JPH0335989B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a temperature control method and apparatus for a hot air circulation type heat treatment furnace, and more particularly, it relates to a temperature control method and apparatus for a hot air circulation type heat treatment furnace, and more specifically, for heat treating articles by circulating hot air in the furnace. Furnace temperature in a heat treatment furnace can be controlled with extremely high responsiveness, and even if the heat load of articles inserted into the furnace fluctuates, waste of thermal energy can be suppressed to achieve energy savings. The present invention relates to a temperature control method and device.

PRIOR ART A so-called hot air circulation heat treatment furnace, which supplies high-temperature gas into a limited space and circulates the high-temperature gas as hot air within the space using a fan to perform various heat treatments on articles, is suitably used in industry. . Examples of this type of hot air circulation heat treatment furnace include paint drying and baking furnaces for color-coated steel plates and heating furnaces that blow hot air used in the manufacturing process of plastic films. Other types of combustion exhaust gas and heated air produced as by-products from combustion deodorizing equipment are generally used. In this case, it is necessary to control the temperature of the high-temperature gas supplied into the furnace to an optimal value depending on the heat capacity and other properties of the object to be heat-treated in the furnace. In cases where extremely delicate control is required, it has generally been difficult to faithfully respond and perform follow-up control.

Therefore, the applicant has developed a "temperature control device" that can be suitably used in the hot air circulation type heat treatment furnace to achieve temperature control with good responsiveness, and has previously filed a patent application for this. As shown in FIG. 1, a partition wall 14 is longitudinally extended in the high temperature gas supply pipe 12 which is connected to the hot air circulation type heat treatment furnace 10 to form a bypass pipe 16 and a heat exchange pipe 18. and a heat exchanger 20 in the heat exchange pipe 18.
is installed internally, and an opening/closing lid 22 is provided at the communication opening of both pipes.
The general gist is that a damper (for example, a flap-shaped damper) is arranged so that the opening ratio of both pipes can be adjusted. In this case, the high-temperature gas is heated to a high temperature by the combustion heating device 24, and then the high-temperature gas supply pipe 1
2 to the bypass pipe line 16 and the heat exchange pipe line 18, and at this time, the proportion of high temperature gas supplied to each pipe line 16, 18 is distributed depending on the degree of opening of the opening/closing lid 22, and the heat exchange The gas whose temperature has dropped by contacting the vessel 20 and the gas whose temperature has not dropped after passing through the bypass pipe 16 are mixed at the communicating outlet of both pipes, and the temperature is adjusted to a predetermined temperature. Note that the opening degree of the opening/closing lid 22 is automatically adjusted according to the temperature inside the furnace detected by a temperature detector 26 inserted into the heat treatment furnace 10. According to this temperature control device,
Although the temperature inside the furnace is controlled with good responsiveness and high precision, a part of the thermal energy of the high-temperature gas in the heat exchange pipe 18 is taken by the heat exchanger 20 and discarded. From a viewpoint, it has the disadvantage of being less economically efficient. In other words, the heat load of the articles inserted into the heat treatment furnace 10 varies depending on their material, external dimensions, etc., so when articles of different sizes are inserted, the heat load changes. Therefore, it is necessary to adjust the temperature inside the furnace accordingly, but since the temperature control device cannot control the supply amount of high temperature gas according to the fluctuations in the heat load, When controlling the temperature using the heat exchanger 20, it is necessary to extract a considerable amount of thermal energy from the high-temperature gas using the heat exchanger 20, resulting in a large energy loss.

Therefore, if you want to adjust the temperature inside the furnace without allowing even a small amount of thermal energy to escape, the second
A thermal loop like the one modeled in the figure can be considered.
That is, the heat treatment furnace 10 and the high temperature gas supply pipe 12 constitute a thermal circulation system, and the high temperature gas supply pipe 1
2, a flow control valve 28 is inserted therein. At this time, since the heat treatment furnace 10 can be considered to be a closed space with a fixed internal volume, the flow rate of the high temperature gas supplied into the furnace through the high temperature gas supply pipe 12 may be adjusted by the flow rate control valve 28. As the amount of stored thermal energy increases or decreases as the flow rate of high-temperature gas supplied to a certain restricted space increases or decreases, the temperature inside the furnace can be adjusted.

Problems to be Solved by the Invention However, in this configuration, the thermal energy of the high-temperature gas only circulates through the heat loop and is not actively captured by a heat exchanger, etc., so from the standpoint of effective energy use, Excellent, but
Because it has poor responsiveness to changes in heat load and can only make very rough temperature adjustments, it is used in industrial heat treatment furnaces that require delicate temperature adjustment in response to the strict temperature requirements of the objects to be treated. I couldn't do it.

Purpose of the Invention The present invention has been devised in view of the current situation, and enables highly responsive and accurate control of the temperature inside the furnace, as well as controlling the heat of articles inserted into the furnace. The purpose is to increase operational efficiency by suppressing the extraction of thermal energy from high-temperature gas to the necessary minimum in response to load fluctuations.

Means for Solving the Problems In order to achieve this object, the temperature control method for a hot air circulation heat treatment furnace according to the present invention provides a method for controlling the temperature of a hot air circulation heat treatment furnace, in which a high temperature gas and a part of the high temperature gas are heat exchanged to generate a temperature difference. When supplying the gas to the hot air circulation type heat treatment furnace through the gas mixing means, after controlling the mixing ratio adjusting means of the gas mixing means so that the mixing ratio of the two gases having the temperature difference becomes constant, the gas mixing means After the temperature inside the hot air circulation heat treatment furnace is stabilized, the temperature inside the furnace is detected and the mixing ratio adjusting means of the gas mixing means is controlled. It is characterized by changing the mixing ratio of both gases with a temperature difference.

In addition, the temperature control device used to suitably implement this temperature control method connects a high-temperature gas supply pipe to a hot air circulation type heat treatment furnace, and connects a part of the high-temperature gas supply pipe to a bypass pipe. and a heat exchange pipe, and an opening/closing lid that can adjust the opening ratio of each pipe is provided at the communication opening on the high temperature gas inlet side of both the pipes, and the high temperature gas inlet side of both the pipes A flow rate control valve is inserted into the communicating high-temperature gas supply pipe, and an in-furnace temperature detector is further provided in the heat treatment furnace, and the opening degree of the front opening/closing lid or the flow rate control valve is controlled according to the detected temperature. It is characterized by being configured to selectively control.

Embodiments Next, the temperature control method and apparatus according to the present invention will be described in detail by way of embodiments with reference to the accompanying drawings.

FIG. 3 shows a schematic configuration of a temperature control device for a hot air circulation type heat treatment furnace that can suitably implement the temperature control method for a hot air circulation type heat treatment furnace according to the present invention, and reference numeral 30 is a heat-resistant material. A heat treatment furnace is shown that is surrounded to form a substantially closed space. The heat treatment furnace 3
A gas heating device 32 is disposed outside of the gas heating device 32, and a high temperature gas supply pipe 34 is led out from the outlet of the gas heating device 32, and its tip is connected to the heat treatment furnace 30 in communication. Further, a gas suction pipe 36 is led out from the heat treatment furnace 30, and the gas heating device 3 is passed through a suction blower 38.
Connect to the inlet of No.2. As a result, the heat treatment furnace 3
A high temperature gas circulation system for 0 is constructed.

A part of the high-temperature gas supply pipe 34 connected to the heat treatment furnace 30 side is swollen as shown in FIG. 3, and a partition wall 40 is provided extending inside the swollen portion along the longitudinal direction of the pipe. A bypass pipe 42 with no heat exchange load and a heat exchange pipe 46 with a heat exchanger 44 installed therein are defined. One end of the bypass pipe 42 and the heat exchange pipe 46 is pivotally supported at a location where the openings communicate with each other (particularly preferably, a communication location on the high temperature gas inlet side) for flap operation. A damper-like opening/closing lid 48 that can adjust the opening ratio of the pipeline is provided, and the bypass pipeline 42 is
and the heat exchange pipe 46 as a whole constitute means for mixing both gases having a temperature difference, which will be described later. In addition,
The opening/closing lid 48 is connected to a suitable actuator 52 via an operating rod 50. As this actuator 52, an electric motor-driven linear actuator is preferably used. Further, the heat treatment furnace 3
0, a temperature sensor 54, preferably consisting of a thermocouple.
is arranged so that its temperature measuring probe 56 faces a desired temperature detection area in the furnace, and the detected value by this temperature detector 54 is input to a temperature control circuit 58. The temperature control circuit 58 sends an appropriate command to the actuator 52 according to the calculated detected temperature,
This allows the degree of opening of the opening/closing lid 48 to be adjusted.

In addition, the bypass pipe line 42 and the heat exchange pipe line 4
High temperature gas supply pipe 3 communicating with the high temperature gas inlet side of 6
A flow control valve 60 is inserted into 4, and this flow control valve 6
An actuator 62 made of, for example, an electric torque motor is provided to drive the flow rate control valve 60, and a temperature control circuit 64 connected to the temperature sensor 54 sends an activation command to the actuator 62 to open the flow rate control valve 60. Adjust the degree. Note that the two actuators 52 and 62 receive common temperature information from the temperature detector 54, but for example, the opening degree of the opening/closing lid 48 is adjusted after the valve opening degree adjustment of the flow rate control valve 60 is completed. , is adapted to operate selectively according to a preset sequence program.

To carry out the temperature control method according to the present invention, the temperature control device is operated as follows. The degree of opening of the opening/closing lid 48 that changes the opening ratio of the bypass line 42 and the heat exchange line 46 is appropriately controlled (for example, the degree of opening of the heat exchange line 46 is set to 30%), and the high temperature gas and the high temperature gas are After setting in advance so that the mixing ratio with the gas whose temperature is lowered through heat exchange to cause a temperature difference is constant, the gas mixing means is adjusted by adjusting the valve opening of the flow rate control valve 60. The flow rate of the high-temperature gas supplied is adjusted, thereby roughly setting the temperature inside the furnace. Next, after the temperature in the furnace has stabilized, the opening degree of the opening/closing lid 48 is adjusted to precisely adjust the temperature to a desired temperature, thereby achieving highly responsive and highly accurate temperature control. The temperature control method and device according to the present invention are extremely effective when used in a paint baking furnace for producing color-coated steel sheets. This will be explained below in connection with this.

FIG. 4 shows a schematic structure of a paint baking furnace for manufacturing color coated steel sheets in which the temperature control method and device according to the present invention are suitably used. Internal cross section shown. Fourth
In the figure, reference numeral 30 indicates a paint baking furnace as a hot air circulation heat treatment furnace, and plenum chambers 66, 66 and
A colored steel plate 70 coated with paint is passed between the plenum chambers 68, and the colored steel plate 70 is caused to float without contact by hot air blown out from nozzles 72 provided on the opposing faces of each plenum chamber.
That is, as can be seen from FIG. 3, each plenum chamber 66, 68 is connected via ducts 74, 76 to an air outlet of a blower 78, and this blower 78 also carries hot gas in the furnace through an inlet 80. The color steel plate 70 is made to float by applying suction and pressurization and jetting hot air upward and downward toward the color steel plate 70 from the nozzle 72 to balance dynamic pressure and static pressure. The paint baking furnace 30 is divided into an evaporation zone A and a curing zone B, as shown in FIG. The high temperature gas supply pipe 34 has a connection opening to the furnace 30. A temperature control device according to the present invention shown in FIG. 3 is installed in each of the high temperature gas supply pipes 34. After the steel plate 70 is subjected to surface treatment, the coater 8
2, the color paint is applied, and as it floats through the oven, the solvent is evaporated in the evaporation zone A, and then it is cured in the curing zone B to bake the paint film. In addition,
In FIG. 4, reference numeral 84 is a forced air cooling chamber, and 86
Reference numeral 88 indicates a water cooling chamber, and 88 indicates a hot air drying device, and the color steel plate 70 is subjected to the same process two to three times as necessary to perform overcoating (two times in this embodiment).

The gas containing the evaporated solvent in the furnace is sucked by the suction blower 38 and sent to the deodorizing heating device 32 via the suction pipe 36, and the evaporated solvent is heated to natural temperature by the burner 90 and deodorized by combustion. . At the same time, the gas is reheated and returned to the paint baking furnace 30 via the high temperature gas supply pipe 34.

In such a paint baking furnace for producing colored steel sheets, the temperature control device according to the present invention is preferably operated as follows. That is, for example, when restarting the operation of a furnace that has been temporarily suspended, in order to raise the temperature inside the furnace to the optimum value, the color steel plate 70 is inserted into the furnace as a heat load, and the heat exchange pipe 4 is
The opening degree of the opening/closing lid 48 at the opening 6 is controlled and set to, for example, 30%. As a result, the mixing ratio between the high-temperature gas passing through the bypass pipe 42 and the gas passing through the heat exchange pipe 46 and having a lower temperature resulting in a temperature difference is kept constant, and then the flow control valve 60 By opening the bypass pipe 42
A high temperature gas is supplied to the gas mixing means consisting of a heat exchange pipe 46 and a heat exchange pipe 46, and a mixture of both gases having a temperature difference is sent into the paint baking furnace 30. Temperature probe 5 of thermocouple 54 inserted into plenum chamber 68
6 detects the temperature inside the furnace and controls the temperature control circuit 64.
energizes the actuator 62 and adjusts the valve opening degree of the flow rate control valve 60 to obtain a substantially desired furnace temperature. Next, another temperature control circuit 58 is operated to energize the other actuator 52 and adjust the degree of opening of the opening/closing lid 48. As a result, the mixing ratio of the two gases having the temperature difference in the open communication section on the high temperature gas outlet side between the bypass pipe line 42 and the heat exchange pipe line 46 changes, and the high temperature gas is precisely controlled to a desired temperature. By feeding this into the furnace, the temperature inside the furnace can be controlled with good responsiveness according to the heat load.

Note that the flow rate control valve 60 controls the paint baking furnace 3.
Even if you change the flow rate of high temperature gas supplied to 0,
Since the blower 78 is configured to blow hot air from the plenum chambers 66 and 68 onto the steel plate 70 independently of the flow rate of high-temperature gas supplied into the furnace, there is no problem with the floating movement of the steel plate 70. No problems will occur.

As described above, according to the temperature control method of the present invention, when gases having different temperatures are mixed and supplied to the hot air circulation heat treatment furnace, the mixing ratio of the two gases having different temperatures becomes constant. After the setting is made, the flow rate of high-temperature gas supplied to the gas mixing means is controlled, and after the temperature inside the furnace is stabilized, the mixing ratio of both gases with the temperature difference is changed, so that the inside of the furnace has good responsiveness. Temperature control can be achieved. In addition, as a temperature control device for implementing this temperature control method, a temperature difference between a bypass pipe, a heat exchange pipe, and an opening/closing lid is installed in the pipe system of the high-temperature gas supply pipe connected to the hot air circulation heat treatment furnace. The required temperature in the furnace determined by the heat capacity of the article to be processed and other factors can be adjusted by having a gas mixing section and a flow rate control valve, which are configured to operate selectively and sequentially depending on the temperature in the furnace. be able to respond quickly.

In addition, since the temperature control device according to the present invention also includes the heat exchanger 44 in the heat exchange pipe 46, some of the thermal energy is taken away when the high temperature gas comes into contact with it. In the present invention, by disposing the flow rate control valve 60 at the front stage, when the heat load in the furnace fluctuates, high-temperature gas can be distributed and supplied to the heat exchange pipe 46 at a flow rate commensurate with the heat load. Therefore, the amount of thermal energy taken by heat exchange can be suppressed, contributing to energy saving. That is, in the device having the structure shown in FIG.
Even if the heat load inserted into the furnace changes from, for example, 100 to 50, a constant flow rate of high-temperature gas is always supplied to the gas mixing section equipped with the heat exchange pipe 18. 18, it is necessary to exchange a large amount of heat, resulting in large heat loss. On the other hand, in the device according to the present invention shown in Fig. 3, when the heat load inserted into the furnace changes from 100 to 50, high-temperature gas is supplied to the gas mixing section at a flow rate commensurate with this heat load. In order to achieve this, the thermal energy taken by heat exchange can be suppressed to the necessary minimum.

Above, the temperature control method and device for a hot air circulation heat treatment furnace according to the present invention have been explained in detail by taking as an example the case where it is used in a paint baking furnace for producing colored steel sheets, but the present invention is limited to this embodiment. However, various improvements and changes can be made within the spirit of the invention.

[Brief explanation of the drawing]

1 and 2 are schematic configuration diagrams of a temperature control device according to the prior art, and FIG. 3 is a schematic configuration diagram of a temperature control device that can suitably implement the temperature control method according to the present invention. A cross-sectional view of the furnace in the embodiment shown in the figure is also shown, and FIG. 4 is a vertical cross-sectional view showing a schematic configuration of a paint baking furnace for manufacturing color steel sheets in which the temperature control method and device according to the present invention are suitably used. It is. 10... Heat treatment furnace, 12... High temperature gas supply pipe, 14
...Partition wall, 16...Bypass pipe line, 18...Heat exchange pipe line, 20...Heat exchanger, 22...Opening/closing lid, 24...Heating device, 26...Temperature detector, 28...Flow rate control valve, 3
0... Heat treatment furnace (paint baking oven), 32... Gas heating device, 34... High temperature gas supply pipe, 36... Gas suction pipe,
38... Suction blower, 40... Partition wall, 42... Bypass pipe line, 44... Heat exchanger, 46... Heat exchange pipe line, 48
... Opening/closing lid, 50... Operating rod, 52... Actuator, 54... Temperature detector, 56... Temperature measuring probe, 5
8... Temperature control circuit, 60... Flow rate control valve, 62... Actuator, 64... Temperature control circuit, 66, 68
...Plenum chamber, 70... Steel plate, 72... Nozzle, 74, 76... Duct, 78... Blower, 80...
Intake port, 82...Coater, 84...Forced air cooling chamber, 86
...Water cooling room, 88...Hot air dryer, 90...Burner.

Claims (1)

[Scope of Claims] 1. A high-temperature gas and a gas in which a temperature difference is generated by heat-exchanging a part of the high-temperature gas are mixed by gas mixing means 42, 4.
The gas mixing means 42, 46, 4 is supplied to the hot air circulation type heat treatment furnace 30 via the gases 6, 48 so that the mixing ratio of the two gases having the temperature difference becomes constant.
After controlling the mixing ratio adjusting means 48 of No. 8, the flow rate of the high temperature gas supplied to the gas mixing means 42, 46, 48 is controlled, and after the temperature inside the hot air circulating heat treatment furnace 30 is stabilized, the A hot air circulation type heat treatment furnace characterized in that the temperature inside the furnace is detected and the mixing ratio adjusting means 48 of the gas mixing means 42, 46, 48 is controlled to change the mixing ratio of the two gases having the temperature difference. temperature control method. 2 High temperature gas supply pipe 3 to hot air circulation heat treatment furnace 30
4, a part of the high temperature gas supply pipe 34 is defined as a bypass pipe 42 and a heat exchange pipe 46, and a communication opening on the high temperature gas inlet side of both the pipes 42 and 46 is formed. is provided with an opening/closing lid 48 that can adjust the opening ratio of each of the pipes 42, 46.
A flow rate control valve 60 is inserted in the high temperature gas supply pipe 34 communicating with the high temperature gas inlet side of the heat treatment furnace 30, and a furnace temperature detector 54 is further provided in the heat treatment furnace 30. A temperature control device for a hot air circulation type heat treatment furnace, characterized in that it is configured to selectively control the opening degree of an opening/closing lid 48 or a flow rate control valve 60.