Device for welding a zip seal in a tobacco pouch, said device comprising; - a sheet supply to provide at least one pliable sheet forming a first wall and an opposite second wall of the tobacco pouch, - a zip seal supply to provide a zip seal comprising a first zip strip and a mating second zip strip, - a guide to position the zip seal in a welding position between the first wall and the second wall, - a welding unit to weld the first zip strip to the first wall and the second zip strip to the second wall, while the zip seal is located in the welding position, - a conveyer to convey the at least one sheet and the zip seal in a conveying direction through the guide and the welding unit, wherein -- the welding unit is an ultrasonic welding unit comprising a first welding head which vibrates against the first wall to weld the first zip strip on the first wall and a second welding head which vibrates against the second wall to weld the second zip strip on the second wall, -- the conveyer continuously conveys the at least one sheet and the zip seal through the welding unit, -- the first welding head and the second welding head are located in a fixed position when seen in the conveying direction, and characterised in that; -- the conveyer continuously moves the at least one sheet and the zip seal relative to the first welding head and the second welding head, while the first welding head and the second welding head vibrate against the first wall and second wall, respectively, -- the welding unit comprises an anvil located between the first welding head and the second welding head, -- in the welding position, the first wall and the first zip strip are located between the first welding head and the anvil, and the first zip strip is pressed against the anvil by the vibrating first welding head, and -- in the welding position, the second wall and the second zip strip are located between the second welding head and the anvil, and the second zip strip is pressed against the anvil by the vibrating second welding head. - a sheet supply to provide at least one pliable sheet forming a first wall and an opposite second wall of the tobacco pouch, - a zip seal supply to provide a zip seal comprising a first zip strip and a mating second zip strip, - a guide to position the zip seal in a welding position between the first wall and the second wall, - a welding unit to weld the first zip strip to the first wall and the second zip strip to the second wall, while the zip seal is located in the welding position, - a conveyer to convey the at least one sheet and the zip seal in a conveying direction through the guide and the welding unit, wherein -- the welding unit is an ultrasonic welding unit comprising a first welding head which vibrates against the first wall to weld the first zip strip on the first wall and a second welding head which vibrates against the second wall to weld the second zip strip on the second wall, -- the conveyer continuously conveys the at least one sheet and the zip seal through the welding unit, -- the first welding head and the second welding head are located in a fixed position when seen in the conveying direction, and characterised in that; -- the conveyer continuously moves the at least one sheet and the zip seal relative to the first welding head and the second welding head, while the first welding head and the second welding head vibrate against the first wall and second wall, respectively, -- the welding unit comprises an anvil located between the first welding head and the second welding head, -- in the welding position, the first wall and the first zip strip are located between the first welding head and the anvil, and the first zip strip is pressed against the anvil by the vibrating first welding head, and -- in the welding position, the second wall and the second zip strip are located between the second welding head and the anvil, and the second zip strip is pressed against the anvil by the vibrating second welding head. -- the welding unit is an ultrasonic welding unit comprising a first welding head which vibrates against the first wall to weld the first zip strip on the first wall and a second welding head which vibrates against the second wall to weld the second zip strip on the second wall, -- the conveyer continuously conveys the at least one sheet and the zip seal through the welding unit, -- the first welding head and the second welding head are located in a fixed position when seen in the conveying direction, and characterised in that; -- the conveyer continuously moves the at least one sheet and the zip seal relative to the first welding head and the second welding head, while the first welding head and the second welding head vibrate against the first wall and second wall, respectively, -- the welding unit comprises an anvil located between the first welding head and the second welding head, -- in the welding position, the first wall and the first zip strip are located between the first welding head and the anvil, and the first zip strip is pressed against the anvil by the vibrating first welding head, and -- in the welding position, the second wall and the second zip strip are located between the second welding head and the anvil, and the second zip strip is pressed against the anvil by the vibrating second welding head.