Induction heating apparatus

An induction heating apparatus for heating an electrically conductive workpiece, said apparatus comprising:

• a generally C-shaped core made of ferrite and having two opposed ends, said core being tapered at said two ends so that the area of a cross-section of said ferrite perpendicular to a path running through the center of said core from end to end is substantially larger throughout most of the core than is the area of such a cross-section near said two ends, and said core having a slidable ram portion on which one of said ends is located so that said one end can be moved toward and away from the other of said ends;
• pushing means for pushing said ram portion so that said one end approaches said other end and for withdrawing said ram portion so that said one end is withdrawn from said other end;
• two workholders, one placed on each of said two ends, made of electrically insulating material for compressing said workpiece when said workpiece is placed between said workholders and said pushing means pushes said one end toward said other end;
• a resonant circuit including a capacitance and an exciting coil surrounding said core;
• and
• driving means for supplying a periodic voltage to said resonant circuit so as to cause an alternating current to flow in said resonant circuit and in said coil which is part of said resonant circuit, said driving means including means for detecting the phase of said current flowing in said resonant circuit and means for altering the frequency and phase of the periodic voltage supplied by said driving means to said resonant circuit so that said supplied voltage has a predetermined phase relationship to said current in said resonant circuit and thus so that said resonant circuit will operate at resonance regardless of the effect upon said resonant circuit of the position of said ram portion.

An induction heating apparatus for heating an electrically conductive workpiece, said apparatus comprising:

• a generally C-shaped core made of a magnetic material having a high magnetic permeability and having two opposed ends, the distance between said ends being substantially less than both the height dimension and the width dimension of said core, and said core being tapered at said two ends so that the area of a cross-section of said magnetic material perpendicular to a path running through said core from end to end is substantially larger throughout most of the core than is the area of such a cross-section near said two ends;
• an exciting core surrounding said core;
• means for supplying a periodic voltage to said coil so as to cause an alternating current to flow in said exciting coil and so as to induce a varying magnetic field into said core and between said two ends;
• and
• a workholder made of electrically insulating material mounted on at least one of said ends for supporting said workpiece between said two ends, the cross-sectional area of said workholder lying in the plane perpendicular to the direction between said two ends being substantially larger than such a cross-sectional area of said core near said end upon which it is placed, and said workholder being made of material having a magnetic permeability close to that of air so that said varying magnetic field induced between said two ends and passing through said workholder is concentrated in an area substantially less than the total area of said workholder.

An induction heating apparatus for heating and compressing an electrically conductive workpiece, said apparatus comprising:

• a generally C-shaped core made of a magnetic material having a high magnetic permeability and having two opposed ends, said core being tapered at said two ends so that the area of a cross-section of said magnetic material perpendicular to a path running through the center of said core from end to end is substantially larger throughout most of the core than is the area of such a cross-section near said two ends, and said core having a slidable ram portion on which one of said ends is located so that said one end can be moved toward and away from the other of said ends;
• pushing means for pushing said ram portion so that said one end approaches said other end and for withdrawing said ram portion so that said one end is withdrawn from said other end;
• an exciting coil surrounding said core;
• means for supplying a periodic voltage to said coil so as to cause an alternating current to flow in said exciting coil and so as to induce a varying magnetic field into said core and between said two ends;
• and
• two workholders, one placed on each of said two ends, made of electrically insulating material for compressing said workpiece when said workpiece is placed between said workholders and said pushing means pushes said one end toward said other end, the cross-sectional area of at least one of said workholders in a plane perpendicular to the direction between said two ends being substantially larger than such a cross-sectional area of said core near said end upon which it is placed, and said at least one workholder being made of material having a magnetic permeability close to that of air so that said varying magnetic field induced between said two ends and passing through said at least one workholder is concentrated in an area substantially less than the total area of said at least one workholder.

An induction heating apparatus for heating an electrically conductive workpiece, said apparatus comprising:

• a generally C-shaped core made of a magnetic material having a high magnetic permeability and having two opposed ends, said core being tapered at said two ends so that the area of a cross-section of said magnetic material perpendicular to a path running through the center of said core from end to end is substantially larger throughout most of the core than is the area of such a cross-section near said two ends, and said core having a slidable ram portion on which one of said ends is located so that said one end can be moved toward and away from the other of said ends;
• pushing means for pushing said ram portion so that said one end approaches said other end and for withdrawing said ram portion so that said one end is withdrawn from said other end;
• two workholders, one placed on each of said two ends, made of electrically insulating material, for compressing said workpiece when said workpiece is placed between said workholders and said pushing means pushes said one end toward said other end;
• a resonant circuit including a capacitance and an exciting coil surrounding said core;
• and
• driving means for supplying a periodic voltage to said resonant circuit so as to cause an alternating current to flow in said resonant circuit and in said coil which is part of said resonant circuit, said driving means including means for detecting the phase of said current flowing in said resonant circuit and means for altering the frequency and phase of the periodic voltage supplied by said driving means to said resonant circuit so that said supplied voltage has a predetermined phase relationship to said current in said resonant circuit and thus so that said resonant circuit will operate at resonance regardless of the effect upon said resonant circuit of the position of said ram portion.