Patent ID: 7892375

Claim:
An apparatus for forming an ultrasonic weld at least partially across, and between, two or more webs of sheet material as they pass through a sealing gap in the apparatus, the apparatus comprising: a sonotrode comprising an ultrasonic actuator coupled to an elongate sealing end face for delivering ultrasonic energy to the webs in the sealing gap; and a rotating cylindrical anvil having at least one raised portion extending longitudinally along an outer surface thereof, said raised portion having a radially outer surface, whereby said sealing gap is defined intermittently between the end face of the sonotrode and the radially outer surface of the raised portion of the anvil as the raised portion rotates past the end face of the sonotrode; wherein the elongate sealing end face of the sonotrode has a substantially helical surface, whereby the sealing gap travels helically along said surface as the raised portion of the anvil cylinder rotates past the end face of the sonotrode.