With complex bicomponent fiber cross sections, such as segmented, splittable pie fibers, very small changes in the melt viscosity can have dramatic effects on the shape and splitability of the fibers.

To solve this problem, it is necessary not only to have excellent temperature control of the polymer distribution system, but also to maintain uniform residence times in the filtration systems. This is necessary even though in many bicomponent spinning lines, the polymer flow rates may be changed frequently.

The new filter is a continuous extended area type of filter, using standard Memtec candle filter elements. For optimum uniformity and minimum polymer degradation, each element is totally enclosed in its own housing, with sliding spool valves to direct the polymer flow to and from the housing. The individual housings are arranged together in a common structure, with common inlet and outlet ports. The capacity of the system may be easily varied by the number and size of the filter elements.

One of the unique features of the filter, is that the polymer cavity in each housing is slightly tapered such that the polymer flow velocity is varied along the length of the filter. This gives the polymer approximately constant residence time as it travels along the length of the filter element.

Another feature of the filter is that individual filter elements may be added or removed from the polymer streams, in order to allow more constant residence times as the polymer flows are changed to obtain different bicomponent polymer ratios. This feature also means that contaminated elements may be individually changed without interrupting the polymer process or causing a major disruption in spinning.

When a filter in any one of the assemblies requires cleaning or replacement, the valves are closed to prevent flow into and out of the clogged assembly. A small amount of polymer is bled from the selected assembly to effect depressurization, and the assembly is removed and replaced. The inlet valve is then opened to allow slow bleeding of polymer into the restored assembly and the bleed valve is opened to allow air and entrapped polymer to be removed from the assembly, before placing it back in service. When the bleed valve flow has stabilized, the outlet valve is opened to allow full flow to be re-established.

Specific design features of the system are covered by US patents.

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