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

氧乙炔火焰线加热工艺是船厂生产中广泛应用于钢板弯曲和/或火焰矫直的工艺。研究的主要目的是找出几种加热条件与引起的角畸变之间的关系，并阐明角畸变的形成机理。对钢板的线加热进行了一系列的实验研究。此外，基于有限元方法对加热方向横向截面内的温度分布进行了数值计算。通过与实测和计算温度分布的比较，发现火焰的热流密度分布可以近似地表示为两个高斯分布的叠加。氧乙炔火焰的热效率用类似的方法估算。根据实验结果，推导出了角变形量随加热条件和板厚变化的经验公式。采用有限元法对上述截面进行了二维弹塑性热应力分析。结果表明，虽然问题本质上是三维的，但如果将截面后表面的垂直位移限制到热源中心穿过截面后走了一段距离所需的时间，则可以用二维分析来模拟角畸变的情况。

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.