| 摘要 |
An injection molding apparatus ( 10, 110 ) for molding an annular thermoplastic element, such as an annular closure element (E) with no more than a single weldline in the annular extent of the thermoplastic element. The thermoplastic element is molded in an annular mold cavity ( 12, 112 ), and moldable thermoplastic material (M) is introduced into the mold cavity from a coaxially-aligned annular flow path ( 18, 118 ) that is defined between a sliding sleeve ( 24, 124 ) and an annular member ( 22, 122 ). The sliding sleeve surrounds and is slideable with respect to a fixed pin ( 26, 126 ) and is slideable between a first, or forward, position, where no thermoplastic material can flow into the mold cavity, and a second, or rearward, position, where thermoplastic material can flow into the mold cavity. Thermoplastic material is introduced into the annular flow path, at a location upstream of the second position of the sliding sleeve, in a single stream through a passage ( 28, 128 ) to limit the weldlines in the molded thermoplastic element to no more than one.
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