| 摘要 |
<p>A central body portion has first, second and third concentric cylinders of successively increasing diameter encircling the central body portion and each other in spaced relationship to form three concentric annular spaces for receiving molten material. Only one end of each of the first, second and third cylinders and the body portion are rigidly attached to each other so as to maintain the rigid spaced relationship. A mandrel is attached to the outer end of the central body portion and a die is attached to the outer end of the outer most concentric cylinder in spaced relationship to the mandrel to shape the molten material into a pipe having a multi-layered wall.</p> |
