| 摘要 |
PURPOSE:To produce easily and correctly the root gap between the end part of a material to be welded and base material by providing plural projections for securing the root gap on the outer peripheral face of the backing jig for welding. CONSTITUTION:A backing jig 1 is placed on the upper face of a box B and moved downward until abutting a column A to a projection 3 with the state of inserting the backing jig 1 into the end part of the column A in case of performing a butt welding of the end part of the column A of a housing frame to the upper face of a joint box B. The root gap H between the end part of the column A and the upper face of the joint box B can be correctly produced because of the bottom face of the backing jig 1 and the back face 4 of the projection 3 abutting the upper face of the joint box B and the upper end of the projection 3 abutting the end part of the column A with above state. The weld of an arc welding, etc. are made thereafter on the space part between the end part of the column A and the upper face of the joint box B.
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