JPS589549B2 - Yuudou Kanetsukino Kidouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for starting an induction heating machine in which a cold heating material (hereinafter referred to as a billet) is fully inserted into a heating coil, the power is turned on, and the billet is heated.

When heating with an induction heating machine, there are various heating methods depending on the size of the material, etc., but here, many billets can be inserted into the heating coil at once, and the billets can be heated while being moved inside the coil at a certain feeding speed. This applies to heating methods when heating.

The method for starting the induction heating machine using this heating method is as follows:
Various methods have been considered and implemented in the past.

These will be explained below.

(1) No-load startup method Leave the heating coil empty and apply the rated voltage.
This method involves sequentially inserting billets into a heating coil after applying a voltage.

This method does not exceed the power supply capacity and can heat almost the initial billet to a predetermined temperature, so it is a simple and reliable starting method.

However, after the operation is finished, the heating coil must be emptied using a device that pushes out the billet inserted into the heating coil.

This method cannot be adopted if the billet transport mechanism is configured so that it is impossible to empty the heating coil.

(2) Method of using a power source with sufficient capacity As shown in Figure 1, in the case of heating a magnetic material, the power at startup is P
m requires approximately twice as much power as the power P in steady state.

For this reason, a power source with a capacity approximately twice the rated power is used.

This method is disadvantageous in that it requires high equipment costs.

(3) Method by switching the power supply voltage In the method shown in Figure 1 above, a power supply with twice the capacity is required, so the applied voltage at startup is controlled by switching in order to suppress excess power at startup, and thereby suppress the source capacity. It is something to do.

That is, as shown in FIG. 2, in a device in which a motor generator consisting of a motor M and a high-frequency generator G is used as a power source, and the output of the generator G is transformed by a matching transformer T to supply power to the heating coil CL, the generator G A plurality of reference devices Ere1. Ere2... is provided, and these are switched by the output contacts of timers T1, T2,... that operate at appropriate intervals to control the exciter Ex output via the phase control device PH, and the generator G output power is controlled. The power is adjusted as shown by the solid line in FIG. 3 to keep the power within the rated value.

D1 and D2 are disconnectors, and C is a power factor correction capacitor.

According to this method, excess power at startup can be suppressed, but switching is not possible when the billet does not exceed the magnetic transformation point.

That is, even if voltage switching is performed, the power still exceeds.

Next, when the material is cold, the heating coil impedance and the impedance seen from the generator G terminal are very small.

Therefore, the rated voltage cannot be applied from the beginning of startup, and the power is suppressed by the rated current, resulting in low power startup as shown by the dotted line in FIG.

In the case of such a low impedance load characteristic, the temperature of the billet cannot rise. Therefore, the magnetic transformation temperature cannot be exceeded, making it impossible to switch to the next set voltage.

That is, this method is difficult to use in low impedance conditions.

(4) Method of using constant current control in combination The previous section is a method of controlling the generator G voltage so that the power used is the rated power, whereas this method is a method of controlling the generator G voltage so that the rated current does not exceed. It is automatically adjusted.

That is, in FIG. 4, in addition to the control system that compares the voltage transformer PT that detects the output of the generator G with the reference voltage signal generator vR and controls the exciter Ex via the phase control device PH,
A current control system is added to compare the current transformer CT that detects the generator output current with the current reference signal generator IR, and the generator voltage is automatically adjusted so as not to exceed the rated current.

Therefore, the output power is controlled as shown in FIG.

That is, since the current is suppressed to the maximum rated current IO, the voltage and power also have voltage and power values determined by the current, and do not reach the rated values Vo and PO, respectively, when starting the cold material.

This method is stable at the transformation point temperature because the power required at startup is low, and if the transformation temperature cannot be exceeded, it is impossible to raise the temperature to a predetermined temperature.

(5) Matching transformer tap switching method This method is used to compensate for the low impedance at startup.
As shown in the figure, the tap t of the matching transformer T is switched to increase the impedance seen from the power supply, thereby improving the low power consumption at startup in items (3) and (4) above.

The purpose of this is to exceed the transformation point temperature.

However, in reality, even this method may not be possible and is not stable.

These conventional methods may be carried out alone or in combination;
At each startup, the feed speed and takt are carried out as rated as soon as the power is turned on.By the way, with induction heating machines, depending on the conveyance method, the power must be turned on with the heating coil fully inserted with the cold material. In some cases, when the operation ends, the billet remains inserted in the coil, so it is often more efficient to restart the system from that state.

In particular, when the cold material is magnetic and has a transformation temperature, such as iron, nickel, or an alloy thereof, when the cold material is started, the cold material is inside the coil, so a lot of power is required at startup, and high-frequency electric It often exceeds the power supply capacity of the generator or silice inverter, making it impossible to start.

The present invention is capable of heating a billet to a predetermined temperature in a short time without exceeding the power supply capacity when the cold material is a magnetic material and due to the function of the conveying device, the cold material is heated while fully inserted into the heating coil. The purpose of the present invention is to provide a method for starting an induction heating machine that can heat up to

One embodiment of the method of the present invention will be described below.

As mentioned above, generally when the coil voltage is constant, if power is applied with cold billet inserted throughout the coil, the heating coil impedance is very small at startup, so the supplied power will be limited to the billet. It requires approximately twice as much power as when the temperature exceeds the transformation point temperature, that is, when the temperature is steady.

Therefore, in the present invention, starting is performed in two stages as shown in FIG.

In this case, the device configuration is basically such that the motor generator MG shown in FIG. 2 is used as a power source and the output of the generator G is supplied to the heating coil CL via a matching transformer T.

Further, the billet is fully inserted over the entire length of the heating coil CL.

Now, as the first stage at the time of starting to apply power, the generator G
The voltage is 100%, and the secondary voltage of matching transformer T is 100/V.
2% and set the billet feed rate to 50%.

With this setting value, approximately 100% power is supplied, and the voltage
Both the current becomes 100%, but both the power and the current gradually decrease, and at t1 after a certain period of time, both the power and the current stabilize at 50%.

At this point, the generator G voltage, matching transformer T secondary voltage, and billet feed rate are all switched to the specified 100 coefficient values.

That is, after time t, both power and current are supplied at 100%, and the billet feed rate is also 100 times the specified value, so that after a certain period of time a billet heated to a predetermined temperature is obtained.

In this case, the billet near the exit side of the heating coil CL will not be heated sufficiently, but this can be heated in the next heating cycle.

In addition, in some cases, the temperature distribution of the billet inside the coil is inappropriate at the time of switching to the first and second stages, that is, there are many billets whose temperature distribution is below the magnetic transformation point, and sometimes when switching to the second stage, the power , and the current will both exceed the rated values.

In such a case, it is necessary to set the generator voltage to 100% or less.

After the temperature distribution of the billet inside the coil reaches the normal value, the generator voltage can be returned to the 100 ratio again. Figure 8 shows the temperature distribution inside the coil corresponding to the time shown in Figure 7. This is what is shown.

Curve 1 indicates the start-up time when 1=0, that is, all the built-in coils are at room temperature.

Curve 2 shows the overall power at t-to below the transformation point temperature,
Both current and rated voltage exceed the power supply capacity.

Curve 3 is 1=11 o'clock, and the billet that has moved close to the coil exit has already exceeded the transformation point temperature, and the coil characteristics are close to a steady state.

That is, the coil characteristics are the characteristics when the temperature distribution shown in curve 4 is achieved.

Therefore, when 1=11, switching from the first stage to the second stage is possible.

In the first stage setting, the secondary voltage of the matching transformer T is set to 100
/vT% because the entire temperature is below the transformation temperature.

In reality, the billet is heated at approximately 1/2 the power density of 100% power.

Therefore, by setting the feed rate to 172 (50%), the temperature rise can be made the same as in the steady state.

If the feed rate is 100%, the power density is 50%, so the temperature will only rise to about 50%, making it impossible to exceed the transformation point temperature.

Therefore, in this case, second stage switching is also impossible.

In the above example, the feed rate was approximately 50% in the first stage, but the feed rate was zero, that is, in a stationary state, only the power was applied at the set value, and when the temperature reached approximately the transformation point temperature, the second stage heating was started. At the same time as changing the voltage setting, the billet feed is changed to 1.
Start at 00 coefficient speed.

According to this method, during static heating, the billet near the heating coil may come out at a temperature higher than the predetermined temperature.
Heating above a predetermined temperature cannot be used if the material is unfavorable.

However, since it can be easily configured in terms of control sequence, it is effective for heating materials that do not have severe temperature conditions.

Furthermore, since the characteristics of the heating coil differ somewhat depending on the material of the heating material, the size (diameter, length) of the billet, etc., in this case, the set values are adjusted accordingly.

Further, in the above embodiment, a motor generator was used as an example of a power source, but a thyrisk inverter may also be used.aHowever, when a thyrisk inverter is used as a power source,
Although it is possible to raise the frequency and make the impedance high when starting a low-impedance cold material, the range of frequency variation increases, making equipment expensive, which is a disadvantage.

According to the present invention described above, even if the heating coil is started with a cold billet inserted over its entire length,
It is possible to provide a method for starting an induction heating machine that can heat a billet to a specified temperature in a short time without exceeding the power supply capacity.

[Brief explanation of the drawing]

Figure 1 is a curve diagram showing the change in starting power when the billet is a cold material, Figure 2 is a circuit diagram for adjusting the output voltage by switching the field current of the power generator, and Figure 3 is based on the circuit shown in Figure 2. A curve diagram explaining excessive power suppression, Figure 4 is a constant current control circuit for a power generator, Figure 5 is a characteristic curve diagram of an example of cold material startup using the circuit in Figure 4, and Figure 6 is a matching transformer. FIG. 7 is a curve diagram explaining the starting method of the present invention, and FIG. 8 is a diagram showing the temperature distribution inside the heating coil in the same starting method. M...Induction motor, G...High frequency generator, Ex...Exciter, T...Matching transformer, CL...Heating coil.

Claims (1)

[Claims] 1. A power source, a heating coil excited by this power source,
An induction heating machine that heats a billet while moving the billet at a certain speed within the heating coil, comprising a matching transformer that is provided between the power source and the heating coil and matches the impedance of the power source and the heating coil, First, in the first step, with a cold billet inserted over the entire length inside the heating coil, power and current are supplied from the power source to the heating coil through the matching transformer, and The secondary voltage of the matching transformer is set to a value commensurate with the inductance of the preheating coil, and the billet is started at a certain feed speed below the rated speed, and after a certain period of time, the electric power and current are transferred to the billet. When the temperature is stabilized at a point commensurate with the impedance of the heating coil, in the second step, the secondary voltage of the matching transformer is varied to 10% of the rated value, and the feeding speed of the billet is switched to the rated speed to heat it. How to start an induction heating machine.