JPS6112830A - Method for cooling steel material - Google Patents

Abstract

PURPOSE:To cool efficiently and uniformly a hot rolled steel materal with spouted water in a short cooling zone without forming soft spots by arranging unit coolers each having a specified flow density of cooling water in series in the forward direction of the steel material. CONSTITUTION:Unit coolers 6 are arranged in series in the forward direction of a steel material 5. Cooling water 3 is fed to the outer pipes 2 of the coolers 6 and spouted from many holes 4 in the inner pipes 1 to cool the steel material 5 passing through the inner pipes 1. Cooling water is spouted at >=250m<3>/hr.m<2> flow density, and the surface temp. of the steel material to be cooled is regulated to about 600-1,000 deg.C. The hot rolled steel material 5 can be cooled uniformly and efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a cooling method that provides uniform and high cooling performance by injecting water onto a hot rolled steel material.

(Prior Art) In recent years, controlled rolling technology that does not rely on alloy addition or heat treatment has become popular as a new technology for making microstructures finer and materials tougher. This technology actively utilizes the hot rolling process not just as a forming process, but also as a processing heat treatment process, and it streamlines the production of high value-added products while saving resources, processes, and energy. It is a technology for manufacturing.

Furthermore, in recent years, controlled cooling technology has been developed that utilizes cooling after controlled rolling to improve material quality, making it possible to obtain high-strength steel materials without sacrificing weldability or toughness. became. Naturally, it is clear that this technology will have similar effects in the rod and wire rod sector, so recently new rolling mills have been installed with large mill motor power to enable controlled rolling. I've been doing it.

However, the finishing speed of recent small-diameter wire rods is 90 to 1 Om/
Due to the high speed of up to S, the cooling time of conventional machining machines would result in a very long cooling zone, causing problems in the suitability of materials. Therefore, if controlled cooling is to be achieved in a short period of time, a cooling technique with uniform and high cooling capacity is required.

Various cooling devices have been proposed for steel materials (particularly rods and wire rods).
No. 9, '% Kosho 51-20, 283, % Kosho 52-3
No. 5,007 9% Publication No. 52-49.40: c, Special Publication No. 56-44,935, Special Publication No. 56-48.566,
Jitko No. 52-18,998, Jitko - 1982-41,
No. 813) Because the relationship between the density of cooling water, uneven cooling, and multiple locations of cooling devices has not been systematized, uniform and high cooling performance cannot be expected with these cooling devices alone. The reason why uniform high cooling cannot be achieved will be explained with reference to the conventionally used cooling device of No. 7.

In FIG. 7, 1 is an inner tube, 2 is an outer tube, 3 is a cooling water, 4 is a hole, 5 is a steel material, and 6 is a unit cooling device.

When cooling a steel material with such a cooling device, if the steel material 5 is uneven in the inner tube 1, the amount of water and dynamic pressure of the water jetted from the holes 4 or slits provided in the inner tube 1 will increase in the circumferential direction of the steel material. This causes uneven cooling. If even more extreme deviation occurs, cooling water will not be able to enter the gap between the inner pipe wall and the steel material, and the cooling capacity will be significantly reduced in that area. Therefore, centering and cooling the steel material 5 within the inner tube 1 of the unit cooling device 6 is the basic method for uniform cooling.

However, considering the suitability of the material, the inner tube of the cooling device is generally made larger in diameter than the steel material, and one cooling device can cool several steel materials with different diameters, so the conventional method remains unchanged. If the unit cooling devices 5 are simply arranged continuously in series in the direction of movement of the steel material, the steel material will become uneven within the inner tube 1 due to changes in the diameter of the steel material or changes in continuous failure during transport, resulting in uneven cooling. become.

In this way, in order to uniformly cool several kinds of steel materials with different diameters using a cooling device in which unit cooling devices of the same type are arranged in series, copper Movable guidance guide 7 that enables centering of material 5
, installation of a caustic cooling device that moves the cooling device according to the unevenness of the steel material, and centering methods that include installing pinch rollers 8 and the like independently or in combination.

However, this measure attempts to forcibly center the guide 7 and the cooling device by moving the guide 7 and the cooling device, and there is a problem that the steel material 5 becomes scratched when it comes into contact with these. In addition, the method using pinch rollers 8 also has problems such as increasing the diameter of the roll to lower the rotation speed and dealing with wear of the bearings as the finishing speed becomes faster. There are disadvantages in terms of cost and maintenance.

(Problems to be Solved by the Invention) The present invention has been made to advantageously solve these problems, and is a method that allows uniform cooling of steel materials without centering them in a cooling device, which is not possible in the prior art. The object of the present invention is to provide a cooling method that provides uniform and high cooling performance, which is indispensable for performing controlled rolling and controlled cooling.

(Means and operations for solving the problems) The present invention will be explained in detail below with reference to the drawings.

The present inventors supplied water 3 between an inner tube 1 and an outer tube 2 as shown in FIG. In a device that injects water to cool the steel material, when the unit cooling devices 6 are arranged continuously in series in the advancing direction of the steel material as shown in Fig. 8, the cooling unevenness and cooling capacity are constant depending on the water density and the steel material temperature. It was found that there is a relationship between

As shown in Figure 1, when steel is stably held in the cooling pipe, the water density (unit time).

Uniform cooling is possible almost unaffected by the amount of cooling water per unit surface area of the material to be cooled, but if the steel material is uneven in the cooling pipe, cooling will suddenly become uneven when the water density is less than 25071i'/h, m'. .

That is, the gap is set to such an extent that the steel material does not come into contact with the inner tube of the cooling device, preferably 2 to 10 I7a, and the water density is 250 i/h, tr? By supplying cooling water in the above manner, it is possible to obtain uniform and high cooling performance. Here, the water density is 250yri! /h
,rr? The reason for the above limitation is that by supplying a large amount of cooling water to unit cooling liquid #6, completely surrounding the steel material with cooling water, and ensuring a foot of cooling water thickness around the steel material, it is possible to The jetted cooling water directly collides with the steel material, expanding the area of the collision area, making the water volume density distribution uniform in the circumferential direction, and stabilizing the film heat transfer coefficient between the copper material shin surface and the cooling water. I am doing it.

Furthermore, by filling the cooling device with a large amount of high-pressure cooling water while injecting it from the nozzle, it also has the role of preventing the steel from becoming uneven within the cooling device. Since the circumferential water density distribution of the cooling device is made uniform in every corner, and the circumferential water volume distribution from the cooling device nozzle is also made uniform, the uniform cooling performance is significantly improved.

In addition, the cooling capacity is a function of the steel material surface temperature, but from 600 to
It has also been practically confirmed that in the range of 1000°C, the heat transfer coefficient is expressed as a function only of the water density. Increasing the water density increases the momentum of the collision part caused by the cooling water jet, shortens the residence time of the cooling water in the cooling device, lowers the film water temperature around the steel material, and reduces the heat transfer resistance in this part. Therefore, it is thought that the cooling capacity increases.

Next, we will discuss the relationship between steel material temperature and cooling capacity.

Figure 2 shows the overall layout of the factory, with #1 cooling zone 9 and #2 cooling zone 1 installed before and after the NT block mill.
This is a layout when steel material is cooled at 0. In the figure, a heating furnace 30, a rough rolling mill 31, an intermediate rolling mill 32, a first
In the existing mill with such a layout, which shows the finishing rolling mill 33, the second finishing rolling mill 34, and the NT block mill 3-5,
If controlled rolling and controlled cooling are to be applied, the length of the cooling zone is limited due to the relationship between the front and rear equipment, so uniform cylinder cooling capacity is required in the specifications of the cooling device, and the application of the present invention is necessary. becomes.

In addition, the length of the s2 cooling zone after the NT diblock mill is said to be limited to a maximum of 45 m due to problems such as bending of the steel material, and extremely strict uniform and high cooling performance is required regardless of new construction or modification of existing facilities. , the application of the present invention is desired as described above. The length of the cooling zone after the NT diblock mill in the conventional method is
The difference between the production amount and the heating/cooling zone length (m)/production amount (T/H) was in the range of 0.55-0.66 (m/T/H), but the finishing speed was 9 om/H. s or more, the above relationship becomes 0, 4. (m/T/H), it is not possible to cool the steel plate surface to the target welding temperature while maintaining the optimum cooling limit temperature or higher using conventional technology.

Here, the appropriate cooling limit temperature refers to line a shown in FIG. 3, which is the lowest limit temperature that does not cause abnormal structure cooling cracks in the cooled steel material, and the target coiling temperature refers to line b.

Therefore, it is necessary to pursue the shortest length of the cooling zone to achieve the target steel material temperature. Figure 3 is a conceptual diagram of how to find the theoretical shortest length. The theoretical shortest length L is the steel material surface heat transfer coefficient is infinite when cooling starts in the cooling zone.
When the surface temperature of the steel material reaches the appropriate cooling limit temperature a, in order to maintain that temperature, the temperature is slowly cooled to prevent the temperature from rising due to recuperation from the Murayama section, and the average temperature of the steel material is reached. It can be defined as the length L required to reach one temperature. 1' is a cooling section with an infinite heat transfer coefficient.

However, in reality, the surface heat transfer coefficient of steel material is finite, and it is also difficult to maintain the steel material surface temperature at the appropriate cooling limit a. Therefore, as shown in FIG. 4, the shortest length L that can be achieved is to carry out as many multi-stage cooling as possible and perform controlled cooling so that the surface temperature of the steel material at the outlet of each cooling zone is approximately constant. In the figure, C is the surface temperature of multistage cooling based on the achievable heat transfer coefficient. The constant temperature at this time is determined by taking measurement errors, control errors, etc. into consideration with respect to the optimum cooling limit temperature.
It's good to have some leeway. The number of cooling zones is determined by taking into consideration the measurement error with respect to the target temperature and the relationship shown in FIG. 5, that is, the margin temperature to the supercooling limit increases as the number of zones increases.

Next, the water density of the present invention is 250? A specific example of a cooling method when a plurality of unit cooling devices of 7Z'/h, - are arranged in series will be described.

For manufacturing multiple steel types and sizes, uniform cooling is performed while ensuring a unit cooling device water flow density of 25077Z3/h, 771' or more ((Measure the steel material temperature in the pre-cooling zone process, and cooling steel specifications, rolling conditions,
and cooling conditions are entered into a computer, the rolled steel material temperature prediction model is used to predict the temperature of the steel material at the entrance of the cooling zone, the cooling zone to be used and the optimum water amount are determined, and the cooling valve and cooling water amount are controlled based on those values. This makes it possible to perform controlled rolling and controlled cooling with the same cooling zone length as before, even if the finishing speed increases. This will be explained with reference to FIG.

FIG. 6 shows a case where there are two cooling zones, the first stage being the #2 cooling zone 9 and the second stage being the #2 cooling zone 10. Each cooling zone is constructed by arranging a plurality of unit cooling devices 6 shown in FIGS. 7 and 8 in series, and in each cooling zone, the unit cooling devices are divided into two groups, namely, in the #1 cooling zone. is 9A.

9B, and the #2 cooling zone is IOA and IOB, and the unit 'cooling device groups 9A, 9B, IOA, and IOB are assumed to spout and stop cooling water all at once within each group.

In the figure, 11 is a steel temperature gauge in the pre-cooling zone process.〕2
is a steel thermometer used in the post-cooling zone process.

5 is a control calculation section that normally uses a computer. 1
4 is an information setting device, which inputs information on the steel material to be cooled. 15 is a cooling water delivery pump, 16 is a main flow meter, 17 is a #1 cooling zone flow meter, 18 is a #2 cooling zone flow meter,
19 is the main valve, 20 is the #1 cooling zone pulp, 21
is the #2 cooling sea/valve, 22 is the valve of the cooling device group 9B of the #1 cooling zone, 23 is the valve of the cooling device group 10'B of the #2 cooling zone, 24 is the cooling group setting device, 25i1
: It is a winding machine.

When cooling the steel material 5, first, the information setting device 14 inputs the steel material specifications such as wire diameter, rolling speed, steel type, target winding temperature, rolling conditions, and cooling conditions to the control calculation section 13.

At the same time, the steel material temperature is input using the steel material thermometer 11 in the cooling zone pre-process. Based on this information, the control calculation section 3 determines the water density of each unit cooling device to be 250.
7/h, - or above, the optimal cooling condition where the steel material winding temperature after cooling is the target value, that is, the movable unit cooling device groups 9A, 9B, 1
．． Select OA and IOH and calculate the amount of cooling water.

Based on this calculation result, the main valve 19, the #1 cooling water pulp 20+$, and the #2 cooling water valve 21 are turned on and off, and the cooling device group valve 22 is turned on and off via the cooling zone selection and cooling group setting device 24. .23 is operated. The cooling water flow rate is determined by the main flow meter 16, the #1 cooling zone flow-teaching meter 17. The $2 cooling zone flowmeter 18 measures each flow, and the results are input to the control calculation unit 13.

In the control calculation unit 13, when the flow rate is different from the set flow rate,
Output the corrected value to each cooling water valve. The steel material temperature measured by the cooling zone post-process thermometer 12 is input to the control calculation section and compared with the target winding temperature, and if it is different, the cooling device group is selected or the amount of cooling water is changed to correct it.

(Effects of the Invention) According to the present invention, it is possible to perform high-performance uniform cooling of rods and wires without uneven heating during rolling, and to realize short cooling seams and controlled cooling.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between cooling unevenness and water density, Figure 2 is an overall explanatory diagram showing the production line for rods and wires, Figure 3 is an explanatory diagram of the theoretical shortest length of the cooling zone, and Figure 4 is a diagram showing the cooling zone. An explanatory diagram of the shortest possible length of a zone, Fig. 5 is a diagram of the relationship between the number of water cooling zones and the margin temperature to the supercooling limit, Fig. 6 is an explanatory diagram of the configuration of an example of implementing the present invention, and Fig. 7 is an explanatory diagram of the configuration of an example of implementing the present invention. FIG. 8, an explanatory diagram of a conventional example, is an explanatory diagram in which a plurality of cooling devices are successively provided. l: Inner pipe 2: Outer pipe 3: Cooling water 4: Hole 5: Diarrhea 6: Cooling device 7: Induction guide 8: Vinci roller 9: #1 cooling zone 9A, 9B: Unit cooling device group 1o:
$2 Cooling zone] OA, IOB: Unit cooling device 1:
Yuyu zone pre-process group thermometer 1
2: Cooling zone post-process 13: Control calculation section thermometer, 14: Information setting section 15; Cooling water supply pump]
6: Non-tube flow meter 17: #'1 Cooling zone flow 1s: $2 Cooling zone flow meter
19; Main pulp 20: #l cooling zone valve 21: $2 cooling zone valve Lube 22.23: Cooling device group bar 24: Cooling group setting device Lube 25: Winding machine

Claims (1)

[Claims] 1. A method of cooling hot-rolled steel by injecting water, the water density being 250 m^3/h. A method for cooling steel materials, characterized in that unit cooling devices of m^2 or more are successively arranged in series in the direction in which the steel materials travel. 2. Claim 1, characterized in that when a plurality of water cooling zones are installed in series in the traveling direction of the steel material, cooling is controlled so that the surface temperature of the steel material at the exit of each water cooling zone is approximately constant. method of cooling steel materials. 3 Based on the output of the steel thermometer installed in the pre-process of the water cooling zone, the specifications of the cooling steel, rolling conditions, and cooling conditions,
Claim 1, characterized in that the temperature of the steel material at the entrance of the cooling zone of the rolled steel material is predicted, the cooling zone to be used and the optimum amount of water are determined, and each cooling water valve and the amount of cooling water are controlled based on this value. Method of cooling the steel described.