Abstract:
A foam duct is provided. Among other applications, it may be used in automotive HVAC systems. The method of making this duct reduces material waste and provides an unexpectedly reliable joint in a duct at a sharp or rounded corner. In place, the airflow further supports the joint. In the method, a first portion of a hollow pre-duct is joined with a second portion of a hollow pre-duct by bending the portions at a cut-out positioned between the portions. The bending is complete when the portions form a mechanical connection, which may be signaled by tactile or audible feedback.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to ducts and methods of making ducts. Improved lightweight air ducts can be used in many applications, including in harsh environments such as but not limited to automotive HVAC ducts. 
       BACKGROUND 
       [0002]    Conventionally, foam air ducts can be formed using sheets, such as in a twin-sheet forming method. When ducts with complex shapes are formed, including those with sharp or rounded corners, conventional formation of these ducts may cause a substantial amount of material to be wasted. This is because, conventionally, half of the complex shape comes in its final shape from the top sheet, and the other half comes in its final shape from the bottom sheet. Conventionally, each half is integrally and contiguously formed. 
       SUMMARY 
       [0003]    Surprisingly, it has been found that half pre-duct shapes need not be integral and contiguous to be sufficiently durable to survive in difficult environments like automotive HVAC systems. This makes it possible to make more ducts with shapes including corners from a single set of foam sheets. Including a cut-out where a corner would be to act as a hinge can straighten the overall shapes out during thermoforming, making the initial shapes more like “I” shape than an “L” shape. Simply stated, waste can be minimized when making generally “I” shapes from a foam sheet rather than generally “L” shapes. More can be fitted onto a single sheet. The reduction in waste, which in some examples may be a reduction of from about 10-15%, may be especially beneficial where waste is from non-recyclable foams such as cross-linked foams. 
         [0004]    After thermoforming, the half pre-duct shapes together, the full pre-duct shapes can be folded or bent at the cut-outs or hinges to make the generally “L” shape with the corner. This minimizes the need for deep draws or stretching during thermoforming. Advantageously, by using cut-outs as hinges in pre-duct devices, wall thickness of a hollow duct can remain substantially uniform. Without the cut-outs, thermoforming may cause stretching in areas such that those regions designed to be corners, thereby thinning walls in those regions of the duct. 
         [0005]    Cut-outs can be configured to include mechanical fastening structures. Such structure may provide tactile or auditory feedback to confirm mechanical engagement. Moreover, cut-outs can be reinforced by, for example, laser welding. Moreover, airflow during use can reinforce the joint in-situ. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is an exemplary full pre-duct device; 
           [0007]      FIG. 2  is an exemplary air duct formed by folding and joining portions of the full pre-duct device of  FIG. 1 ; 
           [0008]      FIG. 3  is a lay-out of half pre-duct shapes with cut-outs on a foam sheet; 
           [0009]      FIG. 4  is an exemplary air duct; 
           [0010]      FIG. 5  is a top view of an exemplary half pre-duct shape with a cut out and a flap; 
           [0011]      FIG. 6  is a view of a corner of an exemplary air duct with a reinforced joint; 
           [0012]      FIG. 7  is a view of a corner of an exemplary air duct with a reinforced joint. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    All figures and examples herein are intended to be non-limiting; they are mere exemplary iterations and/or embodiments of the claims appended to the end of this description. Modifications to structure, materials, the order of steps in procedures, temperature ranges, are contemplated. 
         [0014]    Referring to  FIG. 1  full pre-duct device  10  has been thermoformed into its three-dimensional shape. First portion  12  is separated from second portion  14  by cut-out  18 . First portion  12  includes flap  16  which may have a protrusion that can fit into an aperture on second portion  14 . Second portion  14  has inner walls  17  that fit inside first portion  12 . Other mechanical and/or chemical attachment configurations and mechanisms are contemplated. 
         [0015]    Referring to  FIG. 2 , air duct  20  is formed by folding the device  10  such that first portion  12  is moved toward second portion  14  until a mechanical connection is made between the portions. Corner  26  is formed at joint  22 . Note that the term corner as used herein does not require sharp edges or 90 degree angles. Corner is simply a useful term to describe a complex shape that has a significant bend in its overall shape. 
         [0016]    Referring to  FIG. 3 , a lay-out of half pre-duct shapes  30  with cut-outs on a foam sheet. Note that the term “half” as used herein is not meant to denote precisely 50% of a pre-duct shape as measured by amount of material or surface area or volume. Rather, the term is used as a convenience to denote that, in thermoformed examples formed from two sheets, the portion formed from one sheet is “half” and the portion formed from the other sheet is “half.” The halves become fused together during thermoforming, joined by a ridge. Depending on a shape of a particular duct, the amount of material in one “half” may be the same as, less than, or more than the other “half.” 
         [0017]    In a duct made from half pre-duct shapes  30  as exemplified, about 13% of material savings can be realized if cut-outs  38  are positioned between portions  32  and  34 . Material savings through reduction in waste can be greater or less, depending upon the shape of the duct. This may be particularly advantageous when using non-recyclable material such as cross-linked foams. Otherwise, fewer half pre-duct shapes  30  fit on a sheet. That is, the cut-outs  38  permit the thermoforming to take place with shapes that resemble more of “I” than an “L.” Even though a joint is being introduced into a duct that had been conventionally been made contiguously, surprisingly, the joint is strong and durable in harsh environments such as automotive HVAC environments. 
         [0018]    Cut-outs  38  generally have an origin (that may act as a hinge) and an angle between portions  32  and  34 . The angle can vary in degree depending on the shape of the duct to be formed. In some examples, the angle of the cut-out  38  may be as low as 5 degrees or as high as 175 degrees. More typically, cut-outs  38  vary in angle from about 10 degrees to about 60 degrees. 
         [0019]    Referring to  FIG. 4 , exemplary air duct  200  is shown with corner  260 . Air duct  200  is formed by folding portions of full pre-duct devices together at corner  260 . As is evidenced form the ridge between top and bottom halves of the air duct, the exemplary full pre-duct devices were thermoformed by, for example, twin sheet processing. 
         [0020]    Referring to  FIG. 5 , a top view of an exemplary half pre-duct shape with a cut out  180  flanked by portions  120  and  140 . Portion  120  and  140  at or near cut-out  180  include mechanical structure for joining the portions  120  and  140  to form a joint at a corner and thereby form an air duct. In this non-limiting example, flap  140  has teeth that engage with complementary engagement structure  174 . Any number of connection mechanisms may be used, mechanical or chemical. Hook and loop fasters, snaps, or simply protrusions slidable into apertures. It is not important if structure is that one portion or the other, just that the connection mechanism joins the opposing parts. 
         [0021]    Referring to  FIG. 6 , exemplary air duct  200  includes a mechanical connection  190  at the joint. The mechanical connection  190  can be the one formed at forming the air duct  200 , which could provide auditory or tactile feedback to let a folder know the joint had been formed, or it could be an additional mechanical device providing reinforcement to the joint created during formation of the air duct  200 . That is, in one example, a user can feel and/or hear a mechanical joint being formed when bending a first full pre-duct device toward a second full pre-duct device sufficiently far as the engage the protrusion/aperture connection or other connection. 
         [0022]    Referring to  FIG. 7 , exemplary air duct  200  includes corner  260 . Exemplary reinforcement mechanisms are provided. One such mechanism is the use of the air duct itself. That is, airflow through the duct moves in a direction that tends to keep the portion inside the complementary portion in place. Other examples are latches positioned at  290 , either integrally formed with the foam or added on, or welds such as are indicated at weld line  295 . 
         [0023]    Exemplary air ducts may comprise any of a number of materials, including plastics such as thermoplastics, thermosetting plastics and foamed materials. Exemplary plastics may include polyethylene and/or polypropylene. Fatigue and flexing properties (ASTM D-430 and D-813) of the folding joint/hinge should be sufficient to maintain the integrity of duct  10  in conditions typical of an HVAC environment. Where the duct comprises plastic, mechanical properties of the materials, it may be sufficient impact strength, tensile modulus, and/or flexural strength (ASTM D-790 and D-747) to permit folding as desired and to withstand conditions typical of an HVAC environment. 
         [0024]    As a non-limiting example where the duct comprises foam, the duct may be formed from a closed-cell, cross-linked polyolefin foam material. Exemplary polyolefin foam blends may comprise one or both of polypropylene and polyethylene. The percentage by weight of polypropylene and polyethylene in the polyolefin foam blend may vary as a result of the manufacturing process, but the percentage by weight of polypropylene may be higher than the percentage by weight of polyethylene. Suitable types of foam material are available through Toray Industries, Sekisui Voltek, Armacell, and Qycell Corporation. One non-limiting example may include Toray&#39;s Crosslinked Polyolefin Foam. Another non-limiting example may include Trocellen Class chemically cross-linked, closed cell polyethylene foam, available through Trocellen GmbH. 
         [0025]    The foam sheets may have the same or different density and/or thickness. One or the other or both may have a density in the range of about 2 lb/ft 3  to 4.31 lb/ft 3 , and more specifically, a density of about 4 lb/ft 3 . The foam sheets may have a thickness of about 4 mm. Other thicknesses and densities are contemplated, including those higher and lower than the exemplified ranges. 
         [0026]    The duct may be formed by any of a number of manufacturing methods. Where the duct is plastic, one or more components may be formed through one or more of any of a number of manufacturing processes including extrusion, casting, and injection molding. In a non-limiting example pertaining to foam ducts, a plurality of ducts are formed by twin sheet processing two sheets of foam material, creating a thermoformed seal. 
         [0027]    The foam sheets are properly sized. This may require the foam sheets to be cut or trimmed to a specific length and/or width. The size of the foam sheets may be determined by the size and shape of the foam air ducts that will be formed. Half pre-duct shapes with cut-outs as exemplified in  FIG. 3  can maximize the number of air ducts formable from a particular set of foam sheets and minimize material waste. In certain applications, the size of the foam sheets may also be determined by the size of the press and the dimensions of an upper mold tool and a lower mold tool of the twin sheet processing tool. 
         [0028]    The foam sheets are engaged with a first frame a second frame. The foam sheets may be engaged with the frames using hydraulically operated mechanical clamps or any other suitable fastening mechanisms for holding the foam sheets in place during a heating operation. By clamping the foam sheets to the frames, the foam sheets may also be kept in tension during heating. The foam sheets may be introduced into a heating operation. The process may occur in an oven or any structure capable of heating the foam sheets to a predetermined temperature for a specific period of time. The temperature and time period to complete the heating process are dependent on the density and the thickness of the foam sheets being used to form the foam air duct. In one example, the foam sheets may be heated to a temperature in the range of about 250° F. to 400° F. When the foam sheets are heated within this temperature range, the sheets may be molded into the shape of the desired hollow foam air duct using the twin sheet forming tool including a press, the upper mold tool, and the lower mold tool. 
         [0029]    The upper tool mold and the lower tool mold may include channels or any other suitable structures capable of removing air. Accordingly, a vacuum pump or any other suitable device may be applied to the upper tool mold causing the first foam sheet to take the form of the interior surface of the upper tool mold. This may create a first section of the foam air duct. Similarly, a vacuum pump or any other suitable device may be applied to the lower tool mold causing the second foam sheet to take the form of the interior surface of the lower tool mold. This may create a second section of the foam air duct. The upper tool mold and the lower tool mold may then be compressed together. The effect of the heated sheets and the pressure from the compression bonds the foam sheets together in the desired shape, forming a unified full pre-duct device of a predetermined shape, each device having portions flanking a cut-out. 
         [0030]    Cooling of pre-duct devices may be permitted. Excess material may be removed so the full pre-duct devices are close to a final shape. Then, the full pre-duct shapes may be bent at the cut-out to join first and second portions of a full pre-duct shape to make a joint at a corner of a duct and form a foam duct. Flaps from one portion may be inserted into the other portion. The joint may be mechanical and may be reinforced mechanically and or chemically, such as with a fastening or latching device or structure, a laser weld, or an adhesive. The attachment may or may not involve engagement of a flap or protrusion on a flap on one portion with receiving structure on the other portion. 
         [0031]    With regard to the processes described herein, it should be understood that, although the steps of such processes, have been described as occurring in a certain sequence, such processes could be practiced with the described steps performed in an order other than the exemplary order. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the claimed invention. 
         [0032]    Accordingly, it is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent upon reading the above description. The scope of the invention should be determined with reference to the appended claims along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the invention is capable of modification and variation. 
         [0033]    All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those knowledgeable in the technologies described herein unless an explicit indication to the contrary is made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.