Electromagnetic induction heating apparatus for heating elongated metal workpieces

Induction heating apparatus for heating an elongate meal workpiece of predetermined width w, comprising means to generate time varying magnetic fields having magnitudes with spatial profiles across the width w of the workpiece which respectively correspond to time averaged longitudinal eddy current distributions in the workpiece having distributions across the width of the workpiece which are substantially:

• J(x) Cos .phi.(x) and .sqroot. .kappa.J(x) Sin .phi.(x)
• where
• x is the distance across the width of the workpiece from the center line,
• J(x) is proportional to the magnitude of induced current density in the workpiece at a distance x from the center line required to produce a desired profile P(x) across the width w of heat energy generated in the workpiece,
• .kappa. is the ratio of the time for which said field corresponding to said sine eddy current distribution is generated relative to the time for which said field corresponding to said cosine eddy current distribution is generated, and
• .phi.(x) is a function of x selected such that in substance ##EQU9## and means for controlling said magnetic field generating means to generate said respective fields successively in time.

Induction heating apparatus for heating an elongate meal workpiece of predetermined width w, comprising means to generate time varying magnetic fields having magnitudes with spatial profiles across the width w of the workpiece which respectively correspond to time averaged longitudinal eddy current distributions in the workpiece having distributions across the width of the workpiece which are substantially:

• J(x) Cos .phi.(x) and .sqroot. .kappa.J(x) Sin .phi.(x)
• where
• x is the distance across the width of the workpiece from the center line,
• J(x) is proportional to the magnitude of induced current density in the workpiece at a distance x from the center line required to produce a desired profile P(x) across the width w of heat energy generated in the workpiece, and
• .phi.(x) is a function of x selected such that in substance ##EQU10## said magnetic field generating means having a first part arranged to generate a first of said respective fields and a second part arranged to generate a second of said respective fields simultaneously at the same energizing frequency and phase as said first field, said first and second parts being spaced apart to generate said respective fields over spaced apart regions of a workpiece so that said fields do not interact.

A method of heating by induction an elongate metal workpiece of predetermined with w, comprising the steps of generating time varying magnetic fields having magnitudes with spatial profiles across the width w of the workpiece which respectively correspond to time averaged longitudinal eddy current distributions in the workpiece having distributions across the width of the workpiece which are substantially:

• J(x) Cos .phi.(x) and .sqroot. .kappa.J(x) Sin .phi.(x)
• where
• x is the distance across the width of the workpiece from the center line,
• J(x) is proportional to the magnitude of induced current density in the workpiece at a distance x from the center line required to produce a desired profile P(x) across the width w of heat energy generated in the workpiece,
• .kappa. is the ratio of the time for which said field corresponding to said sine eddy current distribution is generated relative to the time for which said field corresponding to said cosine eddy current distribution is generated, and
• .phi.(x) is a function of x selected such that in substance ##EQU11## and controlling the generation of said fields to have said corresponding eddy current distributions in which J is non-uniform.

A method of heating by induction an elongate metal workpiece of predetermined width w, comprising generating time varying magnetic fields having magnitudes with spatial profiles across the width w of the workpiece which respectively correspond to time averaged longitudinal eddy current distributions in the workpiece having distributions across the width of the workpiece which are substantially:

• J(x) Cos .phi.(x) and .sqroot. .kappa.J(x) Sin .phi.(x)
• where
• x is the distance across the width of the workpiece from the center line,
• J(x) is proportional to the magnitude of induced current density in the workpiece at a distance x from the center line required to produce a desired profile P(x) across the width w of heat energy generated in the workpiece,
• .kappa. is the ratio of the time for which said field corresponding to said sine eddy current distribution is generated relative to the time for which said field corresponding to said cosine eddy current distribution is generated, and
• .phi.(x) is a function of x selected such that in substance ##EQU12## wherein said respective fields are generated successively in time.

A method of heating by induction an elongate metal workpiece of predetermined width w, comprising generating time varying magnetic fields having magnitudes with spatial profiles across the width w of the workpiece which respectively correspond to time averaged longitudinal eddy current distributions in the workpiece having distributions across the width of the workpiece which are substantially:

• J(x) Cos .phi.(x) and J(x) Sin .phi.(x)
• where
• x is the distance across the width of the workpiece from the center line,
• J(x) is the magnitude of induced current density in the workpiece at a distance x from the center line required to produce a desired profile P(x) across the width w of heat energy generated in the workpiece, and
• .phi.(x) is a function of x selected such that in substance ##EQU13## wherein said respective fields are generated simultaneously at the same energizing frequency and phase, but over spaced apart regions of a workpiece so that said fields do not interact.