at the start of the rolling process. Determining the lubrication requirement during the rolling process enables the lubrication to be adapted to changes in the at least one process parameter occurring during the rolling process, for example, changes in the rolling stock speed, compressive strength, and / or roughness of the rolling stock.

[0030] A further embodiment of the invention provides that the lubrication requirement of the contact zone is determined using a Stribeck diagram for a coefficient of friction between the contact surface and the work roll in the contact zone as a function of at least one process parameter. Such Stribeck diagrams are known, for example, from JBAF Smeulders, "Lubrication in the Cold Rolling Process Described by a 3D Stribeck Curve," AISTech 2013 Proceedings, pp. 1681-1689. Determining a coefficient of friction between the contact surface and the work roll in the contact zone advantageously enables a quantitative determination of the lubrication requirement as a function of the determined coefficient of friction.

[0031] In particular, for a rolling mill, the friction coefficient (and thus the required drive power for the work rolls) is strongly dependent on the rolling stock speed and the relative speed between the contact surface of the rolling stock and the surface of the work roll. This can be described by a three-dimensional Stribeck diagram for the friction coefficient as a function of the rolling stock speed and this relative speed. The specific form of this function depends on the lubricating properties of the system, in particular the properties of the lubricant itself, its adhesion to the rolling stock surface, and the roughness of the rolling stock.Using this function, an operating point can be assigned to the rolling stand, which determines the friction coefficient of the rolling stand for the respective values ​​of the rolling stock speed and the relative speed between the contact surface of the rolling stock and the surface of the work roll, taking into account the lubrication properties of the system. This enables a highly differentiated determination of the lubrication requirement of the contact zone, adapted to the specific lubrication properties of the system, depending on the rolling stock speed and the relative speed between the contact surface of the rolling stock and the surface of the work roll. This allows for more targeted lubrication to be set to optimize the rolling process, for example, with regard to the rolling stock throughput, work roll wear, lubricant and coolant consumption, and / or the required drive power for the work rolls.

[0032] A further embodiment of the invention provides for the additional lubricant to be applied to two opposing contact surfaces of the rolling stock. Different amounts of the additional lubricant can be applied to the two contact surfaces of the rolling stock. Applying the additional lubricant to both contact surfaces of the rolling stock advantageously enables coordinated lubrication of both contact zones of the rolling stock with the work rolls. Applying different amounts of the additional lubricant to the two contact surfaces makes it possible, in particular, to influence and optimize the torque distribution between the work rolls.

[0033] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of exemplary embodiments, which are explained in more detail in conjunction with the drawings. FIG 1 a block diagram of a rolling stand, a cooling lubrication device and an additional lubrication device, FIG 2 temporal progressions of a rolling stock speed, a cooling lubricant quantity and an additional lubricant quantity, and FIG 3 schematic of a rolling mill train.

[0034] Corresponding parts are provided with the same reference numerals in the figures.

[0035] Figure 1shows a block diagram of a rolling stand 1 for rolling a rolled product 3, a cooling and lubrication device 5 and an additional lubrication device 7. The rolled product 3 is a metallic rolled strip, for example a steel strip, the thickness of which is reduced by rolling.

[0036] The rolling stand 1 has two work rolls 9, 10 arranged one above the other, which are spaced from each other by a roll gap 11. To roll the rolled stock 3, the work rolls 9, 10 are set in rotation and the rolled stock 3 is pulled through the roll gap 11 by the rotating work rolls 9, 10 in a rolling direction 13. The rolled stock 3 is in contact with the work rolls 9, 10 in two contact zones 15, 16 in the region of the roll gap 11, with an upper contact surface 17 of the rolled stock 3 resting against the upper work roll 9 in a first contact zone 15 and a lower contact surface 18 of the rolled stock 3 resting against the lower work roll 10 in a second contact zone 16.

[0037] A cooling lubricant is introduced into the contact zones 15, 16 using the cooling lubricant device 5. The cooling lubricant is a cooling lubricant emulsion consisting of a cooling liquid and a lubricant, for example, water as the cooling liquid and oil as the lubricant, as well as possibly emulsifiers. The main component of the cooling lubricant emulsion is the cooling liquid, while the lubricant content of the cooling lubricant is only a few percent, for example, two to three percent.

[0038] The cooling-lubricating device 5 comprises a cooling-lubricating pump 19, at least one cooling-lubricating spray bar 21 for each work roll 9, 10, cooling-lubricating lines 23, and a cooling-lubricating control system 25. Each cooling-lubricating spray bar 21 comprises cooling-lubricating nozzles for dispensing cooling-lubricating agent onto the respective work roll 9, 10. The cooling-lubricating agent is pumped by the cooling-lubricating pump 19 through the cooling-lubricating lines 23 to the cooling-lubricating spray bars 21 and sprayed onto the work rolls 9, 10 by the cooling-lubricating spray bars 21. The cooling-lubricating agent quantities C dispensed by the cooling-lubricating spray bars 21 are adjusted by the cooling-lubricating control system 25 by controlling the cooling-lubricating pump 19. The rotation of the work rolls 9, 10 transports the cooling-lubricating agent sprayed onto the work rolls 9, 10 to the contact zones 15, 16.

[0039] The additional lubrication device 7 can be used to apply an additional lubricant to the rolling stock 3. The additional lubricant is a pure lubricant, for example, a rolling oil.

[0040] The additional lubrication device 7 comprises an additional lubricant pump 27, at least one additional lubricant spray bar 29 for each contact surface 17, 18 of the rolling stock 3, additional lubricant lines 31, and an additional lubrication control 33. Each additional lubricant spray bar 29 has additional lubricant nozzles for dispensing additional lubricant onto the respective contact surface 17, 18. The additional lubricant is pumped by the additional lubricant pump 27 through the additional lubricant lines 31 to the additional lubricant spray bars 29 and sprayed onto the contact surfaces 17, 18 by the additional lubricant spray bars 29. The additional lubricant quantities A dispensed by the additional lubricant spray bars 29 are adjusted by the additional lubrication control 33 by controlling the additional lubricant pump 27. Due to the movement of the rolling stock 3, additional lubricant sprayed onto the contact surfaces 17, 18 is transported to the contact zones 15, 16.

[0041] The additional lubricant spray bars 29 are arranged at a predetermined application distance D with respect to the rolling direction 13 upstream of the roll gap 11 in order to apply the additional lubricant to the rolling stock 3 at this application distance D from the roll gap 11. As a result, the additional lubricant acts on the contact surfaces 17, 18 of the rolling stock 3 until it reaches the roll gap 11. During this exposure time, the adhesion of the additional lubricant to the contact surfaces 17, 18 increases. This advantageously improves the lubricating effect (the so-called plate-out) of the additional lubricant in the contact zones 15, 16 compared to applying the additional lubricant to the contact surfaces 17, 18 immediately upstream of the roll gap 11.

[0042] In order to adjust the additional lubricant quantities A to be applied to the contact surfaces 17, 18, a lubrication requirement is determined for each contact zone 15, 16 as a function of at least one process parameter of the rolling process. A rolling stock speed v of the rolling stock 3 is used as a process parameter. The rolling stock speed v is determined, for example, by the additional lubrication control 33 from measurement signals 35 supplied to it by a strip speed sensor 37 for detecting a strip speed of the rolled strip. Optional further process parameters for determining the lubrication requirement are material properties 41 of the respective rolling stock 3, for example a compressive strength and / or a roughness of the rolling stock 3, which are supplied to the additional lubrication control 33 as material property data 41 from a production system 43.

[0043] Furthermore, relative speeds between the contact surfaces 17, 18 of the rolling stock 3 at specified reference locations and the surfaces of the work rolls 9, 10 can optionally be used as process parameters for determining the lubrication requirement. These relative speeds can be determined, for example, from the rolling stock speed v at a reference location and measurement signals 35 from speed sensors 39 for recording the speeds of the work rolls 9, 10 as well as the thicknesses of the rolling stock 3 in front of and behind the roll gap 11. See, for example, equation (3.13) on page 113 in H. Hoffmann, R. Neugebauer, and G. Spur (eds.), "Handbuch Umformen" (Handbook of Forming), 2nd edition, Carl Hanser Verlag, 2012, ISBN 978-3-446-42778-5. Further optional process parameters for determining the lubrication requirement are the viscosity of the cooling lubricant and / or the thickness of the rolling stock 3.If necessary, the cooling lubricant quantities C and / or the lubricant content of the cooling lubricant currently present in the contact zones 15, 16 can also be recorded and used as process parameters. Furthermore, control data 45 can be exchanged between the cooling lubricant control 25 and the additional lubrication control 33 in order to coordinate the settings of the cooling lubricant quantities C and the additional lubricant quantities A.

[0044] The additional lubricant is applied to each contact surface 17, 18 depending on the lubrication requirement determined for the contact zone 15, 16 of this contact surface 17, 18 if the cooling lubricant quantity C currently introduced into the contact zone 15, 16 does not cover the lubrication requirement determined for the contact zone 15, 16, for example because the rolling stock speed v changes or a rolling stock 3 with an increased compressive strength is rolled. The cooling lubricant quantities C applied to the work rolls 9, 10 are either kept constant or also adjusted depending on the at least one process parameter of the rolling process and / or on the additional lubricant quantities A applied to the contact surfaces 17, 18, see the description of Figure 2 .

[0045] Figure 2illustrates a method for rolling a rolling stock 3 with a rolling stand 1, a cooling lubrication device 5 and an additional lubrication device 7, each according to Figure 1 are trained. Figure 2 as a function of a time t, curves v(t), C(t), A(t) of a rolling stock speed v of the rolling stock 3, a cooling lubricant quantity C which is applied to a work roll 9, 10 of the rolling stand 1 by the cooling lubricant device 5, and an additional lubricant quantity A which is applied to a contact surface 17, 18 of the rolling stock 3 in a contact zone 15, 16 on the work roll 9, 10 by the additional lubricant device 7. The cooling lubricant quantity C and the additional lubricant quantity A are each defined as the volume applied per unit of time.

[0046] Figure 2shows a case in which the rolled stock 3 consists of various partial rolled strips that are welded together. First, between times t 0 and t 4, a first partial rolled strip is rolled. Then, between times t 4 and t 5, a first transition region between the first partial rolled strip and a second partial rolled strip is rolled with a first weld seam connecting these two partial rolled strips. Then, between times t 5 and t 8, the second partial rolled strip is rolled. Then, between times t 8 and t 9, a second transition region between the second partial rolled strip and a third partial rolled strip is rolled with a second weld seam connecting these two partial rolled strips. Then, from time t 9, the third partial rolled strip is rolled. The second partial rolled strip has a higher compressive strength than the first partial rolled strip and the third partial rolled strip, which have the same compressive strength.

[0047] The cooling lubricant quantity C and the additional lubricant quantity A are each adjusted by the cooling lubricant control 25 and the additional lubrication control 33 depending on a lubrication requirement, which is determined for the contact zone 15, 16 as a function of the rolling stock speed v and the compression strength of the respective sub-strip, as well as optionally by other process parameters mentioned above. To determine the lubrication requirement, a so-called Stribeck diagram is used, for example, for a friction coefficient between the contact surface 17, 18 and the work roll 9, 10 in the contact zone 15, 16 as a function of the process parameters, as is known, for example, from JBAF Smeulders, "Lubrication in the Cold Rolling Process Described by a 3D Stribeck Curve," AISTech 2013 Proceedings, pp. 1681-1689.

[0048] Between times t 0 and t 1 , the first partial rolled strip is rolled at a first rolling stock speed v 1 . Between times t 1 and t 2 , the rolling stock speed v is increased to a second rolling stock speed v 2 . The second rolling stock speed v 2 is maintained until time t 3 . The lubrication requirement between times t 0 and t 3 can be covered by cooling lubricant alone, so that no additional lubricant is applied. Increasing the rolling stock speed v from the first rolling stock speed v 1 to the second rolling stock speed v 2 increases the lubrication requirement. The increased lubrication requirement is covered by a corresponding increase in the cooling lubricant quantity C.

[0049] Between times t 3 and t 4 , the rolling stock speed v is significantly reduced from the second rolling stock speed v 2 to a third rolling stock speed v 3 in order to prepare for rolling the first transition zone between the first partial rolled strip and the second partial rolled strip with the first weld seam. The first transition zone is then rolled between times t 4 and t 5 at the third rolling stock speed v 3 . Subsequently, the rolling stock speed v is increased between times t 5 and t 6 to a fourth rolling stock speed v 4 , at which the second partial rolled strip is rolled between times t 6 and t 7 .

[0050] The lubrication requirement for rolling the first transition zone is higher than the lubrication requirement for rolling the first partial rolled strip due to the very low third rolling stock speed v 3 . The lubrication requirement for rolling the second partial rolled strip is even higher than the lubrication requirement for rolling the first transition zone due to the high compressive strength of the second partial rolled strip. Therefore, additional lubricant is applied starting at time t 3 , with a larger amount of additional lubricant A being applied for rolling the second partial rolled strip between times t 6 and t 7 than for rolling the first transition zone between times t 4 and t 5 .At the same time, the applied cooling lubricant quantity C is reduced between times t 3 and t 6 and kept constant between times t 6 and t 7 in order to prevent or reduce washing away of applied additional lubricant by the cooling lubricant.

[0051] Between times t 7 and t 8 , the rolling stock speed v is reduced from the fourth rolling stock speed v 4 back to the third rolling stock speed v 3 in order to prepare the rolling of the second transition zone between the second partial rolled strip and the third partial rolled strip with the second weld seam. The second transition zone is then rolled between times t 8 and t 9 at the third rolling stock speed v 3 . Subsequently, the rolling stock speed v is increased between times t 9 and t 10 to the second rolling stock speed v 2 , at which the third partial rolled strip is rolled between times t 10 and t 11 .

[0052] Accordingly, the applied additional lubricant quantity A is initially reduced for rolling the second transition zone, and no additional lubricant is applied for rolling the third partial strip at the second rolling stock speed v 2 . At the same time, the applied cooling lubricant quantity C is increased again.

[0053] Between times t 11 and t 12 , the rolling stock speed v is reduced from the second rolling stock speed v 2 to a fifth rolling stock speed v 5 , at which the third partial rolled strip is rolled from time t 12 .

[0054] Rolling the third partial strip at the fifth rolling speed v 5 requires lubrication that cannot be met with the cooling lubricant alone. Therefore, for rolling the third partial strip at the fifth rolling speed v 5, additional lubricant is applied again, and at the same time, the applied cooling lubricant quantity C is reduced. The applied additional lubricant quantity A and the applied cooling lubricant quantity C are coordinated to meet the lubrication requirement and prevent or reduce the washing away of applied additional lubricant by the cooling lubricant.

[0055] Figure 3shows schematically a rolling mill train 47 of a rolling mill with several rolling stands 1 arranged one behind the other for rolling a rolled product 3. The rolling stands 1 each have two work rolls 9, 10 arranged one above the other and a backup roll 49 for each work roll. The rolling mill train 47 has for each roll stand 1 a Figure 3 not shown cooling and lubrication device 5 and an additional lubrication device 7. The cooling and lubrication devices 5 are each like the ones in Figure 1 cooling-lubricating device 5 shown and the additional lubricating devices 7 are each like the ones shown in Figure 1 illustrated additional lubrication device 7, wherein the additional lubricant spray bars 29 of each additional lubrication device 7 are arranged at the application distance D with respect to the rolling direction 13 in front of the roll gap 11 of the associated roll stand 1.

[0056] Although the invention has been illustrated and described in detail by means of preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

1. Method for rolling a rolled material (3), wherein - the rolled material (3) is guided in a rolling direction (13) through a rolling gap (11) between two working rollers (9, 10) of a roll stand (1), - a cooling lubricant for lubricating the contact zone (15, 16) is introduced into a contact zone (15, 16) in which a contact surface (17, 18) of the rolled material (3) contacts a working roller (9, 10), - a lubrication requirement of the contact zone (15, 16) is determined depending on at least one process parameter of the rolling process, - with respect to the rolling direction (13), an additive lubricant is applied to the contact surface (17, 18) of the rolled material (3) ahead of the rolling gap (11) at a predefined application spacing (D) from the rolling gap (11) when a cooling lubricant quantity (C) currently introduced into the contact zone (15, 16) does not cover the lubrication requirement, wherein the application spacing (D) is dimensioned such that an adhesion of the additive lubricant to the contact surface (17, 18) is increased, and the lubricating effect of the additive lubricant in the contact zone (15, 16) is improved as compared to an application of the additive lubricant to the contact surface (17, 18) directly ahead of the rolling gap (11), - and the cooling lubricant quantity (C) introduced into the contact zone (15, 16) is reduced when additive lubricant is applied to the contact surface (17, 18), characterized in that - a pure lubricant is used as an additive lubricant.

2. Method according to Claim 1, characterized in that an additive lubricant quantity (A) applied to the contact surface (17, 18) of the rolled material (3) is set depending on the lubrication requirement determined for the contact zone (15, 16).

3. Method according to one of the preceding claims, characterized in that a rolled material speed (v) of the rolled material (3), and / or a compressive strength of the rolled material (3), and / or a roughness of the rolled material (3), and / or a relative speed between the contact surface (17, 18) of the rolled material (3) at a reference location and the surface of the working roller (9, 10), and / or a thickness of the rolled material (3), and / or a viscosity of the cooling lubricant are / is used as process parameters for determining the lubrication requirement.

4. Method according to one of the preceding claims, characterized in that the cooling lubricant quantity (C) introduced into the contact zone (15, 16) is set depending on the at least one process parameter of the rolling process.

5. Method according to one of the preceding claims, characterized in that the additive lubricant is applied to the rolled material (3) by spraying.

6. Method according to one of the preceding claims, characterized in that the additive lubricant is applied to the contact surface (17, 18) of the rolled material (3) uniformly across an entire rolled material width of the rolled material (3).

7. Method according to one of the preceding claims, characterized in that the additive lubricant is applied to the rolled material (3) by way of an additional lubricating device (7) which is independent of a cooling lubricating device (5) for introducing the cooling lubricant into the contact zone (15, 16).

8. Method according to one of the preceding claims, characterized in that the lubrication requirement of the contact zone (15, 16) is determined prior to the start of the rolling process and / or during the rolling process.

9. Method according to one of the preceding claims, characterized in that the lubrication requirement of the contact zone (15, 16) is determined depending on at least one process parameter by using a Stribeck diagram for a coefficient of friction of the friction between the contact surface (17, 18) and the working roller (9, 10) in the contact zone (15, 16).

10. Method according to one of the preceding claims, characterized in that the additive lubricant is applied to two mutually opposite contact surfaces (17, 18) of the rolled material (3).

11. Method according to Claim 10, characterized in that mutually dissimilar additive lubricant quantities (A) of the additive lubricant are applied to the two contact surfaces (17, 18) of the rolled material (3).

Images