-Conduit Assemblies and Method of the Same-

Field of the Invention

The present invention relates to a method of fabricating hybrid conduit assemblies and to hybrid conduit assemblies produced thereby, and especially to a method of fabricating hybrid, multi-ply conduit assemblies and to hybrid, multi-ply conduit assemblies produced thereby.

Background of the Invention

For many reasons, it is often necessary for a conduit system to have different physical characteristics over the length of the system. Manufacturers have, therefore, developed hybrid conduit systems (that is, conduit systems having different physical properties over the length thereof) . In an exhaust duct system, for example, it is often desirable to have at least one section over the length of the system that operates provide mobility or to otherwise "absorb" and transfer energy (for example, from the gases flowing therethrough) . Such an energy transfer section may comprise a section of laminated or multi-ply tubing or, more often, a section of bellows.

Under prior manufacturing methods, hybrid conduit and tubing assemblies have been manufactured by the connection of two or more sections of conduit having different physical characteristics (for example, different wall thickness and/or different shape) . Such conduit sections may be attached, for example, by welding in the case of metallic tubing. A typical

prior method of fabricating a hybrid tube/bellows section i discussed below by way of example.

The manufacture of single-ply and multi-ply corrugate tubing (that is, bellows) is well known. In general, the bellow is fabricated from a section of uncorrugated metal tubing (ofte referred to as a blank) using a pressurized fluid to deform th blank into an appropriate die. This technique is commonly referre to as hydroforming. Such a technique is discussed, for example, i U.S. Patent Nos. 4,179,910, 4,453,304, 3,584,367 and 3,160,130 an is illustrated in Figures 1A through IC.

In general, a die set comprising bellows blades 1 and tw seal dies 2 is used to hydroform a bellows 3. Two internal seals are placed within blank 4 at each end of blank 4 and cooperate wit seal dies 2 to create a sealed region within blank 4. Typically, each internal seal 8 is provided with a rubber seal 5 whic cooperates with a recess 6 in corresponding seal die 2. As seen i Figures 1A and IB, introduction of a pressurized fluid into th region between internal seals 8 results in deformation of blank to form bellows 3. As also seen in Figures 1A and IB, seal dies 2, bellows blades 1 and internal seals 8 are designed to be mobil relative to each other during deformation. Seals die 2 and bellow blades 1 are forced towards each other along the axis of blank 4 during pressurization, thereby deforming blank 4 outward fro center line 7 of blank 4.

The increase in the outer diameter of blank 4 i controlled by appropriate choice of the pressure used i deformation (that is, for a given diameter of blank 4, wall thickness of blank 4 and bellows blade 1 spacing) . Finishe bellows 3 is best illustrated in Figure IC.

Although hydroforming has been discussed in the deformation of tubing to fabricate bellows, one of ordinary skill in the art will recognize that other techniques, such as spin forming in which mechanical force is used to deform the' blank, may also be used to deform ductile conduit to a predetermined shape (for example, a bellows) .

After deformation of the blank as described above, the resultant "corrugated" bellows may be connected to an uncorrugated section of tubing to result in a hybrid tube/bellows assembly. Figure ID illustrates an example of the prior practice for the manufacture of hybrid tube/bellows assemblies such as bellowed exhaust ducts. Exhaust duct 9 comprises three (3) separate sections of single-walled, tubing and a single-walled section of corrugated bellows attached by welding. In most such assemblies, the wall thickness of the tubing section is different from that of the bellows section. Generally, the uncorrugated, tubing section of the assembly is constructed to have a wall thickness greater than that of the corrugated or bellows section of the assembly.

During assembly, the fabricator of exhaust duct 8 selects a first tube end 10, which the manufacturer cuts to a desired size and shapes (e.g., flares) . The fabricator then selects an intermediate tube section 20, which the fabricator also cuts to size and shapes (e.g., bends etc. ) . Next, the fabricator selects second tube end 30, which is likewise cut to size and shaped. Finally, an appropriately sized bellows section 40 is selected.

First tube end 10 is attached by welding to bellows section 40 at point A. Intermediate tube section 20 is welded to bellows section 40 at point B. Second tube end 30 is welded to intermediate tube section 20 at point C.

A tube/bellows assembly such as exhaust duct 8 generally assembled by a tube fabricator. Usually, the tu fabricator manufactures tube sections 10, 20 and 30, but purchas bellows section 40 from a bellows fabricator. ^• "

There are a number of drawbacks associated with pri methods for fabricating hybrid conduit assemblies such as t hybrid tube/bellows assemblies discussed above. For example, su prior methods require the handling and inventory of sever separate tubing sections (for example, tubing and bello sections), which may be produced by different entities, resulti in substantial expense. Moreover, the necessity of weldi attachment of such disparate sections results in heat affected we zones which can adversely affect the corrosion resistance of t product. Such weld zones may also fail during use of the assembl

Using once again the example of an exhaust system to s forth prior fabrication methods, exhaust manifolds in automobil very often are required to change directions over their lengt Such a change in direction of the tubing causes a change in t momentum of the fluid flowing therethrough. The change in t momentum of the fluid causes energy to be transferred through th tube wall. Such energy is usually transferred through the tub wall in the form of vibration and, thus, audible noise.

It is known that providing a laminated or multi-ply wal in the area of the change in direction of the exhaust tubing wil attenuate the energy transmission, thereby reducing the nois within the automobile. Under prior manufacturing methods, th exhaust manifold is first formed to a desired shape. Lamination i then applied to areas of vibration by attaching (via welding) a appropriately shaped, bisected tubing shells onto those areas

Such a manufacturing method suffers from many of the same drawbacks discussed in connection with the fabrication of hybrid tube/bellows assemblies.

It is very desirable to develop a method of fabricating hybrid conduit assemblies that does not suffer from these and other drawbacks associated with prior methods.

Summary of the Invention

Accordingly, the present invention provides a method of fabricating hybrid conduit assemblies that avoids many of the drawbacks associated with previous fabrication techniques. The present invention uses telescopic attachment of non-coextensively telescoped sections of conduit to vary the wall structure/composition of a conduit system over its length. By varying the wall composition and preferably the shape of the conduit system over its length, the present invention enables the production of hybrid conduit assemblies while eliminating the need to attach disparate sections of conduit by welding or otherwise.

In general, the present invention provides a method of fabricating a hybrid conduit assembly comprising at least a first section and a second section, in which the first section and the second section have different wall composition. The method comprises the step of telescoping together at least a first segment of conduit and a second segment of conduit. The second segment of conduit has a cross-sectional shape generally similar to the first segment of conduit.

The first segment of conduit and the second segment o conduit are telescoped together to form a telescoped subassembl comprising a first section in which the first segment of condui and the second segment of conduit are telescopically adjacent eac other and at least a second section in which the first segment o conduit and the second segment of conduit are not telescopicall adjacent each other. Depending upon the position and length of th second segment of conduit there may be a third section. Fo example, if the second segment of conduit is shorter than the firs segment of conduit and is not positioned such that an end thereo is positioned evenly with an end of the first segment of meta tubing, there may be a third section in which the first segment o conduit and the second section of conduit are not telescopicall adjacent each other. Other sections of varying wall compositio may be created by telescopic engagement of other segments o conduit.

The present method preferably further comprises the ste of forming (molding or shaping) at least one of first section an the second section to a predetermined shape. The first segment o conduit and the second segment of conduit are thus preferabl fabricated of a ductile material such as a metal or plasti material. The term "ductile" as used in the present applicatio refers to a material that is able to undergo change of form withou breaking or that is capable of being molded or shaped. In general, upon deforming one of the first section and the second section int a predetermined shape, the first segment of conduit and the secon segment of conduit are locked or immobilized with respect to eac other. In a preferred embodiment, one of the first section and th second section are formed into a bellows using a hydroformin technique.

The present invention also provides hybrid conduit assemblies fabricated under the above-described method.

The present method of forming non-ccrextensively, telescopically engaged (laminated) conduit assemblies and the assemblies fabricated thereby provide numerous benefits over existing techniques, including, but not limited to, the following:

(1) a laminated assembly can be built to suit substantially any physical characteristics; (2) a laminated assembly has lower operating stresses for a given displacement than a single-walled conduit or tube of the same wall thickness; (3) a laminated conduit will exhibit hysteresis dampening whereas a solid-walled conduit will not; (4) a laminated conduit will emit less noise that a similarly sized solid-walled conduit in the same application; and

(5) a non-coextensively laminated, formed conduit assembly substantially eliminates the necessity of attachment via, for example, welding, thereby eliminating: (i) the costs associated with welding, (ii) heat affected weld zones (which can adversely affect corrosion resistance) and (iii) failure associated with weld zones.

Brief Description of the Drawings

Figures 1A through IC illustrate the conventional fabrication of a bellows section via hydroforming.

Figure ID illustrates an example of a typical prior method for the manufacture of hybrid tube/bellows assemblies such as bellowed exhaust ducts.

Figure 2 illustrates the telescoping of several tubin sections of different lengths to form a blank or subassembly to b hydroformed.

Figure 3A illustrates in cross-section the hydroformin of the subassembly of Figure 2.

Figure 3B illustrates in cross-section the trimming an sealing of end flares created during hydroforming.

Figure 3C illustrates in cross-section the crimping of subassembly to provide a seal between telescopically adjacen segments thereof.

Figure 4 illustrates in cross section a hybri tube/bellows assembly.

Figure 5A illustrates in cross-section the blan subassembly used to fabricated the hybrid tube/bellows assembly o Figure 4.

Figure 5B illustrates in cross-section an intermediat subassembly created in the assembly of the blank subassembly of Figure 5A.

Figures 6A and 6B illustrate in cross-section the hydroforming of the blank subassembly of Figure 5A to form the hybrid tube/bellows assembly of Figure 4.

Figure 7A illustrates in cross-section an internal seal assembly for use in hydroforming the blank subassembly of Figure 5A in which the internal seals are not actuated.

Figure 7B illustrates in cross-section an internal seal assembly for use in hydroforming the blank subassembly of Figure 5A in which the internal seals are actuated.

Figure 8A illustrates in cross-section a blank subassembly comprising non-coextensively laminated sections.

Figure 8B illustrates a hybrid conduit assembly produced by predetermined deformation/shaping of the subassembly of Figure 8A.

Detailed Description of the Invention

Under the present invention, an integral hybrid conduit assembly can be fabricated without the necessity of welding or other attachment of component sections. Unlike previous techniques, an assembly of non-coextensively, telescoped conduit segments (such as tubes) is used to accomplish this result. As used herein, the terms "conduit", "tube" and/or "tubing" refer to conduit of any cross-sectional shape, including, but not limited to, circular, oval, square and rectangular conduit. Preferably, at least one of the segments of conduit is ductile to allow forming thereof into a predetermined shape. Examples of suitable ductile materials include metals and polymeric materials. In the case of certain polymeric materials it is desirable to heat treat the assembly after forming to provide a thermosetting effect.

In practicing the present invention, a fabricator cuts a first segment of conduit to a desired size. The fabricator then cuts one or more segments of conduit of generally the same cross- sectional shape of the first segment but generally of a different

length than the first segment of conduit to be used as non -coextensive laminates. The first segment of conduit and the othe segment(s) are then assembled into a subassembly. The subassembl can be assembled simply by sliding one conduit segmen telescopically within or without another conduit segment to desired position with respect to that other conduit segment.

The resultant subassembly thus comprises sections o different wall composition (and, therefore, different physica characteristics) over the length of the subassembly. The condui segments comprising the subassembly may be chosen from a variety o materials and to have a variety of wall thicknesses to provid sections over the length of the subassembly having predetermine physical characteristics.

The telescoped tube segments may be immobilized wit respect to each other by crimping or by welding, for example, but such immobilization is not generally necessary. In most applications, one or more sections of the subassembly are deforme to a desired shape, and such deformation acts to fix the positions of the various conduit segments comprising the subassembly.

In the case of an exhaust duct of the same general design as illustrated in Figure ID, a second tube segment 110, having an outer diameter (OD) slightly greater than the OD of a first tube segment 120, is telescopically slid over first tube segment 120 as shown in Figure 2. A third tube segment 130, having an OD slightly less than the OD of first tube segment 120, is telescopically slid within first tube segment 120.

Subassembly 100 thus comprises three sections 132, 134 and 136 distinguished by their wall composition. First

sections 132 and third section 136 have a greater (composite) wall thickness than second, intermediate section 134. In first section 132, first tube segment 120 and second tube segment 110 are telescopically adjacent each other, resulting in a coinposite wall thickness substantially equal to the combined wall thicknesses of first tube segment 120 and second tube segment 110. Similarly, in third tube segment 136, first tube segment 120 and third tube segment 130 are telescopically adjacent each other, resulting in a composite wall thickness substantially equal to the combined wall thicknesses of first tube segment 120 and third tube segment 130. In the case of second section 134, first tube segment is not telescopically adjacent to either second tube segment 110 or third tube segment 130, resulting in a wall thickness equal to that of first tube segment 120.

Referring to Figure 3A, subassembly 100 is then deformed, preferably by a single hydroforming operation, to form bellows section 150 in second, intermediate section 134 and end flares 160 and 165 in first section 132 and third section 136, respectively. In the embodiment of Figure 3A, bellows section 150 thus has a wall thickness equal to the wall thickness of first tube segment 120. End flare 160 and the adjacent section of uncorrugated tubing sections have a composite wall thickness substantially equal to the combined wall thicknesses of first tube segment 120 and second tube segment 110. End flare 165 and the adjacent section of uncorrugated tubing have a composite wall thickness substantially equal to the combined wall thicknesses of first tube segment 120 and third tube segment 130.

Unlike previous hydroforming methods, one or more intermediate internal seals may be necessary to control the hydroforming process in the present invention. In the embodiment

of Figure 3A, three internal seals 170, 175 and 180 are used i hydroforming subassembly 100. Seals 170, 175 and 180 can, fo example, be elastomeric seals or metal-to-metal hermetic seals Seal 170 is placed outside (relative to the center of th subassembly) the desired position of end flare 160. Seal 180 i placed outside the desired position of end flare 165.

In general, one or more intermediate seals may b required when an internal laminate segment (such as third tub segment 130) is present and at some point thereon it is desired t prevent pressurized fluid from entering between such interna laminate segment and an adjacent tube segment. For example intermediate seal 175 is placed in contact with the inner wall o third tube segment 130 adjacent the desired position of bellow section 150, on the side of end flare 165.

One or more intermediate internal seals may also b required in cases where differences in composite wall thicknes and/or material (s) of various sections over the length of subassembly (blank) require different hydroforming pressures and i is desirable to deform two or more such sections concurrently.

An alternative to using intermediate internal seal during hydroforming, is to "crimp" or slightly deform th subassembly at a desired position thereon before hydroforming t create a seal (for example, a metal-to-metal hermetic seal) at tha position between adjacent plies or segments of conduit. Such crimp 187 is illustrated in Figure 3C, creating a metal-to-meta hermetic seal between telescopically adjacent segments 188 and 189.

During hydroforming, subassembly 100 is formed unde pressure into an external die set assembly to form bellows sectio

150 and end flares 160 and 165. Intermediate seal 175 preferably has at least one channel 178 therethrough, resulting in a substantially constant pressure (P) throughout subassembly 100. The positioning of intermediate seal 175 prevents pressurized water from entering between third tube section 130 and first tube section 120 to the right of the position of intermediate seal 175. This positioning of intermediate seal 175 allows pressurized water to enter between third tube section 130 and first tube section 120 in the area of bellows section 150 and results in the formation of an internal protective shield 190 within the exhaust duct. Protective shield 190 substantially prevents direct contact of hot exhaust gases with bellows section 150, thereby extending the life of bellows section 150.

After hydroforming, end flares 160 and 165 are appropriately trimmed and sealed as illustrated in Figure 3B to provide flared end portions 168. The assembly may then be bent to provide an exhaust duct of the general design of exhaust duct 9.

A detailed example of the fabrication of a hybrid tube/bellows assembly will be discussed with reference to Figures 4 through 6B. The finished hybrid tube/bellows assembly 201 for use in connection with a turbine is illustrated in Figure 4. In Figure 4, each segment of conduit is represented by a single solid line. Figure 5A illustrates the subassembly (blank) 250 used to form exhaust manifold 201.

In constructing subassembly 250 as shown in Figure 5A, a first segment of tubing 205 is cut to a length of approximately

18.25 in. First tube segment 205 preferably has a wall thickness of approximately 0.008 in. and an inner diameter of approximately 1.734 in. A second segment of tubing 210 is cut to a length of

approximately 4.625 in. Second tube segment 210 preferably has wall thickness of approximately 0.016 in and an ID of approximatel 1.775 in. A third segment of tubing 215 is cut to a length o approximately 6.500 in. Third tube segment 215 preferably has wall thickness of approximately 0.016 in and an ID of approximatel 1.698 in. A fourth segment of tubing 220 is cut to approximatel 1.90 in. Fourth tube segment preferably has a wall thickness o approximately 0.016 in. and an ID of approximately 1.651 in. Finally, a fifth segment of tubing 225 is cut to a length o approximately 9.75 in. Fifth tube segment 225 preferably has wall thickness of approximately 0.008 in. and an ID o approximately 1.775 in.

Tube segments 205, 210, 215, 220 and 225 ar telescopically assembled into subassembly 250 as illustrated i Figure 5A. During assembly of subassembly 250, second tube segment 210 is first telescopically slid over first segment 205 to b approximately even with the left distal end thereof. Fifth tube segment 225 is then telescopically slid over first tube segment 205 (starting from the right end thereof) until it abuts second tube segment 210.

Third tube segment 215 is then telescopically slid over fourth tube segment 220 such that the left distal edges thereof are approximately even as shown in Figure 5A. Third tube segment 215 and fourth tube segment 220 are preferably attached via autogenous (that is, without use of a filler metal) fusion welding to fix the relative position thereof. Subassembly 260 (Figure 5B) comprising third tube segment 215 and fourth tube segment 220 is then telescopically slid within first tube segment 205 such that the right distal end of subassembly 260 is approximately even with the right distal end of first tube segment 205.

Subassembly 250 thus has five sections distinguished in physical characteristics by their differing wall composition/thicknesses. First section 300 has a length A of approximately 4.625 in. and a composite wall thickness of approximately 0.024 in. (the combined wall thicknesses of first tube segment 205 and second tube segment 210) . Second section 310 has a length B of approximately 7.125 in. and a composite wall thickness of approximately 0.016 in. (the combined wall thicknesses of first tube segment 205 and fifth tube segment 225. Third section 320 has a length C of approximately 1.90 in. and a composite wall thickness of approximately 0.048 in. (the combined wall thicknesses of first tube segment 205, third segment 215, fourth tube segment 220 and fifth tube segment 225. Fourth tube segment 330 has a length D of approximately 0.725 in. and a composite wall thickness of approximately 0.032 in. (the combined wall thicknesses of first tube segment 205, third tube segment 215 and fifth tube segment 225) . Fifth section 340 has a length of approximately 3.875 in. and a wall thickness of approximately 0.024 in. (the combined wall thicknesses of first tube segment 205 and third tube segment 215) . An example of a suitable material for the tube segments is AISI 321 SS Tubing.

Subassembly 250 is then hydroformed essentially as discussed above for subassembly 100 to fabricate semifinished hybrid tube/bellows assembly 200. The hydroforming process is described in Figures 6A and 6B. As shown in Figure 6A, a die set 400 comprising bellows blades 410 and four seal dies 420 is used to hydroform subassembly 250 to form semifinished hybrid tube/bellows assembly 200.

Three internal seals 430, 431 and 432 are positioned within subassembly 250 to cooperate with seal dies 420. Each

internal seal 430, 431 and 432 is provided with an elastomeric (for example, rubber) seal 440 which preferably cooperates with a recess 450 in corresponding seal die 420. For example, elastomeric seal 440 of internal seal 431 provides sufficient" force upon subassembly 250 to deform subassembly 250 slightly, creating a seal between adjacent segments 205 and 215, thereby preventing fluid leakages between adjacent segments 205 and 215.

Introduction of a pressurized fluid into the regions between internal seals 430, 431 and 432 results in deformation of subassembly 250 as shown in Figure 6B. Seal dies 420, bellows blades 410 and internal seals 430, 431 and 432 are adapted to be mobile relative to each other during deformation. Seal dies 420, bellows blades 410 and internal seals 430, 431 and 432 are drawn towards each other along the axis of subassembly 250 during pressurization, thereby deforming subassembly 250 outward from center line 450 to form semifinished, hybrid tube/bellows assembly 200.

As discussed above with respect to the hydroforming of subassembly 100, intermediate internal seal 431 may have at least one channel 435 therethrough so that the region between internal seal 430 and 431 and the region between internal seals 431 and 432 are pressurized to the same pressure during deformation. In the case of hybrid tube/bellow assembly 201 of Figure 4, a pressure of approximately 2000 psi was used during hydroforming.

If the difference in the composite wall thickness to be deformed in the regions between internal seal is sufficient to require different pressures for adequate deformation, intermediate internal seals without channels therethrough may be used. Each

region may then be pressurized to a different pressure in this manner.

The operation of internal seals 431 and -"432 is best illustrated in Figures 7A and 7B. In the embodiment of Figures 7A and 7B, intermediate internal seal 431 is mounted upon slidable cylinder 510. Concentrically positioned within cylinder 510 is actuating cylinder 520. Actuating cylinder 520 is in operative connection with an actuating means such as a hydraulic cylinder 530. Referring to Figures 7A and 7B, upon actuation of hydraulic cylinder 530, end mounts 535 and 540 (such as washers) are drawn together (that is, end mount 535 is drawn towards end mount 540) , thereby compressing elastomeric seal 440 of internal seal 431 to cause elastomeric seal 440 of internal seal 431 to bulge outwardly (see Figure 7B) and create a seal between segment 205 and segment 215 (see Figure 6B) of subassembly 250.

Concentrically positioned outside of cylinder 510 is actuating cylinder 550 which is in operative connection with actuating means such as a hydraulic cylinder 560. Upon actuation of hydraulic cylinder 560, actuating cylinder 550 causes end mount 570 to be drawn toward end mount 575. Elastomeric seal 440 of internal seal 432 is thereby caused to bulge outwardly (see Figure 7B) and create a seal between segment 205 and segment 215 (see Figure 6B) .

End mount 575 of internal seal 432 is positioned against end block 590. During hydroforming, cylinder 510 slides towards internal seal 432, thereby drawing internal seal 431 towards internal seal 432.

Another embodiment of the present invention i illustrated in Figures 8A and 8B. Figure 8B illustrates portion 750 of an exhaust manifold formed by appropriate shaping o subassembly 700 of Figure 8A. Subassembly 700 comprises a firs segment of tubing 710 having two shorter segments of tubing 720 an 730 telescoped thereon as illustrated in Figure 8A. Upo deformation of subassembly 700 into manifold portion 75 illustrated in Figure 8b, the segments 710, 720 and 730 ar immobilized with respect to each other. Subassembly 700 may b shaped into manifold portion 750 by bending as known in the tubin art or, alternatively, by hydroforming as described above (in th case of complex shaping) .

Although in each of the embodiments of the presen invention set forth above, one segment of conduit extended over th entire length of the subassembly, this need not be the case. Th combinations of conduit segments for telescopic attachment to for the subassemblies of the present invention is virtually limitless, thereby providing excellent control over the wall composition o such subassemblies and the physical characteristics of the fina hybrid article.

The present method eliminates the need to handle/inventory individual conduit sections such as tubing an bellows sections and substantially reduces or eliminates attachment operations necessary to join such individual conduit sections.

In the case of a hybrid tube/bellows assembly, the non-bellowed, tubing section of the assembly can be laminated to behave as a single-walled tube and is formed coincidentally with the bellows. A combination of non-coextensive, laminated tubing sections provides control over the physical attributes of the

assembly over its length, allowing the fabricator to from relatively thin-walled bellows sections and relatively thick-walled tubing sections as desired.

Although, the present invention has been described in detail in connection with the above examples, it is to be understood that such detail is solely for that purpose and that variations can be made by those skilled in the art without departing from the spirit of the invention except as it may be limited by the following claims.