초록 ▼

An improved continuous polymer filter of the screen belt type employs a valve arrangement to selectively apportion the extruder output flow through at least two filter paths. In the neutral valve position both filter paths receive polymer at equal flow rates creating a pressure across the screen bel

An improved continuous polymer filter of the screen belt type employs a valve arrangement to selectively apportion the extruder output flow through at least two filter paths. In the neutral valve position both filter paths receive polymer at equal flow rates creating a pressure across the screen belts that is too high to permit the screen belts to be advanced when a clogged belt section requires replacement with a clean section. To effect screen belt advancement, the valve is actuated to reduce the flow rate in the filter path requiring the replacement while increasing the flow rate to the same degree in the other filter path so that the net flow rate remains substantially constant. The screen belt receiving the reduced flow experiences a sufficiently reduced pressure drop thereacross to permit it to be advanced in a conventional manner, after which the valve is returned to its neutral state. The screen belts in both paths are advanced alternately while maintaining a constant net flow and assuring sufficient flow through the reduced flow path to avoid entry of air into the filter path. Valve actuation and screen belt advancement may be effected automatically and in synchronization in response to a pre-set timer, to detected pressure conditions in the flowing polymer, or other parameters.

대표청구항 ▼

A method for filtering flowing molten polymer material comprising the steps of: (a) flowing the molten polymer through a plurality of flow paths; (b) combining the molten polymer from all of said flow paths into a common output flow; (c) extending across each of said flow paths a respective strip of

A method for filtering flowing molten polymer material comprising the steps of: (a) flowing the molten polymer through a plurality of flow paths; (b) combining the molten polymer from all of said flow paths into a common output flow; (c) extending across each of said flow paths a respective strip of filter material such that all polymer flowing through that flow path must pass through a selected length section of the filter strip; then (d) selectively reducing the flow rate of polymer through one of said flow paths in which the filter strip is to be advanced lengthwise to present a clean length section of the strip to the flowing polymer; (e) advancing the filter strip in said one flow path while the polymer flow rate therethrough is reduced in accordance with step (d) until said clean length section of the advanced filter strip is disposed in said one flow path; and then (f) restoring the flow rate through said one flow path to the flow rate present prior to step (d). A continuous polymer filter apparatus comprising: supply means for delivering molten polymer under pressure; means defining first and second separate filter paths; valve means for receiving the delivered molten polymer and selectively apportioning it between said first and second filter paths, said valve means having a normally neutral position in which the flow rates through said filter paths are substantially equal, a first extreme position in which the flow rate of polymer through said first filter path is substantially unrestricted and the flow rate through said second filter path is present but severely restricted, and a second extreme position in which the flow rate of polymer through said second filter path is substantially unrestricted and the flow rate through said first filter path is present but severely restricted; first and second filter screen belts extending substantially transversely through said first and second filter paths, respectively, each screen belt being movable through its respective filter path, when the flow rate through said respective filter path is restricted, to change longitudinal sections of the screen belt through which apportioned polymer flows; first screen advance means, selectively operable only when flow through said first filter path is restricted by said valve means, to advance said first screen belt across said first filter path; second screen advance means, selectively operable only when flow through said second filter path is restricted by said valve means, to advance said second screen belt across said second filter path; and means for combining polymer flow from said first and second filter paths in a common flow path.