A welding unit for welding rails of a track includes a shearing device for removing a weld bead. The shearing device includes a head part having a shearing edge and two side parts which are pivotable towards one another and have a shearing edge. A rail base section to be applied to a rail base is associated with each side part. The rail base sections each include an end region facing towards each another having a tooth system for a form-locking connection which is effective in a longitudinal direction of the rail after the two side parts have been applied to the rail.