US2810400A - Reinforced flexible duct - Google Patents

Description

Oct. 22, 1957 A. E. HEwlTT YRlazINFoRclazD FLEXIBLE DUCT Filed Aug. 24, 1954 W/ WW i wm/ United States Patent C ice REINFoRcED FLEXIBLE DUCT Alvin E. Hewitt, Chanute, Kans., assignor to American Autolastic Corporation, Chanute, Kaus., a corporation of Kansas Application August 24, 1954, Serial No. 451,907

7 Claims. (Cl. 13S-56) This invention relates toa flexible duct construction, and particularlyto a construction of a reinforced, exible, fabric duct in which the spiral reinforcing strand is firmly enclosed within the Wall of the duct. The invention relates more specifically to a duct construction in` which the completed duct is produced by spirally wrapping a tape on a mandrel, cementing or vulcanizing the edges to form a unitary structure.

The invention is illustrated by drawings which show in Figure l the operation of winding the duct on a mandrel. Figures 2-6 show in cross-sections one wall of the duct in five modifications to be described hereinafter.

Heretofore in the manufacture of exibletducts it has been the practice to wrap a sheet or a strip of fabric on the mandrel, then apply a reinforcing strand to the out side if desired, and finally cover the reinforcing with an additional covering of tape or fabric strip. The reinforcing is usually wire, to provide rigidity to the duct in a radial direction while maintaining flexibility in a longitudinal direction. apply the reinforcing-spirally andlock the ends ofthe reinforcing wire to the wall of the duct. jIt has also been the practice to apply a cement, for example, rubber cement, plastic, etc.,'to the fabric before applying the final wrapping,'thereby.securing the `various elements in their desired position. This method of construction has had the disadvantage Vof leaving seams` on the surfaceof the duct:Y where the edges of fabric joined and these were usually fastened by sewing or by cementing. However they were fastened, the seamsA generally required an extra operation to protect them and prevent the wall of theduct opening along the line of the seam. Also-the manufacture of ducts of this typefhas required numerous operations, usually at least three operations being necessary, including the primary winding of fabric, the winding of the'reinforcing wire and the final winding of overlying fabric or tape tohold the reinforcing wire in the proper position.

In another method of making ilexible ducting, the fabric tape was folded over the reinforcing wire and wound into a tubular form by a head whereby a set of rollers coiled the tape into a continuous duct `in which the seams we'reieither cementedvor sewed during the coiling operation. The -resultingductewas not smooth internally, but presented av succession of ridges and .valleys to the fluid stream-transported therein, much as does a corrugated tube. Y.

It is an object of this invention to reduce the number of operations required in the manufacture of ducts of the reinforced flexible type, thereby reducing the cost of manufacture. Another object of the invention is to provide a duct of the reinforced flexible type in which no seams are apparent on the outside or the inside surfaces of the duct.

Another object of the invention is to provide a flexible duct with a smooth, cylindrical interior when extended, thereby providing maximum fluid carrying capacity with minimum turbulence. Previous methods of duct manu- It has usually been the practice toV being employed in the composition'to effect rapid vul-.

Patented Oct. 22, 1957' facture have left ridges on the inside to interfere seriously with flow of air thru theduct.

A further obiect of the invention is to make a sprally wound duct with cemented seams or laps without defects caused by separation of the seams. Ducts of this type haveheretofore not met the rigid requirements of the aviation industry, owing to the hazard resulting from occasional failure of seams not properly cemented orvulcanized. The manner of accomplishing these objects will beshown in thefollowing description of the invention.

lReferring to the drawings, Figure 1 shows the manner. of wrapping the duct on the'mandrel 10. This is done by. applying to thel mandrel a Vtape in which the reinforcing strand 11 is folded within a strip of fabric 12, with the wire 11 at one edge of the tape. `This ismost conveniently done by applying` the tape to a rotating mandrel having the diameter of the desired duct. The tape with wire enfolded can be ,prepared infadvance or the wire can be folded in the tape at the pointof winding on the mandrel.

Thevtape isapplied with suflcient tension to bind the windings firmly against the mandrel, placing .the laps under compression to unite them with a firm bond. Before winding, the tape is impregnated with a suitable adhesive, usually rubber or other elastomer, which not only seals the pores ofthe fabric, but also cements the successive windings -together. use cements of natural rubber or. syntheticrubber such as Buna-S, Buna-N, butyl, neoprene, lactoprene, Thiokol or siliconerubber (polysiloxane), etc. After the duct, is wound, applying the wrappings under tension,

` the entire assembly is vulcanized while under tension by heating in the usual m'anner, for example,'in an auto; clave. In the caseaof rubber, either natural or synthetic,

vulcanization is usually accomplished by heating to va temperature of about 250-300 F., sulfur and accelerators canizatioin.` In the case of certain other elastomers, such as silicone, vulcanization is effected by heat and catalysts, for example, peroxides.

Theimpregnating cement can be applied to the fiber by any ofthe usual methods suchias dipping in a solution ofcement, bythe application iof latex, or"spraying, 'or spreading with a knife. The fabric tape,l which can be cut on the bias if desired, is wrapped about the reinforcing strand which is usually a ste'el wire, but'itcan beany desired strand of high tensile strength. Thus, I may use a heavy filament of plasticsuch as an extruded nylon wire or rod, ora hard-twisted cord of cotton, glass fiber, or other fibrous material. Other metals can also be employed for the reinforcing strand, for example, aluminum'can be employed where it is desiredto keep down the weight of the construction. Itis desirable to coat the mandrel before wrapping with a suitable release agent which will prevent the tape sticking to the mandrel and facilitate removal of the duct. Various materials are available for this purposek such as silicone resins, when rubber ,cementis employed. After curing, the duct is removed 'from thejma'ndrel by theapplication of air pressure and other well known methods o'fstripping. K

An import element in the manufacture of the improved duct is maintenance of tension on thetape and the reinforcing strand during the curing operation, thereby firmly bonding the layers of tape together as shown in Figures 2 6, which are sectional drawings of different methods of assembling the duct. Thus, in Figure 2, the tape is shown wrapped about the wire 13 starting from a point 14, passing under wire 15, then clockwise about the wire 13 to a point 16. This, of course, is repeated for each winding, thereby providing four layers of tape For this purpose, I may` 3 beneath the wire as shown, and making tween Athe layers .of fabric which yare ycompressed between the wires 13, 15, etc. and the mandrel underlying the tape. A thin layer of rubber or other elastomer, 17, liesl next :to .the mandrel. and fllslthesp acesfbetween the-joints of the fabric and the mandrelg'asat' 18,1thus providing a' smoothy inner surface' forLthe 'duct-when vulcanized This layer orv lining 17 is 'usually formed frorn' thegc'ement which isapplied to the tape before Winding. 'l

The duct wall of Figure 2-is triple .plywith theedges bound beneath the adjacent reinforcing-strand, Lone edge passing beneath vtwo strands. 11n Figure T3, a double .ply construction isshown withloneedgel19 ofthe' tape locked and concealed between :two layers `of fabric beneathreinforcing. wire 20. No seamtis' exposed onfthe outer surfaces of duct walls shown in Figures 2 and 3. Figure 4 shows a singleply vconstruction with an external seam at.21.V y"When fwrapping, thetension of the tapecausestit to hugthe wire `closely ,asshown at Y22. The internal surface layer 'is shown at\23.

The single ply wallfconstruction shown in Figures 4, and 6 are designed .for ducts with a highflexibility-requirement. The `,walls shown in Figures 5 and 6 expose no seam on the outside. Thus in Figure 5, the Vfabric extends ,from 24 around ^wire 25, thence to edge 26 beneath wire 27. `Inner liner ZS-completes the assembly.

In Figure 6, the edge 29 is concealed between Vtwo layers of fabric, while the long edge 30 passes beneath the adjacent wire strand 31 and about half `way to the next strand 32, thus providing an'unusually well bonded duct wall having the high exibility of a single ply construction.

Figure 1 shows a double pitch winding in which two strips of tape 33 and 34 are Wound simultaneously. However, I usually prefer to employ a single pitch winding,

applying a single strip of tape with enclosed reinforcing strand. The ends of the wire may be secured to the Wall of the duct in the manner shown in cci-pending lpatent application, Serial Number 297,046, now PatentlNo. 2,697,452, December 21, 1954. I can alsoemploy `two or more strands of reinforcing in a single tape, thus producing a duct with double, single, etc. pitch of the reinforcing strand. For rough service, VI can apply a wear strip to the outside of the duct to overlie the vreinforcing wire. This can be done on the finished duct, 4but for convenience, it can best be applied before Vcuring while the duct is on the mandrel. The wear strip can Vbe of harder, less exible fabric than that employed in'the body of the duct, -providing the edges of the `wear strip are spaced apart sufficiently to allow free movement of theiwall ofthe duct exposed between the reinforcing turns.

Where a soft end is desired on the duct, the reinforcing strand can be removed near the Vend of the duct by slitting the layer. of Vfabric overlying it. Thus, several turnsof wire can be removed at the end lof. the Ycornpleted, vulcanized duct to provide an end which can be stretched or expanded over a rigid'nipple and clamped on to provide a tight, strong connection. A strip of bias tape an be applied to the area where the wire is removed. Other modifications will occur to those skilled in the art. In my improved duct construction, I have provided ducting which can be made simply vand at lower cost than previously while retaining the smooth bore for high velocity transmission of fluids, particularly air and vother gases up to temperatures of 600 F. in the case of silicone impregnated glass fiber.

-Having `thus described my invention, what I claim is:

1. Areinforcediiexibleduct having -a spiral, inelastic reinforcing strand completely enclosed in fabric tape having one free edge with said reinforcing strand folded within the other edge, the windings of said fabric tape forming said duct being spirally wound in the direction exposing said reinforcedV edge on the outside of said duct and cemented together without the free edge of said tape being visible on `the external surface of said duct.

2. The method of making a reinforced flexible duct which comprises enclosing a stii reinforcing strand Within a fabric tape impregnated with a suitable cement, spirally wrapping said tape and strand on a mandrel under tension sufficient to bind together the layers of fabric firmly against the mandrel, the direction of the wrapping being such that the edge of the tape enclosing the reinforcing strand overlies the free edge of the winding previously applied, thereafter curing the assembled Yduct on the mandrel while under said tension to effect a Viirm bond between the-layers of fabric under the pressure applied by the reinforcing, and finally removing the cured duct from the mandrel.

3. The method of making a reinforced exible duct which comprises folding a reinforcing wire within a fabric tape impregnated with a rubber cement, thereby providing a winding strip having a wire enclosed at one edge, spirally'wrapping said strip on a mandrel under tension sufficient `to bind together the layers of fabric by the pressure -eXerted by Vthe said wire and said mandrel, wrapping said -strip on said mandrel in the direction such that theedge of the strip enclosing the reinforcing wire overlies the free edge of the winding previously applied, thereaftervulcanizing the assembled duct while on the mandrel withV -said wire under tension to elfect a rm bond between the layers of fabric maintained under the pressure applied between the reinforcing vwire and the mandrel, and finally removing the cured duct from the mandrel.

Y 4. The method of claim 3 wherein the winding strip is impregnated Ywith rubber cement before enclosing the reinforcing wire therein.

l 5. The method of claim 3 wherein the rubber cement employed is silicone rubber, and thefabric is of glass liber.

6. A flexible, reinforced, fabric duct having a smooth, cylindrical interior, the walls thereof being formed of spirally Wound Vtape enfolding a reinforcing strand in one edge thereof', the freeedge of the tape opposite said strand being bound'at each-turn `beneath the adjacent coil of reinforcing strand,V adjacent coils being firmly cemented together with an elastic, rubberlike cement distributed between the-layers of said spirally wound'tape, only that edge of saidjtape enclosing said reinforcing strand being y visible on the external surface of said duct.

7. 'Ihe duct of claim 6 wherein one of said free edges of tape extends beneath two adjacent coils of reinforcing strand.

Y References cited in the ale of this patent UNITED sTATEs PATENTS

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