초록 ▼

The windings of an electromagnetic device for heat-sealing thermoplastic material having an electrically conductive layer are included as an inductive component in an oscillatory circuit, rather than merely being an external load. Two inductively coupled windings operate as a feedback element to con

The windings of an electromagnetic device for heat-sealing thermoplastic material having an electrically conductive layer are included as an inductive component in an oscillatory circuit, rather than merely being an external load. Two inductively coupled windings operate as a feedback element to control the alternate conduction of two transistors, to produce an oscillating signal. The core of the electromagnetic heating element has a E-shaped cross section, and the windings are wound around the middle limb of the core and are substantially surrounded by the two outer limbs to thereby substantially reduce thermal losses.

대표청구항 ▼

Apparatus for sealing thermoplastic packing material having an electrically conducting layer, comprising: a sealing jaw including a magnetically conductive core having an E-shaped cross-section providing a middle limb which terminates at a surface that defines a sealing plane and a recess in said su

Apparatus for sealing thermoplastic packing material having an electrically conducting layer, comprising: a sealing jaw including a magnetically conductive core having an E-shaped cross-section providing a middle limb which terminates at a surface that defines a sealing plane and a recess in said surface on either side of said middle limb that opens into said sealing plane; and a parallel resonant oscillator circuit comprising a first winding and a capacitor connected in parallel, and further including a second winding inductively coupled to said first winding for controlling the flow of current through said first winding, both said windings being disposed around said middle limb and within the recess in said core adjacent said sealing plane and being substantially entirely surrounded by core structure except for the opening to said sealing plane.