Abstract:
The present invention generally relates to a high-frequency pulse oscillator, and more particularly to a high-frequency pulse oscillator adapted to provide pulse currents having a high frequency and large amplitude so as to transition metallic materials into a plastic state for ease of processing or for closing microcracks formed in metallic parts in order to recover mechanical characteristics thereof. The high-frequency pulse oscillator of the present invention comprises a controllable rectifier, a switching section, and a control system. The controllable rectifier rectifies alternating currents supplied from a current source to output currents having a predetermined waveform, according to a control signal from the control system. The switching section generates pulse currents using the currents from the rectifier, according to another control signal from the control system. The switching section comprises at least one switching block, which is connected so that the amplitude of the pulse currents is increased. The control system controls the rectifier and the switching section according to the signals to start, stop, and reset the operation of generating the pulse currents and the signals to specify or change the frequency and amplitude of the pulse currents, so that the generated pulse currents may have desired frequency and amplitude. The pulse currents generated in the high-frequency pulse oscillator enable the manufacture of various structural parts without degrading their structure.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to a high-frequency pulse oscillator, and more particularly to a high-frequency pulse oscillator adapted to provide pulse currents having a high frequency and large amplitude so as to transition metallic materials into a plastic state for ease of processing or for closing microcracks formed in metallic parts in order to recover mechanical characteristics thereof.  
       BACKGROUND OF THE INVENTION  
       [0002]     Metal works (rolling process in particular), in which a high-frequency pulse oscillator of the present invention may be employed, will be discussed below. Rolling refers to a process that induces plastic deformation of metallic materials by compressing and squeezing the materials between work rolls. Rolling is a type of plastic processing wherein production speed is high and dimensional accuracy can be easily controlled. Since rolling requires relatively lower production costs and provides products having more uniform dimensional accuracy and quality than molding or casting, it is most frequently used. In a rolling process, materials to be processed receive compressive stress caused by the pressing force of the rolls while they pass through the rolls, and further undergo shear stress on the interfaces with the rolls. The shear stress acts to thrust the materials between the rolls.  
         [0003]     There are essentially two types of rolling process, i.e., hot rolling and cold rolling. Cold rolling refers to rolling the materials to be processed, such as ingots, at a normal temperature and is used for providing products such as sheets, strips and foils, which have high strength and good dimensional accuracy. On the other hand, hot rolling refers to rolling metallic materials after applying heat with a heating furnace. Generally, through hot rolling, ingots are processed into blooms or billets and are further processed into boards, sheets, bars, pipes and rails.  
         [0004]     Since cold rolling is performed at a normal temperature, it is advantageous in that there is no need for any special equipments for heating materials such as strips. However, cold rolling typically requires an annealing process. As such, the entire rolling process time becomes lengthened while the productivity is lowered.  
         [0005]     In hot rolling, a metal strip is heated in a heating furnace and is then fed to a rolling device. It is extremely important to heat the metal strip to a specified temperature before rolling. That is, if the heating temperature is much lower than the specified temperature, then various problems may occur (e.g., difficulty in carrying out rolling, excessive loads are imposed on the rolling device, and desirable properties cannot be obtained for the rolled strip). However, if an excessively high temperature is set as the heating temperature (considering that temperature decreases during the transfer of the heated metal strip to the rolling device), then there is an increase in the oxidization of the metal strip. Thus, the resulting energy costs inevitably increase and may even become burdensome. Under these circumstances, it is advisable in hot rolling to heat the metal strips as closely as possible to the work rolls. For such purpose, it is plausible to employ a high-frequency induction heating method and an electric heating method.  
         [0006]     However, a high-frequency induction heating device is usually complicated, expensive and consumes too much power.  
         [0007]     On the other hand, in the electric heating method, the work rolls and the metal strip are heated by their respective electrical resistance when direct currents from a power source are applied to the upper/lower work rolls and the strip. Thus, their temperatures tend to rise. An example of an electric heating type rolling device is disclosed in Japanese Patent Publication No. 1998-180317. However, the prior art electric heating type rolling device consumes too much power. For instance, when a steel strip having a width of 100 mm and a thickness of 2 mm (i.e., a cross-sectional area of 2 cm 2 ) is rolled to have a thickness of 0.25˜0.3 mm by electric-heating, a current density of about 104 A/cm 2  is required. If a direct current is applied, then the current strength reaches 20 kA, which is a multiplication between the current density and the cross-sectional area of the strip to be rolled. In addition to such excessive power-consumption, the steel strip is heated to a temperature ranging from 400° C. to 500° C., which causes oxidization and discoloration on the strip surface. Further, since the work rolls are included in the electric circuit, the life of work rolls may be shortened due to electric corrosion. Also, a cooling device, which prevents the work rolls from being damaged due to heat transfer from the steel strip, is additionally required. Moreover, adverse effects upon the environment may occur around the production premises.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention generally relates to a high-frequency pulse oscillator, and more particularly to a high-frequency pulse oscillator adapted to provide pulse currents having a high frequency and large amplitude so as to transition metallic materials into a plastic state for ease of processing or for closing microcracks formed in metallic parts in order to recover mechanical characteristics thereof.  
         [0009]     The high-frequency pulse oscillator of the present invention comprises: a controllable rectifier for rectifying alternating currents supplied from a current source to output currents having a predetermined waveform; a switching section comprising one or more switching blocks and generating pulse currents having desired amplitude and frequency from said currents having the predetermined waveform, wherein said one or more switching blocks are connected so that the amplitude of said pulse currents is increased; and a control system for generating first and second control pulses, wherein said first control pulse is supplied to said controllable rectifier to control rectifying said alternating currents and said second control pulse is supplied to said one or more switching blocks to control said currents having the predetermined waveform to be transformed into said pulse currents having the desired amplitude and frequency.  
         [0010]     The control system may comprise: a pulse-phase control system for generating said first control pulse; a voltage-controlled oscillator (VCO) for generating said second control pulse; a protection/automation unit for controlling said pulse-phase control system and said voltage-controlled oscillator according to START, STOP, and RESET signals to start, stop, and reset the operation of generating said pulse currents; and a power supply/synchronization unit for providing a stable voltage source using said alternating currents supplied from said current source and generating signals to synchronize said pulse-phase control system.  
         [0011]     When receiving said START signal, said protection/automation unit may generate SWITCH-ON signal for said voltage-controlled oscillator and instruct said pulse-phase control system to release blocking of said first control pulse. When receiving said STOP signal or realizing an excess of current limits of said high-frequency pulse oscillator, the protection/automation unit may stop supplying said SWITCH-ON signal to said voltage-controlled oscillator. It may then instruct said pulse-phase control system to block said first control pulse and invert said controllable rectifier. When receiving said RESET signal, said protection/automation unit may approve the generation of said SWITCH-ON signal only after confirming that said current limit is not exceeded and said current source is completely discharged.  
         [0012]     The control system may further comprise a remote and local control panel for generating signals to start, stop, and reset the operation of generating said pulse currents and signals to specify or change the frequency and amplitude of said pulse current. The control system may also comprise a selector for selectively receiving said signals from either said remote or local control panel according to LOCAL/REMOTE signal from said local control panel.  
         [0013]     The controllable rectifier may be a controllable three-phase rectifier comprising a thyristor. In this case, said first control pulse may be applied to a control electrode of said thyristor.  
         [0014]     The switching section may comprise: a current sensor for measuring currents in the load to which said pulse currents are supplied; a pulse transformer for causing said pulse currents to have the desired amplitude; and a switching thyristor for causing said pulse currents to have the desired frequency. In this case, said control system may receive the measurements of the currents in said load from said current sensor.  
         [0015]     In case the above high-frequency oscillator is employed in a rolling mill, whereas continuous direct currents are applied to the upper/lower work rolls and metallic materials in the prior arts, the high-frequency pulse oscillator provides discrete pulse currents to prevent the temperature of the materials from being excessively increased due to continuous supply of energy. Further, since the upper/lower work rolls need not be included in electric circuits and the pulse currents are directly supplied to the materials using separate contact terminals (e.g., formed from a bunch of copper wires) for the load, the life of work rolls is not shortened and the corrosion resistance of work rolls is not reduced. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0016]     The above features of the present invention will become more apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings.  
         [0017]      FIG. 1  is a schematic diagram illustrating basic components and their connections in the high-frequency pulse oscillator constructed in accordance with the present invention.  
         [0018]      FIG. 2  depicts an embodiment of a switching section of the high-frequency pulse oscillator constructed in accordance with the present invention.  
         [0019]      FIG. 3  depicts an embodiment of a switching section in which the switching blocks in  FIG. 2  are connected in parallel in accordance with the present invention.  
         [0020]      FIG. 4  depicts an embodiment of a switching section in which the switching blocks in  FIG. 2  are connected in series in accordance with the present invention.  
         [0021]      FIG. 5  depicts a block diagram illustrating the control system of the high-frequency pulse oscillator constructed in accordance with the present invention.  
         [0022]      FIG. 6  depicts plots illustrating waveforms from the components of the high-frequency oscillator constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein and accompanying text, could be arranged and designed in a wide variety of different configurations while still utilizing the present inventive concept. Thus, the following detailed description of the preferred embodiments of the high-frequency pulse oscillator of the present invention, as represented in  FIGS. 1 through 6  and accompanying text, is not intended to limit the scope of the invention, as claimed, but it is merely representative of the presently preferred embodiments of the invention. The presently preferred embodiments of the invention will be best understood by reference to the drawings, wherein like parts or steps are designated by like numerals throughout.  
         [0024]      FIG. 1  is a schematic diagram illustrating the basic components and their connections in the high-frequency pulse oscillator constructed in accordance with the present invention.  
         [0025]     As shown in  FIG. 1 , the high-frequency pulse oscillator  100  comprises: a control system  500  for processing instructions to start, stop and reset the operation of generating pulse currents and controlling adjustments to the amplitude and frequency of the generated pulse currents; a controllable rectifier  150  for rectifying alternating currents supplied from a current source  250 , which is in accordance with a control signal from the control system  500 , to output currents having a predetermined waveform; and a switching section for generating pulse currents having desired amplitude and frequency from the currents outputted from the rectifier  150 . The generated pulse currents are supplied to a load R load . The control system  500  and the switching section  200  are connected to a common current source  250 , which preferably provides alternating currents having an amplitude of 380-690 V and a frequency of 50-60 Hz.  
         [0026]     The control system  500  may be connected to a control electrode and an anode of a switching thyristor, which is included in the switching section  200 , to provide a control signal for controlling the switching thyristor. Also, the control system  500  receives measurements of the currents in the load R load , which is connected to the switching section  200 , to control the operations of the high-frequency pulse oscillator  100  according to the measurements. The control system  500  generates START, STOP, and RESET signals to start, stop, and reset the operation of generating the pulse currents, respectively. It also generates F setup  and I setup  signals to indicate the desired frequency and amplitude of the generated pulse currents based on the instructions that a user issues through a remote or local control panel. In accordance with those signals, the control system  500  initiates or discontinues the generation of pulse currents and controls the switching section  200  and the rectifier  150  so that the pulse currents supplied to the load R load  may have the desired amplitude and frequency. The specific constitution of the control system  500  will be described below in view of  FIG. 5 .  
         [0027]     The controllable rectifier  150  may be a three-phase rectifier comprising a thyristor UV. In this case, the control system  500  may be connected to a control electrode of the thyristor UV to provide a control signal (a first control pulse) for controlling the thyristor UV.  
         [0028]     The switching section  200  generates pulse currents having desired amplitude and frequency from the currents outputted from the controllable rectifier  150 , which is in accordance with a control signal (a second control pulse) from the control system  500 , and provides the generated pulse currents to the load R load . An example of its specific constitution is illustrated in  FIG. 2 , along with the rectifier  150  and the control system  500 .  
         [0029]     As shown in  FIG. 2 , the switching section  200  comprises: a current sensor DT for measuring the currents in the load R load ; a pulse transformer PT for causing the pulse currents supplied to the load R load  to have the desired amplitude; and a switching thyristor VS for adjusting the frequency of the pulse currents based on the control signal from the control system  500 . The switching section  200  further comprises: a capacitor C for charging and discharging currents during the operation of generating the pulse currents; a smoothing reactor SR for limiting the currents charging the capacitor C; a discharging diode VD 0  for rectifying the currents discharged from the capacitor C through the pulse transformer PT before supplying the currents to the load R load ; and a first switching reactor KR 1  and an output diode VDB, which are connected in parallel with the switching thyristor VS, for causing the switching thyristor VS to have an inverse voltage after the capacitor C is discharged. The switching section  200  is connected to the load R load  through first and second output contacts, each of which may be formed from a bunch of copper wires.  
         [0030]     Referring to  FIG. 2 , the specific connections between the components of the switching section  200  are described below. As for the pulse transformer PT, a first input on the upper end of a primary winding, which is on the left side of the pulse transformer, is connected to the first switching reactor KR 1  and the switching thyristor VS. Further, a second input on the lower end of the primary winding is connected to a lower (second) pole of the capacitor C and a lower (second) output terminal of the rectifier  150 . A first output on the upper end of a secondary winding, which is on the right side of the pulse transformer PT, is connected via the output diode VDB to the first output contact  210 . Also, a second output on the lower end of the secondary winding is connected via a primary winding of the current sensor DT to the second output contact  220 .  
         [0031]     The connection between the rectifier  150  and the switching section  200  is now described below. An upper (first) output terminal of the controllable rectifier  150  is connected via the smoothing reactor SR to a upper (first) pole of the capacitor C and also to opposing inputs of the switching thyristor VS and the discharging diode VD 0  (an output of the discharging diode VD 0  is connected to the first switching reactor KR 1 ). The second output terminal is connected to the second pole of the capacitor C and the second input of the primary winding of the pulse transformer PT.  
         [0032]     Meanwhile, if the working current is low or the load resistance is large (e.g., the resistance may be very large when the load is disconnected), the switching section  200  may further comprise a second switching reactor KR 2  such as a choke coil. The second switching reactor KR 2  is connected in parallel with the outputs of the secondary winding of the pulse transformer PT. The currents in the load R load  are measured using the current sensor DT.  
         [0033]     Although the switching section  200  described above comprises a single block (i.e., switching block), the switching section may comprise a plurality of switching blocks. In this case, the currents are charged and discharged through a plurality of capacitors (i.e., capacitor bank) and the amount of the charged currents increases. Also, the number of the pulse transformers through which the current are discharged is increased. Therefore, the maximum amplitude of the pulse currents, which are generated from the high-frequency pulse oscillator  100 , may be increased. In this constitution, the plurality of switching blocks may be connected in parallel or in series. Examples where n blocks are connected in parallel or in series are illustrated in  FIGS. 3 and 4 , respectively.  
         [0034]     Referring to  FIG. 3 , the switching blocks, which have the same configuration as the one shown in  FIG. 2 , are connected n times in parallel. The first and second output terminals of the rectifier  150  are connected in parallel with the inputs on the left ends of the smoothing reactors (SR 1 -SRn) and the second poles on the lower ends of the capacitors (C 1 -Cn) in the switching blocks, respectively. The output terminals on the right ends of the output diodes (VDB 1 -VDBn) and the output terminals of the primary windings of the current sensors (DT 1 -DTn) in the switching blocks are connected in parallel with the first and second output contacts  210 ,  220 , respectively.  
         [0035]      FIG. 4  illustrates a switching section  200  wherein n switching blocks are connected in series. That is, a first output terminal of a secondary winding of the pulse transformer PTn in the n th  switching block is connected via the output diode VDB to the first output contact  210 . Further, a second output terminal of a secondary winding of the pulse transformer PT 1  in the first switching block is connected via the primary winding of the current sensor DT to the second output contact  220 . First output terminals of secondary windings of the pulse transformers PT 1 -PTn- 1  in the 1 st  to the n-1 th  switching blocks are connected to second output terminals of secondary windings of the pulse transformers PT 2 -PTn in the 2 nd  to the n th  switching blocks, respectively.  
         [0036]     As discussed above, through serial or parallel connections (or the combination of the two), the maximum amplitude of the pulse currents supplied to the load R load  may be increased. Instead of using a single rectifier, each of the switching blocks may be equipped with an individual controllable rectifier, if necessary.  
         [0037]     Referring now to  FIG. 5 , the constitution of the control system  500 , which is mentioned above, is more specifically described below.  
         [0038]      FIG. 5  depicts a block diagram illustrating the control system  500  of the high-frequency pulse oscillator, which is connected to the switching section  200  as shown in  FIGS. 1-4 . The control system  500  comprises: a power supply/synchronization unit for providing a stable voltage source to all components of the control system  500  and generating a signal U synch  to synchronize the pulse-phase control system  502 ; a pulse-phase control system for generating a signal (a first control pulse) for controlling the rectifier  150  to set up and stabilize the parameters of the generated pulse currents as desired; remote and local control panels  503 ,  504  for generating START, STOP, RESET, F setup  and I setup  signals to control the operation of generating the pulse currents and to specify the frequency and amplitude of the pulse currents; a selector  505  for selectively receiving those signals from either said remote or local control panel according to LOCAL/REMOTE signal from the local control panel  503 ; a protection/automation unit  506  for controlling the pulse-phase control system  502  and the voltage-controlled oscillator  507  according to the signals from the selector  505 ; a voltage-controlled oscillator (VCO)  507  for generating a signal (a second control pulse) for controlling the switching thyristors (VS 1 -VSn) included in the switching section  200 ; and pulse shapers  508 ,  509  for shaping the first and second control pulses, respectively.  
         [0039]     The power supply/synchronization unit  501  energizes all components of the control system  500  with a stable voltage source±Vcc (e.g., ±15 V) using the alternating currents applied thereto, which may be identical to the currents applied to the rectifier  150 . It also provides a synchronization signal U synch  to the pulse-phase control system  502  to synchronize the pulse-phase control system  502  with a clock signal.  
         [0040]     The remote and local control panels  503 ,  504  generate signals (START, STOP and RESET) to start, stop and reset the operation of generating pulse currents supplied to the load R load  and signals (F setup  and I setup ) to specify the frequency and amplitude of the pulse currents. A user may input desired instructions using the input means of the remote or local control panel  503 ,  504 , and then the signals corresponding to those instructions will be provided to the selector  505 . That is, the remote control panel  503  generates START remote , STOP remote , RESET remote , F remotesetup  and I remotesetup  signals, while the local control panel  504 , which is mounted on the high-frequency pulse oscillator  100 , generates START local , STOP local , RESET local , F localsetup , and I localsetup  signals, according to the instructions from the user.  
         [0041]     The selector  505  receives those signals from either the remote or local control panel  503 ,  504  according to LOCAL/REMOTE command that a user specifies through the local control panel  504 . It further provides F setup  signal to the voltage-controlled oscillator  507 , I setup  signal to the pulse-phase control system  502 , and START, STOP, and RESET signals to the protection/automation unit  506 .  
         [0042]     The protection/automation unit  506  provides SWITCH-ON signal to the voltage-controlled oscillator  507  according to the START signal. When the STOP signal is received or protective circuits realize that the maximum current limit, which the electric circuits of the high-frequency pulse oscillator  100  can endure, is exceeded, the protection/automation unit  506  switches off the voltage-controlled oscillator  507  and provides a signal to block the first control pulse and a signal (INV) to invert the rectifier  150  to the pulse-phase control system  502 . Meanwhile, the terminal timing (TT) signal is applied to the protection/automation unit  506  as a clock signal.  
         [0043]     The voltage-controlled oscillator  507  generates the second control pulse for controlling the switching thyristors VS 1 -VSn, which are included in the switching section  200 , on the basis of the F setup  signal from the selector  505  and the SWITCH-ON signal from the protection/automation unit  506 . The second control pulse is applied to the pulse shaper  508  for the switching section  200 .  
         [0044]     The pulse-phase control system  502  receives the signal for generating or blocking the first control pulse and the INV signal from the protection/automation unit  506 , as well as the I setup  signal from the selector  505 . On the basis of those signals, it generates or blocks the first control pulse, which is supplied to the pulse shaper  509  for the rectifier  150 .  
         [0045]     An output terminal of the pulse shaper  508  is connected to the control electrodes and anodes of the switching thyristors VS 1 -VSn to provide the second control pulse for controlling the switching thyristors VS 1 -VSn. An output terminal of the pulse shaper  509  is connected to the control electrode of the thyristor UV, which is included in the rectifier  150 , to provide the first control pulse for controlling the thyristor UV.  
         [0046]     Referring now to  FIGS. 3-5 , the operations of the high-frequency pulse oscillator  100 , which are in accordance with an embodiment of the present invention, are described below.  
         [0047]     In order to generate the pulse currents to be supplied to the load R load , alternating currents from the current source  250  are applied to the power supply/synchronization unit  501  and the rectifier  150 . A user issues START command and specifies desired frequency and amplitude of the pulse currents using a remote or local control panel  503 ,  504  so that the selector  505  may generate START, F setup , and I setup  signals based on the signals from either one of the control panels. When the protection/automation unit receives the START signal, it orders the pulse-phase control system  502  to turn off the blocking of the first control pulse. Then, the first control pulse is transferred from the pulse shaper  509  to the rectifier  150 . In accordance with the first control pulse, the rectifier  150  rectifies the alternating currents from the current source  250  to generate currents having a predetermined waveform (see  FIG. 6 ( a )). When these currents are supplied to the switching section  200 , the capacitors C 1 -Cn are charged to the voltage defined by the I setup  signal. The currents for such charging operation are limited by the smoothing reactors SR 1 -SRn. After some time (e.g., ten to fifteen milliseconds) has passed since the START signal, the capacitors C 1 -Cn are initially charged to said voltage. Then, the SWITCH-ON signal from the protection/automation unit  502  initiates the generation of the second control pulse, which controls the switching thyristors VS 1 -VSn, in the voltage-controlled oscillator  507 . When the second control pulse is supplied from the pulse shaper  508  to the switching section  200 , the capacitors C 1 -Cn are discharged via the pulse transformers PT 1 -PTn, respectively.  FIG. 6 ( b ) shows the variations in the voltage of the capacitors C 1 -Cn while they are charged and discharged. The currents discharged from the capacitors C 1 -Cn are rectified by the discharging diodes VDB 1 -VDBn, which establishes the working cycle for the load R load . When the capacitors C 1 -Cn are discharged, the energy accumulated in the pulse transformers PT 1 -PTn and connecting wires is utilized to open the inverse discharging diodes VD 01 -VD 0   n.  Also, the switching thyristors VS 1 -VSn receive the inverse voltage that has an amplitude and duration depending on the parameters of the switching reactors KR 11 -KR 1   n  (see  FIG. 6 ( c )).  
         [0048]     The duration of the pulse currents supplied to the load R load  depends on the capacitance of the capacitors C 2 -Cn (e.g., from 80 to 200 μms). The amplitude of the pulse currents is varied (either smoothly or in increments) by using the switching blocks connected in parallel ( FIG. 3 ), in series ( FIG. 4 ), or in a combination (see  FIG. 6 ( d )). The frequency and amplitude of the generated pulse currents may be monitored using additional displays on the remote and/or local control panels  503 ,  504  (during both the setup stage and the conventional operation) and corrected when necessary. The generated pulse currents are distributed amongst the switching section  200  in accordance with the resistance of the pulse transformers and the wires. If necessary, each switching block in the switching section  200  may be equipped with an individual controllable rectifier with a variable load distribution.  
         [0049]     In order to terminate the operation of generating the pulse currents, the protection/automation unit  506  takes the STOP signal or a signal from the protective circuits to form the INV signal (which requires the rectifier  150  to work as an inverter). Then, after some time has elapsed (e.g., ten to fifteen milliseconds later), it turns off the voltage-controlled oscillator  507 , terminates providing the SWITCH-ON signal, and sends the control pulse blocking command to the pulse-phase control system  502 . These actions reliably discharge the energy accumulated in the current source  250 . In case of a usual switching off via sending the STOP signal, the current source  250  might be switched on immediately. On the other hand, in case the protective circuits have been involved during the switching off, a user must issue RESET command prior to the switching on, upon receiving a signal from the protection/automation unit  506 , which confirms that the current limit is not exceeded and the current source  250  is completely discharged.  
         [0050]     According to this configuration, the high-frequency pulse oscillator  100 , which has a single switching block with the particular elements described above, can provide pulse currents for energizing the load, the parameters of which are as follows: 
        Current strength: up to 20 kA,     Voltage: up to 100V     Duration: 80-200 μms     Pulse frequency: 0-1000 Hz        
 
         [0055]     These parameters may be varied in accordance with the modifications to the elements of the present invention. The high-frequency pulse oscillator of the present invention can directly supply the pulse currents, which have such parameters, to metallic materials to be processed in devices such as rolling mills. As such, the temperature of the materials is not excessively increased due to the continuous supply of energy. Thus, no cooling device is required and electric corrosion of working rolls may be avoided. Meanwhile, the generated pulse currents may be also utilized for closing microcracks formed in metallic parts in order to recover mechanical characteristics thereof.  
         [0056]     While the present invention has been described above in conjunction with specific preferred embodiments, it is evident that numerous alternatives, modifications and variations will be apparent to those skilled in the art without departing from the scope of the present invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.