Abstract:
A ventilation chimney or exhaust fan flue section for hog barns has inner and outer plastic tubes formed by edge welding plastic sheets. A snug fitting insulation sheet is slid between the tubes. Collars of male and female coupling elements are inserted into the ends of the section between the inner and outer tubes and secured by screws passing through the outer tube and into the collars. The chimney can be installed by combining sections using a suitable adhesive.

Description:
This application claims priority of U.S. provisional patent application No. 60/786,738, Ventilation chimney section and method, to John Waldner, filed 29 Mar. 2006, which is incorporated herein by reference. 

   This invention is directed to a method of manufacture of ventilation chimney sections and ventilation chimney sections, also called exhaust fan flues. 
   BACKGROUND AND PRIOR ART 
   Ventilation is important in livestock raising barns in general and hog barns in particular. Ventilation chimneys typically with an associated fan are used to exhaust air from the barns. Generally these chimneys are assembled from prefabricated sections. 
   Currently sections are made from rotary molded “rotomolded” plastic tubes, and from a plastic sheet welded longitudinally to form a tube. As the chimneys ventilate to the outside air, they tend to ice up in winter. Sometimes chimneys are insulated after installation in the barn attic to overcome the icing problem. Some sections are formed from inner and outer tubes welded longitudinally from plastic sheets, and spaced at the ends by a circular spacer typically ¼ inch thick. 
   None of these solutions are particularly satisfactory, although better than no ventilation. 
   The invention is directed to a method of forming an insulated chimney section by forming inner and outer tubes by welding plastic sheets to form tubes, inserting a sheet of insulation formed into a tube between inner and outer tubes, and attaching a male coupling at one end and a female coupling at the other. The male and female couplings are adapted to engage matingly. The invention is also directed to chimney sections manufactured by the method and chimneys constructed from the sections. 
   Although the invention is described with respect to methods of manufacture of chimney section by welding plastic sheets into inner and outer tubes and inserting a sheet of insulation between the inner and outer tubes and attaching male and female coupling s at the ends, sections manufactured by the method and chimneys constructed from the sections, it will be apparent to those skilled in the art that the invention is not limited to the method of manufacture, sections and chimneys, but extend to similar methods, sections and chimneys. 
   It is a principal object of the invention to provide a chimney section having plastic inner and outer tubes separated by insulation. It is a subsidiary object of the invention to provide a chimney section having male and female couplings fitted into the space between the inner and outer tubes. It is a further principal object of the invention to form a chimney section by welding a plastic sheet to form an outer tube and welding another plastic sheet to form an inner tube, and to insert the inner tube inside the outer tube and slide a sheet of insulation material having touching edges between the inner and outer tubes. It is a further object of the invention to insert a male coupling at one end of the section fitting between the inner and outer tubes and to insert a female coupling at the other end of the section fitting between the inner and outer tubes. Other objects will be apparent to those skilled in the art from the following specification, accompanying drawings and appended claims. 
   DESCRIPTION OF THE INVENTION 
   The invention in one broad aspect is directed to a method of manufacture of a ventilation chimney section comprising welding plastic sheets to form inner and outer cylindrical tubes placing the inner tube within the outer tube and sliding a sheet of insulation between the inner and outer tube. Preferably the plastic sheets are cut to the desired length, and the desired width, that is π times the desired diameter of the tubes, which are then edge welded to form the inner and outer tubes. The sheet of insulation is similarly cut, most preferably slightly shorter in length to allow for the coupling elements. The thickness of the sheet of insulation is set to be slidable within the space between the inner and outer tubes. The sheet of insulation is preferably cut into a plurality into a plurality of segments, alignable parallel to the common axis of the tubes, before sliding the sheet between the inner and outer tubes. Each segment fills a longitudinal portion of space between the inner and outer tubes. Preferably the sheet of insulation is cut into four quarter cylindrical segments, alignable parallel to the common axis of the tubes. Most preferably the sheet fits snugly between the inner and outer tubes. Preferably the collar of a male coupling element is inserted into one end of the section between the inner and outer tubes and secured therein. Preferably the collar of a female coupling element is inserted into the other end of the section between the inner and outer tubes and secured therein. The male coupling element is adapted to matingly engage a female coupling identical to the female coupling element and vice versa. Preferably the collars are secured between the inner and outer tubes by fasteners, which are preferably screws, although plastic rivets may also be used, extending through the outer tube and into the collar. 
   In another broad aspect the invention is directed to a chimney ventilation section comprising coaxial inner and outer plastic tubes separated by a sheet of insulation in the space between the inner and outer tubes. Preferably the sheet of insulation fits snugly between the inner and outer tubes. Preferably the sheet of insulation has four quarter cylindrical segments aligned parallel to the common axis of the tubes. Conveniently the collar of a male coupling element is inserted into one end of the section between the inner and outer tubes and secured therein. Conveniently the collar of a female coupling element is inserted into the other end of the section between the inner and outer tubes and secured therein. The male coupling element is adapted to matingly engage a female coupling identical to the female coupling element and vice versa. Usually the collars are secured between inner and outer tubes by fasteners. Preferably the fasteners are screws extending through outer tubes and into the collars. A preferred form of male coupling element has a first circumferential wall abutting the collar of the male coupling element projecting outward, a first inner cylindrical sleeve at the inner edge of the first circumferential wall. The first sleeve forms a plug to engage a socket of a female coupling element. The preferred form of the female coupling element has a second circumferential wall abutting its collar projecting outward, a second outer cylindrical sleeve at the outer edge of the second circumferential wall. The second sleeve and second wall form a socket to engage a plug of a male coupling element. Both circumferential walls surround a central fluid passage communicating with the fluid passage of the section. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a cross sectional elevational view of a ventilation chimney section of the invention. 
       FIG. 2  shows a cross sectional plan view of the embodiment of claim  1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The invention is now illustrated by reference to preferred embodiments thereof. Numeral  10  indicates a ventilation chimney section of the invention. Section  10  includes cylindrical tube  12 , male end coupling  14  and female end coupling  16 . Tube  12  has outer cylindrical tube  18 , inner cylindrical tube  20 , separated by cylindrical insulation  22  filling space  50  between tubes  18  and  20 . Tubes  18  and  20  are made by welding opposed edges of a plastic sheet to form a cylindrical tube. Typically the sections are 2, 3 and 4 feet long (approximately 60, 90 and 120 cm) and 16, 18, 22 or 25 inches inner diameter (approximately 40, 45, 60 and 63 cm), these dimensions are those requested and preferred by purchasers although other lengths and diameters may be used, and custom supplied. Typically the plastic sheets are polyethylene and about ⅛ inch thick (approximately 3 mm, although other plastics of similar properties can be used instead, and the thickness can be similarly varied, as known by those skilled in the art. Inner tube  20  when placed within outer tube  18  is spaced apart about 1⅛ inch (approximately 2.8 or 2.9 cm) forming space  50 . This gap is filled by a 1 inch thick (approximately 2½ cm) insulating polystyrene sheet  22 , which may be cut into four quarter cylinders, and is typically foamed, other insulating plastics of similar properties can be used instead. In manufacture polyethylene sheets are cut to size, as is a polystyrene sheet. The polyethylene sheets are edge welded to form cylindrical tubes  18  and  20  placed concentrically within each other and polystyrene  22  slid between them preferably as four quarter cylinders  24 . Male coupling  14  and female coupling  16  are inserted into ends  26  and  28  of tube  12  and secured by screws  30  passing through outer tube  18  into couplings  14  and  16 , plastic rivets may be used instead of screws  30 . Male coupling  14  has collar  32  to engage space  50  between inner tube  20  and outer tube  18 , collar  32  joins circumferential wall  34  at the inner edge of which is sleeve  36 , the inner surface of wall  34  and sleeve  36  are aligned with the inner surface of inner tube  20  to form fluid passage  38 . The outer surface of sleeve  36  forms plug  40 . Female coupling  16  has collar  42  to engage space  50 , collar  42  joins circumferential wall  44  at the outer edge of which is sleeve  46 . the inner surface of wall  44  is aligned with the inner surface of inner tube  20  to form fluid passage  48 . Wall  44  and sleeve  46  together form socket or plug insertion port or plug receiving hole  52 , with edge recess  54 . Plug  40  and socket  52  are dimensioned to matingly engage similar elements on other sections. Couplings  14  and  16  are typically polyurethane foam, although other suitable materials of like properties may be used as known to those skilled in the art. Collars  32  and  42  are typically about 1½ inch deep (approximately 3.8 cm) and 1 inch wide (approximately 2½ cm) to fit into space  50 , itself about 1⅛ inch across (approximately 2.8 or 2.9 cm), wall  34  and sleeve  36  together extend about 2½ inch (approximately 6.3 or 6.4 cm) from the end of tube  12 , as do wall  44  and sleeve  46 . Sleeve  36  is about 1 inch (approximately 2½ cm) thick, as is edge recess  54 . Sections  10  are joined together at installation by a suitable compatible plastic adhesive applied between plug  40  and socket  52 . In general tolerances throughout are of the order of ⅛ inch. 
   Although the terms “polyethylene,” “polystyrene,” “foam polystyrene,” and “polyurethane” are used, these are illustrative only, as is well understood by those skilled in the art, each of these substances has equivalents of similar properties that can be used instead, and the invention is not restricted to the particular named conventional substances. 
   As those skilled in the art would realize these preferred described details and materials and components can be subjected to substantial variation, modification, change, alteration, and substitution without affecting or modifying the function of the described embodiments. 
   Although embodiments of the invention have been described above, it is not limited thereto, and it will be apparent to persons skilled in the art that numerous modifications and variations form part of the present invention insofar as they do not depart from the spirit, nature and scope of the claimed and described invention.