Liquid purification or separation – With repair or assembling means – Sliding or rolling on guide means
Reexamination Certificate
2000-06-06
2001-05-29
Lithgow, Thomas M. (Department: 1724)
Liquid purification or separation
With repair or assembling means
Sliding or rolling on guide means
C210S450000, C425S185000, C425S19200R, C425S197000, C425S199000
Reexamination Certificate
active
06238558
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to filter changers for fluids comprising apparatus to replace a clogged filter with a fresh filter within a fluid flow passage. More particularly, it relates to filter changers useful in the polymer industry for the filtration of heated, pressurized polymer in liquid form as it flows from an extruder to any of various types of polymer forming equipment.
Typically, in the polymer application two or more filters are mounted in apertures on a carrier assembly adapted to locate the filters successively in an operative position that communicates between upstream and downstream polymer flow passages. The filter carrier assembly slides within a channel that extends transversely of the polymer flow passages through the operative position to the exterior of the filter changer, whereby clogged filters are made accessible for cleaning or replacement with fresh filters.
U.S. Pat. No. 4,237,014 to Trott and U.S. Pat. No. 3,675,934 to Heston illustrate typical known slide plate screen changers. These patents disclose two distinct sealing mechanisms intended to prevent leakage of polymer into the transducer channel. In the Trott patent sealing force is applied by means of a mechanically loaded assembly. Under predefined displacement the sealing surfaces are brought into contact with sufficient force to resist leakage at low operating polymer pressures. The Heston patent illustrates a different sealing mechanism whereby the polymer pressure is used to effect the sealing force. In either case the polymer or mechanical pressure is applied to a seal member, causing the seal member to bear on the upstream side of the filter carrier assembly or the filter then located in the operative position, thereby containing the polymer and preventing its flow into the filter channel. In this type of changer the sealing surface area is generally of small size and located close to the filter aperture, but it is sufficient to comply with, and remain in sealing contact with, small irregularities in the mating surfaces of the filter carrier, the filter channel and the flow passages.
Difficulties with the sealing means previously employed arise under conditions when the polymer pressure is substantially below the elevated level at which the filter changer is operated in normal use. Such conditions exist, for example, at start up or during idle periods of operation. During such periods the pressure exerted on the upstream seal is insufficient to prevent leakage of fluid into the transverse filter channel.
Problems also arise if filter changer assemblies cannot be easily disassembled for purposes of maintenance.
Accordingly, a principal object of this invention is to provide improved sealing means that are effective not only at normal operating pressures of the polymer, but during start up and idle periods when the polymer pressure is low.
A second object is to provide sealing means effective to establish a threshold force applied to the upstream seal that is effective to prevent polymer leakage when the polymer pressure is below a predetermined value.
A further object of the invention is to provide sealing means that are adapted to allow simple maintenance and disassembly procedures.
BRIEF SUMMARY OF THE INVENTION
With the foregoing objects in view, this invention features a combination of two sealing means effective for the foregoing purposes. The first means comprises mechanically adjustable screws acting on an annular tapered cam surface of the upstream seal to force it into contact with the filter carrier or operative filter. This seal provides complete containment of the polymer during start up or idle periods. The adjustment accommodates manufacturing tolerances and thermal expansion variables. The adjustment also enables the operator to remove the mechanical preload applied by the screws, facilitating removal, maintenance and reassembly of the changer parts including the slide plate and seals.
The second means of effecting a seal utilizes the polymer pressure force resulting from the difference between the upstream and downstream effective surface areas of the upstream seal member. This seal provides complete containment of polymer during the relatively long periods while the filter is online in normal operation. The polymer pressure actuated seal mechanism can be effective up to very high pressures, limited only by the structural integrity of the supporting body of the filter changer and related parts.
The dual means for sealing permit a dramatic improvement in machine operation under predictable operating parameters. Nearly all extrusion operations have periods of low pressure, either during start up or during idle periods. All extrusion operations have higher pressures during normal operation. Bimodal sealing meets the demands of the full range of operating conditions, and the adjustment capability permits reliable operation using cost effectively manufactured components and under adverse temperature conditions.
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patent: 5507498 (1996-04-01), Trott
patent: 6010625 (2000-01-01), Whitman
Beringer LLC
Lahive & Cockfield LLP
Lithgow Thomas M.
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