Study on the Relationship between the Heat Transfer Characteristics of Preheating Gas and Cutting Performance of Oxyfuel Gas Cutting

Plate temperature and heat input in oxyfuel gas cutting process with H2/LP gas and LPG flame are calculated by 3-dimensional FE heat conduction analyses. FE analyses are performed by using moving coordinates, and cutting groove temperature is determined by iterative calculation. The 2-dimensional groove temperature distribution determined by Matsuyama's theory is chosen as the initial values in this iterative calculation. The heat transfer properties of the preheating flame are determined by using the GA-based heat transfer estimation technique proposed in the previous report. The validity of the proposed numerical procedure and the accuracy of the determined groove temperature are examined by comparing the calculated and measured plate temperature and HAZ sizes. Heat input due to preheating, qG, and that due to self burning of steel, qB, are estimated in these analyses, and they are compared with the heat inputs estimated by Wells' and modified Wells' equations. The relation between the heat transfer characteristics of the preheating gas flame and plate temperature distribution is examined, and the cutting performance improvement mechanisms of Hydrogen preheating are discussed. As results, followings are found: 1) The 3-dimensional groove temperature distribution can be calculated by performing the iterative analyses procedure proposed in this study; 2) The critical cutting speed can be estimated once the gas heat transfer parameters are known; 3) It is not appropriate to evaluate the magnitude of cutting thermal deformation only from the preheating gas's total calorific value; 4) Under the conditions chosen, the heat generated by self burning is inadequate to maintain the cutting process, and it is essential to supplement heat by preheating; 5) The faster cutting speed and smaller total heat input of H2/LP gas are results of the larger local heat transfer coefficient below the gas ejection hole. It is supposed that the improvement in oxyfuel gas cutting performance can be achieved by modifying the heating apparatus so that the local heat transfer coefficient becomes larger.