An apparatus and method for sealing an open end of a cardboard-based container containing a powder. A transporter is configured to transport a flow of containers to and from an inductive welding unit. The transporter includes a feeding arrangement to separate the containers and a main conveyor member to convey the spaced containers. A movable gripping arrangement is configured to simultaneously grip at least two containers and simultaneously transfer these containers from the main conveyor member to the welding unit. The welding unit is configured to simultaneously fasten a lid to each of the simultaneously transferred containers.