JPS6386820A - Tension control method for metallic strip in continuous annealing furnace - Google Patents

Abstract

PURPOSE:To prevent the development of heat-buckling or snaking of a strip by presuming a thermal crown quantity of a hearth roll in the heating zone and cooling zone and controlling the tension of strip in the optimum range based on this. CONSTITUTION:In a computing element, the temp. distribusion of strip in a furnace 1 is calculated based on the strip size, furnace temp. and line speed information. Based on this, the net roll crown quantity containing the thermal crown quantity is calculated. The tension is the optimum range corresponding to the roll crown quantity is calculated and the command is outputted to control the tension to the strip S through ATR and ASR. In this control method, the tension corresponding to the strip size is controlled in the optimum range and the continuous range and the continuous heat-treatment is executed without any development of heat-buckling or meandering.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention aims to prevent meandering and heat pancreas of the metal strip due to changes in the thermal crown of the hearth roll when the line speed etc. fluctuate in a continuous annealing furnace. The present invention relates to a method for controlling the tension of a metal strip in a continuous annealing furnace in order to give the metal strip an optimum tension so as to prevent the occurrence of such problems.

[Conventional technology]

Generally, continuous annealing of metal strip is carried out by winding the strip around a number of hearth rolls installed above and below a continuous annealing furnace and passing the strip through the furnace, so the distance the strip passes through the furnace is extremely long. . Therefore, if even a slight meandering occurs in the strip, as the strip is wound around the hearth roll one after another, the meandering will be exacerbated and become larger, and problems such as it will eventually come into contact with the furnace wall and break, will occur. In order to perform stable operations, it is necessary to take measures to prevent this meandering or correct the slight meandering that occurs.

As a means of achieving this, the hearth roll is usually crowned in order to create a centripetal force on the running strip and automatically correct the meandering. This creates a slight difference in the diameter of the hearth roll between the center and both ends, and this includes the Taber crown (Figure 4) and the concave land crown, which has a reduced diameter in an arc shape at both ends. However, tapered crowns are often used because they are easy to manufacture and have the ability to correct meandering. Since the strip is flexible, it wraps tightly around the hearth roll, so when the tapered roll is rotated, the strip moves toward the larger diameter. Since this moment of movement is generated on both sides of the strip in the width direction, a centripetal force is generated between the strip and the roll. In addition, this centripetal force becomes stronger as the tension of the strip increases, so increasing the tension can increase the ability to correct strip meandering, but there is a limit due to the strength of the strip, and it may cause deformation of the strip. A crown (initial crown) is formed when manufacturing a hearth roll by predicting the tension that will not cause breakage.

[Problem that the invention seeks to solve]

However, the continuous annealing furnace has a heating zone, soaking zone and slow cooling zone.
Since the furnace is composed of a quenching zone, etc., the furnace temperature differs depending on the section of the furnace, and therefore the thermal crown of the hearth roll in each section also differs. Therefore, the thermal crown becomes large in the furnace zone where the strip is heated, and if the meandering correction ability becomes too large, the strip strength decreases and heat backing of the strip occurs. On the other hand, in a furnace zone that is cooled, if the thermal crown becomes too small, there is a problem that the strip will meander. Moreover, variations in the thermal crown also occur in response to variations in the line speed of the strip in each section of the furnace, but it has not been easy to find a way to correct the meandering of the strip in response to such variations.

In addition, for this problem, heat the hearth roll.

It has also been proposed to control the amount of crown by cooling or installing a roll bending device (for example, Japanese Patent Laid-Open No. 57-17-7980, Utility Model Laid-Open No. 55-172859, etc.).
However, many problems remain, including the need to install a crown amount control device on each hearth roll, which increases costs.

The present invention was made in view of the conventional situation, and aims to solve the above problems by controlling the tension of the strip based on the varying amount of thermal crown.

[Means for solving problems]

In continuously annealing a metal strip, this invention
The amount of thermal crown of the hearth roll in the heating zone and cooling zone of the continuous annealing furnace is estimated, and based on this estimated value, the tension of the metal strip is controlled within the optimal range that allows stable threading of the metal strip in the furnace. The present invention provides a method for controlling the tension of a metal strip in a continuous annealing furnace.

[Function] If the line speed of the metal strip being threaded falls below the set value for some reason, the strip temperature will rise in the heating zone, and the thermal crown amount of the hearth roll around which the strip is wound will increase. Therefore, buff ring is more likely to occur. At this time, for example, an increase in the amount of thermal crown caused by a decrease in line speed is calculated and estimated, and based on this estimated value, the tension of the strip is corrected to an appropriate value that does not cause hackling. On the other hand, in the cooling zone, the temperature of the strip decreases, and the amount of thermal crown of the hearth roll around which the strip is wound decreases, making it easier to stop meandering.

At this time as well, the amount of thermal crown to be reduced is similarly calculated and estimated, and based on this estimated value, the tension of the strip in this cooling zone is corrected to an appropriate value that does not cause meandering. As described above, the optimum tension of the strip is set based on the estimation of the thermal crown change when the line speed fluctuates.

[Example] The present invention will be described below with reference to the drawings. 1 to 5 are diagrams for explaining embodiments of the present invention.

FIG. 1 is a block diagram showing a method for controlling the tension of the strip according to variations in line speed in a continuous annealing furnace, in which 1 is the continuous annealing furnace, heating zone 2. Soaking zone 3. Gradual cooling zone 4. It is composed of a rapid cooling zone 5 and the like. 6
．． 7 is a hearth roll provided in the furnace, and 7 is a roll equipped with a tension meter for measuring the tension of the strip S. Reference numeral 8 indicates an inlet prydle roll, 9 indicates an in-furnace prydle roll, and IO indicates an outlet prydle roll. M is a motor and these priddle rolls or hearth rolls 11
to drive. ASR is a speed regulator and ATR is a tension regulator, both of which directly control input to the motor M.

In this embodiment, the hearth roll 6.7 has a tapered crown shape as shown in FIG. Dl indicates the roll diameter between E and D2 indicates the roll diameter at both ends of the strip S having the plate width e.

Here, the net crown amount Tc of the roll affected by the furnace temperature during operation is T c #D + (1+αΔT+) Dz (1 mo α
ΔTz). However, α is the linear expansion coefficient of the hearth roll, TR1 is the roll temperature at the portion where the radius is, T■
When is the roll temperature at the portion with a diameter of D2 and TKO is the roll temperature during roll processing, the amount of change ΔT in the roll temperature is ΔT + = T * IT go, ΔT2 =
TRZ Tw.

becomes.

Normally, in the heating zone, the temperature of the roll in the area where the plate is placed is lower than that in the area without the plate, and in the cooling zone, the temperature of the roll in the area where the plate is placed is lower than the temperature in the area where the plate is not placed. is higher than the temperature of the part that is not covered.

This is because the temperature at the center of the roll is approximately equal to the strip temperature, whereas the roll temperature at the edge of the sheet is strongly influenced by the furnace temperature. For this reason, a temperature distribution of the roll occurs in the width direction of the plate.

A schematic diagram of the net crown in consideration of the thermal crown in this case is shown in FIG. In the heating zone, Tc may appear to be negative, but in this case, if the total centripetal force of the part where the plate is wrapped is positive,
We will have to wait for the meandering correction ability.

However, when the line speed changes suddenly, the strip temperature changes rapidly, and the temperature at the center of the roll changes accordingly. On the other hand, since the furnace temperature does not change so quickly, the roll temperature at the end of the plate does not change much either. This difference in temperature responsiveness in the width direction of the roll causes fluctuations in the thermal crown.

This change in crown amount is caused by the difference between the net crown amount and the strip tension, which does not cause either of these problems, such as buckling, which occurs if the crown is too large, and meandering, which occurs if the crown is too small, as explained above. FIG. 4 shows the results of finding out the optimum range of the relationship for the strip sizes that are actually frequently used.

Here, the width of strip S! , when the plate thickness is d, the upper and lower limits of commonly used strip sizes are ff/d=1.5X10", p/d=5.5xl O
”.

And I! A strip with a small /d value has a large plate thickness and a small plate width. Therefore, buffling is less likely to occur, but meandering is more likely to occur. Furthermore, a strip with a large Ild value has a small plate thickness and a large plate width, so buckling is likely to occur, but since the contact area is large, the strip has a strong centripetal force and is difficult to meander. Therefore, the optimum tension range corresponding to the crown of the former and that of the latter are different from each other as shown by the solid line and dotted line in Fig. 4, and therefore, the shaded area where the two overlap is the tension corresponding to the crown common to both. This is the optimal range. That is, the tension of the strip S should be controlled so that the tension (kg/w) on the vertical axis corresponds to the estimated crown ffl (,) shown on the horizontal axis in the shaded range.

Note that the minimum tension line in Figure 4 is based on the tension control function of the equipment.
Indicates that the tension can be stably obtained.

In addition, in the range below Tc≦O, as mentioned above, apparently,
Although Tc is negative, there are parts where the total centering force (centripetal force) is positive. Considering this effect and the fact that if the tension required to prevent meandering becomes too large, it will become inefficient, the minimum Tc is set at TC=-1.

If the line speed decreases for some reason during the continuous annealing operation, the strip temperature will rise in the heating zone of the furnace, and the thermal crown of the hearth roll around which the strip is wound will increase. As shown in Fig. 5 (this figure is a schematic representation of Fig. 4), the net crown 1tTc increases and moves in the right direction of the arrow in the figure, moving away from the closed curve Y indicating the optimum tension range. Become deviant.

On the other hand, in the cooling zone of the furnace, the strip temperature decreases and the thermal crown of the roll decreases. Then, the net crown amount Tc decreases and moves in the left direction of the arrow in the figure, again deviating from the optimum tension range.

Therefore, in this embodiment, in order to prevent this deviation, the tension is controlled to decrease in the former case and increase in the latter case (in Fig. 2, the heating zone tension is decreased and the cooling zone tension is ). For that purpose, the first
The computing units in the figure are the heating side 2.3 and cooling side 4.6 of the furnace.
The strip temperature distribution in the furnace is calculated based on the strip size, furnace temperature, and line speed information, respectively, and the net roll crown TC including the thermal crown is calculated from this, and the temperature distribution is calculated within the optimum range corresponding to this Tc. Calculate the tension and issue a command, ATR, AS
Control the tension on the strip S via R.

As a result of the above, the tension of the metal strip during operation is controlled within the optimum range according to the size of each strip.
Continuous heat treatment is performed without heat backing or meandering.

[Effects of the Invention] As explained above, according to the present invention, the amount of thermal crown of the hearth roll in the heating zone and the cooling zone of a continuous annealing furnace is estimated, and the tension of the metal strip is adjusted to its optimum value based on this estimated value. Since the method is controlled within the range, it is possible to prevent heat backing, meandering, etc. of the strip caused by fluctuations in line speed.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of an embodiment according to the present invention, FIG. 2 is an explanatory diagram of the operation in the embodiment, and FIG. 3 is an outline diagram of a hearth roll.
Figure 4 is a diagram showing the optimal range of tension corresponding to the amount of crown, Figure 5 is a diagram showing the relationship between increase/decrease in crown amount and the optimal range of tension, and Figure 6 is a diagram showing the relationship between the increase/decrease in crown amount and the optimal range of tension. It is a schematic diagram of a crown. S...Metal strip, 1...Continuous annealing furnace, heating zone□2...Heating zone, 3...
Soaking zone, cooling zone□4... Slow cooling zone, 5...
・Rapid cooling zone, 6.7... Hearth roll, Y... Closed curve showing the optimum range.

Claims (1)

[Claims] When continuously annealing a metal strip, the amount of thermal crown of the hearth roll in the heating zone and cooling zone of the continuous annealing furnace is estimated, and the tension of the metal strip is determined based on this estimated value so that the metal strip can be stably threaded through the furnace. A method for controlling the tension of a metal strip in a continuous annealing furnace, characterized in that the tension is controlled within a possible optimum range.