Class 1 Flexible Uninsulated Duct with Polymer Core and Surrounding Fire Resistant Barrier Layer and Method of Use

The invention relates to uninsulated ducts that carry a UL 181 Class 1 duct rating, the uninsulated ducts designed primarily for use in interior wall and floor spaces where duct insulating properties are not needed but flame penetration, high temperature resistance and other testing requirements related to the UL 181 standard are required. The uninsulated duct uses a fire resistant barrier layer and an adhesive combination to permits the uninsulated duct to maintain its integrity when subjected to the certain kinds of UL 181 testing.

The use of smaller diameter uninsulated ducts for interior spaces like floors and walls in a structure is well known. An example of such a duct is the S-TL duct sold by Flexible Technologies, see https://thermaflex.net/products/thermaflex-s-tl-flexible-duct/. This prior art duct uses a fiberglass cloth fabric bonded to a wire helix to provide its Class 1 duct rating.

Reference to a Class 1 duct rating refers to the UL 181 standard published Jul. 25, 2013 and entitled UL Standard for Safety Factory-Made Air Ducts and Connectors. This standard describes a Class 1 rating as air ducts and air connectors having a flame-spread index of not over 25 without evidence of continued progressive combustion and a smoke-developed index of not over 50. Hereinafter, this standard is abbreviated as the UL 181 Class 1 duct standard.

Although the prior art S-TL duct provides the desired Class 1 rating that permits its use in interior spaces, its manufacturing process is complicated and expensive.

Furthermore, the demand for these kinds of duct applications have grown due to the use of different modes of cooling and heating for interior spaces of structures, wherein ductwork is more often utilized in a conditioned space such that the ductwork is not in need of additional insulation. As such, a need exists to provide an alternative to the prior art duct mentioned above, the alternative duct being one that is more economically made and can better meet the increased demand for these kinds of ducts.

In response to this need, the inventive duct provides an improved design that includes uninsulated ducts that use a fire resistant barrier material as a part thereof, the fire resistant barrier material configured in the duct construction with a longitudinal seam having a combination of adhesives or a spirally wound uninsulated duct, wherein the fire resistant barrier material is part of the spirally wound duct construction with a spiral overlap that includes the combination of adhesives, the fire resistant barrier material and combination of adhesives allowing the duct to pass the testing required to qualify as a UL 181 Class 1 duct.

The invention provides an improvement in flexible uninsulated ducts that meet the UL 181 Class 1 duct standard.

In one embodiment, the flexible uninsulated duct that meets Underwriter Laboratories (UL) 181 Class 1 duct standard has a polymer core that includes a helical wire as a part thereof, the polymer core forming an inner space for conditioned air flow, and having an outer surface. A fire resistant barrier layer is provided that surrounds the outer surface of the polymer core, the fire resistant barrier layer providing flame spreading and smoke development resistance such that the flexible uninsulated duct meets the UL 181 Class 1 duct standard. In the inventive duct construction, a first surface of the fire resistant barrier layer faces the outer surface of the polymer core and an outer surface of the fire resistant barrier layer is exposed to form an outer surface of the uninsulated duct.

While the polymer core can be any known polymer core typically used as part of a flexible duct construction, one example is a polymer core that uses a pair of PET layers with a helical wire positioned therebetween.

Since the inventive flexible insulated duct meets the UL 181 Class 1 duct standard, it can be installed in a structure at a length greater than 14 feet so as not to be considered a connector that falls under this standard as such a connector does not meet all of the tests required for a duct falling under the UL 181 Class 1 duct standard.

While the fire resistant barrier layer can be associated with the polymer core in any known fashion to keep the two together to form the composite duct construction, one mode of association is adhering the fire resistant barrier layer to the outer surface of the polymer core using an adhesive. As an alternative association between the fire resistant barrier layer and the polymer core, the fire resistant barrier layer can have first and second opposing longitudinal edges, with the edges sewn or stitched together such that the fire resistant barrier layer surrounds the outer surface of the polymer core.

While the fire resistant barrier layer can be any type of material that, when surrounding the polymer core, the composite duct structure would meet the UL 181 Class 1 duct standard, a preferred material would be a woven or non-woven fabric material containing fiberglass. An alternative material would be a fire resistant fleece comprising fire resistant staple fibers and optionally char scaffold fibers.

The invention also entails the use of one or more of the flexible uninsulated ducts for moving conditioned or unconditioned air therethrough in a given structure, wherein the one or more flexible uninsulated ducts is in an interior space of a structure, e.g., in floor or walls spaces of the structure, wherein further insulation for the inventive duct is not required.

Another aspect of the invention is the use of a combination of adhesives where the fire resistant barrier material is bonded together as part of the uninsulated duct construction, the combination of adhesives maintaining the integrity of the duct when subject to certain testing in conjunction with meeting requirements to qualify as a UL 181 Class 1 duct.

Another embodiment of the invention entails a flexible uninsulated duct that meets some or all of the Underwriter Laboratories (UL) 181 Class 1 duct standard and that uses a combination of adhesives to facilitate passing certain of the tests required under the UL 181 standard. This combination of adhesives enables the bond between the fire resistant barrier material to maintain its integrity and bonded overlap when subjected to high temperature and/or flame penetration testing and, at the same time, maintain the integrity of the duct construction during duct manufacture.

More particularly, the flexible uninsulated duct includes a polymer core having, optionally, a helical wire as a part thereof, the polymer core having first and second opposing surfaces. A fire resistant barrier layer with opposing first and second surfaces is provided, one of the first and second surfaces of the fire resistant barrier layer facing one of the first and second surfaces of the polymer core, the helical wire, if used, arranged therebetween. One of the first and second surfaces of the fire resistant barrier layer or one of the first and second surfaces of the polymer core forming an inside surface of the flexible uninsulated duct that forms a channel for conditioned air flow. When the polymer film forms the channel, the fire resistant barrier layer is exposed as an outside surface of the flexible uninsulated duct. When the fire resistant barrier layer forms the channel, the polymer film is all exposed as an outer surface of the flexible uninsulated duct.

In the duct construction, portions of the fire resistant barrier layer form an overlap, the overlap being either longitudinal seam running along a length of the duct or a spirally wound seam running along the length of the duct.

In one duct construction, a combination of at least first and second adhesives is provided between overlapping portions of the fire resistant barrier layer, the first adhesive is a hot melt adhesive in an effective amount to immediately bond the overlapping portions together, the second adhesive is a high temperature adhesive in an effective amount to maintain the bond between the overlapping portions when the longitudinal seam or spirally wound seam is subjected to at least a flame penetration test according to the UL 181 Class 1 duct standard.

In an alternative duct construction for the portions of the fire resistant barrier layer forming the overlap in either the longitudinal seam or a spirally wound seam of the duct, where again a combination of at least first and second adhesives between overlapping portions of the fire resistant barrier layer is used, the first adhesive is a hot melt adhesive in an effective amount to immediately bond the overlapping portions together, the second adhesive is a cold glue in an effective amount to maintain the bond between the overlapping portions when the longitudinal seam or spirally wound seam is subjected to a high temperature test according to the UL 181 Class 1 duct standard.

Preferably, the duct is the type that uses the longitudinal seam to bind the fire resistant barrier material together as part of the duct construction of the flexible uninsulated duct.

Preferably, the first adhesive is the hot melt adhesive and the second adhesive is a sodium silicate adhesive where the overlap of the duct will be exposed to flame during flame penetration testing.

Preferably, the first adhesive is the hot melt adhesive and the second adhesive is a cold glue where the overlap of the duct will be subjected to high temperature testing but not flame penetration testing.

When the hot melt adhesive is combined with the high temperature adhesive, e.g., sodium silicate, the hot melt adhesive is in contact with a portion of the sodium silicate adhesive located on at least one portion of the fire resistant barrier layer forming the overlap or the hot melt adhesive is adjacent to the sodium silicate adhesive in the overlap.

In another embodiment, the hot melt adhesive can be in contact with a portion of the sodium silicate adhesive as a continuous or discontinuous strip form or a discontinuous form made up of discrete portions of hot melt adhesive dispersed along the overlap.

When the hot melt adhesive is used with the cold glue, the hot melt adhesive and the cold glue can be kept generally separate from each other in the overlap, for example as adjacent strips of adhesive next to each other.

When the hot melt adhesive is combined with the high temperature adhesive, the hot melt adhesive covers 20-40% of an area of the overlap that is covered with the sodium silicate adhesive applied to the fire resistant barrier layer, preferably 25-35%.

The invention also includes a method of using the flexible uninsulated duct for supplying conditioned or unconditioned air to a space in any kind of structure or building needing such supply of air. The uninsulated nature of the flexible duct makes it ideal for use in inside walls of the structure as no insulated is need for such applications.

Another embodiment of the adhesive combination is the combination of a cold glue to provide the adhesion to maintain the integrity of the duct for processing and the high temperature adhesive to provide the ability to pass the flame penetration test. With this embodiment, the cold glue would require a drying/curing step as part of the cold glue application as, unlike the hot melt glue and its ability to create a bond almost instantaneously, the cold glue needs to set before bonding is complete. The combination of these adhesives would maintain bonding for high-temperature and flame penetration testing.

The uninsulated duct provides significant advantages over other and similar type ducts. Whereas the entire duct construction of the prior art duct S-TL is designed to meet the UL 181 Class 1 duct standard, the inventive uninsulated duct can be more economically made due to the ability to use what is essentially a stock polymer core and impart a Class 1 duct rating to the duct by associating the polymer core with an outer fire resistant barrier layer such that the polymer core-fire resistant duct construction meets the UL 181 Class 1 duct standard, wherein the duct would pass all of the 15 tests set forth in the UL 181 standard, as distinguished from the connector category for this particular standard.

The polymer core for use with the inventive duct is a typical helical wire-containing polymer core used as part of flexible ducts for conditioned or unconditioned air. Examples of these kinds of polymer cores are described in U.S. Pat. No. 10,767,892 to Campbell et al. and the other prior art disclosed therein. This patent is incorporated in its entirety herein, particularly with respect to its teachings regarding polymer cores for flexible ducts.

A typical polymer core construction includes two layers of a polymer material, e.g., polyolefin, polyester, polyvinyl chloride or mixtures thereof, with polyester terephthalate (PET) being a more preferred polymer, with a helical wire positioned therebetween. With the two polymer layers adhered to each other, the helical wire, which can be either metal or plastic as is known in the art, becomes an integral part of the flexible polymer core. The helical wire provides additional structure to the duct and allows for its compressibility and expansion. The core outer and/or inner surfaces can be metallized as is also well known in the art if a particular duct application requires such metallization.

shows a schematic and sectional view of one embodiment of the inventive flexible uninsulated duct. The inventive uninsulated duct is designated by the reference numeral. The polymer core is designated by the reference numeral. The helical wire that extends longitudinally through the polymer core is not illustrated infor simplicity purposes. The polymer corehas an outer surfaceand forms a passagewaythat allows for conditioned air or the like to flow therethrough. Surrounding the outer surfaceof the polymer core is a fire resistant barrier layer. The inner surfaceof the fire resistant barrier layer faces the outer surfaceof the polymer core. The fire resistant barrier layerincludes an outer surface, which acts as an exposed surface of the uninsulated duct, meaning no other material covers the outer surfaceof the fire resistant barrier layer. The fire resistant barrier layeris depicted inas a fibrous or felt-like material but the barrier layer is not limited to just these kinds of materials.

shows a typical application of the inventive uninsulated duct wherein a schematic diagram of an internal wall portion with interior wall and floor spaces that can utilize the inventive duct is depicted. The diagram shows just one wall of the internal wall portion so that the inventive duct is readily seen in its application. The internal wall portion includes a pair of studsandthat together with the walls on either side of the studsand(one wall depicted as) form a wall space. The inventive ductis shown positioned inside the wall space, with a terminationthat would allow the conditioned or unconditioned air in the ductto enter the interior space through a vent (not shown) in wall. The ductcan extend through the top silland further extend through the space between the top silland upper floorof a two-story structure. In other words, the inventive duct in this example is used in both a wall space and a floor space. However, the inventive duct can be used in any interior space or combination of spaces of a structure, wherein insulation from heat or cold conditions is not required. The inventive duct can be configured in terms of its positioning in the interior spaces of a given structure in any known way.

For purposes of the invention, uninsulated means that the inventive duct does not use any insulating material surrounding the fire resistant barrier layer. While the fire resistant barrier layer as part of the inventive duct may technically have some finite insulating value, the duct is effectively one that is non-insulating as there is no other insulating material associated with the duct. The insulating value of the fire resistant barrier layer is negligible such that a duct that is solely made up of the polymer core and the fire resistant barrier layer is effectively one that does not provide an effective insulating value.

The fire resistant barrier layer can be any material that would provide the required UL 181 Class 1 flame spreading and smoke development resistance, as part of its surrounding of the polymer core. The materials of the fire resistant barrier layer include woven and nonwoven materials, including fiberglass-containing materials, materials that use Nomex fibers, materials that use Nomex fibers in combination with other fibers, materials that may contain ceramic coated fibers/yarns, and the like.

One example of the material that can be used as the fire resistant barrier layer is a fire resistant fleece as disclosed in U.S. Pat. No. 10,443,190 to Wenstrup, which is incorporated in its entirety herein. This fleece includes a fire resistant (FR) fiber, which is defined to be fibers having a limiting oxygen index (LOI) value of 20.95 or greater as determined by ISO 4589-1. The Wenstrup patent provides different examples of these kinds of fibers, e.g., FR resistant rayon staple fibers wherein these fibers are between 20-80% of the weight of the fleece. The fleece also preferably includes a chloride, plurality of char scaffold fibers, which are defined as fibers once burned retaining a portion (at least 80%) of their original strength. Examples of these include mineral fibers such as silica and basalt, aramids, carbon fibers, partially oxidized polyacrylonitride (PAN) and fully carbonized fibers, with the weight percentage of these preferable fibers similar to the FR fibers, i.e., between 20-80% by weight. The fire resistant fleece can also incorporate a scrim as a part thereof and include other non-fire resistant fibers, e.g., polyester fibers, up to a certain weight percentage that does not comprise the fire resistant properties of the fleece.

It is also believed that the fiberglass fabric used in the S-TL duct described above is also a candidate for the fire resistant barrier layer of the inventive duct. High-Temp Suntex textiles also provide a number of different materials, e.g., fire resistant fiberglass fabric, high temperature fiberglass cloths, and woven fiberglass cloths that are believed to be suitable candidates as the fire resistant barrier layer of the inventive duct, see https://www.coatedfiberglassfabric.com/supplier-307158-fire-resistant-fiberglass-fabric, https://www.coatedfiberglassfabric.com/supplier-305933-high-temperature-fiberglass-cloth, and https://www.coatedfiberglassfabric.com/supplier-305861-woven-fiberglass-cloth. Fiberglast also makes woven and nonwoven fiberglass fabrics that are believed to be suitable for use as the fire resistant barrier layer, see https://www.fibreglast.com. Fiberglass-containing fabrics made by Milliken of Spartanburg, South Carolina are also candidates for the fire resistant barrier layer.

The fire resistant barrier layer can have a variety of thicknesses. However, it is preferred that the thickness of the fire resistant barrier layer be kept to just a thickness that would meet the UL 181 Class 1 duct standard rating. Keeping the fire resistant barrier layer to a minimal thickness while still meeting the UL 181 Class 1 duct standard rating reduces the amount of material need to surround the polymer core and keeps costs down. It also provides an overall smaller duct diameter, which facilitates the use of the duct in wall spaces or floor spaces when being used to move conditioned or unconditioned air. Preferably, the fire resistant barrier layer is less than an inch in thickness so that the compressibility of the polymer core is not compromised and the overall diameter of the uninsulated duct does not interfere with its installation in a given interior space.

For felt/fabric type materials, typical thicknesses of these kinds of materials range from 4 to 200 mils (0.004 to 0.2 inches) with a more preferred thickness of 20 to 200 mils (0.02 to 0.2 inches).

The fire resistant barrier layer can be associated with the polymer core in any known fashion. Examples of associations include the use of an adhesive to adhere the inner surface of the fire resistant barrier layer to the outer surface of the polymer core.shows a schematic of a sectional view of a longitudinal portion of the uninsulated ductwith an adhesive layerdisposed between the polymer core, containing the wire helix, and the fire resistant barrier layer.

Referring now to, when associating the fire resistant barrier layer with the polymer core, the fire resistant barrier layeris provided or cut to a given width W so as to form opposing longitudinal edges, wherein the W corresponds generally to the outer perimeter of the polymer core. The fire resistant barrier layer is wrapped around the polymer core so that the opposing edges either meet or overlap, preferably overlap, to ensure coverage of the polymer core, with one another. As part of the wrapping, an adhesive can be used as described above so that the fire resistant barrier layer is adhered to the polymer core outer surface. Alternatively, the opposing edgescan be sewn or stitched together in a manner so that the fire resistant barrier layer is firmly positioned around the polymer core and not susceptible to any significant movement along a length of the polymer core that would disrupt the composite construction and fire rating of the duct.shows an example of overlapped edges of the fire resistant barrier layerthat is stitched together at.

Mechanical means could also be employed, e.g., clamps, straps, zip ties, wherein the mechanical attachment is such that the fire resistant barrier layer is held in place when positioned against the outer surface of the polymer core. Combinations of attachment techniques described above are also within the scope of the invention.

The manner of association between the polymer core and fire resistant barrier layer can be accomplished in a batch or continuous method. In a batch method, a given length of polymer core and fire resistant barrier layer are provided and the two are associated together using one of the techniques described above.

In a continuous method, the fire resistant barrier layer could be continually fed along side a moving polymer core, wherein the appropriate machinery could wrap the fire resistant barrier layer around polymer core. A means could be additionally provided for the continuous use of an adhesive or stitching to associate the fire resistant barrier layer with the polymer core and produce the flexible uninsulated inventive duct. The manufactured duct could then be cut to a desired length or a stock length, which could be shortened later for a given application.

Typical duct dimensions can range from 2 to 20 inches, which is the range of available sizes for the prior art S-TL duct. However, for the use of the uninsulated duct in interior spaces, smaller sizes are preferred, e.g., less than 8-10 inches, less than 6 inches, less than 4.5 inches in diameter, and even 3.5 inches or less in diameter. The uninsulated duct could come in virtually any length that a particular application would require, similar to the S-TL duct, whose length as a duct is not limited.

Another aspect of the invention addresses the situation wherein the uninsulated duct may be subject to testing wherein the uninsulated duct with either a longitudinal seam or an uninsulated duct that is spirally wound and has a fire resistant barrier material spirally wound seam would be directly involved in the testing and subject to high temperatures and/or direct flame contact. In these kinds of situations, certain modifications to the duct construction are required to ensure that the integrity of the uninsulated duct is maintained during such testing. This modified construction involves the use of a combination of adhesives in the seams noted above, the combination of adhesives bonding the fire resistant barrier material together in the seam areas of the duct so that the duct maintains its integrity during such testing. While the description of the uninsulated duct above focuses on a longitudinal seam-containing duct, this additional aspect of the duct construction and use of the combination of adhesive also applies to spirally wound ducts employing the fire resistant barrier material.

As noted above, there are a number of standards that are required to be met to obtain a UL 181 Class 1 duct rating. These tests include the flame spreading test noted above as well as flame penetration tests, a high temperature test, and various mechanical tests. In the flame penetration test, a section of duct material, including the helical wire, if present, is placed over a furnace at approximately 1400 F and a weight is placed on the inner layer of duct material. The outer layer of the duct faces the furnace during the flame penetration test. Another test is a high temperature test, wherein an interior of a duct is subjected to a temperature of 265° F. for 60 days. There are other mechanical tests which require that the duct is sufficiently strong to meet these tests.

While the fire resistant barrier layer on its own can easily meet the flame penetration test, the ability to meet this test as well as others, e.g., the high temperature test and certain mechanical tests, can create some issues when considering a duct made using an adhesive to make the duct integral in terms of its various components.

An embodiment, wherein the fire resistant barrier layer would be stitched as is described above, may not have such a problem providing that the stitching is such that it can withstand the temperatures of the UL 181 tests noted above. However, if an adhesive is used, the make up of the adhesive is critical in the ability for the adhesive-containing duct to meet the UL 181 Class 1 duct standards and maintain the integrity of the duct for an intended application.

If the stitching mentioned above is replaced with an adhesive for the longitudinal seam-containing uninsulated duct such as shown in, the fire resistant barrier layer material, which wraps around the polymer core, is held together with an adhesive layer such as shown in. In, the adhesive-containing duct is designated by the reference numeral. The ducthas an inner polymer coreand an outer fire resistant barrier layer. A seam is designated by the reference number, wherein a portionof the fire resistant barrier layer overlaps another portionof the fire resistant barrier layer. This overlap zone is designated by the reference “O” and runs circumferentially around the duct for a limited distance, indicated by the bracketed line with the “O” as a part thereof. It is desirable to minimize the overlap distance while still having enough overlap and adhesive to bond the ends of the fire resistant barrier layer together and maintain the integrity of the bond when the uninsulated duct is tested. Minimizing the overlap is desirable as this means that less fire resistant barrier material and adhesive are used and the overall cost of making the duct is reduced. The actual overlap distance when measured circumferentially can vary, but a desirable range of the overlap can be from ½ inch to 2 inches. Less than ½ inch of overlap means that there may be insufficient amount of adhesive to bond the fire resistant material layer end portions together. With the overlap bonded in place, a longitudinal seam runs longitudinally along the length of the duct. For sake of clarity, the adhesive located between the two portionsandto form a bond for the seam is not shown inbut shown in a schematic fashion in, wherein just the overlap is shown.