A welding apparatus for welding overlapping plastic material webs along edges of the overlapping plastic material webs, the welding apparatus including a chassis; and a heating device arranged at the chassis and configured for melting the edges of the overlapping plastic material webs, wherein the chassis includes a support frame which includes at least two running rollers that are arranged offset from each other, at least two pressing and feed rollers that are arranged opposite to each other, wherein a lower pressing and feed roller of the at least two running and feed rollers is fixated at the support frame and an upper pressing and feed roller of the at least two running and feed rollers is pivotably supported at the support frame, and at least one drive unit with a transmission, wherein the at least two running rollers are configured for supporting the chassis on a base.