Steel strip rolling apparatus and rolling method

Abstract

The invention relates to a cold rolling stand for rolling metal strip, comprising a pair of work rolls defining a roll bite, a first set of injectors capable of injecting a first lubricant onto the pair of work rolls, a second set of injectors capable of injecting a second lubricant upstream of the work rolls, recovery means capable of recovering the first and second lubricants, a reversing system, and a tank connected to the recovery means, to the first set of injectors and to the reversing system and capable of containing the injected lubricant, the reversing system being connected to the second set of injectors. The invention also relates to a cold rolling process.

Description

[Technical Field]

[0001] The present invention relates to rolling equipment and rolling methods that improve rolling conditions for all steel grades during cold rolling. More specifically, it can be used in rolling mills equipped with 4 to 6 rolling stands. On the one hand, the present invention improves the rolling mill capacity to produce harder and thinner steel grades such as advanced high-strength steel (AHSS) and electric steel. On the other hand, among other advantages, it can reduce manufacturing costs by avoiding excessive oil consumption, which is necessary for rolling increasingly thinner and harder products, especially when the intensive use of flexible lubricants becomes essential. [Background technology]

[0002] Conventional lubrication systems with recirculation are typically used in plate cold rolling mills, as shown in Figure 1, in which the strip S is generally passed through 4 to 6 rolling stands (labeled S1 to S5) to reduce its thickness and achieve desired mechanical properties. The rolling stands generally comprise a pair of working rolls 1 defining the roll bites 2, at least a pair of backup rolls 3, and a lubrication system 4. The lubrication system generally consists of a series of nozzles 5 that spray an oil-in-water emulsion onto the rolls 1 and the strip S, and pipes connected to an oil-in-water emulsion tank 6. Generally, the oil-in-water emulsion has an oil content of 0.5% to 3% and an average droplet size of 1 to 10 μm. Furthermore, the oil-in-water emulsion may contain additives such as antioxidants, surfactants, and wear-resistant extreme pressure (AW-EP). The lubrication system also serves to cool the rolls and strips that are heated by thermomechanical deformation. In this case, once the lubricant has performed its function, it is recovered by the recovery means 7, stored in the tank 6, and flowed into the lubrication system 4. The lubricant and water are continuously supplied to the lubrication system 4 in a recirculating manner. The management of this conventional lubrication system with recirculation requires the addition of fresh oil and water and is carried out directly in the tank 6 to compensate for oil and water losses due to several factors such as water evaporation, oil adhering to the strips, removal of oil-adhered particles, and skimming operations. The sum of all such oil losses determines the natural oil consumption of the tandem rolling mill.

[0003] In this conventional lubrication system, where lubrication and cooling are fully integrated, the emulsion retention time is generally 15-35 minutes, and due to the low oil concentration and small particle size, the direct-in-water oil emulsion must operate in a stable state. Furthermore, the cooling requires a large amount of emulsion, which cannot adjust the lubrication performance to the characteristic time scale of the cold rolling process, rendering it inoperable for optimal and practical control of friction levels. The main advantage of this type of lubrication was its economical nature due to low oil consumption. However, this lubrication has been considered largely insufficient to meet new challenges, namely, high rolling speeds, increasingly hard and thin materials, and the optimization of energy processes. This is why advanced lubrication systems such as Flexible-Lubrication and Hybrid-Lubrication have been developed, as explained in [M. Laugier, M. Tornicelli, C. Silvy-Leligois, D. Bouquegneau, D. Launet, JA Alvarez, “Flexible lubrication concept, the future of cold rolling lubrication”, extended paper version, Journal of Engineering Tribology, Part J, 2011].

[0004] The development of new steel grades and products that are harder and thinner significantly impacts cold rolling mills because they require greater rolling forces. Equally equal to all other factors, harder and thinner steel sheets require a higher rolling force. Furthermore, for fundamental reasons already widely explained in the cold rolling literature, the required rolling force also depends on many other parameters related to the rolling conditions, namely, parameters related to the pre- and post-roll tension, thickness reduction, and roll bite contact length. In particular, the required rolling force depends on the friction between the rolled product and the working rolls, which can be characterized by the coefficient of friction μ. During cold rolling operations, equally equal to all other factors, a higher coefficient of friction results in a higher required rolling force. Consequently, too much uncontrolled high friction leads to a loss of rolling force capacity. For strip yield stresses exceeding 750 MPa and strip thicknesses less than 2 mm, the sensitivity of rolling force to the coefficient of friction increases dramatically, and has been demonstrated to be almost exponential, as described in [M. Laugier, M. Tornicelli, J. Cebey, D. Lopez Peris, A. Devolder, R. Guillard, F. Kop, "Flexible lubrication for controlling friction in cold rolling, crucial to be successful for the AHSS Challenge," METEC & 2nd ESTAD 15-19 June 2015, Dusseldorf, Germany]. As a result, typical friction fluctuations occurring with conventional lubrication induce significant capacity losses due to rolling force saturation that occurs in classic sheet tandem rolling mills when the required rolling force reaches the technical limit of approximately 3000 tons. For example, if the coefficient of friction is established at 0.050 instead of 0.040, this friction fluctuation can increase the required rolling force by several hundred tons, and has been shown to be clearly detrimental to tandem rolling capacity. Therefore, it is crucial to precisely control the coefficient of friction at the lowest possible level inside the very narrow window. This precise control of the coefficient of friction can only be achieved using more advanced lubrication systems such as Flexible Lubrication.

[0005] Furthermore, the friction coefficient within the optimal range enables obtaining satisfactory surface quality, preventing seizure, avoiding harmful behaviors such as chatter, and reducing energy consumption. This is the reason why advanced lubrication is important for the rolling process to enable the manufacture of harder and thinner products. In summary, due to the wide variety of steel grades produced in cold rolling mills and for all the reasons mentioned above, the lubrication system needs to be flexible.

[0006] As shown in Figure 2, during cold rolling, when the water-in-oil emulsion 8 is directly sprayed onto the steel strip S or into the converging zone at the roll bite inlet, the oil adheres to the strip S and the working roll 1, forming a lubricant film 10 supplied to the roll bite inlet. According to the mixed lubrication theory, the friction coefficient μ of the roll bite can be defined by the following formula: μ = μ L [1 - λ H + λ H .μ H , where it is assumed that μ L is typically the boundary component of friction between 0.100 and 0.120, and μ H is typically the hydrodynamic component of friction between 0.008 and 0.012. The ratio λ H ≒ h L / h S determines the lubrication regime inside the roll bite, where h L is the inlet film thickness, and h S corresponds to the composite surface roughness considering the working roll roughness and the strip roughness. The roughness of the working roll is the dominant parameter and it can be seen that it changes during the rolling operation due to the so-called roll wear phenomenon. This is explained in the aforementioned paper. Therefore, it is clear that controlling the inlet film thickness is an important parameter for controlling the friction coefficient. The inlet film thickness h LAs shown in Figure 2, it can have three origins: a first film 10 formed by a strip plate-out mechanism, a second film 11 formed within the convergence zone by a dynamic concentration mechanism, and, optionally, a third film 12 formed by passing through backup roll-work roll contact and plating out onto the work roll surface and / or onto the recycled film from the roll bite exit, as described in [R. Guillaument, S. Vincent, J. Duclos, M. Laugier, P. Gardin, Plat-out modelling for cold rolling system lubricated with O / W emulsion. ICTMP, Nice June 2010] and [Wilson, WRD, Sakaguchi, Y., and Schmid, SR, “A Dynamic Concentration Model of Emulsions,” Wear, v.161, 1993, pp.207-212]. Generally, the third film is considered to have no significant contribution to the hydrodynamic component compared to the first and second films.

[0007] To date, all advanced lubrication, including flexible lubrication with recirculation, has used a combination of two lubrication systems, as shown in Figure 3. The first recirculation system 13 achieves minimal lubrication by applying a stable oil-in-water emulsion with low oil concentration and small particle size. The recirculation system uses a large amount of emulsion to achieve the cooling function of the strip and roll. The second system 14 is exclusively for flexible lubrication and therefore uses an unstable emulsion with a much smaller emulsion volume and larger particle size compared to the first recirculation system 13. Flexible lubrication systems use various oil film formation mechanisms, mainly strip plate-out mechanisms, by acting on ballistic parameters such as the characteristics of the injected emulsion, i.e., oil concentration, oil particle size, and / or injection parameters, i.e., emulsion flow rate and the effect of the injected emulsion velocity on the solid surface. In the case of lubrication systems using a static mixer, the parameters of the second system can be changed within seconds to modify the plate-out mechanism, e.g., film thickness and its characteristics. For example, the oil concentration can be varied from 0% to 30%, and the emulsion flow rate can be varied from 5 to 30 L / min. -1 It can be changed up to this point. This makes it possible to control the oil penetration film thickness in the roll bite, and therefore the coefficient of friction.

[0008] Japanese Patent Publication No. 2002-172412 discloses a hybrid lubrication system, as shown in Figure 4. This patent discloses a cold rolling method aimed at preventing chattering caused by insufficient lubrication at high rolling speeds. The equipment comprises a circulating rolling lubricant supply system 15 and a separate rolling lubricant supply system 16. The circulating rolling lubricant supply system 15 comprises an injection means 5, a tank 6, and a recovery means 7 that enables the injection of the rolling lubricant to be recovered and transferred to the tank. The separate rolling lubricant supply system 16 comprises a tank 3 and an injection means 5'. The separate system is not always used, but is preferred when the circulating rolling oil cannot maintain the coefficient of friction within a predetermined appropriate range, for example, due to high strip speeds and / or AHSS.

[0009] Today, advanced lubrication systems, such as flexible lubrication and hybrid lubrication, can efficiently adjust the coefficient of friction regardless of the type of manufacturing involved, thus enabling stable cold rolling within a precisely optimized coefficient of friction window, for example, in the range of 0.015 to 0.030.

[0010] However, such a solution has several drawbacks. Even if the same oil is used in the two lubrication systems, the emulsions used will have significantly different properties. Furthermore, the properties of the emulsion injected by the second system, for example, a flexible system, are inevitably very variable. Moreover, some of the emulsion from the second injection system, especially the amount of oil that does not adhere to the sheets, is recovered into the tank of the first recirculation system. This can lead to limitations in use due to time or problems in managing the recirculation lubrication system, as the properties and stability of the recirculated emulsion stored in tank 6 and injected by the injection means 5 are negatively affected. This is due to the fact that the recirculated emulsion can become destabilized if the volume of injected emulsion in the additional system, compared to the recirculated volume of lubricant, exceeds a threshold. For example, it may aggregate, fuse, or break down and become excessively concentrated. Furthermore, this problem is amplified when such a flexible system is used in several rolling stands, as the flow of injected emulsion becomes even larger compared to the natural consumption of a tandem mill. As a result, this solution cannot be used intensively in all stands without limitations, for example, due to time constraints.

[0011] European Patent No. 1193004 ensures that the control of the oil content in the main recirculation emulsion tank by hybrid lubrication is ensured by the following: - Addition of a higher concentration lubricant from another tank if oil addition cannot compensate for the mill's consumption of natural oil. - Addition of dilution water when the amount of oil added exceeds the mill's natural oil consumption. -Add the final emulsifying agent and oil properties. [Preliminary Technology Documents] [License]

[0012] [License 1] Special Announcement No. 2002-172412 [License 2] European Patent No. 1193004 [Non-licensed literature]

[0013] [Non-licensed Document 1] M.Laugier, M.Tornicelli, C.Silvy-Leligois, D.Bouquegneau, D.Launet, JA Alvarez, "Flexible lubrication concept, the future of cold rolling lubrication", extended paper version, Journal of Engineering Tribology, Part J, 2011 [Non-licensed Document 2] M.Laugier,M.Tornicelli,J.Cebey,D.Lopez Peris,A.Devolder,R.Guillard,F.Kop《Flexible lubrication for controlling friction in cold rolling,crucial to be successful for the AHSS Challenge》,METEC&2nd ESTAD 15-19 June 2015 Dusseldorf,Germany [Non-licensed Document 3] R.Guillaument,S.Vincent,J.Duclos,M.Laugier,P.Gardin,Plat-out modeling for cold rolling system lubricated with O / W emulsion.ICTMP,Nice June 2010

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0014] However, it is not suitable for circuit management by flexible lubrication in the case of concentrated use. Furthermore, the control of the oil content in the recirculation circuit by adding dilution water requires an emulsion volume sufficient to compensate for the concentrated use of FL addition, making the circuit management of the circuit difficult and potentially more expensive. Furthermore, chemical treatment may be required in the prior art, and in particular, a formulation needs to be known to adapt the treatment for concentrated use.

Means for Solving the Problems

[0015] The object of this invention is to solve the above problems. This object is achieved by providing the device according to claim 1. The device can also have any of the features of claims 2 to 5. This object is also achieved by providing the cold rolling mill according to claim 6. This object is achieved by the methods according to claims 7 to 11.

[0016] Other features and advantages of the present invention will become apparent from the following detailed description of the present invention.

[0017] To explain the present invention, various embodiments of non-limiting examples will be described with particular reference to the following figures.

Brief Description of the Drawings

[0018] [Figure 1] Shows a first embodiment of a cold rolling mill known in the prior art. [Figure 2]This shows the oil film between the strip and the work roll. [Figure 3] A second embodiment of a cold rolling mill known in the prior art is shown. [Figure 4] A third embodiment of the cold rolling mill relating to the prior art cited is shown. [Figure 5] This shows a model of the same invention. [Figure 6] The composition and structure of the emulsion entering and leaving the inversion system are shown. [Figure 7] An embodiment of the present invention is shown, comprising a system for supplying the aqueous phase to a third set of injection devices. [Figure 8] This shows one embodiment of the mill of the present invention. [Figure 9] A second embodiment of the mill of the present invention is shown. [Figure 10] One embodiment of the steps of the cold rolling method according to the present invention is shown. [Modes for carrying out the invention]

[0019] As shown in Figure 5, the present invention relates to a cold rolling stand for rolling a metal strip S, wherein the cold rolling stand is - A pair of work rolls 1 that secure the roll bite 2, - A first set 17 of an injection device capable of spraying a first lubricant onto the pair of work rolls 1, - A second set 18 of an injection device capable of spraying a second lubricant onto the strip 0.5 to 4 meters upstream of the work roll 1, - A recovery means 7 capable of recovering the first and second lubricants, -Inversion system 19, -The recovery means 7, the first set 17 of the injection device, and the tank 20 connected to the inversion system 19, the tank 20 capable of containing the injected lubricant, Equipped with, - The inversion system is connected to the second set 18 of the injection device.

[0020] In the following specification, the terms “downstream” and “upstream” should be understood in relation to the path of the metal strip. Similarly, the terms “inlet side” and “outlet side” should be understood in relation to the path of the moving metal strip. Furthermore, the term “lubricant” refers to any lubricating emulsion, such as oil-in-water emulsion, water-in-oil emulsion, or water-in-oil emulsion.

[0021] As shown in Figure 5, when the metal strip is moving from left to right, the "inlet side" of the cold rolling stand is to the left of the roll bite 2, and the "outlet side" of the cold rolling stand is to the right of the roll bite 2.

[0022] As shown in Figure 5, the first set of sprayers 17 is preferably capable of spraying the first lubricant onto a pair of work rolls 1 and onto the rolled strip. Preferably, the first set of sprayers comprises a series of nozzles located above and below the metal strip S. Preferably, the first set of sprayers 17 consists of sprayers located upstream and downstream of the roll bite 2, i.e., on the inlet and outlet sides, respectively. Alternatively, the first set of sprayers consists of sprayers located only upstream of the roll bite 2, for example, only on the inlet side.

[0023] A second set of sprayers 18 is preferably located upstream of the roll bite and can spray a second lubricant onto the rolled strip. The second set of sprayers is located on the inlet side of the cold rolling stand.

[0024] A second set of the spraying device can spray a second lubricant onto the strip 0.5 to 4 meters upstream of the work roll, that is, 0.5 to 4 meters upstream of the pair of roll bites 2 of the work roll 1. More preferably, the second set of the spraying device can spray a second lubricant onto the strip 1 to 3 meters upstream of the work roll.

[0025] Preferably, the second set of spraying devices is unable to spray the second lubricant onto the work roll.

[0026] Preferably, the second set of the spraying device consists of a series of nozzles positioned above and below the metal strip. For example, the second set of the spraying device can be positioned 1 to 3 meters upstream of the roll bite.

[0027] Preferably, the second set of the injection device comprises a mixer capable of mixing two fluids, for example, an oil-in-water emulsion and an aqueous phase that forms an oil-in-water emulsion. More preferably, the second set of the injection device comprises a static mixer.

[0028] Optionally, the first set of injection devices may include a mixer capable of mixing two fluids, such as a static mixer.

[0029] The recovery means 7 is primarily intended to recover the first and second lubricants sprayed by the first and second sets of the spraying device. The recovery means can also recover undesirable particles such as iron powder and oil for rolling stand bearings (e.g., mogoyle).

[0030] The inversion system 19 aims to produce, from an incoming oil-in-water emulsion, a reverse water-in-oil emulsion containing a higher proportion of oil than the incoming emulsion, and a second oil-in-water emulsion containing a lower proportion of oil than the incoming emulsion.

[0031] The inversion system 19 may consist of at least one of the following systems: a membrane, an evaporator, and / or a decanter.

[0032] Preferably, the inversion system is configured to generate an inverse emulsion by overconcentration and / or by centrifugal force. More preferably, the inversion system includes a centrifuge.

[0033] For example, as shown in Figure 6, the dark areas represent water, and the white areas represent oil. That is, - Oil-in-water emulsion flow with an oil concentration of -0.5 to 5%, W ENTRY It enters the inversion system. -A water-in-oil emulsion flow with an oil concentration of -70-99%, O EXIT The system exits, - Oil-in-water emulsion flow having an oil concentration lower than the inlet oil concentration, W EXIT It is released from the aforementioned system.

[0034] Tank 20 is connected to the recovery means 7, the first set 17 of the injection device, and the inversion system 19. In other words, fluid can be flowed from the tank to the first set of the injection device and the inversion system. The fluid can be flowed, for example, by using pipes, pumps and valves. Preferably, tank 20 is provided with means 28 for homogenizing its contents. Preferably, an aqueous phase such as water can be added to the tank. More preferably, a lubricant can be added to the tank.

[0035] The rolling stand may also be equipped with means such as a magnetic filter for collecting iron powder to remove undesirable particles from the lubricant. Preferably, these means are located downstream of the recovery means 7 and / or tank 20.

[0036] Preferably, the cold rolling stand includes a system 22 capable of supplying an oil-in-water emulsion to a first set 17 and / or a second set 18 of injection devices. Preferably, the cold rolling stand also includes a system capable of supplying an aqueous phase to a tank.

[0037] Preferably, as shown in Figure 7, the inversion system can flow the water-in-oil emulsion into the second set 18 of the injection device. Such a system enables the injection of the water-in-oil emulsion in water.

[0038] Preferably, the inversion system 19 includes a centrifugal separator. The centrifugal separator enables efficient acquisition of water-in-oil emulsions and oil-in-water emulsions. More preferably, the inversion system can deliver the water-in-oil emulsions and oil-in-water emulsions to a second set 18 of the injection device.

[0039] Preferably, the cold rolling stand includes a decantation system downstream of the tank and upstream of the inversion system. Such a decantation system facilitates the separation of the two phases, the water-in-oil emulsion and the aqueous phase, in the inversion system. More preferably, the highly concentrated phase in the oil from the decantation system is sent to an over-concentration system.

[0040] As shown in Figure 8, the present invention also relates to a cold rolling mill 24 comprising one to seven rolling stands (S1 to S5), at least one of which is as described above. The second injection device of the rolling stand is located downstream of the previous rolling stand.

[0041] Generally, the deceleration rate and speed of the strip passing through each rolling mill differ, resulting in various lubrication needs. Therefore, the concentrations of the first and second lubricants injected may vary from one rolling stand to the other. Generally, lubrication needs to increase at each stand; for example, stand S2 requires more lubricant than stand S1 (e.g., a thicker lubricant film).

[0042] If the oil concentrations and droplet sizes of different first lubricants recovered and stored in tanks differ too much, the lubricating effect can obviously be reduced. For this purpose, a cold rolling mill preferably has two or more tanks, or more preferably one tank for each rolling stand. Having multiple tanks makes it possible to reduce the compositional differences between the recovered lubricants.

[0043] Figure 9 shows a cold rolling mill with five cold rolling stands. The first four cold rolling stands S1-S4 are equipped with a pair of work rolls and first and second sets of sprayers. The fifth rolling stand has only the first set of sprayers. The cold rolling mill also includes three tanks (208, 209, 210). The first tank 208 is connected to the recovery means of the first and second stands, the second tank 209 is connected to the recovery means of the third and fourth stands, and the third tank 210 is connected to the recovery means of the fifth stand. The cold rolling mill also includes two inversion systems. The first inversion system 190 is connected to tank 208 and the second set of sprayers for stands 1 and 2. The second inversion system 191 is connected to tank 209 and the second set of sprayers for stands 3 and 4. In addition, the first set of sprayers for stands S1 and S2 is connected to the first tank 208. The first set of sprayers on stands S3 and S4 is connected to the second tank 209. The first set of sprayers on stand S5 is connected to the third tank 210.

[0044] Preferably, the decantation tank is connected to at least one tank.

[0045] As schematically shown in Figure 10, the present invention also relates to a method for enabling the rolling of a metal strip in the aforementioned cold rolling stand, the method being A1) A step of spraying a first lubricant having a base oil content of 0.2 to 5% by weight onto the pair of work rolls 1 by the first set of the spraying device, A2) A second lubricant having a base oil content of 5-30% by weight at a flow rate of F2 is sprayed onto the strip 0.5-4 meters upstream of the work roll 1 by the second set of the spraying device, B) The steps of recovering the first and second sprayed lubricants with the recovery means 7 and flowing the first and second sprayed lubricants into the tank 20, C1) A step of supplying lubricant from the tank 20 to the first set of injection devices, C2) A step of supplying lubricant from a tank to the reversal system 19, C3) A step of generating a water-in-oil emulsion using the inversion system 19, C4) A step of supplying the water-in-oil emulsion prepared in step B2) to the second set of the sprayer, It is equipped with.

[0046] Steps C1 and A1 allow a portion of the lubricant contained in the tank to flow to a first set of injectors, which inject the first lubricant at a flow rate F1 onto a pair of work rolls. Preferably, in step A1), the first lubricant is injected onto the pair of work rolls and the strip is rolled. The properties of the first lubricant, such as oil concentration and oil droplet size, may change during the rolling process.

[0047] Furthermore, after maintenance, or if the tank is empty, the first process is to fill the tank 20 with the first lubricant.

[0048] Steps C2 and C3 allow for the generation of a water-in-oil emulsion with a portion of the recovered lubricant contained in a tank, as shown in Figure 6. The water-in-oil emulsion can be manufactured by any means.

[0049] The first and second lubricants are different, meaning that they differ in at least one of the following criteria: properties, composition, droplet size, and temperature. Preferably, the second lubricant has a higher oil content than the first lubricant.

[0050] If the decantation tank is located downstream of the tank and upstream of the first set of injectors and the inversion system, in step C1, the first set of injectors is supplied with lubricant from the decantation tank and / or the tank, and in step C2, the inversion system is supplied with lubricant from the decantation tank and / or the tank. Furthermore, there is a further step in which the tank supplies the decantation tank.

[0051] In step B, the first and second lubricants that have been sprayed are recovered by a recovery means and stored in a tank.

[0052] Preferably, in step A1), the flow rate F1 is variable. Preferably, in step A2), the flow rate F2 is variable. This allows the amount of lubricant injected during the rolling process to be changed depending on the rolling conditions and the type of steel being rolled.

[0053] Preferably, in step A1), the first lubricant has an oil droplet size of 1 to 15 μm. Such a base oil concentration and / or such oil droplet size allows for maintaining an optimal range of friction coefficients for most steel grades. Thus, the flow rate F2 of the second lubricant can be reduced during the rolling of strips that do not require a very low friction coefficient, such as AHSS.

[0054] Preferably, in step C3), the water-in-oil emulsion has at least 70% by weight of base oil.

[0055] Preferably, in step C4), an oil-in-water emulsion or water is also supplied to the second set of the spraying device, and in step A2), an oil-in-water emulsion is generated and sprayed by the second set of the spraying device.

[0056] More preferably, in step C3), an oil-in-water emulsion and a water-in-oil emulsion are produced by the inversion system, and in step C4), the water-in-oil emulsion and aqueous phase produced in step C3 are supplied to a second set of injection devices. This reduces water consumption.

[0057] Preferably, in step A2), the second lubricant is sprayed onto the strip 1 to 3 meters upstream of the work roll 1 by the second set of the spraying device.

[0058] Preferably, in step A2), the second lubricant has an oil droplet size of 15 to 40 μm. Preferably, in step A2), the second lubricant has an oil droplet size of 15 to 100 μm. Such an oil droplet size increases lubrication and thus allows the coefficient of friction to be maintained at a lower value. Thus, the rolling of advanced high-strength steel is facilitated.

[0059] Preferably, the recovered lubricant is not heat-treated. Preferably, the recovered lubricant is not chemically treated. If the lubricant undergoes at least one of these treatments, it deteriorates and its lubrication decreases. Furthermore, such treatments, the energy required, and the by-products generated have adverse effects on the environment.

[0060] The invention described in the claims enables the conversion of a useful amount of a low-concentration, stable oil-in-oil (o / w) emulsion from a first set of circulating injectors to a multiple emulsion water-in-oil (w / o / w) emulsion used in a second set of injectors, for example, in a flexible lubrication addition system.

[0061] For example, a reverse emulsion is produced by inverting the emulsion of a first lubrication system that has been recovered by a recovery means and stored in a tank. The reverse-phase emulsion is then used as an internal phase in combination with an aqueous phase as an external phase to form a water-in-oil (w / o / w) emulsion, which is then injected by a second set of injection devices. The water content in the reverse emulsion can be adjusted from a few percent to 30% depending on the required properties of the final w / o / w emulsion (e.g., stability, plate-out properties).

[0062] The present invention offers the advantage of using only one oil to supply both lubrication systems (e.g., a set of injectors) in different emulsion states, accommodating different modes of roll bite supply (dynamic concentration or plate-out). This allows for more intensive use of the flexible lubrication system while reducing the need to add new fresh oil internally. Furthermore, this is achieved without any chemical treatment or excessive oil consumption, compared to known lubrication systems with recirculation. Only the addition of fresh oil is performed to compensate for the mill's natural consumption. The main lubricant loss is attributed to the loss of lubricant on the strip, evaporation, and removal of undesirable particles such as iron filings that trap the lubricant, which can be considered process-specific.

[0063] Furthermore, in contrast to the existing state of the art, such as Japanese Patent Publication No. 2002-172412, in which a new lubricant is exclusively supplied to a separate rolling system, the present invention supplies at least partially recirculated lubricant to a second set of injection devices. As a result, compared to the existing prior art, the lubricant consumption is reduced and the stability of the recirculated lubricant in the tank is not adversely affected.

Claims

1. A cold rolling stand for rolling a metal strip S, A pair of work rolls 1 that secure the roll bite 2, A first set 17 of an injection device capable of spraying a first lubricant onto the pair of work rolls 1, A second set 18 of an injection device capable of spraying a second lubricant onto the strip 0.5 to 4 meters upstream of the work roll 1, A recovery means 7 capable of recovering the first and second lubricants, A reversing system 19 is configured to produce a water-in-oil emulsion and a second oil-in-oil emulsion containing a lower proportion of oil than the incoming emulsion from an incoming oil-in-water emulsion, and the water-in-oil emulsion can be flowed into the second set 18 of the injection device. The recovery means 7, the first set 17 of the injection device, and the inversion system 19 are connected to a tank 20 capable of containing the injected lubricant, Equipped with, The inversion system 19 is connected to the second set 18 of the injection device. Cold rolling stand.

2. The cold rolling stand according to claim 1, further comprising a system 22 capable of supplying an aqueous phase to a first set 17 and / or a second set 18 of the injection devices.

3. The cold rolling stand according to claim 1 or 2, wherein the inversion system 19 comprises a centrifugal separator.

4. The cold rolling stand according to claim 1 or 2, further comprising a decantation system 29 downstream of the tank 20 and upstream of the reversal system 19.

5. A cold rolling mill 24 comprising one to seven rolling stands (S1 to S5), wherein at least one of the rolling stands is as described in claim 1 or 2.

6. A method for rolling a metal strip in a cold rolling stand according to claim 1 or 2, A1) A step of spraying a first lubricant having a base oil content of 0.2 to 5% by weight onto the pair of work rolls 1 by the first set of the spraying device, A2) A second lubricant having a base oil content of 5 to 30% by weight at a flow rate F2 is sprayed onto the strip 0.5 to 4 meters upstream of the work roll 1 by the second set of the spraying device; B) The steps of recovering the first and second sprayed lubricants with the recovery means 7 and flowing the first and second sprayed lubricants into the tank 20, C1) A step of supplying lubricant from the tank 20 to the first set of the injection device, C2) A step of supplying lubricant from the tank to the reversing system 19, C3) A step of generating a water-in-oil emulsion using the inversion system 19, C4) A step of supplying the water-in-oil emulsion prepared in step C3) to the second set of the spraying device, A method for providing this.

7. The method according to claim 6, wherein in step C3), the water-in-oil emulsion has at least 70% by weight of base oil.

8. The method according to claim 6, wherein in step C4) the aqueous phase is supplied to the second set of the injection device, and in step A2) a water-in-oil emulsion is generated and injected by the second set of the injection device.

9. The method according to claim 6, wherein in step C3) the oil-in-water emulsion and the water-in-oil emulsion are generated by the inversion system 19, and in step C4) the oil-in-water emulsion and the water-in-oil emulsion generated in step C3) are supplied to a second set of sprayers.

10. The method according to claim 6, wherein the recovered lubricant is not heat-treated.

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