JPH0445566B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field) When heat-treating a cold-rolled steel plate by a continuous annealing method, the steel plate heat buckles (wrinkles) that often occur during the process are prevented by adjusting the meandering of the steel plate during passing, The technical content described in this specification regarding stable heat treatment of cold rolled steel sheets is included in the field of technology to which continuous annealing treatment of cold rolled steel sheets belongs.

(Problem) After cold rolling, cold-rolled steel sheets, galvanized original sheets, tin plated steel sheets, and stain-free steel sheets are subjected to recrystallization annealing in a short period of several minutes after cold rolling. Continuous annealing furnaces are commonly used.

The first conceptual explanation of the typical configuration of a continuous annealing furnace is
As shown in the figure, heating zone 1, soaking zone 2, rapid cooling zone 3, overaging zone 4 and final cooling zone 5.
Although illustrations are omitted as necessary, the steel plate heated to the soaking temperature in a preheating zone before the heating zone 1, and between the soaking zone 2 and the rapid cooling zone 3 is gradually heated to the rapid cooling start temperature. It may also include a slow cooling zone for cooling, a reheating zone for heating the steel plate that has been rapidly cooled to near room temperature in the rapid cooling zone 3 to an overaging temperature, and the like.

In addition, the inlet side equipment of the furnace main body is basically the inlet side looper 6 and the payoff reel 7, and if necessary, a separate cleaning line etc., and the outlet side equipment is basically the outlet side looper 8 and the tension reel 9. Temper rolling mills may also be added as necessary. In the continuous annealing furnace, inside the compartments for each processing stage, there are many guides to guide the strip in a diagonal detour in order to ensure the necessary residence time of the steel plate in each compartment. A hearth roll 10 was used, and the repetition of detour passing is omitted in the figure.

Regarding the hearth roll 10, the following problems are encountered in the heating zone 1 and especially in the soaking zone 2.

That is, the appearance of a hearth roll 10 commonly used in the past is shown in FIG. 2, and it mainly consists of a parallel portion 11 in the central region and tapered portions 12 tapered toward the outside of the roll on both sides thereof. A rotating shaft 13 for driving is provided at both ends.

The function of this tapered portion 12 is to
Even if some disturbance is applied to the steel plate supported under the zero winding guide and it meanders to the left or right, a centripetal force is generated to help restore the meandering, returning the steel plate to its normal threading state. Contribute to bringing it back.

If the tapered portion 12 were not present, there would be no centripetal force to return the meandering steel plate to the center, which would cause the steel plate to break in the furnace, which is most undesirable in terms of operation.

The tapered hearth roll 10 shown in FIG. 2 is effective in preventing meandering while the steel plate is running, but on the other hand, it is difficult to wrap the steel plate at the boundary between the parallel portion 11 and the tapered portion 12 during sheet passing. Wavy wrinkles may occur in the threading direction of the attached steel plate.
These wrinkles are often called heat buckles due to the following causes.

This is because heat buckles occur frequently in the heating zone 1 and soaking zone 2, where the steel plate is the softest.
This reduces the centripetal force generated by the winding of the steel plate in the tapered part 12 of the hearth roll 10 to the parallel part 12.
The steel plate that is more strongly wrapped around the roll body at the boundary between 1 and the tapered part 12 receives the force, and the steel plate under heating buckles in the width direction to counteract the centripetal force. Occur.

Therefore, a hearth roll having a tapered part inclined at a steeper angle with respect to the parallel part causes less meandering of the plate, but on the other hand, heat buckles are more likely to occur.

On the other hand, if the angle θ of the tapered portion 12 of the roll is gradually reduced, the occurrence of heat buckles will be reduced, but the meandering of the steel sheet will become more severe, making stable sheet threading difficult.

Thus, in the current hearth roll 10, the angle θ of the tapered portion 12 and the length l of the parallel portion 11 are determined so as to minimize both the meandering of the steel plate and the occurrence of heat buckles.

However, in continuous annealing furnaces, the composition, thickness, width, etc. of the steel sheets vary, so the hearth roll 10 cannot be adapted to all steel sheets, and therefore stable operation is often difficult. It has been difficult to continue this process across many types and sizes of steel sheets.

(Purpose of the invention) The inventors have achieved stable operation of continuous annealing regardless of the type of steel sheet by appropriately avoiding heat buckles, which tend to occur frequently in the heating zone, especially in the soaking zone, without meandering. is the purpose of this invention.

(Structure of the Invention) The above object is advantageously achieved by a sheet passing guide having a group of hearth rolls having the following main points.

A cold-rolled steel plate is passed through a continuous annealing furnace that includes a heating zone that is heated to a temperature higher than the recrystallization temperature and a soaking zone that is maintained at a temperature higher than the recrystallization temperature in the order of treatment steps. When performing the cooling process, at least in the latter of the above-mentioned heating zone and soaking zone, the circumference of the area on both sides beyond the width edge of the maximum width steel plate to be threaded at the circumference excluding at least the 200mm width corresponding to the center of the plate width. It is equipped with a large number of suction holes for the furnace atmosphere gas that are distributed on the surface, and the entire circumference is virtually tapered to guide sheet threading by a group of hearth rolls, and the steel sheet being threaded is guided by a group of hearth rolls that face the surface of the winding sheet. A continuous annealing method for a steel plate that does not involve heat buckling or meandering, which consists of winding and guiding under the self-centering effect due to the suction force generated in the suction hole and its left-right balance.

In this case, it is more desirable to supply bleed air from the furnace atmosphere gas through a suction hole opened in the hearth roll body to the pre-processing zone.

As mentioned above, at the outer circumference of the hearth roll 10 excluding at least 200 mm corresponding to the center of the plate width, the furnace atmosphere gas is distributed and opened on the circumferential surface of the both sides beyond the width edge of the maximum width steel plate to be passed. The provision of a large number of suction holes provides a self-centering effect that is effective in preventing meandering, even though the roll cylinder is virtually tapered, and heat buckling does not occur here either.

Fig. 3 shows the external appearance of this hearth roll, and Fig. 4 shows the right half cross section.

In the figure, 14 is a central body without holes, 15 is a side body with many suction holes 16 opened, 17 is an internal cavity, and 18 is an exhaust port.

Although not shown, the exhaust port 18 can be connected to the heating zone 1 in the pre-processing zone, for example, in the soaking zone 2, or to the preheating zone in the case of the heating zone, by means of pipes connected through appropriate rotary joints. shall be.

As is clear from the figure, there is no tapered part at all, so not only is heat buckling caused by the tapered part impossible to occur, but also the serpentine passing of the steel plate, which is a concern due to the roll body being flat over the entire length. can be effectively avoided as in

That is, when an exhaust pump is connected to the exhaust ports 18 at both ends of the hearth roll 10 and the pressure in the internal cavity 17 is lowered relative to the atmospheric gas pressure in the furnace, the steel plate wrapped around the circumference of the roll facing the suction hole 16 is Since it is attracted and comes into close contact with the hearth roll, the apparent coefficient of friction between it and the hearth roll increases.

Since this adsorption force is balanced and stable on the left and right sides in the sheet width direction, a self-restoring force is generated against disturbances that force the steel sheet to meander.

For this self-restoring effect, it is important that the central body 14 of the hearth roll 10 is not provided with suction holes 16. In other words, even in the case where the central body 14 is not particularly provided and the length l=0, the steel plate is still attracted by the suction hole 16, but in this case, no centripetal force acts at all with respect to fluctuations in the winding position of the steel plate. However, it is far from perfect for stable threading of steel plates.

On the other hand, only when the center shell 14 extends over a certain length (experimentally required to be 200 mm or more) does a self-aligning action occur on the steel plate that has begun to meander; This is because, by setting 14 as a neutral zone, a stable balance is automatically created on both sides of the neutral zone to eliminate the difference in total adsorption force between the winding surfaces of the steel plate.

To obtain such an effect, at least
A neutral zone spanning 200mm is required,
On the other hand, the both side shells 15 in which the suction holes 16 are disposed extend beyond the width edges of the plates in order to ensure sufficient self-alignment even at the maximum width of the plate to be threaded.

heating zone 1 of the continuous annealing furnace as described above;
In particular, the steel plate being passed through the soaking zone 2 is suctioned under tension of usually 0.3 to 3.0 kg/mm ² to the hearth roll 10 near both edges of the steel plate, regardless of its width. The adsorption force in the hole 16 is added to ensure a more secure contact, and meandering due to external disturbances is less likely to occur, and even if it does occur, it is immediately restored and corrected. Since it occurs in the direction that eliminates the imbalance, there is no heat buckle.

(Example) In order to confirm the effects of the present invention, a hearth roll with suction holes shown in FIG. 3 was prepared as follows, in contrast to the conventionally used tapered hearth roll shown in FIG. It was installed in the heating zone 1 and soaking zone 2 of the continuous annealing furnace already shown in Figure 1, and a cold rolled steel sheet was actually passed through the furnace to examine the occurrence of meandering and heat buckles.

The size of the roll used and the continuous annealing conditions are as follows.

A Tapered roll (Fig. 2) Parallel part roll diameter: 800 mm, parallel part: 500 mm, taper degree: tan θ = 0.0006 (however, θ is the angle between the parallel part and the tapered part as shown in Fig. 1) Roll length L1 : 1650mm B Roll with suction holes (Fig. 3) Roll diameter: 800mm, center body length L: 300mm, suction length L': 585mm, roll length L2: 1650mm, suction hole shape: Axial width: 9mm, circumference: 29mm, axial pitch: 24mm, circumferential pitch: 44mm, (9mm x 29mm suction holes on one side of the roll)
) Suction pressure (inner furnace pressure): 0.8Kg/cm ² C Continuous annealing conditions Heating: Heating at 8℃/s up to 710℃ Soaking: Holding at 710℃ for 80s Rapid cooling: 53℃/s up to 400℃ (Gas jet cooling) Over-aging: 400℃, held for 120s Final cooling: 8℃/s to 60℃ Line speed: 150m/min Steel plate tension in heating zone and soaking zone: 0.6Kg/
mm ² Steel type: Al killed steel (components (weight%) C: 0.035, Si: 0.01, Mn: 0.22, P:
0.011, S: 0.009, Al: 0.021, N:
0.0029, O: 0.0041) Observation of meandering and heat buckle of the steel plate is as follows:
Observations were made using monitor televisions installed in the heating furnace and soaking furnace.

According to this, when a tapered roll of Al) was used, meandering of the steel plate did not occur at all, but
Heat buckles frequently occurred, necessitating line speed reduction or line stoppage.

On the other hand, when Bl) the roll with suction holes was used, no heat buckling or meandering occurred at all.

The suction holes described above are rectangular holes, but as long as the intended suction can be achieved, the shape, size, and number of the holes do not matter; for example, even a porous roll can serve the purpose.

The gas sucked into the hearth roll may be circulated again to the heating zone and the soaking zone, or may be introduced into the preheating zone in front of the heating furnace to increase the thermal efficiency of the continuous annealing furnace. useful for.

(Effects of the Invention) The present invention fundamentally eliminates the occurrence of troubles in continuous annealing furnaces and has a great effect on stable operation thereof.

[Brief explanation of drawings]

Fig. 1 is a skeleton diagram of a continuous annealing furnace, Fig. 2 is a front view of a tapered hearth roll, Fig. 3 is a front view of a hearth roll with suction holes according to the present invention, and Fig. 4 is a front view of a hearth roll with suction holes according to the present invention. FIG. 3 is a cross-sectional view of main parts.

Claims (1)

[Claims] 1. Passing a cold-rolled steel plate through a continuous annealing furnace that includes, in order of processing steps, a heating zone that heats the sheet to a temperature higher than the recrystallization temperature and a soaking zone that holds the steel plate at a temperature higher than the recrystallization temperature. When the plate is annealed continuously, at least the latter of the above heating zone and soaking zone has a width of at least 200mm corresponding to the center of the plate width.
There are many suction holes for the furnace atmosphere gas distributed around both sides, which extend beyond the width edge of the maximum width steel plate to be threaded, and the entire circumference is virtually tapered. This heat buckle consists of guiding the steel plate through a group of hearth rolls, and guiding the steel plate being threaded under the self-centering action of the suction force generated in the suction holes facing the surface of the winding plate and its left-right balance. , a method for continuous annealing of steel sheets without meandering. 2. The method according to 1, in which bleed gas from the furnace atmosphere is supplied to the pre-treatment zone through a suction hole opened in the hearth roll circumference.