Abstract:
A bushing is disclosed for pivotally mounting a damper in ductwork of the type generally used with heating, ventilation, and air conditioning (HVAC) systems. The bushing is a circular shaped member of silicone rubber material, which is particularly configured and dimensioned to provide an airtight fit with the ductwork to prevent loss of conditioned air at the pivot location, without compromising the rotational capability of the damper to alter the direction of the conditioned air. The bushing is dimensioned to be inserted into the ductwork and includes a peripheral groove which receives the ductwork in a manner which compresses the inner surface of the groove to provide the airtight seal. The bushing also includes a longitudinally tapered square central opening, which opening is dimensioned to engageably receive the damper pivot rod snugly to provide additional sealing at the interface between the bushing and the pivot rod.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to provisional application No. 61/573,679, filed Sep. 9, 2011, the disclosure of which is incorporated herein by reference and made a part of this application. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to improved bushings for pivotally mounting dampers for heating and cooling ductwork systems without loss of conditioned air at the pivotal locations of the damper. The invention also relates to improved ductwork and ductwork dampers which incorporate such improved bushings. One example of such ductwork dampers is disclosed in my co-pending application Ser. No. 12/322,474, filed Feb. 2, 2009, the disclosure of which is incorporated herein by reference. 
         [0004]    2. Description of the Related Art 
         [0005]    Heating, ventilation and air conditioning systems, commonly referred to as “HVAC” systems, generally make extensive use of air ducts which are utilized to transport heated or cooled air (i.e., conditioned air) throughout the system. Such duct systems are generally referred to as “air ductwork,” and components of such ductwork are generally made of sheet metal. While galvanized mild steel is the standard and most common material used in fabricating such ductwork, such ductwork can also be made of other materials such as aluminum, plastics, fiberglass and the like. The present invention is contemplated for use primarily with galvanized steel metal ductwork, but the use of my invention with other types of systems is also envisioned. 
         [0006]    In most systems, the ductwork components are assembled in a manner to best distribute the air to designated locations using such featured components as plenums, take-offs, volume control dampers and the like. Take-offs may be fitted into round or rectangular openings cut into the wall of the main duct. 
         [0007]    Volume control dampers (i.e., “VCDs”) are incorporated in such HVAC ductwork systems to provide a method of adjusting the volume of air flow to various parts of the system. Such VCD&#39;s provide this function. Besides the regulation provided at the registers of diffusers that spread air into individual rooms, dampers can be fitted within the ducts themselves. These dampers may be manual or automatic. Zone dampers provide automatic control in simple systems, while VAVs (i.e., Variable Air Volume Controls) allow control in more sophisticated systems. 
         [0008]    Dampers of the type described are generally pivotally mounted in a section of ductwork on relatively loose fitting hard plastic bushings, primarily nylon bushings. Accordingly, over time, substantial losses of energy have been sustained by leakage of conditioned air through the generous spaces which existed between the bushings and the sheet metal ductwork, and between the bushings and the damper shafts. It has been estimated that such ductwork systems utilizing the prior art bushings have sustained up to three percent (3%) loss of conditioned air. 
         [0009]    In the past, the comparatively low cost of such energy losses did not present serious issues. However, with the rising cost of energy, the focus on such losses have become a serious cause for concern. In particular, it has been determined that such losses are not sustainable. 
         [0010]    The present invention relates to a bushing for mounting such dampers to ductwork intended for transporting conditioned air from place to place, without the loss of such conditioned air at the pivotal locations of the dampers. As well, the invention also relates to a damper unit which incorporates such bushing, and ductwork which incorporates such damper and bushing. 
       SUMMARY OF THE INVENTION 
       [0011]    A bushing is disclosed for pivotally mounting a damper to a section of ductwork for directing conditioned air in a predetermined direction, which comprises a member made of a soft pliable material, and having a generally circular outer periphery, the member defining a peripheral groove over at least a portion of the periphery for attachment of the member to a section of the ductwork by insertion into an opening in the ductwork, the opening preferably being of diameter at least equal to, or generally less than the inner diameter of the peripheral groove. 
         [0012]    A generally central opening extends through the center of the soft pliable member for engaged reception of an elongated damper pivot rod to which the damper can be attached, for permitting the damper to be pivoted relative to the ductwork while the bushing rotates smoothly relative to the ductwork. 
         [0013]    The bushing can be made of a natural or synthetic rubber material, although such materials are not considered to be limited. Silicone rubber or any synthetic rubber material is preferred. 
         [0014]    The generally central opening in the bushing member is preferably tapered, with the opening of lesser dimension on one side being less than the corresponding dimension of the pivot rod, to thereby provide an airtight seal therebetween when the pivot rod is inserted into the opening. Furthermore, the generally central opening has a square cross-section, wherein on the side of lesser dimension, each side of the square opening is of dimension less than the dimension of the corresponding side of the pivot rod. The tapered opening in the bushing is such that one side is dimensioned to snugly receive the pivot rod, and the opposite side is of slightly less dimension than the pivot rod. Upon assembly, when the rod is inserted into the opening (i.e., preferably through the larger end for ease of insertion) a small outward force will be applied by the pivot rod to the body of the bushing member when it reaches the smaller end of the tapered opening in the bushing member. This force will cause the bushing material to expand radially outwardly thus increasing the already tight fit between the periphery of the bushing and the ductwork, thereby improving the seal herebetween. In a typical application, the pivot rod of the damper is square, each side being about 0.375, or about ⅜ inch, and the damper is fixed to pivotally rotate with the pivot rod. Accordingly, the tapered opening of the bushing will be square, with one end having a square opening of about 0.375 inch (i.e., about ⅜ inch), or slightly greater, along each side of the square, and the other end being square and having one side about 0.343 inch (i.e., about 11/32 inch) along each side of the square. 
         [0015]    Preferably, the bushing for pivotally mounting a damper to a section of thin sheet metal ductwork comprises a member made of a soft pliable silicone rubber material, and defining a generally longitudinal axis, the member having a first section of generally circular configuration, preferably monolithically formed with a second section of similar generally circular configuration, the first section having an outer diameter greater than the diameter of the second section to define a radially extending generally annular surface of the first section extending circumferentially around the second section. It is foreseeable that the first section can be of shape other than circular without departing from the invention. For example, the first section can be square while still functioning to retain the bushing member in position in the ductwork. 
         [0016]    At least two diametrically opposed lips (or “ears”) extend radially outwardly from the second section and adjacent the first section, each such lip being longitudinally spaced from the annular surface of the first section. However, it should be appreciated that these lips (or “ears”) are provided in the preferred embodiment, and that an embodiment which does not include such lips can function without departing from the invention. In such case the groove will perform most of the retention function, and therefore, can optionally be made deeper than in the embodiment with the lips. 
         [0017]    A groove extends about the periphery of the second section adjacent the annular surface of the first section, the thickness of the groove in the longitudinal direction being approximately equal in dimension to the thickness of the ductwork sheet metal, and the inner diameter of the groove being equal to, or preferably slightly greater than a corresponding dimension of the aperture in the ductwork intended for insertion of the bushing member, for resilient engaged reception of the bushing member therein, whereby the bushing member may be securely attached to the ductwork by reception of the ductwork in the groove and by retention of the ductwork between the annular surface of the first section and each radially upstanding lip of the second section. As will be explained hereinbelow, the thickness of the groove in the bushing can be somewhat greater than the thickness of the ductwork sheet metal. In such case, it is preferable that the diameter of the groove provides a tight fit between the bushing member and the ductwork. 
         [0018]    A through-opening extends generally centrally and longitudinally of the bushing member, the opening being dimensioned for slidable engaged reception of an elongated pivot rod, the rod having attached thereto, a damper member intended for directing conditioned air within the ductwork in a predetermined direction, the tapered through-opening having a cross-sectional shape similar to the cross-sectional shape of the pivot rod, such that rotation of the pivot rod produces a corresponding rotation of said member, while the member is retained in attached rotatable relation with the ductwork to provide bearing support for the pivot rod. The through-opening is preferably tapered to provide a convenient airtight fit between the pivot rod and the bushing, and as well, to facilitate ease of assembly preferably by first inserting the rod into the end of the central opening of greater dimension. 
         [0019]    The through-opening of the member may have at least one flat surface for engagement with a correspondingly opposed flat surface on the elongated pivot rod. Further, as noted, the through-opening in the member is preferably tapered in the longitudinal direction, wherein the dimensions of the opening on one side of the member is less than the corresponding dimension of the opening on the other side of the member. The through-opening of the bushing member is usually generally square so that the bushing member rotates with the damper pivot rod when the rod is rotated. 
         [0020]    It is envisioned that the bushing of the present invention can be of two-piece construction, each piece being dimensioned and configured to be assembled with the other piece to appear and function as a one-piece bushing. 
         [0021]    A damper is also disclosed for pivotal attachment to a section of sheet metal ductwork, even other types of ductwork, for selectively directing conditioned air in a predetermined direction. The damper is mounted on a pair of bushings constructed according to the present invention, whereby loss of conditioned air between the pivot rod of the damper and the bushing, and between the bushing and the ductwork, is eliminated. 
         [0022]    Improved ductwork is also disclosed for directing conditioned air in a predetermined direction, which comprises a damper rotatably mounted in the ductwork on bushings constructed according to the present invention, whereby loss of conditioned air between the pivot rod of the damper and the bushing is eliminated due to the unique bushings on which the damper is pivotally mounted. 
       Assembly 
       [0023]    The sequence for assembling the damper and the bushings with the ductwork can vary. For example, the bushings can be inserted in the ductwork in one of two alternative orientations, i.e., with the larger end of the central square opening facing either the inside or the outside of the ductwork. The pivot rod can then be inserted into the bushings having the damper slidably positioned thereon. Once the rod is in position, the damper can be attached to the rod by forming an indentation, or dimple, into both the damper metal and the rod. Other sequences of assembly, and the specific method of attachment, can be envisioned by persons skilled in the art. 
       Silicone Rubber 
       [0024]    As noted, the bushing of the present invention is preferably made of a soft pliable flexible and resilient material, such as natural or synthetic rubber. Silicone rubber is preferred, due particularly to its physical characteristics, as well as its capability to be formed and dimensioned within predetermined units. Silicone rubber is a rubber-like material composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are elastomers comprised of either one—or two-part polymers, and may contain fillers to improve properties or reduce cost. Silicone rubber is generally non-reactive, stable, and resistant to extreme environments and temperatures from minus 55° C. (i.e., −55° C.) to plus 300° C. (i.e., +300° C.), while still maintaining its useful properties. 
         [0025]    There are also many special grades and forms of silicone rubber, including: steam resistant, metal detectable, high tear strength, extreme high temperature, extreme low temperature, electrically conductive, chemical/oil/acid/gas resistant, low smoke emitting, and flame-retardant. A variety of fillers can be used in silicone rubber, although most are non-reinforcing and lower the tensile strength. 
         [0026]    The silicone rubber contemplated by the present invention may be of hardness in a range of hardness levels, expressed as Shore A or IRHD, between 10 and 100, the higher number being the harder compound. It is also available in virtually any colour and can be colour matched. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Preferred embodiments of the invention will be described hereinbelow with reference to the drawings, wherein: 
           [0028]      FIG. 1  is an enlarged front, left side and top perspective view of a prior art bushing for ductwork dampers and the like, the bushing being made of a relatively rigid plastic material such as nylon or the like; 
           [0029]      FIG. 2  is an enlarged cross-sectional view of the bushing of  FIG. 1 , taken along lines  2 - 2  of  FIG. 1 , and installed in a section of ductwork for pivotally mounting a damper within the section of ductwork, and illustrating the relatively loose fit of the bushing in the ductwork, which loose fit allows the transfer of energy by leakage of conditioned air, i.e., cooled or heated air, through several paths as shown, from the passageway of the ductwork to the outside atmosphere; 
           [0030]      FIG. 3  is an enlarged front, left side and top perspective view of a soft and pliable bushing constructed as shown, according to the present invention; 
           [0031]      FIG. 4  is an enlarged cross-sectional view of the bushing of  FIG. 3 , taken along lines  4 - 4  of  FIG. 3 , and inserted into a section of ductwork from the inside of the ductwork, and pivotally mounting a rotatable damper to the ductwork via a damper pivot rod, this FIG. illustrating the improved tight fit of the bushing with the ductwork, which tight fit prevents loss of conditioned air, and consequent loss of energy from inside the passageway of the ductwork to the outside of the ductwork, while facilitating pivotal motion for the damper along with the pivot rod and the bushing; 
           [0032]      FIG. 5  is a cross-sectional view, similar to  FIG. 4 , of the bushing of the present invention, mounted on each side of a section of ductwork, the bushing being inserted on both sides of the ductwork from the outside of the ductwork, this FIG. illustrating one possible arrangement available with the present bushing, with the smaller end of the tapered inner opening for the damper shaft facing inwardly of the ductwork; 
           [0033]      FIG. 6  is a cross-sectional view which illustrates alternative configurations and mounting positions and orientations available with the present inventive bushing, the view on the left side of  FIG. 6  showing the square opening for the damper pivot rod tapering toward the inner passageway of the ductwork, and the view on the right side of  FIG. 6  illustrating the square opening for the damper pivot rod tapering toward the outside of the ductwork in each instance, the respective bushing having been inserted into the opening from the inside of the ductwork; 
           [0034]      FIG. 7  is a cross-sectional view of the bushing of the present invention, mounted on an arcuate section of ductwork, and illustrating how the soft pliable material of such bushing combines with the configuration to conform the bushing to the curvature of the ductwork to enhance the seal provided between the bushing and the ductwork, without adversely affecting the pivotal movement of the damper relative to the ductwork; 
           [0035]      FIG. 8  is an enlarged cross-sectional view of the bushing of the present invention mounted to a section of ductwork made of a ductwork material of thinner gauge than in the previous views, the soft and pliable property of the bushing facilitating a tight fit without compromising the airtight arrangement between the bushing and the thinner gauge ductwork; 
           [0036]      FIG. 9  is a cross-sectional view of an alternative embodiment of the present invention, wherein the bushing member is of two-piece construction, each piece providing relative ease of assembly with the other, and with the ductwork, all other features being the same as in the previously described embodiments; 
           [0037]      FIG. 10  is a top perspective view of the two-piece bushing member of  FIG. 9 , with parts separated for illustration purposes; and 
           [0038]      FIG. 11  is a front, right side and top perspective view, of a section of ductwork showing a typical installation of a damper mounted on bushings constructed according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    Referring now to the drawings,  FIG. 1  is an enlarged front, left side and top perspective view of a prior art bushing  10  for pivotally mounting ductwork dampers, the bushing being made of a relatively rigid plastic material such as nylon or the like. 
         [0040]      FIG. 2  is an enlarged cross-sectional view of the bushing  10  of  FIG. 1 , taken along lines  2 - 2  of  FIG. 1 , the bushing installed in a section  12  of sheet metal ductwork for pivotally mounting a damper within the section of the metal ductwork. As can be readily seen from  FIG. 2 , the relatively loose fit of the rigid plastic bushing in the sheet metal ductwork provides avenues of escape for the conditioned air, which may be either heated or cooled for the user&#39;s comfort. In particular, the conditioned air can escape, inter alia, along the paths illustrated by arrows  14 ,  16  in  FIG. 2 . 
         [0041]    In general, such prior art bushings provide a relatively overall loose fit with the ductwork, providing significant avenues of escape for the conditioned air, significant enough to cause concern. As can be seen in  FIG. 2 , leakage of conditioned air occurs between the prior art bushing and the ductwork, and between the bushing and the damper shaft, all due to the loose fit and rigid character of the prior art bushing. For example, it can be observed from  FIGS. 1 and 2 , that dimension “G” between the annular flange  11  of the bushing and its retaining ear  13  is greater than dimension “D”, the thickness of the ductwork  12 , providing yet another avenue for escape of conditioned air, due to the overall configuration and dimensional irregularities which exist between the bushing and the ductwork, as well as the rigid character of the prior art bushing. Furthermore, the prior art bushing does not contain a groove for reception of the ductwork metal, as compared with the bushing of the present invention as will be seen in the description which follows. 
         [0042]    Referring now to  FIGS. 3 and 4 , a bushing  20  constructed according to the present invention is shown. In  FIG. 4 , the bushing is installed in a section  42  of sheet metal ductwork. As shown in the preferred embodiment, the bushing  20  is made of a soft silicone rubber material which is not only pliable, but which also provides a significant degree of lubricity, a feature unique to silicone rubber, which feature permits the bushing to pivotally rotate with ease when such pivotal rotation of the damper is necessary. This feature is significant, particularly since the present invention requires a snug fit between the bushing and the ductwork, and between the bushing and the pivot rod  38 , while permitting pivotal rotation of the damper when required to alter the direction of conditioned air in a branch of the network. In one respect the bushing functions somewhat like a bearing when pivotally rotated. 
         [0043]    In  FIGS. 3 and 4 , the bushing  20  of the present invention includes a circular shaped member  20  made of silicone rubber material, the member  20  having a first section  22  of a first diameter, and a second section  24  of lesser diameter, preferably monolithically molded with the first section  22 . As can be seen, first section  22  has an outer circumferential and peripheral surface  21  of diameter which is greater than the outer circumferential and peripheral surface  23  of the second section  24  to form annular surface  26  extending radially outward from the second section  24 . 
         [0044]    A peripheral groove  27  extends about the entire periphery of the second section  24  between first section  22  and the second section  24  as shown. This groove  27  receives and interfaces with the sheet metal ductwork  42  as shown in  FIG. 4 , to provide an airtight seal between the bushing  20  and the ductwork  42 . As can be seen further, the bushing  20  is retained in the ductwork  42  in a circular aperture  30 , the diameter of which is preferably slightly less than the inner diameter  15  of peripheral groove  27 . The thickness of such sheet metal ductwork is generally about 0.012 and 0.095 inch. Depending upon the application, other thicknesses greater or lesser, can be used. 
         [0045]    In the FIGS., the inner diameter  15  of peripheral groove  27  appears to match the diameter of aperture  30  in ductwork  42 , a condition which is acceptable. However, in the preferred embodiment, the diameter of aperture  30  formed in the ductwork  42 , is preferably slightly less than the initial inner diameter  28  of the peripheral groove  27  (indicated by dash line  28  in  FIG. 4 ) to provide a predetermined amount of compression of the bushing material, which in turn provides even an improved airtight seal. In  FIG. 4 , phantom lines  28  show the original uncompressed inner surface of groove  27 , prior to insertion of the bushing into aperture  30 . For example, should the diameter of aperture  30  in ductwork  42  be about 0.610 inch, then the uncompressed inner diameter  15  of peripheral groove  27  in bushing  20  can be approximately 0.625 (i.e., ⅝) inch. Thus the diameter of aperture  30  in the ductwork is about 2% to 3% less than the uncompressed diameter of peripheral groove  27  in bushing  20 . Such relative dimensions can be altered, depending upon the seal desired. If desired, both diameters can be made equal. 
         [0046]    Referring again to  FIGS. 3 and 4 , bushing  20  also includes diametrically opposed radially extending lips (or “ears”)  32 ,  34  which conveniently assist groove  27  in permanently retaining the bushing  20  in the aperture  30 . Lips  32 ,  34  are attached to, or otherwise extend radially outwardly from the second section  24  for resilient pivot-like movement about axis B-B (shown in  FIG. 3 ) axis which is perpendicular to the longitudinal axis A-A of the bushing  20 . Such resilient pivotal movement of lips  32 ,  34  is provided by longitudinal cuts  29 ,  31  (best shown in  FIGS. 3 and 10 ), and facilitates one-way insertion into aperture  30  of ductwork  42  to permit entry thereof through the aperture until the ductwork  42  enters groove  27 , and corresponding resilient return of lips  32 ,  34  to the engaging positions shown in  FIG. 4 . Lips  32 ,  34  are spaced from annular surface  26  by distance “G”, which is approximately equal to the thickness of the sheet metal ductwork and the groove  27 . As noted, the invention can be practiced without the lips (or “ears”)  32 ,  34 . In such case the groove may be made deeper to retain the bushing in place within the ductwork between the groove and the annular radial surface. In any event, the lips (or “ears”)  32 ,  34  are preferred. 
         [0047]    In  FIGS. 3 and 4 , bushing  20  also defines a central longitudinal axis A-A which extends through central square aperture  36 , through which correspondingly shaped and dimensioned pivot rod  38  extends. As seen in  FIG. 9 , pivot rod  38  is attached to damper  40  which is mounted to ductwork section  42  for pivotal movement to direct conditioned air through the ductwork in a predetermined direction. Although two spaced apart lips  32 ,  34  are shown separate and apart from each other, a person of ordinary skill in the art will appreciate that a continuous lip can circumscribe the groove  27 . Still, alternatively a greater plurality of such lips can be positioned about the circumference of the second section  24 , spaced from each other by a predetermined number of degrees. 
         [0048]    As shown in  FIGS. 4 AND 11 , the pivot rod  38  of square cross section is in turn, mounted on bushings  20  constructed according to the present invention. 
         [0049]    Referring again to  FIGS. 3 and 4 , the central aperture  36  of bushing  20  is conveniently tapered, with dimension “C” of pivot rod  38  being greater than the initial (i.e., pre-insertion) dimension “B” of opening  36  of bushing  20 . Dimension “B” is preferably less than the corresponding dimension “C” of the pivot rod  38  to ensure a tight seal between the bushing  20  and the pivot rod  38 . For a pivot rod  38  of square cross-section the dimensionally tight fit is along all sides of pivot rod  38 . For pivot rods of other cross-sections, i.e., circular or the like, the tight fit between the bushing  20  and the pivot rod  38  extends entirely about the pivot rod. 
         [0050]    In  FIG. 4 , the initial configuration of square opening  36  is shown as being tapered, i.e., from initial greater dimension “D” of the inner side of the bushing  20  to smaller dimension “B” on the outer side of bushing  20 . After insertion of damper pivot rod  38 , the opening  36  substantially conforms to the outer surface and dimensions of the pivot rod  38  as shown in the FIG. 
         [0051]    As noted, the initial taper of square opening  36  facilitates convenience of assembly with the damper pivot rod  38 , while assuring a tight fit between the pivot rod  38  and at least the opening of dimension “B”. For example, the pivot rod  38  can be inserted into the inner side of opening  36  of greater dimension “D”, ultimately to reach the outer side opening of dimension “B” of lesser dimension, to form a tight seal with the pivot rod  38 . In addition, the dimension “G”, i.e., the width of the ductwork sheet metal, can be equal to the width of the groove  27  sufficient to fit snugly in the groove. The airtight seal is provided primarily by the compressive engagement between the sheet metal of ductwork  42  and the inner diameter of groove  27 , since the diameter of the aperture  30  is less than the uncompressed inner diameter of groove  27 , as shown by phantom lines  28  in the drawings, which show the groove  27  prior to insertion of the bushing  20  in the aperture  30 . This arrangement ensures a tight fit between the ductwork and the bushing  20 . Additionally, as noted, when the pivot rod  38  of square cross section is inserted into the inner end of opening  36  of greater dimension “D”, as it reaches the smaller end of the taper of initial dimension “B”, it applies outward force against bushing  20  which increases the tight fit between the sheet metal and groove  27 . 
         [0052]    It can be readily appreciated that the snug fit between bushing  20  and ductwork section  42 , and between bushing  20  and pivot rod  38 , both ensure a significantly improved airtight seal therebetween, while permitting pivotal rotation of the pivot rod  38 , as facilitated by the relatively low friction surface of the silicone rubber and the bearing support provided by the bushing member  20 . 
         [0053]    It should also be appreciated that while silicone rubber is the preferred material for fabricating the bushing, any soft and pliable material may be used, such as synthetic or natural rubber, or other known elastomers. 
         [0054]    Referring now to  FIG. 5 , alternative constructions and configurations of the bushing of the present invention are disclosed, whereby the taper of the square opening  36  of the bushing can be oriented in either of two directions. Such alternative configurations make convenient, the assembly of the damper pivot rod  38  with the bushings  20 , as well as the assembly of the bushings with the section of ductwork. For example, the damper pivot rod  38  may be first assembled with the damper blade and the bushings by first inserting the rod  38  into the large end “D” of opening  36  of bushing  20 , or alternatively, by first inserting the rod  38  into the smaller end “B” of bushing  20 . The assembly procedure will be dependent upon the preferred sequence of assembly of the pivot rod  38  with the damper  40  and then the assembly of the damper assembly with the section of ductwork. In either sequence, the smaller size of dimension “B” will always assure an airtight fit with the rod  38 . At one point in the assembly sequence, the damper plate  40  shown in  FIG. 11  can be attached to pivot rod  38  by forming an indentation, or dimple,  44  to create the attachment. 
         [0055]      FIG. 6  illustrates yet another alternative embodiment, wherein the bushings  20  are shown with the central aperture  36  respectively oriented in opposite directions with respect to the ductwork. These orientations will in turn accommodate any of several alternative sequences of steps to assemble the components together. It should be noted that generally, the damper plate  40  is attached to pivot rod  38  by an indentation  44  in the center of the rod, which retains the assembly. 
         [0056]    Referring now to  FIG. 11 , the damper plate  40  and bushings  20  are shown in assembled relation with the ductwork  42 . As noted, the damper plate  40  is attached to pivot rod  38  by an indentation  44  formed in the damper sleeve  41  in which the rod  38  is inserted. This indentation  44  serves to retain the damper  40  and pivot rod  38  in assembled relation such that pivotal rotation of the pivot rod  38  will cause corresponding rotation of the bushings  20  and the damper plate  40 . Accordingly, the pivot rod  38  can first be assembled to the bushings  20 , and later to the damper  40 ; or alternatively, the damper  40  can first be assembled with pivot rod  38 , and later assembled to the section of ductwork  42  utilizing bushings  20 . The various orientations of the central square aperture  36  in bushing  20  make these alternative methods of assembly possible. 
         [0057]    In general, although the preferred method of assembly is to first insert the pivot rod  38  into the larger end of the tapered aperture  36  of bushing  20 . Because of the flexible resilience of the silicone rubber material of bushing  20  if necessary, using slightly greater force, the pivot rod can first be inserted into the smaller end of the tapered aperture  36  of bushing  20 , since the airtight seal therebetween will still be maintained. 
         [0058]    It should be noted that the central aperture  36  of bushing  20  shown in the FIGS. is square in shape. The use of the square pivot rod is fairly common in the industry, as it can be easily be made to rotate the damper, and it can readily be attached to the damper by forming an indentation, or dimple  44 , in the center of the damper. However, a pivot rod of any shape which facilitates simultaneous rotation of the damper with the pivot rod  38  is contemplated for use with the invention. For example, the pivot rod and the central aperture  36  of bushing  20  can be triangular in cross-section, or even circular, provided that the appropriate structure and dimensions to secure the components together are accommodative for simultaneous pivotal rotation. 
         [0059]      FIG. 7  illustrates an advantage of the bushing of the present invention which accommodates the curvature of the section of ductwork to ensure an airtight seal, due to the pliable and resilient nature of the bushing. 
         [0060]      FIG. 8  illustrates yet another advantage of the present bushing which makes it possible to achieve an airtight seal, even with ductwork made of sheet materials which are thinner than the sheet materials in common use. In such instance, although spaces  46  may be present, leakage of conditioned air will be prevented by the engagement between the ductwork  42  and the groove  27  as shown, which promotes an airtight seal. This seal is facilitated by initial inner diameter “E” of groove  27  being greater than the final compressed diameter “F” of aperture  30  of ductwork  42 . 
         [0061]    In each of the embodiments described, it is contemplated that the bushings  20  can be made in several sections, i.e., two or more pieces, which can be assembled to function as a single bushing as described herein.  FIGS. 9 and 10  illustrate such bushing  20 , which can be made in two pieces, for example, male piece  50  and female piece  52  each of which can be respectively dimensioned for assembly in interference relation as shown in  FIG. 9 . The resilience of the silicone (or other) rubber material of each piece shown in  FIG. 10  facilitates ready snapped interference alignment and assembly of the two half sections  50  and  52  as shown in  FIG. 9 . 
         [0062]    As noted previously,  FIG. 11  illustrates a section of ductwork having a damper assembly mounted for pivotal rotation thereon, incorporating the bushing of the present invention. 
         [0063]    While the present invention is contemplated for use with conventional ductwork made of thin galvanized sheet metal, of thickness between 0.012 and 0.60 inches, and having a generally tubular configuration of circular cross-section, it may be used with alternative ductwork materials such as plastics, fiberglass, flexible ducting or the like. In addition, the ductwork can be of alternative designs, such as ductwork having a rectangular or square cross-section. In such installations the structure which incorporates the damper would necessarily be structured and arranged to facilitate installation of the damper of the present invention and the damper configuration will be arranged to match the ductwork. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           11  annular flange 
           12  section of sheet metal 
           13  retaining ear 
           14 ,  16  arrows 
           15  inner diameter 
           20  bushing 
           21  outer peripheral surface 
           22  first section 
           23  outer peripheral surface 
           24  second section 
           26  annular radial surface 
           27  peripheral groove 
           28  phantom lines denoting initial inner diameter of peripheral groove  27   
           29 ,  31  cuts adjacent lips (or ears)  32 ,  34   
           30  circular aperture 
           32 ,  34  diametrically opposed radially extending lips (or ears) 
           36  central square opening of inventive bushing  20   
           38  damper pivot rod 
           40  damper plate 
           41  damper sleeve 
           42  sheet metal ductwork section 
           44  indentation dimple 
           46  spaces between thin sheet metal ductwork and peripheral groove  27   
           50  male piece of two piece embodiment 
           52  female piece of two piece embodiment