JP3642031B2 - Hot strip strip cooling system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot-rolled steel strip cooling device for cooling a hot-rolled high-temperature steel strip.
[0002]
[Prior art]
Generally, a hot-rolled steel strip heats a slab to a predetermined temperature in a heating furnace, and the heated slab is rolled to a predetermined thickness with a roughing mill to form a rough bar, and then the rough bar is continuously heated by a plurality of stands. Finish rolling in an intermediate finish rolling mill to form a steel strip having a predetermined thickness. And after cooling this hot-rolled steel strip in the cooling stand on a run-out table, it manufactures by winding up with a winder.
[0003]
In such an on-line cooling device that transports the rolled high-temperature steel strip on a line and continuously cools it before it is wound up by a winder, firstly, the plate-passability of the steel strip is taken into consideration. There must be.
[0004]
For example, in order to cool the upper surface of the steel strip, a cylindrical laminar cooling nozzle is provided in a straight line over the width direction of the steel strip at a position directly above the transport roll for transporting the steel strip, and laminar cooling water is supplied from each cooling nozzle. Water is being poured. Therefore, even if the steel strip is pushed from above by water pressure, it does not have to be pushed into the steel strip pass line.
[0005]
On the other hand, as a method for cooling the lower surface of the steel strip, a spray nozzle is provided between the conveying rolls, and a method of injecting cooling water therefrom is common. In such a cooling mode, the cooling with respect to the upper and lower surfaces of the steel strip is not strictly symmetrical, and the cooling of the steel strip becomes intermittent and rapid cooling (for example, a plate thickness: 3 mm and a cooling rate of 200 ° C./s). This is almost impossible.
[0006]
[Problems to be solved by the invention]
By the way, in recent years, a hot-rolled steel strip with a fine crystal grain size has been demanded because of its excellent workability and high strength even at low Ceq, and rapid cooling (strong cooling) is required for that purpose. ing.
[0007]
In particular, in a steel having a low carbon concentration such as an extremely low carbon steel, the grain size of the austenite grains after rolling rapidly increases due to recrystallization and causes coarsening. Therefore, this type of steel requires rapid cooling such that the cooling rate exceeds 200 ° C./s from the Ar3 temperature or higher.
[0008]
Moreover, since the steel strip tip is transported in a free state from the rolling mill to the winder, the steel strip is likely to be wavy while vibrating up and down. Then, in order to make a steel strip pass stably, a conveyance roll is arrange | positioned closely and the spray nozzle is installed between the conveyance rolls as a cooling device of a steel strip lower surface.
[0009]
However, strictly speaking, such a cooling device cannot be said to be continuous cooling, and the cooling capacity itself is low.
[0010]
For example, in Japanese Patent Application Laid-Open No. Sho 62-259610, a cooling device is disposed between transport rolls. This cooling device has a flat injection surface, and is provided with a plurality of rows of cooling water injection holes and nozzles drilled at different angles toward the pass line, close to the steel strip.
[0011]
However, in this cooling device, if the guide is sufficiently close to the steel strip in order to stabilize the plate-passability of the hot-rolled steel strip, the nozzle injection hole will be close to the steel strip. Water flows in a narrow space between the steel strip and the cooling water injection surface.
[0012]
Eventually, the cooling water is discharged from the distance between the front and rear sides of the cooling device and the conveying roll and from both ends of the steel strip in the width direction, but the cooling water cannot flow out smoothly, so-called metabolism is poor and inefficient cooling is performed. Yes, the temperature of the cooling water rises and temperature unevenness tends to occur in the width direction of the steel strip.
[0013]
Further, the contact between the steel strip and the guide is unavoidable, the injection nozzle becomes clogged, and the hot-rolled steel strip cannot be uniformly cooled. That is, since the nozzle hole drilled in the guide is as small as several millimeters, the nozzle hole is deformed by contact with the steel strip, and foreign matters are likely to adhere to the nozzle hole.
[0014]
Furthermore, since only the lower surface is cooled, in some cases, a hot-rolled steel strip, particularly a steel strip having a small plate thickness, is lifted, and there is a problem that uniform cooling cannot be performed due to a change in cooling ability.
[0015]
Next, as another example, in Japanese Patent Laid-Open No. 4-238618, a guide having a height not exceeding the pass line of the steel strip is provided, and the water surface surrounded by the guide and the front and rear rolls contacts the lower surface of the steel strip. Thus, a cooling method for forming stagnant water is disclosed.
[0016]
In this case, the momentum of the water jetted from the nozzle is absorbed by the staying water when passing through the staying water layer, and the collision force is lowered and the cooling capacity is lowered.
[0017]
In addition, since the high-temperature cooling water that comes into contact with the steel strip stays between the nozzle and the steel strip, the temperature of the staying water rises and the cooling capacity decreases, and cooling locally causes film boiling. It becomes a state and uneven cooling occurs.
[0018]
Therefore, if the volume of the stagnant water is increased so that the water temperature of the stagnant water zone does not rise, the distance between the hot-rolled steel strip and the guide is increased, and as a result, the stability of the plate passing through the steel strip is hindered.
[0019]
The present invention has been made in consideration of the above circumstances, and the object of the present invention is to provide a cooling device for a hot-rolled steel strip that can pass through the hot-rolled steel strip stably and can be rapidly cooled. Is to provide.
[0020]
[Means for Solving the Problems]
In the present invention, a flat apron guide is provided between a plurality of conveying rolls at a distance of 10 to 30 mm from a steel strip to be conveyed, and a guide hole for passing cooling water is provided in the apron guide. The diameter of the guide hole of the apron guide is set to 3 to 10 times the cooling water injection hole diameter of the cooling means. Place such cooling means above and below the hot-rolled steel strip being conveyed, By injecting columnar cooling water into the hot-rolled steel strip through the guide holes, Cool symmetrically with the steel strip.
[0021]
Therefore, the hot-rolled steel strip can be traveled stably from the tip, and rapid cooling is possible. The cooling conditions for the upper and lower surfaces of the hot-rolled steel strip during cooling are exactly the same, and bending during cooling and the occurrence of residual stress after cooling are reduced.
[0022]
By installing the apron guide only at the center in the width direction of the hot-rolled steel strip to be transported, the metabolism of cooling water is improved, and the occurrence of uneven cooling due to stagnant water and the lack of cooling capacity are solved. As a result, a hot-rolled steel strip homogeneous in the width direction, the longitudinal direction and the thickness direction can be obtained stably.
[0023]
Moreover, it cools on the same conditions as it cools in the state in which the tension | tensile_strength was applied with the winder even until the most advanced of a steel strip reaches a winder. Therefore, the product yield is high and the quality of the steel strip is improved.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0025]
As a first embodiment, FIG. 1 (A) schematically shows a production facility for hot-rolled steel strip, and FIG. 1 (B) shows a cooling device.
[0026]
The coarse bar 2 rolled by the coarse rolling mill 1 is continuously led to seven continuous finish rolling mills 3 and is sequentially rolled to a predetermined thickness. The high-temperature hot-rolled steel strip carried out from the final finish rolling mill 3Z is guided to a run-out table 5 provided immediately after the rolling mill 3Z.
[0027]
The runout table 5 is provided with a cooling device (cooling means) 4 which will be described later. After the hot hot-rolled steel strip P is rapidly cooled here, it is guided to the winder 6 at the rear. It is wound up and becomes a hot rolled coil.
[0028]
The runout table 5 is composed of a transport roll 7 having a diameter of 310 mm arranged at a pitch of 500 mm along the transport direction of the hot-rolled steel strip P. A total of 12 sets of cooling boxes 8 are provided between the respective transport rolls 7 and constitute a part of the cooling device 4.
[0029]
The narrower the gap between the transport rolls, the more stable the strips of the steel strip are. However, if the distance is too narrow, there is no space for providing cooling means such as a cooling box, so the cooling length is short and the cooling efficiency is deteriorated. Therefore, it is desirable that the distance between the transport rolls 7 is a roll diameter +100 mm to a pitch of about three times the roll diameter.
[0030]
Each cooling box 8 has a length direction along the conveyance direction of the hot-rolled steel strip P of 180 mm, and a width direction perpendicular to the length direction of 1860 mm. The distance between the end face of the cooling box 8 and the hot-rolled steel strip P to be conveyed is set to 80 mm.
[0031]
A steel plate having a thickness of 16 mm is fitted on the surface of the cooling box 8 facing the steel strip P. In this steel plate, holes of 4 mmφ are provided in a staggered manner at intervals of 40 mm in the vertical and horizontal directions so as to eject cooling water. Since the steel plate is thick and the holes are straight cut holes, when the cooling water is injected from these holes, the cooling water becomes a columnar laminar flow.
[0032]
As shown also in FIG. 2, an apron guide 10 is provided between the cooling box 8 and the hot-rolled steel strip P to be conveyed. The end surface of the apron guide 10 and the steel strip P are set to have an interval of 10 mm to 30 mm.
[0033]
For example, when the distance between the apron guide 10 and the hot-rolled steel strip P is set to 30 mm or more, the tip of the steel strip P is folded downward when passing through the cooling device as shown in FIG. It collides with the next transport roll 7 and jumps up. As the tip of the steel strip P advances, vertical vibration of the steel strip is promoted and the stable threading plate is damaged. In the worst case, as shown in FIG. 3 (B), the steel strip P is bent almost in an accordion shape, and there is a possibility that it will eventually become impossible to run.
[0034]
If the distance between the apron guide 10 and the hot-rolled steel strip P is set to 10 mm or less, the steel strip P will always come into contact with the apron guide 10, and the steel strip will become sticky or cooling water will be difficult to escape, resulting in a cooling effect. Extremely worse.
For the above reasons, the distance between the apron guide 10 and the hot-rolled steel strip P is preferably set to 10 to 30 mm.
[0035]
For the surface of the apron guide 10 facing the hot-rolled steel strip P, a material softer than the steel strip, such as a synthetic resin plate, is selected so that the steel strip does not wrinkle even when the steel strip contacts the apron guide. .
[0036]
4 (A) to 4 (D) show different forms of the apron guide 10. (A) is an apron guide 10A having the above-described shape structure, (B) is an apron guide 10B formed in a bowl shape, (C) is an apron guide 10C formed in a lattice shape, and (D) Is an apron guide 10D made of expanded metal, any of which can be used.
[0037]
For example, when the hot-rolled steel strip P comes into contact with the apron guide 10, if the contact portion is narrow, the surface pressure at the contact portion increases as in the case of point contact, and seizure or indentation marks are likely to occur.
[0038]
For this reason, the apron guide 10 is provided with a guide hole 11 having a minimum necessary diameter through which the cooling water sprayed from the cooling device passes smoothly as shown in FIG.
[0039]
The apron guide 10 has a thickness of 5 mm or more in the case of steel, although it depends on the material. Although it is better to be thinner, particularly when the thickness is less than 5 mm, the hot-rolled steel strip P to be transported collides to cause breakage or deformation, which hinders cooling.
[0040]
Although it is conceivable to increase the thickness in order to provide rigidity, if it is too thick, the distance between the cooling box 8 and the steel strip P is increased and the cooling capacity is weakened. As will be described later, the distance between the cooling box 8 and the hot-rolled steel strip P has an upper limit of 100 mm because of the cooling capacity, and the range within this condition is the upper limit.
[0041]
Therefore, the apron guide 10 is made of a synthetic resin plate having a thickness of 30 mm as a base, and a steel plate having a thickness of 10 mm is bonded to the back surface as a reinforcing plate to form an apron guide 10 having a total thickness of 40 mm. However, the present invention is not limited to this, and various steel plates and resin plates can be combined within the above thickness range.
[0042]
The guide holes 11 of the apron guide 10 are opened coaxially with the central axis of the cooling water injection holes provided in a staggered manner in the cooling box 8. The diameter of the guide hole 11 is set to 3 times or more the cooling water injection hole diameter.
[0043]
When the diameter of the guide hole 11 is less than three times the diameter of the cooling water injection hole, as shown in FIG. 5A, the gap between the steel strip P and the apron guide 10 is filled and jetted by the reverse flow of the cooling water that has lost its place of travel. The momentum of the cooling water injected from the hole is hindered, and the cooling capacity is attenuated.
[0044]
However, if the diameter is too large, the apron guide 10 becomes full of holes, and when the steel strip P comes into contact, the contact area of the steel strip becomes narrow and the surface pressure increases, and seizure and indentation marks are likely to occur. Therefore, this diameter has an upper limit of about the nozzle pitch. A nozzle arrangement with a normal nozzle diameter of about 2 to 10 mm corresponds to about 10 times the cooling water injection hole diameter.
[0045]
A case where the diameter of the guide hole 11 is suitable is shown in FIG. This figure shows the case where the diameter of the guide hole 11 is four times the diameter of the cooling water injection hole. The cooling water does not stay between the apron guide and the steel strip. Further, there is no momentum of the cooling water to the guide hole that hinders the injection of the cooling water.
[0046]
For the above reasons, the diameter of the guide hole 11 provided in the apron guide 10 coaxially with the central axis of the cooling water injection hole of the cooling box 8 should be about three times the cooling water injection hole diameter or about the nozzle pitch. More preferably, it may be set to 3 to 10 times the cooling water injection hole diameter.
[0047]
In the above-described embodiment, the distance between the apron guide 10 and the end face of the cooling box 8 is set to 30 mm. This is due to the following reason.
When the clearance between the apron guide 10 and the end face of the cooling box 8 is set to 5 mm or less, there is no backflow escape space, the cooling water stays between the steel strip P and the apron guide 10, and the pressure in this portion increases. So-called water drainage worsens, and the momentum of jet cooling water weakens.
[0048]
In order to generate a certain amount of back flow and improve the escape of the cooling water, the clearance between the apron guide 10 and the cooling box 8 needs to be 5 mm, and preferably 10 mm or more is ensured. However, if they are separated too much, the distance between the cooling box 8 and the steel strip P is increased, and the cooling capacity is weakened. The distance between the cooling box 8 and the hot-rolled steel strip P has an upper limit of 100 mm or more because of the cooling capacity, and the range within this condition is the upper limit of the gap between the cooling box 8 and the apron guide 10. Here, since it is set to 30 mm, no problem occurs.
[0049]
An extreme example is shown in FIG. This is a case where the apron guide 10 and the cooling box 8 are integrated to eliminate the gap, but most of the injected cooling water A stays around the guide hole 11 and the steel strip P, and the pressure in this portion Rises and the so-called water drainage becomes worse, and the momentum of the jet cooling water is remarkably increased. Therefore, the collision speed to the steel strip P is further reduced and the cooling capacity is lowered.
[0050]
On the other hand, the cooling water that has cooled the steel strip P passes through the gap between the steel strip and the apron guide 10 and flows out from the gap between the apron guide 10 and the transport roll 7 or from both sides of the cooling box 8.
[0051]
As described above, the interval between the end face of the cooling box 8 and the hot-rolled steel strip P to be conveyed is set to 80 mm, for the following reason.
[0052]
If the interval between the cooling box 8 and the steel strip P is further expanded, the momentum of the injected cooling water is absorbed by the fluid (cooling water) existing between the steel strip P and the cooling box 8 and weakens. On the other hand, if the distance is too close, the entire surface of the steel strip cannot be covered unless the number of cooling water nozzles is increased, and there is no choice but to increase the number of nozzles per area or increase the amount of cooling water. So it becomes uneconomical.
[0053]
Ideally, the steel strip P must pass through a position where the surface pressure received from the cooling water from the upper surface and the surface pressure received from the lower surface are balanced, thereby centering the vibration of the steel strip P and the unbalanced travel. The effect works.
[0054]
In various experiments, the surface pressure, which is the pressure at which the fluid (cooling water) acts on the steel strip P, is 0.01 to 0.2 kg / cm. ² If it is about G, the result which can anticipate the above-mentioned centering effect was obtained.
[0055]
At this time, in order to cool the steel strip P with laminar cooling water, the interval between the cooling box 8 and the steel strip P cannot be separated by a predetermined value or more. When the diameter of the cooling water injection hole forming the laminar flow is 2 to 5 mm, the interval between the cooling box 8 and the steel strip P is set to 30 to 100 mm.
[0056]
If it is 100 mm or more, the momentum of the cooling water flow weakens and strong cooling becomes impossible. On the contrary, if it is too close to 30 mm or less, the entire surface of the steel strip cannot be covered unless the number of cooling water nozzles is increased, and it is necessary to take measures to increase the number of nozzles per area or increase the amount of cooling water. It becomes inefficient and uneconomical.
[0057]
From these things, it is good to set the space | interval of the hot-rolled steel strip P conveyed by the end surface of the cooling box 8 to 80 mm as mentioned above.
[0058]
As shown in FIGS. 1B and 2 again, the cooling box 8 is arranged as a device for cooling the lower surface of the steel strip P. However, the upper surface of the steel strip P is arranged above the steel strip to perform the same cooling. An upper surface cooling box 12 serving as a cooling means is also disposed at the site.
[0059]
And the drive roll 14 which supports the conveyance driving of the steel strip P and rotates in the opposite direction at the same peripheral speed as the transport roll 7, that is, the direction in which the steel strip P is sent from the finish rolling mill 3 to the winder 6 is provided.
[0060]
An upper surface side apron guide 13 is provided between the upper surface cooling box 12 and the hot-rolled steel strip P to be conveyed. The shape structure of the apron guide 13, the cooling water injection conditions of the cooling box 12, and the relative positional relationship between the cooling box 12, the apron guide 13, and the steel strip P are all set to be the same as the conditions on the lower surface side.
[0061]
Note that the amount of cooling water injected as a laminar flow for cooling the steel strip P is 1 m on one side of the steel strip. ² About 3500L / minm ² It has been adjusted so that At this time, the temperature of the cooling water was 25 ° C.
[0062]
In the cooling device 4 configured as described above, a hot-rolled steel strip P having a thickness of 3.2 mm after rolling, a width of 1500 mm, and a temperature of 900 ° C. is guided while being transported at a transport speed of 600 pm, and is then transported after being cooled. did.
[0063]
On the exit side of the cooling device 4, the temperature of the steel strip P is reduced to 710 ° C., and the temperature difference between the width direction and the longitudinal direction is within a range of about 20 ° C., and a steel strip having an almost uniform temperature distribution is obtained. It was.
[0064]
Moreover, the tip of the steel strip P passes between the cooling boxes 8 and 12 on the upper and lower surface sides in a stable state, and the steel strip P is always cooled stably. Further, there was no generation of wrinkles or indentation marks as a whole, including the tip of the steel strip P.
[0065]
Next, a second embodiment will be described.
As a cooling device, a cooling nozzle is used in place of the cooling box in the first embodiment. This cooling nozzle is a circular tube laminar nozzle that ejects columnar cooling water.
[0066]
FIG. 7A shows details of the cooling device 4A. Although only the cooling device on the lower surface side is shown, an upper surface cooling device having the same structure as the lower surface cooling device is arranged as in the first embodiment.
[0067]
Headers 16 are arranged between transport rolls 7 of the same diameter provided in the longitudinal direction at the same pitch as in the first embodiment, and a circular tube laminar having a coolant water injection hole diameter of 4 mm and a straight pipe portion length of 100 mm in each header 16. The nozzles 15 are arranged in a staggered manner at intervals of 40 mm in the width direction and the longitudinal direction.
[0068]
The distance between the tip of the circular tube laminar nozzle 15 and the steel strip P is set to 80 mm, and the flow of cooling water sprayed from the circular tube laminar nozzle 15 reaches the steel strip P as a columnar laminar flow A. To do.
[0069]
An apron guide 10 having a thickness of 40 mm is provided between the tip of the circular tube laminar nozzle 15 and the steel strip P. The distance between the apron guide 10 and the steel strip P is set to 10 mm. The surface of the apron guide 10 with respect to the steel strip P is made of a material softer than the steel strip, for example, a flat plate made of synthetic resin, so that wrinkles are not generated in the steel strip due to contact with the steel strip P.
[0070]
The apron guide 10 is provided with a guide hole 11 having a minimum diameter necessary for the columnar cooling water A sprayed from the circular tube laminar nozzle 15 to pass therethrough. The thickness of the apron guide 10 depends on the material, but is 5 mm or more in the case of steel. Although it is better to be thinner, particularly when the thickness is less than 5 mm, the hot-rolled steel strip P to be transported collides to cause breakage or deformation, which hinders cooling.
[0071]
In addition, the apron guide 10 may be increased in thickness in order to have rigidity. However, if the apron guide 10 is too thick, the distance between the circular tube laminar nozzle 15 and the steel strip P may be increased to reduce the cooling capacity, or the circular tube laminar nozzle 15. The length of the straight pipe becomes longer, which hinders cooling capacity. As will be described later, the distance between the tip of the circular tube laminar nozzle 15 and the hot-rolled steel strip P has an upper limit of 80 mm because of the cooling capacity, and therefore the range within this condition is the upper limit.
[0072]
Therefore, the apron guide 10 is made of a synthetic resin plate having a thickness of 30 mm as a base, and a steel plate having a thickness of 10 mm is bonded to the back surface as a reinforcing plate to form an apron guide 10 having a total thickness of 40 mm. However, the present invention is not limited to this, and various steel plates and resin plates can be combined within the above thickness range.
[0073]
The guide hole 11 of the apron guide 10 is designed to be coaxial with the central axis of the cooling water injection hole of the circular tube laminar nozzle 15, and the diameter of the guide hole 11 is four times the cooling water injection hole diameter, that is, 16 mm. .
[0074]
In addition, the diameter of the guide hole 11 is set to 3 to 10 times the injection hole diameter of the circular tube laminar nozzle 15. When the diameter is 3 times or less, the flow velocity is reduced due to flow resistance while passing through the guide hole 11, and the collision speed to the steel strip is attenuated. If the diameter is 10 times or more, the reverse flow of the cooling water filled between the steel strip P and the apron guide 10 hinders the momentum of the injected cooling water and the collision speed against the steel strip is attenuated.
[0075]
If the diameter is too large, the apron guide 10 becomes full of holes, the contact area when contacting with the steel strip P is narrowed, and the surface pressure is increased. Then, image sticking, indentation marks, etc. are likely to occur.
[0076]
The circular tube laminar nozzle 15 has a ratio of the cooling water injection hole diameter to the length of the straight pipe portion set in a range of 5-20.
[0077]
That is, the cooling water injection hole position at the tip of the circular tube laminar nozzle 15 and the height of the inlet surface of the guide hole 11 on the lower surface of the apron guide 10 are arranged so as to coincide with each other.
[0078]
When the accompanying flow described above is generated in the guide hole 11 of the apron guide 10, the cooling water flow in the form of a column is less attenuated, and the collision speed of the cooling water at the collision point with the steel strip P increases. High cooling efficiency can be obtained.
[0079]
On the other hand, as shown in FIG. 7B, when the distance between the header 16 of the circular tube laminar nozzle 15 and the apron guide 10 is 5 mm or less, the accompanying flow is almost eliminated, and the guide hole 11 from the steel strip side. The cooling water flows backward to the cooling box side, and the columnar cooling water flow passing through the guide holes is significantly attenuated.
[0080]
In order to form a sufficient accompanying flow, the interval between the header 16 of the circular tube laminar nozzle 15 and the apron guide 10 is more than 5 mm, and preferably 10 mm or more.
[0081]
As shown in FIG. 8A, when the apron guide 10 and the header 16 of the circular tube laminar nozzle 15 are in close contact with each other, water jetted from the nozzle 15 flows backward from the guide hole 11 and the periphery of the steel strip P. In addition, since the momentum of the injected cooling water is suppressed, the collision speed of the columnar cooling water against the steel strip is reduced, and the cooling capacity is reduced.
[0082]
As shown in FIG. 8B, if the distance between the apron guide 10 and the header 16 of the circular tube laminar nozzle 15 is large, the length of the circular tube portion of the circular tube laminator 15 must be extremely increased. Therefore, the flow resistance increases, and the supply pressure of the cooling water has to be increased, which is not economical. Further, the distance between the tip of the circular tube laminar nozzle 15 and the steel strip P is increased, and the cooling capacity is weakened. The distance between the tip of the circular tube laminar nozzle 15 and the hot-rolled steel strip P has an upper limit of 100 mm because of the cooling capacity, and the range within this condition is the upper limit of the gap between the header 16 of the circular tube laminar nozzle 15 and the apron guide 10. Become.
[0083]
Conversely, if the circular tube portion of the circular tube laminator 15 is too short, it will not be a columnar cooling water flow, and will be disturbed and the impact force on the steel strip will be weakened. Therefore, the ratio of the diameter of the cooling water injection hole of the circular tube laminar nozzle to the length of the straight pipe portion is preferably 5-20.
[0084]
If it is less than 5, it does not become a columnar cooling water flow but a turbulent flow, the water flow spreads at the nozzle outlet, and the momentum of the cooling water is weakened before reaching the steel strip. On the other hand, if it exceeds 20, the straight pipe portion becomes longer and the flow resistance increases, so that a high injection pressure is required to obtain a columnar cooling water flow.
[0085]
On the other hand, the cooling water that has cooled the steel strip P passes through the gap between the steel strip P and the apron guide 10, the gap between the apron guide 10 and the transport roll 7, both sides of the cooling device 4, or the apron guide 10. It flows out along the side wall of the guide hole 11.
[0086]
The interval (80 mm) between the tip of the circular tube laminar nozzle 15 and the steel strip P was determined as follows.
[0087]
That is, if the interval between the nozzle 15 and the steel strip P is extremely separated, the momentum of the cooling water is absorbed by the fluid existing between the steel strip P and the nozzle 15 and weakens. On the other hand, if you approach too much, you will not be able to cover the entire surface of the steel strip unless you increase the number of cooling water nozzles. So it becomes uneconomical.
[0088]
Ideally, the steel strip P passes through a position where the surface pressure received from the upper surface and the surface pressure received from the lower surface are balanced, and the effect of centering the vibration of the steel strip P and the unbalanced running works.
[0089]
The pressure at which the fluid (cooling water) acts on the steel strip P is 0.01 to 0.2 kg / cm ² If it is about G, the above-mentioned centering effect can be expected. At this time, in order for the laminar cooling water to reach the steel strip P and cool the steel strip, the distance between the cooling device and the steel strip cannot be increased more than necessary.
[0090]
If the diameter of the coolant injection hole of the circular tube laminar nozzle 15 is about 2 to 5 mm, the distance between the tip of the circular tube laminar nozzle and the steel strip is preferably 30 to 100 mm.
If it is 100 mm or more, the momentum of the cooling water flow is weakened and strong cooling becomes impossible. On the other hand, if it is too close to 30 mm or less, it is difficult to obtain a good water flow due to the absence of cooling water, rapid cooling is impossible, and the flow of the cooling water is different between the central part and the side edge of the steel strip, Cooling unevenness will occur.
[0091]
That is, the distance between the tip of the circular tube laminar nozzle 15 and the steel strip P is optimally 80 mm.
[0092]
In this embodiment, one side of the steel strip P is 1 m. ² In contrast, the amount of cooling water is approximately 7300 L / minm. ² Adjusted to ensure. The temperature of the cooling water was 25 ° C.
[0093]
The cooling device 4A configured as described above is cooled while passing a steel strip P having a sheet thickness after rolling of 5.7 mm, a sheet width of 1200 mm, and a temperature after rolling of 870 ° C. at a conveyance speed of 450 pm. did.
[0094]
At this time, on the outlet side of the cooling device 4A, the temperature of the steel strip P decreases to 725 ° C., and the temperature difference between the width direction and the longitudinal direction falls within the range of about 20 ° C., and a steel strip having a substantially uniform temperature distribution is obtained. It was.
[0095]
Further, the steel strip P passed through the cooling device 4A in a stable state, and the cooling of the tip portion was stable. There was no occurrence of wrinkles or indentation marks including the tip of the steel strip P.
[0096]
Next, as a comparative example of the above-described first embodiment, FIGS. 9A and 9B will be described with reference to a schematic view and a sectional view of the cooling device 4Z.
[0097]
The apron guide 10Z is directly provided with a cooling water injection hole b, and the cooling water is injected from the injection hole b. Steel plate guides 18 are provided at both ends of the apron guide 10Z.
[0098]
The cooling device 4Z is composed of cooling boxes 17 in which a total of 12 sets are arranged one by one between the transport rolls 7 under the same conditions, and has a width of 1860 mm. The space between the cooling water jetting surface of the cooling box 17 and the steel strip P is at a position 10 mm below the pass line in order to allow the steel strip tip to pass through stably, and this cooling water jetting surface also serves as the apron guide 10Z. ing.
[0099]
The cooling box 17 is provided with holes of 4 mmφ in a staggered shape with a length of 40 mm and a width of 40 mm. Since the steel plate is thick and the hole is a straight guide hole, the injected cooling water becomes a columnar laminar flow.
[0100]
The steel plate guide 18 is provided at the height of the pass line facing both sides of the steel strip P so as to accumulate cooling water between the transport rolls 7 to form a stagnant zone. Therefore, the cooling water that has cooled the steel strip P flows out from the water level adjusting drain 4, the gap between the steel strip P and the steel plate guide 18, the gap between the steel plate guide 18 and the transport roll 7, or both sides of the cooling device. .
[0101]
Although not particularly shown, a cooling box having the same structure is provided above the lower surface cooling box 17 so as to cool the upper surface of the steel strip by injecting cooling water under the same injection conditions. In addition, about the cooling of the steel strip upper surface, since the steel plate guide 18 for forming a stagnant zone is unnecessary, it is not provided.
[0102]
In this comparative example, the cooling condition for the hot-rolled steel strip P is 1 m on one side of the steel strip. ² About 3500L / minm ² The cooling water was adjusted to be jetted. The temperature of the cooling water is 25 ° C., and these cooling conditions are the same as those in the first embodiment.
[0103]
A steel strip having a rolled plate thickness of 3.2 mm, a plate width of 1500 mm, and a temperature of 900 ° C. was passed from the tip at a conveyance speed of 600 pm to be cooled with respect to the 4Z cooling device. However, on the exit side of the cooling device 4Z, the temperature of the steel strip can only be reduced to 860-720 ° C., and the temperature difference between the width direction and the longitudinal direction is about 120 ° C., which is extremely large. In addition, streaky temperature unevenness occurred in the width direction.
[0104]
That is, since the apron guide 10Z is brought close to the steel strip P in order to give priority to the traveling property of the steel strip P, a circulating flow is generated between the apron guide 10Z and the cooling box 17, and this flow is the momentum of the injected cooling water. Is significantly inhibited.
[0105]
This circulating flow interferes with the cooling water that is about to collide with the steel strip to cool the steel strip P. Therefore, since the cooling water that has lost its place of stay stays in the narrow area many times, the water temperature of the accumulated water rises and the collision point of the cooling water cools well. This is probably because of this.
[0106]
Cooling water amount is 1m on one side of steel strip ² About 7300L / minm ² However, the stripe-like temperature unevenness was not eliminated. Further, if the cooling box 17 is separated from the steel strip by 30 mm or more, the steel strip tip vibrates and it becomes difficult to stably pass the tip. In the case of a thin steel strip of 2 mm or less, the plate was not passed when the cooling box was separated from the steel strip by 30 mm or more.
[0107]
Next, a cooling device according to a third embodiment will be described.
[0108]
The rolling equipment and the cooling device as shown in FIGS. 1 (A) and 1 (B) are used. That is, the cooling device 4 is provided with cooling boxes 8 and 12 in which a total of 15 sets are provided, one set between each transport roll 7 in the longitudinal direction on both the upper and lower surfaces.
[0109]
In particular, the interval between the cooling box 8 and the steel strip P is set to 80 mm, and a steel plate having a thickness of 20 mm is fitted on the surface of the cooling box 8 with respect to the steel strip P. In this steel plate, holes having an inner diameter of 4 mmf are arranged in a staggered manner at intervals of 40 mm in the width direction and 40 mm in the longitudinal direction. Since the steel plate is thick and the hole is a straight cut, the injected cooling water becomes a columnar laminar flow.
[0110]
An apron guide 10S as shown in FIGS. 10A and 10B is provided between the cooling box 8 and the steel strip P.
The apron guide 10S has a thickness d of 40 mm, a width k of 200 mm, a length m of the lower surface of the guide of 180 mm which is the same as the longitudinal length of the cooling box 8, and a length n of the upper surface side of 330 mm. Formed.
[0111]
The distance between the apron guide 10S and the steel strip P is set to 10 mm, but may be in the range of 10 to 30 mm. The surface of the apron guide 10S that contacts the steel strip P is preferably made of a softer material (for example, resin) than the steel strip so as not to generate wrinkles, and the form thereof may be selected from those described above with reference to FIG.
[0112]
The shape of the apron guide 10S should be rounded by dropping the corners on both sides in the width direction. Therefore, the surface pressure when the steel strip P comes into contact with the apron guide 10S end can be suppressed, and the occurrence of scuffing is prevented.
[0113]
The apron guide 10S is disposed so as to face the center portion in the width direction of the steel strip P to be conveyed, that is, the center portion L in the width direction of the cooling box 8.
[0114]
For example, when the apron guide 10S is installed over the entire surface in the width direction, after the injected cooling water collides with the steel strip, between the cooling box 8 and the apron guide 10S, and between the apron guide 10S and the steel strip P And from both ends of the steel strip.
[0115]
However, since the apron guide 10S is installed on the entire surface in the width direction, the cooling water tends to stay particularly in the vicinity of the center in the width direction of the steel strip, the metabolism of the cooling water becomes worse, the cooling water temperature rises, and the cooling Becomes inefficient. Furthermore, the collision speed of the cooling water jetted from the cooling box 8 to the steel strip P is attenuated by the influence of the staying water that has lost its escape.
[0116]
Cold experiments were conducted on the impact pressure on the steel strip when the apron guide 10S was installed in the third embodiment and when the apron guide was installed so as to face the entire width direction of the cooling box 8. Measured and compared.
[0117]
As a result, if the conditions of the third embodiment were adopted, there was almost no pressure difference due to the presence or absence of the apron guide, and the collision pressure was almost uniform over the entire width direction of the steel strip P.
[0118]
On the other hand, when the apron guide across the entire width direction was installed, the collision pressure was almost uniform in the width direction, but the collision pressure was about 30% lower than when there was no apron guide across the entire surface. . As described above, this is considered to be the influence of the accumulated water between the apron guide and the cooling device and between the apron guide and the steel strip.
[0119]
Therefore, the conclusion that the apron guide 10S should be installed facing the central portion in the width direction of the steel strip to be conveyed is obtained.
[0120]
Further, the apron guide having a width of 200 mm used in the above embodiment is divided into three in the width direction, and is installed at a position of 100 mm from the width direction end of the steel strip P and at the center in the width direction, and collides with the steel strip. The pressure was measured by a cold experiment.
[0121]
As a result, the collision pressure at the position where the split apron guide was installed was reduced by about 15% compared to the case where it was only installed at the center. That is, by installing the split apron guide at the end in the width direction of the steel strip, the cooling water dropout at the end is worse than when only the center is installed. Also from the above, the apron guide 10S should be installed only in the center in the width direction of the steel strip to be conveyed.
[0122]
The width of the apron guide 10S to be used was not only 200 mm, but also 400 mm, 600 mm, 800 mm, 1000 mm, and 1200 mm, and the impact pressure on each steel strip P was determined by a cold experiment.
[0123]
As a result, the collision pressure when the width of the apron guide was set to 400 mm to 1000 mm was almost equal to that of the width of 200 mm, and the collision pressure at other portions in the width direction of the steel strip was almost uniform.
[0124]
On the other hand, when the width of the apron guide was 1200 mm, the collision pressure at the apron guide installation position was reduced by about 15% compared to the area where the apron guide was not installed.
[0125]
Thus, when the width dimension of the apron guide 10S is increased, the cooling water is likely to stay in the vicinity of the center portion L in the width direction of the steel strip P. Furthermore, it has been found that the impact speed of the cooling water injected from the cooling box 8 to the steel strip is attenuated by the influence of the staying water, and the collision pressure is reduced.
[0126]
Conceptually, it is desirable that the width dimension of the apron guide 10 </ b> S installed in the width direction of the steel strip P is at least ½ or less of the width dimension of the transport roll that transports the steel strip. In addition, the plate | board property of the steel strip P front-end | tip was 200 mm-1000 mm, and there was no difference in particular, and all were favorable.
[0127]
A gap of 30 mm is provided between the apron guide 10S and the cooling box 8. When the gap is 5 mm or less, the accompanying flow is reduced, a back flow is generated from the steel strip P to the cooling box 8 side in the guide hole 11 of the apron guide, and the columnar cooling water flow passing through the guide hole 11 is significantly attenuated.
[0128]
When there is no gap between the apron guide 10S and the cooling box 8, the cooling water always accumulates in the guide hole 11, and the injected cooling water causes a pressure loss when passing through the guide hole and collides with the steel strip. The collision speed at the time of dampens.
[0129]
In the cold experiment, when there is no gap between the cooling box 8 and the apron guide 10S and when there is no gap at all, as a result of measuring the pressure at which the cooling water collides with the steel strip P, Compared with the case where there is, the collision pressure was attenuated to ½ or less.
[0130]
When there is no gap between the cooling box 8 and the steel strip P, even if the apron guide 10S is installed only in the central portion L in the width direction, the collision pressure of the cooling water in the width direction becomes non-uniform, resulting in Temperature unevenness occurs in the width direction of the steel strip.
[0131]
From the above, when installing the apron guide 10S of this embodiment, the result that a clearance of at least 10 mm or more is required between the cooling box 8 and the apron guide 10S was obtained.
[0132]
【The invention's effect】
As is clear from the above description, the following effects can be obtained according to the present invention.
[0133]
(1) While maintaining a stable steel strip passage, it was uniform in the longitudinal and width directions of the steel strip, enabling strong cooling.
[0134]
(2) The temperature unevenness in the width direction and the longitudinal direction of the steel strip is reduced, the product quality is stabilized, the material variation is reduced, and the shape defect due to thermal strain is eliminated.
[0135]
(3) Stable cooling was performed from the most advanced part of the steel strip, and the yield was greatly improved.
[0136]
(4) The trouble of passing through the cooling device has been reduced and the operating rate of the equipment has been increased. The occurrence rate of wrinkles in the steel strip has been greatly reduced and no longer wrinkles.
[0137]
(5) Yield loss due to material slippage was reduced and the generation rate of scrap was reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a rolling device and a schematic configuration of a cooling device according to a first embodiment of the present invention.
FIG. 2 is a view showing a state of plate passing at a front end of a steel plate that passes between a cooling device and an apron guide according to the embodiment;
FIG. 3 is a diagram for explaining a state in which a steel strip is not transported.
FIG. 4 is a diagram showing various apron guide configurations.
FIG. 5 is a view for explaining the arrangement configuration and laminar flow shape of the cooling device and apron guide for the steel strip in the embodiment;
FIG. 6 is a diagram for explaining the arrangement of a cooling device and an apron guide for a steel strip for comparison, an example having a defect less than three times and an example of a preferred range.
FIG. 7 is a view showing a state of plate passing at the front end of a steel plate passing between a cooling device and an apron guide according to the second embodiment of the present invention.
FIG. 8 is a diagram for explaining the arrangement of a cooling device and an apron guide for a steel strip for comparison.
FIG. 9 is a perspective view and a schematic cross-sectional view of a cooling device (also used as an apron guide) of a comparative example.
FIG. 10 is a plan view and a schematic sectional view of a cooling device according to a third embodiment.
[Explanation of symbols]
3Z ... Final finish rolling mill,
P ... hot rolled steel strip,
7 ... Conveying roll,
10 ... Apron guide (lower side),
11 ... Guide hole,
4 ... Cooling device (cooling means),
8 ... Cooling box (lower side),
12 ... Cooling box (top side),
13 ... Apron guide (top side),
15: Circular tube laminar nozzle (cooling nozzle).

Claims (5)

A plurality of rotating conveying rolls arranged at predetermined intervals and conveying a hot hot-rolled steel strip guided from a final finish rolling mill;
A planar apron guide disposed between these transport rolls and in a position close to the hot-rolled steel strip to be transported,
Cooling water passage guide holes provided in each apron guide;
A cooling device for a hot-rolled steel strip, which is arranged with a gap between the apron guide and a cooling means for injecting columnar cooling water into the hot-rolled steel strip through the guide hole of the apron guide ,
The distance between the hot-rolled steel strip to be conveyed and the apron guide is set to 10 to 30 mm, and the diameter of the guide hole of the apron guide is set to 3 to 10 times the cooling water injection hole diameter of the cooling means. A cooling device for hot-rolled steel strip. The apparatus for cooling a hot-rolled steel strip according to claim 1, wherein a gap between an end face of the cooling means and the apron guide is set to 5 mm or more. The cooling means is a circular laminar cooling nozzle ,
The hot rolled steel strip according to claim 1 or 2, wherein the circular pipe laminar cooling nozzle has a ratio of a cooling water injection hole diameter to a length of a straight pipe portion of 5 to 20. Cooling system. The hot-rolled steel according to any one of claims 1 to 3 , wherein the transport roll and the apron guide are provided at symmetrical positions on both the upper and lower surfaces through the hot-rolled steel strip to be transported. Belt cooling system. The said apron guide is arrange | positioned facing the width direction center part of the hot-rolled steel strip conveyed , The cooling apparatus of the hot-rolled steel strip in any one of Claim 1 thru | or 4 characterized by the above-mentioned.

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