JP4583255B2 - How to use heat treatment furnace - Google Patents

Description

The present invention relates to a method of using a heat treatment furnace such as a thick steel plate.

  Conventionally, in a batch-type hot air circulation heat treatment furnace using a fan, particularly when the processing material has good heat conduction, the hot air temperature sent by the fan passes between the materials, and the hot air temperature decreases. There was a considerable difference in heating speed between the windward and leeward of the fan. In order to shorten this temperature difference, Patent Document 1 describes, as the prior art, “a method in which the rotation direction of the fan is periodically reversed by a timer is conventionally employed” (Patent Document 1). 1 (see FIG. 2).

The prior art has a drawback in that it takes a long time to raise the temperature to a predetermined time because the forward / reverse operation of the fan is repeated several tens of times.
Therefore, in the invention described in Patent Document 1, the temperature raising time is shortened by switching the forward / reverse switching only once (see FIG. 3 of Patent Document 1).
Japanese Patent Publication No.53-29281

In any of the dozens of forward / reverse switching operations shown in FIG. 2 of Patent Document 1 and the operation by only one switching shown in FIG. There is a difference in the time until the temperature is raised (hereinafter, this difference is referred to as “temperature rise time difference”). That is, a temperature distribution is generated until the entire material to be heated reaches the target temperature uniformly.
When a temperature rise time difference occurs in the material to be heated in the heat treatment furnace for the thick steel plate, the strength distribution in the thick steel plate varies.

  By the way, although the temperature “LC1” and “LC2” of the heated material described in Patent Document 1 are the temperatures at both ends to which the hot air of the heated material is supplied, the technique of Patent Document 1 is applied to an actual site. In this case, it was found that the temperature of the intermediate portion (center portion) of the material to be heated is lower than the temperatures (LC1, LC2) of both ends. That is, in a heat treatment furnace that heats the material to be treated by flowing hot air along the surface of the material to be treated from one end portion to the other end portion of the material to be heated (material to be treated) by a blowing means. As a matter of fact, there is a problem that the temperature rise at the end of the substrate is faster than the other portions. As in Patent Document 1, it is only necessary to reduce the temperature rise time difference by focusing only on both ends of the material to be treated. There was a problem that the variation in quality such as the strength could not be eliminated.

Then, an object of this invention is to provide the usage method of the heat processing furnace which made temperature rising time uniform over the whole to-be-processed material.

In order to achieve the above object, the present invention has taken the following measures.
That is, the feature of the present invention is that a furnace chamber for storing the material to be processed placed on the material mounting table, a heating means for heating the atmospheric gas in the furnace chamber, and a heating means for heating. In the method of using a heat treatment furnace having a blowing means for blowing the atmospheric gas as hot air, the velocity boundary layer formed on the surface of the material to be treated by the hot air has the same thickness from one end to the other end of the material to be treated. such that, said a one end portion of the material to be treated can you provided velocity boundary layer generating means on the upstream side in the hot air flow direction, as the velocity boundary layer generating means, a plurality of baffle having different heights Prepare a plate, select a baffle plate that is flush with the surface of the material to be treated, and then fix the material to be treated so as to contact one end of the material to be treated. on one of said workpiece by said blowing means By passing hot air from section along the surface of the 該被 treatment material to the other end, characterized by heating the 該被 treatment material.

  The inventors of the present application have a furnace chamber for storing the material to be processed, a heating unit for heating the atmospheric gas in the furnace chamber, and a blowing unit for blowing the atmospheric gas heated by the heating unit, The temperature (plate) of the material to be treated is measured in a heat treatment furnace for the thick steel plate that heats the material to be treated by flowing hot air along the surface of the material to be treated from one end to the other end of the material by means Temperature) was confirmed.

As a result, the plate width direction end (end in the width direction of the material to be processed) is heated faster than the central portion, resulting in a temperature rise time difference that is the difference between the calculated value of the temperature rise time and the actual value. It became. In order to grasp the phenomenon, we hypothesized that “the heat transfer coefficient distribution is generated in the plate width direction by the velocity boundary layer”.
FIG. 3 is an explanatory diagram of the above hypothesis. The hypothesis is that the heat transfer rate is high because the velocity boundary layer is thin at the front end of the steel sheet with respect to the gas flow, and the heat transfer rate decreases as the velocity boundary layer grows. The temperature rise time difference in the plate width direction is caused by the influence.

  Under the above hypothesis, the plate temperature was actually measured and calculated under the condition that the width (plate width) of the material to be processed was 4.5 m. It should be noted that the heat transfer coefficient distribution changes according to the influence of the velocity boundary layer by “−0.2” of the distance from the end of the material to be processed. FIG. 4 is a graph showing the relationship between the distance from the end portion and the heat transfer coefficient ratio (the ratio between the heat transfer coefficient at the center of the material to be processed and the heat transfer coefficient at a predetermined position).

FIG. 5 is a diagram showing a calculation result of the heating time based on the hypothesis and an actual measurement result thereof. The temperature increase time indicated on the vertical axis in this figure indicates the time difference from the part having the slowest temperature increase time in the plate width direction. It is clear that the calculation result of the heating time based on the hypothesis and the actual measurement result have the same tendency, and the heating time difference in the plate width direction can be explained by this hypothesis.
Therefore, the present invention provides a velocity boundary layer formed on the surface of the material to be treated by hot air by the blowing means so that the thickness of the material to be treated is the same from one end to the other end of the material to be treated. The velocity boundary layer generating means is provided at the upstream end. By doing so, the end portion of the material to be processed is virtually extended upstream, and the thickness of the velocity boundary layer is substantially constant in the width direction in the original portion of the material to be processed. In other words, the portion where the thickness of the velocity boundary layer is distributed while changing is positioned so as to correspond to the velocity boundary layer generation means.

Since the thickness of the velocity boundary layer is the same at the end portion and the center portion of the material to be processed, the uniformity of the temperature rise can be maintained throughout and the temperature rise time difference can be reduced.
Also, the air blowing means is a capable forward and reverse operation, it is preferable to blow the hot air alternately from both sides of the workpiece by the forward and reverse operation of the air blowing means.
Furthermore, the above-mentioned material to be treated is a steel plate having a thickness, a width, and a longitudinal direction. Regarding the above-described heat treatment furnace, the furnace chamber is partitioned into a plurality of control zones in the longitudinal direction, and each heating zone includes the heating means. and yet it is preferably the blowing means is provided.

  According to the present invention, the temperature raising time is uniform over the entire workpiece.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of a heat treatment furnace used in the method of the present invention. In this embodiment, a cart furnace for heat treating a thick steel plate is exemplified as the heat treatment furnace.
The heat treatment furnace has a furnace chamber 1 filled with combustion exhaust gas (atmosphere gas). The furnace chamber 1 stores the material 2 to be processed. The heat treatment furnace has a heating means 3 for heating the atmospheric gas in the furnace chamber 1. Further, the heat treatment furnace has a blowing means 4. The air blowing means 4 circulates the atmospheric gas heated by the heating means 3 in the furnace chamber 1. The air blowing means 4 can be operated forward and backward.

The periphery of the furnace chamber 1 is covered with a furnace wall 5. The bottom of the furnace chamber 1 is closed by a carriage 6. The cart 6 is provided with a processing material mounting table 10, and the processing material 2 is mounted on the mounting table 10.
In this embodiment, the workpiece 2 is exemplified by a thick steel plate. The workpiece 2 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 the front-rear direction orthogonal to the paper surface.

The furnace chamber 1 is divided vertically by a partition wall 11. The partition wall 11 is horizontally arranged so as to close the upper part with a predetermined interval from the upper surface of the workpiece 2.
The upper furnace chamber 1 partitioned by the partition wall 11 is a heating chamber 12, and the lower furnace chamber 1 is a heat treatment chamber 13 for processing the workpiece 2. A heating means 3 is provided in the heating chamber 12. As an example of the heating means 3, a burner that burns combustion gas generated in a coke oven or a blast furnace is illustrated. The heating means 3 is attached to the furnace body ceiling (the ceiling of the furnace chamber 1), and is configured to emit a flame toward a substantially vertical downward side.

  A first hot air passage 14 penetrating vertically is formed inside the furnace chamber 1 at the right end of the cross section (right side in FIG. 1), and also on the opposite end (left side in FIG. 1). The second hot air passage 15 is provided so as to penetrate vertically, and the blowing means 4 is disposed in the second hot air passage 15. An axial flow fan is illustrated as the blowing means 4. The forward / reverse operation of the blowing means 4 is performed by a motor 16 capable of forward / reverse operation. The atmospheric gas in the heating chamber 12 is supplied from the first hot air passage 14 to the heat treatment chamber 13 by the forward rotation of the blowing means 4, and the atmospheric gas in the heating chamber 12 is supplied from the second hot air passage 15 to the heat treatment chamber 13 by the reverse rotation. The inside of the furnace chamber 1 is circulated forward and backward.

As long as the rotation speed is constant, the blowing amount of the blowing means 4 is not equal when the forward rotation is (Q forward) and the reverse rotation is (Q reverse), and (Q forward ≠ Q reverse) Has been.
The first hot air passage 14 is provided with first temperature measuring means 17, and the second hot air passage 15 is provided with second temperature measuring means 18. These temperature measuring means 17 and 18 measure the temperature of the hot air blown from the blowing means 4.

The first and second temperature measuring means 17 and 18 and the motor 16 of the air blowing means 4 are connected via a control device 19. Therefore, it is preferable that the first and second temperature measuring means 17 and 18 can transmit the measurement result to the control device 19 as an electric signal.
FIG. 2 is a plan view of the heat treatment furnace. The furnace chamber 1 is divided into a plurality of control zones in the longitudinal direction. Each control zone is more divided into vertical partition wall provided in the position shown in phantom. In this embodiment, five control zones are provided, and one heating means 3 and one air blowing means 4 are provided in each control zone. Hot air flows in the width direction along the upper and lower surfaces of the material to be treated by each blowing means 4.

The heat treatment furnace heats the material to be treated 2 by causing hot air to flow along the surface of the material to be treated 2 from one end to the other end of the material to be treated 2 by the blowing means 4. When the hot air flows along the surface of the material 2 to be processed, a velocity boundary layer (see FIG. 3) is formed on the surface side of the material 2 to be processed.
In the present invention, the velocity boundary layer generating means is provided on the upstream side of the hot air at one end of the material to be processed 2 so that the velocity boundary layer has the same thickness from one end to the other end of the material to be processed 2. 23 is provided.

In this embodiment, since the air blowing means 4 can be operated forward and backward, the speed boundary layer generating means 23 is provided on both sides of the workpiece 2.
As the velocity boundary layer generating means 3, a baffle plate arranged so as to be flush with the surface of the workpiece 2 is illustrated. This baffle plate is fixed to the workpiece mounting table 10. Since the size of the workpiece 2 changes, this baffle plate is provided so that the position can be changed and the shape can be changed.

Specifically, the baffle plate has a hollow box shape formed of a heat-resistant steel plate, and is disposed so as to be in contact with the workpiece 2 on the workpiece mounting table 10 as shown in FIG. . A baffle plate having a plurality of sizes (heights) is prepared, and a baffle plate that matches the size (height) of the workpiece 2 is selected and used.
FIG. 6 shows a simulation result of the temperature rise time difference when the baffle plate is installed and not installed. The calculation condition is that “the plate width of the material to be processed 2 is 4.5 m, and baffle plates of 0.75 m are installed on both sides of the material to be processed 2 in the plate width direction”.

In addition, when heating the to-be-processed material 2 using the said heat processing furnace, it is preferable to use the following method.
That is, a method in which hot air is alternately supplied from both sides of the material to be treated 2 by forward / reverse operation of the blower means 4 to heat the material to be treated 2 to a target temperature, and the temperature on both sides of the material to be treated 2 is The forward / reverse operation of the air blowing means 4 is controlled so as to minimize the time difference for reaching the target temperature. In this embodiment, both sides of the workpiece 2 are both sides in the width direction of the steel plate.

In the above control, when the rotational speed at the time of forward rotation of the air blowing means 4 and the rotational speed at the time of reverse rotation are the same, the forward and reverse air blown according to the respective forward and reverse air flow amounts (Q forward, Q reverse). It is preferable to operate the air blowing means 4 by determining the ratio of time (T normal, T reverse). That is, as an example of a relationship between a forward / reverse air blowing time ratio and a forward / reverse air flow rate ratio, the relationship of Expression (1) may be employed.

T forward / T reverse = (Q forward / Q reverse) ^a (1)
However, a = 0.8-0.9

When the rotational speed at the time of forward rotation of the blower 4 is not the same as the rotational speed at the time of reverse rotation, the forward / reverse operation of the blower 4 can be controlled as follows.

In other words, the forward / reverse operation of the blower 4 is controlled so that the forward and reverse airflows (Q forward, Q reverse) of the blower 4 are the same. In this control, the rotational speed of the motor 16 is controlled by inverter control or the like, and the rotational speed of the fan in the forward / reverse operation is changed to (Q forward = Q backward). In this case, the forward and reverse air blowing times are the same (T positive = T reverse).
In the present embodiment, the interior of the furnace chamber 1 is preheated before the workpiece 2 is stored in the furnace chamber 1.

By preheating, the amount of heat transfer to the furnace body is reduced, the temperature difference between the upstream and downstream of the atmospheric gas is reduced, and the temperature increase time difference of the steel sheet is reduced.
Further, in the present embodiment, the upstream furnace temperature (t upstream) and the downstream furnace temperature (t downstream) of the atmospheric gas with respect to the material to be processed 2 are measured by the first and second temperature measuring means 17 and 18, Each blowing means 4 is controlled via the control device so that the temperature difference is the same in each control zone.

By controlling each zone as described above, the temperature increase time difference of the steel plate for each zone can be reduced. That is, the temperature increase time difference can be minimized over the width direction and the longitudinal direction of the workpiece 2.
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 thick steel plates.

It is front sectional drawing (width direction sectional drawing) of a cart furnace. It is a top view of a cart furnace. It is explanatory drawing of the speed boundary layer generate | occur | produced on the to-be-processed material surface. It is a figure which shows the relationship between the distance from the width direction edge part of a to-be-processed material, and heat-transfer coefficient ratio. It is the figure which showed the distance from the width direction edge part of a to-be-processed material, and temperature rising time difference (a calculated value and a track record value). It is the figure which showed the temperature increase time difference at the time of using a speed boundary layer production | generation means (calculated value).

DESCRIPTION OF SYMBOLS 1 Furnace room 2 To-be-processed material 3 Heating means 4 Blowing means 23 Speed boundary layer production | generation means

Claims (3)

A furnace chamber for storing the material to be processed placed on the material mounting table, a heating unit for heating the atmospheric gas in the furnace chamber, and a blowing unit for blowing the atmospheric gas heated by the heating unit as hot air In a method of using a heat treatment furnace having
The velocity boundary layer formed by the hot air on the surface of the material to be treated has the same thickness from one end to the other end of the material to be treated, and is at one end of the material to be treated in the flow direction of the hot air. can you provided velocity boundary layer generating means on the upstream side,
As the velocity boundary layer generation means, a plurality of baffle plates having different heights are prepared,
After selecting a baffle with a height that is flush with the surface of the material to be processed, it is fixed to the material mounting table so as to be in contact with one end of the material to be processed.
Then, the material to be treated is heated by flowing hot air along the surface of the material to be treated from one end to the other end of the material to be treated by the blowing means . how to use. The air blowing means is capable of forward / reverse operation ,
Using heat treatment furnace according to claim 1, characterized in that for blowing hot air alternately from both sides of the workpiece by the forward and reverse operation of the air blowing means. The material to be treated according to claim 1 or 2 is a steel plate having a thickness, a width and a longitudinal direction,
The heat treatment furnace according to claim 1 or 2, wherein the furnace chamber is divided into a plurality of control zones in the longitudinal direction, and the heating means and the air blowing means are provided in each control zone. How to use the furnace .

Images