Orbital heat sealing apparatus and method

Apparatus for heat sealing a continuously moving tubular liner and the like wherein the opposite sides of the liner in the area to be sealed are repeatedly contacted by the same pair of heating elements to incrementally form a relatively narrow continuous line of seal, liner advancing means for continuously advancing the liner in a straight-line path of travel, an opposing pair of elongated sealing bars lying in face-to-face relation on opposite sides of the path of the liner, said sealing bars being positioned to contact the opposite sides of the liner only in the area thereof to be heat sealed, means mounting said sealing bars for movement relative to each other in orbital paths of travel in which the sealing bars during each orbital cycle advance and retract in the direction of their length as they concurrently move toward and away from each other while maintaining their face-to-face relationship, means for moving said sealing bars in unison in their orbital paths of travel, and means for driving said sealing bar moving means and said liner advancing means in timed relation such that the sealing bars will repeatedly move into and out of contact with the area of the liner being sealed as the liner advancing means advances the liner between the sealing bars, the sealing bars moving in the direction of the path of travel of the liner and at the same effective lineal rate of speed throughout the portion of each orbital cycle during which the sealing bars are in contact with the area of the liner being sealed.