JPH0261010A - Continuous annealing furnace for steel strip - Google Patents

Abstract

PURPOSE:To eliminate the development of pickup flaw and to enable high speed annealing by setting tension developing devices at inlet and outlet sides of a furnace and arranging a guide device passing a steel strip under non- contacting with gas injecting at a turning part. CONSTITUTION:The vertical type furnace is constituted by connecting with preheating zone 1, heating zone 2 and soaking zone 3, cooling zone 4 through the turning part 5 as U-shape. The steel strip is passed from upper part to lower part and the direction thereof is turned at the turning part 5. The guide device 6 is set at the turning part 5 to introduce the steel strip under non- contacting. Tension bridle rolls 7a, 7b are arranged at the inlet side of the preheating zone 1 and the outlet side of the cooling zone 4 to give the steel strip the tension. The guide device 6 is composed of plural divided chambers 6b connected to each piping 6a from a circulating fan 10 and the gas sent with the circulating fan 10 is injected to the steel strip passing the turning part 7 from nozzle hole 6c formed in each divided chamber 6b.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a continuous annealing furnace for steel strips, and particularly aims to prevent the occurrence of pick-up flaws 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. 4, the annealing furnace 11 has a preheating zone 12,
It is composed of a heating zone 13, a soaking zone 14, and a cooling zone 15.
A plurality of steel strips S are installed, and a direct-fired burner 17 as a heating means and a cooling header 18 as a cooling means are installed above and below the steel strip S to be threaded. Then, the steel strip S is moved in the direction of the arrow while catenary supported by the hearth roll 16, 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 oxidized scale adheres to and grows on the hearth roll and causes flaws in the steel strip, so-called pick-up flaws.

These pick-up flaws are more likely to occur as the belt conveyance speed is faster, 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 a catenary. As long as hearth rolls are used, pick-up scratches cannot be avoided, and since the hearth rolls are internally water-cooled, there are disadvantages in that heat loss is large and temperature unevenness occurs in the steel strip.

To solve these problems, Japanese Unexamined Patent Application Publication No. 1986-
” 163219. Namely, as shown in FIG. 5, it is proposed to support the rope S in a non-contact manner using a floating support device (floater) 19 instead of the hearth roll. The floater 19 supports the steel strip by blowing gas from its nozzle portion onto the steel strip using the blower 20 and using the pressure generated at that time.

In addition, the furnace of the type shown in Fig. 6 has a heating section for preheating, heating, and soaking zone and a cooling zone vertically arranged side by side, and the steel strip S is made into a free loop between the deflation crawls 21 and released from the inside of the furnace. Eliminates hearth rolls.

(Problems to be Solved by the Invention) In the direct-fired continuous annealing furnace for steel strips described above, pick-up flaws do not occur at all because there are no hearth rolls in the furnace, but the following problems remain. . First, in the furnace shown in Fig. 5, multiple floaters must be installed, which increases the equipment cost, and since the weight of the steel strip is supported by the ejected gas, a large-capacity blower is required. Running costs 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.

Further, in the furnace shown in FIG. 6, the steel strip is threaded in a free loop in the furnace, that is, no tension is applied to the steel strip, and the steel strip hangs down in a loop shape due to its own weight. Therefore, the steel strip during threading is very unstable and prone to vibrations, run-out, etc. This phenomenon becomes especially noticeable when the conveying speed of the strip is increased, leading to problems such as breakage of the steel strip and poor heat treatment. Occur.

In other words, there is a limit to the conveyance speed, and in reality it is at most 20
m/min, and no improvement in production capacity could be expected.

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 does not generate pick-up flaws and is capable of high-speed annealing.

(Means for Solving the Problems) The present invention is a two-pass system in which a heating zone and a series of soaking zones and cooling zones arranged in parallel on the side of the heating zone are connected in a U-shape via a turning section. A continuous steel strip forming furnace, which is equipped with tension generators on the inlet and outlet sides of the furnace, and a guide device in the turning section to guide the non-contact threading of the steel strip by gas injection. An annealing furnace (first invention) and a continuous annealing furnace for steel strips, the first invention further comprising a preheating zone (
2nd invention).

(Function) The continuous annealing furnace for steel strip according to the present invention eliminates the hearth roll from inside the furnace, and realizes non-contact threading by gas injection at the turning part of the steel strip, so that the steel strip surface is Even if oxide scale is formed, no pick-up flaws will occur.

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, so it is possible to apply a predetermined tension to the strip, and therefore the steel strip It is possible to achieve stable annealing treatment without meandering even when heat treatment is performed at high speed.

Furthermore, since the non-contact type guide device does not need to support the weight of the steel strip like a conventional floater, the amount of gas to be ejected can be much smaller.

As mentioned above, the continuous annealing furnace according to the present invention is effective in heat treatment 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, in which a vertical pre-heating zone 1 and a heating zone 2, a vertical soaking zone 3 and a cooling zone 4 are connected to each other by an arcuate passage. Via part 5,
It becomes a two-pass vertical furnace connected in a U-shape. That is, with the turning section 5 as a boundary, the first half of the furnace has a pre-heating zone 1 and a heating zone 2, and the second half has a soaking zone 3 and a cooling zone 4.

Note that the preheating zone 1 may be omitted, and heating may be performed using a radiant tube.

The steel strip S is threaded from top to bottom in the direction of the arrow, changes direction at the turning section 5 at the bottom of the furnace, and threaded from bottom to top. A guide device 6 is installed in the turning section 5 to guide the non-contact threading of the steel strip S, and the steel strip S is installed on the entrance side of the preheating zone 1 and the exit side of the cooling zone 4.
Tension pry roll 7 for applying tension to
A and 7b are installed. Note that 8a is a burner, 8b is a cooling header, 9 is a deflector roll, and 10 is a circulation fan for sucking combustion exhaust gas in the furnace and then blowing it out from the guide device 6.

As shown in FIG. 2, the guide device 6 consists of a plurality of compartments 6b to which piping 6a from the circulation fan 10 is connected, and the air is sent by the circulation fan IO from a nozzle hole 6c formed in each compartment 6b. The exhaust gas is ejected toward the rope S that passes through the turning section 5. The gas ejection here is set to a pressure that corresponds to the tension applied to the steel strip S.

The steel strip S is given a predetermined tension by the tension pry rolls 7a, 7b and the guide device 6, and threading is achieved in a tight state.While the steel strip S is moving through the furnace, preheating and heating are performed in the front half of the furnace. It is rotated 180° while being pressed downward by the combustion exhaust gas (equal to the temperature of the steel strip) ejected from the guide device 6, and then soaked and cooled to a temperature of 100 to 150°. The temperature reaches below C and exits the furnace.

Since the temperature of the steel strip S outside the furnace is sufficiently low, there is almost no chance that oxide scale will adhere to or grow on the roll and generate pick-up flaws.

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

FIG. 3 shows the results of annealing a 5US304 cold-rolled steel strip having a thickness of 1 mm and a width of 1000 M 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. 4 are also shown in FIG. 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 figure, it can be seen that when the furnace according to the present invention is used, the number of pick-up flaws is significantly reduced. In addition, in conventional furnaces, the threading speed is 20 to 30 m/
However, in the furnace according to this invention, the threading speed was limited to 12 min, and the hearth roll had to be replaced frequently.
There was no problem even when the heat treatment was performed at 0 m/min.

Although some scratches occurred in the furnace according to the present invention, none of them were pick-up scratches.

Furthermore, Table 1 shows the results of a comparison with the conventional furnace shown in FIG. 5 in similar continuous annealing.

Table 1 From the same table, it can be seen that although the pick-up flaws were at the same level, there was a large difference in the cost of the blower that supplied exhaust gas to the steel strip flotation device in the conventional furnace or the guide device in the furnace of the present invention. Recognize. In particular, the electric power in the furnace of this invention was 1/20 that of the conventional furnace.

In addition, in the conventional furnace shown in Fig. 6, the conveying speed is at most 2.
As mentioned above, it can only be raised up to 0m/IIain.

(Effects of the Invention) According to this invention, since the hearth roll in the furnace is eliminated, pick-up scratches can be avoided, and the furnace is equipped with a gas injection type that presses the steel strip from above instead of a rope flotation device. A guide device is installed, and a tension generator is installed on the exit side of the furnace to apply tension to the steel strip, so it does not meander even when processed at high speeds, greatly improving productivity and reducing running time in the guide device. The cost is also negligible.

[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, Fig. 3 is a graph showing the relationship between strip passing speed and flaw occurrence rate, and Figs. 4 to 6. is a schematic diagram of a conventional continuous annealing furnace. ■... Pre-warming zone 2... Heating zone 3... Soaking zone 4... Cooling zone 5... Turning section
6...Guide device 6a...Piping
6b... Compartment chamber 6c... Nozzle hole

Claims (1)

[Claims] 1. A two-pass vertical furnace in which a heating zone and a series of soaking zones and cooling zones arranged in parallel on the side of the heating zone are connected in a U-shape via a rotating section. A continuous annealing furnace for steel strips, in which tension generators are installed on the inlet and outlet sides of the furnace, and a guide device for guiding the steel strip through non-contact by gas injection is installed in the turning section. 2. The continuous annealing furnace for steel strip according to claim 1, wherein a preheating zone and a heating zone are arranged on the entry side of the turning section.