JPS60251228A - Method for controlling temperature of heat treating installation - Google Patents

Abstract

PURPOSE:To maintain always constant the temp. of a steel strip in the outlet of the 2nd heating furnace in the stage of heat-treating the steel strip in the 1st heating furnace having fast responsiveness and the 2nd heating furnace having slow responsiveness by controlling the quantity of the heat input to both furnaces by the temp. of the steel strip in the outlet of both furnaces. CONSTITUTION:The steel strip 38 is heated to about 1,000 deg.C to burn the org. materials sticking thereto in the direct firing type 1st heating furnace 40 having fast responsiveness. Said strip is heated to about 1,200 deg.C in a reducing atmosphere and is thus annealed in the 2nd heating furnace 42 using radiant tubes 50 and having slow responsiveness. The temp. of the strip 38 in the outlet of the furnace 42 is measured by a thermometer 60 and if said temp. is lower than the target temp., the quantity of the heat input is increased by controlling the control valve 64 for the fuel supply pipe 46 of the furnace 40 with the signal thereof. The temp. of the strip in the outlet of the furnace 40 is measured by a thermometer 52 and the quantity of the heat input to the inside of the radiant tubes in the 2nd heating furnace is made higher as the temp. is higher so that the heating temp. of the steel strip by the 1st heating furnace having fast responsiveness and the heating furnace having slow responsiveness is maintained always constant.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a temperature control method for heat treatment equipment, and more particularly to a technique for achieving stable heat treatment without variation regardless of fluctuations in the running speed of a member to be heated.

One type of prior art heat treatment equipment is one in which a member to be heated is subjected to heat treatment by running it through a first heating furnace with a fast response and then through a second heating furnace with a slow response. . In this type of heat treatment equipment, the amount of heat input is generally adjusted so that the temperature of the member to be heated at the outlet of the first heating furnace and the outlet of the second heating furnace each becomes a predetermined constant value. However, according to this type of heat treatment equipment, when a load fluctuation such as a change in the running speed of the heated member occurs, sufficient heat treatment is applied to the heated member for a while until the second heating furnace responds. There were disadvantages that I could not get. Particularly when the member to be heated is continuously moved at high speed, there will be a large number of defective parts that cannot be subjected to sufficient heat treatment, resulting in extremely large economic losses.

FIG. 1 is a schematic diagram of an example of the heat treatment equipment, in which a member to be heated 10 such as a strip is moved through a first heating furnace 12 and a second heating furnace 14. A member to be heated 1 is provided at the outlet of the first heating furnace 12 and the second heating furnace 14.
Temperature meters 16 and 18 are provided to detect the temperature of 0, respectively, and the temperature meters 16 and 18 output signals representing the temperature of the heated member 10 to temperature controllers 20 and 22, respectively. be done. The temperature controller 20 controls the amount of heat input to the first heating furnace 12 by outputting an adjustment signal to a flow rate adjustment valve 26 provided in a fuel supply path 24 for supplying fuel to the first heating furnace 12. The temperature of the member to be heated 10 placed at the outlet of the first heating furnace 12 is adjusted to a predetermined constant value. Similarly, the temperature controller 22 also has a flow M provided in the fuel supply path 28 that supplies fuel to the second heating furnace 14.
A control signal is output to the control valve 30 to adjust the temperature of the member to be heated 10 at the outlet of the second heating furnace 14 to a predetermined constant value. The first heating furnace 12 employs a fast-response furnace body structure, such as a direct-fired structure in which the combustion gas combusted by the burner is directly applied to the heated member 10. Conversely, the second heating furnace 14 employs a slow-response furnace body structure, such as one in which fuel is burned in a radiant tube and the member to be heated 10 is heated by heat radiation from the wall surface of the radiant tube. has been done.

In this type of heat treatment apparatus, heat treatment is applied to the member to be heated 10 according to the target heat profile shown by the solid line in FIG.
When the running speed of the 0 is suddenly increased, the actual heat profile is changed as shown by the dashed line in FIG. Heated member 1 at the outlet
In order to bring the temperature of 0 closer to the target value, the amount of heat input into the first heating furnace 12 and the second heating furnace 14 is increased. However, since the thermal response of the first heating furnace 12 is quick, but the thermal response of the second heating furnace 14 is extremely slow, the temperature of the member to be heated 10 at the exit of the first heating furnace 12 can be quickly brought into agreement with the target value. However, the temperature of the member to be heated 10 at the exit of the second heating furnace 14 is as shown by the broken line in FIG.
It cannot be quickly matched to its target temperature for some time. Furthermore, even when the running speed of the heated member 10 suddenly slows down, the temperature of the heated member 10 at the outlet of the second heating furnace 14 remains deviated from the target temperature for a certain period of time. In such a case, the broken line indicating the actual temperature of the heated member 10 will be shown at a symmetrical position with respect to the solid line in FIG. Therefore, according to this type of heat treatment equipment, when the running speed of the heated member 10 changes, the heated member 10 cannot be subjected to heat treatment under predetermined conditions for a certain period of time. It becomes. Therefore, when the member to be heated 10 is made to run at high speed, a large amount of defective products will be produced.

Problems to be Solved by the Invention To address the above-mentioned disadvantages, while controlling the inside of the second heating furnace 14 at a constant temperature, the temperature of the member to be heated 10 at the outlet of the second heating furnace 14 is controlled based on the temperature of the member to be heated 10 at the outlet of the second heating furnace 14. A heat treatment furnace in which the amount of heat input can be adjusted is considered. According to this type of heat treatment furnace, the amount of heat input into the first heating furnace 12 which has a quick response is equal to the amount of heat input to the member to be heated 1 at the outlet of the second heating furnace 14.
0, the temperature of the member to be heated 10 at the exit of the second heating furnace 14 is suitably controlled without delay.
There is a drawback that the heat profile within the heating furnace 4 becomes unstable, and it may not be possible to perform sufficient heat treatment on the member to be heated, particularly within the second heating furnace 14, which is an important area for heat treatment.

Figure i3 shows an example of such heat treatment equipment.

Note that parts common to those in FIG. 1 are denoted by the same reference numerals, and explanations thereof will be omitted. The second heating furnace 14 is provided with an in-furnace thermometer 32 for detecting its internal temperature, and the temperature controller 34 uses the temperature signal transmitted from the in-furnace thermometer 32 to The amount of heat input into the second heating furnace 14 is adjusted to maintain the temperature inside the second heating furnace 14 at a predetermined constant value. On the other hand, the temperature controller 36 controls the flow rate control valve 26 based on the temperature of the member to be heated 10 at the outlet of the second heating furnace 14.
and adjusts the amount of heat input to the first heating furnace 12 so that the temperature of the member to be heated 10 becomes a predetermined constant value. According to such a heating furnace, the member to be heated 10 is subjected to heat treatment using the target heat profile shown by the solid line in FIG. For example, when the running speed of the member to be heated 10 suddenly increases, the actual heat profile of the member to be heated 10 becomes the state shown by the dashed line in FIG.
Since the response in is extremely fast, the amount of heat input here is rapidly increased. Therefore, the temperature of the member to be heated 10 at the outlet of the second heating furnace 14 is maintained constant, with the heat profile shown by the broken line in FIG. However, since the amount of heat brought into the second heating furnace 14 along with the member to be heated 10 increases as the amount of heat input into the first heating furnace 12 increases, the controller 34 controls the temperature inside the second heating furnace 14. In order to keep the heat profile constant, the amount of heat input to the second heating furnace 14 is reduced, and the heat profile becomes
The state shown by the broken line in the figure is reached. As a result, the controller 36 controls the second heating furnace 14. In order to maintain the temperature of the heated member 10 at tJ1, the amount of heat supplied to the first heating furnace 12 is further increased, so that the heat profile is gradually shifted as shown by the two-dot chain line in FIG. When the traveling speed of the member to be heated 10 suddenly slows down, the dashed-dotted lines, dashed lines, and dashed-double-dotted lines in FIGS. 4 and 5 become symmetrical positions with respect to the supply heat profile shown by the solid line, and in the above case Similarly, although the temperature of the member to be heated 10 at the exit of the second heating furnace 14 is maintained, the heat profile deviates greatly from the target profile and becomes unstable. Therefore, with this type of heat treatment furnace, the heat treatment conditions for the member to be heated 10 will deviate from a predetermined range.

Structure of the Invention The present invention has been made against the background of the above circumstances.
The object thereof is to provide a temperature control method for heat treatment equipment that can stably perform a predetermined constant heat treatment regardless of fluctuations in the traveling speed of a member to be heated.

In order to achieve such an object, the gist of the present invention is to detect the temperature of the member to be heated at the outlet of the second heating furnace, and the lower the temperature of the member to be heated, the lower the amount of heat input to the first heating furnace. At the same time, the temperature of the member to be heated at the outlet of the first heating furnace is detected, and as the temperature of the member to be heated becomes higher, the amount of heat input to the second heating furnace is increased.

Effects of the Invention With this method, even if the temperature of the heated member at the outlet of the second heating furnace decreases due to fluctuations in the traveling speed of the heated member, the amount of heat input to the first heating furnace, which has a quick response, can be increased. Therefore, the temperature of the member to be heated at the outlet of the second heating furnace is suitably maintained. Furthermore, when the temperature of the member to be heated at the outlet of the first heating furnace rises due to an increase in the amount of heat input into the first heating furnace, the amount of heat input into the second heating furnace is increased. When the temperature of the material to be heated at the outlet of the second heating furnace starts to rise, the amount of heat input to the first heating furnace is controlled to keep it constant. In other words, the salinity of the member to be heated at the inlet of the second heating furnace and the temperature of the member to be heated at the outlet of the second heating furnace are maintained in a constant relationship. That is, the heat profile within the heating furnace, particularly within the second heating furnace, is maintained at a predetermined constant level. Therefore, a constant heat treatment can be stably applied to the member to be heated regardless of fluctuations in its running speed.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

In FIG. 6, a metal strip 38 such as steel as a member to be heated is run in a direct-fired heating furnace 40 as a first heating furnace, and then in an annealing furnace as a second heating furnace. It is designed to be able to run within 42. The direct-fired heating furnace 40 and the annealing furnace 42 heat the strip 38 to about 1000° C. prior to continuous plating treatment, for example, to remove organic substances on the surface of the strip 38, and
The strip 38 is continuously subjected to a constant annealing treatment at a temperature of about 00 to 1300°C. Above, strip 38
can be passed through the direct-fired heating furnace 40 and annealing furnace 42 in about 10 seconds at a speed of about 120 m/min, for example. The direct-fired heating furnace 40 is of a type in which combustion gas is directly blown into the furnace. It has a fast thermal response in which the temperature and the temperature of the strip 38 passed through the oven are relatively sensitive. The annealing furnace 42 is configured such that the fuel supplied to the burner 48 is combusted within the radiant tube 50, and the strip 38 within the annealing furnace 42 is heated by the radiant heat from the wall surface of the radiant tube 50. There is. Therefore, the annealing furnace 42 has a slow thermal response, contrary to the direct-fired heating furnace 40.

Note that the inside of the annealing furnace 42 is made into a reducing atmosphere with hydrogen gas, nitrogen gas, etc., and surface oxidation of the strip 138 is prevented.

A first strip thermometer 52 for detecting the temperature of the strip 38 is provided at the outlet of the direct-fired heating furnace 40, and a temperature control word 154 controls the burner temperature based on the temperature signal from the first strip thermometer 52. 48 is controlled, and the amount of heat input to the annealing furnace 42 is increased as the temperature of the strip 38 at the outlet of the direct-fired heating furnace 40 increases, Conversely, the lower the temperature of the strip 38, the lower the temperature of the annealing furnace 4.
Reduce the input heat amount for 2. Further, a second strip thermometer 60 is provided at the outlet of the annealing furnace 42 to detect the temperature of the strip 38, and the temperature controller 62 controls the fuel supply path 46 based on the temperature signal from the second strip thermometer 60. A signal inverter 66 is connected to the flow control valve 64 provided in the
A control signal is outputted through the annealing furnace 42 to control the amount of fuel supplied to the burner 44 so that the temperature of the strip 38 at the outlet of the annealing furnace 42 is constant. That is, if the temperature of the strip 38 at the outlet of the annealing furnace 42 is too high, the amount of heat input to the direct-fired heating furnace 40 is decreased, and conversely, if the temperature of the strip 38 is too low, the amount of heat input is increased. .

Therefore, for example, if the running speed of the strip 38 is suddenly reduced, the target heat profile (solid line) becomes a heat profile shown by a dashed line, as shown in FIG. The temperature control resistor 62 reduces the amount of heat input to the direct-fired heating furnace 40 so that the temperature of the strip 38 at the exit of the annealing furnace 42 is lowered. Since the direct-fired heating furnace 40 has high thermal response, the direct-fired heating furnace 40 can be quickly replaced.
The amount of heat applied to the strip 38 in the annealing furnace 42 is reduced so that the temperature of the strip 38 at the exit of the annealing furnace 42 matches the temperature of the target heat profile. The broken line in FIG. 7 indicates this state. In the above state, the temperature of the strip 38 at the outlet of the direct-fired heating furnace 40 is still higher than the target heat profile temperature, so the temperature controller 54 increases the amount of heat input to the annealing furnace 42. Therefore, the temperature difference between the strip 3 and the tube 38 at the entrance and exit of the annealing furnace 42 approaches the target heat profile. The controller 62 reduces the amount of heat input to the direct-fired heating furnace 40 . As a result, the heat profile shown by the broken line in FIG. 7 is brought closer to and matched with the heat profile shown by the solid line.

In addition, when the running speed of the strip 38 is rapidly increased, the dashed-dotted line and the broken line in FIG. It will be done.

As described above, according to this embodiment, the strip 3 at the outlet of the annealing furnace 42 is
8 temperature is quickly brought into agreement with the target value, and
Since the heat profiles in the annealing furnace 42 and the direct-fired heating furnace 40 are made to match the target heat profile, the strip 38 can be stably subjected to heat treatment under predetermined conditions without variation. A4 Ru.

Although the embodiment shown in FIG. 6 shows only the basic configuration for applying the present invention, other control loops may be added as shown in FIG. 8. That is, the temperature controller 68 is for cascade control,
An adjustment signal is supplied to the flow rate controller 72 so that the difference between the target signal supplied from the temperature controller 54 and the temperature signal from the in-furnace thermometer 70 provided in the annealing furnace 42 becomes zero. Flow rate controller 72 controls flow rate regulating valve 58 so that the difference between the signal representing the actual fuel flow rate supplied from orifice 74 and the signal from temperature controller 68 is zero. The orifice 74.69 is a signal inverter for inverting the signal supplied from the first strip thermometer 52 to the temperature controller 54. Flow rate controller 72. The flow rate control valve 58 is connected to the annealing furnace 42
It constitutes a feedback control loop to stably control the fuel flow rate to the furnace temperature gauge 70. Temperature controller 68. Flow rate controller 72. The flow rate control valve 58 is connected to the annealing furnace 4
This constitutes a feedback control loop for stably controlling the temperature inside the furnace. The same applies to the direct-fired heating furnace 40, and the temperature controller 76
supplies a flow rate signal to the flow rate controller 80 so that the difference between the temperature signal from the in-furnace thermometer 78 provided in the direct-fired heating furnace 40 and the target temperature signal from the temperature controller 62 becomes zero.

The flow rate controller 80 operates the flow rate control valve 64 so that the difference between the flow rate signal and the actual flow rate supplied from the orifice 82 becomes zero.

According to this embodiment, in addition to the effects of the above-described embodiments, the fuel flow rate in the fuel supply path 46, 56 and the direct-fired heating furnace 40
．． There is an advantage that the temperature inside the annealing furnace 42 becomes stable against disturbances, and the temperature of the entire heat treatment apparatus can be controlled more stably. The direct-fired heating furnace 40 and annealing furnace 42 in FIGS. 6 and 8 are schematic diagrams used to explain the configuration of the control system, and the inside of each furnace is generally divided into a plurality of zones. Burner 44. Alternatively, a burner 48 and a radiant tube 50 are provided in each zone.

6. The above-mentioned effects have also been confirmed through simulations conducted by the present inventors, as described below.

9 to 11 relate to the heat treatment equipment shown in FIG. 1, FIG. 9 is a schematic diagram of the equipment, and FIG. 10 is a block diagram showing the control system. Here, it is assumed that the first heating furnace 12 and the second heating furnace 14 are first-order lag system processes, and the transfer functions C, (S) and G2 (S) are as shown in the following equations (11 and (21). .

Also, the transfer function PiD(S) of the temperature controllers 20 and 22
As shown in equation (3), <PI axis movement was assumed. Set the temperature controllers 20 and 22 to 1 and 27, for example from O to 0.5 Y, and from 0.3 Y to 0.
When the temperature is changed stepwise to 8Y, Y3 and Y7 in the block diagram, in other words, the temperature of the first heating furnace 12 and the temperature at the beginning of the second heating furnace 14 change as shown in FIG.

12 to 14 relate to the heat treatment equipment shown in FIG. 3, FIG. 12 is a schematic diagram showing the equipment, and FIG. 13 is a control block diagram. put it here,
Transfer function Gt of the first heating furnace 12 and the second heating furnace 14
(S), G2 (S).

And the transfer function PiD(S) of the temperature controller 36 is the above (
11, (2L (31).If the setting value of the temperature controller 36 is changed to 3 in steps from 0.3Y to 0.8Y, for example, Y3 and Y7 in the block diagram
In other words, the outlet temperatures of the first heating furnace 12 and the second heating furnace 14 change as shown in FIG.

8. Furthermore, FIGS. 15 to 17 relate to the heat treatment equipment shown in FIG. 7. FIG. 15 is a schematic diagram for explaining the equipment, and FIG. 16 is a control diagram thereof. Here, the transfer functions C, (S) and G2 (S) of the direct-fired heating furnace 40 and the annealing furnace 42 are (11, (2
1 type, and the transfer functions PID(S) of the temperature controllers 54 and 62 were set to the above-mentioned formula (3). If the set values of temperature controllers 54 and 62 are changed stepwise from 4 and 5 from 0 to 0.5Y, and from 0.3Y to 0.8Y, Y3 and Y6 in the control block diagram, in other words, are changed. For example, the temperature at the outlet of the direct-fired heating furnace 40 and the strip temperature at the outlet of the annealing furnace change as shown in FIG.

That is, Fig. 11, 14th TI! J and the simulation results in FIG. 17, the heated part +4 at the exit of the second heating furnace I4 of the heat treatment equipment shown in FIG.
At a temperature of 10, there is a large response delay, and the temperature of the first heating furnace 12 and the second heating furnace 1 in the heat treatment equipment shown in FIG.
The temperature of the member 10 to be heated at the fourth outlet is unstable, and the temperature of the member 10 to be heated at the outlet of the first heating furnace 12 increases significantly, making it impossible to obtain a predetermined heat profile.

On the other hand, the stability (responsiveness) of the temperature of the strip 3B at the outlet of the annealing furnace 42 in the heat treatment equipment shown in FIG. Strip 3 at the exit
It can be seen that the difference from the temperature of No. 8 can be appropriately obtained, and in particular, a predetermined heat profile can be stably obtained in the annealing furnace 42.

Although one embodiment of the present invention has been described above, the present invention is also applicable to other aspects.

For example, in the above-described embodiment, the direct-fired heating furnace 40 and the annealing furnace 42 were provided with burners 44 and 48, but they may also be provided with ground heating means such as an electric heater, or Instead of the heating furnace 40 and the annealing furnace 42, heating furnaces for other purposes may be provided. In short, the present invention can be applied to any temperature control system for heat treatment in which a member to be heated is run through a heating furnace with a fast response and a heating furnace with a slow response.

In addition, in FIGS. 6 and 8 described above, a process control computer is provided in place of the temperature controller 54, 62, 68, 76 and the flow rate controller 72, 80, and this computer executes a pre-stored control program. By executing this, the same temperature control or flow rate control as in the above-described embodiment may be performed.

Further, the signal inverter 66 in FIG.
The temperature controllers 54 and 62 may be provided between the second strip thermometer 60 and the temperature controller 62, or the temperature controllers 54 and 62 may be configured to operate in opposite directions. If so, there is no problem with it being removed. The same applies to the signal inverter 69 in FIG.

The above-mentioned embodiment is merely one embodiment of the present invention, and the present invention can be modified in various ways without departing from its spirit.

[Brief explanation of the drawing]

1 FIGS. 1 and 3 are model diagrams showing conventional heat treatment equipment. FIG. 2, FIG. 4, and FIG. 5 are heat profile diagrams illustrating the temperature control operation of the above-mentioned conventional heating equipment. FIG. 6 and FIG. 8 are model diagrams each showing an example of heat treatment equipment to which the present invention is applied. FIG. 7 is a heat profile diagram illustrating the operation of the embodiment shown in FIG. FIGS. 9, 12, and 15 are schematic diagrams showing the heat treatment equipment shown in FIGS. 1, 3, and 6, and FIGS.
16 are block diagrams showing control systems of the heat treatment equipment shown in FIGS. 1, 3, and 6, respectively. Figure 11,
FIGS. 14 and 17 are diagrams showing the results of simulations based on the block diagrams showing the control systems in FIGS. 10, 13, and 16, respectively. 38 Ni strip (heated member) 40: Direct-fired heating furnace (first heating furnace) 42: Annealing furnace (second heating furnace) 2 Figure 1 Figure 3 Figure 2 Figure 4 Figure 5 Figure 7 Figure 6-161- Reima

Claims (1)

[Claims] A temperature control method for heat treatment equipment in which a member to be heated is subjected to heat treatment by running a first heating furnace with a fast response and then running a second heating furnace with a slow response. The temperature of the member to be heated at the outlet of the second heating furnace is detected, and as the temperature of the member to be heated becomes lower, the amount of heat input to the first heating furnace is increased. A temperature control method for heat treatment equipment, comprising: detecting the temperature of a member to be heated; and increasing the amount of heat input into the second heating furnace as the temperature of the member to be heated increases.