| 摘要 |
An extruder die head comprises an internal cylindrical mandrel and a shell, which encloses the mandrel concentrically. Between the mandrel and shell an annular channel is formed, which is connected to an annular die slit. A polymer melt is fed through a line to the annular channel. To prevent the polymer melt in the area of the start of the annular channel from penetrating into any spaces that form between the mandrel and the shell due to differential thermal expansion, a ring is located between the mandrel and the shell. The material of the ring is chosen to have a coefficient of thermal expansion such that when the die head is heated up due to the polymer melt, the ring seals any spaces between the shell and the mandrel. In an alternative arrangement, the materials of the mandrel and the shell are chosen such that the seat, which connects the mandrel to the shell and is located below the annular channel, becomes more tightly sealed on heating.
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