JP6394913B2 - Metal strip cooling method - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method for cooling a metal strip, and more specifically, to a method for cooling a metal strip in a continuous annealing facility in which the metal strip is levitated with a floater and subjected to continuous heat treatment while being conveyed. is there.

  As a method for continuously transporting a strip-shaped metal such as a hot-rolled steel strip or a cold-rolled steel strip (hereinafter simply referred to as “metal strip”), a method of transporting it in contact with a support such as a roll is often used It has been. However, the roll transport method described above may cause scratches on the metal strip due to contact with the roll, press scratches due to composite oxide deposition (pickup) on the roll surface, peeling of the coating formed on the surface of the metal strip, etc. May be a problem.

  Therefore, a floater device has been developed in which a metal strip is levitated by gas pressure and conveyed in a non-contact state with a support. In particular, in recent years, with the stricter demands on the quality of metal products, especially the appearance quality, the metal belt is lifted by a floater device, etc. There is an increasing expectation for a non-contact type conveyance method that conveys the material in a non-contact manner.

  However, the method of conveying the metal band by floating it with a floater device does not cause frictional force between the metal band and the support, so that the metal band is liable to skid (meander) in the width direction, or sprayed from the floater. There are problems such as the metal band fluttering due to the gas flow, and there are still many problems to be solved in order to stably transport the metal band.

  In addition, one of the means for cooling a metal strip in a continuous annealing furnace is a technique that uses a gas as a cooling medium, for example, a gas jet cooling in which a cooling gas is blown onto the metal strip and cooled by convection heat transfer, There is known a cooling method such as mist cooling in which the formed water is sprayed onto a metal strip and cooled by sensible heat or latent heat of the water.

  In this regard, since the floater device uses a jet of gas having a high heat transfer coefficient to levitate the metal strip, the high temperature gas or the cooling gas is used as the gas while Heating and cooling can also be performed efficiently. However, as described above, there is a problem that the metal band is likely to buckle and deform due to thermal contraction during cooling because the restraining force on the metal band does not work as in the case of roll conveyance.

  As a technique for preventing buckling deformation at the time of transporting a metal strip, for example, in Patent Document 1, when a steel strip after heating is levitated and transported in a continuous annealing furnace, the heated gas is conveyed inside the curved portion of the steel strip A technique for preventing the occurrence of buckling deformation of a steel strip by spraying on the steel is disclosed. Patent Document 2 discloses a technique for preventing the drawing of a steel sheet by heating the steel sheet in advance and generating one wrinkle in the width direction of the steel sheet when rapidly heating the steel sheet. . However, these techniques are techniques for preventing buckling deformation when the metal strip is heated, and are not applicable to cooling.

  Further, in Patent Document 3, a metal band plate drawing (wrinkle-like defect) generated when a metal band is heat-treated using a horizontal (horizontal) heat treatment furnace, local plate temperature fluctuation in the metal band traveling direction is disclosed. There is disclosed a technique for preventing the amount by controlling the amount to less than the limit plate temperature fluctuation amount at which thermal deformation occurs. However, although this technique can also be applied to cooling, there is a problem that the cooling rate is limited in order to suppress plate temperature fluctuations.

  Moreover, in patent document 4, when manufacturing a high intensity | strength cold-rolled steel plate by a water quenching process, the spray nozzle which injects a cooling water is arrange | positioned or arrange | positioned many at the plate width end part side, and from the plate width direction edge part of a steel plate. By forming a temperature distribution that increases the steel plate temperature toward the center in the plate width direction and then immersing it in cooling water, the steel plate is deformed into a plurality of streaks (waves) in the plate width direction. Techniques for preventing this are disclosed.

Japanese Patent Laid-Open No. 08-092659 JP 2013-043772 A JP 2002-069536 A JP 2012-177145 A

  However, in a continuous annealing facility using a floater as a transfer facility or a heating / cooling facility, changing the shape of the injection port of the cooling floater as in the technique of the above-mentioned Patent Document 4 will hinder the stable passage of the steel plate. It is not preferable because it comes. For example, stable levitation cannot be achieved by injecting gas only to both width ends of the metal strip. In addition, when the steel plate end is cooled in front of the floater, if it is cooled to the dark clouds, the C warp (width direction warp) of the metal strip becomes large, the levitation of the metal strip is not stable, and the meander is large on the contrary There is a big problem in the plate passing property, such as the contact with the floater frequently occurs.

  The present invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to inject a gas from a floater to float the metal strip and continuously heat-treat the metal strip while being conveyed. Then, when cooling, it is to propose a method for cooling the metal band that not only stably conveys the metal band but also effectively prevents shape defects such as a restriction during cooling.

  The inventors have intensively studied to solve the above problems. As a result, it is possible to effectively prevent throttling of the metal band by performing pre-cooling that cools both width ends of the metal band before the main cooling that cools the metal band while floating and transporting with a floater. As a result, the present invention has been developed.

  That is, the present invention relates to a method for cooling a metal strip in a continuous annealing facility in which a metal strip is levitated with a floater and continuously subjected to heat treatment while being conveyed, and then the width of the metal strip is set to W [mm] When the difference between the maximum temperature at the central portion of the band and the minimum temperature at both width ends is ΔT [° C.], the ratio of ΔT to W (ΔT / W) is in the range of 0.01 to 0.16. A cooling method for a metal strip, characterized by pre-cooling both ends of the metal strip before cooling with a floater. Here, the minimum temperature of both width end portions means the average temperature of the minimum temperatures of both width end portions.

  The method for cooling the metal strip according to the present invention is characterized in that both end portions of the metal strip are precooled so that the (ΔT / W) is in the range of 0.03 to 0.15.

  The metal band cooling method of the present invention is characterized in that the preceding cooling of both ends of the metal band is performed by a gas jet method in which a cooling gas is injected from a nozzle.

  Moreover, the cooling method of the said metal strip of this invention uses the gas which cooled the atmospheric gas in an annealing furnace as the said cooling gas.

  According to the present invention, in a continuous annealing facility in which a metal strip is floated by a floater and continuously heat-treated while being transported, when the metal strip is cooled by a floater, both width ends of the metal strip are preceded and cooled in advance. As a result, not only can the metal band be transported stably, but also the convex buckling deformation at the center of the metal band width direction that accompanies rapid cooling can be suppressed, improving the productivity and quality of the metal band product. Greatly contributes to.

It is a figure explaining the continuous annealing equipment which has a floater, (a) is a side view, (b) is a top view. It is a figure explaining the mechanism in which the meandering correction force generate | occur | produces with a floater. It is a figure explaining the convex buckling deformation which generate | occur | produces in the width | variety center part of a metal strip. It is a figure explaining the reason that meandering correction force does not arise when C curvature occurs in a metal belt. It is a figure explaining the continuous annealing equipment which has the floater used for this invention, (a) is a side view, (b) is a top view.

The present invention will be described below.
FIG. 1 shows that heat is continuously applied to a metal band while the metal band 1 is lifted and conveyed by injecting a gas from a floater 2 (2a, 2b) installed below the metal band 1 toward the lower surface of the metal band 1. This figure shows the soaking zone and the cooling zone in the continuous annealing facility. In addition, 3 in a figure is the furnace wall which divides a soaking zone and a cooling zone of a continuous annealing equipment.

  Gas is supplied into the inside of the floater 2 from a blower (not shown) or the like, and is maintained at a pressure higher than the ambient pressure. On the upper surface of the floater 2, two nozzles 4 are provided in the direction perpendicular to the metal band traveling direction so that the gas injection directions are opposed to each other. By injecting gas from the two nozzles 4 toward the lower surface of the metal band 1, a static pressure is generated between the metal band 1 and the upper surface of the floater 2, and the metal band 1 is conveyed while floating. . In addition, side plates 5 having a height substantially the same as the flying height of the metal band are provided at both width ends of the upper surface of the floater 2 in parallel with the metal band traveling method.

  The principle by which the metal strip 1 can be stably conveyed without meandering by the floater 2 will be described with reference to FIG. FIG. 2 shows a state in which the metal band 1 floating on the upper surface of the floater meanders on one side (left side in FIG. 2) in the cross-sectional view of the floater 2 in the metal band traveling direction. If the metal band 1 meanders, the space between the side plate 5 on the meandering side and the metal band 1 becomes narrow, so that the static pressure generated on the lower surface of the metal band in this part increases. As a result, the flying height (flying height) of the metal strip 1 increases on the meandering side, and the metal strip 1 is inclined. The static pressure acting on the lower surface of the metal band acts in a direction perpendicular to the lower surface of the metal band. Therefore, when the above force is divided into a vertical force and a horizontal force, the vertical force acts as a levitation force that supports the weight of the metal strip 1, and the horizontal force is a force in a direction opposite to the meandering direction, that is, It can be seen that this works as a correction force to correct the meandering of the metal strip 1. For this reason, in the floater 2, the correction force automatically works even if the metal band 1 meanders, and therefore the metal band 1 can be stably conveyed without continuing to meander.

  The floater 2 not only floats and conveys the metal strip by the gas jetted from the nozzle provided on the upper surface of the floater, but also heats the metal strip by using the jetted gas as a high-temperature gas or a cooling gas. Or can be cooled. For example, the floater 2a shown in FIG. 1 has a floating function and a heating function, and the floater 2b has a floating function and a cooling function for a metal strip.

  By the way, in the floater 2b which has the said cooling function, a metal strip is rapidly cooled with the low temperature cooling gas injected from the nozzle of the upper surface of a floater. At that time, buckling deformation called “drawing” or “heat buckle” may occur in the metal strip. This is because the compressive stress acts on the higher temperature side, that is, the central portion of the width of the metal band on the upstream side of the cooling zone due to the width contraction due to the rapid temperature drop of the metal band. When the metal strip and the transport roll are in contact with each other as in roll transport, the friction force obtained by multiplying the contact surface pressure between the metal strip and the roll due to its own weight and tension by the friction coefficient becomes the restraining force, and the buckling is performed. Deformation is suppressed to some extent. However, since the restraint force is not generated in the floater conveyance, it easily buckles and causes buckling deformation with a convex cross section as shown in FIG.

  Therefore, the inventors have repeatedly studied a method for suppressing the convex buckling deformation, focusing on the cooling condition of the metal strip. As a result, before the metal strip is actually cooled with the floater, both ends of the width of the metal strip are cooled in advance, and both ends of the width of the metal strip are cooled at a lower temperature than the center of the width of the metal strip. The present inventors have found that a metal band with good appearance quality can be produced by suppressing convex buckling deformation at the center of the width at the time. The reason for this is considered to be that the plate width end portion is a free end, and therefore, even when contracted by cooling, the deformation of the steel plate is hardly affected.

  However, if an excessive temperature difference is applied between the width center portion of the metal strip and the width end portions, as shown in FIG. 4, a large C warp occurs in the width direction of the metal strip. It has also been found that it is difficult to transport the metal strip stably. As shown in FIG. 4, when a large upward C-warp occurs in the metal band, the static pressure generated between the lower surface of the metal band and the upper surface of the floater becomes unstable. The metal band comes into contact with the floater and scratches are generated. Also, if a large upward C-warp occurs in the metal band, the gap between the side plate on the meandering side and the metal band does not become narrow when the meandering occurs, so the ability to correct the meander by tilting the metal band decreases. is there.

  As described above, in order to prevent buckling deformation at the center of the width of the metal strip, which occurs during rapid cooling with the floater, cool both width ends of the metal strip in advance before the main cooling with the floater. However, it is effective to provide a temperature difference between the width center portion and both width end portions of the metal strip, while maintaining the flatness of the metal strip and realizing stable conveyance is excessive. It has been found that the application of a temperature difference is not preferable.

  Therefore, the inventors studied the pre-cooling condition for ensuring both the suppression of the buckling deformation and the stable conveyance. As a result, when the temperature difference between the temperature at the center in the width direction of the metal strip and the lowest temperature at both ends is ΔT [° C.] and the width of the metal strip is W [mm], the ratio of ΔT to W It has been found that by controlling (/ W) within the range of 0.01 to 0.16, convex buckling deformation can be suppressed and stable conveyance can be achieved. Here, the minimum temperature of both width end portions means the average temperature of the minimum temperatures of both width end portions. Further, the positions of both width end portions are positions on the inside of 1/10 the plate width from the plate width end portion. When (ΔT / W) is less than 0.01, the effect of suppressing the convex buckling deformation is small. On the other hand, when (ΔT / W) exceeds 0.16, the C warp (upward warp) increases, and the floater Makes it difficult to stably transport the product. Preferred (ΔT / W) is in the range of 0.03 to 0.15.

  Here, the reason why the condition (ΔT / W) for determining the critical condition for the convex buckling deformation of the metal band does not include the thickness of the metal band and the Young's modulus as parameters is as follows. I am thinking. The compressive stress that causes convex buckling deformation at the center of the width of the metal strip on the high temperature side, that is, the upstream side of the cooling zone, is a thermal stress caused by width shrinkage due to a temperature drop in the longitudinal direction of the metal strip. On the other hand, the thermal stress is also caused by the temperature difference ΔT in the metal band width direction applied to suppress the convex buckling deformation. The plate thickness and Young's modulus that affect both thermal stresses are the same and can be dimensionally discarded. Therefore, the above critical condition can be determined by the temperature difference ΔT and the width W of the metal strip.

  Here, as shown in FIG. 5, as a method for pre-cooling the both ends of the metal strip before the main cooling of the metal strip with the floater as described above, a pre-cooling facility is provided at the front stage of the floater 2b. It is preferable to cool the both ends of the metal strip by providing. In addition, in FIG. 5, although the example which provided the prior cooling equipment in the soaking zone was shown, you may provide in the cooling zone side.

  As a pre-cooling means for the metal strip in the equipment using the floater, since it is necessary to perform the contact without contacting the metal strip, a cooling medium is jetted from the nozzle and cooled, for example, gas jet cooling or mist cooling is used. desirable. However, since mist cooling uses water as a cooling medium, the steel plate surface is oxidized. Therefore, it is preferable to employ gas jet cooling when oxidation of the steel sheet surface is not desirable.

  In the preceding cooling, when the plate thickness is large (for example, 1 mm or more), if only the upper surface or the lower surface of the metal strip is cooled, the metal strip will cause a shape defect if there is a difference in the cooling rate between the front and back surfaces. Since it may be difficult to stably convey, it is preferable to cool the upper and lower surfaces of the metal strip evenly.

  Moreover, it is preferable that the range which cools both said width | variety edge parts shall be the range of (0.1-0.4) * W with respect to the width W of a metal strip on one side. This is because if the temperature is less than 0.1 times the plate width, the buckling deformation prevention effect is small even if the temperature difference ΔT is provided. Moreover, since it will become difficult to attach a temperature difference when it exceeds 0.4 times the board width, the buckling deformation prevention effect becomes small.

  Moreover, it is preferable to use non-oxidizing gas, for example, nitrogen, hydrogen, argon etc., from a viewpoint of preventing the oxidation of the metal strip surface as the cooling gas. However, the gas is expensive and causes an increase in manufacturing cost. Therefore, it is preferable to cool the non-oxidizing furnace atmosphere gas being circulated and use it as a cooling gas. The temperature of the cooling gas is desirably lower than the ambient temperature.

In a continuous annealing facility in which a metal strip is levitated by the floater shown in FIG. 5 and continuously heat-treated while being conveyed, cold-rolled steel strips having various plate thicknesses and plate widths shown in Table 1 are 100 m / s. After performing heat treatment while passing through the plate at a speed, when rapidly cooling with the floater 2b, the both ends of the cold-rolled steel strip are precooled with a precooling device installed in the previous stage of the floater 2b. A temperature difference ΔT shown in Table 1 was given in the plate width direction, and the height of buckling deformation at the center of the width generated in the floater 2b, the size of meandering, and the presence or absence of scratches were evaluated.
Here, the floater in the above-mentioned continuous annealing equipment has a length of 1.5 m, the distance between the floaters 2 a and 2 b is 9 m between the floater centers, and the pressure of the cooling gas supplied into the floater 2 b is the plate thickness, It adjusted suitably in the range of 0.5-1.0 kPa according to the cooling rate and the flying height. Moreover, the furnace temperature in the cooling zone in which the floater 2b was installed was appropriately adjusted within a range of 500 to 800 ° C. in order to change the cooling rate.
In addition, the pre-cooling device installed on the soaking side of the tropical zone adopts a gas jet method in which cooling gas is injected onto the steel strip surface from slit nozzles installed above and below the steel strip. The length of the pre-cooling device is 4 m, and 11 slit nozzles having an opening width of 10 mm are arranged at intervals of 400 mm in the traveling direction of the steel strip. The cooling gas sprayed from the nozzle uses a soaked atmosphere gas inside the furnace, the nozzle header pressure is over 0 kPa and below 5 kPa, and the distance between the upper and lower slit nozzles and the steel strip is about 100 mm. Was set to be. In addition, the installation position in the width direction of the pre-cooling equipment is variable according to the fluctuation of the steel strip width and the amount of meandering, so that the pre-cooling is always performed in a range of 200 mm from both width ends of the steel strip to the width central portion side. I made it.

Here, the temperature difference ΔT in the steel strip width direction is obtained by using a contact-type thermometer, the steel strip width central portion immediately before the cooling zone entry side, and 1/10 inside the plate width from both ends of the steel strip. The plate temperature was measured, and the difference between the average temperature and the center temperature of the lowest temperatures at both width ends was determined as ΔT.
The height of the convex part of the buckling deformation that occurred in the central part of the steel strip width was measured with a laser displacement meter on a platen by shearing the coil on the exit side of the annealing equipment and collecting a sample.
The meandering amount is measured by detecting the end of the steel strip using a two-dimensional laser sensor on the exit side of the cooling zone, and the maximum meandering amount is 50 mm or less. A value exceeding 50 mm was evaluated as a meandering prevention defect (x). The plate passing time per condition was set to 30 minutes or longer so that the maximum amount of meandering can be sufficiently measured in consideration of the meandering frequency.
Further, the occurrence of scratches was determined by visually inspecting the surface of the steel sheet under a sufficiently bright fluorescent lamp on the exit side of the continuous annealing equipment, and determining the presence or absence from the traces in contact with the floater.

  The results of the above experiment are also shown in Table 1. From this result, under the conditions suitable for the present invention, the height of the convex part due to buckling deformation at the central part of the steel strip width can be suppressed to 1.7 mm or less, and the meandering amount does not exceed 50 mm. Moreover, it can be seen that the steel strip can be stably conveyed without generation of scratches. On the other hand, in the condition outside the scope of the present invention, the height of the convex portion due to buckling deformation at the central portion of the steel strip width is 2.0 mm or more, or the meandering amount exceeds 50 mm, and It can be seen that scratches due to unstable floating occurred and stable conveyance was not possible.

  In the said Example, although the example which used the steel strip whose thickness is 0.35 and 0.50 mm was shown as a metal strip, the technique of this invention is not limited to the said steel strip, It may be of a size and can also be applied to other metal bands such as stainless steel and aluminum.

1: Metal strip (steel strip)
2: Floater 3: Slit nozzle 4: Furnace wall between soaking zone and cooling zone 5: Side plate 6: Advance cooling device

Claims (4)

In the method of cooling a metal strip in a continuous annealing facility that is cooled after the metal strip is levitated with a floater and continuously subjected to heat treatment while being conveyed,
The width of the metal strip W [mm], and temperature of the width center portion of the cooling zone inlet side just before the metal strip, the difference between the average value of the temperature of both width ends of the same time was set to [Delta] T [° C.] In this case, the metal band is characterized by precooling both ends of the metal band before cooling with a floater so that the ratio of ΔT to W (ΔT / W) is in the range of 0.01 to 0.16. Cooling method . 2. The metal band cooling method according to claim 1, wherein both end portions of the metal band are precooled so that the ([Delta] T / W) is in a range of 0.03 to 0.15. The metal band cooling method according to claim 1 or 2, wherein the preceding cooling of both ends of the metal band is performed by a gas jet method in which a cooling gas is injected from a nozzle. The method for cooling a metal strip according to claim 3, wherein a gas obtained by cooling an atmospheric gas in an annealing furnace is used as the cooling gas.

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