Method for rolling a rolled material, and method for manufacturing a metal strip.

Abstract

The present invention provides a method for rolling a rolled material and a method for manufacturing a metal strip, which can stably roll the material while avoiding rolling troubles and quality problems caused by changes in friction conditions during rolling. [Solution] A method for rolling a rolled material, wherein the rolled material is rolled through a lubricating oil film formed between a pair of rolling rolls, the lubricant containing a load-bearing additive with a molecular chain length greater than or equal to the oil film thickness of the lubricant alone between the rolled material and the rolling rolls (step S7), and the concentration of the load-bearing additive in the lubricant is 1.0% by mass or more and 50.0% by mass or less.

Description

Technical Field

[0001] The present invention relates to a method for rolling a material to be rolled and a method for manufacturing a metal strip.

Background Art

[0002] In cold rolling of a material to be rolled, the material to be rolled is sandwiched between a pair of rolls and rolled continuously. At this time, it is common to roll the material to be rolled while supplying a lubricant between the material to be rolled and the roll in contact with the material to be rolled. By doing so, the frictional state between the material to be rolled and the roll is controlled to ensure and improve the surface quality of the rolled material after rolling. Also, the productivity of the rolled material is ensured and improved. Examples of the cold rolling mill (hereinafter sometimes referred to as a rolling mill) that performs the above-described cold rolling include a reversing rolling mill and a tandem rolling mill (sometimes referred to as a continuous rolling mill). The reversing rolling mill has a pair of rolls, and between the rolls, the material to be rolled is reciprocated and rolled to a predetermined thickness. The continuous rolling mill has a plurality of roll pairs, and the material to be rolled is conveyed in one direction with respect to those roll pairs and rolled to a predetermined thickness.

[0003] The material to be rolled is primarily transported to the rolling mill in a coiled state. The leading end of the coiled material is then discharged towards the rolling mill and supplied to the mill for rolling. When the material is rolled in the rolling mill, the rolling speed inevitably changes in the direction of travel of the material, at the leading end, the trailing end, and other parts of the material. In a reverse-type rolling mill, for example, the leading and trailing ends of the material are the starting and ending points of rolling in the reverse-type rolling mill, and changes in rolling speed are unavoidable. This is because acceleration and deceleration occur due to the acceleration and deceleration of the main motor, as well as the synchronization of the rotational speed of the winding reel, the adjustment of tension and rolling load, and speed adjustments for quality control such as surface defects. Furthermore, in continuous rolling mills, for example, when welding the tail end of one coil currently being rolled to the leading end of the other coil to be rolled, the rolling speed is reduced to allow sufficient welding time. In addition to these factors, the rolling speed may change depending on the surface defects and condition of the material being rolled, regardless of the type of rolling mill. Such changes in rolling speed can alter the friction between the material being rolled and the rolls, potentially leading to chattering or seizing.

[0004] To address these challenges, for example, Patent Document 1 discloses a method for adjusting rolling oil when rolling a highly deformation-resistant material into a thin sheet using high-viscosity rolling oil, which adjusts the amount of rolling oil supplied between the highly deformation-resistant material and the roll in accordance with changes in the rolling speed. When using high-viscosity rolling oil, the friction coefficient of the rolling oil is maximum in the intermediate rolling speed range of the rolling mill. Therefore, the amount of rolling oil supplied is increased in the intermediate rolling speed range to suppress the increase in the friction coefficient and suppress the occurrence of chattering and seizure. In addition, the amount of rolling oil supplied is adjusted to suppress the occurrence of slip due to overlubrication. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-251209 [Overview of the project] [Problems that the invention aims to solve]

[0006] The method disclosed in Patent Document 1 adjusts the amount of rolling oil in accordance with changes in rolling speed, thereby avoiding serious defects such as chattering and seizure. However, there are differences in the friction state when comparing the lowest rolling speed with the highest rolling speed. Therefore, rolling troubles caused by differences in friction state and resulting variations in the surface quality of the rolled material may be unavoidable.

[0007] Furthermore, we will consider the case where the method disclosed in Patent Document 1 is applied to a continuous rolling mill. In a continuous rolling mill, multiple materials having different components may be rolled in succession. If the components of these materials differ from each other, the hardness of each material will also differ. In addition, the required surface quality of the rolled material after rolling will differ for each material. Therefore, it is necessary to manage the polishing state of the rolls according to the hardness and required surface quality. Considering the polishing state of the rolls according to the hardness and required surface quality of each material, friction conditions that cannot be covered by the method disclosed in Patent Document 1 may occur. In addition, control to avoid the range of rolling speeds and rolling oil amounts that cause slip and chattering, and the range of rolling speeds and rolling oil amounts that cause seizing, may become complex and difficult.

[0008] Furthermore, it is clear that even within the intermediate rolling speed range, the friction state fluctuates depending on the rolling speed. Therefore, it is difficult to avoid fluctuations in surface quality due to fluctuations in the friction state, as well as problems during transient conditions. In addition, rolling oil also plays a role as a coolant to cool the rolls. Therefore, simply increasing or decreasing the supply amount of rolling oil according to the rolling speed may not completely prevent problems caused by temperature rise within the roll bite or the occurrence of surface defects.

[0009] The present invention was made to solve the above-mentioned problems, and aims to provide a method for rolling a rolled material and a method for manufacturing a metal strip that can stably roll the material while avoiding rolling troubles caused by changes in friction conditions during rolling and quality problems resulting from rolling troubles. [Means for solving the problem]

[0010] The means to solve the above problems are as follows: [1] A method for rolling a rolled material, wherein the rolled material is rolled through a lubricating oil film formed between a pair of rolling rolls, the lubricant contains a load-bearing additive with a molecular chain length equal to or greater than the oil film thickness of the lubricant alone between the rolled material and the rolling rolls, and the concentration of the load-bearing additive in the lubricant is 1.0% by mass or more and 50.0% by mass or less. [2] The rolling method of the rolled material according to [1], wherein the lubricant is a water-soluble lubricant and the load-bearing additive is an oily agent. A method for manufacturing a metal strip, comprising the step of rolling the metal strip using the rolling method for a rolled material described in [3] [1] or [2]. [Effects of the Invention]

[0011] According to the present invention, rolling troubles caused by changes in friction conditions during rolling, and quality problems resulting from rolling troubles, can be avoided, and the rolled material can be rolled stably. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows an example of a continuous tandem rolling mill to which the rolling method for rolled materials according to the present invention can be applied. [Figure 2] This is a diagram illustrating the configuration of the control device. [Figure 3] This is a flowchart illustrating the addition of load-bearing additives to lubricants. [Modes for carrying out the invention]

[0013] The embodiments of the present invention (hereinafter referred to as "this embodiment") will be described below. The rolling method for a rolled material according to this embodiment is characterized by maintaining a constant lubrication state at the roll bite by adding a load-bearing additive to the lubricant with a molecular chain length longer than the oil film thickness of the lubricant alone formed at the roll bite. While the oil film thickness of the lubricant is variable with temperature and pressure, molecular chains can maintain a constant thickness while having a certain degree of elasticity, and are therefore considered to form a protective film in place of the oil film. For this reason, in this embodiment, a load-bearing additive with a molecular chain length longer than or equal to the oil film thickness of the lubricant during rolling is used. There is no particular upper limit to the molecular chain length, but it is preferably 300 nm or less, and more preferably 200 nm or less, from the viewpoint of actual polymers that have the efficacy of an oily agent and molecular chain retention. First, a rolling mill to which the rolling method for a rolled material according to this embodiment can be applied will be described. Next, the rolling method for a rolled material according to this embodiment will be described.

[0014] The rolling method for the rolled material according to this embodiment can be applied to a cold rolling mill that continuously rolls or repeatedly rolls the rolled material. Examples of cold rolling mills include single-stand rolling mills, reverse rolling mills such as cluster or Zenzimir type mills, and continuous tandem rolling mills. The rolling method for the rolled material according to this embodiment can be applied to any of these rolling mills. In addition, the rolling roll surface and the material of the rolled material (hardness, strength, surface roughness) and rolling conditions (rolling speed) are not limited in the rolling method for the rolled material according to this embodiment.

[0015] Examples of materials to be rolled include metal strips. While metal strips are not limited to this, examples of metal strips that are hard and require strict surface quality after rolling include metal strips. This is because when rolling such metal strips (sometimes called hard materials), the load becomes extremely high, causing the lubricating film to break down, and a defect called "seizing" is likely to occur, where the newly formed surface of the rolled material adheres to the roll surface. Specifically, examples of metal strips include stainless steel strips, electrical steel strips, can steel strips, and titanium strips. Metal sheets may be used instead of metal strips.

[0016] (Rolling mill) Figure 1 shows a continuous tandem rolling mill. The rolling mill 1 has multiple rolling stands 3-7 for rolling the steel strip 2, a payoff reel 8, a welding machine 9, a looper 10, a shear 11, a carousel reel 12, and a control device 13. By passing the steel strip 2 through the multiple rolling stands 3-7 in one direction and rolling it, the thickness of the steel strip 2 is adjusted to the target thickness. In the example shown in Figure 1, the rolling mill 1 has five rolling stands 3-7, which are labeled as the first rolling stand 3, second rolling stand 4, third rolling stand 5, fourth rolling stand 6, and fifth rolling stand 7 from upstream in the direction of transport of the steel strip 2. Note that the number of rolling stands is not limited.

[0017] (Rolling stand) Each rolling stand 3-7 has a pair of rolling rolls (sometimes called work rolls) 14 and backup rolls 15 that support the rolling rolls 14. The pair of rolling rolls 14 are arranged side by side in the vertical direction of the rolling mill 1 (vertical direction in Figure 1), and the steel strip 2 is clamped between the pair of rolling rolls 14. The backup rolls 15 are arranged on both sides of the pair of rolling rolls 14 in the vertical direction of the rolling mill 1.

[0018] In the conveying direction of the steel strip 2 (the right direction in Fig. 1, which may be referred to as the rolling direction), coolant nozzles (not shown) are provided before and after the rolling rolls 14 of each of the rolling stands 3 to 7. A lubricant for lubricating and cooling the steel strip 2 and the rolling rolls 14 is sprayed from the coolant nozzles toward at least one of the steel strip 2 and the rolling rolls 14. By doing so, an oil film of the lubricant is formed on the steel strip 2 on the inlet side of each of the rolling stands 3 to 7. The thickness of the oil film of the lubricant formed on the steel strip 2 is calculated by the control device 13 based on the discharge amount of the lubricant from the coolant nozzles of each of the rolling stands 3 to 7, the rolling conditions, the past rolling results, the temperature of the lubricant and the steel strip 2, etc. The thickness of the oil film of the lubricant calculated by the control device 13 is stored in the storage unit 28 described later. The discharge amount of the lubricant from the coolant nozzles can be calculated based on the supply amount of the lubricant to the coolant nozzles measured by a flow meter provided in the middle of the pipe supplying the lubricant to the coolant nozzles, the nozzle diameter of the coolant nozzles, etc. Instead of calculating the oil film of the lubricant, a film thickness meter may be provided on the inlet side of at least one of the rolling stands 3 to 7, and the thickness of the oil film of the lubricant may be actually measured by the film thickness meter. For example, as shown in Fig. 1, a film thickness meter 16 may be provided on the inlet side of the first rolling stand 3. The thickness of the oil film of the lubricant measured by the film thickness meter 16 is stored in the storage unit 28.

[0019] (Payoff reel) The payoff reel 8 is a device that pays out the coiled steel strip 2 toward the rolling mill 1. In the example shown in Fig. 1, two payoff reels 8 are provided. For example, the steel strip 2 is paid out from one payoff reel 8, and then the steel strip 2 is paid out from the other payoff reel 8. That is, the steel strip 2 is paid out alternately.

[0020] (Welding machine) The welding machine 9 is a device that joins the trailing end of the preceding steel strip 2 and the leading end of the succeeding steel strip 2 by welding. The welding machine 9 is provided on the downstream side of the payoff reel 8 in the conveying direction of the steel strip 2. By joining the preceding steel strip 2 and the succeeding steel strip 2, the steel strip 2 is continuously rolled in the rolling mill 1.

[0021] (Looper) The looper 10 is a device that stores the steel strip 2 so that the cold rolling of the steel strip 2 by the rolling mill 1 can be continued during the period until the trailing end of the preceding steel strip 2 and the leading end of the succeeding steel strip 2 are joined by the welding machine 9. The looper 10 is provided on the downstream side of the welding machine 9 in the conveying direction of the steel strip 2.

[0022] (Shear) The shear 11 is a device that cuts the product steel strip rolled by the rolling mill 1. In the example shown in FIG. 1, it is provided between the outlet side of the rolling mill 1 and the carousel reel 12 in the conveying direction of the steel strip 2. When the carousel reel 12 winds up the product steel strip of a predetermined length, the product steel strip is cut.

[0023] (Carousel Reel) The carousel reel 12 is a device that winds up the product steel strip rolled by the rolling mill 1. In the example shown in FIG. 1, it is provided on the downstream side of the shear 11 in the conveying direction of the steel strip 2.

[0024] (Lubricant and Load - Bearing Additive Supply Device) The configuration for supplying lubricant to the rolling rolls 14 and the steel strip 2 will be described. The rolling mill 1 further has a lubricant tank 17, a supply pipe 18, an oil pump 19, a return pipe 20, a filtration facility 21, a load - bearing additive tank 22, an additive supply pipe 23, and an adding device 24.

[0025] The lubricant tank 17 is a facility for storing lubricant. The lubricant tank 17 and each of the rolling stands 3 to 7 are connected to each other via supply pipes 18. An oil pump 19 is provided at each of the supply pipes 18. The oil pumps 19 supply the lubricant stored in the lubricant tank 17 to each of the rolling stands 3 to 7. At each of the rolling stands 3 to 7, the supply pipes 18 are connected to the coolant nozzles described above, and lubricant is supplied from the coolant nozzles to the rolling rolls 14 and the steel strips 2. A cooling device may be provided at the lubricant tank 17 to cool the lubricant as its temperature rises due to rolling in the rolling mill 1.

[0026] The bottoms of each rolling stand 3-7 and the lubricant tank 17 are connected to each other via a return pipe 20. The lubricant that has lubricated and cooled the rolling rolls 14 and steel strips 2 flows from the bottoms of each rolling stand 3-7 into the return pipe 20 and returns to the lubricant tank 17 via the return pipe 20. In this way, the lubricant is circulated between each rolling stand 3-7 and the lubricant tank 17. In addition, in the example shown in Figure 1, a filtration device 21 for cleaning the lubricant is provided in the return pipe 20. This is to remove foreign matter that has mixed into the lubricant. Examples of foreign matter include scum and oxides that have peeled off from the steel strips 2.

[0027] The load-bearing additive tank 22 is equipment for storing load-bearing additives and is connected to the lubricant tank 17 via, for example, an additive supply pipe 23. The additive supply pipe 23 is equipped with an additive device 24 for adding a predetermined amount of load-bearing additive to the lubricant tank 17. The additive device 24 may include a flow control valve (not shown) or a pump (not shown). The control device 13 may control the operation of the flow control valve or pump to add a predetermined amount of load-bearing additive to the lubricant tank 17. It is preferable to have multiple load-bearing additive tanks 22 that store load-bearing additives with different molecular chain lengths. This is because it is possible to select load-bearing additives having molecular chain lengths greater than or equal to the oil film thickness of the lubricant alone at the roll bite. The roll bite refers to the point where the steel strip 2 and the rolling roll 14 come into contact with each other via the lubricant.

[0028] The lubricant tank 17 has a first supply port 25, a second supply port 26, and an agitator 27. Lubricant is supplied into the lubricant tank 17 through the first supply port 25, and a diluent for diluting the lubricant is supplied into the lubricant tank 17 through the second supply port 26. The agitator 27 also agitates the lubricant and diluent inside the lubricant tank 17.

[0029] (Lubricants and diluents) A water-soluble lubricant can be used in the rolling mill 1 to which the rolling method for the rolled material according to this embodiment can be applied. This water-soluble lubricant may be, for example, type A1 (emulsion type), type A2 (soluble type), and type A3 (solution type) as specified in JIS K 2241:2017. The water-soluble lubricant is used after being diluted to a predetermined concentration with a diluent according to the rolling conditions of the steel strip 2 in the rolling mill 1. Furthermore, in the rolling mill 1 shown in Figure 1, if the steel strip 2 is rolled continuously, the water contained in the water-soluble lubricant gradually evaporates due to the heat generated during rolling, causing a change in concentration. Therefore, even in such cases, a diluent is mixed with the water-soluble lubricant to adjust its concentration. Examples of diluents include tap water and industrial water.

[0030] (Load-bearing additive) An example of a load-bearing additive used in a rolling mill 1 to which the rolling method for the rolled material according to this embodiment can be applied is an additive called an oily agent. The load-bearing additive is added to the lubricant and functions to maintain a constant friction state at the roll bite by physically or chemically forming an adsorption film of the load-bearing additive at the roll bite.

[0031] Here, "physical" means that an adsorbent film of the load-bearing additive is formed on the roll bite by van der Waals forces. "Chemical" means that an adsorbent film of the load-bearing additive is formed on the roll bite by a polar reaction.

[0032] Examples of load-bearing additives include oily agents composed of polar groups such as hydroxyl groups, carboxyl groups, and amino groups, and polymers such as hydrocarbon chains and alcohols. Furthermore, it is preferable that the load-bearing additive has molecular chains longer than the oil film thickness of the lubricant on the roll bite in a mixed lubrication state. The thickness of the adsorbed film varies depending on the rolling conditions, but this thickness generally coincides with the molecular chain length of the load-bearing additive. Therefore, in this embodiment, the thickness of the adsorbed film and the molecular chain length of the load-bearing additive are considered to be the same value. The mass percentage concentration (hereinafter simply referred to as concentration or "%") of the load-bearing additive in the mixed solution after adding it to the lubricant is preferably 1.0 to 50.0% or less. This concentration is the concentration of the load-bearing additive after adding it to the lubricant diluted in water. If the load-bearing additive concentration is less than 1.0%, the effect of adding the load-bearing additive cannot be obtained. In other words, a sufficient adsorbed film of the load-bearing additive cannot be formed on the roll bite. In contrast, if the load-bearing additive exceeds 50.0%, it alters the performance of the lubricant. Specifically, it may fail to form a sufficient lubricating film on the roll bite, or it may cause the lubricant to separate.

[0033] The molecular chain length of a load-bearing additive can be determined by model calculation or experimentally. While a free-linked chain model is one possible model for calculating molecular chain length, it is not limited to this. For example, the total length of the load-bearing additive, calculated by multiplying the bond length by the number of bonds, may be used as the molecular chain length. Alternatively, the molecular chain length of the load-bearing additive may be measured using gel permeation chromatography or dynamic light scattering.

[0034] (Control device) The control device 13 controls the various devices of the rolling mill 1 as described above. Figure 2 is a diagram illustrating the configuration of the control device. The control device 13 shown in Figure 2 has a storage unit 28, an acquisition unit 29, an additive device control unit 30, an input unit 31, and an output unit 32. The control device 13 is mainly composed of a microcomputer. The control device 13 functions as the storage unit 28, acquisition unit 29, additive device control unit 30, input unit 31, and output unit 32 by executing a program read from the storage unit 28. The control device 13 also performs calculations based on various data and outputs the results.

[0035] (Storage part) The storage unit 28 may be, for example, an updatable flash memory, a hard disk that is built-in or connected via a data communication terminal, an information recording medium such as a memory card, and a device for reading and writing such recording media. The storage unit 28 stores programs for the control device 13 to execute each function, as well as data used by such programs.

[0036] The memory unit 28 further stores a database 33. The database 33 stores various data that are input to the control device 13. Examples of data input to the database 33 include the rolling conditions at the rolling mill 1, the actual rolling data at the rolling mill 1, and the oil film thickness of the lubricant at the entry side of each rolling stand 3 to 7, calculated by the control device 13. The oil film thickness may be the oil film thickness of the lubricant at the entry side of the first rolling stand 3, measured by the film thickness gauge 16, instead of a calculated value.

[0037] The input unit 31 is used to input the rolling conditions for the steel strip 2 in the rolling mill 1, and the rolling conditions are input from the input unit 31 by the operator. The rolling conditions input from the input unit 31 are stored in the memory unit 28 and output from the output unit 32 to each rolling stand 3 to 7. The output unit 32 outputs various data and command signals to the outside.

[0038] The acquisition unit 29 acquires the oil film thickness of the lubricant at the entry side of each rolling stand 3 to 7, calculated by the control device 13, or the oil film thickness of the lubricant at the entry side of the first rolling stand 3, measured by the film thickness gauge 16, from the storage unit 28. The acquisition unit 29 outputs the acquired oil film thickness to the additive device control unit 30. Furthermore, the acquisition unit 29 acquires sensor information from various sensors (not shown) and stores it in the storage unit 28. In this way, the acquisition unit 29 acquires various rolling performance data and stores it in the storage unit 28.

[0039] When the additive control unit 30 obtains the oil film thickness from the acquisition unit 29, it reads the rolling conditions and rolling performance data from the storage unit 28 and calculates the oil film thickness of the lubricant at the roll bite based on this data. The additive control unit 30 also selects a load-bearing additive with a molecular chain length equal to or greater than the calculated oil film thickness of the lubricant at the roll bite and calculates the amount of load-bearing additive to add to the lubricant.

[0040] The output unit 32 outputs a control command signal to the additive device 24 to add the load-bearing additive selected and calculated by the additive device control unit 30 to the lubricant. Alternatively, the output unit 32 may display the amount of load-bearing additive selected and calculated by the additive device control unit 30 on a monitor (not shown) to notify the operator.

[0041] (Rolling method for rolled material) Figure 3 is a flowchart illustrating the addition of a load-bearing additive to the lubricant. The flowchart shown in Figure 3 is initiated when rolling of the steel strip 2 begins in the rolling mill 1 shown in Figure 1. In the example shown in Figure 3, first, the rolling conditions for the steel strip 2 in the rolling mill 1 are input by the operator from the input unit 31 to the control device 13 of the rolling mill 1 (step S1). Then, based on the rolling conditions, various operating devices of the rolling mill 1 are controlled and the rolling mill 1 is operated, and rolling of the steel strip 2 begins (step S2). At the time when rolling of the steel strip 2 begins, a lubricant without a load-bearing additive is stored in the lubricant tank 17, and the steel strip 2 is rolled using this lubricant without a load-bearing additive. Step S2 described above corresponds to the rolling process in this embodiment.

[0042] When rolling begins, rolling performance data is acquired (step S3). Specifically, the oil film thickness of the lubricant formed on the steel strip 2 at the inlet side of each rolling stand 3 to 7 is calculated by the control device 13 based on the amount of lubricant discharged from the coolant nozzle, rolling conditions, past rolling performance, and the temperature of the lubricant and steel strip 2, and stored in the storage unit 28. The acquisition unit 29 acquires the oil film thickness of the lubricant from the storage unit 28 and outputs it to the additive device control unit 30. The acquisition unit 29 also acquires sensor information from various sensors installed on the rolling mill 1 and stores it in the storage unit 28. Note that the oil film thickness of the lubricant at the inlet side of each rolling stand 3 to 7 is different from each other. Therefore, the acquisition unit 29 may acquire the thinnest oil film thickness among those lubricant oil films from the storage unit 28 and output it to the additive device control unit 30. Alternatively, the oil film thickness of the lubricant at the entrance side of the first rolling stand 3 may be obtained from the storage unit 28 and output to the additive control unit 30. The following explanation will use the case where the oil film thickness of the lubricant formed on the steel strip 2 at the entrance side of the first rolling stand 3 is obtained from the storage unit 28 as an example.

[0043] The additive control unit 30, upon obtaining the oil film thickness of the lubricant formed on the steel strip 2 at the entry side of the first rolling stand 3, reads rolling conditions and rolling performance data from the storage unit 28 and calculates the oil film thickness of the lubricant alone at the roll bite of the first rolling stand 3 based on these data (step S4). Step S4 described above corresponds to the oil film thickness acquisition process in this embodiment.

[0044] This section explains how to calculate the oil film thickness of a lubricant alone in a roll bite. The oil film thickness of a lubricant alone in a roll bite can be calculated using the following equations (1) to (5). Of equations (1) to (5), equations (4) and (5) are formulas for calculating the oil film thickness of the lubricant formed on the steel strip 2 under atmospheric pressure. Equation (4) is used when the lubricant is soluble or solution type, and equation (5) is used when the lubricant is soluble or emulsion type. In this embodiment, the oil film thickness h1 directly below the roll bite at the point when material deformation begins in the roll bite during rolling is calculated based on the oil film thickness h2 of the lubricant calculated by equations (4) and (5) and equations (1) to (3).

[0045]

number

number

number

[0046] The oil film thickness of the lubricant alone in the roll bite may be measured instead of being calculated using the above-mentioned equations (1) to (5). In that case, for example, it may be measured using a commercially available oil film thickness measuring instrument. Alternatively, the deposits on the rolled steel strip may be collected, and the amount of the collected deposits may be converted into the oil film thickness of the lubricant in the roll bite. It should be noted that the oil film thickness is generally thinner than 0.1 μm. Therefore, it is preferable to determine the oil film thickness of the lubricant in the roll bite by calculation and simulation. An example of the oil film thickness measuring instrument mentioned above is the eddy current type film thickness gauge manufactured by Elcometer.

[0047] Next, the additive control unit 30 selects a load-bearing additive with a molecular chain length equal to or greater than the calculated oil film thickness of the lubricant alone at the roll bite, and calculates the amount of the selected load-bearing additive to be added to the lubricant (step S5). For example, it is preferable to pre-determine the molecular chain length for each type of load-bearing additive and the amount of load-bearing additive to be added so that the concentration of the load-bearing additive relative to the lubricant is 1.0 to 50.0%, and to store these molecular chain lengths and amounts in the storage unit 28. Alternatively, a table summarizing the relationship between the oil film thickness of the lubricant alone at the roll bite, the molecular chain length of the load-bearing additive, the amount of load-bearing additive to be added, and the rolling conditions may be created in advance and stored in the storage unit 28. When the additive control unit 30 obtains the oil film thickness of the lubricant alone at the roll bite, it reads the above-mentioned table from the storage unit 28 and selects a load-bearing additive based on the table, the current oil film thickness of the lubricant alone at the roll bite, and the rolling conditions, and calculates the amount to be added. Step S5 described above corresponds to the load-bearing additive addition step of this embodiment.

[0048] This explains the reason for the formation of an adsorbed film of the load-bearing additive. During cold rolling, the roll bite is considered to be in a mixed lubrication state of fluid lubrication and boundary lubrication. The coefficient of friction in the fluid lubrication state is lower than the coefficient of friction in the boundary lubrication state, and the coefficient of friction changes depending on the increase or decrease in the oil film thickness of the lubricant. In the boundary lubrication state, the surface of the steel strip 2, which is the material to be rolled, and the surface of the rolling roll are in contact via an adsorbed film of the lubricant. If an adsorbed film of the load-bearing additive with a thickness exceeding the oil film thickness of the lubricant formed at the roll bite is formed at the roll bite, boundary lubrication becomes dominant at the roll bite. In other words, by adding a load-bearing additive to the lubricant, an adsorbed film of the load-bearing additive with a thickness exceeding the oil film thickness of the lubricant formed at the roll bite is formed at the roll bite.

[0049] Furthermore, the additive control unit 30 outputs the selected load-bearing additive and its amount to the output unit 32. The output unit 32 outputs a control command signal to the additive device 24 to add the load-bearing additive selected and calculated by the additive control unit 30 to the lubricant. Alternatively, the output unit 32 displays the load-bearing additive selected by the additive control unit 30 and its amount on a monitor to inform the operator.

[0050] The additive device 24 is selected by the additive device control unit 30, and the calculated amount of load-bearing additive is added to the lubricant (step S6). Instead of controlling the additive device 24 to add the load-bearing additive to the lubricant, the operator may do so based on the information displayed on the monitor. As a result, the lubricant in the lubricant tank 17 contains the load-bearing additive, and the lubricant containing the load-bearing additive is supplied to each rolling stand 3 to 7 to roll the steel strip 2 (step 7). After that, the control shown in the flowchart in Figure 3 is terminated.

[0051] (Effects / Actions) According to this embodiment, by adding a load-bearing additive to the lubricant, an adsorbed film of the load-bearing additive with a thickness exceeding the oil film thickness of the lubricant alone formed on the roll bite can be formed on the roll bite. As a result, an adsorbed film of the load-bearing additive is further formed on the roll bite in a mixed lubrication state, and this adsorbed film can lubricate or protect the surface of the steel strip 2 and the surface of the rolling roll 14. As a result, rolling troubles and quality problems caused by deterioration of friction conditions during rolling can be avoided. This enables highly efficient and stable rolling of the steel strip 2.

[0052] This embodiment is not limited to the examples described above. For example, instead of adding load-bearing additives to the lubricant, a lubricant containing multiple load-bearing additives with different load-bearing additive content may be prepared in advance. In that case, multiple lubricant tanks may be prepared, and each of the lubricants containing multiple load-bearing additives with different load-bearing additive content may be stored in a separate lubricant tank. Then, the supply source of the lubricant containing load-bearing additives supplied to the rolling stands 3 to 7 may be switched according to the oil film thickness of the lubricant alone at the roll bite. This embodiment can also be applied when rolling steel plates instead of steel strips. Furthermore, in a method for manufacturing metal strips by rolling a rolled material such as a slab, bloom, or billet, the method may include a step of rolling the metal strip using the rolling method of the rolled material according to this embodiment described above. [Examples]

[0053] Rolling of steel strips was carried out using a rolling mill configured similarly to rolling mill 1 shown in Figure 1. Stainless steel strips made of SUS430 and low-carbon steel strips were used. The entry plate thickness of each steel strip into the rolling mill was 3.0-4.0 mm, the plate width was 1000-1200 mm, and the unit weight was 20 tons. The rolling roll diameter of each mill was 500 mm, and the maximum rolling speed was approximately 1000 mpm. The lubricant supply oil was 2000-3000 L / min, which was the optimized flow rate at each station based on previous rolling experience.

[0054] As a lubricant, a soluble lubricant was used, diluted to 5% with water. The lubricant temperature in the lubricant tank was maintained at 40°C, and this temperature was kept constant during the rolling of each steel strip. As a load-bearing additive, an oily polyalkylene glycol was used. Two types of load-bearing additives were prepared by varying the polymerization number of the polyalkylene glycol: one with a molecular chain of 2 nm and the other with a molecular chain of 20 nm.

[0055] After rolling, test specimens were taken from both the leading edge and the center of each steel strip in the longitudinal direction, and the gloss (Gs20°) of each specimen was measured. Specifically, at both the leading edge and the center of the steel strip, three test specimens were taken from the center of the strip in the longitudinal direction along the width direction. In addition, three test specimens were taken at both the leading edge and the center of the steel strip in the width direction. The gloss was measured for each specimen, and the average value was taken as the gloss of the steel strip. If the difference between the gloss of the leading edge and the gloss of the center was 50 or less, it was considered a pass; if it was greater than that, it was judged that a difference in surface quality had occurred and it was considered a fail. Also, if a problem occurred during rolling, it was considered a fail. In addition, for stainless steel strips, in order to investigate the effect on surface quality, only when the thickness was rolled from 4 mm to 1 mm before rolling, it was annealed and pickled after rolling to a No. 2B finish (JIS G4305:2021). Therefore, the effect on surface quality was not investigated for stainless steel strip No. 9. Table 1 summarizes the types of steel strips used for rolling in the examples, the rolling conditions, and the rolling results.

[0056] [Table 1]

[0057] Furthermore, low-carbon steel strips are not required to have surface gloss as a surface quality. Therefore, gloss level control and measurement were not performed, and the gloss level column in Table 1 is left blank. On the other hand, stainless steel strips are required to have a No. 2B finish and surface gloss, but the gloss level changes when the cold reduction ratio changes. Therefore, in this example, the surface gloss of samples with the same thickness on the entry and exit sides was compared and used as one of the acceptance criteria.

[0058] Case No. 1 is an example of rolling low-carbon steel strip without the addition of load-bearing additives. During acceleration and deceleration when passing the welded section through the rolling mill, the coefficient of friction increased with increasing speed, causing gauge fluctuations and resulting in a slightly thicker plate after passing through. When passing a welded section through the rolling mill, the speed is lower and the coefficient of friction is higher compared to passing other sections. On the other hand, as the speed increases, the coefficient of friction gradually decreases. Normally, the plate thickness after passing through becomes constant when the speed is increased to a stable speed. Therefore, when rolling coil ends such as welded sections, where the speed is low, setting the same rolling roll gap as other sections with high speeds increases the load during rolling and also increases the plate thickness. For these reasons, Case No. 1 could not be rolled to the target plate thickness and was deemed unacceptable.

[0059] Case No. 2 is an example in which 30% by mass (hereinafter referred to as "%") of a load-bearing additive was added during the rolling of a low-carbon steel strip. However, the molecular chain length of the load-bearing additive was shorter than the oil film thickness of the lubricant at the roll bite. Similar to Case No. 1, during acceleration and deceleration when passing the welded section of the sheet through the rolling mill, the coefficient of friction increased, causing gauge fluctuations and resulting in a thicker sheet thickness after passing through. The sheet could not be rolled to the target thickness and was deemed unacceptable.

[0060] Case No. 3 is an example where 30% load-bearing additive was added during the rolling of stainless steel strip. However, the molecular chain length of the load-bearing additive was shorter than the oil film thickness of the lubricant. Compared to the leading edge, where the sheet was passed at a low speed near the weld, the glossiness in the central part, where the maximum speed was reached, decreased by more than 100 compared to the leading edge, resulting in significant variation in surface quality. Therefore, it was not possible to manufacture a steel sheet with the target surface quality, and it was deemed unacceptable.

[0061] Case No. 4 is an example where 0.5% load-bearing additive was added during the rolling of stainless steel strip. However, the amount of load-bearing additive was insufficient, resulting in a significant decrease in glossiness of more than 100 points in the center compared to the tip, and thus large quality fluctuations. As a result, it was not possible to manufacture a steel sheet with the target surface quality, and it was deemed unacceptable.

[0062] No. 5 is an example where the concentration of soluble lubricant was reduced to 3% to ensure gloss even during high-speed rolling. Although the gloss level was within the acceptable range, seizing occurred during rolling, resulting in defects, and therefore it was deemed unacceptable.

[0063] Examples No. 6-11 show the use of a load-bearing additive with a molecular chain length of 20 nm, which is longer than the oil film thickness of the lubricant at the roll bite, during the rolling of stainless steel strips. Examples No. 12-14 show the use of a load-bearing additive with a molecular chain length of 20 nm, which is longer than the oil film thickness of the lubricant at the roll bite, during the rolling of low-carbon steel strips.

[0064] While the gloss level of No. 6 is within the acceptable range, the concentration of the load-bearing additive in No. 6 is lower compared to Nos. 7-14. As a result, the gloss level in the central part is lower than that of the tip. This is thought to be because the adsorption film was not sufficiently formed.

[0065] Samples No. 7-11 had sufficiently high concentrations of load-bearing additives. All samples met the acceptable gloss level. For samples No. 7, 8, 10, and 11, there was almost no difference in gloss between the leading edge and the center when the feed speed was changed. Note that gloss increases with increasing cold reduction ratio. Therefore, thinner exit plate thickness results in higher gloss. Consequently, when the entry plate thickness is constant, a higher cold reduction ratio smooths out surface defects and improves gloss.

[0066] In samples No. 12 and 13, there was no variation in plate thickness due to fluctuations in the feeding speed when accelerating and decelerating the plate with the welded section through the rolling mill.

[0067] In No. 14, chattering occurred, resulting in defects on the steel plate surface, leading to a rejection. This is thought to be due to an excessively high concentration of the load-bearing additive, which caused the adsorbed film of the load-bearing additive to become dominant at the roll bite. In other words, it is thought that the formation of the lubricant oil film and the adsorbed film of the load-bearing additive competed with each other, resulting in unstable lubricant oil film formation. [Explanation of Symbols]

[0068] 1. Tandem rolling mill 2 Steel strip 3. First Rolling Stand 4. Second Rolling Mill Stand 5. Third Rolling Stand 6. Fourth Rolling Mill Stand 7. Fifth Rolling Stand 8 Payoffriel 9 Welding machine 10 Looper 11 Shah 12 Carozel Reel 13 Control device 14 Rolling Rolls 15 Backup Role 16 Oil film thick liquid 17 Lubricant Tank 18 Supply pipe 19 Oil pump 20 Return tube 21 Filtration equipment 22 Load-bearing coating tanks 23 Additive supply pipe 24 Addition equipment 25 1st supply port 26 2nd supply port 27 Agitator 28 Memory section 29 Acquisition Department 30 Additive device control unit 31 Input section 32 Output section 33 Databases

Claims

1. A method for rolling a rolled material, wherein the rolled material is rolled through a lubricating oil film formed between a pair of rolling rolls, The lubricant contains a load-bearing additive with a molecular chain length greater than or equal to the oil film thickness of the lubricant alone between the material to be rolled and the rolling rolls. A method for rolling a rolled material, wherein the concentration of the load-bearing additive in the lubricant is 1.0% by mass or more and 50.0% by mass or less.

2. The aforementioned lubricant is a water-soluble lubricant. The rolling method for a rolled material according to claim 1, wherein the load-bearing additive is an oily agent.

3. A method for manufacturing a metal strip, comprising the step of rolling the metal strip using the rolling method for a rolled material described in claim 1 or 2.

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