KR101138181B1 - Method for reducing the difference of cooling rates between center portion and outer portion of hot-rolled wire rod - Google Patents

Abstract

The present invention relates to a method for uniformly cooling a hot rolled wire rod to reduce the cooling deviation caused by the overlap density difference in the width direction of the wire rod loaded on the roller conveyor after being rolled in a ring shape at the laying head after hot rolling. will be.

The uniform cooling method of the hot-rolled wire rod according to the present invention to cover the open space between the slow cooling cover installed at a predetermined interval behind the laying head on the roller conveyor to increase the ambient temperature It is characterized in that to provide a heating plate having a predetermined width and extending from the tip of the slow cooling cover to the vicinity of the laying head.

The heating plate is made of an inner heat-transfer body and a metal which is the outer shell, and has a width of 50 to 100% of the wire width and a length of 1 m or more, and is maintained at 650 ° C. or more.

Wire Rod Process, Hot Rolled, Slow Cooling, Head Laying, Insulation, Cooling Deviation

Description

Uniform cooling method of hot rolled wire {Method for reducing the difference of cooling rates between center portion and outer portion of hot-rolled wire rod}

1 is a schematic diagram of a conventional wire rod processing line.

FIG. 2 is a schematic diagram showing the lamination density in the width direction of the wire rod loaded and conveyed in the roller conveyor as shown in FIG. 1.

3 is a schematic view of a wire processing line according to an embodiment of the present invention.

4 is a graph showing data measured according to a conveying distance from a laying head of the temperature at the center and the edge of the wire rod transported along a conventional wire rod process line.

5 is a graph showing the temperature deviation between the center portion and the edge portion of the wire rod according to the feeding distance from the laying head using the measurement data of FIG. 4.

<Description of the symbols for the main parts of the drawings>

1: rolling mill 2: water cooling system

3: laying head 4: wire rod

5: roller conveyor 6: nozzle

10: slow cooling cover 20: heating plate

The present invention relates to a method for uniformly cooling a hot rolled wire, and more particularly, the hot rolled wire is wound by a ring shape in a laying head and then cooled by overlapping density in a width direction of a wire rod loaded on a roller conveyor. The present invention relates to a method for uniformly cooling a hot rolled wire rod to reduce the deviation.

Generally, as shown in FIG. 1, the wire rod is rolled into a wire rod by a rolling mill 1 and cooled by a water cooling device 2, and then the rolled wire rod is wound by a laying head 3. It consists of the process of air-cooling while loading in a ring form on the roller conveyor 5, and conveying it.

At this time, the air-cooled wire rod is quenched or slow cooled according to the required mechanical properties. In the case of the wire rod which requires strength, the wire rod is sprayed onto the surface of the wire rod 4 to which wind and water vapor are transferred from the nozzle 6 installed under the roller conveyor. In the case of the wire rod 4 which is quenched and needs high elongation, a slow cooling of the wire rod is used using a slow cooling cover 10 covering the upper portion of the roller conveyor as shown in FIG. 1. Generally, the slow cooling cover is installed to be opened and closed.

2 is a diagram showing the lamination density in the width direction (that is, in the width direction of the roller conveyor) of the wire rod loaded on the roller conveyor. The wire rod has a ring shape, and the lamination density at the center portion is higher than the edge portion of the wire rod width direction. Appears low. Therefore, the wire edge with high lamination density has a small surface area to mass and thus has a low heat loss, and the center portion of a wire having low lamination density has a large surface area to mass, thus resulting in a relatively large annual loss. It undergoes different cooling history and accordingly the microstructure changes, resulting in a difference in mechanical properties.

In addition, the difference in mechanical properties of the wire rod due to such cooling deviation occurs seriously when the slow cooling material is long due to the slow progress of the roller conveyor and the difference in lamination density at the center and the edge of the wire rod. There is a problem in that it causes a characteristic deviation for each location, which degrades the quality, makes it difficult for end users to set the reference point of work when machining the wire rod, and reduces the reliability of the product.

Conventionally, in order to reduce the cooling deviation in the center portion and the edge portion of the wire rod as described above, a method of installing a separate heating device on the inner side of the slow cooling cover for heating the wire rod central portion or selectively heating the wire rod central portion has been introduced. However, this method is based on the judgment that the cooling deviation occurs intensively in the section where the slow cooling cover is installed, and the difference in mechanical properties due to the cooling deviation is still a problem in the wire rod of the final product, and it is very effective in terms of cost and effect. Was not.

The present invention has been proposed to solve this problem, and the hot rolled wire rod without the cooling deviation by observing the section where the cooling deviation in the central portion and the edge portion of the wire rod that is loaded and transported on the roller conveyor in the rear of the laying head It is an object of the present invention to provide a method for allowing uniform cooling.

The uniform cooling method of the hot-rolled wire rod according to the present invention for achieving the above object, the open space between the slow cooling cover installed at a predetermined interval behind the laying head to cover the central portion of the wire rod to be moved on the roller conveyor It is characterized by providing a heating plate having a predetermined width and extending from the tip of the slow cooling cover to the vicinity of the laying head so as to increase the ambient temperature.

The heating plate surrounds the heating element with metal to allow the heat of the heating element to be released to the surroundings for a long time, to absorb the heat transferred from the wire rod and to release it again, and to reduce the cooling deviation of the wire rod by the heating plate. In order to have a width of 50 to 100% and a length of 1m or more relative to the wire width, it is preferable to maintain at 650 ℃ or more. Reference numeral 21 is a lower surface of the heating plate.

The present invention is focused on the fact that the change in the mechanical properties of each location of the slow cooled wire rod occurs due to the difference in temperature history and cooling speed of each part and that the temperature difference between the center and the edge of the wire rod occurs before entering the slow cooling cover. Thus, a heating plate is installed in the center immediately after the laying head and immediately before entering the slow cooling cover to reduce the cooling deviation between the wire center and the edge.

Hereinafter, with reference to the accompanying drawings looks at in detail with respect to the uniform cooling method of the hot rolled wire according to the present invention.

As can be seen in Figure 3, the wire rod process line according to the present invention, unlike the conventional, roller spaced open space between the slow cooling cover 10 installed at a predetermined interval (3 ~ 5m) spaced behind the laying head (3) The heating plate 20 which covers the center part of the wire rod 4 which is mounted and moved on a conveyor is provided. The heating plate 20 has a predetermined width and extends from the upper end of the slow cooling cover 10 to the vicinity of the laying head 3. At this time, the heating plate is preferably such that the inner heating body is surrounded by a metal shell.

Meanwhile, the reason why the slow cooling cover 10 is not applied immediately after the laying head 3 in the existing system is that the wire rod rolled to the final thickness falls into the roller container 5 at a high speed from the laying head in this section. This is because there is a high possibility that operation abnormalities may occur, and therefore the operators always need to observe them in order to deal with them promptly. Therefore, in order to reduce the cooling deviation of the wire rod while satisfying such working conditions, it is preferable that the heating plate 20 has a width of 50 to 100% of the wire rod width. If the width of the heating plate is too large, it is difficult to secure the operator's view.

In addition, the length of the heating plate is 1m or more, but if it is less than that, the effect of reducing the cooling deviation of the wire rods is insignificant, and the maximum length does not cause interference with the laying head 3 or the wire rod 4 falling away therefrom. It is set to a length not to be set.

The working principle of the heating plate is as follows. Heat loss due to radiation is proportional to the fourth power of the absolute temperature. Therefore, if the section just before the slow cooling cover is opened as in the conventional method, the loss is assumed to be {(830 + 273) ⁴ assuming that the initial temperature of the wire rod is 830 ℃ and the temperature of the open area is 25 ℃. -(25 + 273) ⁴ } = 1.47x10 ¹² However, if the wire temperature is left as it is and the surrounding temperature is raised to 700 ° C, the heat loss at this time is proportional to {(830 + 273) ^4- (650 + 273) ⁴ } = 7.54x10 ¹¹ . Comparing the heat loss in both cases, we can see that the heat loss is reduced by about 60% by increasing the ambient temperature.

In the present invention, the heating plate is selected as a method of increasing the ambient temperature. The heating plate is made of a metal plate as an outer shell and a heating element is applied therein, and the temperature is maintained at 650 ° C. or higher so that the central temperature of the wire rod is maintained. Is prevented from falling sharply in the section between the laying head and the slow cooling cover.

This heating plate has the advantages compared with the uniform cooling method of the hot-rolled wire using the heat insulating plate (re-radiation plate consisting of a metal shell and a high-temperature heat insulating material) developed by the present inventors are as follows. That is, in the case of the heat insulating plate, since the heat source that heats it is heat from the wire rod, the maximum temperature that the heat insulating plate can reach is low, but the heating plate has a higher temperature because the heat source is the radiant heat from the inner heating element and the wire rod. It becomes possible. Therefore, even when the wire passes and the section is empty, the heating plate continuously reduces the heat loss of the surrounding area, so when the new wire enters this section, the heat that the wire heats the surrounding system can be reduced. In addition, even if the width of the heating plate is small, it is possible to obtain a high heat retention effect, it is easy for the operator to secure the field of view for observing the rear end of the laying head.

[Comparative Example]

When the wire is transported along the conventional wire processing line with the slow cooling cover opened from the laying head, the center of the wire rod and the edge of the wire head along the length from the laying head to find the section where the cooling deviation between the center and the edge of the wire is concentrated. The temperature at the parts and their deviations were observed.

After the wire is rolled and before the wire placed on the transfer table through the laying head enters the slow cooling cover, about 3 ~ 5m section is progressed slowly without the slow cooling cover (0.12 ~ 0.25m / sec). The wire rod running at 0.25m / sec, which is the wire progression speed, was divided into a center part and an edge part from the rear end of the laying head 1.8m to the rear end of the laying head 5.4m.

As can be seen in Figure 4, the temperature measurement results of the wire rod edge of about 740-750 ℃, 690-700 ℃ in the center portion 5.4m after the laying head from the laying head temperature difference between about 50 ~ 60 ℃ I could confirm that it came. At this time, the cooling rate of the central part was measured at about 5 ° C. per second and the side part at about 2.5 ° C. per second. In other words, it can be seen that the temperature difference occurs by more than about 2 ℃ per second. The main reason for the temperature difference between the center and the edge is due to the difference in radiant energy loss due to the difference in lamination density of wire rod in the section of the laying head just before the slow cooling cover. The reason why the temperature difference between the two parts is large in this section is that heat loss at high temperature is mainly caused by radiation.

Temperature measurement of the wire rod in the slow cooling cover was carried out using three infrared thermometers. The temperature was measured at the center and side of the wire rod, and the temperature was measured at the rear end of the laying head by 8.4 m, 29.4 m, and 53.4 m using an infrared thermometer. The slow cooling cover was covered from 5.4m to 54m after the laying head. As a result of measuring the wire temperature of 8.4m at the rear end of the laying head, the temperature at the side was 715 ℃ and the center temperature was 636 ℃ in the 3m section of the slow cooling cover (12 seconds after entering). In the case of 29.4m after the laying head, 96 seconds after entering the slow cooling cover, the side temperature is 633 ℃ and the center temperature is 544 ℃. In the case of 53.4m after the laying head, the temperature of the side is 600 ℃ and the center temperature is 496 ℃ after 192 seconds after entering the slow cooling cover.

5 is a graph analyzing the temperature difference between the center part and the edge part. Initially, the temperature of the wire exiting the laying head is constant regardless of the site, which is about 830 ° C. However, the temperature of this uniform wire rod reached 8.4m after the laying head (that is, 34 seconds after leaving the laying head, 12 seconds after entering the slow cooling cover), and the temperature difference between the center and the edge was about 70 ° C. . At 29.4m after the laying head, the value is about 90 ° C and about 110 ° C at the 53.4m after the laying head. Analyzing these results, it can be seen that the site where the temperature difference occurs mainly in the center and edge of the wire rod is not the slow cooling cover section but before the wire rod enters the slow cooling cover. In other words, before the wire rod enters the slow cooling cover, the temperature difference between the side and the center is about 2 ℃ per second, but when entering the slow cooling cover, the difference is reduced to about 0.23 ℃ per second.

In conclusion, it can be seen that in manufacturing the slow cooling wire, it is important to reduce the temperature difference in the section just before entering the slow cooling cover from the laying head in order to reduce the temperature difference between the center part and the edge part of the wire rod.

[Examples]                     

In order to confirm the effect of the heating plate according to the invention the Inconel 601 having a thickness of 0.5mm and the inside of the heating plate is heated to 700 ℃ while varying the width and length of the heating plate to which the heating element is applied, the center of the wire rod-edge portion The degree of reducing the temperature deviation of the liver was measured. The results are shown in Table 1 below.

The temperature measurement of the wire rod was carried out 8.4m away from the laying head, and the heating plate was installed at 5.4m after the laying head.

As can be seen in Table 1 below, when the width of the heating plate was too small (30%), the temperature difference between the center portion and the edge portion by the heating plate was found to be small. However, if the width of the heating plate is too large (120%) compared to the wire width, the heating cost is too high compared to the effect and it is difficult to apply the field because it is impossible to secure the field of view of the operator.

On the other hand, when the length of the heating plate is 0.5m or less, the effect is insignificant and there was no significant effect, and it was found that it is preferable to apply 1m or more.

Table 1. Result Data

Hot plate
Length (m) Width of heating plate to wire width (%) 30 50 70 100 120 0.5 X X X X X One X △ △ △ △ 1.5 X △ ◎ ◎ △ 2 X △ ◎ ◎ △ 3 X ◎ ◎ ◎ △ 4 X ◎ ◎ ◎ △ 5 X ◎ ◎ ◎ △

(Double-circle): Excellent (within 15 degreeC of temperature deviation between wire part center part and edge part)

(Triangle | delta): Normal (within the temperature difference of 30 degreeC between a wire center part and edge part)

X: poor (temperature deviation 30 degreeC or more between wire part center part and edge part)

According to the uniform cooling method of the hot-rolled wire rod having the structure as described above, the hot-rolled wire rod is cooled by installing a heating plate in the open section between the laying head and the slow cooling cover in which the cooling deviation between the wire center and the edge portion is large. It can be cooled uniformly without.

Claims (3)

The hot rolled wire cooling method in which the wire rod wound on the laying head in a ring shape after being hot rolled is transferred by the roller conveyor to be slowly cooled while passing through a slow cooling cover installed at a predetermined interval behind the laying head. To Both side regions of the wire rod, which are loaded and moved between the laying head and the slow cooling cover on the roller conveyor, cover the center of the upper region while increasing the ambient temperature while opening the open space between the laying head and the slow cooling cover. And a heating plate extending from the side to the vicinity of the laying head. The method of claim 1, The heating plate is wrapped in a metal inside the hot rolled wire rod cooling method characterized in that to release the heat of the heat transfer body at the same time to absorb the heat transferred from the wire rod and to release again. The method of claim 2, The heating plate has a width of 50 to 100% of the wire width and a length of 1m or more, and the hot rolled wire cooling method characterized in that to maintain a temperature of 650 ℃ or more.

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