JP2007002301A - Heating method in heat-treating furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for heating a material to be treated at uniformly distributed temperatures along a longitudinal direction of the material in a heat-treating furnace. <P>SOLUTION: The heat-treating furnace has a heat treatment chamber 2 longitudinally sectioned into a plurality of control zones, a heating means 5 for heating an atmospheric gas in the heat treatment chamber 2 and a circulating means 4 for circulating the atmospheric gas heated by the heating means 5 as hot blast. The method for heating a material to be treated includes supplying the hot blast from one side of the material in a width direction to the other side in the above heat treating furnace; measuring each temperature of the hot blast in the respective control zones (i = 1 to n), specifically each temperature in upstream ((t) in upstream (i)) and each temperature in downstream ((t) in downstream (i)); and controlling an air quantity (Qi) of the circulating means in the respective control zones so that the difference of the temperatures (Δti=(t) in upstream (i)-(t) in downstream (i)) becomes equal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heating method in a heat treatment furnace for heat-treating a material to be treated such as a thick steel plate and a shape steel.

The thing of patent document 1 is well-known as a heating furnace of the long to-be-processed material.
The one described in this publicly known document is to heat a material to be treated along its longitudinal direction with a uniform temperature distribution, and the heating furnace has a plurality of heating along the longitudinal direction of the furnace body. It has zones A, B, and C, and first brings it to a high temperature in the central heating zone B, and then sets the temperature of the heating zones A and C at both ends to a predetermined temperature with a time delay thereafter, or heating zone The fuel flow rate of each gas burner was controlled.
However, this prior art is intended to maintain the heating chamber in each heating zone at a high temperature and a uniform temperature distribution, so that the structure of the furnace body is complicated.

On the other hand, a technique for uniform heating by improving a contact method between hot air and a material to be processed without using a furnace having a complicated structure as in Patent Document 1 is known as disclosed in Patent Document 2, for example. It is.
The prior art described in Patent Document 2 is a batch-type heating method in which hot air from a heating source is stirred by a hot air circulation fan to heat the material, and the hot air sent by the circulation fan passes through the material. The hot air temperature decreases, and there is a considerable difference in the heating speed between the windward and leeward of the fan, and uneven heating occurs based on the temperature difference, so the temperature difference is shortened and the workpiece is heated uniformly. In order to do this, the rotation direction of the fan is reversed.

Since the furnace body structure described in Patent Document 2 does not uniformly heat the heating chamber itself, the structure of the furnace body can be simplified as compared with that described in Patent Document 1.
Japanese Utility Model Publication No.59-8159 Japanese Patent Publication No.53-29281

However, a furnace having a simple structure as described in Patent Document 2 was used as a method of uniformly heating a long workpiece having a thickness, width and longitudinal direction such as a thick steel plate over the longitudinal direction. In this case, the control method is important. However, as such a control method, it is difficult to directly apply the control described in Patent Document 1 in which only a rough control for heating with a uniform temperature distribution along the longitudinal direction is disclosed. A beneficial control method that changes (heating method in a heat treatment furnace) has not yet been developed.
In view of this, the present invention provides a heat treatment chamber for storing a long workpiece having a thickness, width and longitudinal direction, such as a thick steel plate, which is partitioned into a plurality of control zones in the longitudinal direction, and heats the air in the heat treatment chamber. Using a heat treatment furnace having a simple structure having heating means and circulation means for circulating air heated by the heating means as hot air in the control zone in the width direction, the hot air is sent in the width direction of the material to be treated An object of the present invention is to provide a heating method in which the material to be processed is supplied from one side to the other side to heat the material to be processed, and can be heated along the longitudinal direction with a uniform temperature distribution.

In order to achieve the above object, the present invention has taken the following measures.
That is, a feature of the present invention is that a heat treatment chamber capable of storing a long material to be processed having a thickness, a width, and a longitudinal direction and partitioned into a plurality of control zones in the longitudinal direction, and the heat treatment Using a heat treatment furnace having heating means for heating the atmospheric gas in the room and circulation means for circulating the atmospheric gas heated by the heating means as hot air in the width direction of each control zone, the hot air is treated A heating method in a heat treatment furnace for supplying the material to be processed from one side in the width direction to the other side to heat the material to a target temperature, in each control zone (i = 1 to n), upstream of the hot air Side temperature (t upstream i) and downstream temperature (t downstream i) are measured, and the air volume of the circulating means in each control zone is equalized so that the temperature difference (Δti = t upstream i−t downstream i) becomes equal. (Qi) is to be controlled.

In the present invention, it is preferable that the air volume (Qi) of each control zone is set to satisfy the following equation.

Qi = f (Qmax, Δtmax, Δti)

However,
Δti: Temperature difference in the control zone
Δtmax: Temperature difference in the control zone with the largest temperature difference
Qmax: Air volume in the control zone with the largest temperature difference
Qi: Air volume of remaining control zone It is preferable that the circulating means supply the hot air alternately from both sides in the width direction of the material to be processed by forward / reverse operation.

  ADVANTAGE OF THE INVENTION According to this invention, it can heat with uniform temperature distribution along the longitudinal direction of a long to-be-processed material.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 3 show a heat treatment furnace used in the method of the present invention.
This heat treatment furnace heats a material to be treated 1 (object to be heated) having a thickness, a width, and a longitudinal direction uniformly over the longitudinal direction. In this embodiment, a cart furnace for heat treating a thick steel plate. Is illustrated.
The cart furnace has a furnace chamber R for storing the material 1 to be processed. The periphery of the furnace chamber R is covered with a furnace wall 10. The bottom of the furnace chamber R is closed by a carriage 9. The carriage 9 is provided with a workpiece mounting table 13, and the workpiece 1 is mounted on the mounting table 13.

The material to be treated 1 has a thickness, a width, and a longitudinal direction. In FIG. 1, the thickness direction is the vertical direction, the width direction is the left-right direction, and the longitudinal direction is perpendicular to the paper surface. Direction.
The furnace chamber R is divided vertically by a horizontal partition wall 16. The horizontal partition wall 16 is horizontally arranged so as to close the upper portion with a predetermined distance from the upper surface of the workpiece 1. The upper side defined by the horizontal partition wall 16 is a heating chamber 3, and the lower side is a heat treatment chamber 2 for processing the material 1 to be processed.

The heat treatment chamber 2 and the heating chamber 3 are partitioned into a plurality of control zones (i = 1 to n, i is a control zone number, and n is the number of control zones) in the longitudinal direction. Then, heating means 5 for heating the atmospheric gas in the room for each control zone (i = 1 to n), and circulation means 4 for circulating the atmospheric gas heated by the heating means 5 in the width direction as hot air. Have.
The heating means 5 is not necessarily provided for each control zone, and may be common over a plurality of control zones.
The circulation means 4 (circulation fan) circulates the atmospheric gas heated by the heating means 5 in the furnace chamber R (heat treatment chamber 2 and heating chamber 3), and can be operated forward and backward by the circulation fan motor 11. Has been. By this circulation means 4, hot air flows in the width direction along the upper and lower surfaces of the workpiece 1.

Each of the control zones (i = 1 to n) is partitioned by a heating chamber zone partition wall 6 and a heat treatment chamber zone partition wall 7 provided at positions indicated by phantom lines in FIG. In this embodiment, the partition walls 6 and 7 provide five (n = 5) control zones for the heat treatment chamber 2 and the heating chamber 3, and the heating means is provided in each control zone (i = 1 to 5). 5 and one circulation means 4 are provided.
FIG. 3 shows one side surface cross section (cross section facing the length direction of the material to be processed) of the control zone. Specifically, the heating chamber zone partition wall 6 is provided so as to hang down from the ceiling of the heat treatment chamber 2, and a horizontal partition wall 16 is attached to the lower portion of the heating chamber zone partition wall 6 so as to be substantially vertical. The heat treatment chamber zone partition wall 7 is configured by disposing the heat-resistant steel plate from the partition wall 16 so as to be suspended just above the workpiece 1. The heat treatment chamber zone partition wall 7 is not limited to one made of a heat-resistant steel plate, and may be made of other metal materials or heat-resistant heat insulating materials.

A heating means 5 is provided in the heating chamber 3. As an example of the heating means 5, a burner for burning is illustrated. The heating means 5 is attached to substantially the center of the ceiling of the heating chamber 3 and is configured to emit a flame downward.
In the vicinity of the circulation means 4 of the horizontal partition wall 16, a first hot air passage 14 penetrating vertically is formed. A second hot air passage 15 is provided at the end of the horizontal partition wall 16 opposite to the circulation means 4 so as to penetrate vertically. An example of the circulation means 4 is an axial fan. The forward / reverse operation of the axial flow fan is performed by a circulation fan motor 11 capable of forward / reverse operation. With the forward rotation of the axial fan, the hot air in the heating chamber 3 is supplied from the first hot air passage 14 to the heat treatment chamber 2, and by the reverse rotation, the hot air in the heating chamber 3 is supplied from the second hot air passage 15 to the heat treatment chamber 2, The heat treatment chamber 2 and the heating chamber 3 are circulated forward and backward.

When the rotational speed is constant, the axial flow fan is not equal when the forward rotation is (Q positive) and the reverse rotation is (Q reverse), (Q forward ≠ Q reverse). It is said that.
First temperature measuring means 8 is provided in the first hot air passage 14, and second temperature measuring means 9 is provided in the second hot air passage 15. These both temperature measuring means 8 and 9 measure the temperature of the hot air on both sides of the workpiece 1.
That is, the first and second temperature measuring means 8 and 9 are arranged in the control zones (i = 1 to n) in the upstream temperature (t upstream i) and the downstream temperature (t downstream i). ).

The first and second temperature measuring means 8 and 9 and the circulation fan motor 11 are connected via a control device 17. Therefore, it is preferable that the first and second temperature measuring means 8 and 9 can transmit the measurement result to the control device 17 as an electric signal.
The control device 17 calculates the temperature difference (Δti = t upstream i−t downstream i) based on the measured temperatures from the first and second temperature measuring means 8 and 9, and based on the calculation result, The air volume (Qi) of the circulation means 4 in each control zone is controlled so that the material to be treated is uniformly heated in the longitudinal direction.

That is, in the air volume control of each control zone, the temperature difference of the zone having the largest temperature difference (Δti) is Δtmax, the air volume of the control zone of Δtmax is the maximum value (Qmax), and the air volume ( Qi) is set as Qi = f (Qmax, Δtmax, Δti).
The heating method of the present invention using the heat treatment furnace will be described with reference to FIGS. 4 corresponds to FIG. 1, and FIG. 5 is a block diagram corresponding to FIG. In these figures, “t upstream i” is the hot air temperature before spraying the material 1 to be processed in each control zone (i = 1 to n), and “t downstream i” is the hot air after passing the material to be processed. “T upstream i” is the temperature of the workpiece 1 on the hot air blowing side, and “T downstream i” is the temperature of the workpiece 1 on the opposite side of the hot air blowing side.

The processed material 1 has end portions in the longitudinal direction at i = 1 and i = n, and a continuous intermediate portion at i = 2 to (n−1).
As shown in FIG. 6, when the temperatures of “t upstream 1” and “t upstream 2” are the same, the hot air is deprived of heat by the material to be treated 1 (object to be heated) and the furnace body, and the temperature drops. Due to the difference in the weight of the material to be treated for each zone, the downstream temperature “t downstream 1” and “t downstream 2” of the hot air differ as time passes, as shown in the figure.
As a result, as shown in FIG. 6, a temperature difference also occurs between “T downstream 1” and “T downstream 2” of the material 1 to be processed, and uniform heating in the longitudinal direction cannot be achieved.

Therefore, in the embodiment of the present invention, paying attention to the fact that the downstream hot air temperature is determined by the amount of hot air and the amount of heat taken away from the hot air, the variation in the temperature of the material to be processed is controlled by controlling the amount of hot air in each zone. To do.
As shown in FIG. 7, for example, in order to set the air volume at the elapsed time a, the upstream and downstream temperatures (t upstream i, t upstream i) of the hot air are measured.
From this measured value, the temperature difference between upstream and downstream in each zone (Δti = t upstream i−t downstream i) is calculated.

The hot air volume in the zone with the largest temperature difference is set as the equipment specification maximum value, and the remaining zones are controlled according to Δti and Δtmax, and the hot air volume is reduced to control the downstream hot air temperature in each zone. Controls variation in direction.
FIG. 8 is a flowchart of the control. That is, according to the embodiment of the present invention, in each control zone (i = 1 to n), the upstream furnace temperature (t upstream i) and the downstream furnace temperature (t downstream i) with respect to the material to be treated of the hot air. ).
Next, the temperature difference (Δti = t upstream i−t downstream i) is obtained.

Thereafter, based on the temperature difference Δti, the air volume (Qi) of the circulating means in each control zone is controlled so that the material to be processed is uniformly heated in the longitudinal direction.
In this air volume control, the temperature difference of the zone having the largest temperature difference (Δti) is set to Δtmax, the air volume of the control zone of Δtmax is set to the maximum value (Qmax), and the air volume (Qi) of the remaining control zones is set to

Qi = f (Qmax, Δtmax, Δti) (1)

And set.

FIG. 9 shows equation (1), for example,

Qi = K · Δti / Δtmax · Qmax (2)
However, K = 1

FIG. 9 shows an example of a change in hot air temperature when the amount of the material to be processed 1 in the control zone is different in the heat treatment furnace. Here, the amount of the material 1 to be processed in the two zones is approximately 1/4 of the amount of the material 1 to be processed in the one zone. The form of the heat treatment furnace is that shown in FIGS.

As can be seen from the figure, when there is no heating control and the air volumes in the 1st and 2nd zones are the same, t downstream 2 is at a higher temperature than t downstream 1. However, by adopting the heating method of the present invention, in other words, the air volume control, the downstream 2 and the downstream 1 have the same temperature transition, and the hot air temperature (circulating gas temperature) is the same, so that the workpiece 1 The temperature can also be made uniform.
In this example, K = 1, but the value of K may be adjusted according to each control zone or the equipment to be used, and need not always be 1. Further, in the present embodiment, the air volume Qi defined by the formula (1) or the formula (2) is used. However, the value of Qi / Qmax is conventionally known such as PID control with Δti / Δtmax = 1 as a target value. You may make it control by the control method which has.

In the embodiment of the present invention, the circulating means 4 alternately supplies hot air from both sides in the width direction of the workpiece 1 by forward and reverse operations. This alternating operation control is performed as follows.
When the rotational speed during forward rotation of the axial fan is the same as the rotational speed during reverse rotation, the forward / reverse air blowing time (T forward / backward) depends on the forward / reverse air flow (Q forward, Q reverse) of the axial fan. , T reverse) is determined and the circulating means 4 is operated.
If the rotational speed is the same at the time of forward / reverse rotation and the rotational speed is the same, (Q forward ≠ Q reverse). Therefore, if the forward / reverse operation is performed alternately for the same time, the material to be processed 1 The amount of heat applied is not the same, and a temperature rise time difference occurs.

Therefore, the ratio of the forward and reverse blowing time (T forward, T reverse) is determined so that the temperature rise time difference is not more than the predetermined range.
Specifically, an experiment was performed using the equipment shown in FIGS. 1 and 2 in order to determine the ratio. Then, the forward rotation ratio that can minimize the temperature rise time difference is calculated from the plate temperature calculation (temperature calculation of the material to be processed), and the forward / reverse blowing time (T forward, T reverse) ratio is calculated from the calculated forward rotation ratio. It was determined.
The forward rotation ratio (operating time ratio) is defined by equation (1).

Forward rotation ratio = T forward / (T forward + T reverse) (3)

Experimental results and calculation results are shown in FIGS.
[Calculation condition]
1) Plate size: 28 mm (thickness) x 4500 mm (width) x 18000 mm (length)
2) Target plate temperature: 600 ° C
3) 1 cycle blowing time: 20 minutes 4) Blowing volume: Q forward = 780 m ³ / min, Q reverse = 520 m ³ / min
Table 1 shows forward and reverse blowing times (T forward, T reverse), the sum, the forward rotation ratio, the temperature rise time difference, and the heating time. The forward rotation ratio is defined as “T forward / (T forward + T reverse)”.

FIG. 10 is a graph of the operating time ratio and the temperature rise time difference.
FIG. 11 is a graph of a plate temperature calculation example when the forward rotation 15 minutes and the reverse rotation 5 minutes are alternately repeated. The forward blowing air temperature is the temperature of hot air measured by the first temperature measuring means 8, and the reverse blowing air temperature is the temperature of the hot air measured by the second temperature measuring means 9. The upstream side plate temperature, the central plate temperature during forward rotation, and the upstream side plate temperature during reverse rotation are calculated.
FIG. 12 is a partially enlarged view of the graph of FIG.
In the graph of FIG. 10, the difference in temperature rise time is 5 minutes or less within the scope of the present invention. That is, the “shortest” in the present invention means 5 minutes or less.

As a result, it has been found that the ratio is represented by the following formula (4).

T forward / T reverse = (Q forward / Q reverse) ^a (4)
However, a = 0.8-0.9

When the rotational speed at the time of forward rotation of the circulation means 4 and the rotational speed at the time of reverse rotation are not the same, the forward / reverse operation control of the axial fan can be performed as follows.

That is, the forward / reverse operation of the axial fan is controlled so that the forward / reverse air flow (Q forward, Q reverse) of the axial fan is the same. In this control, the rotational speed of the circulation fan motor 11 is controlled by inverter control or the like, and the rotational speed of the axial fan in the forward / reverse operation is changed to (Q forward = Q reverse). In this case, the forward and reverse air blowing times are the same (T positive = T reverse).
In the present embodiment, the inside of the heat treatment chamber 2 is preheated before the material to be treated 1 is stored in the heat treatment chamber 2.
Preheating reduces the amount of heat transfer to the furnace body, reduces the temperature difference between the upstream and downstream of the hot air, and reduces the temperature rise time difference of the steel sheet.

  In addition, this invention is not limited to what was shown to the said embodiment, As the heating means 3, you may employ | adopt the electric heater as described in Unexamined-Japanese-Patent No. 2000-144239. . Moreover, as a heat treatment furnace, a heating chamber may be provided below and a heat treatment chamber may be provided above, and the form is not limited.

  The present invention can be used for heat treatment of a material to be treated such as a thick steel plate or a shape steel.

It is front sectional drawing (width direction sectional drawing) of a cart furnace. It is a top view of a cart furnace. It is side surface sectional drawing (longitudinal direction sectional drawing) of a control zone. It is a front block diagram of a cart furnace. It is a top block diagram of a cart furnace. It is a figure which shows the relationship between hot air temperature and to-be-processed material temperature. It is a figure which shows hot air temperature and progress of time. It is a flowchart which shows embodiment of this invention. It is a figure which shows the change of hot air temperature. It is a figure which shows the relationship between an operating time ratio and temperature rising time difference. It is a figure which shows the result of having computed the operation time ratio which can make temperature rising time difference the shortest from the temperature of a to-be-processed material. FIG. 12 is a partially enlarged view of FIG. 11.

Explanation of symbols

1 Material to be treated 2 Heat treatment chamber 3 Heating chamber 4 Circulating means 5 Heating means

Claims (3)

A heat treatment chamber capable of storing a long material to be processed having a thickness, a width, and a longitudinal direction and partitioned into a plurality of control zones in the longitudinal direction; and a heating means for heating an atmospheric gas in the heat treatment chamber; Using a heat treatment furnace having circulation means for circulating the atmospheric gas heated by the heating means as hot air in the width direction of each control zone, the hot air is directed from one side in the width direction of the material to be treated to the other side. A heating method in a heat treatment furnace for supplying and heating the material to be processed to a target temperature,
In each of the control zones (i = 1 to n), the upstream temperature (t upstream i) and the downstream temperature (t downstream i) of the hot air are measured, and the temperature difference (Δti = t upstream i−t). A heating method in a heat treatment furnace, characterized in that the air volume (Qi) of the circulation means in each control zone is controlled so that the downstream i) becomes equal. The heating method in the heat treatment furnace according to claim 1, wherein the air volume (Qi) of each control zone is set to satisfy the following formula.

Qi = f (Qmax, Δtmax, Δti)

However,
Δti: Temperature difference in the control zone
Δtmax: Temperature difference in the control zone with the largest temperature difference
Qmax: Air volume in the control zone with the largest temperature difference
Qi: Air volume in the remaining control zone   The heating method in a heat treatment furnace according to claim 1 or 2, wherein the circulating means alternately supplies the hot air from both sides in the width direction of the material to be processed by forward and reverse operations.

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