A radially expansible press plunger has a base plate, a first expansion tool and a second expansion tool. The first expansion tool and the second expansion tool are movable in relation to each other in the axial direction. The first expansion tool has at least one inclined plane surface. The second expansion tool has at least one inclined plane surface corresponding to the at least one inclined plane surface on the first expansion tool. Each inclined plane surface on the first expansion tool contacts and applies pressure to the corresponding inclined plane surface of the second expansion tool when the expansible press plunger is in the radially expanded state. An attachment unit for attaching a container sealing element to a container body and a method for attaching a container sealing element to a container body are also disclosed.

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.

A method (400) for assessing quality of a transversal sealing (102) of a paperboard-based food package (100), wherein the food package (100) comprises a longitudinal scaling (104), and is provided with an reference imprint (106) in connection to the transversal sealing (102) is provided. The method (400) comprising, capturing (S402), by a camera (202), image data of the transversal scaling (102), determining (S404), in the image data, a position of the reference imprint (106), determining (S406), in the image data, a position of a reference line (104), determining (S408) quality measurement data of the transversal sealing (102) based on the position of the reference imprint (106) relative to the position of the reference line (104).