JPS62219489A - Method of induction heating of metal strip material with limited length - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for heating a finite length metal strip by induction heating using dual frequencies in order to continuously obtain a good and uniform temperature distribution. It is.

[Conventional technology]

When inductively heating finite length metal strips such as rails, steel pipes, m-bars, etc., the appropriate frequency is determined based on requirements for size, shape, heating depth, etc.

Therefore, if the above-mentioned strip of finite length with one end is heated continuously with a single frequency and a single electric power.

Because the ends are thermally and electrically discontinuous, one end can be overheated or underheated depending on the applied frequency.

Furthermore, when the finite length metal strip is heated at a heating frequency higher than the appropriate frequency, the edges will be overheated more than the middle section due to the edge effect; conversely, if the heating frequency is low, the edges will There will be insufficient heating from the middle part.

That is, FIG. 6 shows the edge effect when the steel pipe is heated at a heating frequency higher than the appropriate frequency.

Furthermore, FIG. 7 shows the edge effect when the steel pipe is heated at a heating frequency lower than the appropriate frequency.

Therefore, in the past, in order to prevent overheating or underheating at both ends, power was controlled while detecting the heating temperature, or by switching only one end to a different frequency from the middle part. It was producing results.

[Problem that the invention seeks to solve]

In general, electric power control for induction heating is easy, so it is possible to control any part of a strip to any heating temperature, but since the heated area is not a line but a width, even if power control is performed at a single frequency. , it is not possible to heat the ends and the vicinity of the ends of the strip to the same temperature.

If the end of the strip is heated only at a frequency suitable for heating the end, which is different from the frequency suitable for heating the middle part excluding the end, the end and the vicinity of the end will be heated. Although it can be heated to the same temperature, this only concerns the surface temperature, and the heating depth is not the same in the middle part and is discontinuous.

Even if a variable frequency induction heating device is used for continuous heating, since the frequency is a single frequency, it is not possible to uniformly heat the middle and end portions.

The inventors of the present invention attempted to overcome the above-mentioned problems by simultaneously heating with a plurality of induction heating power sources with different frequencies. However, due to the electromagnetic coupling between the heating coils, a short-circuit current flows through the induction heating voltage generator, forcing the heating coils to be spaced widely apart, making accurate heating impossible and causing simultaneous heating. Heating failed.

[Means for solving problems]

The present invention has been made for the purpose of solving the problems of the prior art as described above and providing an induction heating method that can continuously and uniformly heat a finite length metal strip. is a method of continuously heating a finite length metal strip using induction heating, in which the heating distribution trends of the intermediate portion excluding the ends of the strip and the end portions are opposite to each other at a plurality of different frequencies. A uniform temperature distribution is obtained by alternately applying an induction heating voltage of 1 to the same coil in a time-divided manner.

[For production]

That is, the method of the present invention provides an appropriate frequency for heating the intermediate portion of a finite length metal strip excluding the ends, and compensates for the temperature increase distribution tendency between the intermediate portion and the end portion of the strip due to the frequency. In order to achieve this, by time-sharing and alternately applying induction heating voltages of multiple different frequencies to the same heating coil, the frequency is appropriate for heating the ends with contradictory temperature rise distribution trends. This provides substantially the same effect as heating, and enables uniform heating over the entire length of the strip, which was not possible with a single frequency.

Therefore, the plurality of frequencies are not necessarily two waves as long as they complement the temperature increase distribution tendency for each frequency or in combination. Furthermore, when the heating coil approaches the end of the strip,
Needless to say, the application time of each frequency may be changed, the power may be changed while each application time is kept constant, or both may be changed.

Furthermore, since a single heating coil is used, there is no restriction on the distance between the coils in the case of two coils arranged due to different frequencies, and the heating treatment width can be narrowed.

Generally speaking, the method of heating using multiple frequencies is also used in heat treatment, hot bending, and heating of laminated materials, but the common thing is that the two types of frequencies mentioned above are greatly different and cannot be used in a single When applying voltage to one coil, if it is difficult to match, it is of course possible to use separate coils.In this case, if the voltage is applied in a time-divided manner, mutual interference will not occur. Therefore, it is naturally possible to install them close to each other, and it is possible to easily obtain the desired heating temperature.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

Figure 1 shows an example of a circuit configured to facilitate matching between the heating coil and the power supply when actually heating a finite length metal strip using induction heating, and Figure 2 shows When heating is performed using the circuit shown in Fig. 1, an example of a peripheral circuit is required, and the frequencies fl and f applied to the heating coil HC are
2, the tap Tl of the matching transformer Tr provides good matching.
, switch SVI to T2, 5111' and 5112
．． 5112', a high frequency generator [11FG1.
IIFG2 is connected, and the gate controller FC heats the switch while opening and closing according to the divided times tl and t2, and heat-treats the finite length metal strip while compensating the temperature of the middle part and the end part excluding the end part. Alternatively, by bending it, the desired treatment can be achieved.

In the figure, CI and C2 are capacitors, Zl and Z2 are discharge coils, and the capacitor C1 and the discharge coil Z1 and the capacitor C2 and the discharge coil Z2 constitute a power factor compensation circuit. The rate compensation circuit is placed in parallel with the primary side circuit of the matching transformer, and EXI
, EX2 is a high frequency generator HFG1. Wave height el of HFG2.

This is a peak value adjuster that adjusts C2.

FIG. 3 is a time chart showing the operation of SWI, SW2, etc., where tl and t2 indicate the energization time of the switches, respectively.

Moreover, FIG. 4 is a circuit diagram in which a power factor compensation circuit is connected in series to the primary side circuit of the matching transformer Tr.

actually.

Limited long strip (steel pipe) material 5TPG 38 outer diameter 89.
1niI+(3B) Thickness 7.6+nm (sch80) Heating frequency Inventive method: 20001(z, 15011z) 2 frequencies Conventional method: 200011z Single frequency: 15
011z single frequency specification, inductively heating the steel pipe over its entire length;
The results of measuring the heating temperature at the end of the tube are as shown in the chart in FIG. was about the same as that for most of the changes.

〔Effect of the invention〕

The present invention is as described above, and provides an appropriate frequency for heating the intermediate portion of a finite length metal strip excluding the ends, and compensates for the temperature increase distribution tendency between the intermediate portion and the end portions of the strip. In order to achieve this, by time-sharing and alternately applying induction heating voltages of multiple different frequencies to the same heating coil, the frequency being appropriate for heating the ends with contradictory temperature rise distribution trends, the heating coil can be heated at the same time. Since it has almost the same effect as heating, it is possible to uniformly heat a finite length metal strip over its entire length.
It has excellent effects when applied to heat treatment of rails, etc.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of the method of the present invention, FIG. 2 is a diagram showing an example of a peripheral circuit necessary for carrying out the method of the present invention, and FIG. 3 is a diagram showing an example of a time chart in the method of the present invention.
FIG. 4 is a diagram showing another example of the peripheral circuit, FIG. 5 is a chart showing the heating temperature at the end of the pipe when steel pipes are induction heated by the method of the present invention and the conventional method, and FIGS. 6 and 7 are FIG. 3 is a diagram showing frequency and edge effects in a conventional method.

Claims (1)

[Claims] 1. In a method of continuously heating a finite length metal strip using induction heating, a plurality of different frequencies are used in which the temperature increase distribution trends in the intermediate portion excluding the ends of the strip and the ends are contradictory. A method for induction heating a finite length metal strip, characterized by obtaining a uniform temperature distribution by applying an induction heating voltage alternately to the same coil in a time-divided manner.