SU936466A1 - Method and device for induction heating - Google Patents

Description

(54) METHOD OF INDUCTION HEATING AND DEVICE FOR ITS IMPLEMENTATION

 .1 The invention relates to electrothermal and can be used in the field of induction heating by high frequency currents. Inductive installations are installed in which the load in the form of an oscillating circuit is connected to the power supply generator - the machine generator, and the PJ products are heated. Usually, the connected loads are made by contactors, which are sufficiently inertial elements. Therefore, the heating cycle includes the transient time associated with the power source and the switching time. At low heating times, for example, less than 2 s, it is difficult to dose the amount of energy that the power source delivers heating to a wet product. Installations for induction heating are also known, which contain a power source, the power output of which is connected to the load via a thyristor switch, and a control output connected to the input of the amplifier-former, the output of which is connected to the control input of the switch, to which the output relay is also connected. of time. In these installations, the load is connected to a power source, a cycle of heating the device to a predetermined temperature is carried out, controlling the current of the power source, and then disconnecting the load 2. Using a thyristor key as a switching element eliminates the effect of the inertia of the key, but does not exclude § heating transition associated with the power source. When the heating times are less than 2 seconds, the duration of the transient process, especially when using machine generators, becomes commensurate with the heating time%. This leads to the fact that due to the uncontrollability of the transition process it is impossible

but accurately dose the heat. In addition, the average power delivered to the load during the transient process is almost half the power delivered after the end of the transient process. All this reduces the accuracy of heating.

The purpose of the invention is to improve the accuracy of heating during short cycles.

The objective is achieved by the fact that before connecting the load, the equivalent load is connected to the power source for a time longer than the transition process, and the load is connected at the moment the source current passes through zero.

To implement this method, the described device must be equipped with a load equivalent connected to the output of the second key, whose input is connected to the second at the power output of the power source, and a switch, through the first output of which the time relay and the amplifier form the first key, and through the second output with the control input of the second key.

The drawing shows a block diagram of a device that implements the method of induction heating.

The device contains amplifier 1, a programmable time relay 2, the outputs of which are connected to the switch 3. The outputs of the switch are connected to the control inputs of the thyristor switches 4 and 5. The power inputs of which are connected to the outputs of the power source 6, for example, a machine generator. The outputs of the keys are connected to the equivalent load 7 and load 8.

The operation of the device illustrates the expected method of induction heating,

In the initial state, the machine generator 6 is excited and the sinusoidal voltage from its output goes to the input of the amplifier-former 1, the output of which has narrow rectangular pulses coinciding in time with the beginning of the half-cycle of the sinusoid. The start of heating is the activation of the first stage of the software time relay 2, which sets switch 3 to such

condition. That the impulse amplifier amplifier 1 is supplied to control the thyristor key 5. As a result, the voltage of the machine generator 5 of the torus 6 is applied through the open thyristor key 5 to the equivalent of the load 7. The uncontrolled transient process starts. After a while, somewhat longer transition time.

o process, the second step of the program time relay 2 is triggered and sets the switch 3 to a state in which the pulses of the amplifier-former, 1 are transferred to the thyristor switch 5, and arrive at the thyristor switch 4; which leads to its unlocking, the work of the machine generator 6 on the load 8 begins, Switching

The load is almost inertia-free; current is produced at the moment the generator current passes through zero. In this case, the voltage on the load 8 is supplied in the steady state

5 press and after counting a predetermined number of periods, the second stage of the program time relay 2 is triggered. The device is prepared for heating the next part,

In case performance

one heating station will be less than the required one; several more heating stations can be powered from the same high-frequency source. In this case, each additional Heating station should have its own tristor key. All posts are connected in parallel, and the order of switching on the posts is controlled by a special

distribution device.

Using the proposed method and device for induction heating, it is possible to significantly expand the range of application of inductive heating to increase the accuracy of the regulation of short heatings. The minimum possible time during which heating can be conducted is equal to one period of the frequency of the machine generator, with an accuracy of one half-period of the same frequency. In addition, the installed power of the generator can be almost halved.

Claims (2)

1. The method of induction heating, in which the load is connected to the power source, conducts the heating cycle of the product to a predetermined temperature, monitors the current of the power source, and then disconnects the load that differs from the TSiM, which, in order to determine the accuracy of the heating mode for short cycles, to the power source the equivalent of the load for a time longer than the duration of the transient process, and the load is connected at the moment of the source current passing through zero, 2. A device for implementing the method according to claim I, comprising a power source, for example, a machine generator, the power output of which is connected to the load through the first key and the control output is connected to the input of the shaping amplifier, the output of which is connected to the control input 6 of the first key, to which the time relay output is also connected, which is tl and -. It is characterized by the fact that it is equipped with a load equivalent, combined with the output of the second key, whose input is connected to the second power output of the power source, and a switch, through the first output of which the indicated connections are connected to the time relay and the amplifier -for-. The controller with the first key, and through the second output - the connection with the control input of the second key. Sources of information taken into account in the examination 1.Shamov A.N., Bodhodkov V, D. Design and operation of induction installations, M., Mashgiz, 1974, p., 18-117,; 2. Thyristors, Technical Reference Book ed., B, Labuntsova, Energie, 1971, p. 176-266