JPS5855534A - Method and apparatus for annealing cold-rolled coil - Google Patents

Abstract

PURPOSE:To enable to control the temperature of atmospheric gas and to perform annealing with excellent thermal efficiency and annealing ratio, in annealing the cold-rolled coil of a steel strip in a batch oven, by using the atmospheric gas for annealing heated by a heat exchanger. CONSTITUTION:The coils 3 of cold-rolled steel strips are piled up in several layers, covered with an inner cover 4 and further covered with an outer cover 5. Atmospheric gas for annealing is heated at an objective temperature by the combustion heat of fuel 31 from a burner 21, when it passes through a heat exchanger 20. The heated atmospheric gas is fed through a circulating line 23 into the inner cover 4 to anneal the coils 3 with heat, and the atmospheric gas whose temperature has been lowered is returned into the heat exchanger 20 again, heated therein and fed into the inner cover 4. The combustion exhaust gas from the burner 21 is the heat exchanger 20 is let flow through an annular space 26 between the inner cover 4 and the outer cover 5 to heat the inner cover 4 and then used for heating air 27 and fresh atmospheric gas 28 for the burner 21 by heat exchangers 29, 30. Consequently, the temperature of the atmospheric gas for annealing is easily controlled, and sintering caused by overheating the coils is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of annealing a cold-rolled coil, and more particularly to a method of annealing a cold-rolled coil using an atmospheric gas heated to a sufficient temperature in a heat exchanger.

Cold-rolled coils, that is, coils obtained by cold rolling, have poor workability due to work hardening.

Generally, this is annealed to soften the steel and improve workability. There are two types of softening annealing methods for cold-rolled coils: one is a continuous annealing method in which the cold-rolled coil is sent to an annealing step continuously from the cold rolling step, and the other is a method in which a cold-rolled coil that has been wound once is annealed in a batch method. .

When performing the batch process, the cold-rolled coil is placed on the hearth in stage e (8 to 8).
This is then covered with an inner cover and then an outer cover, and heat is transferred to the inner cover by direct fire or indirect heating (radiant cheese) using a burner attached to the outer cover.

FIG. 1 shows a schematic cross-sectional view of a conventional batch-type annealing furnace. In the figure, a punch-type annealing furnace 1 includes an inner cover 4 and an outer cover 5 that cover cold-rolled coils 8 (8 stages in the illustrated example) stacked in several stages (3 to 4 stages) on a hearth 2. A convection plate 6 is provided between the coils, and atmospheric gas circulated by a circulation fan 7 provided in the hearth 2 flows between the coils. Reference numeral 1M' indicates a motor for a circulation fan. In such a conventional device, the heat source is the burner 8 provided on the outer cover, so that heat is transferred to the coil through the outer cover, the inner cover, the atmospheric gas, and I@ to the coil.

Heat is transferred from the burner installed on the outer cover to the inner cup (2-) by direct flame or indirect heating (radiant tube).Meanwhile, inside the inner cover, atmospheric gas circulates as shown by the arrow in Figure 1. After being heated by the inner cover, the convection plate is heated by convection, and then transmitted to the coil through this convection plate.(Generally, the total amount of heat transferred from the width direction of the coil is 5A, and the amount of heat transferred from the outer circumference of the coil is the remaining amount. 6) However, in such conventional devices, the atmospheric gas is mainly heated by convection with the inner cover;
Since the gas flow inside the inner cover changes depending on the coil diameter, the atmospheric gas temperature varies, and generally the upper part of the coil tends to be higher. In addition, since it is not possible to control the temperature of the atmospheric gas, strict temperature control according to the material of the cold-rolled coil cannot be performed. In addition, heat is transferred from the outer circumferential direction of the coil by radiation from the inner cover, which may cause overheating and seizure, and in particular, the top part of the annealed coil or the upper coil may suffer from seizure or defective products due to uneven heat.

The purpose of the present invention is to reduce the temperature in the annealing furnace as much as possible,
It is an object of the present invention to provide a method and apparatus that can annealing a cold-rolled coil in a short period of time and with reduced energy consumption, while also allowing the temperature to be changed arbitrarily.

Here, the present invention provides: (1) The cold-rolled coils stacked on the hearth are divided into an inner cup (-) to define a space for accommodating the cold-rolled coils, and the inner cup is further divided into an outer cup (-). A batch-type cold-rolled coil annealing method in which an annular guide path is formed between the inner cover and the inner cover, and the cold-rolled coil is heated by atmospheric gas circulating in the space inside the inner cover, the method comprising: a combustion device; An indirect heat exchanger equipped with a heat exchanger is provided outside, and the atmospheric gas heated by the indirect heat exchanger is introduced and circulated into the space inside the inner cup (-), and the combustion exhaust gas of the indirect heat exchanger is transferred to the outer heat exchanger. (2) A method for annealing a cold-rolled coil, characterized in that the atmospheric gas is supplied to the annular conduit in - and indirectly heated through the inner cover, and (2) a hearth on which cold-rolled coils are stacked; an inner cover disposed on the hearth so as to surround the cold-rolled coil; an outer cover disposed on the hearth so as to surround the inner cover, and an annular guide path formed between the inner cover and the inner cover; an indirect heat exchanger for atmospheric gas equipped with a combustion device that heats the atmospheric gas that heats the cold-rolled coil in the inner cover; and a space portion that accommodates the cold-rolled coil in the inner cover and supplies the heated atmospheric gas to the space portion that accommodates the cold-rolled coil. an atmospheric gas circulation path that guides and reinflames atmospheric gas into the indirect heat exchanger for reheating; and an exhaust gas conduit that guides combustion exhaust gas from the indirect heat exchanger to the annular conduit in the outer cover. This is a cold-rolled coil annealing device consisting of:

As described above, according to the present invention, since the atmospheric gas for heating the cold-rolled coil is heated in the heat exchanger provided outside, a desired temperature can be ensured, and the temperature can also be controlled.

Therefore, it is possible to increase the difference between the atmospheric gas and the coil heating temperature, thereby making it possible to shorten the sintering time. On the other hand, by allowing the combustion exhaust gas discharged from the heat exchanger 4 for heating the atmospheric gas to flow through the annular conduit in the outer cover, additional heat can be transferred to the coil through the inner/cover, the atmospheric gas, and the thermal efficiency. It is possible to save energy by making adjustments. Furthermore, since there are no places in the furnace that are heated by direct flame, local overheating is prevented, and a constant heating temperature is achieved throughout the furnace.

The invention will be further explained with reference to the drawings. FIG. 2 is a schematic cross-sectional view of the device according to the invention. In the figure, the same members as in FIG. 1 are denoted by the same reference numerals. The indirect heat exchanger 20 installed outside the furnace is equipped with a burner 21, and the combustion heat from this burner causes atmospheric gas (generally N1
gases such as H, H, etc.) are heated.

The atmospheric gas is sent to the heat exchanger for heating the atmospheric gas by the circulation fan 22 and heated to a predetermined temperature, and then sent into the furnace through the air gas circulation path 28, which is a space in which the cold-rolled coil 8 is accommodated. After the heat is transferred to the coil while circulating through the section 24, the OIZ is reheated to the heat exchanger 20 by the circulation fan 22 and reheated. The flow direction of the atmospheric gas is shown by the arrow in the figure.

The combustion exhaust gas 25 is sent from the heat exchanger 620 to the annular conduit 26 in the outer cover, and is further exchanged with the fuel combustion air 27 and the newly supplied atmospheric gas 28, respectively.
29.80 and is discharged after heat exchange. Fuel supply path 3
If necessary, the fuel from step 1 may be preheated with the combustion exhaust gas.

After being heated to a predetermined temperature for a predetermined time in this manner, the heating coil must be cooled down, which can be easily done by stopping the operation of the heat exchanger.

According to the present invention, the fA node of the atmospheric gas can be adjusted to any high temperature gas, so that the heat transfer to the coil can be increased.

For example, FIG. 8 graphically shows the relationship between the heating time and the coldest point temperature when the atmospheric gas temperature is supplied at 750 to 780'C. The heating plane according to the present invention is represented by a white circle and a solid line.

The data shown is for four cold-rolled coils using the equipment shown in Figure 2.
The results were obtained when the coils were stacked in layers and heated, and the coldest point was measured at the point indicated by the mark (■) on the side of the coil shown in a schematic side view in FIG. In the figure, numeral 41 is a cold-rolled coil;
42 is a convection plate.

As can be seen from the illustrated results, when the intended heating temperature of the coil is 680° C., according to the present invention, the heating time during annealing can be shortened by 85 hours in the illustrated example compared to the conventional example. A conventional example is an apparatus shown in FIG.

Furthermore, since the atmospheric gas temperature is controlled to be constant, there is no burning due to overheating, and the quality can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a conventional cold-rolled coil annealing device; FIG. 2 is a schematic cross-sectional view of a cold-rolled coil annealing device according to the present invention; FIG. 8 is a graph showing the relationship between the coldest spot temperature and time. and FIG. 4 is a schematic side view of the coil O showing the measurement point of the coldest point temperature. 1: Annealing furnace 20: Indirect heat exchanger 2: Hearth floor
21: Burner 3: Cold rolled coil 22: Circulation fan 4: Inner cover 28: Atmospheric gas circulation path b: Outer cover 2
9.80: Heat exchange breasts 4 figure 7f

Claims (2)

[Claims] (1) The cold-rolled coils stacked on the hearth are covered with an inner cover to define a space for accommodating the cold-rolled coils, and the inner cover is further covered with a seven-outer cover to create a space between the outer cover and the inner cover. A batch-type cold-rolled coil annealing method in which the cold-rolled coil is heated by atmospheric gas that forms an annular conduit and circulates in the space within the inner cover, the method comprising: The atmospheric gas heated by the indirect heat exchanger is introduced into and circulated in the space in the inner cover, and the combustion exhaust gas of the indirect heat exchanger is supplied to the circulation conduit in the outer cover. A cold-rolled coil annealing method characterized by indirectly heating atmospheric gas through an inner cover. (2) A hearth on which the cold-rolled coils are stacked, an inner cover disposed on the hearth so as to recess the stacked cold-rolled coils, and an inner cover disposed on the hearth to surround the inner cover, and an inner cover disposed on the hearth so as to surround the inner cover. an outer cover in which an annular guide path is formed between the covers; an indirect heat exchanger 6 for atmospheric gas equipped with a combustion device that heats the atmospheric gas that heats the cold-rolled coil in the inner cover; An atmospheric gas circulation path that guides atmospheric gas into the space that accommodates the cold-rolled coil in the inner cover and also supplies S* to the indirect heat exchanger for reheating, and combustion from the indirect heat exchanger. A cold rolled coil annealing device comprising: an exhaust gas conduit that guides exhaust gas to an annular conduit in the actuator cover.