Apparatus and method for ultrasonically joining sheets of termoplastic materials

Apparatus for creating a lap-type welded seam between two sheets of thermoplastic material, said welded seam including a uniform intermix zone, said apparatus including

• sheet material handling means, said handling means including a supporting structure, a pair of nip rollers mounted upon said structure and at least one of said rollers being driven, said rollers defining a nip transverse to the longitudinal dimension of the seam to be formed,
• an ultrasonic horn having a tip thereon, said horn being capable of reciprocating movement along the axis thereof, said horn being carried by said supporting structure and removably positionable within said nip, with the axis of said horn being transverse to said nip, said tip having serrated surfaces defining a plurality of intermixing channels, and
• a control circuit adapted to position said tip within said nip, to actuate said ultrasonic horn, and to operate said driven roller,
• whereby said sheets may be welded together along proximate edges with a strong and uniform seam.

Apparatus for welding two sheets of themoplastic material together along proximate edges of said sheets to form a welded seam, said apparatus including

• a supporting frame,
• an upper and a lower joining roller, separate upper and lower arms securing said upper and said lower rollers, respectively, to said frame, with said rollers having parallel axes and forming a nip therebetween, said nip having an axis parallel to said axes, whereby said sheets may be brought together in overlapping relationship in said nip,
• means for driving at least one of said rollers,
• a horn having a tip thereon, said tip having a leading edge running transverse to the longitudinal dimension of said horn, and means for mounting said horn on said supporting frame with said tip proximate to said nip with the leading edge of said tip parallel to the axis of said nip, and
• means for reciprocating said horn and said tip at ultrasonic frequencies, said last-named means including an ultrasonic transducer,
• whereby said sheets may be overlapped within said nip and said reciprocating tip will rub against the inner surface of said sheets and create frictional heat energy sufficient to melt said material and so weld said sheets together.

The method of welding together proximate edges of sheets of thermoplastic material including the steps of

• continuously moving said proximate edges together so said sheets overlap and form a nip,
• melting the inner surfaces of said sheets as they are moved together,
• generating frictional heat energy proximate to said nip to cause said melting by rapidly reciprocating a horn tip against said inner surfaces, said reciprocation being in a direction transverse to the axis of said nip, and
• pressing said surface together in said nip as said melting sheets cool.