Method of preventing sag of panel and apparatus therefor

摘要

A method and apparatus for preventing a sag of a panel, in which plate to be attached to a skeleton is located on the skeleton supported by a support means, both end parts of the plate are gripped by grasp electrodes of a resistance heating device, current is caused to flow through the plate by the grasp electrodes so as to preheat the plate to a predetermined temperature and to thermally expand it, the plate is welded to the skeleton by a welding machine, and a residual tensile stress is developed in the plate by the thermal shrinkage deformation attendant upon cooling of the plate after the welding. In the case where the plate has a cut-away part, electric conduction members for short-circuiting the cut-away part are interposed in this part so as to form electric conduction paths for the preheating of the plate.