| 摘要 |
<p>Tools for injection moulding elongated hollow mouldings where the mandrel for forming the core cavity is surrounded by a tubular sleeve which can be retracted independently of the cor mandrel. The sleeve is withdrawn as the melt front advances, so that all parts of the core mandrel remain supported either by the sleeve or by the melt. The core is retracted after the melt has set, to allow the mouldings to be ejected from the mould cavity. Tools are suitable for moulding shapes such as knitting needles with a coaxial cavity open at only one end to accept a reinforcing rod. The sleeve inhibits misalignment or bending of the core by non uniform hydrostatic pressures near the tip of the core.</p> |
