CN2150944Y - Silicon control medium frequency induction furnace - Google Patents

Abstract

The utility model relates to an induction heating device, particularly a silicon control medium frequency induction furnace, which is composed of a main loop, a control loop and a furnace body, wherein, the main loop is composed of a rectifying bridge, an LC filter circuit and an inversion bridge. An induction heating coil is connected with a compensating capacitor in parallel. The inversion bridge is composed of two controlled silicon, a capacitor and an adjustable induction coil. A delay switching switch is composed of a Schmitt trigger, a capacitor and a resistor in the control circuit, and an independent-excitation operating mode is converted into a self-excitation operating mode. A through protecting circuit takes voltage signals from the both ends of the bridge arms of the controlled silicon to be connected with a bistable circuit (I) through an optical coupling element GD, and the controlled silicon are closed through the capacitor charged inversely to realize the through protection.

Description

Silicon control medium frequency induction furnace

The invention belongs to the forging firing equipment, a kind of electromagnetic induction diathermic furnace that adopts controllable silicon medium frequency inverter circuit is applicable to the heating of various medium and small forging.

At present, the controllable silicon Medium Frequency Induction Heating Furnace generally adopts shunt chopper.For example, equal about 700 volts of the intermediate frequency furnace output voltage that ground electric furnace factories such as domestic most widely used Shanghai, Wuxi, Xi'an make, induction coil length is all more than 1 meter, longer to medium and small forging heat induced coil, the number of turn is more, need to use the intermediate-frequency transformer step-down, efficient is low, noise is big, current-rising-rate when inverter bridge adopts additional measures restriction thyristor commutation, the inversion circuit complex circuit, one group of silicon controlled shutoff of working on the inverter bridge shifts to an earlier date conducting by another group controllable silicon and realizes, if tiltedly logical short circuit then takes place pulse missing.In addition, advance angle is big more, and power factor is low more, so advance angle can not be very big, causes frequency to be confined to about 2500HZ, and it is low to heat medium and small forging electrical efficiency.

It is less that task of the present invention provides a kind of volume, and structure is more simple, reduces power consumption, raises the efficiency, and is applicable to the heat transmitting furnace of medium-frequency induction of medium and small forging heating.

Basic design of the present invention is: inverter bridge two arms in electromagnetic induction electric furnace major loop are made up of two controllable silicons, and diode reverse parallel connection is with it arranged; Two arms are that two groups of electric capacity are connected with the controllable silicon brachium pontis by adjustable inductor in addition.Load coil is in parallel with building-out capacitor, these parallel circuit one termination two electric capacity brachium pontis tie points, the other end and thyristor bridge knee-joint point link, the frequency of its resonant frequency decision controllable silicon triggering and conducting, two groups of electric capacity are powered to load coil by controllable silicon periodically, produce the intermediate frequency alternating flux thus and pass the body of heater heated parts.

Fig. 1 is the schematic circuit of major loop of the present invention;

Fig. 2 is the schematic diagram of control circuit of the present invention.

The present invention mainly contains major loop, control circuit and body of heater and forms, and describes its structure in detail below in conjunction with accompanying drawing.

As shown in Figure 1, major loop comprises rectifier bridge, LC filter circuit, inverter bridge and L₁C ₁Shunt-resonant circuit (body of heater). 380 volts of three-phase main-frequency alternating currents are through SCR₁～SCR ₆The controllable silicon full-wave rectification bridge and the L that consist of₄、C ₄Become the single-phase DC electricity above 500V after the filtering. Work as SCR₈During controlled silicon conducting, capacitor C₂Through inductance L₂, forward is by load discharge, simultaneously power supply through above-mentioned path to capacitor C₃Charging is because C₁、C ₂And L₂The intrinsic frequency of the series resonant tank that consists of is higher than C₁、L ₁The intrinsic frequency of the shunt-resonant circuit that consists of is so pass through inductance L₂Electric current in capacitor C₁Front tens microseconds of voltage zero-cross have decayed to zero, controllable silicon SCR₈Close voluntarily. At this moment, V_C2－V _C1＜0, reversing the current is by resistance R, diode D₁, inductance L₂Return power supply, the pressure drop on the resistance R provides controllable silicon SCR₈Back-pressure, impel controllable silicon to accelerate to close. Work as V_C1During zero passage, control circuit produces trigger impulse and makes controllable silicon SCR₉Conducting. Capacitor C₃Oppositely by load and inductance L₃The discharge, power supply through this path to C₂Charging. In like manner, when passing through inductance L₃When electric current is zero, controllable silicon SCR₉Close voluntarily V_C1During zero passage, trigger impulse makes again controllable silicon SCR again₈A cycle of oscillation is finished in again conducting.

Control circuit as shown in Figure 2, ［ I ］ bistable circuit among the figure: ［ II ］ astable circuit; ［ III ］, ［ IV ］ Schmidt trigger.

Astable circuit in the control circuit of the present invention ［ II ］ is the oscillation source of output square wave, through differential circuit C ₆, R ₁₀Trigger triode T ₁Produce burst pulse, by pulse transformer B ₂Trigger the rectifier bridge controllable silicon.

The present invention adopts Schmidt circuit to realize the working method that separate excitation starts changes the self-excitation operation.Schmidt trigger ［ III ］ and capacitor C ₉, resistance R ₁₁, R ₁₂, R ₁₄Constitute the time-delay change-over switch.In the blowing out stage, the K switch closure, the input of ［ III ］ is an electronegative potential, output is a high potential, diode D ₇, D ₈Be in reverse bias, the square wave of oscillation source ［ II ］ output is through resistance R ₉, diode D ₉, K switch goes into ground.During startup, cut-off switch K, square-wave signal is through R ₉, R ₁₇Go into the input of Schmidt trigger ［ IV ］.The forward position of the output output square wave of ［ IV ］ is by circuit C ₇, R ₁₃Differential is through triode T ₃After amplifying slicing, by pulse transformer B ₃Trigger the inverter bridge controllable silicon SCR ₈Square wave back edge is then by circuit C ₈, R ₁₈Differential is through triode T ₄Swing to and triode T ₅After amplifying slicing, by pulse transformer B ₄Trigger the inverter bridge controllable silicon SCR ₉The startup stage, the output of ［ III ］ keeps high potential, triode T ₂Do not work, ［ IV ］ do not had influence by the body of heater feedback signal.After K switch disconnected, power supply passed through resistance R ₁₁To capacitor C ₉Charging, the input terminal voltage of ［ III ］ raises gradually, and when reaching certain threshold value, ［ III ］ be counter-rotating suddenly, and output becomes electronegative potential, diode D ₇, D ₈Conducting, his energizing signal is through R ₉, D ₈Go into ground, simultaneously triode T ₂Enter duty, the sinusoidal signal at body of heater two ends 3,4 is by signal transformer B ₁Step-down provides triode T ₂Base flow, the negative half-wave of sinusoidal signal is through diode D ₄Make T ₂End the output high potential; Positive half-wave makes T ₂Full closing, the output electronegative potential produces square wave and supplies with ［ IV ］, and electric furnace enters the self-excitation duty.

The present invention adopts and blocks rectifier bridge and inverter bridge silicon controlled trigger impulse simultaneously, realizes straight-through protection.When the electric furnace duty, bistable volt circuit ［ I ］ two inputs by light idol GD and normally closed switch QT ground connection, are low level respectively simultaneously, and output output high level is as the triode T on no stable state road ［ II ］ ₂And power supply; Straight-through holding circuit is pressed signal from the power taking of controllable silicon brachium pontis two ends, connects through light idol element and bistable circuit, and when shoot through, two controllable silicon SCR on the inverter bridge ₈And SCR ₉Conducting simultaneously, 1,2 liang of point voltage approaches zero, and light idol GD ends R ₄The lower end is in high level, ［ I ］ upset output low level, astable circuit ［ II ］ and triode T ₂Quit work locking pulse.When restarting, press the normally closed QT of opening, make R ₅The lower end is in high level, ［ I ］ upset, and output HIGH voltage enters duty again.

Embodiment:

Do 40 kilowatts of induction heaters of a rated power, 200 volts of output voltages, operating frequency 4000HZ, controllable silicon electric current 160A adds hot forging diameter phi 30, and 1200 ℃ of heating-up temperatures, productivity ratio are 2.1Kg/min.

Induction heater inverter bridge key data: controllable silicon KK200, two of 1600V; Diode 50A, two of 1400V; Electric heating capacitance 500V, 240 kilovars one casees.

The present invention is because dc source and capacitor C ₂, C ₃Power to the load by the inverter bridge controllable silicon simultaneously, source current only accounts for 1/2, so load voltage is more than 200 volts less than dc source voltage 1/2.Can adopt length only is the direct medium and small forging of heating of induction coil about 30 centimetres, has saved intermediate-frequency transformer.It is simple in structure, thermal efficiency height, and the heated object oxidation is light.The inverter bridge controllable silicon is to close voluntarily, can avoid tiltedly logical short circuit, and close the work controllable silicon earlier, makes another controllable silicon conducting again, and straight-through probability is little.The inverter bridge controllable silicon is to trigger when the load voltage zero passage simultaneously, needn't shift to an earlier date conducting, the power factor height.Inverter bridge reverse parallel connection diode D in addition ₁, D ₂Make controllable silicon keep the long period back-pressure, can improve the electric furnace operating frequency, heat medium and small forging electrical efficiency height.

Claims (1)

1, controllable silicon heat transmitting furnace of medium-frequency induction is made up of major loop, control circuit and body of heater, it is characterized in that inverter bridge two arms in the major loop are by two controllable silicon SCR ₈, SCR ₉Form, and diode D is arranged ₁, D ₂In parallel in the other direction with it respectively, two arms are two groups of capacitor C in addition ₂, C ₃Respectively by adjustable inductor L ₂, L ₃Be connected load coil L with 1,2 of controllable silicon brachium pontis ₁With building-out capacitor C ₁Parallel connection, this parallel circuit one termination capacitor brachium pontis tie point 3, the other end and thyristor bridge knee-joint point 4 link, and adopt Schmidt trigger [III] and capacitor C in the control circuit ₉, resistance R ₁₁, R ₁₂, R ₁₄Constitute the time-delay change-over switch, realize that separate excitation starts commentaries on classics self-excitation operation working method, straight-through holding circuit is pressed signal from 1,2 power takings of controllable silicon brachium pontis two ends, and GD is connected with bistable circuit [I] through light idol element.

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