Shrinkage of Pipe due to Annular Limited Heating
Toshiaki Araki, Takeshi Yamada, Hiroyuki Matsumura, Toshiharu Nomoto
Thermal plastic process for reducing a diameter of metal pipe by heating an annular limited section of the pipe while cooling adjacent sections has been developed.
This report is concerned with the method of the process, its principle and the effect of parameters for shrinkage of pipe.
The principle of shrinkage of pipe is explained that the limited section of pipe heated by an annular induction coil tends to radially expand outwardly. However, due to the self-restriction against thermal expansion and reducing the yielding strength because of high temperature condition, the heated section's diameter is not increased so much as that of free expansion. As a result, a diameter of thermal plastic processed part is reduced in comparison with initial one after cooling.
As for the parameters, maximum temperature, coil length, diameter, wall-thickness and number of repetition are given. Effects of parameters for shrinkage of pipe are as follows.
As maximum temperature becomes higher and coil length becomes shorter, the shrinkage of pipe is increased. And as diameter and wall-thickness of the pipe become bigger respectively, the shrinkage is increased slightly.
Furthermore, if this process is repeated for the same pipe, the shrinkage is increased.