Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F3/00—Plate-like or laminated elements; Assemblies of plate-like or laminated elements
  • F28F3/08—Elements constructed for building-up into stacks, e.g. capable of being taken apart for cleaning
  • F28F3/10—Arrangements for sealing the margins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
  • B29C55/005—Shaping by stretching, e.g. drawing through a die; Apparatus therefor characterised by the choice of materials
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/02—Sealings between relatively-stationary surfaces
  • F16J15/06—Sealings between relatively-stationary surfaces with solid packing compressed between sealing surfaces
  • F16J15/10—Sealings between relatively-stationary surfaces with solid packing compressed between sealing surfaces with non-metallic packing
  • F16J15/104—Sealings between relatively-stationary surfaces with solid packing compressed between sealing surfaces with non-metallic packing characterised by structure
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C53/00—Shaping by bending, folding, twisting, straightening or flattening; Apparatus therefor
  • B29C53/56—Winding and joining, e.g. winding spirally
  • B29C53/58—Winding and joining, e.g. winding spirally helically
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C63/00—Lining or sheathing, i.e. applying preformed layers or sheathings of plastics; Apparatus therefor
  • B29C63/02—Lining or sheathing, i.e. applying preformed layers or sheathings of plastics; Apparatus therefor using sheet or web-like material
  • B29C63/04—Lining or sheathing, i.e. applying preformed layers or sheathings of plastics; Apparatus therefor using sheet or web-like material by folding, winding, bending or the like
  • B29C63/08—Lining or sheathing, i.e. applying preformed layers or sheathings of plastics; Apparatus therefor using sheet or web-like material by folding, winding, bending or the like by winding helically
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2027/00—Use of polyvinylhalogenides or derivatives thereof as moulding material
  • B29K2027/12—Use of polyvinylhalogenides or derivatives thereof as moulding material containing fluorine
  • B29K2027/18—PTFE, i.e. polytetrafluorethene, e.g. ePTFE, i.e. expanded polytetrafluorethene
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
  • B29L2031/00—Other particular articles
  • B29L2031/26—Sealing devices, e.g. packaging for pistons or pipe joints

Definitions

• the present invention relates gasket and seal materials, and especially gasket materials for use in sealing multiple layers of an apparatus together to contain fluid flow therethrough, such as in a plate and frame heat exchange or filter apparatus.
• the functional plates comprise filter elements; in the case of heat exchange apparatus, the plates comprise thin (e.g. 0.6 to 1.0 mm) thermally conductive material,
• a plate and frame heat exchanger uses a large number of plates, often ranging from 8-16 to 500 or more plates in a single
• each of the plates comprises an essentially rectangular element with upper
• Heat exchange is accomplished by stacking many plates in this manner and establishing two distinct fluid paths through the heat exchanger.
• a first path passes up and down the faces of the plates in every other cell (e.g. passing from left to right in the apparatus through the first, third, fifth, etc. cells); and an counter-current second fluid path passes down and up the plates in the alternating cells (e.g. passing from right to left in the apparatus through the sixth, fourth, second cells).
• a typical heat exchanger seal comprises a ring of elastomer (e.g. butyl rubber, neoprene, ethylene-propylene diene monomer (EPDM), etc.) or compressed sheet (e.g. asbestos or synthetic fiber) that is mounted around the periphery of each plate and around appropriate ports to assure proper fluid separation and orientation.
• elastomer e.g. butyl rubber, neoprene, ethylene-propylene diene monomer (EPDM), etc.
• compressed sheet e.g. asbestos or synthetic fiber
• Non-optimum plate and frame apparatus support the plates through use of an ill-fitted connection between the plates and guide rails. As a result, the plates must be carefully torqued down to assure that proper alignment is maintained between the plates.
• PTFE polytetrafluoroethylene
• gasket As a gasket, PTFE has exhibited utility as a material for use in harsh chemical environments which normally degrade many conventional metals and polymeric materials. PTFE has a usable temperature range from as high as 260°C to as low as near -273°C.
• PTFE may be produced in an expanded porous form as taught in United States Patent 3,953,566 issued April 27, 1976, to Gore.
• Expanded polytetrafluoroethylene (ePTFE) is of a higher strength than conventional PTFE, has the chemical inertness of conventional PTFE, and has an increased temperature range of up to 315°C in service.
• ePTFE gasket material is available from W. L. Gore & Associates, Inc., of Elkton, Maryland, under the trademark G0RE-TEX ⁇ Joint Sealant. Porous ePTFE joint sealants have proven to have excellent seals in many applications.
• the sealing material comprises a PTFE felt encapsulated by a porous PTFE sheet laminated to a melt-processible thermoplastic fluoropolymer.
• a PTFE sealing material can be produced with limited long-term creep by wrapping a core of elongated or expanded PTFE with a high strength film of expanded PTFE.
• the high strength film is resistant to deformation and stretching and serves to contain the PTFE core in place within a compressed gasket.
• This material has proven to be quite effective in sealing plate and frame heat exchangers—providing thermal and chemical protection, long-life and durability, and ease in replacement.
• the present invention is an improved gasket material for use in a variety of plate and frame apparatus, such as plate and frame heat exchangers and filter units.
• the basic material of the present invention comprises a core of elongated polytetrafluoroethylene (PTFE) tightly wrapped in a high strength film.
• PTFE polytetrafluoroethylene
• the preferred gasket material of the present invention comprises an expanded PTFE core wrapped in a high strength PTFE film and then pre-compressed to vastly reduce the time and effort required to install the gasket material in a plate and frame apparatus.
• the pre-compressed gasket material includes a pattern or "footprint" which matches the texture of an adjoining plate from the plate and frame device.
• a conformable layer such as a soft PTFE tape, on the pre-compressed gasket further assists in establishing an improved initial seal in the plate and frame device.
• the gasket material of the present invention has numerous benefits over previous plate and frame sealing material. Among the improvements are longer life and greater durability in environments of harsh chemicals and/or extreme temperatures. In addition, even after an extended period of high compression, the gasket material of the present invention releases very readily from a plate, usually completely intact. This greatly improves plate reconditioning time and effort.
• Figure 1 is a three-quarter perspective view of a conventional plate and frame heat exchanger
• Figure 2 is an elevational view of a conventional plate from a plate and frame heat exchanger with a gasket material of the present invention mounted thereon;
• Figure 3 is a three-quarter isometric view of an uncompressed gasket material of the present invention.
• Figure 4 is a three-quarter isometric view of a fully compressed gasket material of the present invention.
• Figure 5 is a side elevational view of another embodiment of a gasket material of the present invention, pre-compressed and provided with a plate pattern on its bottom side and a conformable sealing layer on its top side;
• Figure 6 is a side elevational view of the embodiment of gasket material shown in Figure 5 following full compression in a plate and frame heat exchanger;
• Figure 7 is a top plan view of a cord of gasket material of the present invention cut to correct length for installation on a plate;
• Figure 8 is a top plan view of a cord of gasket material of the present invention joined into a loop for installation on a plate;
• Figure 9 is a top plan view of a cord of gasket material of the present invention joined into a loop and shaped into correct contours for installation on a plate.
• the present invention is a gasket material suitable for use in a variety of applications, and especially in applications requiring minimal cold flow or "creep.”
• plate and frame apparatus e.g. plate and frame filters or heat exchangers
• multiple elements must be stacked together and then compressed.
• FIG. 1 Shown in Figure 1 is a conventional plate and frame heat exchanger 10.
• the heat exchanger 10 comprises a fixed end frame 12, a movable end frame 14, multiple plates 16 mounted between the two end frames 12, 14, compression bolts 18a, 18b, 18c, 18d, 18e, 18f, 18g, 18h spanning between the two end frames 12, 14, and compression nuts 20a, 20b, 20c, 20d holding the moveable end frame 14 in tight contact with the plates 16.
• upper ports 22a, 22b and lower ports 24a, 24b are provided in the end plates 12, 14 corresponding to ports in each of the plates 16. Threaded studs 26 are provided around each of the ports 22, 24 to accommodate fluid line attachments (not shown).
• FIG. 2 Shown in Figure 2 is a representative heat exchanger plate 16 for use in a heat exchanger.
• the plate includes upper ports 28a, 28b and lower ports 30a, 30b corresponding to ports 22, 24 in heat exchanger 10.
• a series of corrugations 34 or other texturing is provided in order to increase contact area between the plate and fluid flowing over its surface 32.
• the plate's edge 36 is likewise corrugated with a groove 37 typically provided for attachment of a gasket material 38.
• the corrugations contact one another to help support the plates in order to resist plate fatigue and improve mechanical integrity of the unit.
• Gasket material 38 of the present invention is installed on the plate to establish a fluid flow path across it.
• an outer perimeter gasket 38a forms a cell 40 communicating fluid flow between upper port 28b and lower port 30b. Fluid flow will pass between the surfaces of the two plates through various channels created between corresponding corrugations 34 in the two plates.
• Gasket material 38b, 38c is also installed around ports 28a and 30a to direct alternate (i.e. countercurrent) fluid flow pass this plate into a fluid flow path established across the next plate stacked in series.
• the gasket material 38b, 38c around ports 28a, 30a serve to assure that fluid leakage does not occur from the heat exchanger and that fluid does not intermix with the fluid in cell 40.
• each of the port gaskets 28a, 30a includes a vent 41a, 41b to allow release of fluid to the atmosphere and away from cell 40 in the case of some failure in either port gasket 38b or 38c.
• the gasket material 38 is installed on each of the plates 16 to create two distinct fluid paths through the heat exchanger 10.
• a first path passes up and down the faces of the plates in every other cell (e.g. passing from upper port 22b left to right through the apparatus through every other cell (e.g. odd numbered cells) and out a lower port (not shown) in the moveable end plate 14); and an counter-current second fluid path passes down and up the plates in the alternating cells (e.g. passing from an upper port (not shown) in the moveable end plate 14 right to left in the apparatus through the alternative cells (e.g. even number cells) and out lower port 24a).
• the plates are stacked in series and mounted between the frames 12, 14.
• the heat exchanger has been provided with guide rails 42, 44 running the length of the apparatus. Slots 46, 48 are provided in each of the plates 16 corresponding to these rails 42, 44. By aligning the slots in the plates along the guide rails such that lateral movement of the plates is not feasible, "optimal" alignment of the plates is assured during installation and use.
• each of the compression nuts 20 are tightened down along compression bolts 18. Care must be exercised to assure that the plates are evenly torqued down in this manner, with a limited amount of torque applied to any one bolt at a time.
• FIG. 3 One embodiment of the gasket material 50 of the present invention is shown in Figure 3.
• This material comprises a core 52 of elongated, or preferably porous expanded, polytetrafluoroethylene (PTFE) tightly wrapped in a high strength film 54, such as a highly oriented film of expanded PTFE.
• PTFE polytetrafluoroethylene
• the high strength film wrap serves to contain the PTFE core and prevent it from creeping even when placed under extensive compression and heat cycling.
• the goal here is to prevent substantial lateral flow of the PTFE core under stress. In this manner a desired height-to-width ratio in the compressed gasket is maintained such that compressive force continues to be shared between the plates and the gasket material and is not relieved from the gasket.
• the core material is prepared by paste extrusion of PTFE fine powder to form a rod or beading by methods and equipment known in the art.
• the paste extruded rod or beading is then expanded to form a flexible porous structure of nodes interconnected by fibrils by stretching it according to the process taught in United States Patent 3,953,566 to Gore.
• the paste extruded PTFE rod or beading is stretched in the longitudinal direction an amount in the range 2:1 to 25:1, preferably an amount in the range 3:1 to 12:1, depending on the strength and compressibility properties desired in the core material.
• the elongated porous PTFE core material 52 Prior to wrapping, has a surface shape that permits the film 54 to be wrapped in continuous contact with the surface of the core material.
• the elongated porous PTFE core material 52 is wrapped in a circular cross-section and then the wrapped material is molded to establish a rectangular cross-section for installation.
• the core may also be wrapped in virtually any shape having no recessed surfaces (e.g. rectangular, oval, square, triangular, etc.). More complex shapes, e.g., surfaces with depressions or projections, can be formed after the core material has been wrapped.
• the elongated PTFE core may contain a particulate filler.
• the term "particulate” is meant to include particles of any aspect ratio and thus includes particles, chopped fibers, whiskers, and the like.
• the particulate filler may be an inorganic filler which includes metals, semi-metals, metal oxides, carbon, graphite, and glass.
• the particulate filler may be an organic filler, which includes polymeric resins. Suitable resins include, for example, polyether ether ketone (PEEK), fluorinated ethylene propylene (FEP), copolymer of tetrafluoroethylene and perfluoro(propylvinyl ether)(PFA), and other similar high melting polymers.
• PEEK polyether ether ketone
• FEP fluorinated ethylene propylene
• PFA perfluoro(propylvinyl ether)
• Particulate fillers when used, are selected to impart or enhance certain properties in the core or wrapping film according to the application in which the composite gasket material of the invention will be used. For example, they can be used to impact or enhance properties such as electrical conductivity and thermal conductivity, and can also be used to modify compressibility and dimensional stability properties of the composite gasket material. Particulate fillers can be used in concentrations as high as 90 volume percent, but are more generally used in the concentration range 10-70 volume percent. The particulate filler and PTFE fine powder may be combined using conventional dry mixing methods after which they can be formed to provide the core material of the invention by the process taught in United States Patent 3,953,566 to Gore.
• the particulate filler may be mixed with PTFE in aqueous dispersion and coagulated together to form a wet mixture of solids.
• the water is removed from the mixture by standard drying methods and the mixture further processed in the same manner as dry mixed materials.
• the high strength film 54 is preferably a porous expanded PTFE film as produced by the process taught in United States Patent
• a porous expanded polytetrafluoroethylene film having high strength is produced.
• the high strength porous PTFE film may be made by stretching uniaxially, either in longitudinal or transverse direction; or biaxially, in both longitudinal and transverse directions, sequentially or simultaneously.
• the film is preferably uniaxially stretched in the longitudinal direction an amount in the range 2:1 to 150:1, more preferably an amount in the range 2:1 to 80:1.
• Longitudinal direction as used herein indicates the planar direction of manufacture of the film; transverse direction indicates the planar direction normal to the direction of manufacture.
• the preferred core comprises an expanded PTFE with a density of 1.1 g/cc (within a range of 0.9 to 1.2 g/cc) after being wrapped and shaped, which has general pre-installed dimensions of about 7.6-8.9 mm by 10.2-12.7 mm in cross section.
• a dual film layer is used comprising an inner film and an outer film coaxially wrapped around the core.
• the preferred inner film Prior to installation on the core, the preferred inner film is about 2 mil thick and about 1 inch wide, and has a tensile strength of 212.7 MPa and a modulus of elasticity at 2% strain of about 7212 MPa; the preferred outer film is about 6 mil thick and 1.5 inches wide, and has a tensile strength of about 19.9 MPa and a modulus of elasticity at 2% strain of about 590 MPa.
• the ideal adhesive comprises a composite adhesive material comprising a pressure sensitive adhesive layer (e.g. rubber or acrylic) applied to either side of a woven or non-woven carrier sheet (e.g. MYLAR ⁇ polyester).
• a pressure sensitive adhesive layer e.g. rubber or acrylic
• a woven or non-woven carrier sheet e.g. MYLAR ⁇ polyester.
• the adhesive be easily removed from the plate for reconditioning of the plate.
• an adhesive layer of styrene-butadiene rubber (SBR) on both sides of a MYLAR polyester carrier sheet can be quickly removed from the plate by merely pulling on the carrier sheet. Any adhesive residue can be wiped off the plate with a solvent such as acetone or rubbing alcohol.
• SBR styrene-butadiene rubber
• the high strength PTFE film 54 is a composite film comprising a high strength porous expanded PTFE film adhered to a thin layer of melt-processible thermoplastic fluoropolymer.
• thin is meant a thickness of 30 micrometers or less, preferably 20 micrometers or less, and more preferably 10 micrometers or less.
• the expanded layered composite film is produced in the following manner.
• PTFE fine powder which may be combined with the same particulate filler materials and prepared as described above, is mixed with a hydrocarbon extrusion aid, usually an odorless mineral spirit, to form a paste.
• a hydrocarbon extrusion aid usually an odorless mineral spirit
• the paste is compressed into a billet and subsequently extruded through a die in a ram-type extruder to form a coherent planar sheet.
• the coherent PTFE sheet, with or without particulate filler materials, is optionally calendered and then dried by volatilizing the hydrocarbon extrusion aid with heat. Evaporation of the hydrocarbon extrusion aid results in the PTFE sheet having a small degree of porosity.
• porous PTFE sheet is now ready to be combined with a melt-processible thermoplastic fluoropolymer film and the combined sheets expanded together.
• the porous PTFE sheet may be preliminarily expanded by stretching it at 200 - 300 V C about 1.5 to 5 times its original length prior to combining it with the melt-processible thermoplastic fluoropolymer.
• the porous PTFE sheet is combined with the melt-processible thermoplastic fluoropolymer film by placing the melt-processible film on the porous PTFE sheet and heating the combination to a temperature between the melt point of the melt-processible fluoropolymer and 365"C.
• the porous PTFE sheet is kept under tension when heated thereby maintaining its dimensions while the melt-processible fluoropolymer layer is combined with it.
• the melt-processible fluoropolymer layer in contact with the porous PTFE sheet at least partially melts and flows onto the surface of the porous PTFE sheet thereby forming a composite precursor, i.e., a coated porous PTFE sheet ready to be expanded.
• the coated porous PTFE sheet may be expanded according to the method taught in United States Patent 3,953,566 to Gore.
• the temperature range at which expansion of the coated porous PTFE sheet is performed is between a temperature at or above the melt point of the melt-processible thermoplastic fluoropolymer layer and a temperature at or below the melt point of PTFE.
• the coated porous PTFE sheet may be stretched uniaxially, either in a longitudinal or transverse direction; or biaxially, in both longitudinal and transverse directions, sequentially or simultaneously. It may be stretched in one or more steps.
• the coated porous PTFE sheet forms a porous expanded PTFE film as it is stretched.
• the expanded PTFE film is characterized by a series of nodes interconnected by fibrils.
• the melt-processible thermoplastic fluoropolymer layer adhered to it is carried along the surface of the expanding sheet while in a melted state, thereby becoming progressively thinner and forming a thin melt-processible thermoplastic fluoropolymer layer on the porous expanded PTFE sheet.
• the thin melt-processible fluoropolymer layer has a thickness of 30 micrometers or less.
• the thin melt-processible fluoropolymer layer preferably has a thickness of one half, more preferably one tenth, of the thermoplastic fluoropolymer film's original thickness.
• a thermoplastic fluoropolymer film originally having a thickness of 25.4 micrometers (1 mil) could produce a thin thermoplastic fluoropolymer layer having a thickness as low as about 2.5 micrometers (0.1 mil) or less after expansion of the porous PTFE sheet into the porous expanded PTFE article.
• the means for heating the porous expanded PTFE sheet may be any means for heating commonly known in the art including, but not limited to, a convection heat source, a radiant heat source or a conduction heat source.
• the conduction heat source may be a heated surface such as a heated drum, roll, curved plate, or die.
• a conduction heat source is used as the means for heating the coated porous expanded PTFE sheet
• the uncoated surface of the sheet should be against the conduction heat source so to prevent sticking and melting of the melt-processible fluoropolymer layer upon the conduction heat source.
• Thermoplastic fluoropolymers which are of utility as the melt- processible thermoplastic fluoropolymer layer have melt points of 342 V C or less.
• FEP tetrafluoroethylene and hexafluoropropylene
• PFA perfluoro(propylvinyl ether)
• PCTFE polychlorotrifluoroethylene
• ECTFE ethylene-chlorotrifluoroethylene
• ETFE ethylene-tetrafluoroethylene
• PVDF polyvinylidene fluoride
• PVF polyvinylfluoride
• Thermoplastic fluoropolymers are preferred as the melt-processible thermoplastic fluoropolymer since they are similar in nature to PTFE, having melt points near the lowest crystalline melt point of PTFE, and therefore are relatively high temperature thermoplastic polymers.
• Thermoplastic fluoropolymers are also relatively inert in nature and therefore exhibit resistance to degradation from many chemicals.
• melt-processible thermoplastic fluoropolymer film When applied under sufficient temperature and/or pressure, the melt-processible thermoplastic fluoropolymer film can act as an adhesive to adhere the high strength porous expanded PTFE film to the surfaces of other materials.
• the expanded layered composite film 54 is wrapped on the core of elongated PTFE 52 so that the thin layer of melt-processible thermoplastic fluoropolymer contacts the core of elongated polytetrafluoroethylene 52.
• the composite film layer is then heated to cause the thin layer of melt-processible thermoplastic fluoropolymer to at least partially melt and adhere to the core of elongated PTFE core 52.
• the PTFE film 54 may be wrapped on the core 52 in any desired manner.
• the film 54 can be wrapped on the core 52 in a helically so that the film forms a helical seam on the composite gasket material.
• the high strength film 54 may be wrapped on the core 52 in a longitudinal manner so that the film forms a longitudinal seam on the composite gasket material.
• the film 54 may be wrapped on the core 52 by hand, it is preferred that the wrapping is accomplished through the use of high-speed mechanical wrapping apparatus, such as a conventional tape-wrap machine used to wrap dielectric tape layers on conductors.
• high-speed mechanical wrapping apparatus such as a conventional tape-wrap machine used to wrap dielectric tape layers on conductors.
• a conventional tape-wrap machine used to wrap dielectric tape layers on conductors.
• One such machine is disclosed in United States Patent 3,756,004 to Gore.
• the tape wrap machine applies a degree of back tension to the high strength film as it wraps it in a helical fashion around the core which applies a compressive force to the core and thereby somewhat densifies the core in the process.
• the degree of back tension applied to the high strength film may be varied so that the density of the core and final dimensions of the assembly may also be varied.
• Densification i.e. reduction in porosity
• Densification results in no change to the tensile strength or tensile modulus properties which were developed in it by the expansion process, however, densification has a substantial effect on the flex and compressive characteristics of the material.
• a composite gasket material is produced such that a compressive load sufficient to provide an excellent seal can be applied to the composite gasket material with relatively little movement together of the sealing surfaces.
• the composite gasket material of the invention can provide a much thicker gasket that covers a much smaller sealing surface area than can be obtained from existing PTFE gasket materials having lower density or strength.
• the high strength porous expanded PTFE film wrapped upon the elongated PTFE core imparts a substantially increased measure of circumferential strength and restraint to the PTFE core.
• the result is a composite gasket material with a reduced tendency to creep (i.e. a gasket material that has much greater resistance to becoming thinner and wider under steady compressive loads when compared to a PTFE gasket without the high strength wrap).
• a second porous expanded PTFE film which likewise may be coated with a melt-processible thermoplastic fluoropolymer as described above, may be wrapped upon the first high strength film.
• the second wrapped film can have tensile properties which provide additional strength and creep resistance to the composite gasket material or, alternatively, can have lower tensile strength and tensile modulus properties than the first wrapped film in order to enhance sealing surface confor ability of the gasket material .
• a 2.54 cm (1.0 inch) wide by 20.3 cm (8.0 inches) long sample of the film is obtained. Thickness of the film is determined with a snap micrometer gauge and width of the film is determined with a linear gauge.
• a constant rate-of-jaw-separation machine (Instron testing machine, Model 1122) is used to test samples to break. The gauge length of the specimen is 10.16 cm (4.0 inches). The strain rate employed is 2.54 cm/min (1.0 inch/min). Samples are tested to break. The tensile modulus at 2% extension and maximum stress are calculated and recorded as described in ASTM Standard Test Method D 882-91. A population of five to eight samples is averaged to give each value listed herein.
• Two sections of gasket material each 12.7 cm (5 inches)in length are obtained.
• the samples are mounted, in parallel alignment approximately 20 cm (8 inches) apart, between two 25.4 cm (10 inches) square rigid flat platens.
• An initial compressive load of 8.01 kN/linear cm (1800 lbf/linear in) is applied to the samples.
• the samples remain compressed for a period of 10 minutes at a temperature of 200"C.
• the compressive load is reduced by creep of the samples during the 10 minute compression period. No effort is made to maintain a constant load.
• a composite gasket material of the instant invention was produced in the following manner:
• a 0.0127 mm (0.5 mil) FEP tape 50A available from E. I. duPont de Nemours & Co. was laminated to a porous PTFE sheet through the introduction of enough heat to melt and attach the FEP sheet to the porous PTFE sheet as follows:
• the combined sheets were first longitudinally stretched an amount 1.5:1 at a temperature of approximately 330 * C over a heated curved platen, and then further longitudinally stretched an amount 1.5:1 in a second heated zone at a temperature of approximately 340 C, thus forming a high strength composite film having a total amount of expansion of 2.25:1.
• the composite film was subsequently heated at a temperature of 335 N C in a third heated zone at a stretch ratio of 1:1 so that no additional expansion occurred.
• the composite film was slit lengthwise and helically wrapped upon a core of porous expanded polytetrafluoroethylene beading that had not been previously subjected to an amorphous locking process.
• the high strength composite film was wrapped so that 1/2 of the film was overlapped on the previously applied wrap.
• the wrapped beading was passed through an oven at about 405 s C to amorphously lock the high strength expanded polytetrafluoroethylene film and to melt the FEP layer, thus adhering the composite film to the porous expanded polytetrafluoroethylene beading.
• a second layer of the high strength composite film was wrapped upon the wrapped gasket material described above and amorphously locked as the previously applied first layer. Back tension was applied on the composite film so that when the wrapping of the beading was completed, the outside diameter of the wrapped beading was reduced to 11.7 mm (0.46 inch). The result was a composite gasket material of the instant invention.
• Example 1 Tensile properties of high strength composite film prepared as described in Example 1 were tested as described above. Tensile strength was 19.87 MPa (2882 psi) and 2% secant tensile modulus was 589.7 MPa (85520 psi). The composite gasket material of Example 1 was tested by the Gasket Flow Test described above and the results shown in Table 1.
• Example 2 A second example of the composite gasket material of the instant invention was produced in the following manner:
• a 0.0254 mm (1.0 mil) FEP tape 100 A available from E. I. duPont de Nemours & Co. was laminated to a porous PTFE sheet, which had been preliminarily stretched an amount 1.9:1 at a temperature of about 250 V C, through the introduction of enough heat to melt and attach the FEP sheet to the porous PTFE sheet as follows:
• the combined sheets were first longitudinally stretched an amount 2:1 at a temperature of approximately 330 s C over a heated curved platen, and then further stretched an amount 10:1 in a second heated zone at a temperature of approximately 340 V C, thus forming a high strength composite film having a total amount of expansion of about 38:1.
• the composite film was subsequently heated at a temperature of 335 C in a third heated zone at a stretch ratio of 1:1 so that no additional expansion occurred.
• the composite film was slit lengthwise and helically wrapped upon a core of porous expanded polytetrafluoroethylene beading that had not been previously subjected to an amorphous locking process.
• the high strength composite film was wrapped so that 1/2 of the film was overlapped on the previously applied wrap.
• a second layer of the high strength composite film was wrapped upon the wrapped gasket material described above and amorphously locked as the previously applied first layer. Back tension was applied on the composite film so that when the wrapping of the beading was completed, the outside diameter of the wrapped beading was reduced to 13.3 mm (0.52 inch).
• Example 2 Tensile properties of high strength composite film prepared as described in Example 2 were tested as described above. Tensile strength was 173.7 MPa (25200 psi) and 2% secant tensile modulus was 5838 MPa (846700 psi). The composite gasket material of Example 2 was tested by the Gasket Flow Test described above and the results shown in Table 1.
• a third example of the composite gasket material of the instant invention was produced in the following manner:
• a 0.0254 mm (1.0 mil) FEP tape 100 A available from E. I. duPont de Nemours & Co. was laminated to a porous PTFE sheet, which had been preliminarily stretched an amount 1.9:1 at a temperature of about 250"C, through the introduction of enough heat to melt and attach the FEP sheet to the porous PTFE sheet as fol1ows:
• the combined sheets were first longitudinally stretched an amount 2:1 at a temperature of approximately 330"C over a heated curved platen, and then further stretched an amount 20:1 in a second heated zone at a temperature of approximately 340"C, thus forming a high strength composite film having a total amount of expansion of about 76:1.
• the composite film was subsequently heated at a temperature of 335"C in a third heated zone at a stretch ratio of 1:1 so that no additional expansion occurred.
• the composite film was slit lengthwise and helically wrapped upon a core of polytetrafluoroethylene beading that had not been previously subjected to an amorphous locking process. Prior to wrapping the porous expanded polytetrafluoroethylene beading had a density of about 0.3 g/cc and an initial outside diameter of 17.8 mm (0.7 inch).
• the high strength porous expanded polytetrafluoroethylene film in the form of the composite film was wrapped so that 1/2 of the film was overlapped on the previously applied wrap. Back tension was applied on the composite film so that when the wrapping of the beading was completed, the outside diameter of the wrapped beading was reduced to 12.2 mm (0.48 inch).
• the wrapped beading was passed through an oven at about 405"C to amorphously lock the high strength expanded polytetrafluoroethylene film and to melt the FEP layer, thus adhering the composite film to the porous expanded polytetrafluoroethylene beading.
• a second layer of the high strength composite film was wrapped upon the wrapped gasket material described above and amorphously locked as the previously applied first layer. Back tension was applied on the composite film so that when the wrapping of the beading was completed, the outside diameter of the wrapped beading was reduced to 11.9 mm (0.47 inch).
• Example 3 The result was a composite gasket material of the instant invention.
• Tensile properties of high strength composite film prepared as described in Example 3 were tested as described above.
• Tensile strength was 212.7 MPa (30850 psi) and 2% secant tensile modulus was 7212 MPa (1046000 psi).
• the composite gasket material of Example 3 was tested by the Gasket Flow Test described above and the results shown in Table 1.
• a fourth example of the composite gasket material of the instant invention was produced in the following manner:
• a 0.0254 mm (1.0 mil) FEP tape 100 A available from E. I. duPont de Nemours & Co. was laminated to a porous PTFE sheet, which had been preliminarily stretched an amount 1.9:1 at a temperature of about 250"C, through the introduction of enough heat to melt and attach the FEP sheet to the porous PTFE sheet as fol1ows:
• the combined sheets were first longitudinally stretched an amount 2:1 at a temperature of approximately 330"C over a heated curved platen, and then further stretched an amount 10:1 in a second heated zone at a temperature of approximately 340"C, thus forming a high strength composite film having a total amount of expansion of about 38:1.
• the composite film was subsequently heated at a temperature of 335"C in a third heated zone at a stretch ratio of 1:1 so that no additional expansion occurred.
• the composite film was slit lengthwise and helically wrapped upon a core of porous expanded polytetrafluoroethylene beading that had not been previously subjected to an amorphous locking process. Prior to wrapping the porous expanded polytetrafluoroethylene beading had a density of about 0.3 g/cc and an initial outside diameter of 17.8 mm (0.7 inch) .
• the high strength porous expanded polytetrafluoroethylene film in the form of the composite film was wrapped so that 1/2 of the film was overlapped on the previously applied wrap. Back tension was applied on the composite film so that when the wrapping of the beading was completed, the outside diameter of the wrapped beading was reduced to 12.2 mm (0.48 inch).
• the wrapped beading was passed through an oven at about 405"C to amorphously lock the high strength expanded polytetrafluoroethylene film and to melt the FEP layer, thus adhering the composite film to the porous expanded polytetrafluoroethylene beading.
• Example 4 Tensile properties of high strength composite film prepared as described in Example 4 were tested as described above. Tensile strength was 212.7 MPa (30850 psi) and 2% secant tensile modulus was 7212 MPa (1046000 psi). The composite gasket material of Example 4 was tested by the Gasket Flow Test described above and the results shown in Table 1 Comparative Example 1
• the basic film wrapped material of the present invention provides a very distinct improvement over PTFE sealing materials and thus can be effectively utilized as a plate and frame sealing material.
• this material continues to have some deficiencies.
• One very limiting characteristic of this basic material is that it must be compressed approximately 3:1 in the plate and frame apparatus during assembly. Often times, the frame that the plates are compressed between is not long enough to fit all of the plates that are gasketed with this much thicker sealant, requiring burdensome compression in batches. More debilitating, however, is the problem of plate shifting. There is significant "travel" or compression of the plates when the plate pack is assembled together with thicker wrapped PTFE sealant.
• the plate and frame device does not have a suitable guide bar to provide "optimal" packing (i.e. rigidly fixed to prevent sliding or bending of the plates), the plates sealed with the basic wrapped gasket material are prone to shifting and sliding. This is further aggravated by the high compressive forces that are required to adequately compress the gasket If even one plate shifts out of alignment, a leak will form.
• use of the basic wrapped gasket material, installed in this fashion is limited to those applications where risk of debilitating plate movement is minimal. Examples of such applications include: plate and frame apparatus with thicker plates; "optimal" plate and frame apparatus with suitable guide bar designs; and plate and frame apparatus with tighter control over plate movement (e.g.
• FIG. 4 a further embodiment of the present invention is shown in Figure 4.
• the gasket material of the present invention undergoes a significant decrease in thickness before reaching sufficient density and compression to assure creep stability.
• the contours of the gasket will achieve a pattern complementary to the texture of the plate to which it is attached.
• One such pattern is shown on the gasket 56 in Figure 4, comprising a series of projections 58 and indentations 60 corresponding to the corrugated texture of a plate to which the gasket was attached. From a typical starting density of 1.0 to 1.3 g/cc, the fully compressed gasket normally achieves a density of about 1.8-1.9 g/cc.
• the gasket material of the present invention can be greatly enhanced by pre- compressing the gasket material prior to installation.
• the gasket material is mounted on a plate or other mold containing the desired texture and then compressed under pressure to impart the desired contours to the material, such as is shown in Figure 4.
• the gasket material and plate can then be installed, or the material may then be removed from the mold and installed on a similarly textured plate.
• One method to perform this procedure employs a hydraulic press capable of generating a compressive force of about 35 to 50 tons or more.
• the gasket material is installed on one plate, or between two plates, in a conventional manner and then compressed to impart at least an initial reduced thickness to the material.
• Spacer bars or similar stops should be provided on either side of the plate to prevent the press from over compressing the material or damaging the plate/mold.
• a typical compression procedure comprises applying approximately 1,200 lbs per linear inch of force to the sealant for a period of approximately 5 seconds, with or without heat. Less force is required if heat is applied to the gasket material, such as through use of a heat mold plate.
• the force applied to a core of expanded PTFE wrapped with an expanded PTFE film should be at least 500 to 800 lbs per linear inch.
• the gasket material will be compressed enough to decrease significantly the amount of travel experienced during installation and to provide a "footprint" of the adjoining plate on to the gasket to help prevent shifting of the plates.
• densification should not be so great that further compression and fitting of the gasket cannot occur during actual installation.
• a density of about 1.6 to 1.8 g/cc should be sought.
• Shown in Figure 5 is a cross section of a gasket material 62 which has been partially compressed in this manner. In this case, the gasket 62 has been compressed on its lower face 64 to impart a series of indentations 66 to the gasket corresponding to corrugated texturing of a mounting plate. The gasket has not been fully densified and in this case its top surface 68 remains planar, allowing for further customized fitting once installed. This material has been pre-compressed to approximately 50% of its original thickness.
• the embodiment of Figure 5 also includes a conformable sealing layer 70 which is installed on the gasket 62 after pre-compression.
• the conformable sealing layer 70 comprises a strip of low density, expanded PTFE sealing tape with thickness of about 0.5 to 1.0 mm.
• a suitable tape including a self-adhesive layer on one side, permitting quick and easy installation, is commercially available from W. L. Gore & Associates, Inc., of Elkton, Maryland, under the trademark G0RE-TEX ⁇ Gasket Tape. This tape becomes a conformable member of the composite sealant once installed and fully compressed in place.
• FIG. 6 is illustrative of the composite gasket 62 of Figure 5 once installed in place.
• the sealing layer 70 compresses and densifies in close contact with the gasket material 62, while filling in slight differences between the plates (e.g. the raised areas of the sealing layer 70 shown in Figure 6).
• the sealing layer 70 also creates a seal between a dense base gasket material and an adjoining plate with far less force than would be required without such a layer.
• the function of the gasket tape strip on the slightly compressed gasket is at least threefold: 1. It allows a seal to be created with much lower bolt force such that hot fluids can be held within the plate and frame apparatus to soften the gasket before final compression of the final seal with the compression bolts. Much higher bolt forces are required to effect this initial seal without the gasket tape strip, and, thus, would promote plate shifting. Furthermore, some plate and frame devices may not capable of achieving enough sealing pressure without the aid of a conformable layer;
• the gasket material may be provided in a variety of forms to solve specific sealing needs.
• Figure 7 illustrates a cord gasket material 72, with typical dimensions of 12.7 mm wide, 7.6 mm thick.
• the cord gasket material can be provided in continuous lengths, such as on a spool, to allow it to be cut to size for particular installation demands.
• tho cord 72 can be cut to provide specialized sealing, such as around ports 28a, 30a in the plate of Figure 2, for most plate and frame uses the cord gasket material 72 is joined to itself to form a continuous loop 74 like that shown in Figure 8.
• the joint 76 is then connected together by simply splicing the ends.
• One such splicing technique comprises cutting the ends with a 1 inch minimum scive cut, joining the ends together, wrapping the joined ends with a tape (which ideally should be similar or identical to the film wrapping the gasket material), and then heat setting the tape in place with a mold press.
• the gasket material of the present invention provides significant improvements in the durability, longevity, chemical and thermal resistance, and ease in installation of gasket material for use in plate and frame devices. Moreover, the nature of expanded PTFE allows the material to release very easily and intact from the plate, even after it has been installed under heavy pressure for a long period of time.
• the gasket material is removed by merely prying the material away from the plate and pulling the rest of the material intact away from the plate.
• Residue adhesive if employed, can be stripped by removing an adhesive carrier sheet and/or by wiping with a suitable solvent.
• a gasket material for sealing a multiple layered plate and frame apparatus which gasket material comprises: a core of elongated polytetrafluoroethylene (PTFE); a tight film wrap around the PTFE core of sufficient tensile strength to limit creep of the PTFE core when the gasket is placed under pressure; wherein the amount of creep of the gasket material is constrained enough to allow gasket material to be mounted between multiple plates in series and placed under compressive pressure to establish and maintain a seal between the plates; and wherein the gasket material is pre-compressed, requiring minimal travel of the plates during installation.
• PTFE polytetrafluoroethylene
• the gasket material of claim 1 wherein the plates include a textured surface at least in the area where the gaskets are mounted; and the gasket material includes a first and second sealing surface, with a pattern on at least one of the sealing surfaces corresponding to the textured surface of the plates to allow the gasket to be readily mated therewith. 3.
• the gasket of claim 2 wherein the gasket material includes a pattern on both of its sealing surfaces corresponding to the textured surface of the plates. 4.
• the gasket material of claim 2 wherein the gasket material includes a pattern on one sealing surface and a conformable sealing layer mounted on the opposite sealing surface, the conformable sealing layer forming a tight seal against a plate when compressed in place. 5.
• the gasket material of claim 1 wherein the gasket material comprises a pre-shaped pattern adapted to be directly installed on a plate. 6.
• the gasket material includes an adhesive layer on at least one side to assist in retaining the gasket material in place on a plate. 7.
• the adhesive layer comprises a releasable coating of pressure sensitive adhesive.

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• Engineering & Computer Science (AREA)
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• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Gasket Seals (AREA)

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Citations (11)

• 1993
  • 1993-10-19 JP JP7508651A patent/JPH09502512A/ja active Pending
  • 1993-10-19 WO PCT/US1993/009985 patent/WO1995007422A1/en not_active Application Discontinuation
  • 1993-10-19 AU AU54074/94A patent/AU5407494A/en not_active Abandoned
  • 1993-10-19 CA CA 2169749 patent/CA2169749A1/en not_active Abandoned
  • 1993-10-19 EP EP93924359A patent/EP0717820A1/de not_active Ceased

Patent Citations (11)

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