Research And Application Of Preheating Control Equipment Technology For Thermite Welding

This paper has used a preheating control equipment to regulate and control the preheat gas flow in the preheating process of thermite welding.The working principle of this equipment is that the Mass Flow Controllers can be adjusted by PLC in accordance with the commands,and the data will be fed back to touch panel with the adjustment completed so as to achieve closed loop control.This equipment is applied in a series of tests and field applications.The 60 kg/m U75V rail under different preheat flow parameters are to be measured by means of contact temperature measurement.The experiment results demonstrate that the preheat temperature of different parts of the rail section will vary with the change of the preheating control equipment flow,namely,the preheating control equipment can effectively regulate the preheating process;the temperature distribution of the section is more uniform with the preheating completed when the rates of preheated flows of oxygen and propane are respectively 100 L/min and 36 L/min.The temperature measurements of different rail slot have been conducted with the above flow parameters.The experiment results demonstrate that the above preheating parameters can be used in preheating if the rail slot is 28mm-34 mm;but obviously,the rail jaw is preheated insufficiently when the rail slot is 26mm;it's not suitable for thermite welding when the rail slot is less than 25mm,since flame in the preheating lance is blocked by the rail head,resulting in a too high preheat temperature at the rail head and a too low preheat temperature at the bottom of the rail.In the optimizing experiments of the above flow parameters,the results show that adjustments of propane flow from the 4th min can help enhance the preheating of the rail head section.The mechanical properties of the welded joints will meet the standards in the welding test where the above preheating flow parameters are applied.This preheating control equipment has been applied for the plateau groove rail thermite welding and the welded joints are with good performance.