Gasket for heat exchanger and method and apparatus for manufacturing same

An apparatus for manufacturing a large-diameter gasket in which a pair of holding presses have press members which selectively bears against an elongate band while a bending press pivots against a portion of the band. The drive press bears against a portion of the band, and with the holding presses released, moves longitudinally to move a next portion of the band into the bending press. A method of manufacturing the large-diameter gasket is disclosed, together with a jig for applying a patch of sealing material to a joint formed between opposing distal ends of the gasket.

TECHNICAL FIELD
 The present invention relates to large-diameter gaskets. More particularly,
 the present invention relates to large-diameter gaskets for heat
 exchangers and to apparatus and methods for the manufacture of
 large-diameter gaskets.
 BACKGROUND OF THE INVENTION
 Heat exchanger are large pieces of mechanical air and fluid handling
 equipment having large cross-sectional dimensions. Adjacent components of
 heat exchanger connect together at flanges with bolts. Gaskets seal the
 connection of the adjacent components to prevent leakage from the heat
 exchanger.
 Periodically, or as necessary, the gaskets that seal the connections in
 heat exchanger are replaced. It has been the practice in the industry for
 the new gaskets to be custom manufactured, typically by a gasket
 distribution company local to the facility requiring the new gaskets.
 There are several reasons for this practice. Generally, no major company
 manufacturing small-diameter gaskets provides large-diameter gaskets for
 heat exchanger. Small diameter gaskets are generally available in a wide
 range of inner and outer diameters, generally having overall diameters of
 up to about twelve inches. For large-diameter applications, generally of
 twelve inches and greater, there are a number of different gasket
 patterns, and replacement typically is an infrequent occurrence. It is
 impractical to inventory replacement gaskets for large diameter
 applications.
 In contrast, the smaller gaskets for fluid flow control devices are used
 more frequently, and manufacturers of gaskets maintain dies in a wide
 range of inner and outer diameters to manufacture small-diameter gaskets
 up to approximately twelve inches. Such smaller gaskets are easier to
 store in warehouses and ship to distributors or end-users for
 installation. The large-diameter gaskets however are more difficult to
 handle and store due to their size, the flexibility of the gasket, and the
 brittle nature of the sealing material of the gasket.
 Presently, replacement large-diameter gaskets are generally made by gasket
 distributors which are local to the site requiring replacement gaskets.
 The replacement gaskets are made with a metal ring overlaid with sealing
 materials. The ring is cut using a gasket template laid over a large plate
 of sheet metal. The sealing material is typically cut from a sheet of
 calendared graphite having a layer of adhesive. Such product is available
 commercially in a number of thicknesses and densities. The sheet is laid
 on a table and the ring is placed on the adhesive layer. The gasket is
 then cut from the sheet. The ring is turned over and placed on a second
 sheet to coat the opposing side of the ring. The remaining materials are
 generally scrapped as waste, which comprises an additional cost. The
 gasket is then moved carefully to the heat exchanger and installed.
 While these locally-manufactured gaskets have provided replacement gaskets
 for large-diameter sealing applications, there are drawbacks to their
 usage. These drawbacks include the inability to incorporate into the large
 diameter gaskets the improvements found in modern small diameter gaskets.
 The uniformity of the custom-made gasket varies one to another, and the
 overall quality depends upon the experience of the technician
 manufacturing the gasket.
 Accordingly, there is a need in the art for an improved heat exchanger
 gasket, together with an apparatus and method of manufacturing improved
 heat exchanger gaskets. It is to such that the present invention is
 directed.
 SUMMARY OF THE INVENTION
 The present invention meets the needs in the art by providing an apparatus
 and method for manufacturing a large diameter heat exchanger gasket. The
 apparatus comprises a holding press and a bending press which are disposed
 coaxially and spaced-apart for receiving an elongate band therethrough.
 Each press is selectively positionable in a first position for allowing
 the elongate gasket band to move longitudinally through the holding press
 and the bending press and a second position holding the band rigidly from
 movement relative to the respective press. A drive press is disposed
 coaxially with and spaced-apart from the holding press and operative in
 opposite mode to the holding press and the bending press, whereby the
 elongate gasket band is held tightly when the holding press and the
 bending press is in the first position. The drive press is also movable
 longitudinally from a first position to a second position for moving a
 portion of the elongate gasket band through the bending press. The bending
 press is pivotable from a first position to a second position at an
 oblique angle relative to a longitudinal axis of the elongate band for
 bending the band at an oblique angle relative to the longitudinal axis.
 Pneumatic cylinders move the respective presses. The holding press and the
 bending press operate in unison to move to the second position to hold the
 elongate band during a bending step when the bending press pivots from the
 first position to the second position. The drive press operates in a
 holding mode for gripping the elongate gasket band while the holding press
 and the bending press are in the first position in order for the drive
 press to move a portion of the elongate band longitudinally through the
 bending press.
 The apparatus of the present invention provides a preferred embodiment of a
 large diameter gasket, comprising an elongate, narrow band having distal
 ends joined together to define a closed loop with a diameter exceeding
 twelve inches. A jacket of a sealing material enwrapps substantially the
 entire band. A patch of the sealing material enwrapps a portion of the
 loop where the distal ends join together.
 The present invention provides a method of manufacturing a large diameter
 gasket, in which an elongate band moves a predetermined distance to
 advance a portion of the elongate band into a bending press. An adjacent
 holding press and the bending press hold the elongate band firmly. The
 bending press pivots adjacent the holding press from a first position to a
 second position to bend the portion of the band at an oblique angle
 laterally. The elongate band is released from being secured in the holding
 press and the bending press. The steps are repeated until a loop of a
 predetermined diameter is formed. The loop is separated from the band, and
 opposing distal ends joined together to form a large-diameter gasket.
 Objects, advantages and features of the present invention will become
 apparent from a reading of the following detailed description of the
 invention and claims in view of the appended drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring now in more detail to the drawings in which like parts have like
 identifiers, FIG. 1 illustrates in perspective view an apparatus 10
 according to the present invention for manufacturing a large-diameter
 gasket particularly useful for heat exchanger applications. The apparatus
 10 includes a table 12 to support the components of the apparatus. A feed
 channel 14 defines a U-shaped body which aligns an elongated narrow band
 16 for being machined into a gasket of the present invention. The feed
 channel 14 is preferably made from a polymeric block and defines opposing
 sidewalls 18. The band 16 is received between the sidewalls 18 which align
 the band for passing through the apparatus 10.
 A drive press 20 is coaxially disposed adjacent the feed channel 14. The
 drive press 20 includes a base 22 for a press housing 24. A connector
 block 26 at a first side of the base 22 connects to a cylinder rod 28
 extending from a pneumatic cylinder 30. The cylinder 30 communicates with
 supply of pressurized air through pneumatic hoses 32. A controller
 controls the operation of the cylinder 30 and the other pneumatic
 cylinders discussed below. The base 22 receives a channel member 34 and a
 press member 36. The channel member 34 and the press member 36 include
 urethane skins 38 on respective opposed facing surfaces. The press member
 36 attaches to a pneumatic cylinder 40 mounted to the top of the press
 housing 24 and communicates through pneumatic hoses 42 to the supply of
 pressurized air. The press member 36 is movable from a first position
 retracted away from the channel member 34 to a second position bearing
 against the channel member.
 The base 22 connects to a pair of bolts 44 on opposing sides. The bolts 44
 extend from the base 22 through respective slots 46 defined in the table
 12 and engage sliding members 48 below the table. The drive press 20 is
 moveable from a first position close to the end of the feed channel 14 to
 a second position spaced-apart from the feed channel, for a purpose
 discussed below.
 A first holding press 50 is coaxially aligned and spaced-apart from the
 drive press 20. The first holding press 50 is similar to the drive press
 20, but is rigidly connected to the table 12. A base 52 supports a press
 housing 54 which contains a channel member 56 and a press member 58. The
 channel member 56 and the press member 58 include urethane skins 60 in
 opposing surfaces. The press member 58 attaches to a pneumatic cylinder
 (not illustrated, but similar to the cylinder 30) mounted to the top of
 the press housing. The cylinder communicates through pneumatic hoses 62 to
 the supply of pressurized air under direction of the pneumatic cylinder
 controller. The press member 58 is movable from a first position retracted
 away from the channel member 56 to a second position bearing against the
 channel member 56.
 An intermediate channel 64, U-shaped in configuration, is disposed between
 the first holding press 50 and a second holding press 66. The channel 64
 has opposing side walls 68 that guide the opposing side edges of the
 elongate band 16 as it moves through this portion of the apparatus 10. The
 second holding press 66 includes a U-shaped channel 70 with a channel
 member 71 and an upright support 72 on one side. A flange 73 extends
 laterally from the upright support 72 over the channel member 71 and a
 press member 74 attaches to the flange 73. The channel member 71 and the
 press member 74 have urethane skins 75 on facing surfaces.
 The upright support 72 connects to a rod 76 having a cam 78 at a distal
 end. A drive shaft 80 extends a cam block 79 and connects to the cam 78.
 The drive shaft 80 also connects to a pinion gear 82 that rotates on a
 rack 84. The rack 84 moves between a first and a second position in
 response to operation of a pneumatic cylinder 86 to which the rack
 connects. Rotation of the pinion gear 82 causes the shaft 80 to rotate and
 move the cam 78 against the cam block 79. The rod 76 thereby moves
 relative to the shaft 80. This movement causes the upright support 72 to
 move between a first position with the press member 74 retracted from the
 channel member 71 to a second position with the press member bearing
 against the channel member. A frame 88 for the cam 78, the drive shaft 80,
 the pinion 82, and the rack 84, fixedly connects to supports (not
 illustrated). The support 72 accordingly is moveable relative to the frame
 88.
 A bending press 90 pivotally connects by a pivot pin 91 adjacent the second
 holding press 66. The bending press 90 includes a channel 92 which
 receives the elongate band 16 on a channel member 93 (shown in cut-away
 view below the band 16). A side wall 94 bears on a side edge of the band
 16. An opposing side wall extends away at an oblique angle. The bending
 press 90 pivots between a first position with the side wall 94 parallel to
 a longitudinal axis of the band 16 in the second holding press 66 and a
 second position with the side wall 94 at an oblique angle relative to the
 axis.
 Similar to the second holding press 66, the bending press 90 includes an
 upright support 97 on one side of the channel 92. A flange 98 extends
 laterally from the upright support 97 over the channel 92 and a press
 member 99 attaches to the flange. The channel member 93 and the press
 member 98 include urethane skins 95 on facing surfaces. A pneumatic
 cylinder 96 attaches to the table 12 and a cylinder rod engages a plate
 101 on the pivot press 90.
 The upright support 97 connects to a rod 100 having a cam 102 at a distal
 end. The cam 102 engages a drive shaft 104 which extends through a cam
 block 103. The drive shaft 104 also connects to a pinion gear 106 that
 rotates on a rack 108. The rack 108 moves between a first position and a
 second position in response to operation of a pneumatic cylinder 110 to
 which the rack connects. This causes the shaft 104 to rotate the cam 102
 against the cam block 103. This movement causes the upright support 97 to
 move between a first position with the press member 98 retracted from the
 channel member 93 to a second position with the press member bearing
 against the channel member. A frame 112 for the drive shaft 104, pinion
 106, and rack 108 fixedly connects to supports (not illustrated). The
 support 97 accordingly is moveable relative to the frame 112.
 FIG. 2 is a perspective view of a jig 140 for forming a patch of sealing
 material over a joint made by connecting opposing distal ends of a loop
 gasket together, which loop gasket is made with the apparatus 10
 illustrated in FIG. 1, as discussed below. The jig 140 defines a U-shaped
 frame having opposing side walls 142, 144 which each define a plurality of
 opposing threaded bores 146. A plurality of bolts 148 are received
 separately in a respective one of the bores 146 with distal ends 150
 inwardly of the sides. The bolts 148 are movable in the bores 146 to
 dispose the respective distal ends 150 of the bolts between a retracted
 position close to the respective side 142, 144 and an extended position
 spaced inwardly from the sides. A pair of spaced-apart plates 152, 154 are
 disposed between the distal ends 150 of the bolts 148. A pair of resilient
 pads 156, 158 are received between the plates 152, 154 for sandwiching a
 portion 160 of a loop formed with the apparatus 10, for coating the
 portion with gasket materials, as discussed below. A plunger 162 has an
 arcuate shape conforming to an arc of the gasket being manufactured. The
 plunger 162 connects to a rod extending from a hydraulic cylinder (not
 illustrated). Operation of the hydraulic cylinder causes the plunger 162
 to move from a retracted position to a bearing position between the plates
 152, 154 against the pad 158.
 FIG. 3 is a plan view of a portion of a gasket 170 made from a loop formed
 by the apparatus illustrated in FIG. 1. The gasket 170 comprises a
 separated portion of the narrow band 16 that is moved through the
 apparatus 10. The band 16 preferably is a narrow, thin ribbon 172 coated
 with a sealing material 174. In a preferred embodiment, the ribbon 172 is
 metal. The loop includes an exposed portion 176 from which the sealing
 material 174 is removed. The loop formed by the apparatus 10 has opposing
 distal ends 178, 180 which are rigidly joined, preferably with welds 182,
 at a joint 184. This joint 184 defines the endless ring gasket 170. The
 exposed portion 176 is then re-coated with sealing material using the jig
 140, as discussed below. It is to be appreciated that the loop is formed
 by a series of chords, or portions 183 of the band 16 bent at an oblique
 angle 185 relative to the adjacent portion, as illustrated for several
 portions 183a, 183b, 183c, 183d, and 183e of the gasket 170.
 FIG. 4 is a perspective view of a roller apparatus 190 for corrugating the
 ribbon 172 used to form gaskets with the apparatus 10. The roller
 apparatus 190 includes a frame 192 in which a pair of rollers 194, 196 are
 mounted on axles 197 for rotation. The rollers 194, 196 rotate by motors
 (not illustrated) connected to the axles 197. The arcuate faces 198 of the
 rollers 194, 196 define mating corrugated surfaces having ridges 199 and
 valleys 200. The ribbon 172 passes between the rollers 194, 196 which bear
 forcibly against the band to define longitudinally extending corrugations
 173 in the band.
 With reference to FIGS. 1-3, the apparatus 10 and the jig 140 are used to
 manufacture a gasket 170 according to the present invention. The gasket
 170 preferably comprises a narrow, elongated metal ribbon 172 coated with
 gasket sealing material 174. In a preferred embodiment, the gasket sealing
 material is expanded intercalated graphite worms applied to and compressed
 against the body of the band 172. Expanded intercalated graphite worms
 result from expanding intercalated graphite flakes. Expandable
 intercalated flake graphite is formed by treating natural or synthetic
 flake graphite with an intercalating agent such as fuming nitric acid,
 fuming sulphuric acid, or mixtures of concentrated nitric and sulphuric
 acid. Expandable intercalated graphite flakes can then be expanded to form
 a low density, worm-like form of particulate graphite. The production of
 expandable intercalated flake graphite as an intermediate step in the
 production of expanded intercalated flake graphite is described in U.S.
 Pat. No. 3, 404,061. In a preferred embodiment of the present invention,
 the band 172 includes the plurality of longitudinally-extending
 corrugations 173. With reference to FIG. 4, the corrugations 173 are
 defined by moving the elongate band 172 between the pair of rollers 194,
 196. U.S. Pat. No. 5,499,827, incorporated herein by reference, describes
 an apparatus and method for applying a coating of a sealing material to an
 elongate core. Such apparatus and method disclosed therein is gainfully
 used to coat the elongated band 172 with the sealing material 174 to form
 the elongated coated band 16.
 With continued reference to FIGS. 1-3, the elongated coated band 16 is
 received in the feed channel 14. This is accomplished by moving the press
 members 36, 58, 74, and 99 to their respective first positions, whereby
 gaps are opened between the press members and the respective channel
 members 34, 56, 71, and 92, for receiving the band 16 through the drive
 press 20, the first and second holding presses 50 and 66, and the bending
 press 90. A distal end portion of the band 16 is positioned in the bending
 press 90. The length of the distal end portion is based on the diameter of
 the gasket to be formed.
 The apparatus 10 is then positioned for operation. The pneumatic cylinders
 in the first and second holding presses 50 and 66 and in the bending plate
 90 are operated to move the respective press members 58, 74, and 99 to
 their second positions bearing against the channel members 34, 56, and 93,
 respectively. This sandwiches the band 16 between the channel members and
 the press members. The urethane skins 38, 60, and 95 on the respective
 channel members and press members provide a smooth surface which does not
 mar or damage the sealing material 174 on the band 16.
 The pneumatic cylinder 96 operates to pivot the bending press 90 on the
 pivot pin 91 to the second position at an oblique angle 185 to the
 longitudinal axis of the band 16 in the second holding press 66. The side
 94 of the channel 92 bears against the side edge of the band 16. The
 bending press 90 thereby forces the band 16 to bend at a line defined by
 the adjacent second holding press 66 and the bending press 90. The press
 member 74 and 99 hold the band 16 firmly from slipping as the bending
 press 90 pivots. While the holding press 50 secures a distal end of the
 band 16, the holding press may not be necessary for successful use of the
 present invention. The angle 185 of bend is controllable by the extension
 of the cylinder rod from the cylinder 96. The angle of the bend is based
 on the diameter of the gasket being formed by the apparatus 10.
 The pneumatic cylinder 96 is again operated to pivot the bending press back
 to its first position. The distal end portion of the band 16 has a bend
 formed therein as illustrated in FIG. 3, which bend extends at an oblique
 angle 185 relative to the adjacent portion 183.
 The pneumatic cylinders in the first holding press 50, the second holding
 press 66, and the bending press 90 are then operated to move the
 respective press members 58, 74, and 99 to the first positions. The
 pneumatic cylinder 30 is then operated to push the drive press 20 from its
 first position to the second position. As the drive press 20 moves in
 guidance of the bolts 44 in the slots 46, the elongate coated band 16 is
 moved longitudinally relative to the holding presses 50 and 66 and the
 bending press 90. The drive press 20 moves a predetermined distance to
 push a new portion of the band 16 into the bending press 90.
 The pneumatic cylinders in the first holding press 50, the second holding
 press 66, and the bending press 90 are then operated to move the
 respective press members 58, 74, and 99 to their second positions. The
 band 16 is then fixed in position in the apparatus 10. The pneumatic
 cylinder 40 in the drive press is then operated to move the press member
 36 to its first position. The band 16 is then free of engagement to the
 drive press 20. The pneumatic cylinder 30 is operated to retract the drive
 press 20 from the second position to the first position. The cylinder 40
 is again operated to move the press member 36 to the second position
 bearing against the channel member 34 and the band 16. The bending press
 90 is then operated as discussed above to place a bend in another portion
 183 of the elongate coated band 16. This process is repeated in succession
 until a loop for a large diameter gasket is formed and a portion of the
 band 16 overlaps another portion. The bending step effectively places a
 chord in the band 16, and a sufficient number of chords substantially
 defines a large diameter gasket.
 As shown in FIG. 3, the overlapped portion of the band 16 is cut to
 separate the loop from the band 16 and define opposing distal ends 178,
 180. The sealing material 174 at the distal ends 178, 180 is removed for
 the exposed portion 176 of the gasket. The opposing distal ends 178, 180
 are joined together to form a joint 184 and thereby close the gasket.
 Preferably, the ends are welded at weld points 182.
 With reference to FIG. 2, the exposed portion 176 of the gasket 170 is then
 patched with sealing materials using the jig 140. In a preferred
 embodiment, the sealing material is a plurality of expanded intercalated
 graphite worms. The sealing material is placed on the lower resilient pad
 156 between the plates 152, 154. The exposed portion 176 of the gasket 170
 is positioned on sealing material between the plates 152, 154. Additional
 sealing material is placed over the exposed portion 176. The upper
 resilient pad 158 is placed between the plates on the sealing material.
 The bolts 148 are threaded in the bores 146 to move the distal ends 150
 firmly against the plates 152, 154. The plunger 162 is moved by a
 hydraulic cylinder (not illustrated) from a first position away from the
 jig 140 to a second position in bearing contact with the sandwich of the
 pads 156, 158, the sealing material, and the exposed portion 176 of the
 gasket 170. The plunger 162 firmly compresses the sealing material around
 the exposed portion 176. The plunger 162 may be pushed and retracted
 several times to assure compressive bonding of the sealing material. The
 plunger 162 is then retracted to its first position. The bolts 148 are
 disengaged from the plates 152, 154, and the patched gasket 170 removed
 from the jig 140. The resulting gasket 170 is thereafter secured, for
 example, between two substantially rigid sheets, for storage,
 transportation, and handling.
 It is thus seen that an improved large-diameter gasket for heat exchanger
 and the like is provided, together with an apparatus and method for
 manufacturing such large-diameter gaskets. While this invention has been
 described in detail with particular reference to the preferred embodiments
 thereof, the principles and modes of operation of the present invention
 have been described in the foregoing specification. The invention is not
 to be construed as limited to the particular forms disclosed because these
 are regarded as illustrative rather than restrictive. Moreover, many
 modifications, variations and changes may be made by those skilled in the
 art without departure from the spirit and scope of the invention as
 described by the following claims.