The present disclosure relates to equipment for notching a joint of steel strips, a method of notching a joint of steel strips, a cold rolling facility, and a method of cold rolling.
Typically, in a cold rolling process for a steel strip, in order to improve productivity and yield, a preceding material (preceding steel strip) and a succeeding material (succeeding steel strip) are continuously supplied to a cold rolling line by joining a trailing end of the preceding material and a leading end of the succeeding material to each other. Thus, the steel strip can be rolled with tension applied to the entire length thereof. This makes the thickness and the shape possible to be highly accurately controlled even at the leading end and the trailing end of the steel strip.
Along with being higher alloy components in cold rolled steel strips and advancement of laser welding machines, laser welding is becoming mainstream instead of related-art flash butt welding and the like in joining the preceding material and the succeeding material to each other. However, regardless of whether the flash butt welding or the laser welding is used as welding means, widthwise step portions are unavoidably formed at end portions (edge portions) of a joint (weld) of the preceding material and the succeeding material in a sheet width direction due to the difference in steel strip width and a shift in widthwise position between the preceding material and the succeeding material. When rolling is performed in this state, stress may be concentrated on the widthwise steps to occasionally lead to breaks in the weld. Occurrence of the breaks in the weld (weld break) makes the cold rolling line stop, thereby, reducing productivity significantly and replacing a work roll which leads to an increase in production cost.
Particularly in recent years, a demand for reduction in thickness of cold rolled steel strips has been more increasing for the purposes of reducing the weight and improving the characteristics of members. Along with this tendency, presently, the reduction ratio required for cold rolling is increasing, and the weld brake rate is increasing.
In order to prevent the breaks in the weld, notching has been performed before rolling. The notching involves forming notches (cutouts) at end portions of the weld in the sheet width direction. This notching is also aimed at cutting portions of the steel strip having low strength (about 30 mm at sheet width ends in the steel width), because at the sheet width end portions of the steel strip, strength is likely to be reduced due to insufficient welding caused by poor butting accuracy.
As a method of notching, for example, mechanical shearing to form a semi-circular shape without a corner as disclosed in Patent Literature 1 is typical. However, the curvature of the outer edge of the semi-circular notches is uniform, and the width of the steel strip is smallest in the joint. Thus, maximum stress is generated in the joint.
In contrast, in order to eliminate the problem with Patent Literature 1, Patent Literature 2 discloses a method of notching. By this method, substantially isosceles trapezoidal notches are formed so as to cause maximum stress to be generated at positions other than the weld.
PTL 1: Japanese Unexamined Patent Application Publication No. 5-076911
PTL 2: Japanese Unexamined Patent Application Publication No. 2014-50853
However, the above-described methods can not perform sufficient effects in case of notching particularly in cold rolling of brittle materials and high alloy materials such as silicon steel sheets and high-tensile steel sheets with high Si and Mn contents. Thus, presently, it is impossible to sufficiently prevent the breaks in the joint (weld breaks) in cold rolling.
The present disclosure has been made in view of the above-described situation. An object of the present disclosure is to provide notching equipment for a steel strip, a method of notching a steel strip, a cold rolling facility, and a method of cold rolling that which make it possible to perform cold rolling on a material without the breaks in the joint (weld breaks) even if the material would be a brittle material or a high alloy material such as a silicon steel sheet or a high-tensile steel sheet with high Si and Mn contents.
Although the details will be described later, as a result of earnest study to achieve the above-described object, the inventors found that when notching the weld by shearing as in the related-art, work hardening occurs at the end portions of the weld in the sheet width direction, and this causes the weld breaks. The inventors, in order to prevent the weld from breaking, conceived formation of notches substantially without forming work hardened portions at the end portions of the weld in the sheet width direction. In particular, this notching is formed by grinding or combination of shearing and grinding.
The present disclosure has been made in accordance with the above-described conception and includes the following exemplary disclosed embodiments.
[1] Notching equipment for a steel strip for forming notches at both edge portions of a joint in a steel-strip width direction, the joint at which a trailing end of a preceding steel strip and a leading end of a succeeding steel strip are joined to each other, the equipment including: a shearing device that performs shearing on both edge portions in the steel-strip width direction including the joint to form first notch; and a grinding device that grinds end surfaces of both the edge portions of the joint in the steel-strip width direction to form second notch.
[2] Notching equipment for a steel strip for forming notches at both edge portions of a joint in a steel-strip width direction, the joint at which a trailing end of a preceding steel strip and a leading end of a succeeding steel strip are joined to each other, the equipment for notching including: a grinding device that grinds end surfaces of both edge portions in the steel-strip width direction including the joint to form notches.
[3] A method of notching a steel strip for forming notches at both edge portions of a joint in a steel-strip width direction where a trailing end of a preceding steel strip and a leading end of a succeeding steel strip are joined to each other, the method including the steps of: performing shearing on both edge portions in the steel-strip width direction including the joint, to form first notch; and thereafter, grinding end surfaces of both the edge portions of the joint in the steel-strip width direction, to form second notch.
[4] A method of notching a steel strip for forming notches at both edge portions of a joint in a steel-strip width direction where a trailing end of a preceding steel strip and a leading end of a succeeding steel strip are joined to each other, the method including the step of: grinding end surfaces of both edge portions in the steel-strip width direction including the joint, to form notches.
[5] A cold rolling facility including: the equipment according to [1] or [2] described above.
[6] A method of cold rolling including the steps of: forming the notches the notching method according to [3] or [4] described above; and thereafter, performing cold rolling.
According to the present disclosure, it is possible to perform cold rolling on a material without breaks in a joint (weld breaks), even if the material is a brittle material or a high alloy material such as a silicon steel sheet or a high-tensile steel sheet with high Si and Mn contents.
As has been described, the inventors found that a cause of breaks in a weld is work hardening at end portions of the weld in a sheet width direction occurring due to notching performed on the weld by shearing as in the related-art. The inventors, in order to prevent the weld from breaking, conceived a method of notching so as to form notches substantially without forming work hardened portions at the end portions of the weld in the sheet width direction. First, the finding and conception of the inventors will be described in detail.
That is, in order to find the causes of easy breaking of the weld, the inventors conducted a laboratory-scale rolling experiment as described below.
2 mm thick silicon steel sheets containing a content of Si of 3.3 mass % were used as a sample, and, as illustrated in
The sample 4 fabricated as described above was cold rolled without applying tension. In this cold rolling, the total reduction ratio is 90% through three passes. A rolling mill used for this cold rolling has the work roll diameter of 500 mm.
Then, end portions in the sheet width direction was cut along the sheet width direction in a step in which the shearing had been performed on the weld 3, that is, in a step before the cold rolling, thereby forming a cross section (edge cross section) to be observed. A structure of the section was observed and hardness testing was performed on this section. The result is illustrated in
Accordingly, the inventors earnestly studied the method of notching for forming notches substantially without forming work hardened portions at the end portions of the weld in the sheet width direction and tried to grind the weld.
That is, the above-described rolling experiment involves shearing the weld of the rolling evaluation sample 4; performing a mechanical grinding on the weld by 1 mm in the sheet width direction to remove the cutout therefrom; and then performing cold rolling similar to that described above. The mechanical grinding was performed by using (A) and (B) below: (A) a disc grinder using a #120 grindstone made by 3M; and (B) a disc grinder using a #36 grindstone made by FUJI grinding wheel mfg. Co., Ltd.
It has been found that, as has been described, the edge fractures in the weld are largely affected by work hardening of the weld occurring due to shearing, and removing the work hardened portions by grinding makes it possible to prevent the edge fractures.
Although grinding with (A) the #120 grindstone can eliminate the work hardening due to shearing, the grinding performance is low, and it took eight seconds to grind 1 mm in the above-described experiment. In contrast, grinding with (B) the #36 grindstone makes the grinding performance high, and it took no more than one second to grind 1 mm in the above-described experiment. In this case, however, some work hardening occurred in the edge portions.
Here, the work hardening refers to a state in which the Vickers hardness of the sheet width end portions is greater than the Vickers hardness of a base material portion (an inner portion separated from the sheet width end portions by 2 mm or more) by 50 HV or higher.
The following can be said from the above description. That is, it is important that there is no work hardened portion in the weld in the step where the notches have been formed in the weld, that is, before the cold rolling is performed.
Next, exemplary embodiments of the present disclosure will be described.
Thus, the first embodiment can form the notches 13 substantially without work hardened portions at the end portions of the weld 3 in the sheet width direction. Accordingly, it is possible to perform cold roll without the breaks in the weld even on a brittle material or a high alloy material such as a silicon steel sheet or a high-tensile steel sheet with high Si and Mn contents.
Thus, the second embodiment can form the notches 15 substantially without forming work hardened portions at the end portions of the weld 3 in the sheet width direction. Accordingly, it is possible to perform cold roll without the breaks in the weld even on a brittle material or a high alloy material such as a silicon steel sheet or a high-tensile steel sheet with high Si and Mn contents.
The grain size of the grindstone is preferably #80 or finer in order to grind the edge portions without work hardening according to the above-described first and second embodiments, although it depends on the type of abrasive grain and pushing pressure.
Furthermore, an industrial robot or the like can grind the edge portions of the steel strip in a cold rolling line ground safely and in a short time. For example, grinding of the weld can be performed with a disc grinder installed in a robot such as MOTOMAN-MH50II (“MOTOMAN” is a registered trademark) made by YASUKAWA Electric Corporation.
Furthermore, whether to apply the above-described first embodiment or the above-described second embodiment may be appropriately determined from viewpoints of time, an installation space, the cost of the equipment, and so force allowed for formation of the notches.
It is required that the notches be formed in a short time in order to maintain the efficiency of a cold rolling process (the notching is preferably completed within about ten seconds, although the time depends on the length of the steel belt and the performance of loopers).
Furthermore, according to the present disclosure, the notches may have a semi-circular shape as described in Patent Literature 1 or a substantially isosceles trapezoidal shape as described in Patent Literature 2. Furthermore, there is no problem with notches having a shape other than the above-described shapes. According to the present disclosure, the shape of the notches is not particularly defined.
Furthermore, in the case of normal low carbon steel, the edge fractures do not occur even in shearing. However, with brittle materials and high alloy materials such as silicon steel sheets and high-tensile steel sheets with high Si and Mn contents, workability of the weld is poor. Thus, the edge fractures easily occur when these materials are work hardened due to shearing. That is, the present disclosure is not necessarily applied to the types of steel such as low carbon steel and the like in which the edge fractures do not occur and substantially no weld break occurs even in shearing. The present disclosure is to be applied to the type of steel such as a brittle material or a high alloy material in which a weld breaks by shearing. However, some cold tandem mills are dedicatedly used for silicon steel sheets or high-tensile steel sheets and other cold tandem mills are, instead of being dedicatedly used for silicon steel sheets or high-tensile steel sheets, used also to roll low carbon steel and so forth. In this case, the present disclosure is also applied to low carbon steel without a problem.
The silicon steel sheets with high Si and Mn contents refer to, for example, steel sheets containing Si: 1.0 to 6.5 mass % and Mn: 0.2 to 1.0 mass %. The high-tensile steel sheets with high Si and Mn contents refer to, for example, steel sheets containing Si: 1.0 to 2.0 mass % and Mn: 1.5 to 20.0 mass % and having a tensile strength of 590 to 1470 MPa.
As an example of the present disclosure, silicon steel sheets were produced by cold rolling equipment equipped with a five-stand cold tandem mill and evaluated.
In so doing, as a related-art example, performing shearing on specified regions including the weld formed semi-circular notching.
In contrast, a first present example performed notching according to the above-described first embodiment of the present disclosure. That is, the first notching was performed to form semi-circular notches by shearing on specified regions including the weld. Thereafter, as the second notching, the weld and regions near the weld were ground by 2 mm by a #80 grindstone.
Furthermore, a second present example performed notching according to the above-described second embodiment of the present disclosure. That is, semi-circular notches are formed by grinding specified regions including the weld by a #36 grindstone.
In each of the examples, 100 coils of steel strips that contain Si content of 3.1 mass % or more and less than 3.5 mass % and have a thickness of 1.8 or more and 2.4 mm or less were prepared and cold rolled by using the 5-stand cold tandem mill having been described above, so that the finished steel strips have a thickness of 0.3 or more and 0.5 mm or less. Weld break rates were mutually compared in the examples. The result is illustrated in
As illustrated in
Thus, the effectiveness of the present disclosure has been confirmed. That is, when the notching the weld between the preceding steel strip and the succeeding steel strip, the present disclosure is applied so as to form the notches substantially without forming work hardened portions at the end portions of the weld in the sheet width direction. Thus, the weld breaks due to cold rolling can be prevented, and accordingly, improvement in productivity and yield can be achieved.
Number | Date | Country | Kind |
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JP2016-027855 | Feb 2016 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2017/001844 | 1/20/2017 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2017/141616 | 8/24/2017 | WO | A |
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2000-280093 | Oct 2000 | JP |
2006-341276 | Dec 2006 | JP |
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Number | Date | Country | |
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20200030862 A1 | Jan 2020 | US |