Method of using multiple stressed sealing plugs to filter polymeric material

In a process for filtering a substance which is capable of being annealed by heating and cooling same, which has a high coefficient of friction, and which exhibits negligible shrinkage or positive expansion characteristics upon cooling from an elevated temperature flowing through a passage in a filter housing, including the steps of introducing an elongated filter medium in said passage by passing it through inlet and outlet ports which flank said passage and communicate therewith so that a part of the filter extends across the passage, forcing the substance under elevated pressure and temperature conditions through the filter part of the passage to filter the substance, while providing temperature conditions at said inlet and outlet ports resulting in the formation therein of sealing plugs of said substance and, when desired, effecting movement of said filter medium through said ports to introduce another part of said filter into said passage under conditions providing for movement of the plugs of sealing at said inlet and outlet ports, the improvement comprising the steps of:

• a. providing at least an outlet port having first, second and third spaced sections in uninterrupted communication with each other for sealing purposes extending away from the passage, the sections being thermally isolated from each other and from the filter housing, with said first section being positioned nearest to the filtering passage and said third section being positioned furthest from the filtering passage, and said sections being initially filled with substance being filtered under elevated pressure and at an elevated temperature;
• b. cooling said port while the substance therein is subjected to elevated pressure to a sufficient extent that a stressed plug if formed therein, the stressed plug being attached to the filter medium and normally blocking the movement of the filter medium through the port;
• c. heating and then cooling said second and third sections to substantially anneal the substance in said second and third sections to form a substantially unstressed sealing plug therein, while the stressed plug in said first section remains in place in sealed engagement with the port and in cooled condition;
• d. subsequently, when movement of the filter across the passage is required, heating said first section to enable movement of the stressed plug therein along the port and heating said third section while said first section is in such heated condition, the heating of said third section being carried out only to the extent necessary to enable the annealed sealing plug therein to be controllably extruded from the port

In a filtering device including a body defining a passage through which a substance to be filtered can be caused to flow, the substance being heated to a liquifying temperature and an elevated pressure in the passage, and inlet and outlet ports flanking the passage through which an elongated filter extends for movement to introduce different filter parts across the passage, said ports communicating with the passage whereby relatively solid sealing plugs of the substance being filtered can be formed in said ports during a filtering operation by cooling the substance therein to a solidifying temperature, said plugs being subject to elevated pressure forces derived from the substance being filtered, and being movable through said ports under suitable temperature conditions providing for maintenance of sealing of the ports, the improvement comprising:

• at least one of said ports having first, second and third spaced sections in uninterrupted communication with one another of sealing purposes;
• the sections being thermally insulated from one another and from the body of the device;
• said first section being positioned nearest to the filtering passage and said third section being positioned furthest from the filtering passage;
• said first and second sections being each provided with selectively operable heating means and selectively operable cooling means;
• said third section being provided with selectively operable heating means;
• and means for independently and selectively controlling each of said heating and cooling means.