This invention pertains to apparatus and methods for processing workpieces on a moving continuous web using ultrasonic energy. The ultrasonic system includes one or more sets, each set containing first and second ultrasonic application devices, corresponding to an ultrasonic horn and a corresponding anvil. A first element of the set is mounted on a rotating work drum which carries the web of workpieces while the workpieces are being processed with ultrasonic energy. The second element of the set is mounted for rotation with the work drum. As the work drum rotates, the second element rotates with the drum. With each rotation of the work drum, the second element extends over the work drum and the first element, ultrasonic energy is applied to the workpiece, and the second element withdraws from over the work drum and the first element.