| 摘要 |
Three embodiments of an expandable screen are described. In the preferred embodiment, the base layer, filtering layer, and outer layer are joined together in a sintering furnace in the form of a flat sheet which is in turn rolled up. The layered sheet is then formed into a tube by rolling it to make a longitudinal or spiral joint which is welded with connections placed on ends. In an alternative embodiment, the base layer and filtering layer are sintered together and formed into a tube which is in turn inserted into an outer protective tube. In a third embodiment, a base pipe is perforated and its exterior surface threaded. A wire runs through the threads with a protective jacket over the underlying assembly. Upon expansion, the opening sizes remain relatively constant.
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