JPH0576145B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a heating control method for uniformly heating steel materials in the longitudinal direction in an induction heating furnace.
More specifically, the present invention relates to an induction heating control method for uniformly heating red-hot steel heated in a combustion furnace to a higher temperature.

[Conventional technology]

There are two problems when batch heating steel materials in an induction heating furnace.

One of these is how much power should be input to the induction heating furnace, and the second is how much heating power frequency should be set for the induction heating furnace.

The value of the heating power input to the induction heating furnace and the frequency of this heating power determine the heating temperature distribution and heating time of the steel material, which affect the quality assurance of the steel material, heating efficiency, etc. .
Therefore, it is necessary to select the optimum value for the shape of the steel material to be treated and the heating process.

In particular, in the heating process where steel is heated in a combustion heating furnace and then heated evenly to a higher temperature in an induction heating furnace, when the steel material is charged into the induction heating furnace, and when it is transported from the combustion heating furnace to the induction heating furnace, Due to natural cooling, a temperature distribution occurs in this steel material in the longitudinal direction, so it is necessary to heat the entire steel material in which this temperature distribution occurs to a uniform temperature.

FIG. 5 shows an outline of a heating process in which the steel material heated in this combustion heating furnace is subsequently heated in an induction heating furnace. The steel material 1 that has been uniformly heated to a certain temperature in the combustion heating furnace 2 is immediately charged into the induction heating furnace 3 having an induction coil 4 after being carried out from the combustion heating furnace 2, and is further heated to a high temperature. Yes, but
By being allowed to cool naturally while being transported from the combustion heating furnace 2 to the induction heating furnace 3, the temperature of the end portions 1a is lower than that of the center portion 1b. When the temperature of the steel material 1 is measured while the steel material 1 is allowed to cool naturally along the temperature measuring portion 1A, which is the central portion along the longitudinal direction x of the steel material 1 shown in FIG. 2, the obtained temperature distribution Θ is shown in FIG. 3. It becomes as follows.

As is clear from FIG. 3, the temperature distribution Θ of the steel material 1 has a temperature gradient at the end portion 1a, but the temperature is almost uniform in the center portion 1b; The temperatures at the ends A and B are the lowest, and as they approach the center portion 1b, the temperature increases.

In this way, the steel material 1 supplied from the combustion heating furnace 2 to the induction heating furnace 3 has a temperature distribution Θ in an almost constant form. Since there is a certain temperature distribution Θ where the temperature difference is large and the temperature difference is small when the time is short, the induction heating furnace 3 eliminates this temperature distribution Θ and heats the entire steel material 1 uniformly. It is necessary to raise the temperature. For this reason, the steel material 1 in the induction heating furnace 3
The heating control mode is such that the end portion 1a of the steel material 1 is heated more than the center portion 1b.
Measures are taken to select a high frequency of heating power.

Japanese Patent Application No. 60-240420 is a typical conventional technique for this heating control means. This patent application 1986-240420
The technology shown in the No. 1 changes the frequency of heating power to a high value during the soaking period, and as shown in FIG. Measure temperatures at point 1H and point 1C in the thick central part of central portion 1b, and when temperature ΘH at point 1H reaches the planned maximum heating temperature of steel material 1, as shown in Fig. 7, The heating power W is decreased, and when the temperature ΘH has decreased to a certain level, the heating power W is decreased again, and the frequency of the heating power W is increased to reduce the heating power to the end 1a of the steel material 1 to the center of the steel material 1. The heating power is increased more than the heating power for portion 1b. The temperature drop in the central portion 1b due to the increase in the heating power for the end portion 1a and the decrease in the heating power W for the entire steel material 1 is controlled to match the temperature ΘC of the central portion 1C of the wall thickness of the central portion 1b of the steel material 1. By making the temperatures ΘH and ΘL equal to the temperature ΘC which has reached a predetermined value, uniform heating of the entire steel material 1 to the target temperature is achieved.

This uniform heating method heats the steel material 1 using the induction heating furnace 3 by initially setting the frequency of the heating power W as low as possible.
Achieves internal temperature rise and reduces heating power W during soaking period
The frequency is increased to make the heating efficiency for the end portion 1a of the steel material 1 higher than for the center portion 1b.

Furthermore, if there is no temperature drop at the end 1a of the steel material 1, there is no need for heat compensation for the end 1a of the steel material 1, so as shown in Japanese Patent Publication No. 52-47179, the steel material 1 is heated by combustion. A method has been considered in which a removable cover 7 made of a heat insulating material is attached to the end of the steel material 1 (see FIG. 8) when the steel material 1 is transported from the furnace 2 to the induction heating furnace 3.

[Problem that the invention seeks to solve]

However, the means shown in Japanese Patent Application No. 60-240420 has a problem in that the heating power of the induction heating furnace 3 during the soaking period for increasing the temperature of the end portion 1a of the steel material 1 is low. Even if the end 1a
The heat rise is slow, and therefore a long time is required for the temperature of the end portion 1a to recover. Particularly, if the temperature of the end portion 1a decreases significantly at the start of induction heating, the delay in heating up the end portion 1a becomes significant.

In addition, the means disclosed in Japanese Patent Publication No. 52-47179 requires a complicated device for attaching and detaching the cover 7 to the steel material 1, and requires a new work process for attaching and detaching the cover 7 to the steel material 1. , the possibility of implementation is extremely low.

The present invention was devised to eliminate the drawbacks and dissatisfied points of the conventional examples described above, and utilizes the difference in the heating form for steel materials due to the difference in the frequency of heating power in an induction heating furnace. By selecting the frequency of the heating power according to the temperature distribution form of the steel material, the heating power for the edges of the steel material is greater than the heating power for the center of the steel material, and the entire supplied steel material can be heated quickly. The technical challenge is to achieve uniform heating.

[Means and actions for solving problems]

Hereinafter, the induction heating control method according to the present invention will be explained with reference to FIGS. 1 to 4.

The means of the present invention relates to a technique for heating the steel material 1 heated in the combustion heating furnace 2 at a higher temperature and uniformly in the induction heating furnace 3; and for heating given to the induction coil 4 of the induction heating furnace 3. The frequency of the electric power of the induction heating furnace 2 is selected to be a predetermined high frequency value.
Based on the temperature distribution along the longitudinal direction of the steel material 1 when the steel material 1 is charged, the value shall be selected to make the temperature difference between the center portion 1b and the end portion 1a of the steel material 1 zero; The heating of the steel material 1 with the heating power of the frequency selected based on the temperature distribution of the steel material 1 is performed at a time when the heating power given to the induction heating furnace 3 is large.

The temperature difference between the end portion 1a and the center portion 1b of the steel material 1, which is the basis for selecting the frequency of the heating power applied to the induction coil 4 of the induction heating furnace 3, is determined when the steel material 1 is installed in the induction heating furnace 3. The steel material 1 is selected based on the temperature difference between the end portion 1a and the center portion 1b when the steel material 1 is charged into the induction heating furnace 3, and the temperature at the end portion 1a of the steel material 1 is the highest. Since this is the period when the temperature is decreasing, the temperature difference between the end portion 1a and the center portion 1b of the steel material 1 is at its largest.

For this reason, the heating of the steel material 1 by the method of the present invention is as follows:
The end portion 1a of the steel material 1 is heated more than the central portion 1b of the steel material 1.
heating is much more powerful.

In addition, since the heating of the steel material 1 by setting the frequency of the heating power of the induction heating furnace 3 as described above is carried out at a time when the heating power given to the induction heating furnace 3 is large, the end of the steel material 1 is heated. The degree of heating of the portion 1a becomes even more intense, and therefore the end portion 1a of the steel material 1 fed to the induction heating furnace 3 is rapidly heated to a high temperature by carrying out the method of the present invention.

Generally, in the induction heating furnace 3, a large amount of electric power is supplied at the beginning of heating in order to rapidly heat the supplied steel material 1 to a desired high temperature in a short time, and then the supplied electric power is reduced to equalize the target temperature. Since the steel material 1 is heated, the method of the present invention is carried out at the beginning of the heating operation of the steel material 1 by the induction heating furnace 3.

When the steel material 1 is charged into the induction heating furnace 3, the overall temperature of the steel material 1 is the lowest, and the end portion 1 of the steel material 1 is the lowest.
Since the temperature difference between a and the central portion 1b is the largest, the induction heating furnace 3 for the end portion 1a of the steel material 1
heating will be achieved extremely efficiently,
This temperature increase can be achieved in a short time.

Once the temperature of the end portion 1a of the steel material 1 has been raised to the desired temperature, the frequency and value of the heating power are controlled in accordance with the conventional heating control method in the induction heating furnace 3. good.

[Example] In the case of the example shown in FIG. 1, the temperature distribution Θ of the steel material 1 when charging into the induction heating furnace 3, that is, the temperature difference ΔΘ in the longitudinal direction of the steel material 1, is determined by induction heating of the steel material 1 from the combustion heating furnace 2. The temperature is measured by a radiation thermometer 5 placed on the conveyance path 6 to the furnace 3 just before the entrance of the induction heating furnace 3 . As shown in FIG. 2, the temperature measurement of the steel material 1 by the thermometer 5 is carried out at the temperature measurement part 1A, which is the part along the longitudinal direction of the center of the short side of the steel material 1, for stable temperature measurement. can be obtained.

An example of the temperature distribution Θ of the steel material 1 measured with the thermometer 5 is shown in FIG. In this Fig. 3, steel material end A is the measurement start point and steel material end B is the measurement completion point.
has the lowest temperature, and the temperature at the end 1a is the lowest at the center 1b.
It can be seen that the value increases as the value approaches .

The temperature difference ΔΘ is the thickness t of the steel material 1, the combustion heating furnace 2
Although it varies depending on the transportation time from the to the induction heating furnace 3 and other factors, from the relationship between the temperature difference ΔΘ of the steel material 1 depending on the plate thickness and the frequency when the heating time is set constant as shown in Fig. 4. , when the plate thickness is t3 and the temperature difference is ΔΘ, the frequency of the heating power in the induction heating furnace 3 can be determined to be 3 Hz. If the frequency of the heating power at this time is 3 Hz or less, the temperature of the end 1a of the steel material 1 cannot be raised sufficiently, and on the other hand, if the frequency of the heating power is 3 Hz or more, the end 1a will be fried. This may result in dissolution or other problems.

Note that the means for measuring the temperature distribution Θ along the longitudinal direction of the steel material 1 is not to directly obtain it with the thermometer 5, but to measure the temperature distribution Θ of the steel material 1 from the combustion heating furnace 2 to the induction heating furnace 3. This occurs in an almost constant pattern with respect to the plate thickness due to the transportation time of the steel material 1 and the difference between the temperature during transportation of the steel material 1 from the combustion heating furnace 2 and the ambient temperature.
A detector for detecting the steel material 1 may be provided in the conveyance path 6, and the temperature distribution Θ and the temperature difference ΔΘ may be calculated based on the conveyance time of the steel material 1 detected by the detector. In this case, it goes without saying that the temperature of the steel material 1 and the ambient temperature at the time of conveyance from the combustion heating furnace 2 are given as known values.

Heating power frequency and temperature difference ΔΘ shown in Figure 4
The relationship can be determined by off-line electromagnetic heat transfer analysis as a value specific to the induction heating furnace 3.

Specific Example When the steel material 1 with a thickness of 200 mm was transported from the combustion heating furnace 2 to the induction heating furnace 3 in a transport time of 10 minutes, the temperature difference ΔΘ of the steel material 1 was 200°C. In order to uniformly raise the temperature of this steel material 1 to the specified temperature in 65 minutes, if the first half heating time is 10 minutes and the first half heating frequency is 350Hz, the second half heating time is 55 minutes and the second half heating frequency is 200Hz.
Hz.

〔Effect of the invention〕

As is clear from the above description, the present invention can quickly raise the temperature of the ends of the steel material, so the temperature of the entire steel material can be brought to a uniform temperature quickly, thereby ensuring uniform temperature rise of the entire steel material. The temperature can be achieved smoothly and satisfactorily, and the operation is simple as all you have to do is select and set the heating power frequency at the initial stage of heating.Furthermore, this frequency selection and setting can be set with high precision, making it possible to It exhibits many excellent effects such as being able to accurately control the temperature of the air.

[Brief explanation of drawings]

FIG. 1 is a simplified diagram of a heating process line configured to carry out the method of the present invention. FIG. 2 is an explanatory diagram showing an example of a temperature measurement part of the steel material, in which each part of the steel material is divided and displayed. FIG. 3 is a temperature distribution of a steel material showing an example of the temperature measurement results in the temperature measuring section shown in FIG. FIG. 4 is a diagram showing the temperature difference-frequency characteristics of steel materials according to plate thickness in an induction heating furnace. FIG. 5 is a simplified configuration diagram showing the basic line configuration of a heating process in which steel is fed from a combustion heating furnace to an induction heating furnace to uniformly heat the steel to a higher temperature. FIG. 6 is an explanatory diagram showing temperature measurement locations of steel materials in the prior art. FIG. 7 is a temperature characteristic diagram for explaining the operating characteristics of the prior art shown in FIG. FIG. 8 is a perspective view of an end of a steel material for explaining another conventional technique. Explanation of symbols, 1... Steel material, 1a... End, 1b
... Central part, A, B ... Steel material end, 1A ... Temperature measurement part, 2 ... Combustion heating furnace, 3 ... Induction heating furnace, 4 ...
...Induction coil, 5...Radiation thermometer, Θ...Temperature distribution, ΔΘ...Temperature difference.

Claims (1)

[Claims] 1. When heating steel materials heated in a combustion heating furnace at a higher temperature and uniformly in an induction heating furnace,
When heating by increasing the induction heating power applied during initial temperature rise to the scheduled heating temperature, compared to the induction heating power applied during soaking after temperature rise,
The frequency of the heating power applied during the initial temperature rise of the steel material is determined based on the temperature distribution in the longitudinal direction of the steel material when it is loaded into the induction heating furnace, and is set to a high frequency that makes the temperature of the center and end portions of the steel material uniform. An induction heating control method characterized by heating a steel material by selecting a numerical value of .