A button-fastening upper die includes a die body, a button-holding member and a cylindrical elastic member arranged between the die body and the button-holding member. By providing the elastic member with an annular recess recessed radially outward from the inner surface e.g. at the middle of the surface, the elastic member is sectioned into a thin-walled section located radially outward from the recess and two or more thick-walled sections remaining above and below the recess and the thin-walled section.

An inductor for transverse sealing a packaging material tube filled with food product comprises a main body comprising first and second sealing surfaces facing the packaging material during a sealing state, a recess in the main body for receiving a knife during a cutting state, and an electric conductor arrangement, in the main body for inducing eddy currents in the packaging material during the sealing state. The first/second sealing surfaces each comprise a top section, an inner sealing section between the recess and the top section, and an outer sealing section between the top section and an outer edge of the inductor. The inner sealing section is inclined towards the recess, and the outer sealing section is inclined towards the outer edge, so that product in the tube is pushed away from a sealing band of the tube as the first/second sealing surfaces are pressed towards the sealing band.

A method for transversally sealing a packaging material tube, comprises placing a transversal sealing section of the tube between a sonotrode and an anvil. The transversal sealing section comprises a first two-layer sub-section, a three-layer sub-section and a second two-layer sub-section, transmitting ultrasonic acoustic vibrations, having a frequency and an amplitude, from the sonotrode into the transversal sealing section, thereby melting the plastic foil in the transversal sealing section, and pressing the tube together between the sonotrode and the anvil to bond the plastic foil such that transversal sealing is formed. The anvil has a ridge comprising various sub-sections for receiving various ones of the sub-sections of the tube, wherein the ridge has equal height in at least some of the sub-sections. The frequency, amplitude, pressure and paperboard properties are chosen to achieve equal temperature in the first two-layer sub-section, the three-layer sub-section and the second two-layer sub-section.