Surface defect suppression device, cold rolling equipment, and cold rolling method

Abstract

The present invention provides a surface defect suppression device and the like for suppressing the occurrence of surface defects such as stains on the surface of a metal strip, which are caused by a mixture of dirt formed by a lubricating oil and roll wear powder generated during rolling. The surface defect suppression device (20) includes an injection device (21) for injecting a cleaning liquid (21a) toward a work roll (4a), and water draining devices (22a), (22b) for preventing droplets (W) containing the lubricating oil (8a), roll wear powder generated during rolling, and the cleaning liquid (21a) from falling onto the metal strip (S). The water draining devices include water absorbing members (22aa), (22ba) for absorbing the droplets (W), and inclined members (22ab), (22bb) which, together with the water absorbing members, are inclined obliquely downward at an angle of 5 to 15° from the leading end to the opposite end with respect to the rolling direction. The water absorbing member is disposed at a position such that the gap (Δ22a), (Δ22b) between the work roll and the water absorbing member is 0.2 to 0.8 mm during low speed rolling, and 1.0 to 5.0 mm during high speed rolling.

Description

[Technical field]

[0001] The present invention relates to a surface defect suppression device for suppressing the occurrence of surface defects such as stains, a cold rolling facility, and a cold rolling method. [Background technology]

[0002] Generally, cold-rolled steel sheets are produced by hot rolling a steel slab, followed by cold rolling, annealing, and then temper rolling at a reduction ratio of about 0.5 to 3.0%. This temper rolling is carried out for the purposes of eliminating the yield point elongation of the steel sheet after annealing, adjusting the surface roughness, correcting the shape, adjusting the surface hardness, etc., and does not contribute much to thinning the steel sheet. Therefore, when manufacturing thin steel sheets such as steel sheets for cans, secondary cold rolling with a reduction ratio of about 10 to 40% (hereinafter referred to as DR (Double Reduced) rolling) may be performed instead of temper rolling. DR rolling contributes to increasing the strength of the steel sheet as well as reducing its thickness, and is therefore an effective method for obtaining hard thin steel sheets.

[0003] Generally, DR rolling is performed using a rolling mill having at least two stands: a main reduction stand for rolling to the desired reduction ratio, and a finishing stand for adjusting the sheet shape and surface roughness. In the main reduction stand, lubrication is required to obtain the desired reduction ratio, so bright rolls that have been ground with a grindstone to give scratches are used as work rolls, and wet rolling is performed by applying lubricating oil to the surface of the steel sheet. In the finishing stand, the surface roughness of the steel sheet is adjusted by a work roll with a roughness according to the user's requirements. As mentioned above, DR rolling is performed under wet conditions, so dirt (a mixture of roll wear powder and lubricating oil) generated during rolling falls onto the steel sheet, and a quality defect called stain is likely to occur on the surface of the steel sheet. Stain is a whitish speckled pattern.

[0004] 2. Description of the Related Art Conventionally, a cold rolling apparatus as disclosed in Patent Document 1, for example, has been known as a device for suppressing the occurrence of surface defects such as stains. The cold rolling apparatus shown in Patent Document 1 includes a rolling mill work roll for cold rolling a steel sheet, a rolling mill lubrication nozzle for supplying a lubricant to the rolling mill work roll, and an electrostatic applicator arranged in a stage upstream of the rolling mill work roll and the rolling mill lubrication nozzle. The electrostatic applicator applies the lubricant to the surface of the steel sheet by an electrostatic application method while supplying the lubricant from the rolling mill lubrication nozzle to the rolling mill work roll before the steel sheet is threaded through the rolling mill work roll. The cold rolling apparatus disclosed in Patent Document 1 can ensure a sufficient rolling reduction while suppressing the occurrence of surface defects such as stains and mottling. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-103252 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the cold rolling apparatus disclosed in Patent Document 1 has the following problems. That is, in the case of the cold rolling apparatus shown in Patent Document 1, although it is possible to suppress the occurrence of stains due to uneven adhesion of lubricant to the steel sheet, it is not possible to suppress the occurrence of stains due to contamination caused by a mixture of lubricant and roll wear powder generated during rolling. When stains form on the surface of a steel sheet due to a mixture of this lubricant and roll wear powder generated during rolling, there are issues such as the sheet not being able to be harvested as a product or the need for additional processes to remove the stains.

[0007] The present invention has been made to solve the above-mentioned problems in the prior art, and its object is to provide a surface defect suppression device, cold rolling equipment, and cold rolling method capable of suppressing the occurrence of surface defects such as stains on the surface of a metal strip, which are caused by a mixture of lubricating oil and roll wear powder generated during rolling. [Means for solving the problem]

[0008] As a result of intensive research by the present inventors, it was found that in order to suppress the occurrence of stains, it is important to prevent droplets of a mixture of lubricating oil and roll wear powder generated during rolling from falling onto the surface of the metal strip. In addition, it was found that simply improving the drainage condition would result in other surface defects besides stains, such as roll scratches and roll marks caused by roll wear powder, and therefore it is important to spray the cleaning liquid onto the work rolls and to establish appropriate drainage conditions. The present invention was made based on such findings.

[0009] In order to solve the above problems, a surface defect suppression device according to one embodiment of the present invention is a surface defect suppression device installed on the exit side of a work roll that cold rolls a metal strip coated with a lubricating oil, and includes an injection device that injects a cleaning liquid from the exit side of the work roll toward the work roll, and a draining device that is disposed adjacent to the work roll and the injection device and prevents droplets containing the lubricating oil, roll wear powder generated during rolling, and the cleaning liquid from falling onto the metal strip, the draining device including a water-absorbing member that absorbs the droplets, and an inclined member that has the water-absorbing member attached to its tip and is inclined together with the water-absorbing member from the tip to the opposite end obliquely downward at an angle of 5 to 15° with respect to the rolling direction, and the water-absorbing member is disposed at a position such that the distance between the water-absorbing member and the work roll is 0.2 to 0.8 mm during low-speed rolling immediately after the start of rolling, and 1.0 to 5.0 mm during high-speed rolling during steady rolling.

[0010] A cold rolling facility according to another aspect of the present invention includes the above-mentioned surface defect suppression device. Furthermore, a cold rolling method according to another aspect of the present invention is characterized in that a metal strip coated with a lubricant is cold rolled using the above-mentioned cold rolling equipment. Effect of the Invention

[0011] The surface defect suppression device, cold rolling equipment, and cold rolling method according to the present invention can suppress the occurrence of stains on the surface of a metal strip caused by a mixture of lubricating oil and roll wear powder generated during rolling. Also, the washing effect of spraying a cleaning liquid from an spraying device toward the work rolls can suppress the occurrence of surface defects other than stains, such as roll marks caused by foreign matter being caught, and roll marks caused by roll wear powder, on the surface of the metal strip. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of a cold rolling facility equipped with a surface defect suppression device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an explanatory diagram of the surface defect suppression device shown in FIG. [Diagram 3] 3 is a front view of an upper-stage water draining device and a discharge mechanism in the surface defect suppression device shown in FIG. 2. [Figure 4] 4 is a plan view of the upper draining device and the discharge mechanism shown in FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention is not limited to the following embodiments in terms of the materials, shapes, structures, arrangements, etc. of the components. In addition, the drawings are schematic, and therefore, it should be noted that the relationship between thickness and planar dimensions, ratios, etc. may differ from the actual relationship between thickness and planar dimensions, and the drawings may include parts in which the relationship between dimensions and ratios differ from one another.

[0014] FIG. 1 shows a schematic configuration of a cold rolling facility equipped with a surface defect suppression device according to one embodiment of the present invention. The cold rolling equipment 1 shown in Fig. 1 performs DR rolling on a steel sheet S as a metal strip that has been cold rolled and annealed. The cold rolling equipment 1 includes, from the upstream side to the downstream side, a payoff reel 2, a bridle roll 3, a main reduction stand 4, a finishing stand 5, a bridle roll 6, and a tension reel 7 in this order. The payoff reel 2 delivers a rolled steel sheet S that has been cold rolled and annealed toward the bridle rolls 3 and the main reduction stand 4. The bridle rolls 3 and 6 determine the line speed (the conveying speed of the steel sheet S) and generate tension by the frictional force between the rolls and the steel sheet S.

[0015] The main reduction stand 4 rolls the steel sheet S at a desired reduction ratio (for example, a reduction ratio of 10 to 40%) and includes a pair of upper and lower work rolls 4a that roll the steel sheet S and a pair of upper and lower backup rolls 4b that support the work rolls 4a. In the main reduction stand 4, lubrication is required to obtain a desired reduction ratio, so a bright roll that has been ground with a grindstone to give scratches is used as the work roll 4a, and wet rolling is performed by applying lubricating oil 8a to the surface of the steel sheet S before rolling. For this reason, a lubricating oil application nozzle 8 that applies the lubricating oil 8a to the steel sheet S is provided on the inlet side of the main reduction stand 4. A pair of lubricating oil application nozzles 8 are installed on the upper and lower sides of the steel sheet S, and the lubricating oil 8a is applied to the front and back sides of the steel sheet S from each of the lubricating oil application nozzles 8. The work rolls 4a of the main reduction stand 4 cold roll the steel sheet S to which the lubricating oil 8a has been applied.

[0016] The finishing stand 5 performs rolling to adjust the surface roughness of the steel sheet S, and includes a pair of upper and lower work rolls 5a that press down the steel sheet S, and a pair of upper and lower backup rolls 5b that support the work rolls 5a. As the work rolls 5a of the finishing stand 5, rolls corresponding to the roughness of the surface of the target steel sheet S are used. In addition, the tension reel 7 winds up the steel sheet S whose surface roughness has been adjusted by the finishing stand 5. At the delivery side of the main reduction stand 4, a cobble guard 9 is provided to prevent the steel sheet S from wrapping around the work roll 4a of the main reduction stand 4 if the steel sheet S breaks during rolling. Also, at the delivery side of the finishing stand 5, a cobble guard 11 having a similar function is provided.

[0017] Here, in the main reduction stand 4, lubricating oil 8a is applied to the front and back surfaces of the steel sheet S for wet rolling. As a result, dirt (droplets) that are a mixture of the lubricating oil 8a and roll wear powder generated during rolling falls onto the steel sheet S, and a quality defect called a stain is likely to occur on the surface of the steel sheet S. In this embodiment, a surface defect suppression device 20 for suppressing the occurrence of surface defects such as stains on the steel sheet S is installed on the delivery side of the work roll 4 a of the main reduction stand 4 .

[0018] 1 and 2, the surface defect suppression device 20 includes an injection device 21, an upper-stage water draining device 22a, and a lower-stage water draining device 22b. The injection device 21, the upper-stage water draining device 22a, and the lower-stage water draining device 22b may be configured separately or integrally. The spraying device 21 is installed at the exit side of the work roll 4a and sprays the cleaning liquid 21a from the exit side toward the work roll 4a. In DR rolling, roll wear powder is generated due to contact between the work roll 4a of the main reduction stand 4 and the steel sheet S. This roll wear powder becomes dirt mixed with the lubricating oil 8a, and this dirt generates stains on the surface of the steel sheet S through the work roll 4a. To prevent this, the spraying device 21 sprays the cleaning liquid 21a toward the work roll 4a to clean the work roll 4a. In addition, as a secondary effect, by spraying the cleaning liquid 21a toward the work roll 4a, foreign matter that causes roll marks is washed away, and the occurrence of roll marks other than stains on the surface of the steel sheet S can be suppressed. In addition, in order to obtain a sufficient roll cleaning effect, the discharge amount of the cleaning liquid 21a is preferably 150 L / min or more.

[0019] In FIG. 1, reference numeral 25 denotes an injection device that injects a cleaning liquid toward the work roll 4a. The upper-stage draining device 22a is disposed at a position adjacent to the work roll 4a and the spraying device 21 at the exit side of the work roll 4a, and prevents droplets W (see FIG. 2) containing the lubricating oil 8a, roll wear powder generated during rolling, and cleaning liquid 21a from falling onto the steel sheet S. The work roll 4a is washed with the cleaning liquid 21a from the spraying device 21, but the droplets W contain the cleaning liquid 21a, the lubricating oil 8a, and dirt that is a mixture of the roll wear powder generated during rolling. The droplets W falling onto the steel sheet S also cause stains. Therefore, the upper-stage draining device 22a is provided to prevent the droplets W from falling onto the steel sheet S. The upper-stage draining device 22a is installed at the tip of the cobble guard 9 described above.

[0020] The lower-stage draining device 22b is disposed below the upper-stage draining device 22a on the exit side of the work roll 4a, and prevents the above-mentioned droplets W from falling onto the steel sheet S. Although the upper-stage draining device 22a alone has the effect of preventing the droplets W from falling onto the steel sheet S, in this embodiment, the lower-stage draining device 22b is also provided to enhance this effect. As shown in FIG. 2, the lower-stage draining device 22b is provided at the tip of a separate cobble guard 10 attached to the cobble guard 9 by a support member 10a. Here, as shown in FIG. 2, each of the upper draining device 22a and the lower draining device 22b is equipped with a water-absorbent member 22aa, 22ba that absorbs liquid droplets W, and an inclined member 22ab, 22bb having the water-absorbent member 22aa, 22ba attached to its tip (the left end in FIG. 2). Each of the water-absorbent members 22aa, 22ba is made of a water-absorbent material such as felt, and is capable of absorbing the liquid droplets W and preventing the liquid droplets W from falling onto the steel sheet S.

[0021] In addition, each of the inclined members 22ab, 22bb is disposed with an inclination of 5 to 15° downward with respect to the rolling direction from the tip to the opposite end (the right end in FIG. 2) together with each of the water-absorbent members 22aa, 22ba. Specifically, as shown in FIG. 2, the inclined members 22ab and the water-absorbent members 22aa are disposed so that the angle θ22aa between their center lines CL22a and the horizontal line L extending in the rolling direction is 5 to 15°. The opposite end of the inclined member 22ab is attached to the tip of the cobble guard 9 described above. In addition, the inclined members 22bb and the water-absorbent members 22ba are disposed so that the angle θ22ba between their center lines CL22b and the horizontal line L extending in the rolling direction is 5 to 15°. The opposite end of the inclined member 22bb is attached to the tip of the separate cobble guard 10 described above.

[0022] If the water-absorbing members 22aa, 22ba are arranged horizontally, the droplets W may become saturated and fall from the water-absorbing members 22aa, 22ba onto the steel sheet S. If the water-absorbing members 22aa, 22ba are arranged tilted obliquely upward from the leading end to the opposite end with respect to the rolling direction, the droplets W may fall onto the steel sheet S without being absorbed by the water-absorbing members 22aa, 22ba. For this reason, the inclined members 22ab, 22bb are arranged with the water-absorbing members 22aa, 22ba tilted obliquely downward by 5 to 15 degrees from the leading end to the opposite end with respect to the rolling direction. This allows the droplets W to pass from the water-absorbing members 22aa, 22ba over the inclined members 22ab, 22bb and guide them to the opposite end side of the inclined members 22ab, 22bb, and discharge the droplets W outside the plate path by the discharge mechanisms 23a, 23b described later.

[0023] If the inclination angles of the inclined members 22ab, 22bb and the water-absorbing members 22aa, 22ba are smaller than 5°, the liquid droplets W cannot be guided to the opposite end of the inclined members 22ab, 22bb, and may fall onto the steel plate S. On the other hand, if the inclination angles of the inclined members 22ab, 22bb and the water-absorbing members 22aa, 22ba are larger than 15°, it becomes difficult to install the inclined members 22ab, 22bb and the water-absorbing members 22aa, 22ba (it becomes difficult to set the lifting angle of the draining devices 22a, 22b, which will be described later, and to ensure the distance between the draining devices 22a, 22b and the steel plate S, etc.). In addition, each water-absorbing member 22aa, 22ba needs to be positioned so that the gap Δ22a, Δ22b between the work roll 4a and the member is 0.2 to 0.8 mm during low-speed rolling immediately after the start of rolling, and 1.0 to 5.0 mm during high-speed rolling during steady rolling.

[0024] First, when each water-absorbing member 22aa, 22ba is brought into contact with the work roll 4a, roll wear powder generated during rolling scratches the work roll 4a, causing roll mark defects on the surface of the steel sheet S. For this reason, each water-absorbing member 22aa, 22ba is arranged with a gap Δ22a, Δ22b between it and the work roll 4a. On the other hand, if the gap Δ22a, Δ22b is too large, droplets W containing the above-mentioned cleaning liquid 21a, lubricating oil 8a, and dirt mixed with roll wear powder generated during rolling will fall onto the steel sheet S. For this reason, the gaps Δ22a, Δ22b are set to appropriate sizes when the water-absorbing members 22aa, 22ba are arranged. The appropriate size of the gaps Δ22a, Δ22b varies depending on the rolling speed of the steel sheet S, so they are arranged at positions that are 0.2 to 0.8 mm during low-speed rolling immediately after the start of rolling, and 1.0 to 5.0 mm during high-speed rolling during steady rolling.

[0025] Here, during low-speed rolling immediately after the start of rolling (for example, when the rolling speed is 10 mpm), the rotation speed of the work roll 4a is low, so the centrifugal force is weak and the drainage is poor (the drainage effect due to the centrifugal force is weak). For this reason, if the intervals Δ22a, Δ22b between each water-absorbing member 22aa, 22ba and the work roll 4a are large, the liquid droplets W tend to fall, so during low-speed rolling, the intervals Δ22a, Δ22b are made small, such as 0.2 to 0.8 mm. In other words, if the intervals Δ22a, Δ22b are smaller than 0.2 mm, there is a risk that roll marks will occur on the surface of the steel sheet S due to roll wear powder caused by rolling scratching the work roll 4a. On the other hand, if the intervals Δ22a, Δ22b are larger than 0.8 mm, there is a risk that the liquid droplets W will fall onto the steel sheet S.

[0026] In addition, during high-speed rolling in steady rolling (for example, when the rolling speed is 900 mpm), the work roll 4a rotates at a high speed, so that foreign matter such as roll wear powder is generated in large quantities. If the intervals Δ22a, Δ22b between the work roll 4a and each water-absorbing member 22aa, 22ba are small, the foreign matter causes scratches on the work roll 4a, which leads to roll marks on the steel sheet S. Even if the intervals Δ22a, Δ22b (0.2 to 0.8 mm) during low-speed rolling described above are secured, roll wear powder and the like generated during rolling may adhere to and accumulate on each water-absorbing member 22aa, 22ba. As a result, scratches may occur on the work roll 4a due to contact with the work roll 4a, which may result in roll marks on the steel sheet S. Therefore, during high-speed rolling, the intervals Δ22a, Δ22b are secured to be 1.0 mm or more. On the other hand, if the intervals Δ22a, Δ22b are made larger than 5.0 mm, there is a risk that the liquid droplets W may fall onto the steel sheet S, so the upper limit of the intervals Δ22a, Δ22b is set to 5.0 mm.

[0027] Next, the detailed configuration of the water-absorbing member 22aa and the inclined member 22ab constituting the upper-stage draining device 22a will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is a front view of the upper-stage draining device and discharge mechanism in the surface defect suppression device shown in Fig. 2. Fig. 4 is a plan view of the upper-stage draining device and discharge mechanism shown in Fig. 3. The basic configuration of the lower-stage draining device 22b is the same as that of the upper-stage draining device 22a, so a description thereof will be omitted. 3 and 4, the water-absorbent member 22aa is a rectangular plate-like member having a predetermined thickness and made of a water-absorbent material such as felt, and extending in an elongated manner in the width direction of the steel plate S. Although not shown, the water-absorbent member 22aa has a length sufficient to cover the entire width of the steel plate S and is capable of absorbing liquid droplets W flowing down from the entire width of the steel plate S and preventing the liquid droplets W from falling onto the steel plate S.

[0028] The inclined member 22ab is provided with the water-absorbent member 22aa at its tip, and is disposed with the water-absorbent member 22aa at an inclination of 5 to 15 degrees downward from its tip to its opposite end with respect to the rolling direction. The inclined member 22ab is a rectangular plate-like member that is elongated in the width direction of the steel sheet S having a predetermined thickness, and is provided with a plurality of protrusions 22ac that protrude upward from the upper surface at predetermined intervals along the width direction of the steel sheet S. The adjacent protrusions 22ac of the inclined member 22ab form a liquid droplet guide portion 22ad that guides the liquid droplets W from the water-absorbent member 22aa at the tip to the opposite end of the inclined member 22ab. A dish-shaped recess 22ae that receives the liquid droplets W from the water-absorbent member 22aa is formed on the bottom surface of the liquid droplet guide portion 22ad. A discharge hole 22af that discharges the liquid droplets W received from the water-absorbent member 22aa downward is formed on the bottom surface of the dish-shaped recess 22ae.

[0029] The inclined member 22ab is provided with a discharge mechanism 23a for discharging the droplets W from the water-absorbing member 22aa out of the plate path. That is, the lower surface of the inclined member 22ab is provided with a discharge mechanism 23a for discharging the droplets W discharged from each discharge hole af out of the plate path. As shown in FIG. 2, the inclined member 22bb is provided with a discharge mechanism 23b for discharging the droplets W from the water-absorbing member 22ba out of the plate path. That is, the lower surface of the inclined member 22ab is provided with a discharge mechanism 23b for discharging the droplets W discharged from each discharge hole af out of the plate path. The discharge mechanism 23b has the same basic configuration as the discharge mechanism 23a, so a description thereof will be omitted. The discharge mechanism 23a includes a gutter section 23aa that extends elongatedly in the width direction of the steel sheet S on the lower surface of the inclined member 22ab and collects and drains the liquid droplets W discharged from each drain hole af. The discharge mechanism 23a also includes a water collection section 23ab that is provided at the end of the gutter section 23aa in the width direction of the steel sheet S and collects the liquid droplets W from the gutter section 23aa and drains them into a vertical gutter 23ac described below. The discharge mechanism 23a also includes a vertical gutter 23ac that drains the liquid droplets W collected in the water collection section 23ab to the outside of the plate path.

[0030] The surface defect suppression device 20 also includes a gap adjustment mechanism 24 that adjusts the gaps Δ22a, Δ22b between the water absorbent members 22aa, 22ba and the work roll 4a. The gap adjustment mechanism 24 is composed of the aforementioned cobble guard 9 attached to the opposite end of the inclined member 22ab of the upper-stage water draining device 22a, and the aforementioned separate cobble guard 10 attached to the opposite end of the inclined member 22bb of the lower-stage water draining device 22b. The cobble guard 9 and the separate cobble guard 10 are raised and lowered in the directions indicated by the arrows in FIG. 2 by a lifting means (not shown) to adjust the gaps Δ22a, Δ22b between the water absorbent members 22aa, 22ba and the work roll 4a.

[0031] Next, the operation of the surface defect suppression device 20 thus configured will be described. The steel sheet S delivered from the payoff reel 2 passes through the bridle rolls 6 and is subjected to DR rolling in the main reduction stand 4. When the steel sheet S is rolled in this main reduction stand 4, lubricating oil 8a is sprayed from a lubricating oil application nozzle 8 toward the surface of the steel sheet S to apply the lubricating oil 8a to the surface of the steel sheet S. The work rolls 4a of the main reduction stand 4 cold roll the steel sheet S to which the lubricating oil 8a has been applied. In DR rolling, roll wear powder is generated due to contact between the work roll 4a of the main reduction stand 4 and the steel sheet S. This roll wear powder becomes contaminants mixed with the lubricating oil 8a, and this contaminants cause stains on the surface of the steel sheet S through the work roll 4a. To prevent this, a cleaning liquid 21a is sprayed from the spraying device 21 of the surface defect suppression device 20 toward the work roll 4a to clean the work roll 4a. At this time, spraying the cleaning liquid 21a toward the work roll 4a washes away foreign matter that causes roll marks, thereby making it possible to suppress the occurrence of roll marks other than stains on the surface of the steel sheet S.

[0032] The work roll 4a is washed with the washing liquid 21a from the spraying device 21, and droplets W containing the washing liquid 21a, lubricating oil 8a, and dirt mixed with roll wear powder generated during rolling attempt to fall onto the steel sheet S from the work roll 4a side as shown in FIG. 2. If the droplets W fall onto the steel sheet S, they will cause stains. At this time, the droplets W fall onto the water absorbing member 22aa of the upper-stage draining device 22a and the water absorbing member 22ba of the lower-stage draining device 22b, and are absorbed by the water absorbing members 22aa, 22ba. The droplets W that cannot be absorbed by the water absorbing members 22aa, 22ba are guided from the water absorbing members 22aa, 22ba side through the inclined members 22ab, 22bb to the dish-shaped recesses 22ae at the opposite ends of the inclined members 22ab, 22bb. At this time, each of the inclined members 22ab, 22bb is disposed with the water-absorbent members 22aa, 22ba inclined obliquely downward from the tip to the opposite end by 5 to 15 degrees with respect to the rolling direction. Therefore, the liquid droplets W can be easily guided from the top of each of the inclined members 22ab, 22bb to the dish-shaped recess 22ae without dropping. The droplets W guided to the dish-shaped recesses 22ae of the inclined members 22ab and 22bb are discharged from the discharge holes 22af formed in the dish-shaped recesses 22ae to the gutter portion 23aa of the discharge mechanism 23a. The droplets W discharged to the gutter portion 23aa are collected in the water collecting portion 23ab, and are discharged from the water collecting portion 23ab to the outside of the plate road via the vertical gutter 23ac.

[0033] Thus, the surface defect suppression device 20 according to this embodiment includes an injection device 21 that injects cleaning liquid 21a toward the work roll 4a from the exit side. The surface defect suppression device 20 also includes water draining devices 22a, 22b that are disposed adjacent to the work roll 4a and the injection device 21 and prevent droplets W, including the lubricating oil 8a, roll wear powder generated during rolling, and cleaning liquid 21a, from falling onto the steel sheet S. The water draining devices 22a, 22b also include water absorbing members 22aa, 22ba that absorb the droplets W, and inclined members 22ab, 22bb that have the water absorbing members 22aa, 22ba attached to their tips and that are inclined obliquely downward at 5 to 15 degrees with respect to the rolling direction from the tips to the opposite ends. Furthermore, the water-absorbing members 22aa, 22ba are arranged at positions such that the gaps Δ22a, Δ22b between them and the work roll 4a are 0.2 to 0.8 mm during low-speed rolling immediately after the start of rolling, and 1.0 to 5.0 mm during high-speed rolling during steady rolling.

[0034] This makes it possible to suppress the occurrence of stains on the surface of the steel sheet S, which are caused by a mixture of the lubricating oil 8a and the roll wear powder generated during rolling. In addition, the washing effect of spraying the cleaning liquid 21a from the spraying device 21 toward the work roll 4a makes it possible to suppress the occurrence of surface defects other than stains, such as roll marks caused by foreign matter getting caught and roll marks caused by roll wear powder, on the surface of the steel sheet S. Furthermore, according to the surface defect suppression device 20 of this embodiment, the inclined members 22ab, 22bb are provided with the discharge mechanisms 23a, 23b for discharging the liquid droplets W from the water absorbing members 22aa, 22ba to the outside of the plate path. As a result, the discharge mechanisms 23a, 23b discharge the droplets W from the absorbent members 22aa, 22ba outside the plate path, and the generation of stains on the surface of the steel plate S caused by a mixture of the lubricating oil 8a and roll wear powder generated during rolling can be reliably suppressed.

[0035] Furthermore, the surface defect suppression device 20 according to this embodiment is provided with a gap adjustment mechanism 24 that adjusts the gaps Δ22a, Δ22b between the water absorbing members 22aa, 22ba and the work roll 4a. This allows the gap adjustment mechanism 24 to adjust the gaps Δ22a, Δ22b between the water-absorbing members 22aa, 22ba and the work roll 4a to 0.2 to 0.8 mm during low-speed rolling immediately after the start of rolling, and to 1.0 to 5.0 mm during high-speed rolling during steady rolling.

[0036] Moreover, the surface defect suppression device 20 according to this embodiment has a plurality of water draining devices 22a, 22b. This can enhance the effect of preventing the droplets W from falling onto the steel sheet S compared to the case where a single water draining device is provided. Moreover, the cold rolling equipment 1 according to this embodiment is provided with a surface defect suppression device 20. With this, by using the surface defect suppression device 20, it is possible to cold roll the steel sheet S in which the occurrence of stains caused by the mixture of the lubricating oil 8a and roll wear powder generated during rolling and roll marks caused by the inclusion of foreign matter are suppressed. In addition, it is possible to cold roll the steel sheet S in which the occurrence of surface defects other than stains, such as roll marks caused by roll wear powder, is suppressed. According to the cold rolling method of this embodiment, the steel sheet S is cold rolled using the cold rolling equipment 1. This makes it possible to cold roll the steel sheet S while suppressing the occurrence of surface defects other than stains, such as stains caused by a mixture of the lubricating oil 8a and roll wear powder generated during rolling, roll marks caused by foreign matter entrapment, and roll marks caused by roll wear powder.

[0037] Although the embodiment of the present invention has been described above, the present invention is not limited to this and various modifications and improvements can be made. For example, the surface defect suppression device 20 has two draining devices, an upper draining device 22a and a lower draining device 22b, but it may have only one of them, or three or more. In addition, in the embodiment, the steel sheet S is cold-rolled as the metal strip, but a metal strip other than the steel sheet S may be cold-rolled. EXAMPLES

[0038] Steel having a composition containing, by mass%, 0.04% C, 0.3% Mn, 0.015% P, 0.015% S, 0.04% SolAl, 0.002% N, and the balance being Fe and unavoidable impurities, was subjected to hot rolling, primary cold rolling, and annealing. Next, in order to verify the effects of the present invention, secondary cold rolling (DR rolling) was performed under the conditions shown in Table 1 using a secondary cold rolling mill (DR rolling mill) consisting of a main reduction stand and a finishing stand.

[0039] All main reduction stands used lubricating oil, the line speed of the steel plate was 10 to 900 mpm, and the conditions of the work roll washing water and the conditions of the water draining device were changed to evaluate the quality of the steel plate. The evaluation items were stains, wear powder roll marks, and roll marks. The evaluation was based on the inclusion rate of each quality defect relative to the total length of the coil, with O: inclusion rate of 0.5% or less, △: inclusion rate of more than 0.5% to 5.0% or less, and ×: inclusion rate of more than 5.0%. The overall evaluation was given as O when stains, wear powder roll marks, and roll marks were all O, × when at least one of them was ×, and △ when none of stains, wear powder roll marks, and roll marks were × but at least one of them was △. The conditions and evaluation results are shown in Table 1.

[0040] [Table 1]

[0041] In Table 1, in Comparative Example 1, there was no spray device for discharging cleaning water for the work roll and no water drainage device, so the stain evaluation was × and the overall evaluation was ×. In Comparative Example 2, cleaning water was ejected from an ejector onto the work roll, but no draining device was provided, and the stain evaluation was ×, resulting in an overall evaluation of ×. In addition, in Comparative Examples 3 and 4, although a sprayer was used to eject washing water for the work roll and a draining device was provided, the tip member of the draining device was made of rubber and was not a water-absorbent material. For this reason, the stain evaluation was △ in Comparative Example 3 and × in Comparative Example 4, and the overall evaluation of Comparative Example 4 was ×. However, in Comparative Example 3, the gap between the tip member and the work roll during low-speed rolling (10 mpm) was 0 mm, and since there was no such gap, the evaluations of the wear powder roll marks and roll marks were ×, and the overall evaluation was ×.

[0042] In Comparative Examples 5 to 8, the sprayer did not eject cleaning water from the work roll, and the stain evaluation was ×, resulting in an overall evaluation of ×. In Comparative Example 5, the gap between the tip member and the work roll during low-speed rolling (10 mpm) was 0 mm, and the evaluations of the wear powder roll marks and roll defects were also ×. In Comparative Example 8, the gap between the tip member and the work roll during low-speed rolling (10 mpm) was 1 mm, and the gap was too large, resulting in an × stain evaluation.

[0043] In Comparative Examples 9 to 12, the work roll was washed with water by an injection device and a draining device was used, but the inclination of the tip member (water-absorbing member) and the inclination member in the draining device was small at 0°. Therefore, the stain evaluation was △ in Comparative Examples 9 to 11 and × in Comparative Example 12. However, in Comparative Example 9, the gap between the tip member and the work roll during low-speed rolling (10 mpm) was 0 mm, and the evaluations of the wear powder roll marks and roll marks were ×, resulting in an overall evaluation of ×. In Comparative Example 12, the gap between the tip member and the work roll during low-speed rolling (10 mpm) was 1 mm, and the gap was too large, resulting in an evaluation of O for the wear powder roll marks and roll marks, but an evaluation of × for stains and ×, resulting in an overall evaluation of ×. In addition, in Comparative Example 13, although a spray device was used to eject washing water for the work roll and a water drainage device was used, the distance between the tip member and the work roll was 0 mm during low-speed rolling (10 mpm), and the evaluations of the wear powder roll marks and roll marks were ×, resulting in an overall evaluation of ×.

[0044] In invention examples 1 and 2, a sprayer is used to eject washing water from the work roll, and a draining device is used, the tip member in the draining device is made of felt (water-absorbent material), and the inclination of the tip member and inclination member is appropriate at 10°. In invention examples 1 and 2, the distance between the tip member and the work roll during low-speed rolling (10 mpm) is appropriate at 0.2 mm and 0.8 mm, respectively, and stains, wear powder roll marks, and roll marks were all rated O, resulting in an overall rating of O.

[0045] On the other hand, in Comparative Example 14, although a spray device was used to eject washing water for the work roll and a water drainage device was provided, the gap between the tip member and the work roll during low-speed rolling (10 mpm) was 1 mm, which was too large, resulting in a stain evaluation of × and an overall evaluation of ×. In Comparative Examples 15 to 19, the sprayer did not eject cleaning water from the work roll, and the stain evaluation was ×, resulting in an overall evaluation of ×. In Comparative Examples 15 and 16, the gap between the tip member and the work roll during high-speed rolling (900 mpm) was 0 mm and 0.5 mm, respectively, and the gap was too small, resulting in an evaluation of × for the roll marks and roll defects caused by wear. In Comparative Example 19, the gap between the tip member and the work roll during high-speed rolling (900 mpm) was 10 mm, resulting in an evaluation of × for the stain, due to the large gap.

[0046] In Comparative Examples 20 to 24, the work roll was washed and drained by an injection device, but the inclination of the tip member (water-absorbing member) and the inclination member in the draining device was small at 0°. Therefore, the stain evaluation was △ in Comparative Examples 20 to 23 and × in Comparative Example 24. However, in Comparative Examples 20 to 21, the interval between the tip member and the work roll during high-speed rolling (90 mpm) was 0 mm and 0.5 mm, respectively, and the interval was small, so the evaluations of the wear powder roll marks and roll marks were ×, and the overall evaluation was ×. In Comparative Example 24, the interval between the tip member and the work roll during high-speed rolling (900 mpm) was 10 mm, and the interval was too large, so the evaluations of the wear powder roll marks and roll marks were O, but the stain evaluation was ×, and the overall evaluation was ×. In Comparative Examples 25 to 26, the work roll was washed with water by an injector and a water drainage device was used, but the gap between the tip member and the work roll was 0 mm and 0.5 mm, respectively, during high-speed rolling (900 mpm), and the gap was small. Therefore, the evaluations of the wear powder roll marks and roll marks were ×, and the overall evaluation was ×.

[0047] In invention examples 3 and 4, a sprayer is used to eject washing water from the work roll, and a draining device is used, the material of the tip member in the draining device is felt (water-absorbent material), and the inclination of the tip member and inclination member is appropriate at 10°. In invention examples 3 and 4, the distance between the tip member and the work roll during high-speed rolling (900 mpm) is appropriate at 1 mm and 5 mm, respectively, and stains, wear powder roll marks, and roll marks were all rated O, resulting in an overall rating of O.

[0048] On the other hand, in Comparative Example 27, although a spray device was used to eject washing water for the work roll and a water drainage device was provided, the gap between the tip member and the work roll during high-speed rolling (900 mpm) was 10 mm, which was too large, resulting in a stain evaluation of × and an overall evaluation of ×.

[0049] As described above, in Examples 1 to 4 of the present invention, the sprayer discharged washing water onto the work rolls, and the draining device drained the water. In addition, the tip member of the draining device was made of a water-absorbing member, and the tip member (water-absorbing member) and the inclination member were inclined at an angle of 10° downward with respect to the rolling direction, and the distance between the tip member (water-absorbing member) and the work rolls was set to an appropriate distance according to the rolling speed. This made it possible to prevent the occurrence of any of the surface defects, such as stains, wear powder roll marks, and roll marks, and good steel sheet quality was obtained. [Explanation of symbols]

[0050] 1. Cold rolling equipment 2 Payoff Reel 3 Bridle Roll 4. Main rolling stand 4a Work roll 4b Backup role 5 Finishing Stand 5a Work Roll 5b Backup role 6 Bridle Roll 7 Tension Reel 8 Lubricant application nozzle 8a Lubricating oil 9 Cobble Guard 10 Separate Cobble Guards 10a Support member 11 Cobble Guard 20. Surface defect suppression device 21 Injection device 22a Upper drainage device 22aa Water-absorbent material 22ab Inclined member 22ac protrusion 22ad Droplet guide 22ae Dish-shaped recess 22af discharge hole 22b Lower drainage device 22ba Water-absorbent material 22bb Inclined member 23a Ejection mechanism 23aa Gutter 23ab Water collection section 23ac downspout 23b Ejection mechanism 24 Spacing adjustment mechanism 25 Injection device W droplet S Steel plate (metal strip)

Claims

1. A surface defect suppression device that is installed on the delivery side of a work roll that cold rolls a metal strip coated with lubricating oil, comprising: an injection device that injects a cleaning liquid toward the work roll from the delivery side of the work roll; a draining device disposed adjacent to the work rolls and the spraying device for preventing droplets containing the lubricating oil, roll wear powder generated during rolling, and the cleaning liquid from falling onto the metal strip, The draining device includes a water-absorbent member that absorbs the droplets, and an inclined member that is inclined from the tip to the opposite end together with the water-absorbent member at an angle of 5 to 15 degrees downward with respect to the rolling direction, The surface defect suppression device is characterized in that the water-absorbing member is arranged at a position where the gap between the water-absorbing member and the work roll is 0.2 to 0.8 mm during low-speed rolling immediately after the start of rolling, and 1.0 to 5.0 mm during high-speed rolling during steady-state rolling.

2. 2. The surface defect suppression device according to claim 1, wherein said inclined member is provided with a discharge mechanism for discharging droplets from said water absorbing member to the outside of said plate path.

3. 3. The surface defect suppression device according to claim 1, further comprising a gap adjustment mechanism for adjusting the gap between the water absorbing member and the work roll.

4. 3. The surface defect suppression device according to claim 1, further comprising a plurality of the water draining devices.

5. A surface defect suppression device as described in claim 3, characterized in that it has a plurality of water drainage devices.

6. A cold rolling facility comprising the surface defect suppression device according to claim 1 or 2.

7. A cold rolling equipment characterized by being equipped with the surface defect suppression device described in claim 3.

8. A cold rolling equipment characterized by being equipped with the surface defect suppression device described in claim 4.

9. A cold rolling equipment characterized by being equipped with the surface defect suppression device described in claim 5.

10. A cold rolling method comprising cold rolling a metal strip using the cold rolling equipment according to claim 6.

11. A cold rolling method comprising cold rolling a metal strip using the cold rolling equipment according to claim 7.

12. A cold rolling method comprising cold rolling a metal strip using the cold rolling equipment according to claim 8.

13. A cold rolling method comprising cold rolling a metal strip using the cold rolling equipment according to claim 9.

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