JP3125510B2 - Induction heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating device for forging, and more particularly to an induction heating device capable of reducing the amount of discarded material while a post-stage press device is stopped.

[0002]

2. Description of the Related Art FIG.
FIG. 6 is a block diagram showing the configuration of a conventional induction heating device described in Japanese Patent Application Publication No. 2000 (issued by the Japan Industrial Furnace Association). FIG. 6 is a curve showing the temperature rise characteristics of the conventional induction heating device shown in FIG. FIG. In the figure, 1 is a first heating coil for a low temperature region, 2 is a second heating coil for a high temperature region, and 3 is a first heating coil.
A first high-frequency inverter device for a low-temperature region that supplies high-frequency power to the heating coil 1, a second high-frequency inverter device for a high-temperature region that supplies high-frequency power to the second heating coil 2, and a first high-frequency inverter device 5. And a material to be heated such as a steel material conveyed through the pinch rollers 6 in the second heating coils 1 and 2,
Reference numeral 7 denotes a motor for driving and rotating the pinch roller 6, reference numeral 8 denotes a speed control device for controlling the rotation speed of the motor 7, and reference numeral 9 denotes a control device for controlling the speed control device 8 and the high-frequency inverter devices 3 and 4, respectively.

Hereinafter, the operation of the conventional induction heating apparatus configured as described above will be described. First, in the case of a steady operation, the material 5 to be heated is continuously conveyed in the first heating coil 1 and the second heating coil 2 by the pinch roller 6 and reaches a predetermined temperature (usually around 1200 ° C.). After the temperature is raised, it is discharged out of the apparatus and sent to a post-process (press apparatus) not shown. The first operation during the steady operation
In the process of raising the temperature of the material 5 to be heated in the second heating coils 1 and 2, the temperature gradually increases from room temperature to a predetermined temperature as shown by a curve a in FIG. During this time, the power output from the first and second inverter devices 3 and 4 is controlled by the control device 9.
Is controlled so as to follow the curve a.

[0004] Next, a description will be given of the case of the warming operation.
First, during the continuous operation of the induction heating device, when the press device in the subsequent process is stopped due to, for example, a failure, the speed control device 8
, A stop command is issued, the motor 7 stops, and the pinch roller 6 stops rotating, so that the conveyance of the heated material 5 also stops. At the same time, the first and second high-frequency inverter devices 3 and 4 are stopped under the control of the control device 9, and the power supply to the first and second heating coils 1 and 2 is also stopped.

[0005] Next, when the press device resumes operation, the process of raising the temperature of the material 5 to be heated in both heating coils 1 and 2 is as follows.
Compared with the curve a in FIG. 6 showing the temperature rise process during the steady operation, the temperature has decreased as a whole. The degree of this decrease increases as the stop time increases. Therefore, even if the operation of the induction heating device is restarted, the temperature of the material to be heated 5 located at the outlet of the second heating coil 2, that is, the temperature of the material to be heated 5 discharged from the induction heating device, is maintained in the normal temperature rising process. Therefore, the temperature has not reached the predetermined temperature. In such a state, all the materials 5 to be heated existing in both the heating coils 1 and 2 when the induction heating device is stopped are present, and these materials 5 to be heated cannot be properly pressed by the press device. , And is discharged out of the line by a bypass device (not shown) before the press device.

The heat keeping operation is performed to reduce the quantity of the material 5 to be heated discharged out of the line by the bypass device. When the press device stops, the control device 9 switches to the speed control device 8. A heat retention speed command is issued, the speed control device 8 controls the rotation speed of the motor 7, and reduces the transport speed of the material 5 to be heated via the pinch roller 6 to about の of the steady transport speed. The value of the power supplied to both heating coils 1 and 2 from both high-frequency inverter devices 3 and 4 from control device 9 to both high-frequency inverter devices 3 and 4 according to the heat retention rate is also calculated as the supply power value during steady operation. 1/2
A command is issued to lower it. In addition, the electric power is reduced by half.
In this case, the voltage values output from the high-frequency inverter devices 3 and 4 are approximately √ times (approximately 0.7 times) the voltage values output during the steady operation.

As described above, in the conventional apparatus, the transport speed during the warming operation is reduced to の of the transport speed during the steady operation, thereby reducing the number of materials 5 to be discharged out of the line. Also, the electric power supplied to the heating coils 1 and 2 is not completely reduced to 0, but is reduced to の of that in the normal operation.
By supplying this power, it is possible to reach the predetermined temperature relatively quickly after returning to the normal operation. When the press restarts the operation, the transport speed and the power supplied from the high-frequency inverters 3 and 4 are respectively returned to the values at the time of steady operation, and the induction heating device resumes the steady operation.

[0008]

The conventional induction heating apparatus is configured as described above, and the heated material 5 is discharged as waste material out of the line even during the warming operation. In order to reuse this, there is a problem that it takes time to cool down once, and it takes a lot of time to take measures for measures such as a space for discarded materials and hot air. Therefore, in the conventional apparatus, in order to reduce this waste material, the transport speed during the warming operation is reduced to half. However, when the transport speed is reduced, as shown in a curve b in FIG. There is a phenomenon that the temperature decreases on the high temperature side.

This is because when the transport speed is reduced to 1 / N, the power supplied to the heating coils 3 and 4 is also reduced to 1 / N to obtain a temperature increasing process as shown by a curve c in FIG. But,
Since the heat radiation loss emitted from the material to be heated 5 is substantially constant depending on the temperature of the material to be heated, the heat radiation loss is higher than the power supply in a high temperature region where the power supply value is low. In order to prevent such a phenomenon that the temperature decreases on the high temperature side, the supply power may be increased to more than 1 / N. However, if the supply power becomes excessively large, the temperature rises excessively in the second heating coil 4. Thus, the material to be heated 5 may be melted. Note that the limit at which the transfer speed can be reduced from the transfer speed in the steady operation is generally about 40% of the steady transfer speed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide an induction heating apparatus capable of minimizing the amount of waste material during a warming operation. is there.

[0011]

Means for Solving the Problems Claim 1 according to the present invention.
The induction heating device includes a conveying means for conveying in succession a plurality of material to be heated at a steady rate S _0, of at least 2 or more of induction heating to a predetermined temperature higher than the normal temperature the material to be heated is continuously conveyed A heating coil divided into sections, a plurality of inverter devices for supplying high-frequency power to each of the divided heating coils, and a first conveyance having a conveyance speed of a conveyance unit smaller than the steady speed S ₀ by a heat retention command. first the first second and control the conveying speed S ₂ of the conveying speed S ₁ value less than predetermined time after as well as the speed S _1, than the steady speed S ₀ the conveying speed of the conveying means by heat insulating command release small and a second conveying speed control means for controlling so as to return to a steady rate S ₀ after a predetermined time has elapsed while the second third transport speed S ₂ greater than the conveying speed S _3, each inverter instrumentation Each supply high-frequency power voltage speed each carry the S of _0, S _1, S _2, the voltage V ₀ which value corresponding to S _3,
Voltage control means for controlling V ₁ , V ₂ , and V ₃ respectively.

In the induction heating apparatus according to a second aspect of the present invention, the voltage control means according to the first aspect is configured such that each of the voltages V ₁ , V ₂ , and V ₃ during the warm-up operation with respect to the voltage V ₀ during the steady-state operation. The voltage drop ratio is controlled to be smaller in the inverter device in the high temperature region than in the inverter device in the low temperature region.

[0013]

According to a first aspect of the present invention, the conveying speed control means of the induction heating apparatus decreases the conveying speed of the material to be heated from the steady operation speed to the warming operation speed in response to the warming operation command. The release speed is controlled so that the transport speed of the material to be heated is stepwise increased from the warming operation speed to the steady operation speed, and the voltage control means is controlled to each transport speed controlled stepwise by the transport speed control means. Accordingly, the voltage of each high-frequency power supplied from each high-frequency inverter device to each heating coil is controlled.

According to a second aspect of the present invention, the voltage control means of the induction heating apparatus is adapted to determine a voltage drop ratio of each of the voltages V ₁ , V ₂ , V ₃ during the warm-up operation with respect to the voltage V ₀ during the steady-state operation. The device controls less than the inverter device in the low temperature range.

[0015]

【Example】

Embodiment 1 FIG. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an induction heating device according to a first embodiment of the present invention, FIG. 2 is a curve diagram showing a temperature rise characteristic of the induction heating device shown in FIG. 1, and FIG. FIG. 4 shows a change in the transport speed in each operation state.
FIG. 4 is a diagram showing a relationship between a magnitude of each supply power and a heat radiation loss in each operation state of a general induction heating device. 1, the first and second heating coils 1 and 2, the first and second high-frequency inverter devices 3 and 4, the material to be heated 5, the pinch roller 6, the motor 7, and the speed control device 8 are shown in FIG. It is the same as that of the conventional device. 9 is a pinch roller 6
The pinch roller rotation speed detector 10 detects the rotation speed of the motor 7, and changes the rotation speed of the motor 7 via the speed control device 8 when the warming operation command is issued, so that the conveying speed of the material 5 to be heated is changed as shown in FIG.
The transfer speed control means 11 for controlling as shown in FIG. 3 is provided with a power supply corresponding to each transfer speed controlled by the transfer speed control means 10 to each of the heating coils 1 and 2, This is voltage control means for controlling the voltage.

Next, the operation of the induction heating apparatus according to the first embodiment configured as described above will be described. First, as shown by the curve a in FIG. 2, the temperature rising process during the steady operation is the same as that of the conventional device of the curve a in FIG. Next, when the press device in the post-process is stopped due to, for example, a failure or the like and a heat retention command is issued, the transport speed control means 10 changes the rotation speed of the motor 7 via the speed control device 8 as shown in FIG. Then, the transport speed of the material 5 to be heated is controlled to shift from the steady speed to the transition speed. On the other hand, voltage control means 11
Controls the high frequency inverter devices 3 and 4 to supply power to both heating coils 1 and 2 according to the transition speed.

The period during which the transition speed is maintained, that is,
The length of the transition period is detected by the pinch roller rotation speed detector 9, and when the transition period of the predetermined length ends, the transport speed control unit 10 and the voltage control unit 11 respectively change the transition speed to the heat retention speed, The speed control device 8 and the two high-frequency inverter devices 3, so as to shift from the supply power corresponding to the transition speed to the supply power corresponding to the heat retention speed, respectively.
4 to start the warming operation. Then, after the warming operation period has been continued to some extent, when the press device is restarted and the warming command is released, the speed control means 10 and the voltage control means 11 change the transport speed from the warming speed to the transition speed, and Then, control is performed so that the supply power returns from the value corresponding to the heat retention speed to the value corresponding to the transition speed, and the process returns to the transition operation again, and after a transition period of a predetermined length as described above, returns to the steady operation. I do.

Here, the reason why it is necessary to enter the warming operation period after the transition period of the predetermined length as described above will be described. That is, when the operation is shifted from the steady operation to the warming operation without providing the transition period, the heating process changes from the state of the curve a shown in FIG. 2 to the state of the curve b in a short time.
The temperature of each material to be heated 5 present in the first and second heating coils 1 and 2 is different between the case of the steady operation and the case of the heat keeping operation, and cannot be changed in a short time. In particular, when the speed ratio between the two operations is large, the difference between the heating processes is large, and instantaneous transition is difficult. Therefore, by temporarily operating at an intermediate speed between the steady operation speed and the warming operation speed and adjusting the heating process to an intermediate value, it is possible to smoothly shift from the steady operation to the warming operation. .

The relationship between the heating process in the heating coils 1 and 2 shown in FIG. 2 and the conveying speed and the supplied power is as follows. That is, the power required for heating is generally proportional to the total weight of the material 5 to be heated passing through the two heating coils 1 and 2 per unit time. In other words, the power is proportional to the transport speed. Therefore, the high frequency inverter devices 3 and 4 are controlled by the voltage control means 11 and supply electric power corresponding to the respective transport speeds to the heating coils 1 and 2 by changing the voltage.

On the other hand, since the heat radiation loss of the material 5 to be heated is proportional to the fourth power of the temperature of the material 5 to be heated according to Stefan-Boltzmann's law, as shown in FIG. The ratio to the power supply increases,
Also, since this heat dissipation loss is not related to the transfer speed, if the supply power decreases as the transfer speed decreases, the ratio of the heat dissipation loss to the supply power increases. May be exceeded.
In this case, as described in the section of the prior art, the temperature at the outlet side of the second heating coil 2 decreases in the high temperature region, so that the power supplied in the high temperature region is reduced by the conveyance speed. A value larger than a value proportional to the reduction rate corresponding to the reduction is required.

As an example, assuming an induction heating device having a rated power of 1,000 kW, a material to be heated 5 having a diameter of
When the temperature is raised to 200 ° C., the total length of the heating coil is about 3,
2,000 mm, but the length of the high temperature region, that is, the length of the second heating coil 2 (about 1,100 ° C. or more) is about 1,
000 mm. In this case, the heat radiation loss (converted to the heating coil power) in the low temperature region, that is, in the first heating coil 1 is only about 10 kW, but the heat radiation loss in the high temperature region is about 50 kW. At the transfer speed using the rated power, the power supplied to the low temperature area is about 800 kW.
Even if the transport speed is reduced to 1/5, the supplied power is about 16
Since there is also 0 kW, which is much larger than the heat dissipation loss, the heat dissipation loss can be ignored. On the other hand, the supply power is about 200 kW in the high temperature region, so the heat dissipation is larger at the transfer speed using the rated power, but when the transfer speed is reduced to 1/5, the supply power is reduced to about 40 kW in proportion thereto. Lower than the heat dissipation loss.

From the above viewpoints, the transport speed during the transition period and the warming operation period is determined by the following equation. The transport speed during the warming transition period S ₁ = K ₁ × S ₀ The transport speed during the warming operation period S ₂ = K ₂ × S ₀ The transport speed during the steady return transition period S ₃ = K ₃ × S ₀ where, S ₀ is the transport speed during the steady operation period,
K ₁ , K ₂ , and K ₃ indicate speed reduction coefficients, respectively.

The speed reduction coefficients K ₁ , K ₂ ,
K ₃ sets the conveying speed of the maintenance operation period as 10% of the conveying speed of the steady operation period (K ₂ = 0.1). Also,
The transfer speed during the heat transfer transition period is set to approximately the middle between the transfer speed during the steady operation period and the transfer speed during the heat retention operation period (K ₁ = 0.
5) At the same time, the transport speed during the steady return transition period is set similarly (K ₃ = 0.5).

The power supplied during the transition period and the warm-up operation period, that is, the output voltage of each of the high-frequency inverter devices 3 and 4 is determined by the following equation. (1) of the first high-frequency inverter unit 3 (for low temperature range) the output voltage V _A2 = √K ₂ × V _A0 steady recovery transition period of the output voltage V _A1 = √K ₁ × V _A0 maintenance operation period of warmth transition period Output voltage V _A3 = √K ₃ × V _A0 where V _A0 represents the output voltage during the steady operation period. (2) Second high-frequency inverter device 4 (for high-temperature region) Output voltage V _B1 = √K ₁ × V _B0 during transition to heat retention
× K _B1 Output voltage during warm-up operation period V _B2 = √K ₂ × V _B0
× K _B2 Output voltage in the transition period to steady return V _B3 = √K ₃ × V _B0
× K _B3 where V _B0 is the output voltage during the steady operation period and K
_B1 , _KB2 , and _KB3 indicate correction coefficients, respectively.

As described above, the output voltage of the first high-frequency inverter device 3 for the low-temperature region is set by the square root of the speed reduction rate, whereas the output voltage of the second high-frequency device for the high-temperature region is set. As described above, the output voltage of the inverter device 4 must be set to a value larger than the square root of the speed reduction rate in order to compensate for the heat dissipation loss of the material 5 to be heated. That is, since the ratio of the heat dissipation loss to the supplied power increases as the speed decreases, the correction coefficients are set to approximately K _B1 = 1.2, K _B2 = 1.5, and K _B3 = 1.2, respectively.

As described above, according to the first embodiment, the heating coil is divided into the first heating coil 1 for the low-temperature region and the second heating coil 2 for the high-temperature region. 4, different powers are supplied, so that the warming operation can be performed in a range where the conveying speed is low, and when shifting to the warming operation,
Provide a transition period in which the transfer speed is once operated at an intermediate value between the transfer speed in the steady operation and the transfer speed in the warm-up operation, and provide the same transition period when the warm-up operation is canceled and the operation returns to the steady operation. As a result, the heating process in both heating coils 1 and 2 can be maintained normally,
The material 5 to be heated can be constantly discharged from the second heating coil 2 at a stable temperature.

Further, the ratio of the voltage drop of each output voltage V _A2 , V _B2 during the warm-up operation to the output voltage V _A0 , V _B0 of both high-frequency inverter devices 3, 4 during the steady operation is defined as that for the high temperature region. The output voltage V _B2 of the second high-frequency inverter device is lower than the output voltage V _A2 of the first high-frequency inverter device for the low-temperature region. The power that exceeds the loss can be always supplied, the proper temperature rise process can be maintained even during the low-temperature heat-retention operation, and the temperature immediately rises to the predetermined temperature when the press device resumes operation. The material to be heated 5 can be supplied to the press device.

Embodiment 2 FIG. According to the first embodiment, the heating coil is divided into the first and second heating coils 1 and 2, and both coils 1 and 2 are provided with two first and second high-frequency inverters 3 and 4. Although the description has been given of the case where the power is supplied, the same effect as that of the first embodiment can be obtained by supplying the electric power to three or more high-frequency inverter devices in the induction heating device requiring a large power. It goes without saying that you get in this case,
As a matter of course, the higher the frequency of the high-frequency inverter device in the high-temperature region, the smaller the rate of voltage drop during low-speed operation is controlled so as to compensate for heat dissipation loss.

[0029]

As evident from the foregoing description, according to the first aspect of the present invention, a conveying means for conveying in succession a plurality of material to be heated at a steady rate it S _0, the material to be heated is continuously conveyed Heating coil divided into at least two sections for inductively heating the heating coil to a predetermined high temperature from room temperature, a plurality of inverter devices for supplying high-frequency power to each of the divided heating coils, first second and control the conveying speed S ₂ of the conveying speed S ₁ value smaller than after the first predetermined time has elapsed while the speed to the first transport speed S ₁ of the constant velocity S ₀ value less than warmth returning to the steady speed S ₀ after the lapse second predetermined time while the third conveying speed S ₃ of the small and the second conveying speed S ₂ greater than than the steady speed S ₀ the conveying speed of the conveying means by a command released Control to let A conveying speed control means that, each conveying speed S ₀ the voltage of each supply a high-frequency power of each inverter,
S _1, S _2, and a voltage control means for controlling each of the S voltage V ₀ which value corresponding to _{3, V 1, V 2,} V 3,

According to a second aspect of the present invention, the voltage control means according to the first aspect is characterized in that a voltage drop ratio of each of the voltages V ₁ , V ₂ , V ₃ during the warm-up operation to the voltage V ₀ during the steady operation. Is controlled so that the inverter device in the high-temperature region is controlled to be less than the inverter device in the low-temperature region. An induction heating device capable of minimizing waste material can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an induction heating device according to a first embodiment of the present invention.

FIG. 2 is a curve diagram showing a temperature rise characteristic of the induction heating device shown in FIG.

FIG. 3 is a diagram showing a change in a conveying speed in each operation state of the induction heating device shown in FIG. 1;

FIG. 4 is a diagram showing a relationship between a magnitude of each supply power and a heat radiation loss in each operation state of a general induction heating device.

FIG. 5 is a block diagram showing a configuration of a conventional induction heating device.

FIG. 6 is a curve diagram showing a temperature rise characteristic of the induction heating device shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 2 1st and 2nd heating coil 3, 4 1st and 2nd high frequency inverter device 5 Material to be heated 6 Pinch roller 7 Motor 8 Speed control device 9 Pinch roller rotation speed detector 10 Transport speed control means 11 Voltage Control means

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B21J 17/02 B21K 27/00

Claims (2)

(57) [Claims] And conveying means according to claim 1] to convey multiple consecutive material to be heated at a steady rate S _0, of at least 2 or more of induction heating the respective material to be heated is continuously conveyed to a predetermined temperature higher than room temperature A heating coil divided into sections, a plurality of inverter devices for supplying high-frequency power to each of the divided heating coils, and a transfer speed of the transfer means set to a first value smaller than the steady speed S ₀ by a heat retention command. conveying speed S ₂ transport speed to the first after a predetermined time has elapsed while the S ₁ the first second transport speed S ₁ value less than the
Controlling the second predetermined time with the conveying speed of the conveying means by heat insulating command released to third conveying speed S ₃ of the small and the second conveying speed S ₂ greater than than the steady rate S ₀ A conveyance speed control means for controlling to return to the steady speed S ₀ after the lapse of time, and a voltage of each supply high-frequency power of each inverter device to each of the conveyance speeds S ₀ ,
An induction heating device comprising: voltage control means for controlling voltages V ₀ , V ₁ , V ₂ , and V ₃ having values corresponding to S ₁ , S ₂ , and S ₃ , respectively. 2. The voltage control means according to claim 1, wherein the voltage V ₀ at the time of steady operation is provided.
_2. The induction heating device according to claim ₁ , wherein the voltage reduction ratio of each of the voltages V ₁ , V ₂ , V ₃ during the heat retention operation is controlled to be smaller in the high temperature region inverter device than in the low temperature region inverter device. .