ONE SIDE WELDING APPARATUS

PROBLEM TO BE SOLVED: To sufficiently clamp steel plates to be welded regardless of the plate thicknesses of the plates in a simple structure by utilizing the force pushing down the welding steel plates abutted at side edges as the attracting force of a first and a second magnetic attracting devices due to the weights of a first and a second magnetic bodies and the thickness of each welding steel plate and each magnetic body. SOLUTION: A welder 10 disposed on a carrier 18 so as to be freely movable along a welding line 3 is moved above the welding line 3 to perform one side welding on steel plates 2, 2 along the welding line 3. In this one side welding apparatus 1, a first and a second clamping means respectively constituted of a first and a second clamp beans 20, 21 for clamping the welding steel plates 2, 2 and a first and a second electro magnets 30 (31) just below the clamp beams are arranged. These devices are positioned outside a backing device 5 in the direction parallel with the welding line 3 and disposed on each welding steel plate 2, 2. The weight of the clamp beams 20, 21 is decided considering e.g. the plate thickness T1 of a magnetic hollow body of a steel material, etc., having a rectangular cross section at the abutting side on the welding steel plates 2, 2.