JPS6227129B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for reheating a hot-rolled steel strip (hot strip) that is wound into a coil in a winder after hot rolling. In recent years, it has become common practice to wind up a coil at a high temperature and heat-treat it using the heat possessed by the coil itself, without reheating the coil. At this time, if there is a temperature difference in the width direction or length direction of the strip, uneven heat treatment will occur in the strip, so the wound coil is first placed in a heat retention furnace or recuperation furnace for a predetermined period of time, and the coil itself is heated. Make the entire temperature uniform. At this time, the inside of the heat-retaining furnace is also heated if necessary. However, in the heat retention furnaces or recuperation furnaces known so far, sufficient effects could not be obtained due to the temperature difference between the strip edge portion and the central portion. However, in the heat retention furnaces or recuperation furnaces known so far, not only the temperature of the entire coil is lowered due to the above-mentioned temperature equalization, but also the temperature difference between the strip edge part and the center part, which is especially important, is significantly improved. It cannot be done. The present invention proposes an efficient method for recuperating heat in the above-mentioned heat retention furnace or recuperation furnace. Adjacent coils are placed horizontally (commonly known as down-end) and the side end faces of the coils (the laminated end faces of the strip widthwise edges)
A method for recuperating heat from a coiled hot strip is characterized in that recuperation is carried out by bringing two coiled hot strips close to each other. The recuperator usually consists of a recuperator chamber lined with a heat insulating material or a heat insulating material, and is appropriately equipped with a heating device. In this recuperation chamber, heat radiation (radiation)
phenomenon and convection phenomenon occur. This heat radiation/convection only increases the atmosphere within the recuperation chamber and does not directly contribute to uniform heating of the hot strip coil, which is the material to be recuperated. Ideally, the temperature of each part of a coiled hot strip can be uniformly equalized only by heat conduction from the upper high temperature part to the lower temperature part while keeping the hot coil completely insulated from the outside, but in reality, this is not possible industrially. There is nothing that makes it possible. For this reason, a recuperator is used. The present inventors have proposed the present invention as a result of various studies on the behavior of heat such as heat radiation and convection within the recuperator. Generally, a plurality of hot coils are installed in a recuperator to perform heat recuperation, but the behavior of heat within the recuperator differs depending on how the coils are placed. If we closely observe the shape and winding of the hot coil, we can see that the edges in the width direction of the strip are exposed at the end of the coil, but the exposed condition does not form a flat part, but is rather uneven and appears to have gaps (first
figure). This is thought to be due to the width accuracy, winding accuracy, and telescopic effect of the coil during hot rolling, but for this reason, the exposed area per apparent unit area at the end of the coil becomes large, and the degree of heat dissipation is reduced. It is larger than the other parts of the . This transfer of heat from the end of the coil is, for example, a point A at the end of the coil, as schematically shown in FIG.
From a point of view, when thermal radiation F is generated as shown in the figure, the heat in the atmosphere becomes convection T, forming an upward flow, and the hot air carried by the convection is thought to further transfer heat to the surroundings. Applying this heat transfer phenomenon to conventional hot coil recuperation, Figures 2 and 3 show a coil 1 placed vertically in a cylindrical position for recuperation. This shows how they are lined up inside the furnace. FIG. 2 shows a front view, and FIG. 3 shows a plan view. In this type of vertical installation, the coil ends (surfaces) 2 located above and below
Strip edge (width direction) due to heat dissipation from
As the strip cools down, the temperature difference with the center of the strip increases, which lengthens the time required to complete soaking, lowers the soaking temperature, and prevents efficient heat recovery. On the other hand, a placement method (commonly known as a down-end) in which FIG. 3 (plan view) is replaced with a front view is not as efficient as the vertical placement method. In the present invention, as shown in FIG. 4 (front view) and FIG. 5 (plan view), the coil end faces are opposed to each other in the recuperator and placed horizontally (down-end) as close as possible to each other. Do heat. If this is done, as schematically shown in Figure 9, if we look at the heat radiation at point A as in Figure 8, it will be blocked by the coils facing each other with a predetermined gap Δl in between, and will directly escape into the atmosphere. The thermal radiation F is only small in the range of angles θ ₁ and θ ₂ shown in the figure, and the rest is radiated toward the opposing coil end faces. It can be seen that the range of θ ₁ and θ ₂ becomes smaller as Δl becomes smaller. Since the temperature difference between opposing coils is not so large, the transfer of heat is not large, and the donut-shaped coil end faces with approximately the same diameter face each other, and the spacing Δl between the coil end faces is approximately equal, so heat radiates from each other. As a result, heat convection is reduced, so there is less heat transfer from the end of the coil to the atmosphere in the furnace, and as a result, heat can be recuperated without increasing the temperature difference in the width direction of the strip. Table 1 shows an example of a hot coil that weighs 10.3 tons, has a coil diameter of 1470 mm, an inner diameter of 720 mm, a width of 1020 mm, and has a winding temperature of 700°C using a heat insulating cover. Temperature measurements were taken 1 hour after incubation.

[Table] Figure 10 shows the tendency of the temperature difference between the coil end E and the coil center C. Symbols E and C indicate temperature measurement positions. As is clear from this experimental example, when the coil side end surfaces are opposed and brought close to each other according to the present invention, it is possible to prevent the temperature difference from increasing in the strip width direction. It can also be seen that the smaller Δl is, the higher the effect is. FIG. 6 shows an example of a recuperator for implementing the present invention. This recuperator 3 is a tunnel type recuperator, and a walking beam type coil support device 5 is installed at the bottom of a tunnel type furnace body 4 . The furnace body 4 is made of a heat insulating material or is lined with a heat insulating material, and has a structure that prevents heat from escaping to the outside of the furnace. It is preferable to provide a double door type partition 6 made of heat insulating material at the entrance and exit. The coil support device 5 has a predetermined lifting height and a predetermined traveling speed, has a truck 8 installed on a track 7, and connects a coil support stand 10 to the truck 8 via an elevating cylinder 9. The cylinder 11 is for running. 12 indicates wheels of the truck. If this coil support device 5 is divided into two parts, an inlet side and an outlet side, as shown in the example shown in the figure, and the advancing speed of each can be changed arbitrarily, the coils can be charged close to each other in the recuperator. It's convenient for that. Since the coil support stand 10 is in direct contact with the hot coil 1, it is preferably made of a heat insulating material, and at least the inside of the furnace should be made of a heat insulating material. The gaps between the furnace body 4 and each moving part are sufficiently sealed to prevent heat inside the furnace from escaping. The partition 6 is made of a heat insulating material and is shaped like a curtain, and is raised and lowered (opened and closed) by a cylinder 13 or the like. In this way, it is convenient to move the coil support device 5 up and down without any hindrance. The curtain-shaped partition 6 can achieve good results when the coils 1 are inserted in close proximity to each other by using a heat-shielding cloth that is as thin as possible and has a large heat-insulating effect. In order to reheat the hot coil 1 that has been wound up after hot rolling using such a recuperator 3, first, use a C-hook or the like to place the hot coil 1 on the inlet side of the coil support 10 (on the left side of the drawing) as shown in the figure. Place it like this. Then, using the walking beam mechanisms 8, 9, 10, 11, they are sequentially charged into the recuperator 3 with double partitions 6, 6. In this case, it is convenient for close loading if the walking beam on the entrance side is set to move at a faster speed than on the exit side. After a predetermined time, the coils that have completed reheating are extracted one by one from the outlet (on the right side of the drawing). This example is a walking beam type example,
The drive system can be modified in various ways, such as a chain conveyor system or a pusher system. According to the present invention, since the heat held by the hot coil itself in the recuperator is difficult to escape into the furnace, the hot coil can be uniformly heated efficiently, and the industrial benefits are extremely large.

[Brief explanation of the drawing]

Figure 1 is a partially cutaway front view to explain the state of the hot coil side end face, Figures 2 and 3 are diagrams to explain how to place the coil in a conventional general recuperation furnace, and Figure 2 is a front view. Figures 4 and 5 are plan views, and Figures 4 and 5 are explanatory diagrams of how to place the coils of the present invention.
Figure 5 is a front view, Figure 5 is a plan view, Figure 6 is a vertical sectional view illustrating an example of a recuperator implementing the present invention, Figure 7 is a sectional view of Figure 6, and Figure 8 is a hot coil. FIG. 9 is a schematic diagram for explaining the heat radiation of a hot coil in the case of the present invention, and FIG. 10 is a diagram for explaining the experimental results of the present invention.

Claims (1)

[Claims] 1. When recuperating multiple coiled hot strips together as coils, the adjacent coils are placed horizontally in the recuperator, and the side end surfaces of the coils (the laminated end surfaces of the strip widthwise edges) are brought close to each other to face each other. A method for recuperating coiled strips, characterized by heating.