JP5928412B2 - Steel plate vertical cooling device and method for producing hot dip galvanized steel plate using the same - Google Patents

Description

  The present invention relates to a steel plate vertical cooling apparatus and a method for producing a hot-dip galvanized steel sheet using the same.

  When a steel sheet having a yield point elongation such as a BH steel sheet (baking hardening type steel sheet) is used as a plating base plate and a hot dip galvanized steel sheet is manufactured in a continuous hot dip galvanizing facility, the product has defects such as stretcher strain and hip breakage. May occur.

  On the other hand, as a technique for preventing hip breakage, Patent Document 1 discloses a technique for applying a strain in advance before hip breakage occurs. In addition, as a technique for preventing stretcher strain generated in the forming process in the process of using a hot-dip galvanized steel sheet, for example, many techniques related to temper rolling after plating and material design have been disclosed (Patent Document 2). 3).

  Here, in the continuous hot dip galvanizing equipment, the steel sheet is immersed in a hot dip galvanizing bath and then pulled up, and after the amount of adhesion is controlled by gas wiping, it is cooled as it is or after it is heated and alloyed. Is done. As a cooling method after the plating treatment, mist cooling or gas cooling is generally used, but a mist cooling method having a high cooling capacity is often selected in order to efficiently perform cooling with a short equipment length.

  In Patent Document 4, for the purpose of preventing water droplet leakage from the lower part of the mist cooling box, the air supply pad at the bottom of the mist cooling box is adjacent to two types of high pressure and low pressure, and the water receiving pan is arranged at a predetermined position. And the cooling method which makes the wind speed of the updraft from an air supply pad 20 m / s or more is disclosed.

  In general, a hot-dip galvanized steel sheet manufactured has a plate width exceeding 1000 mm, and the maximum plate width may approach 1900 mm, so that quality uniformity in the width direction is required. In the case of steel plates, the material / shape changes often occur due to temperature changes such as heating / cooling as described above, so the uniformity of heating / cooling in the plate width direction is an important requirement. The control is not easy. In particular, in steel sheets that yield at a yield point below 500 ° C, such as 340BH steel sheets, there is a high possibility that stretcher strain will occur in the cooling process after hot dip galvanizing, and temperature control in the sheet width direction is particularly important. It is.

JP 2004-107682 A JP-A-4-323345 JP 2007-327104 A JP 2000-73125 A

  According to the method described in Patent Document 1, it is necessary to bend and unbend the steel strip in the sheet with a roll, and in that case, wrinkles may occur on the roll and transfer to the steel sheet may occur. . In addition, since the yield elongation of the material does not completely disappear, it was found that if temperature irregularities occur in the steel strip during cooling after the subsequent alloying, stretcher strain is eventually generated.

  Similarly, even when the methods described in Patent Documents 2 and 3 are used, it has been found that if temperature unevenness occurs in the steel strip during cooling after alloying, the occurrence of stretcher strain cannot be avoided.

  In addition, the method described in Patent Document 4 can certainly prevent water droplet leakage from the lower part of the mist cooling box, but is less effective for water droplet retention in the box, and is not effective in preventing the occurrence of stretcher strain. It is enough.

  Thus, conventionally, for example, when hot-dip galvanizing a steel sheet having a yield point elongation in a continuous hot-dip galvanizing equipment, the stretcher in the continuous hot-dip galvanizing equipment, particularly in the cooling process after hot-dip galvanizing. Strain generation could not be prevented properly.

  The present invention solves the above-mentioned problems, and in a continuous hot dip galvanizing facility, even after hot dip galvanizing a steel sheet having a yield point elongation such as a BH steel sheet, cooling after hot dip galvanizing is performed. It is an object of the present invention to provide a saddle type cooling apparatus capable of appropriately preventing the generation of stretcher strain in the process and a method for producing a hot dip galvanized steel sheet using the same.

  The present inventors made the mist supplied in the cooling device into droplets and remained without being discharged out of the box, and the droplets aggregated and reattached to the steel sheet due to slight disturbance of the plate shape, etc. It has been found that stretcher strain occurs when local supercooling occurs only in part of the direction. It has also been found that the above problem can be solved by providing a discharge port for discharging droplets and setting the interval between the nozzle headers in the cooling device to a predetermined interval.

The present invention is based on the above findings, and features are as follows.
[1] Nozzle header provided with a box having upper and lower openings and a steel plate traveling upward or downward inside, and a plurality of spray nozzles arranged in the longitudinal and / or width direction of the steel plate for spraying water mist onto the steel plate And a steel plate vertical cooling device comprising a sealing mechanism for preventing water leakage from the lower opening, and a discharge port for discharging droplets in the box, the nozzle headers having an opening area ratio A vertical cooling apparatus for steel sheets, which is spaced apart so as to have a discharge gap of 30% or more.
The opening area ratio is a ratio of the total area of the gap between the nozzle headers in the cross-sectional area formed by the nozzle header and the box on one side viewed from the steel plate side and the box area (between the nozzle headers). This is a value obtained by (total area of gap / box area) × 100.
[2] The steel plate vertical cooling apparatus according to [1], wherein the interval between the nozzle headers is formed by dividing the nozzle header in a longitudinal direction of the steel plate.
[3] The steel plate vertical cooling apparatus according to [1] or [2], wherein the interval between the nozzle headers is formed by dividing the nozzle header in the steel plate width direction.
[4] The vertical cooling apparatus for steel sheets according to any one of [1] to [3], wherein the discharge port is divided into three or more in the steel sheet width direction.
[5] A method for producing a hot-dip galvanized steel sheet, comprising producing a hot-dip galvanized steel sheet using the vertical cooling apparatus for a steel sheet according to any one of [1] to [4].

According to the present invention, even when a steel sheet having a yield point elongation such as a BH steel sheet is hot dip galvanized, it is possible to appropriately prevent the occurrence of stretcher strain in the cooling process after the hot dip galvanizing process. Can do.
By using the vertical cooling device of the present invention, for example, even when cooling in a region where the steel plate temperature is 300 to 500 ° C., the occurrence of quality defects due to uneven cooling is prevented, and a steel plate with good quality is manufactured. be able to.

It is a figure which shows typically the continuous hot-dip galvanization equipment of this invention. It is the schematic which shows an example of the vertical cooling device of this invention. It is the schematic which shows an example of the vertical cooling device of this invention. It is a figure which shows the relationship between local resistance coefficient (zeta) and opening area ratio. It is a figure which shows the cooling characteristic of water mist by the relationship between steel plate temperature and cooling capacity. It is a figure which shows the nozzle header division example of this invention.

  Hereinafter, the present invention will be specifically described.

  FIG. 1 schematically shows one embodiment of the present invention, and is a diagram (a diagram showing a side view of the facility) for explaining the entire continuous hot dip galvanizing facility. In FIG. 1, 1 is a hot dip galvanizing bath, 2 is a sink roll, 3 is an alloying treatment device, 4 is a vertical cooling device (mist cooling device), 5 is a gas wiping nozzle, and 6 is a (scanning radiation) thermometer. , 7 is a support roll in the bath, 8 is a support roll on the bath, and S is a steel plate. In the continuous hot dip galvanizing equipment, after the steel sheet S is annealed (not shown), it is immersed in a hot dip galvanizing bath 1 and subjected to hot dip galvanizing treatment, and the amount of adhesion is controlled by the gas wiping nozzle 5. Next, the alloying treatment device 3 performs the alloying treatment, or without performing the alloying treatment, the surface of the plated steel sheet is cooled by spraying water mist with a vertical cooling device (mist cooling device) 4. A hot-dip galvanized steel sheet is produced.

  2 and 3 are schematic views of the vertical cooling device (mist cooling device) 4 of the present invention. Nozzle header 9 having an opening in the upper and lower sides, a steel plate traveling upward or downward inside, a box 15 divided into two, and a plurality of spray nozzles 10 arranged in the steel plate width direction for spraying water mist onto the steel plate. And a sealing device 14, a droplet leakage preventing device 11, and a discharge port 13 for discharging droplets in the box 15 as a sealing mechanism for preventing water leakage from the lower opening. Furthermore, a water receiving pan 12 that receives the mist (droplets) supplied into the vertical cooling device (mist cooling device) 4 is provided.

  When water mist is sprayed from the spray nozzle 10 onto the steel plate S, the water mist collides with the steel plate S and evaporates or rebounds and is collected from the discharge port 13. The liquid droplets that are condensed by contact with the inner wall of the mist cooling device 4 or the nozzle header 9 flow downward and are collected by the water receiving pan 12. A sealing device 14 and a droplet leakage preventing device 11 are provided at the bottom of the mist cooling device 4 as a sealing mechanism for preventing water leakage to the lower portion. For example, examples of the sealing device 14 include a static pressure pad that forms a pressure pool on the steel plate surface. However, the sealing device is not limited to this form. The droplet leakage prevention device 11 is a gas nozzle that forms an upward flow near the steel plate.

  Further, in the present invention, the nozzle headers 9 are spaced apart so as to have a discharge gap having an opening area ratio of 30% or more. As described above, in the vertical cooling device of the present invention, the nozzle headers 9 are spaced apart from each other, so that there is a discharge gap between the nozzle headers 9. As a result, the mist (droplet) supplied into the cooling device is discharged without staying in the box 15, and it is possible to appropriately prevent the occurrence of stretcher strain in the cooling process after the hot dip galvanizing process.

  A gas flow of 1 to 50 m / sec is usually generated in the box by the water mist injection and the discharging mechanism from the box. If the area of the gap between the nozzle headers, that is, the opening area is narrow, pressure loss occurs and it becomes difficult to discharge gas and droplets. Here, the pressure loss ΔP is generally expressed by the following formula (1) (for example, Maruzen “Duct Design and Construction Manual” P.34).

  The smaller the local resistance coefficient ζ, the better the discharge performance. Therefore, the relationship between the local resistance coefficient ζ and the opening area ratio of the gap between the nozzle header 9 was investigated. The opening area ratio is the ratio of the total area of the gap between the nozzle headers and the box area in the cross-sectional area formed by the nozzle header and the box on one side viewed from the steel plate side, and (the gap between the nozzle headers) (Total area / box area) × 100. The obtained results are shown in FIG. From FIG. 4, the local resistance coefficient ζ is smaller as the opening area ratio is larger. Moreover, it turns out that it falls large from 20% to 30%. Therefore, in actuality, when the aperture area ratio is 30% and the water mist having a particle diameter of 300 μm or less is cooled with the same nozzle arrangement and water amount conditions as those of the examples described later, it is understood that almost 100% of the droplets can be discharged. It was. Therefore, the opening area ratio is set to 30% or more. The opening area ratio can be adjusted by moving the nozzle header in the longitudinal or width direction or removing the nozzle header.

  The pitch between the spray nozzles 10 is preferably arranged so that a uniform amount of water can be sprayed onto the steel sheet in the width direction of the steel sheet. For example, the spread angle of droplets when spraying water mist with only the spray nozzle 10 is investigated in advance, and in the width direction in consideration of the overlapping state of water mist injection when a plurality of spray nozzles 10 are installed. The spray nozzle 10 can be arranged so that an appropriate amount of water can be sprayed onto the steel plate. By arranging in this way, uneven cooling can be avoided.

  Moreover, it is preferable that the position of the spray header 10 in the nozzle header width direction is shifted from the adjacent nozzle header by about 1/2 to 1/5 of the pitch of the spray nozzle 10 in the width direction. By arranging in this way, it becomes possible to uniformly cool the width direction by colliding the cooling water uniformly with the continuously passing steel plate.

  Specifically, the steel plate vertical cooling apparatus is installed in a continuous hot dip galvanizing line or the like as described above. As a steel plate size to be produced, it is necessary to correspond to a width of about 2 m. Since the water mist which collided with the steel plate is easily discharged from the steel plate edge portion, it is desirable that the discharge port 13 is divided into three or more in the width direction so that the discharge amount can be adjusted respectively. For example, in the case of dividing into three equally in the width direction, it is particularly preferable that the discharge amount at the central portion of the plate width is set larger than the discharge amount at the edge portion of the plate width. By setting the discharge amount at the center of the plate width to be larger than the discharge amount at the plate width edge portion, the mist droplet is prevented from being biased toward the plate width edge, and the droplet stays at the plate width edge in the box. Local supercooling can be prevented from occurring due to reattachment to the steel sheet. In addition, it is possible to provide a fan for discharging, and one fan may be provided for each outlet. One box is used to suck the entire box, and each outlet has a damper. It is also possible to change the format.

  Here, it is generally known that the water boiling phenomenon as shown in FIG. 5 is related to the cooling characteristics of water mist cooling (for example, “Forced Cooling of Steels of Japan Iron and Steel Institute” p. 47). If the water mist cooling is within the film boiling region, the cooling ability is almost constant regardless of the steel plate temperature. However, when the steel plate temperature is lowered to the transition boiling region, the cooling capability is increased as the steel plate temperature is lower, and the temperature difference in the plate width direction is easily increased. In particular, if there is heating unevenness before cooling, the plate width direction temperature deviation before cooling will increase several times after cooling. Therefore, from FIG. 5, it is preferable that the water mist cooling is performed in the film boiling region. However, the temperature range in which the present invention actually cools is 200 to 500 ° C. Although the transition temperature at which transition boiling transitions varies depending on the amount of water, in the case of water mist, it is 200 to 500 ° C., and the temperature range targeted by the present invention and the transition boiling region overlap. From this point, water volume control is very important.

  In addition, the inventors used the continuous hot dip galvanizing facility in FIG. 1 and the vertical cooling apparatus in FIG. 2 to perform the same plating treatment (cooling) as in the examples on the same steel sheet as in the examples described later. And examined the cause of temperature deviation in the width direction. The amount of fluctuation of the amount of water sprayed from the spray nozzle 10 was within ± 10% in the width direction. As a result, even though the amount of water sprayed from the spray nozzle 10 is sprayed in a well-balanced state within ± 10% in the width direction, monitoring with the thermometer 6 on the cooling zone exit side causes unevenness in the width direction (generally temperature) It was found that a difference of 50 ° C. or more) occurred and a stretcher strain quality defect might occur.

  And when a temperature difference arises in the width direction, the droplets ejected from the spray nozzle 10 remain in the vertical cooling device 4 without being quickly discharged and agglomerate in part, so that the amount of water has increased. And local supercooling occurs.

  From the above points, in order to improve the discharge property of the droplets, it is desirable that there is a sufficiently wide flow path to the discharge port and the liquid is discharged quickly. However, even if the tip of the spray nozzle 10 is small, the nozzle header 9 needs to have a large internal cross-sectional area in order to ensure the uniformity of the amount of water in the width direction and the amount of air, and the nozzle header 9 is large. I have to be. When the nozzle header 9 is enlarged, there is no way for droplets and gas to escape. On the other hand, if the space between the nozzle headers 9 is made larger than necessary, the droplet discharge performance and the gas discharge performance are improved, but the cooling capacity is lowered, so that the equipment length is increased. Therefore, in the present invention, it is preferable that the nozzle header 9 is divided, and the interval between the nozzle headers 9 is formed by dividing the nozzle header in the steel plate longitudinal direction and / or the steel plate width direction. To do. As a dividing method, a method of dividing in the longitudinal direction, that is, a method of using one column in the width direction as one header as shown in FIG. 6A, a method of dividing in the width direction and the longitudinal direction, that is, FIG. For example, as shown in b), one header is used for several widths and lengths. By opening a gap between the nozzle headers 9, the discharge opening area can be increased. Note that the header dividing method is not limited to that shown in FIG. 6, and various combinations are conceivable depending on the cooling capacity adjustment method in the width direction and the longitudinal direction or restrictions on the equipment. By dividing the nozzle header 9, the droplets ejected from the spray nozzle 10 are quickly discharged, and local overcooling can be prevented.

  A hot-dip galvanized steel sheet is manufactured using the vertical cooling apparatus for steel sheets according to the present invention. Specifically, after the steel sheet is continuously annealed, it is immersed in a hot dip galvanizing bath, and after adjusting the zinc adhesion amount with a gas wiping nozzle, it is heated and alloyed by an alloying treatment device as necessary, and thereafter The steel plate is cooled by the vertical cooling device of the present invention.

A component composition consisting of C: 0.001%, Si: 0.12%, Mn: 0.8%, P: 0.020%, S: 0.005%, the balance Fe and inevitable impurities. A steel sheet having a thickness of 0.65 mm and a tensile strength TS of 340 MPa was used as a raw steel sheet, and a hot dip galvanized steel sheet was manufactured using the continuous hot dip galvanizing equipment shown in FIG. In a continuous galvanizing line, after continuous annealing a steel sheet was immersed in a galvanizing bath 1 bath temperature 470 ° C., was adjusted so that the zinc deposition amount of 45 g / m ² by gas wiping nozzle 5, The alloying treatment device 3 was heated to 520 ° C. for alloying treatment, and then the mist cooling device 4 was cooled to 300 ° C. In an off-line cooling experiment in which there is no bias or stagnation of cooling water, the amount of water is such that no transition boiling occurs.

  In the example of the present invention, an infrared thermography (not shown) was installed at the exit side position of the mist cooling device 4. Further, water mist mixed with water and air is used as a refrigerant, and as the spray nozzle 10, flat spray nozzles are provided at nine locations at intervals of 200 mm in the width direction of the steel sheet, and the amount of water mist injection from each nozzle is set as the cooling water flow rate. It was made possible to control by adjusting the amount of cooling water by a regulating valve (not shown). On the other hand, the cooling air for water mist was always injected at a constant pressure (50 kPa at each pipe header portion). In addition, the spray nozzle 10 is arrange | positioned by 200 mm from a steel plate to a nozzle injection port so that the spray nozzle 10 which adjoins in the steel plate advancing direction (steel plate longitudinal direction) at intervals of 200 mm, and the adjacent spray nozzle 10 may shift | deviate 50 mm at a time in the width direction. In addition, when it is difficult to install a flow meter in each spray nozzle 10, the coolant injection nozzle group is divided into a plurality of zones in a row unit in the steel plate traveling direction, and the cooling water amount for each zone is measured. Can grasp the relationship between the flow rate immediately before the refrigerant injection nozzle, the flow rate adjustment valve opening degree, and the pipe pressure in advance, and can always manage the flow rate adjustment valve opening degree and the pipe pressure so as to be managed under appropriate conditions. The exhaust capacity of the blower for discharging the water mist was selected to be larger than the total amount of cooling air and cooling water, and the discharge port in the box was divided into three in the width direction. The width of the discharge port was 1100 mm at the center and 550 mm on both sides. Table 1 shows conditions such as the header type and the opening area ratio.

  On the other hand, the comparative example is an example in which the number of nozzles and the amount of water are the same as those of the present invention example, and the opening area ratio is 24%.

  In the example of the present invention, a uniform temperature distribution was realized, and a steel plate free from stretcher strain could be manufactured. On the other hand, in the comparative example, since the discharge of mist droplets was poor, local supercooling occurred, and stretcher strain occurred during the subsequent press working.

1 molten zinc bath 2 sink roll 3 alloying treatment device 4 vertical cooling device (mist cooling device)
Reference Signs List 5 Gas wiping nozzle 6 Thermometer 7 Support roll in bath 8 Support roll on bath 9 Nozzle header 10 Spray nozzle 11 Droplet leakage prevention device 12 Water receiving pan 13 Discharge port 14 Sealing device 15 Box S Steel plate

Claims (5)

A box having upper and lower openings, and a steel plate traveling upward or downward inside,
A nozzle header comprising a plurality pieces arranged to spray nozzles steel plate steel longitudinal and / or transverse direction for injecting water mist,
In a vertical cooling apparatus for a steel plate, which is provided with a seal mechanism for preventing water leakage from the lower opening,
A discharge port for discharging droplets in the box;
The vertical cooling apparatus for steel plates, wherein the nozzle headers are spaced apart so as to have a discharge gap with an opening area ratio of 30% or more.
The opening area ratio is a ratio of the total area of the gap between the nozzle headers in the cross-sectional area formed by the nozzle header and the box on one side viewed from the steel plate side and the box area (between the nozzle headers). This is a value obtained by (total area of gap / box area) × 100.   The vertical cooling apparatus for steel sheets according to claim 1, wherein the interval between the nozzle headers is formed by dividing the nozzle header in the longitudinal direction of the steel sheet.   The steel plate vertical cooling apparatus according to claim 1 or 2, wherein the interval between the nozzle headers is formed by dividing the nozzle header in a steel plate width direction.   The said discharge port is divided | segmented into 3 or more in the steel plate width direction, The vertical cooling apparatus of the steel plate as described in any one of Claims 1-3 characterized by the above-mentioned.   The manufacturing method of the hot dip galvanized steel plate characterized by manufacturing a hot dip galvanized steel plate using the vertical cooling apparatus of the steel plate as described in any one of Claims 1-4.

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