a plastic closure device must be welded by means of ultrasound onto a tubular bag consisting of a multilayer plastic film . for this purpose , an energy introduction arrangement on the underside of a flange is proposed , in which at least one energy conduction rib concentric with the outer edge of the flange is present , as well as a plurality of outwardly - directed energy conduction ribs . these energy conduction ribs can intersect in the region of intersection or they can be interrupted in the region of intersection .