A Study on Rationalization of Line Heating Process by Oxy-acetylene Flame for Plate Bending of Ship Steels

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Line heating process with oxy-acetylene flame is widely used for plate bending and/or flame straightening of steel paltes in ship-yard production. Main aims of the study are to find a relation between several heating conditions and induced angular distortions, and to clarify formation mechanism of it. A series ofexperimental studies for line heating of steel plates are performed. Also, a number of numerical calculations based on the finite element method are executed for temperature distribution in a section taken transverse to the heating direction. Comparing with the measured and calculated temperature distributions, it is found that the heat flux distribution of flame can be expressed approximately by superposition of two gaussian distributions. Heat efficiency of the oxy-acetylene flames is estimated in a similar way. An empirical formula to predict the amount of angular distortions as a function of heating conditions and plate thickness is derived from the experimentally obtained results. Two-dimensional elastoplastic thermal stress analyses using the finite element method are executed for the above-mentioned sections. It is shown that though the problem is essentially three-dimensional, the situation of angular distortion may be simulated by the two-dimensional analysis if vertical displacement on the back surface of the section is constrained until a time required for which the center of the heat source proceeds a few distance after passing through the section.