JPS5821395B2 - How do you know what to do? - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of measuring heating temperature when heat treating a steel pipe or the like by high frequency induction heating.

Induction heating using high-frequency current is widely used for bending steel pipes and heat treating steel, etc., but the heating temperature at that time has a great effect on the quality of the product, so it is important to always heat to a constant and appropriate temperature. is desirable, and for that purpose the heating temperature must be measured accurately.

Conventionally, there are various methods for measuring this temperature, but as a simple and relatively accurate method, there is a method described in Japanese Patent Publication No. 41-20399 related to the patent application filed by the applicant of the present invention. There is.

In this method, as shown in FIG. 1, a first coil 3, which is electromagnetically coupled to a high-frequency induction heating coil 1 and also to a heating part of a heated object 2, and the heating part are electromagnetically coupled. A second coil 4 that is not coupled but electromagnetically coupled only to the heating coil 1
and the first coil 3 and the second coil 4 are differentially connected in series with equal mutual induction coefficients between the heating coil 1 and the first coil 3 and between the heating coil 1 and the second coil 4. This is a method in which the phase difference between the electromotive force generated by this and the voltage applied to the heating coil 1 is measured with a phase meter F, and the phase meter F is made to indicate the temperature of the heated body 2. C. The difference between the voltages generated between the first coil 3 and the second coil 4 is measured by the resistor 6.
The power supply voltage is added to the fixed wire 5 through the capacitor 7, and is applied to one movable wire 8 through the capacitor 7, and is connected to the other movable wire 9 through the resistor 10, and the pointer 11 adjusts the temperature. It looks like this.

Although this method can measure the heating temperature relatively accurately, it has the following problems.

(2) An error occurs as the temperature of the first coil 3 and second coil 4 increases.

2) The mutual induction coefficients M2 and Ml of the first coil 3 and the second coil 4 must be made equal, but this is extremely difficult and a difference will always occur between them, resulting in an error.

3) Since the first coil 3 is interposed between the heating coil 1 and the heating body 20, the gap between the heating coil 1 and the heating body 2 increases accordingly, and the transmission efficiency deteriorates.

4) It is not possible to measure temperatures exceeding the magnetic transformation point of ferromagnetic materials.

5) In induction heating, in order to improve transmission efficiency, a silicon steel plate with high magnetic permeability is sometimes inserted into the external magnetic path of the heating coil 1. In such a case, the second coil 4 is made of silicon steel. It is magnetically shielded by a steel plate, etc., making temperature measurement impossible.

6) Heat-resistant insulation is required for the heating coil 1, first coil 3, and second coil 4.

7) Incorporating the first coil 3 and the second coil 4 into the heating coil 1 is expensive.

8) When replacing the heating coil 1 according to the heating element 2, it takes four times to attach and detach the first coil 3 and the second coil 4.

9) Since the heating coil 1 is constantly subjected to expansion and contraction stress,
Therefore, the first coil 3 and the second coil
The state of coupling with the coil 4 changes, making it difficult to maintain accuracy.

The above-mentioned problems in the above-mentioned invention are mainly caused by the first coil 3 and the second coil 4 attached as search coils.
The heating temperature is caused by If a method that can do this is developed, it would be effective for bending and heat treating metal strips.

From the above-mentioned viewpoint, the present invention has been made for the purpose of providing a method that can easily and accurately measure heating temperature in high-frequency induction heating without using a search coil. In high-frequency induction heating, changes in the impedance or phase angle of the heating device based on changes in specific resistance and relative permeability as the temperature of the heated object increases, or a combination of these changes can be detected from the heating power supply side. The heating temperature of the object to be heated is measured by detecting the cracking.

That is, the present invention detects the specific resistance and relative magnetic permeability of the heated object due to temperature changes in high-frequency induction heating, and measures the heating temperature by detecting this change from the heating power supply side. This is the way to do it.

For this measurement, there are methods that use changes in impedance, methods that use changes in phase angle, and methods that use a combination of changes in impedance and phase angle.

Next, specific examples of those methods will be explained.

b) Method using changes in impedance or phase angle This method is carried out as shown in the block diagram shown in Figure 2, and detects changes in the impedance or phase angle of the heated object using an impedance detector or a phase angle detector. The temperature is displayed by amplifying the output of these detectors to the value required for the indicator and inputting it to the indicator, but in cases where the temperature exceeds the transformation point, such as in heat treatment of steel, the temperature is shown in Figure 3. As shown in the figure, since the direction of increase and decrease changes based on the transformation point, the El level is detected for the impedance Z, and the E2 level is detected for the phase angle θ, and the subsequent temperature measurement measures the deviation from each E 1 yE2 level. When this is necessary, a transformation point detector is used.

This transformation point detector can be easily obtained by using a known servo motor or by combining known electronic components.

In addition, errors occur because the resistivity and relative permeability differ depending on the material of the heated object, so a material setting device is used to compensate for this error. Since reactance with respect to space changes and errors occur, a shape factor setting device is used to compensate for this error.Furthermore, if the object to be heated is a ferromagnetic material such as steel, the polarity is set based on the transformation point. Therefore, it is necessary to switch the polarity for measurements in a low temperature range below the transformation point or in a high temperature range above the transformation point, and in such cases a polarity switch is used.

A) Method using a combination of changes in impedance and phase angle This method detects a combination of changes in impedance and phase angle as shown in the block diagram shown in Figure 4, and then the block diagram in Figure 2. This is the same method as .

According to the above method, without using a search coil as shown in FIG.
22 is detachably attached, and a device B as shown in the block diagram of FIG. 2 is connected to one conductor 22, and the conductor 21
．． By connecting 22 to the device B through other conductive wires 23 and 24, the temperature of the object to be heated can be accurately measured.

In addition, when induction heating metals with low melting temperatures such as aluminum, temperature control is performed by detecting rapid changes in electrical resistivity during the state change from solid phase to liquid phase at the melting temperature. By doing so, it is possible to prevent the metal from melting.

The present invention is as described above, and includes changes in the impedance or phase angle of a heating device based on changes in specific resistance and relative permeability as the temperature of the object to be heated increases, or a combination of these changes on the heating power supply side. Since the heating temperature of the heated object can be measured by detecting it from By controlling the heating temperature based on this measured temperature, when bending steel pipes or heat treating steel, etc., it is possible to always perform appropriate heating without fear of melting the heated object, thereby improving the quality of the finished product. It is extremely helpful in contributing to the improvement of
The method of the present invention can also be applied to inspecting cracks on metal surfaces.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram showing the principle of the invention described in Japanese Patent Publication No. 41-20399, Fig. 2 is a block diagram of an example of the method of the present invention, and Fig. 3 is a diagram showing heating during heat treatment of objects to be heated. A diagram showing changes in impedance and phase angle when the temperature exceeds the transformation point, FIG. 4 is a block diagram of a separate part of the method of the present invention, and FIG. 5 is a diagram showing the blocks and induction heating coil in the method of the present invention. FIG. 1... Heating coil, 11, 12, 13, 14... Conductor wire, B... Device shown in the block diagram.

Claims (1)

[Claims] 1 In high-frequency induction heating, changes in the impedance or phase angle of the heating device, or a combination of these changes, based on changes in specific resistance and relative permittivity as the temperature of the heated object increases, are detected from the heating power supply side. A temperature measuring method in high frequency induction heating, characterized in that the heating temperature of a heated object is measured by this method.