JPH0563527B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a continuous annealing furnace for steel strip, and in particular,
The aim is to prevent thermal deformation and pick-up flaws in the steel strip while increasing the speed of annealing.

(Prior Art) A steel strip, such as a stainless steel strip, after cold rolling is subjected to an annealing treatment. The annealing furnace used here is typically a direct-fired continuous annealing furnace as described in Japanese Patent Publication No. 50-28048.

That is, as shown in FIG.
5, a plurality of hearth rolls 26 are installed on the entrance/exit side and inside the annealing furnace 21, and a direct-fired burner 27 as a heating means and a cooling means as a cooling means are installed above and below the steel strip S through which the sheet is passed. A cooling header 28 is installed. Then, the steel strip S is moved in the direction of the arrow while catenary supported by the hearth roll 26, and is subjected to a predetermined heat treatment by the heating/cooling means described above.

However, the steel strip S is oxidized in the furnace, and oxide scale is generated on its surface. This oxide scale adheres to and grows on the hearth roll and causes scratches on the steel strip, causing so-called pick-up scratches.
These pick-up flaws are more likely to occur as the steel strip is conveyed at a higher speed, so the hearth roll must be replaced more frequently, which reduces productivity.

In addition, in this type of furnace, measures are taken to prevent pick-up scratches, such as applying asbestos rolls (internally water-cooled) to the hearth rolls, and reducing the number of rolls as much as possible and supporting the steel strip in catenaries. As long as hearth rolls are used, pick-up scratches cannot be avoided, and since the hearth rolls are internally water-cooled, there is a disadvantage in that heat loss is large and temperature unevenness occurs in the steel strip.

As a solution to such problems, there is a method described in Japanese Patent Application Laid-open No. 163219/1983. That is,
As shown in FIG. 6, it has been proposed to support the steel strip S in a non-contact manner using a floating support device (floater) 29 instead of the hearth roll. floater 2
Reference numeral 9 is for blowing gas from the nozzle portion onto the steel strip using a blower 30, and supporting the steel strip by the pressure generated at that time.

The furnace shown in FIG. 7 is a one-pass vertical furnace in which the hearth roll is removed from the furnace.

Furthermore, the furnace of the type shown in Fig. 8 has a heating section for preheating, heating, and soaking zones and a cooling zone vertically arranged side by side, and the steel strip S is made into a free loop between the deflector rolls 31 and the hearth is drawn from inside the furnace. Eliminating roles.

(Problem to be solved by the invention) In the direct-fired continuous annealing furnace for steel strips described above,
Since there are no hearth rolls in the furnace, pick-up scratches do not occur at all, but the following problems remain. First, in the furnace shown in Figure 6, multiple floaters must be installed, which increases the equipment cost.Also, since the weight of the steel strip is supported by the ejected gas, a large-capacity blower is required, and the The cost will also be very high. Furthermore, there is a problem that the flying height is not sufficient and it cannot be applied to thick objects.

Furthermore, since the furnace shown in Figure 7 has a vertical structure from the pre-cooling zone to the cooling zone, the furnace height is very high, increasing construction costs. It is difficult to increase processing power.

In the furnace shown in FIG. 8, the steel strip is threaded in a free loop in the furnace, that is, no tension is applied to the steel strip, and it hangs down in a loop due to its own weight. Therefore, the steel strip during threading is very unstable and prone to vibrations, etc., and this phenomenon becomes especially noticeable when the steel strip is conveyed at a faster speed, leading to problems such as strip breakage and poor heat treatment. occurs. In other words, there is a limit to the conveyance speed, and in practice it is at most 20
m/min, and no improvement in production capacity could be expected.

Furthermore, in each of the furnaces shown in FIGS. 7 and 8, there is a problem in that a deformation phenomenon of the steel strip, so-called canoeing, occurs. Canoeing is a type of shape defect in which a steel strip warps in the width direction, and the cause of its occurrence is not yet clear, but it is thought to be roughly as follows. In other words, in the soaking zone, thermal strain occurs in the strip width direction due to thermal expansion, while in the cooling zone, conversely, thermal strain occurs due to thermal contraction, so the steel strip located between the soaking zone and the cooling zone has It is believed that a large relative thermal strain occurs, resulting in warpage in the width direction. This canoeing hardly occurs in the furnaces shown in FIGS. 5 and 6 above. This is thought to be because even if canoeing occurs, the bending is corrected by the hearth roll or steel strip flotation device. In the furnace shown in Fig. 7, there is no in-furnace straightening means, so canoeing occurs, and in the furnace shown in Fig. 8, there is a bend at the bottom of the furnace, but at this lowest point, the weight of the steel strip Since there is no tension and there is almost no correction effect, canoeing occurs.Furthermore, the higher the conveyance speed, the more severe the temporal fluctuation between the soaking zone and the cooling zone becomes, and the canoeing becomes more pronounced.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a continuous annealing furnace for steel strips that is capable of efficient high-speed annealing without causing thermal deformation of steel strips or pick-up flaws. shall be.

(Means for Solving the Problems) This invention provides a first turning section in which a heating zone, a soaking zone, and a cooling zone are arranged in parallel, and a U-shaped steel strip is forced to pass between the heating zone and the soaking zone. An inverted U is installed between the soaking zone and the cooling zone.
It is a three-pass vertical furnace equipped with a second turning section that forces the strip to pass in a shape. A continuous annealing furnace for steel strips (first invention) comprising a flotation device for floating and supporting the steel strip by gas injection, and tension generators installed on the inlet and outlet sides of the furnace; This is a continuous annealing furnace for steel strips (second invention) which is further equipped with a preheating zone.

(Function) The continuous annealing furnace for steel strip according to the present invention eliminates the hearth roll from inside the furnace and realizes a non-contact bullet plate by gas injection at the turning part of the steel strip. Even if oxide scale forms on the surface, no pick-up scratches will occur. By providing a heating zone, a soaking zone, and a cooling zone in parallel through the turning section of the steel strip, each zone was separated and the division of functions was made clear. In other words, by making the heating zone, soaking zone, and cooling zone independent,
The desired processing was achieved in each zone, and in particular, thermal efficiency was significantly improved.

In addition, tension generators are installed on the inlet and outlet sides of the furnace, and a non-contact guide device is installed inside the furnace, making it possible to apply a predetermined tension to the steel strip. Even when heat treating a steel strip at high speed, stable annealing can be achieved without meandering.

Furthermore, unlike conventional floaters, the non-contact type guide device does not need to support the weight of the steel strip, so the amount of gas to be blown out can be much smaller.

Furthermore, the flotation device located between the soaking zone and the cooling zone does not need to use high-temperature gas; room-temperature air is sufficient, so the amount of air required is much smaller, and it has a cooling effect, which is extremely advantageous in terms of energy conservation. becomes.

And, since this flotation device can apply sufficient bending tension between the soaking zone and the cooling zone,
The occurrence of canoeing can be avoided.

As described above, the continuous annealing furnace according to the present invention is
It is effective in heat treating at high speeds and high temperatures and is therefore particularly suitable for continuous annealing of stainless steel strips.

(Example) A continuous annealing furnace according to the present invention will be specifically described below with reference to FIG.

The illustrated example is a direct-fired continuous annealing furnace, and is a three-pass vertical furnace having a series of pre-heating zones 1, heating zones 2, soaking zones 3, and cooling zones 4 arranged in parallel. The heating zone 2 and the soaking zone 3 form part of a path bent in an arc shape, and a guide device 5 that injects gas in the radial direction onto the steel strip S
A first turning section 6 is provided for forcing the steel strip S to pass through in a U-shape, and a flotation device 7 is provided between the soaking zone 3 and the cooling zone 4 to float and support the steel strip S using the jet gas pressure. 7
A second turning section 8 is provided to force the steel strip S to pass in an inverted U-shape, and on the entrance side of the preheating zone 1 and the exit side of the cooling zone 4, there are tension bride rolls 9a for applying tension to the steel strip S. 9b is installed.

That is, with the first turning section 6 as the border, the first pass passes through the pre-heating zone 1 and the heating zone 2, and the second pass passes through the soaking zone 3.
Also, a cooling zone 4 is arranged in the third pass with the second turning section 8 as a boundary.

Note that the soaking zone 1 may be elevated or may be heated using a radiant tube.

The steel strip S has a preheating zone 1 and a heating zone 2 in the direction of the arrow.
The plate is passed from top to bottom, the direction is changed in the first rotary furnace 6 at the hearth bottom, and the plate is passed through the soaking zone 3 from the bottom to the top, and then the direction is changed again in the second rotary furnace 8 and the plate is passed from top to bottom. The board is passed through.

In addition, 10 is a burner, 11 is a cooling header, 12
13 is a deflector roll; 13 is a circulation fan for sucking combustion exhaust gas in the furnace and then blowing it out from the guide device 5; and 14 is a blower for sucking atmospheric air and blowing it out from the flotation device 7.

As shown in FIG. 2, the guide device 5 or flotation device 7 consists of a plurality of compartments 16 to which piping 15 from a circulation fan 13 or blower 14 is connected, and the circulation is carried out from a nozzle hole 17 formed in each compartment 16. The exhaust gas sent by the fan 13 or the blower 14 is ejected toward the steel strip S passing through the first turning section 6 or the second turning section 8. The gas ejected by the guide device 5 corresponds to the pressure applied to the steel strip 7, and the ejected gas by the flotation device 7 is applied to the steel strip S.
The tension applied to the steel strip S and the self-weight of the steel strip S are taken into consideration and set respectively.

The steel strip S is a tension braid roll 9a, 9b.
A predetermined tension is applied by the guide device 5 and the flotation device 7, and threading is realized in a tight state.
While moving through the furnace, the front half of the furnace is preheated and heated, and while being pressed downward by the combustion exhaust gas (approximately the temperature of the steel strip) ejected from the guide device 5, the steel strip is rotated 180 degrees. The sheet is rotated in direction, soaked, and then floated and supported by the flotation device 7, turned around 180 degrees, passed downward again, cooled to a temperature of 100 to 150° C., and then exited from the furnace. Since the temperature of the steel strip S outside the furnace is sufficiently low, there is almost no possibility that oxide scale will adhere to or grow on the roll and cause pick-up flaws.

Continuous annealing of a stainless steel strip using the continuous annealing furnace shown in FIG. 1 will also be described.

Figure 3 shows the results of annealing a SUS304 cold-rolled steel strip with a thickness of 1 mm and a width of 1000 mm at a soaking temperature of 1100°C and a soaking time of 20 seconds. For comparison, the results of a similar annealing process using the conventional furnace shown in FIG. 5 are also shown in FIG. 3. In this figure, the horizontal axis shows the conveyance speed, and the vertical axis shows the flaw generation rate. In the figure, the black circles show the results when the conventional furnace was used, and the white circles show the results when the furnace according to the present invention was used. From the same figure,
It can be seen that pick-up scratches are significantly reduced when the furnace according to the invention is used. Also,
In conventional furnaces, the threading speed was limited to 20 to 30 m/min, and the hearth rolls had to be replaced frequently, but in the furnace according to the present invention, the threading speed can be increased to 120 m/min.
There was no problem even when the heat treatment was performed at a rate of m/min. Although some scratches occurred in the furnace according to the present invention, none of them were pick-up scratches.

Furthermore, regarding the occurrence of canoeing during similar continuous annealing, the results of a comparison with the conventional furnace shown in FIGS. 7 and 8 are shown in FIG. From the same figure, it can be seen that when the furnace according to the present invention is used, the amount of canoeing generated is significantly reduced.

(Effect of the invention) According to the invention, since the hearth roll in the furnace is eliminated, pick-up scratches can be avoided, and
Between the heating zone and the soaking zone, a gas injection type guide device that presses the steel strip from above is installed instead of a steel strip flotation device, and on the other hand, between the soaking zone and the cooling zone, there is a flotation device that can use room temperature air as the injection gas. In addition, a tension generator was installed on the inlet and outlet sides of the furnace to apply tension to the steel strip, so even when processed at high speed, there is no canoeing or meandering, which greatly improves productivity. At the same time, running costs can also be reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a continuous annealing furnace for steel strip according to the present invention, Fig. 2 is a schematic diagram of a guide device or flotation device, Fig. 3 is a graph showing the relationship between strip passing speed and flaw occurrence rate, and Fig. 4 The figure is a graph showing the relationship between the sheet passing speed and the amount of canoeing, and Figures 5 to 8 are schematic diagrams of conventional continuous annealing furnaces. 1... Pre-preparation zone, 2... Heating zone, 3... Soaking zone, 4... Cooling zone, 5... Guide device, 6... First turning section, 7... Flotation device, 8... Second turning section, 9a, 9b... Tension Bridle roll, 10... Burner, 11... Cooling header, 12... Deflector roll, 13... Circulation fan, 14... Air blower, 15... Piping, 16... Compartment, 17... Nozzle hole.

Claims (1)

[Claims] 1. A heating zone, a soaking zone, and a cooling zone are arranged in parallel,
A first turning section was provided between the heating zone and the soaking zone to force the steel strip to pass in a U-shape, and a second turning section was provided between the soaking zone and the cooling zone to force the steel strip to pass in an inverted U-shape. , a 3-pass vertical furnace, the first turning section is equipped with a guide device that guides the non-contact threading of the steel strip by gas injection,
A continuous annealing furnace for steel strips, in which the second turning section is equipped with a flotation device for floating and supporting the steel strip by gas injection, and tension generators are installed on the entrance and exit sides of the furnace. 2. The continuous annealing furnace for steel strip according to claim 1, further comprising a preheating zone provided on the entry side of the heating zone.