JP2016020536A - Hearth roll equipment for continuous annealing furnace and method for controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide hearth roll equipment for a metal strip capable of preventing meander and restriction phenomena during the carriage of a metal strip caused by the thermal expansion profile of a hearth roll in a continuous annealing furnace and achieving the stable carriage, and a method for controlling the same.SOLUTION: Provided is hearth roll equipment used for carrying a metal strip in a continuous annealing furnace of continuously heat-treating a metal strip, comprising: a draft screw of holding the roll barrel part side of a chock holding a roll neck part so as to be the fulcrum of a flexure moment from the upper part or lower part of housing; and a hydraulic cylinder of applying force in the upper and lower directions at the edge part side of the chock, and the hearth roll barrel part has an almost parabolic shape.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a hearth roll facility used in a continuous annealing furnace, and in particular, prevents meandering and buckling during transport of a metal strip due to the thermal expansion profile of the hearth roll, and enables stable transport. The present invention relates to a hearth roll facility for a continuous annealing furnace and a control method thereof.

  A metal strip work hardened by cold rolling is usually subjected to an annealing (annealing) treatment by heat treatment. This is because when the metal strip is formed by a press or the like, the workability such as bending or drawing is inferior in the work-hardened state, so that dislocation is removed by heat treatment to improve workability. In addition, the annealing process is also used for processes such as rapidly cooling and quenching the material immediately after annealing to manufacture a product with higher strength.

  In recent years, high-productivity continuous annealing furnaces are frequently used for annealing metal strips, enabling continuous heat treatment over a long period of time while joining the tail end and the tip in the longitudinal direction discharged from the metal strip coil sequentially. It has become. Usually, the continuous annealing furnace is composed of a heating zone, a soaking zone, and a cooling zone in order from the entrance side of the metal zone, and the temperature of each zone is set according to a heat treatment pattern for performing a desired annealing treatment. The metal strip is transported while changing the plate passing direction in order from the heating zone to the cooling zone by a plurality of transport rolls installed at the upper and lower portions of each zone in the furnace.

  Taking the continuous annealing treatment of a thin steel strip as an example, in the heating zone, the thin steel strip is heated from a normal temperature state to a maximum temperature of about 600 to 800 ° C. during conveyance. Thereafter, soaking in the vicinity of the temperature is carried out in the soaking zone, and cooling processing is performed in a stepwise temperature pattern setting until the temperature of the thin steel strip becomes 100 ° C. or less in the cooling zone. At this time, the in-furnace roll for conveying the thin steel strip (hereinafter also referred to as a hearth roll) is not only heated to the atmospheric temperature in each zone in the furnace, but also by contact with the thin steel strip. Temperature distribution occurs in the roll axis direction due to heat input (soaking zone, cooling zone) and heat removal (heating zone), and the roll surface changes to a concave shape or a convex shape due to a difference in thermal expansion.

  At this time, if the roll surface has a concave shape, a thin steel strip meandering phenomenon, and if the roll surface has a convex shape, buckling phenomenon of the thin steel strip (a wrinkle-like wrinkle is generated, hereinafter may be referred to as a squeeze), Empirically, measures have been taken to reduce the change in roll shape by lowering the sheet passing speed, which is a factor in reducing productivity. In recent years, tin gauges used for beverage cans and the like are becoming thinner, and it is important to improve the heat treatment productivity in a continuous annealing furnace.

  In order to solve the above-mentioned problems, the initial profile of the hearth roll body is determined in consideration of the amount of thermal expansion that occurs during operation as a technique for improving the trouble caused by the thermal expansion profile of the hearth roll for continuous annealing furnaces. Technology (for example, Patent Documents 1 and 2), technology for improving the thermal expansion profile by installing cooling or heating equipment inside the hearth roll (for example, Patent Documents 3 and 4), and others A technique (for example, Patent Document 5) that prevents the buckling or meandering of a metal band by disposing a expansion / contraction transmission material in the section to make the roll crown profile variable is disclosed.

JP-A-7-138656 JP 2008-280586 A JP-A-7-145424 JP-A-8-283870 JP-A-61-2101258

  However, each of the above conventional techniques has the following problems.

  First, in the techniques disclosed in Patent Documents 1 and 2, the hearth roll barrel (hereinafter also referred to as a hearth roll barrel) based on the thermal expansion profile of the hearth roll calculated assuming a specific condition. Since the initial shape is determined, when operating according to the conditions, the effect of stabilizing the metal strip passing plate is exhibited. However, since it is necessary to manufacture products with various plate thicknesses and widths in actual operations, these technologies have constraints such as limiting the amount of plate width reversal with respect to changes in plate width during the cycle. There is a problem that it is necessary to make assumptions and that it is difficult to cope with unsteady changes such as acceleration / deceleration at the joint between the coils.

  In addition, in the techniques disclosed in Patent Documents 3 and 4, since the cooling or heating equipment is built in the hearth roll, local temperature control of the roll is possible, but the roll structure is complicated and heavy. However, when the inside of the roll is cooled, a mechanism for discharging after injecting the refrigerant is also required, so that the roll structure becomes more complicated and becomes very expensive equipment. There are challenges.

  Furthermore, in the technique disclosed in Patent Document 5, the expansion / contraction transmission mechanism is installed inside the hearth roll, so that the roll structure becomes complicated and the weight increases, so that the rotational inertia increases and the acceleration / deceleration rate of the metal strip increases. There are problems such as an unsteady part length that is restricted and cannot be subjected to a predetermined heat treatment.

  The present invention has been made in view of the above problems, and prevents the meandering and squeezing phenomenon during metal band conveyance due to the thermal expansion profile of the hearth roll in the continuous annealing furnace, and enables stable conveyance. It is an object of the present invention to provide a hearth roll facility for a metal strip and a control method thereof.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies and compensated so as to stably cancel the change in the hearth roll profile due to thermal expansion, and can continuously prevent meandering and squeezing during transportation of the metal strip. A hearth roll equipment for annealing furnace and its control method were devised.

The above problems can be solved by the following invention.
[1] A hearth roll facility used for transporting a metal strip in a continuous annealing furnace for continuously heat-treating the metal strip,
A reduction screw that holds the roll body side of the chock holding the roll neck so that it becomes a fulcrum of bending moment from the upper or lower part of the housing;
A hydraulic cylinder that applies a vertical force on the end side of the chock,
A hearth roll equipment for a continuous annealing furnace, characterized in that the shape of the hearth roll body is substantially parabolic.
[2] In the hearth roll facility for a continuous annealing furnace as described in [1] above,
A hearth roll facility for a continuous annealing furnace, wherein a plurality of thermocouples for measuring the inner peripheral surface temperature of the roll are installed inside the hearth roll body.
[3] A method for controlling a hearth roll facility for a continuous annealing furnace as described in [1] above,
The amount of roll bending required to estimate the amount of thermal expansion of the hearth roll barrel from the furnace temperature, plate passing speed, plate passing time, and plate width of the metal strip, and to compensate so as to offset the estimated amount of thermal expansion A method for controlling a hearth roll facility for a continuous annealing furnace, wherein a roll bending force is calculated and a bending moment is applied to the roll neck portion.
[4] A method for controlling a hearth roll facility for a continuous annealing furnace according to [2] above,
Based on the temperature distribution on the inner peripheral surface of the roll measured by the thermocouple, the heat expansion amount distribution of the hearth roll, and the roll bending amount and roll bending force necessary to compensate for the thermal expansion amount are calculated to calculate the roll neck portion. A method for controlling a hearth roll equipment for a continuous annealing furnace, wherein a bending moment is applied to the furnace.

  According to the present invention, meandering and squeezing phenomenon during transportation of a metal strip due to the thermal expansion profile of a hearth roll used in a continuous thermal annealing furnace can be prevented, and stable operation can be performed.

It is a figure which shows the hearth roll surface profile in a continuous annealing furnace heating zone. It is a figure which shows the hearth roll surface profile in a continuous annealing furnace cooling zone. It is a figure which shows an example of the hearth roll equipment for continuous annealing furnaces and the control method which concern on this invention. It is a figure which shows another example of the hearth roll equipment for continuous annealing furnaces which concerns on this invention, and its control method. It is the figure which showed typically the shape of the hearth roll for continuous annealing furnaces of a general metal strip.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 5 is a diagram schematically showing the shape of a general metal hearth hearth roll for continuous annealing furnace. The inside of the broken line in the figure is a space.

  This is because, for example, a thin steel strip does not apply a large force to the roll, so excessive rigidity is not required, and it is also possible to change the passing speed according to the mechanical characteristics and plate dimensions of each coil. Since it is necessary to reduce the rotational inertia in order to cope with this, the shell thickness of the roll body portion has a hollow structure of about 15 to 30 mm. The profile of the outer peripheral surface of the roll has a symmetrical shape with respect to the axial center position, and the range indicated by w in the figure is a cylindrical portion having a constant diameter Dc, and the outer diameter is De ( <Dc) has a tapered shape (hereinafter also referred to as a trapezoidal shape).

  When the metal strip is wound around the tapered cylindrical portion and passed through, a difference in the conveyance speed according to the roll diameter difference at each position in the axial direction is generated, and a force in the direction in which the roll diameter is large is generated in the metal strip. It is known. Therefore, by adopting a tapered shape that is symmetrical with respect to the axial center position as shown in FIG. An effect of returning the band to the center position, that is, an effect of suppressing meandering is obtained.

  However, if the inclination of the taper portion is excessively increased, the centripetal force along the taper portion becomes excessive, and a flaw occurs locally near the boundary between the flat portion and the taper portion, resulting in a throttling. The initial shape of the hearth roll is determined according to the operating conditions at At this time, it is necessary to consider the heat expansion profile of the hearth roll according to the temperature state at each position in the continuous annealing furnace, and the atmospheric temperature and metal at each position in the heating zone, soaking zone, and cooling zone. It is necessary to determine the flat portion width w and the taper shape of the outer peripheral portion of the hearth roll from the temperature of the belt.

  In general, in a heating zone of a continuous annealing furnace, a normal-temperature metal strip is sequentially raised to a necessary annealing temperature. For example, the annealing temperature of the mild steel strip work-hardened by cold rolling is about 600 to 800 ° C., and the ambient temperature in the heating zone is set to gradually increase to the maximum temperature of about 800 ° C. While the metal strip, whose initial state is normal temperature, is proceeding in the heating zone, the metal strip temperature is lower than the ambient temperature at each position in the furnace, so the hearth roll body in the heating zone is metal. The temperature at the band plate portion is low, and a high concave temperature distribution is formed on the outside thereof. For this reason, it is inevitable that the thermal expansion profile of the roll also becomes a concave shape corresponding to the temperature distribution.

  FIG. 1 is a diagram showing a hearth roll surface profile in a continuous annealing furnace heating zone. This is an example in which the surface profile of the hearth roll body was calculated by the finite element method from the set ambient temperature in the heating zone and the predicted plate temperature when heat treating the mild steel strip in a continuous annealing furnace. After the initial profile and conventional roll thermal expansion It is the figure which compared this profile and the profile at the time of applying this invention mentioned later.

  The range indicated by the plate width Ws in the figure is the plate passing position of the mild steel strip, and plots so that the roll radial direction position at the center position of the roll barrel is the same for easy comparison of roll profiles under each condition. doing. In contrast to the trapezoidal initial profile indicated by the thin solid line, the profile after thermal expansion of the conventional roll indicated by the broken line is a profile in which the tapered portion is greatly expanded.

  This is because the heat expansion of the hearth roll barrel became concave because the temperature of the mild steel strip was lower than the roll temperature, as described above, and the initial trapezoidal shape and the thermal expansion profile overlapped and became complicated. It has become a shape. In this case, although the centripetal effect of the mild steel strip at the taper portion is reduced, especially when a coil having a plate width wider than Ws is passed through in this state, the meandering of the mild steel strip is more likely to occur. Become. For this reason, generally, the amount of change in the plate width between the coils is restricted.

  Further, in the cooling zone of the continuous annealing furnace, the metal zone heated to the annealing temperature required in the heating zone and the soaking zone is cooled to near room temperature. In the cooling zone, the temperature of the metal zone is the highest at the entrance side of the cooling zone, and the temperature of the metal zone in progress in the cooling zone is higher than the ambient temperature at each position in the furnace. The hearth roll body temperature is high at the metal band plate and has a low convex distribution on the outside. For this reason, it is inevitable that the thermal expansion profile of the roll also has a convex shape corresponding to the temperature distribution.

  FIG. 2 is a diagram showing the hearth roll surface profile in the continuous annealing furnace cooling zone. This is an example of calculating the surface profile of the hearth roll body by the finite element method from the set ambient temperature in the cooling zone and the predicted plate temperature when heat treating a mild steel strip in a continuous annealing furnace. After the initial profile and conventional roll thermal expansion It is the figure which compared this profile and the profile at the time of applying this invention mentioned later.

  As in FIG. 1, the range indicated by the plate width Ws in the drawing is the passing position of the mild steel strip, and is plotted so that the roll radial direction position at the roll barrel center position is the same under each condition. In contrast to the trapezoidal initial profile indicated by the thin solid line, the profile after thermal expansion of the conventional roll indicated by the broken line is a profile in the direction in which the inclination of the tapered portion increases. This is because the heat expansion profile of the hearth roll barrel became convex because the temperature of the mild steel strip was higher than the roll temperature, as described above, and the initial trapezoidal shape and the thermal expansion profile overlapped. , Has a larger convex shape. In this case, the centripetal effect of the mild steel strip at the taper portion increases, but when an excessive centripetal force acts, a local buckling phenomenon occurs near the boundary between the roll barrel flat portion and the taper portion, Wrinkle-like folding (squeezing) occurs.

  The present inventors diligently investigated the thermal expansion behavior of the hearth roll at each position in the continuous annealing furnace, and according to the relationship between the atmospheric temperature and the metal band temperature at each position in the furnace, the degree of concave and convex Although there is a difference, the present inventors have found that the thermal expansion profile has a substantially parabolic shape with respect to the roll axis direction. And, while preventing the meandering of the metal band by the trapezoidal profile formed on the hearth roll body, the initial roll profile is maintained by compensating so as to cancel the parabolic thermal expansion profile growing in the furnace. The idea was that a stable threading would be possible if possible.

  FIG. 3 is a diagram illustrating an example of a hearth roll facility for a continuous annealing furnace and a control method thereof according to the present invention. Moreover, FIG. 4 is a figure which shows another example of the hearth roll equipment for continuous annealing furnaces and the control method concerning the present invention. That is, it has been found that by applying the roll bending shown in FIGS. 3 and 4, it is possible to compensate so as to cancel out the thermal expansion profile at various locations in the continuous annealing furnace. When a bending force is applied to both ends of the cylindrical roll and bent, the shape becomes a substantially parabolic shape, and the shape can be controlled by adjusting the bending force.

  For example, the bending force of the chock holding the roll neck is pinched so that it becomes the fulcrum of the bending moment with the reduction screw from the upper or lower part of the housing, and the hydraulic cylinder on the roll neck end side of the chock It is possible to apply a bending moment by applying a vertical force.

  FIG. 3 shows the bent shape of the hearth roll when the bending fulcrum 2 is installed at the neck portion of the hearth roll and a downward bending force 3d is applied to the outside thereof. In this case, due to the downward bending moment 4d, the hearth roll has a convex parabolic bend shape with the central portion of the trunk portion being the maximum point. In other words, by introducing the hearth roll equipment of FIG. 3 into the heating zone of the continuous annealing furnace, it is optimally bent downward in order to compensate so as to offset the thermal expansion profile of the hearth roll grown into a substantially parabolic concave shape. By applying a force 3d to give the bent shape of the convex parabola in the opposite direction, it is possible to cancel both. In the present invention indicated by a bold line in FIG. 1, the change from the initial trapezoidal profile can be suppressed very small as a result of overlapping the concave thermal expansion profile and the convex bending profile.

  FIG. 4 shows the bent shape of the hearth roll when the bending fulcrum 2 is installed at the neck portion of the hearth roll and the upward bending force 3u is applied to the outside thereof. In this case, due to the upward bending moment 4u, the hearth roll has a concave parabolic bend shape in which the central portion of the trunk is the minimum point. That is, by introducing the hearth roll equipment of FIG. 4 into the cooling zone of the continuous annealing furnace, it is compensated so as to cancel out the thermal expansion profile of the hearth roll grown into a substantially parabolic convex shape. By applying a bending force 3u to give a concave parabolic bending shape in the opposite direction, it is possible to cancel both. In the present invention indicated by a bold line in FIG. 2, the change from the initial trapezoidal profile can be suppressed very small as a result of the superposition of the convex thermal expansion profile and the concave bending profile.

  Next, as illustrated in FIG. 1 and FIG. 2, a description will be given of how to obtain the optimum bending force necessary to compensate so as to cancel out the thermal expansion profile of the hearth roll.

  First, the thermal expansion profile of each hearth roll is sequentially calculated by monitoring the atmospheric temperature and the metal band temperature at each position in the furnace with thermometers installed at each position in the continuous annealing furnace. At this time, the thermal expansion profile can be calculated by, for example, combining roll temperature distribution calculation and thermal expansion calculation by a simplified two-dimensional difference method. In addition, a temperature measuring roll with a plurality of thermocouples installed in the axial direction on the inner peripheral surface of the hearth roll body which is a hollow structure is introduced, and the thermal expansion of the hearth roll is sequentially calculated based on the measured temperature distribution. Is also possible.

  The bending shape of the cylindrical roll due to the bending force is calculated in advance by the finite element method or the formula of elastic mechanics, and the bending force necessary to obtain a predetermined parabolic shape is arranged in order, so that it changes sequentially. By calculating the bending force necessary to cancel out the thermal expansion profile of the hearth roll and applying it to the neck portion, it is possible to control the change in the surface profile of the hearth roll to a minimum. At this time, the target bending force may be determined so that, for example, the square sum of the deviation between the roll profile after thermal expansion calculated in the direction of the hearth roll cylinder and the initial roll profile is minimized. Further, if the roll bending amount and the roll bending force necessary for compensating the thermal expansion amount are sequentially calculated and the on-line control in which a bending moment is applied to the roll neck portion is performed, a more sufficient effect can be expected.

  The hearth roll equipment and the control method thereof according to the present invention need not be applied to all the hearth rolls in the continuous annealing furnace, and the unevenness of the thermal expansion profile of the hearth roll is particularly remarkable in the heating zone and the cooling zone. A sufficient effect is exhibited by applying it only to the part.

  The effects of the present invention will be described below based on examples.

  In a continuous annealing furnace for annealing a mild steel strip, a hearth roll having the conventional shape and structure shown in FIG. 5 was placed at each position of the heating zone, the soaking zone, and the cooling zone. The heating zone and the cooling zone of this continuous annealing furnace are each composed of 1 to 3 zones from the entrance side in the sheet passing direction. The heart roll equipment and the control method according to the present invention are applied to each zone of the heating zone and the cooling zone. By introducing (with roll bending) or a combination of conventional methods (without roll bending), the presence or absence of a meandering phenomenon in the heating zone and the occurrence of a squeezing phenomenon in the cooling zone were evaluated. The evaluation of meandering was carried out using monitor images installed at various locations in the furnace. The passed material is a mild steel material, and the dimensions are a thickness of 0.15 mm to 0.35 mm and a width of 700 to 1050 mm.

  Tables 1 and 2 show the evaluation results. Table 1 shows the evaluation results in the heating zone, and Table 2 shows the evaluation results in the cooling zone. Cases 1 to 12 show the results of operations performed independently for about one month. In addition, the size configuration of the material passed through each evaluation period (the ratio of the number of plates passing through the material of each thickness and width) is almost the same.

  ○ in Table 1 indicates that no meandering phenomenon occurred during the period, △ means that some meandering phenomenon occurred but did not significantly affect the operation, and x means that the meandering phenomenon occurred. This is a case where the speed is reduced. In Case 6, which is a conventional method (no roll bending) in each zone, remarkable meandering occurred particularly under a thin plate thickness of 0.15 mm, and a fracture trouble occurred. On the other hand, the hearth roll equipment according to the present invention was introduced, and the amount of thermal expansion of the hearth roll body was estimated from the furnace temperature, the plate passing speed, the plate passing time, the plate width of the metal strip, and the amount of thermal expansion was calculated. In Cases 1 to 5, in which the roll bending amount and roll bending force necessary to compensate so as to cancel each other are sequentially calculated and a bending moment is applied to a part or all of the zones at the roll neck, the operating conditions must be changed. No meandering phenomenon was observed.

  ○ Evaluation in Table 2 indicates that when no squeezing phenomenon occurred during the period, △ when squeezing phenomenon occurred but did not significantly affect the operation (in terms of quality, the squeezed part was defective and the yield dropped) , X is a case where a reduction phenomenon occurs and a countermeasure for lowering the sheet passing speed is taken. In Case 12, which is a conventional method (no roll bending) in each zone, the coil full length becomes poor due to a remarkable drawing phenomenon particularly when the plate thickness is as thin as 0.15 mm. Incorporation of the material into the cycle was discontinued. On the other hand, the hearth roll equipment according to the present invention was introduced, and the amount of thermal expansion of the hearth roll body was estimated from the furnace temperature, the plate passing speed, the plate passing time, the plate width of the metal strip, and the amount of thermal expansion was calculated. In Cases 7 to 11 in which the roll bending amount and roll bending force necessary to compensate so as to cancel each other are sequentially calculated and a bending moment is applied to a part or all of the zones at the roll neck, the operating conditions must be changed. No squeezing phenomenon was observed.

  In the example of the present invention, the bending force applied to the hearth roll equipment is estimated by estimating the thermal expansion amount of the hearth roll body from the furnace temperature, the plate passing speed, the plate passing time, and the metal strip width. Although it was calculated, it was confirmed that the same effect can be obtained even when the roll bending force is calculated based on the temperature distribution on the inner surface of the roll measured online at another timing.

  Also, according to the heat treatment pattern applied in this example (furnace temperature setting in each zone (heating, soaking, cooling) differs for each steel type), in the present invention example, each zone in the heating zone and cooling zone The effect when applied is different. Since the effect obtained by the present invention is greatly affected by the temperature pattern in the continuous annealing furnace, when the present invention is partially applied to a part of the continuous annealing furnace, the material that passes through the line In consideration of the heat treatment pattern, it may be applied to the most effective place.

1 Hearth roll 2 Bending fulcrum 3d Bending force 3d downward Bending force 4d Bending moment 4d Bending moment 4u

Claims (4)

A hearth roll facility used to transport the metal strip in a continuous annealing furnace for continuously heat-treating the metal strip,
A reduction screw that holds the roll body side of the chock holding the roll neck so that it becomes a fulcrum of bending moment from the upper or lower part of the housing;
A hydraulic cylinder that applies a vertical force on the end side of the chock,
A hearth roll equipment for a continuous annealing furnace, characterized in that the shape of the hearth roll body is substantially parabolic. In the hearth roll equipment for a continuous annealing furnace according to claim 1,
A hearth roll facility for a continuous annealing furnace, comprising a plurality of thermocouples for measuring a roll inner peripheral surface temperature inside a hearth roll body. It is a control method of the hearth roll equipment for continuous annealing furnaces according to claim 1,
The amount of roll bending required to estimate the amount of thermal expansion of the hearth roll barrel from the furnace temperature, plate passing speed, plate passing time, and plate width of the metal strip, and to compensate so as to offset the estimated amount of thermal expansion A method for controlling a hearth roll facility for a continuous annealing furnace, wherein a roll bending force is calculated and a bending moment is applied to the roll neck portion. It is a control method of the hearth roll equipment for continuous annealing furnaces according to claim 2,
Based on the temperature distribution on the inner peripheral surface of the roll measured by the thermocouple, the heat expansion amount distribution of the hearth roll, and the roll bending amount and roll bending force necessary to compensate for the thermal expansion amount are calculated to calculate the roll neck portion. A method for controlling a hearth roll equipment for a continuous annealing furnace, wherein a bending moment is applied to the furnace.

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