JPH0533042A - Method for controlling heating of metallic material - Google Patents

Abstract

PURPOSE:To appropriately control the heating of a metallic material even when the molten scale is generated by obtaining a corrected time to adjust the heating time when the surface temp. of the material is lowered from the temp. at the preceding sampling by a specified temp. CONSTITUTION:A desired temp. theta0 and a heating time t0 are set, and a material is induction-heated or electrically heated while comparing the detected surface temp. theta or the material with the theta0. In this case, the surface temp. is detected at the sampling pitch of DELTAt while keeping the voltage or current constant. When thetan-thetan-1<0 where thetan is the detected temp. at the time t and its absolute value is larger than the limiting temp. difference set value alpha, the appropriate heating time DELTAtn between thetan and theta0 is obtained at the actual heating velocity V up to that time. When the remaining time DELTAt0=t0-tn after the time t0 is DELTAt0<DELTAtn, DELTAt0 is heated by the constat heating power, voltage or current. Meanwhile, when DELTAt0>DELTAtn, the DELTAtn is heated by the constant heating voltage or current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling a heating temperature in induction or electric heating of a metallic material such as a grain-oriented electrical steel slab.

[0002]

2. Description of the Related Art A metal material is heated to a high temperature of 1000 ° C. or higher to be heat treated. Depending on the heating material, the heating temperature error must be kept within 20 to 30 ° C. An induction heating furnace or an electric heating furnace is used for such high temperature heat treatment. For example, the grain-oriented electrical steel slab is preheated to about 1250 ° C. in a gas combustion type heating furnace, and then heated at a high temperature of 1300 to 1400 ° C. for a short time in an induction heating furnace controlled to an inert atmosphere.

Conventionally, the heating rate and the heating time are set in advance, and the heating material is heated at a constant voltage (or constant current). In the heating stage, the surface temperature of the heating material is detected and compared with the target temperature. Then, when the surface temperature detection value exceeds the target temperature or the heating time exceeds the set heating time, it is determined that the target temperature has been reached, the temperature increase is stopped, and the process proceeds to the soaking stage.

[0004]

In the above high temperature heat treatment, a radiation thermometer is used to detect the surface temperature of the heating material. Further, depending on the heating material, molten scale is generated during the high temperature heat treatment. The surface temperature of the molten scale is lower than the surface temperature of the heating material by, for example, about 30 to 50 ° C. Therefore, the surface temperature of the heating material is detected lower than the actual temperature, so that the heating material is overheated. In order to prevent overheating due to the generation of such molten scale, it is necessary to set the heating time to an appropriate value and take care not to cause overheating or insufficient heating. However, it is difficult to preset an appropriate heating time because the initial temperature of the heating material differs depending on the material, and the heating material size and the furnace condition (heat storage state of the furnace) are not constant. As a result, there is a problem that it is difficult to avoid overheating or insufficient heating.

In the present invention, even if molten scale is generated,
An object of the present invention is to provide a heating control method for a metal material that does not cause overheating or insufficient heating.

[0006]

According to the heating control method of the present invention, the target temperature θ _o and the heating time t _o are set in advance, the surface temperature θ of the heating material is detected, and the heating is performed while comparing with the target temperature θ _o. In the method of induction or electric heating of the material,
Sampling pitch Δ with a constant surface temperature of the heating material with the heating power, heating voltage or heating current kept constant.
detected by t, the sampling instants t _i the temperature difference between the temperature detection value theta _i-1 in (i = 1,2 ...) and the detected temperature theta _i at sampling instant t _{i-1 θ i} -θ _i- Sequentially obtain ₁ .

Temperature difference θ _n −θ at sampling time t _n
n-1 is negative and its absolute value is a predetermined limit temperature difference α
If it becomes larger, with the actual Atsushi Nobori rate v seek average heating rate on the basis of temperature detection value theta _nk, the _{θ nk-1 ... θ n-} 1 at the sampling time t _n at that time,
A corrected heating time Δt _n from the detection temperature θ _n at the sampling time t _n until the target temperature θ _o is reached is calculated based on the actual temperature increase rate v.

The remaining time Δ obtained by subtracting the heating time up to the sampling time t _n from the set heating time t _o
When t _o is shorter than the modified heating time Δt _n , the remaining time Δt _o is heated with the constant heating power, constant heating voltage or constant heating current from the sampling time t _n .

Further, when the remaining time Δt _o is longer than the corrected heating time Δt _n , the sampling time t _n
Therefore, the correction heating time Δt _n is heated with the constant heating power, the constant heating voltage or the constant heating current.

It depends on the material and size of the heating material, the heating temperature, the heating accuracy, the response of the heating furnace, etc.
The sampling pitch is about 10 to 30 seconds, and the limit temperature difference α is about 3 to 5 ° C. The limit temperature difference α takes into consideration the variation in the molten scale generation temperature. The sampling number k for obtaining the actual temperature increase rate v is 2 to
It is about 5.

The above heating control is performed by an ordinary process computer or control sequencer. The sampling pitch, the limit temperature difference α, the number of samplings k for obtaining the actual temperature increase rate v, and the like are obtained by experiments on an actual machine and stored in the process computer.

When the temperature difference θ _n -θ _n-1 does not become negative, or when the temperature difference θ _n -θ _n-1 is negative but its absolute value does not become larger than the limit temperature difference α, , As it is, is heated to the target temperature θ _o . In this case, since the molten scale does not occur, the heating error due to the molten scale does not occur.

[0013]

As described above, the surface temperature of the molten scale is lower than the surface temperature of the heating material. Therefore, the temperature difference θ _i −
When θ _i-1 is negative and the absolute value thereof is larger than the predetermined limit temperature difference α, it is determined that melt scale has occurred. Generally, the temperature at which the molten scale is generated is close to the heating target temperature θ _o . Therefore, by heating the heating material for the corrected heating time Δt _n obtained by the actual heating rate v, it is possible to heat the heating material substantially to the target temperature θ _o without causing a large heating error.

[0014]

[Example] Hereinafter, high temperature heating of a grain-oriented electrical steel slab by an induction heating furnace will be described as an example.

The slab to be heated at a high temperature is preheated to a temperature of 1150 ° C. at a relatively low heating rate by a gas combustion type heating furnace. The dimensions of the slab are 9000 to 11000 mm in length, 900 to 1100 mm in width, and 190 to 240 mm in thickness. Then, the slab is charged into an induction heating furnace and heated to a high temperature of 1350 ° C. The high temperature heating includes a heating step and a soaking step as shown in FIG.

As shown in FIG. 3, the slab S is loaded into the induction heating furnace 1 in a vertical posture (a posture in which the side surface of the slab is horizontal). The power supplied to the heating coil 2 is supplied from the power supply 3 via the inverter 4. The heating control device comprises a process computer 5, a control sequencer 6 and an inverter 4. The heating target temperature θ _o , the inverter output voltage, the heating time t _o, etc. are stored in advance in the process computer 5, and these data are output to the control sequencer 6. In addition, the control sequencer 6
A heating control program shown in the flow chart of FIG. 1 is set in. The radiation thermometer 7 detects the surface temperature at three points on the surface of the slab. The heating control is performed as follows.

The output voltage is calculated from the initial temperature, size, target temperature, heating time, etc. of the slab S, and the inverter 4 is adjusted. Moreover, the surface temperature of the slab S is measured by the radiation thermometer 7 to 3
The sampling pitch Δt of 0 seconds is used for detection. The detected surface temperature is input to the control sequencer 6. At this time, the maximum value of the detected values at the three locations is adopted. The data table of the control sequencer 6 stores k + 1 pieces (five pieces in this embodiment) of data, and the data table is updated every sampling. Sampling time t _i (i = 1,
2 ...) sequentially obtaining the temperature difference θ _i -θ _i-1 of the detected temperature theta _i-1 at the temperature detection value theta _i sampling time point t _i-1 at.

Temperature difference θ _n −θ at sampling time t _n
n-1 is negative and its absolute value is a predetermined limit temperature difference α
When it becomes larger, the average heating rate is obtained based on the detected temperature values θ _nk , θ _nk-1 ... θ _n-1 at the sampling time t _n at that time, and is set as the actual heating rate v. That is, the actual temperature increase rate v is Σθ _i / kΔt. Next, the corrected heating time Δt _n from the detection temperature θ _n at the sampling time t _n until the target temperature θ _o is reached is calculated based on the actual temperature increase rate v. In FIG.
The broken line shows the temperature rising curve when molten scale occurs. In the temperature rising curve, the temperature once drops and rises because the molten scale flows down the surface of the slab S, and the slab surface appears outside the field of view of the radiation thermometer 7.

The remaining time Δ obtained by subtracting the heating time up to the sampling time t _n from the set heating time t _o
If t _o is shorter than the modified heating time Δt _n , the remaining time Δt _o is heated with the output voltage from the sampling time t _n .

Further, when the remaining time Delta] t _o is greater than the corrected heating time Delta] t _n heats the modified heating time Delta] t _n from a sampling point t _n at the output voltage.

When the temperature difference θ _n −θ _n-1 does not become negative,
Alternatively, if the absolute value of the temperature difference θ _n −θ _n-1 is not larger than the limit temperature difference α even if the temperature difference θ _n −θ _n−1 is negative, the temperature is heated up to the target temperature θ _o at the set temperature increase rate v _o .

In this example, the degree of superheat from the target temperature of 1350 ° C. was 3 to 5 ° C. On the other hand, according to the conventional method, the degree of superheat from the target temperature of 1350 ° C. is 20 to 3
It was 0 ° C.

[0023]

According to the present invention, the heating time is adjusted by detecting the molten scale. Therefore,
Even if the molten scale occurs, the heating material can be heated to the target temperature without causing overheating or insufficient heating, and product quality and yield can be improved.

[Brief description of drawings]

FIG. 1 is a flowchart showing an example of a heating control method of the present invention.

FIG. 2 is an example of a temperature rising curve of a slab.

FIG. 3 is an apparatus configuration diagram showing an example of an apparatus for implementing the heating control method of the present invention.

[Explanation of symbols]

 1 induction heating furnace 2 heating coil 3 power supply 4 inverter 5 process computer 6 control sequencer 7 radiation thermometer S slab

Claims (1)

1. The target temperature θ _o and the heating time t _o are set in advance, and the surface temperature θ of the heating material is detected to detect the target temperature θ _o.
In the method of inductively or electrically heating the heating material, the surface temperature of the heating material is kept constant while the heating power, heating voltage or heating current is kept constant.
detected by t, the sampling instants t _i the temperature difference between the temperature detection value theta _i-1 in (i = 1,2 ...) and the detected temperature theta _i at sampling instant t _{i-1 θ i} -θ _{i- 1} is sequentially obtained, and when the temperature difference θ _n −θ _n-1 is negative at the sampling time t _n and its absolute value becomes larger than a predetermined limit temperature difference α, the sampling time t _n at that time is calculated. in the temperature detection value theta _nk, with the actual Atsushi Nobori rate v by the average value of the heating rate on the basis of _{θ nk-1 ... θ n-} 1, the target temperature from the detected temperature theta _n in the sampling time point t _n θ _o
To the corrected heating time Δt _n until the actual heating rate v
When the remaining time Δt _o obtained by subtracting the heating time from the set heating time t _o to the sampling time t _n is shorter than the corrected heating time Δt _n , the sampling time t
heating from _n to the remaining time Δt _o with the constant heating power, constant heating voltage or constant heating current, and if the remaining time Δt _o is longer than the modified heating time Δt _n , correct from the sampling time t _n Heating time Δ
A heating control method for a metal material, comprising heating t _n with the constant heating power, the constant heating voltage or the constant heating current.