A device for ultrasonic sealing includes a drive unit, a horn with a long and narrow sealing surface, and one or more reaction bodies which at least partially surround the drive unit. The length of the device consists of a half wave length.

An ultrasound sealing unit includes a drive unit and a body. The drive unit consists of a number of piezoelectric ceramic plates with interjacent, conductive metal sheets connected to an a.c. source. The drive unit further consists of a counterweight and a clamping screw. The clamping screw holds together under a certain pretensioning the ceramic plates, the metal sheets and the counterweight. Moreover, the clamping screw fixedly secures the drive unit to the body. The body is a homogeneous body consisting of reaction bodies which surround the drive unit, a nodal plane with an anchorage edge and a horn with an elongate, narrow sealing surface. A gasket is disposed so that it constitutes a spacer between the body of the sealing unit and the ceramic plates. The gasket permits the oscillation of the ultrasound sealing unit, but prevents residual flexural stresses from reaching the drive unit. The spacing dimension of the gasket may be selected so as to govern the amplitude of the sealing unit to a predetermined, preselected amplitude.

The invention relates to a method for steering resonance frequencies of interfering oscillation modes. The invention is applicable to that type of ultrasound sealing unit (1) which has a drive unit (2), centrally placed above the point of intersection between the two planes of symmetry (8) into which the sealing unit may be divided. The sealing unit (1) has reaction bodies (3) surrounding the drive unit (2), and a horn (4) with an elongate, narrow sealing surface (5). The sealing unit has a nodal plane between the reaction bodies (3) and the horn (4) in which plane the sealing unit is fixed with the aid of the anchorage edge (7). The resonance frequencies of the interfering oscillation modes which negatively influence the function of the sealing unit are steered in that symmetrically placed grooves (9) are provided in the reaction bodies (3). The grooves (9) are placed where the interfering oscillation modes have a maximum of potential, or alternatively a maximum of displacement.

The invention relates to an arrangement in a drive unit (2) for an ultrasound sealing unit (1). The drive unit (2) is of the type which has a number of piezoelectric ceramic plates (7) disposed with interjacent, conductive metal sheets (8) coupled to an a.c. source. The ceramic plates (7) and the metal sheets (8) are held together with a counterweight (9) by a clamping screw (10) which partly secures the drive unit (2) to the ultrasound sealing unit (1), and partly realises a clamping force on the drive unit (2). The counterweight (9) has an inner and an outer diameter. In order to obtain a uniform pressure loading on the ceramic plates (7), a groove (12) is provided in the inner diameter of the counterweight (9).