Pipe bending process using high frequency local induction is an advanced process to bend pipes with a small bending radius and a large diameter. Bent pipes are widely used in power, chemical plants, shipbuilding, and several areas of construction to shorten the lead-time, instead of the traditional ...
Pipe bending process using high frequency local induction is an advanced process to bend pipes with a small bending radius and a large diameter. Bent pipes are widely used in power, chemical plants, shipbuilding, and several areas of construction to shorten the lead-time, instead of the traditional elbows that lead to enormous welding process. Even though the pipe bending process is a quite widespread engineering practice, the bending process depends heavily upon trial-and-error method by field engineers with several years of experience. So it is necessary to develop integrated methodology for optimum design of pipe bending process. Induction heating involves placing an electrically conducting workpiece in a varying magnetic field. The magnetic field induces is generally referred to as an eddy current. The workpiece heats up because it has a resistance to the eddy current flow. The induction heating of the workpiece is dependent on the magnitude of electric current flowing in the workpiece, the resistivity of the workpiece, and the depth of current penetration. The goal of induction heating for forging is to uniformly heat a workpiece to the proper forging temperature. 87% of the induced energy is generated within the depth of current penetration. This is described as the skin effect of induction heating. Since most of the energy goes into the depth of penetration, time must be provided to allow the energy to soak into the center of the workpiece. During the bending of a pipe, the outside wall is thinned by tensile stress and the inside wall is thickened by the compression stress. In engineering design, the thinning of pipe wall is not allowed to exceed 12.5% because pipe bent is used as transport pipe of fluid which state high pressure and temperature, so the bending radius is generally greater 3.5 time than the outside diameter of the pipe when using conventional pipe-bending techniques with local induction heating. Therefore, in order to satisfy design requirement in small bending radius, it is necessary to load axial compressive force in pipe bending process and give circumferential temperature gradient in induction heating process. For the calculation of reverse moment, it is very important to consider effects of each process parameters such as pipe dimension, bending radius, pipe feeding velocity and heating condition. For the determination of circumferential temperature gradient, it is very important to determine heating width, clearance between pipe and heating coil and cooling condition. But previous researchers only have been interested in the prediction of the reverse moment concern with one process parameter or simple process parameters. However, practical hot pipe bending process has many flexible and various process parameters should be considered, and besides these is rare previous work for the investigation of proper temperature gradient. Therefore, practical pipe bending process requires integrated process design method that explores the relations between several process parameters. The main objective of the present study is process design for the pipe bending process with small bending radius high frequency local induction heating to satisfy design requirement. There are two fields to be designed in the hot pipe bending process. One is bending process by bending machine and the other is induction heating process. So, for this purpose, pipe bending mechanism is theoretically examined in order to estimate that each process parameters have an effect on bending process. FE model is established and FE analysis is performed for verification of propriety of theoretical analysis and obtaining the optimum conditions of process parameters, especially reverse moment and circumferential temperature gradient. And then, as the induction heating program have been developed on the basis of finite difference method(FDM), it is investigated to get optimum induction heating and cooling condition which are obtained by FE analysis for the distribution of uniform temperature and the proper circumferential temperature gradient. The next, pipe bending program has been developed using theoretical analysis results and material test data on hot temperature. Also, the results of theoretical, finite element analysis and developed programs have been verified through the experiment of pipe bending.
Pipe bending process using high frequency local induction is an advanced process to bend pipes with a small bending radius and a large diameter. Bent pipes are widely used in power, chemical plants, shipbuilding, and several areas of construction to shorten the lead-time, instead of the traditional elbows that lead to enormous welding process. Even though the pipe bending process is a quite widespread engineering practice, the bending process depends heavily upon trial-and-error method by field engineers with several years of experience. So it is necessary to develop integrated methodology for optimum design of pipe bending process. Induction heating involves placing an electrically conducting workpiece in a varying magnetic field. The magnetic field induces is generally referred to as an eddy current. The workpiece heats up because it has a resistance to the eddy current flow. The induction heating of the workpiece is dependent on the magnitude of electric current flowing in the workpiece, the resistivity of the workpiece, and the depth of current penetration. The goal of induction heating for forging is to uniformly heat a workpiece to the proper forging temperature. 87% of the induced energy is generated within the depth of current penetration. This is described as the skin effect of induction heating. Since most of the energy goes into the depth of penetration, time must be provided to allow the energy to soak into the center of the workpiece. During the bending of a pipe, the outside wall is thinned by tensile stress and the inside wall is thickened by the compression stress. In engineering design, the thinning of pipe wall is not allowed to exceed 12.5% because pipe bent is used as transport pipe of fluid which state high pressure and temperature, so the bending radius is generally greater 3.5 time than the outside diameter of the pipe when using conventional pipe-bending techniques with local induction heating. Therefore, in order to satisfy design requirement in small bending radius, it is necessary to load axial compressive force in pipe bending process and give circumferential temperature gradient in induction heating process. For the calculation of reverse moment, it is very important to consider effects of each process parameters such as pipe dimension, bending radius, pipe feeding velocity and heating condition. For the determination of circumferential temperature gradient, it is very important to determine heating width, clearance between pipe and heating coil and cooling condition. But previous researchers only have been interested in the prediction of the reverse moment concern with one process parameter or simple process parameters. However, practical hot pipe bending process has many flexible and various process parameters should be considered, and besides these is rare previous work for the investigation of proper temperature gradient. Therefore, practical pipe bending process requires integrated process design method that explores the relations between several process parameters. The main objective of the present study is process design for the pipe bending process with small bending radius high frequency local induction heating to satisfy design requirement. There are two fields to be designed in the hot pipe bending process. One is bending process by bending machine and the other is induction heating process. So, for this purpose, pipe bending mechanism is theoretically examined in order to estimate that each process parameters have an effect on bending process. FE model is established and FE analysis is performed for verification of propriety of theoretical analysis and obtaining the optimum conditions of process parameters, especially reverse moment and circumferential temperature gradient. And then, as the induction heating program have been developed on the basis of finite difference method(FDM), it is investigated to get optimum induction heating and cooling condition which are obtained by FE analysis for the distribution of uniform temperature and the proper circumferential temperature gradient. The next, pipe bending program has been developed using theoretical analysis results and material test data on hot temperature. Also, the results of theoretical, finite element analysis and developed programs have been verified through the experiment of pipe bending.
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#파이프벤딩 high frequency local induction heating 고주파 유도가열 pipe bending
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