Large Pipe Of Three-point Bending Press Straightening Technology Research

In the production and processing, due to welding thermal stress and inhomogeneity ofthe material properties, large-diameter longitudinal seam weld steel pipe caused bending,which does not conform to the requirements of operation and needs to bestraightened .The way of being straightened to use pressure straightening because of theparticularity of the large welded pipe. Pressure straightening method is based on the staticload and bend backward deformation in order to achieve the parts produced straightening,so the process is also called corner straightening technology. Scholars both at home andabroad on the pressure straightening research is not a few, but more focus on thecalculation of the quantity of compressive deformation, not intuitive reaction straighteningprocess, so it is necessary to research on its theory.Three-point bending is the basic mechanical model of pressure straightening, thispaper, based on the assumption of small deformation and corner straightening equivalenceprinciple, using the bilinear material hardening model established the mathematical modelof pressure straightening of pipe, obtained the corresponding with the initial curvaturestraightening bending moment distribution, and based on this, puts forward some specificstraightening scheme. First of all, measured straightening pipe initial deflectiondistribution, through the curve fitting, get its corresponding initial curvature distribution.Then, according to the theory analysis will get completely straightening the pipe bendingmoment distribution. Finally, the bending moment for discretization, obtained multiplethree-point bending corresponding load size and the position of the pressure point andfulcrum. It provides theoretical guide for production practice, and rationale for fitting to beautomatic straightening.In this paper, the measured length of 12m for large-diameter longitudinal seam weldsteel pipe straightening maximum deflection for 60-75mm, according to the physicalsimilarity, the maximum deflection of 1m long, for 4-10mm steel tube are theory analyzed,obtained the corresponding straightening scheme. Based on the scheme, numericalsimulation and experimental research, both results show that the scheme can straightening of steel tube, which verify the correctness of the theory and straightening schemefeasibility and reliability. And gives correction factor of three-point bending straighteningload, put forward the pieces of the three- point bending corner straightening controlstrategy , which can reduce the number of straightening, improve the efficiency of thestraightening.Studies of whole thesis will enrich straightening technology theory and have wellengineering value.