Abstract:
A mold assembly includes a mold mounted for rotation within a vacuum chamber. The mold includes a central drum having a hollow interior into which resin is poured. A plurality of hollow blade molds is radially disposed about the central drum. A plurality of radially disposed struts is secured to the central drum and each strut is received within an associated blade mold. Openings are formed in the central drum and in the struts. Elongate bundles of woven fiberglass are weaved in and out of the openings, beginning in the drum and extending to the respective ends of each strut. A motor spins the mold assembly and resin in the central drum is urged by centrifugal force to flow along the length of the woven fiberglass bundles until each blade mold is filled with resin. The resulting product is a monolithic structure having plural blades radiating from a central hub.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to vacuum assisted molding. More particularly, it relates to fabrication of large composite elements using an infusion system supplemented by centrifugal force in a vacuum. 
   2. Description of the Prior Art 
   The manufacturing of large molded objects, such as boat hulls, large blades for an electricity-generating wind farm windmill, and the like, is problematic. Such large objects are typically molded by a time-consuming manual process. This drives up the cost of the individual products. Items made by manual labor are also more likely to be of inconsistent quality as no two products will be exactly alike. 
   What is needed, then, is a new manufacturing process for making large molded monolithic products. More particularly, there is a need for a manufacturing process that reduces the amount of manual labor needed to produce such objects. The needed process would reduce the cost of such objects. There is also a need for a new process that provides products having consistently high quality. 
   However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in this art how the identified needs could be met. 
   SUMMARY OF INVENTION 
   The long-standing but heretofore unfulfilled need for an improved manufacturing process for making large molded objects is now met by a new, nonobvious, and useful invention. 
   The novel mold assembly includes a vacuum chamber having a top piece and a bottom piece that share a common structure and which form a stationary, non-rotating vacuum chamber when said top and bottom pieces are positioned in confronting relation to one another. 
   A mold for making a preselected monolithic part is mounted for rotation within the vacuum chamber. The mold includes a central drum having cylindrical sidewalls, a bottom wall, an open top, and a hollow interior. In a first embodiment, a cylinder having a plurality of micro perforations formed throughout the cylinder and one large opening has a diameter less than the diameter of the central drum and is positioned concentrically within the central drum so that a toroidal space is defined between said cylinder and central drum. The cylinder is pressed, welded, glued, or secured within the central drum by some other suitable means. 
   In a second embodiment, the micro perforated cylinder is not used. Instead, a micro perforated lid or cover is installed in closing relation to the open top of the central drum. 
   The cylinder of the first embodiment having the micro perforations formed therein acts as a dam to prevent overflowing of the resin that is pumped into it. The viscosity of the resin prevents it from free-flowing but does nothing to stop evacuation of air from the blade molds. 
   The mold further includes a plurality of hollow blade molds disposed in circumferentially spaced relation to one another about the central drum and in radial relation to a longitudinal axis of the central drum. Each of the hollow blade molds includes a top piece and a bottom piece adapted to be releasably secured to one another. The top and bottom pieces abut one another along a parting line when placed into confronting relation to one another. 
   A plurality of struts is secured to the central drum in circumferentially spaced relation to one another and in radial relation to the longitudinal axis of the central drum. A plurality of openings is formed in the cylindrical sidewalls of the central drum and a plurality of openings is formed in each strut of the plurality of struts. 
   Each elongate bundle of a plurality of elongate bundles of woven glass (preform) extends through at least one opening of the plurality of openings formed in the central drum and through at least one opening formed in an associated strut of the plurality of struts. These struts and holes prevent the glass bundles from being spun to the outside and piling up in the tip or distal end of the blade mold. In the first embodiment, the radially innermost part of each bundle of woven glass is positioned within the toroidal space between the micro perforated cylinder and the central drum. In the second embodiment, the radially innermost part of each bundle of woven glass is positioned within the hollow interior of the central drum. 
   The woven glass may be provided in the form of a unidirectional stitched material, or a braided, woven material. It may be preformed woven glass, i.e., material that is sewn, knitted, or otherwise secured together. The preform fiberglass bundles may include fiberglass, Kevlar®, carbon fiber, a fiber coated with metal such as boron wire, nylon, and other synthetic fibers. The fiber architecture may change depending upon the application. Thus it is understood that this invention is not limited to any particular fiber architecture because those of ordinary skill in the art may select a fiber architecture that best fits the needs of a particular application. 
   Each of the struts and its associated bundle of woven glass (preform) is housed by an associated top piece and bottom piece of the hollow blade molds when the top and bottom pieces are placed into confronting relation with one another and releasably secured to one another. 
   A resin reservoir is positioned externally of the vacuum chamber and is adapted to deliver resin or other moldable material to the hollow interior of the cylinder having the large opening and the micro perforations formed therein. A resin tube provides fluid communication between the resin reservoir and the hollow interior of the cylinder (first embodiment) or drum (second embodiment). A sealed opening formed in a center of the vacuum chamber top piece accommodates the resin tube. 
   A motor mounted outside of the stationary vacuum chamber is adapted to rotate the mold within the stationary vacuum chamber. The central drum sits atop a flat platform that surmounts an upstanding shaft. A sealed opening formed in a center of the vacuum chamber bottom piece accommodates the rotating shaft. A motor rotates the upstanding shaft and hence the flat platform, the central drum, and the blade molds mounted about the periphery of the central drum. 
   Centrifugal force created by rotation of the mold causes resin in the hollow interior of the cylinder to flow radially outwardly of the cylinder through the large opening formed therein and into the toroidal space between said cylinder and central drum in the first embodiment. In the second embodiment, there is no cylinder so the resin flows into the blade molds from the central drum. From the toroidal space, (or from the hollow interior of the central drum) the resin flows through the openings formed in the central drum and along the respective extents of the preform, until each blade mold is filled with resin. Any moldable material such as a ceramic composite material may also be used instead of resin. The micro perforations formed in the cylinder prevents the resin or other moldable material from overflowing into the vacuum chamber. The viscosity of the resin or other moldable material prevents it from flowing freely through the micro perforations. 
   Resin or other moldable material is not introduced into the hollow interior of the cylinder (first embodiment) or drum (second embodiment) until the air within the vacuum chamber has been substantially pumped out. Although the novel mold can be used without the vacuum chamber, the amount of centrifugal force required to drive resin to the radially outermost ends of the blade molds is greatly reduced when the air is removed prior to rotation of the mold assembly. 
   The novel apparatus produces a finished molded product having a monolithic structure. The finished molded product is removed from the novel apparatus by releasing the vacuum, separating the vacuum chamber top piece from the vacuum chamber bottom piece, followed by separating each blade mold top piece from each blade mold bottom piece. 
   A circular dam is built along a top wall of the central drum in surrounding relation to the central opening of the drum to prevent resin from spinning out of said central drum if excess resin accumulates in the cylinder and in the toroidal space. The micro perforated cylinder may be wedged by press fit into the central opening of the drum or welded into the dam. 
   The primary object of this invention is to provide a method for making very large structures by employing a molding process. 
   Another object is to provide large monolithic structures that lack seams and which therefore cannot come apart along said seams. 
   Still another object is to provide large structures at greatly reduced cost and consistent quality by eliminating many hours of manual labor per object. 
   These and other important objects, advantages, and features of the invention will become clear as this description proceeds. 
   The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which: 
       FIG. 1  is a side sectional view of a first embodiment of the novel mold assembly; 
       FIG. 2A  is an exploded perspective view of the central drum and struts welded thereto with the micro-perforated cylinder depicted outside of said central drum; 
       FIG. 2B  is a top plan view of a second embodiment depicting the central drum and a micro perforated cover for the central opening of the central drum; 
       FIG. 3A  is perspective view like  FIG. 2A  but including a bottom blade mold filled with resin; and 
       FIG. 3B  is a perspective view like  FIG. 3A  but with the micro-perforated cylinder of the first embodiment positioned concentrically within the central drum. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIG. 1 , it will there be seen that a first illustrative embodiment of the invention is denoted as a whole by the reference numeral  10 . 
   Mold assembly  10  includes a stationary, non-rotating vacuum chamber  12  defined by vacuum chamber top piece  14  and vacuum chamber bottom piece  16  that share a common structure and cooperatively confront one another to form said vacuum chamber. Top piece  14  includes radially-outwardly extending annular flange  14   a  and bottom piece includes radially-outwardly extending annular flange  16   a . Said flanges abut one another and are positioned on opposite sides of the horizontal axis of symmetry of vacuum chamber  12 . Air is pumped from vacuum chamber  12  through hose  13  which is in fluid communication with a source of negative pressure, not shown. 
   In this illustrative embodiment, a mold  18  for making a four-blade fan of the type having utility in wind farms, cooling towers, ventilation systems, hydroelectric turbines, counter rotating compressor blades and the like is mounted for rotation within vacuum chamber  12 . The number of blade molds  20  is not critical, nor is the shape and side thereof; four generic blades are shown for illustrative purposes. Each blade mold  20  has an upper part  20   a  and a lower part  20   b  that meet along parting line  20   c . Flange  21   a  is formed integrally with and circumscribes top part  20   a  and flange  21   b  is formed integrally with and circumscribes bottom part  20   b . Said flanges are bolted or otherwise secured together to prevent separation of top part  20   a  and bottom part  20   b  during the molding process. After the process is completed, the bolts or other clamping means are removed from said flanges so that mold top and bottom parts  20   a ,  20   b  can be separated from one another so that the completed product can be removed. 
   Central drum  22  is supported by flat platform  24  that surmounts upstanding shaft  26  and rotates conjointly therewith. Collectively, platform  24  and shaft  26  are known in the industry as a drive dog. 
   Rotation of drive dog shaft  26  and hence rotation of blade mold  18  is caused by motor  28  having output shaft  30  to which is secured first speed regulating step pulley  32 , also known as a variable speed pulley. Any other variable speed drive or speed reducing means is within the scope of this invention. Belt  34  interconnects first speed regulating step pulley  32  to second speed regulating step pulley  36  that is keyed to drive dog shaft  26  for conjoint rotation therewith. 
   A plurality of couplers and shaft seals, collectively denoted  38 , is centrally apertured to receive drive dog shaft  26  and is slideably and sealingly but not fixedly connected thereto. Said couplers and shaft seals  38  do not rotate because they are in fluid communication with a plurality of air and hydraulic hoses, collectively denoted  40 , that are not mounted for rotation. Said air and hydraulic hoses are connected at their respective, unillustrated proximal ends to suitable stationary sources of compressed air and hydraulic fluid, respectively. The use of hoses  40  is not depicted. The vacuum chamber can also be used with prepreg and thermoset resin as well as ceramic and ceramic composite materials. Hoses  40  are used when thermal set resins and prepeg are used. Hoses  40  are also used when large structures are blow molded using the novel apparatus. 
   An opening is formed in the center of vacuum chamber bottom piece  16  to accommodate drive dog rotating shaft  26 . The opening is sealed internally of vacuum chamber  12  by internal seal  42  having bearing packing glands therewithin and the opening is sealed externally of vacuum chamber  12  by external seal  44  having bearing packing glands therewithin. 
   An opening is formed in the center of vacuum chamber top piece  14  to accommodate resin tube  46 . Resin reservoir  48 , adapted to contain resin  49 , surmounts resin tube  46  and the flow rate of resin from said reservoir into said tube is under the control of manually-operated valve  50 . A sheet of centrally-apertured Plexiglas®  52  is bolted to an exterior surface of said top piece  14  to reinforce said top piece at the point of entry of said resin tube. It also enables a user to look into the mold to see if central drum  22  is full of resin. Bearing packing glands are provided where the opening is formed for resin tube  46  because said resin tube rotates as the resin flows therethrough to fill central drum  22 . Ceramic composite materials may be used instead of resins. 
   Resin in reservoir  48  can be pumped at any pressure into the central drum by metering catalyzing mixing dispenser. Accordingly, the resin feed is accomplished under active positive control as distinguished from a feed that results passively from gravity and atmospheric pressure. Both passive and active feeds are within the scope of this invention. 
   As best understood in connection with  FIGS. 2A , and  3 A,  3 B, central drum  22  is substantially cylindrical in configuration and has a plurality of openings, collectively denoted  22   a , formed in its cylindrical sidewalls. The openings are provided so that preformed woven glass  23  may be woven therethrough and so that resin may flow through said openings. The glass is preferably unidirectional and biaxial winding glass. 
   Cylinder  27  of the first embodiment has a diameter less than a diameter of central drum  22  and is positioned concentrically within central drum  22 . It is pressed, welded, or glued into said position. A laser is used to form a large plurality of micro holes or micro perforations  27   a  in cylinder  27 . The size, number, and density of such micro holes will vary greatly from application to application, i.e., the size of the item being molded will dictate the size, number, and density of the micro holes. In addition to the very small openings formed throughout cylinder  27 , there is one (1) large (an inch or more in diameter) opening  27   b  formed in said cylinder as depicted in  FIG. 2B  so that resin charged into the space bordered by cylinder  27  can flow out of said space through said opening  27   b  and into toroidal space  29  between cylinder  27  and central drum  22 . The preformed woven glass  23  that is woven through openings  22   a  formed in central drum  22  is confined to said toroidal space, i.e., said preformed woven glass does not extend into the interior of cylinder  27 . 
     FIG. 2B  depicts the second embodiment where micro perforated cylinder  27  is eliminated. The open top in central drum  22  is closed with a flat, micro perforated closure means  27   c  having central aperture  27   d  formed therein to accommodate resin tube  46 . Closure means  27   c  prevents overflow of resin from central drum  22 . There is no toroidal space  29  in this embodiment, but resin charged into the hollow interior of central drum  22  flows through openings  22   a  into the blade molds as in the first embodiment. 
   In both embodiments, the preformed woven glass is woven through openings  22   a  to hold the preformed woven glass in place. This prevents centrifugal force from pulling the preformed woven glass radially outward. 
   A predetermined number of stainless steel struts, collectively denoted  19 , are welded to drum  22  in radial relation thereto. Each strut  19  has several large openings, collectively denoted  19   a , formed in it along its extent. 
   Glass  23  that is woven through openings  22   a  formed in central drum  22  is also woven through openings  19   a  formed in struts  19 . Struts  19  may extend all the way to the end of their associated blade molds  20 , or they may extend any fractional part thereof. In this particular embodiment, each strut  23  extends about half-way between central drum  22  and the radially outermost end of its associated blade mold  20 . Woven glass  23 , however, extends all the way to the radially outermost end of each blade mold  20 . 
   Centrifugal forces acting on the resin collected in central drum  22  causes the resin to migrate radially outwardly from toroidal space  29  along the entire extent of woven glass  23 . The resistance to such outward flow is nominal in view of the vacuum created prior to introduction of resin. In this way, resin is carried all the way to the end of each blade mold  20 . 
   Annular dam  25 , depicted in  FIGS. 2A ,  3 A and  3 B, is built along a top wall of central drum  22  in surrounding relation to the central opening of the drum to prevent resin  49  from spinning out of toroidal space  29  if said toroidal space overflows. 
   Core material may also be provided with struts  19  and woven glass  23  to facilitate construction of the final product within the mold. 
   Atmospheric pressure acting on resin  49  in reservoir  48 , or pressure provided by a pumping system as mentioned above, pushes the resin or other moldable material into the hollow interior of cylinder  27 . A pump may be supplied so that the resin is charged into said hollow interior at a pressure greater than atmospheric pressure. Centrifugal force causes the resin to exit cylinder  27  through large opening  27   b  and to flow radially outwardly along the extent of toroidal space  29  and hence openings  22   a  and along the length of each bundle of woven glass  23 . The resin accumulates on and conforms to the shape of the interior of each blade mold  20 . The vacuum in vacuum chamber  12  also enables mold  18  to spin at a high rotational velocity so that the centrifugal forces are high. 
   Hydraulic hoses and couplers  40 , mentioned above, are needed when a particular molding technique requires heating fluids, cooling fluids, hydraulic power, air pressure, and the like. Molding compounds such as ceramic and ceramic composites, for example, have widely varying needs that are met by such hoses and couplers  40 . 
   When resin fills cylinder  27  and toroidal space  29 , i.e., when the resin level begins to climb relative to annular dam  25 , the operator knows that each blade mold  20  has accepted its maximum amount of resin  49  and motor  28  is shut down. Micro perforated cylinder  27  prevents mold  20  from accepting further resin when the mold is full. The bolts or other clamps are removed from flanges  21   a ,  21   b  and the finished product is removed from the mold. 
   Significantly, the resin inside toroidal space  29  is formed integrally with the resin that impregnates woven glass  23 . The welded joint between each strut  19  and central drum  22  is thus reinforced by the resin in toroidal space  29 . The resin enters into the micro perforations of cylinder  27  before curing. Each blade is therefore integrally formed with said cylinder, thereby overcoming the blade/hub separation problem of the prior art. Micro perforated cylinder  27  provides the needed flow-stopping characteristics. 
   It will be seen that the advantages set forth above, and those made apparent from the foregoing description, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
   It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween.