COLD-ROLLED STEEL STRIPS MANUFACTURING PLANT AND METHOD FOR MANUFACTURING COLD-ROLLED STEEL STRIPS.
Patent Information
- Authority / Receiving Office
- MX · MX
- Patent Type
- Patents
- Current Assignee / Owner
- JFE STEEL CORP
- Filing Date
- 2022-08-30
- Publication Date
- 2026-05-19
Smart Images
Figure MX433743B0
Abstract
Description
COLD-ROLLED STEEL STRIPPING MANUFACTURING PLANT AND METHOD FOR MANUFACTURING COLD-ROLLED STEEL STRIPPING FIELD OF INVENTION The present invention relates to a manufacturing installation for cold-rolled steel strips and to a method for manufacturing cold-rolled steel strips. BACKGROUND OF THE INVENTION In a cold rolling line for steel strip, the trailing end of a leading material (front steel strip) and the leading end of a trailing material (next steel strip) are joined. By continuously feeding the joined steel strip to a cold rolling mill, cold rolling is performed without interruption. Then, by rolling the steel strip under tension along its entire length, the thickness and shape can be controlled with high precision, even at the leading and trailing ends. With the advancement of laser welding machines, joining the main and backing materials via laser welding is becoming commonplace, improving the strength and workability of the steel strip joint after joining. However, with the progress of high-alloy and thinner steel strips, the likelihood of fracture at the joint during cold rolling has increased. Fracture at the joint leads to cold rolling line shutdowns, resulting in a significant decrease in productivity. Furthermore, it necessitates replacing the work rolls, which in turn increases production costs. Therefore, conventionally, to prevent fracture at the joint portion of the steel strip, measures such as optimizing welding conditions according to the alloy content and thickness of the steel strip have been taken. For example, Patent Literature 1 describes a method for stably rolling a joint portion by defining the supply conditions of a weld filler and optimizing the shape and hardness of the weld metal when joining steel strips. Additionally, Patent Literature 2 describes a method for stably rolling a joint portion by notching the joint portion of the steel strip using a laser and eliminating work hardening of the steel strip's cross-section during notching. List of appointments Patent Literature Patent Literature 1 Japanese Open Patent Application No. 2011-140026 Patent Literature 2 Japanese Open Patent Application No. 2014-50853 BRIEF DESCRIPTION OF THE INVENTION Technical problem As in the previous case, many techniques have been developed to stably transfer a bonding portion when rolling a high-Si silicon steel sheet. However, although conventionally developed methods provide some effect, the current situation is that they have not been able to prevent fracture of the bonding portion during cold rolling to an operationally acceptable level. The present invention has been made in view of the foregoing, and an objective of the present invention is to provide a manufacturing facility for cold-rolled steel strips and a method for manufacturing cold-rolled steel strips capable of eliminating the occurrence of fracture of a joining portion during the cold rolling of a silicon steel sheet. Solution As a result of diligent studies to achieve the goal described above, the inventors discovered that only optimizing the strength of the joining portion and the notching method is not sufficient to stably cold roll the joining portion of a silicon steel sheet and that controlling the rolling temperature of the joining portion is very effective, which led to the following invention. To solve the problem described above and achieve the objective, a cold-rolled steel strip manufacturing installation according to the present invention includes: a joining device configured to join a rear end of a preceding steel strip and a leading end of a subsequent steel strip to form a joined steel strip; a winder configured to store the joined steel strip; a heating device configured to heat a joining portion between the preceding steel strip and the subsequent steel strip throughout a width direction;and a cold rolling mill configured to cold roll the bonded steel strip for which the bonding portion was heated by the heating device, wherein the heating device is switchable between an output state and a non-output state, and during a period in which the bonding portion passes through the heating device, it is switched to the output state. Furthermore, in the cold-rolled steel strip manufacturing installation described above according to the present invention, a pickling device configured to pickle the bonded steel strip is arranged between the winding and the heating device. Furthermore, in the cold-rolled steel strip manufacturing installation described above according to the present invention, when the Si content of a steel strip, the preceding steel strip, and the following steel strip having a higher Si content is less than 3% by mass, the heating device heats the joining portion so that the temperature of the joining portion on an inlet side of the cold rolling mill must be 35°C or higher. Furthermore, in the cold-rolled steel strip manufacturing installation described above according to the present invention, when the Si content of at least one of the preceding steel strips and of the following steel strips is 2% by mass or higher, the heating device heats the joining portion so that the temperature of the joining portion on an inlet side of the cold rolling mill must be 50°C or higher. To solve the problem described above and achieve the objective, a method for manufacturing cold-rolled steel strips that performs sequential processes according to the present invention includes: a joining step of, by means of a joining device, joining an exit end of a preceding steel strip and a main end of a subsequent steel strip to form a joined steel strip; a storage step of, by means of a joining device, storing the joined steel strip;a heating stage of, by means of a heating device, heating a joining portion between the preceding steel strip and the following steel strip in a full width direction and a cold rolling stage, by means of a cold rolling mill, for cold rolling the joined steel strip for which the joining portion was heated by the heating device, wherein the heating device is switchable between an output state and a non-output state, and the heating stage switches the heating device to the output state, during a period in which the joining portion passes through the heating device. Furthermore, in the method for manufacturing cold-rolled steel strips according to the present invention, a pickling stage is carried out in which the bonded steel strip is pickled by a pickling device, between the storage stage and the heating stage. Furthermore, in the method for manufacturing cold-rolled steel strips according to the present invention, when the Si content of a steel strip, the preceding steel strip, and the following steel strip having a higher Si content is less than 3% by mass, the heating device heats the joining portion so that the temperature of the joining portion on an inlet side of the cold rolling mill is 35°C or higher. Furthermore, in the method for manufacturing cold-rolled steel strips according to the present invention, when the Si content of at least one of the preceding steel strips and of the following steel strips is 2% by mass or more, the heating device heats the joining portion so that the temperature of the joining portion on an inlet side of the cold rolling mill is 50°C or higher. Advantageous effects of the invention According to the present invention, the occurrence of fracture of a joining portion during the cold rolling of a silicon steel sheet can be eliminated, so that the joining portion of the silicon steel sheet can be stably cold rolled. BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a graph illustrating the effect of steel strip temperature on bending cracks in a joint portion. Figure 2 is a diagram illustrating a schematic configuration of a cold-rolled steel strip manufacturing facility according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION A manufacturing plant for cold-rolled steel strip and a method for manufacturing cold-rolled steel strip according to an embodiment of the present invention shall be described with reference to the drawings. The constituent elements of the following embodiment include those that can be readily replaced by those skilled in the art or those that are substantially the same. The inventors first investigated the supports where fracture occurs in a joining portion when the joining portion of a steel strip is cold-rolled by a tandem rolling mill having five rolling stands. As a result, it was found that in some cases, the fracture occurs in the stand on the upper side, such as #1 std (hereafter, the ninth stand from the upper side in the transport direction of the steel strip is referred to as “#N std”) and #2 std, while in other cases, the fracture occurs in the stand on the lower side, such as #4 std and #5 std. Furthermore, as a result of diligent investigation into the cause of each fracture, it was found that the cause differs between fractures on the upper and lower sides of the support. Regarding fractures on the lower side, many resulted from edge cracking originating at the wide end of the joint, or from changes in the cross-sectional shape of the weld metal. When these are the causes of the fracture, it is possible to repair it using the methods described in Patent Literature 1 and Patent Literature 2 above. Meanwhile, on the upper support side, edge cracking in the end portion of the width and changes in the cross-sectional shape of the weld metal are unlikely. Therefore, as a result of the most diligent investigation into the cause of the fracture, particularly the fracture in the joining portion immediately below Std #1 or on the exit side of it, it was presumed that the causes were local stretching of the steel strip shape, such as center elongation and edge elongation, or bending deformation in the sheet passage rolls or a shape detector. That is, it was presumed that a local brittle fracture occurs in the weld metal portion when the joining portion is wound onto Std #1, leading to fracture due to local stretching, bending deformation between the supports, or similar factors. As a result of further investigation into the fracture of a bonding portion in the support on the upper side, the fracture rate (rate of fracture occurrence) differs depending on the season; for example, the fracture rate is higher in winter than in summer, and it was therefore presumed that the outside air temperature (temperature in the rolling mill) affects the fracture rate. In the present embodiment, the “fracture rate” indicates the fracture rate in the support on the upper side, and the presence of fracture in the support on the lower side is not considered. To verify the theory described above, the flexural cracking resistance of a joint portion was evaluated on a laboratory scale when flexural stress was applied to the joint portion. This is because the flexural cracking resistance in this experiment is considered to correlate with the cracking property at the time of local stretching during rolling and the cracking property at the time of roller bending, as described above. As test materials, four types of silicon steel strips, each with a sheet thickness of 2 mm and a Si content of 2.1% by mass, 2.7% by mass, 3.3% by mass, and 3.7% by mass (hereafter referred to simply as “%”), were annealed at 800°C (corresponding to the annealing of hot-rolled sheet). The annealed silicon steel strips were then pickled and joined using a laser welder, and the test materials were subsequently cut to a width of 30 mm and a length of 300 mm. Silicon steel strips of 2.1% and 2.7% (hereafter referred to as "M% Si steel") are grades of steel in which fracture is unlikely to occur on an actual continuous cold rolling line. Meanwhile, silicon steel strips of 3.3% and 3.7% are grades of steel in which the bonding portion fractures with a frequency of several percentage points, especially at the top supports, on an actual continuous cold rolling line. Typically, in cold rolling, the temperature of the steel strip at the inlet of the rolling mill is approximately the same as the temperature in the plant, and in winter, it is around 10°C.Therefore, with regard to the flexural cracking resistance of the joining part, the temperature dependence was investigated when the temperature of the steel strip (i.e., the temperature of the joining part) is in the range of 10 to 110°C. In this experiment, the resistance to flexural cracking was evaluated by passing a 2 mm thick steel strip through a roller flattener. The roller flattener includes nine working rollers with a diameter of 70 mm at the top and bottom, and a roller interval of 100 mm. The flexural stress on the surface of the steel strip can be varied by changing the amount of pressure applied to the upper working rollers. In this experiment, the temperature of the steel sheet was modified in 20°C increments, and the clamping force was varied in 0.5 mm increments. The fracture limit of the joint portion was determined. It is considered that the greater the clamping force at the time of fracture, the more difficult the fracture will be, even on the cold rolling line. Figure 1 shows the results obtained in this experiment. As illustrated in Figure 1, when comparing each Si content, with the 2.1% Si steel, fracture occurred at a tightening amount of 5.0 mm, regardless of the joint temperature. Additionally, with the 2.7% Si steel, fracture occurred at a tightening amount of 3.5 mm when the joint temperature was 10°C, but when the temperature exceeded 30°C, fracture did not occur until a tightening amount of 5.0 mm. With 3.3% Si steel, fracture occurred at a tightening amount of 1.0 mm when the joint temperature was 10°C, and then, for each 20°C increase, fracture occurred at 1.5 mm, 2.5 mm, 3.5 mm, 4.5 mm, and 5.0 mm. With 3.7% Si steel, fracture occurred at a tightening amount of 0.5 mm when the joint temperature was 10°C, and then, for each 20°C increase, fracture occurred at 1.0 mm, 2.0 mm, 3.5 mm, 4.5 mm, and 5.0 mm. As a result of the experiment described above, it was confirmed that the silicon (Si) content has a significant effect on the fracture properties of the weld portion, and that as the Si content increases, the weld portion becomes more prone to fracture. This also aligns with the actual fracture behavior observed in a continuous cold rolling mill. Specifically, with 3.3% Si and 3.7% Si steels, the experiment conducted while varying the temperature of the weld portion revealed that weld fracture is eliminated as the temperature increases. When heated to 50°C, fracture did not occur until a clamping force of 2.0 mm was reached. Furthermore, it was found that when heated to 70°C, fracture of the weld portion did not occur until a clamping force of 3.5 mm was reached. From this, it was discovered that by cold rolling silicon steel sheet having a Si content of 3% or more, heating the bonding portion to 50°C or higher before cold rolling can sufficiently eliminate fracture of the bonding portion. Although the upper limit of the heating temperature is not restricted from the standpoint of preventing fracture of the bonding portion, because cold rolling is subsequently performed, it is necessary to set the temperature lower than that unsuitable for cold rolling, and it is preferable that it be 150°C or lower, for example. As mentioned above, it was found that the bending crack property of the bonding portion is greatly affected by the Si content of the base material and the heating temperature of the bonding portion, which led to the realization of the present invention. Cold-rolled steel strip manufacturing facility The configuration of the cold-rolled steel strip manufacturing facility (hereinafter referred to simply as the “manufacturing facility”) is described below in accordance with the present modality. Figure 2 illustrates an example of the configuration of a manufacturing facility 1. The manufacturing facility 1 includes a dispensing machine 11, a joining device 12, a uncoiler 13, a heating device 14, a thermometer (sheet temperature measuring device) 15, a cold rolling mill 16, a cutting machine (cutting device) 17, and a winding machine 18 arranged in the above order. The manufacturing facility 1 is a facility that dispenses steel strip using the dispensing machine 11, passes it through the joining device 12, the uncoiler 13, and the cold rolling mill 16, and winds the cold-rolled steel strip using the winding machine 18.From now on, each device will be described. The dispensing machine 11 is an apparatus responsible for the dispensing process of steel strapping (dispensing process) and is loaded with a heat-retaining coil. The manufacturing facility 1 may be equipped with a plurality of dispensing machines 11. In this case, each of the dispensing machines 11 dispenses different steel strapping. The joining device 12 is an apparatus responsible for the joining (welding) process of the end of a preceding steel strip dispensed by the dispensing machine 11 and the beginning of the next steel strip dispensed by the dispensing machine 11, thus forming a joined steel strip S (joining process). A laser welder, as described above, is conveniently used as the joining device 12. The uncoiler 13 is an apparatus responsible for the storage process of the bonded steel strip S (storage process) so that cold rolling can continue by the cold rolling mill 16 until the steel strips are bonded by the bonding device 12 (until bonding is complete). The heating device 14 is an apparatus responsible for the heating process of the joining portion between the previous and subsequent steel strips in the entire width direction (heating process) in the joined steel strip S. The heating device 14 is configured to be switchable between an output state in which the object passing through the heating device 14 is heated and a non-output state in which the passing object is not heated. The heating device 14 switches to the output state during the period in which the joining portion of the steel strip S passes through the corresponding heating device 14. That is, the heating device 14 switches to the output state (a state of heating the passing object) during the period in which the joining portion passes through the corresponding heating device 14. The heating device 14 switches to the non-output state (a state in which the passing object is not heated) in other periods (the period in which the joining portion does not pass through the heating device 14). In the heating process, it is preferable that when the silicon content of the steel strip, between the preceding and following strips with a higher silicon content, is less than 3%, the heating device 14 heats the corresponding joining portion so that the temperature of the joining portion on the inlet side of the cold rolling mill 16 is 35°C or higher. This allows for more effective elimination of fracture in the joining portion. Additionally, during the heating process, it is preferable that when the silicon content of at least one of the preceding and subsequent steel strips is 2% or higher, the heating device 14 heats the corresponding joining portion so that the temperature of the joining portion on the inlet side of the cold rolling mill 16 is 50°C or higher. This allows for more effective elimination of fracture in the joining portion. Thermometer 15 is the device responsible for measuring the surface temperature of the bonded steel strip S (temperature measurement process). In manufacturing facility 1, based on the distance between the joining device 12 and thermometer 15, and the conveying speed of the bonded steel strip S in the corresponding section, the temperature of the joined portion is identified from the temperature of the bonded steel strip S, which is continuously measured by thermometer 15. Under normal operating conditions, the bonding portion of the bonded steel strip S cools as it passes through the winding 13 and reaches approximately the same temperature as the portions other than the bonding portion in the bonded steel strip S. Therefore, the temperature at any given time, continuously measured by thermometer 15, can be treated as the temperature of the bonding portion. The cold rolling mill 16 is an apparatus responsible for the cold rolling process in which the thickness of the bonded steel strip S, for which the bonding portion is heated by the heating device 14, is made to be a target thickness. Specifically, the cold rolling mill 16 is a tandem rolling mill having a plurality of rolling stands. The cold rolling mill 16 is equipped with five rolling stands in the present embodiment, but the number of rolling stands is not particularly limited. The cutting machine 17 is an apparatus responsible for the cutting process of the bonded steel strip S (cutting process) after cold rolling. The winding machine 18 is, for example, a carousel winder and is an apparatus responsible for the winding process (coiling process) of the steel strips cut by the cutting machine 17. The manufacturing installation 1 may be equipped with a plurality of winders 18. In this case, the winders 18 continuously wind a plurality of steel strips. The equipment included in manufacturing installation 1 is not limited to the equipment described above. Manufacturing installation 1 only needs to have the heating device 14 and the cold rolling mill 16 arranged very close to each other (or more preferably adjacent to each other) in this order. Therefore, for example, when the cold rolling process and the pickling process, which is a pre-rolling process, are continuous, a pickling device for pickling the bonded steel strip S can be placed between the winding unit 13 and the cold rolling mill 16. rj / ηιη / ζζηζ / Β / γίΛΐ Details of the heating process The details of the heating process of a bonded portion using the heating device 14, which is a feature of the present embodiment, will now be described. In the continuous cold rolling of bonded steel strip S, the bonded portion must be cut by the cutting machine 17 on the exit side of the cold rolling mill 16, and the preceding and following steel strips must be wound separately by the winding machine 18. Therefore, the conveying speed of the bonded steel strip S must be reduced. Consequently, the conveying speed of the bonded steel strip S on the infeed-outside side of the cold rolling mill 16 is extremely slow compared to the stationary portion. In the present embodiment, taking advantage of this situation, the bonded portion of the bonded steel strip S is partially heated. The specific heating means in the heating device 14 are not particularly limited, but in the present embodiment, the case where the heating device 14 is an induction heating device will be described as an example. Examples of heating means other than induction heating include an infrared heater, a hot water bath, and the like. The heating device 14 determines a target output value based on the bonding portion temperature measured by thermometer 15, the target bonding portion temperature on the outlet side of the heating device 14, and the time the bonding portion passes through the heating device 14 (i.e., the heating time). The target temperature on the outlet side of the heating device 14 may be the same as the target temperature on the inlet side of the cold rolling mill 16 or it may be higher than the target temperature on the inlet side of the cold rolling mill 16. For example, when the heating device 14 and the cold rolling mill 16 are located close together (positions separated to the point that the temperature of the joining portion does not drop substantially between the heating device 14 and the cold rolling mill 16), the target temperature on the outlet side of the heating device 14 and the inlet side of the cold rolling mill 16 only needs to be the same. Meanwhile, when the heating device 14 and the cold rolling mill 16 are located far apart (positions separated to the point that the temperature of the joining portion drops significantly between the heating device 14 and the cold rolling mill 16), the target temperature of the joining portion on the outlet side of the heating device 14 only needs to be set to a higher temperature to compensate for the temperature drop.From the standpoint of production cost and productivity, it is preferable to position both as close to each other as possible. In this case, it is preferable for each apparatus to be arranged so that the distance between the heating device 14 and the cold rolling mill 16 is less than the distance between the winding unit 13 or the pickling device and the heating device 14. To partially heat the joining portion instead of the entire joined steel strip S, it is necessary to identify the period during which the corresponding joining portion passes through the heating device 14. The period during which the joining portion passes through the heating device 14 (the period from the moment the joining portion enters through the inlet side of the heating device 14 until the moment the joining portion exits through the outlet side of the heating device 14) can be identified based on the distance between the joining device 12 and the heating device 14 and on the transport speed of the joined steel strip S in the corresponding section. Next, at manufacturing facility 1, during the identified period, the state of heating device 14 is changed to the output state to heat the through object (i.e., the joining portion) to the target output value described above. At manufacturing facility 1, time t, which is the time taken from output value 0 to the target output value, is calculated such that at time T, when the joining portion enters the inlet side of heating device 14, the output value of heating device 14 reaches the target output value described above. Therefore, at manufacturing facility 1, the time at which heating device 14 transitions from the non-output state to the output state is set to Tt. Additionally, it is preferable that the heating device 14 transition from the output state to the non-output state after the bonding portion has exited the heating device 14. The transition to the non-output state after the bonding portion has exited the heating device 14 reliably heats the bonding portion to the target output value. In other words, strictly speaking, the heating device 14 heats not only the bonding portion of the bonded steel strip S, but also the portions upstream and downstream of the bonding portion, depending on the time it takes to transition between the output and non-output states. As will be described later, it is desirable that the target output value in the heating device 14 be determined based on the Si content. When a plurality of steel strips with different Si content are conveyed in the same row of devices, the heating device 14 only needs to acquire information indicating the Si content of the preceding and following steel strip to determine the target output value based on the relevant information, and to switch between the output state and the non-output state. The heating device 14 heats at least one of the lower and upper surfaces of the bonded steel strip S, but it is preferable to heat both the lower and upper surfaces. In the present embodiment, the material to be rolled has been described as an electromagnetic steel sheet, but the type of steel sheet is not particularly limited. Examples of steel sheets to which the technology of the present invention can be suitably applied, apart from electromagnetic steel sheets, include high-strength steel sheets and high-alloy steel sheets. According to the cold-rolled steel strip manufacturing plant 1 and the method for manufacturing cold-rolled steel strip in the present embodiment, as in the previous embodiment, the heating device 14 is switched to the output state during the period in which the bonding portion passes through the corresponding heating device 14, so that the fracture of the bonding portion can be eliminated. Therefore, according to the cold-rolled steel strip manufacturing plant 1 and the method for manufacturing cold-rolled steel strip in the present embodiment, the occurrence of bonding portion fracture during the cold rolling of a silicon steel strip can be eliminated, so that the bonding portion of the silicon steel strip can be cold-rolled stably. EXAMPLE An example demonstrating the effect of the present invention will be described. In the present example, after welding the steel strip using a laser beam welder, the joining portion of the joined steel strip was heated using an 800 kW induction heating device on the inlet side of the cold rolling mill to the predetermined temperature indicated in Table 1 below (“inlet-side joining portion temperature” in Table 1). The joined steel strip, after heating, was then cold-rolled on a 5-stand tandem rolling mill to a predetermined finish thickness (“final thickness” in Table 1). rj / ηιη / ζζηζ / Β / γίΛΐ & hcha ω ω nnto ui o ui o ui o en ? Table 1 Silicon content (% by mass) Thickness before rolling Final thickness (mm) Rolling reduction rate (%) Temperature of the entry side joint (°C) Fracture occurrence rate (%) Remarks Previous steel strip Subsequent steel strip No. 1 0.9-1.2 0.9-1.2 1.8-2.4 0.3-0.5 75-83 10°C 0.5% Reference example No. 2 0.9-1.2 0.9-1.2 1.8-2.4 0.3-0.5 75-83 35°C 0.2% Inventive example No. 3 0.9-1.2 0.9-1.2 1.8-2.4 0.3-0.5 75-83 50°C 0.1% Inventive example No. 4 0.9-1.2 0.9-1.2 1.8-2.4 0.3-0.5 75-83 90°C 0.0% Inventive Example No. 5 2.6-2.9 2.6-2.9 1.8-2.4 0.3-0.5 75-83 10°C 3.1% Comparative Example No. 6 2.6-2.9 2.6-2.9 1.8-2.4 0.3-0.5 75-83 35°C 2.8% Inventive Example No. 7 2.6-2.9 2.6-2.9 1.8-2.4 0.3-0.5 75-83 50°C 1.1% Inventive Example No. 8 2.6-2.9 2.6-2.9 1.8-2.4 0.3-0.5 75-83 90°C 0.2% Inventive Example No. 9 2.6-2.9 2.6-2.9 1.8-2.4 1.2-1.4 36-40 35°C 2.0% Inventive Example No. 10 3.2-3.5 3.2-3.5 1.8-2.4 0.3-0.5 75-83 10°C 7.3% Comparative Example No. 11 3.2-3.5 3.2-3.5 1.8-2.4 0.3-0.5 75-83 35°C 4.8% Comparative Example No. 12 3.2-3.5 3.2-3.5 1.8-2.4 0.3-0.5 75-83 50°C 1.9% Inventive Example No. 13 3.2-3.5 3.2-3.5 1.8-2.4 0.3-0.5 75-83 90°C 0.7% Inventive Example No. 14 0.9-1.2 2.6-2.9 1.8-2.4 0.3-0.5 75-83 35°C 2.6% Inventive Example No. 15 0.9-1.2 2.6-2.9 1.8-2.4 0.3-0.5 75-83 50°C 1.0% Inventive Example No. 16 3.2-3.5 2.6-2.9 1.8-2.4 0.3-0.5 75-83 35°C 4.5% Comparative Example No. 17 3.2-3.5 2.6-2.9 1.8-2.4 0.3-0.5 75-83 50°C 1.7% Inventive Example. Five days were established as the evaluation period for each condition in which the temperature of the bonded portion of the steel strip was modified in various ways on the infeed side of the cold rolling mill. Then, for 100 to 200 steel strips of each Si content that were cold rolled during the evaluation period, the fracture occurrence rate (hereafter referred to as the “fracture rate”) of the bonded portion on the infeed side of the cold rolling mill was compared. As illustrated in Table 1, the fracture rate of the bonded portion of the steel strip tends to be higher as the Si content increases. In Table 1, numbers 1, 5, and 10 indicate examples where the joining portion of the steel strip joined by the induction heating device has not been heated. In the same table, those with a fracture index of less than 3.0% (Nos. 2 to 4, 6 to 9, 12 to 15, and 17) are taken as examples of the invention, and those with a fracture index of 3.0% or higher (Nos. 5, 10, 11, and 16) are used as comparative examples. No. 1 is used as a reference example to illustrate an instance where the fracture rate is low even without induction heating if the silicon content is low. Nos. 1 to 4 Items 1 to 4 provide examples of cases where the silicon content of the preceding and following steel strips is 1.2% or less. Under these conditions, when not heated with the induction heating device (see item 1), the fracture rate is relatively low. However, when heated using the induction heating device (see items 2 to 4), the fracture rate is further reduced. In particular, when heated to 90°C with the induction heating device (see item 4), the fracture rate is significantly reduced. Nos. 5 to 9 Items 5 to 9 provide examples of cases where the silicon content of the preceding and subsequent steel strips exceeds 2% but is less than 3%. Under these conditions, when not heated with the induction heating device (see item 5), the fracture rate is relatively high. However, when heated with the induction heating device (see items 6 to 9), the fracture rate is reduced. In particular, when heated to 50°C or higher with the induction heating device (see items 7 and 8), the fracture rate was significantly reduced. Furthermore, when heating to the same heating temperature was carried out by the Induction heating device (see Nos. 6 and 9, for example), by decreasing the reduction rate of the rolling (see No. 9, for example), the fracture rate could be reduced. Nos. 10 to 13 Numbers 10 to 13 indicate cases where the silicon content of the preceding and following steel strip exceeds 3%. Under these conditions, when not heated with the induction heating device (see number 10) and when heated to less than 50°C with the induction heating device (see number 11), the fracture rate is high. Meanwhile, when the induction heating device heated to 50°C or higher (see numbers 12 and 13), the fracture rate was reduced. In particular, when the induction heating device heated to 90°C (see number 13), the fracture rate was significantly reduced. Nos. 14 to 17 Nos. 14 to 17 describe cases where the silicon content of one of the preceding steel strips and the subsequent steel strips exceeds 2%. In this condition, when heated to 50°C or higher using the induction heating device (see Nos. 15 and 17), compared to cases where it is heated to less than 50°C (see Nos. 14 and 16), the fracture rate is reduced to less than half. As in Nos. 14 to 17, when the silicon content differs between the preceding and subsequent steel strips, the heating temperature should only be set based on the steel strip with the higher silicon content. As in the foregoing, by applying the present invention and heating the joining portion of the steel strip joined at the inlet of the cold rolling mill, weld fracture can be eliminated. In particular, when the Si content is 2% or more, starting cold rolling at 50°C or higher can significantly reduce the fracture rate, thereby improving productivity and performance. As in the foregoing, the cold-rolled steel strip manufacturing facility and the method for manufacturing cold-rolled steel strip according to the present invention have been specifically described with reference to the embodiment and examples for carrying out the invention, but the spirit of the invention is not limited to these descriptions and must be interpreted broadly based on the scope statement of the claims. It goes without saying that various changes, modifications, and the like based on these descriptions are also included in the substance of the present invention. List of reference signs MANUFACTURING FACILITY DISPENSING MACHINE JOINING DEVICE WINDER HEATING DEVICE THERMOMETER COLD ROLLING MILL CUTTING MACHINES WINDING MACHINES S STEEL STRIPS JOINED
Claims
1. A cold-rolled steel strip manufacturing installation characterized in that it comprises: a joining device configured to join a rear end of a preceding steel strip and a leading end of a subsequent steel strip to form a joined steel strip; a winder configured to store the joined steel strip; a heating device configured to heat a joining portion between the preceding steel strip and the subsequent steel strip in the entire width direction; and a cold rolling mill configured to cold roll the joined steel strip whose joining portion was heated by the heating device, wherein the heating device is switchable between an output state and a non-output state, and during a period in which the joining portion passes through the heating device, it is switched to the output state.
2. The installation for manufacturing cold-rolled steel strips according to claim 1, further characterized in that a pickling device configured to pickle the bonded steel strip is arranged between the unwinder and the heating device.
3. The installation for manufacturing cold-rolled steel strips according to claim 1 or 2, further characterized in that when the Si content of a steel strip, the preceding steel strip, and the following steel strip having a higher Si content is less than 3% by mass, the heating device heats the joining portion so that the temperature of the joining portion on an inlet side of the cold rolling mill is 35°C or higher.
4. The installation for manufacturing cold-rolled steel strips according to claim 1 or 2, further characterized in that when a Si content of at least one of the preceding steel strips and of the following steel strips is equal to or greater than 2% by mass, the heating device heats the joining portion so that a temperature of the joining portion on an inlet side of the cold rolling mill is equal to or greater than 50°C.
5. A method for manufacturing cold-rolled steel strips that performs sequential processes, characterized in that it comprises: a joining step consisting of joining, by means of a joining device, a rear end of a preceding steel strip and a main end of a subsequent steel strip to form a joined steel strip; a storage step consisting of storing the joined steel strip by means of a heating device; a heating step consisting of heating, by means of a heating device, a joining portion between the preceding steel strip and the subsequent steel strip along the entire width direction;and a cold rolling stage consisting of cold rolling, by means of a cold rolling mill, the joined steel strip whose joining portion has been heated by the heating device, wherein the heating device is switchable between an output state and a non-output state, and the heating stage switches the heating device to the output state, during a period in which the joining portion passes through the heating device.
6. The method for manufacturing cold-rolled steel strips according to claim 5, further characterized in that a pickling step is carried out in which the bonded steel strip is pickled by a pickling device, between the storage step and the heating step.
7. The method for manufacturing cold-rolled steel strips according to claim 5 or 6, further characterized in that when the Si content of a steel strip, of the preceding steel strip and of the following steel strip having a higher Si content is less than 3% by mass, the heating device heats the joining portion so that the temperature of the joining portion on an inlet side of the cold rolling mill is 35°C or higher.
8. The method for manufacturing cold-rolled steel strips according to claim 5 or 6, further characterized in that when a Si content of at least one of the preceding and subsequent steel strips is 2% by mass or more, the heating device heats the joining portion so that a temperature of the joining portion on an inlet side of the cold rolling mill is 50°C or higher.