Abstract:
A urethane wheel that is manufactured by molding, casting, or vacuum forming methods in a mold having a wheel shaped cavity that a wheel core formed from a rigid material such as steel or aluminum has been supported in to receive a flow of a urethane material directed therearound, encapsulating the entire wheel core and forming a wheel capable of supporting a car or light truck traveling at highway speeds.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   This invention pertains to methods and apparatus for vacuum forming a vehicle wheel from a mixture of urethane constituents. 
   2. Prior Art 
   The present invention is in a wheel that is formed from a urethane material in a vacuum forming apparatus in a single casting operation to have at least the strength, or greater, of a like size and load bearing standard steel or aluminum wheel for mounting a tire thereon. The vacuum forming apparatus includes a mold having a cavity wherein is formed a wheel. Or the cavity is formed to accommodate a wheel core fitted therein, that is preferably formed from a light gauge steel or appropriate aluminum compound, and is supported in the mold by spacers to receive a urethane coating. In practice, a urethane material, that is a compound formulated to produce a steel like strength, is pulled under vacuum into a mold cavity. Whereby, after curing, the mold is opened and a homogenous wheel, or a wheel containing a core, is removed. 
   Relating to vacuum forming apparatus, heretofore it was recognized that venting air from a tire tread mold cavity early in a casting process could eliminate the necessity for venting the cavity through spaced holes in the mold that materials from the tread will flow into during casting and form projections or “tits”. Such extensions or “tits” project from the tread surface and were either pulled off when the tire was removed from the mold, had to be cut off or wore off during tire use. To prevent this undesirable cosmetic anomaly it was recognized that air could be vented from the mold cavity just before tread casting, eliminating a necessity for providing flow passages or vents from the tire tread mold while still obtaining a smooth, un-pocketed or un-blemished, finished tread surface. Examples of such an introduction of a vacuum into a tire mold just prior to forming a tire tread are shown in U.S. Pat. Nos. 4,573,894 and 5,152,951. Specifically, U.S. Pat. No. 4,573,894 sets out a tire mold having a cavity that is for receiving and finally shaping the tire. The patent is defined by a surface that is for contacting the exterior of the tire during tire curing. The cavity is fluid connected to a single vacuum source for evacuating air from within the cavity during an early portion of a tire curing cycle to prevent air and any other fluid from becoming trapped between the tire and the surface that defines the cavity that will become the tire tread. Visual effects in the form of voids in the tire exterior are, thus eliminated. Like the &#39;894 patent, U.S. Pat. No. 5,152,951 also provides for the elimination of fluid from the mold cavity during an early portion of a tire curing cycle. The patent provides for fluid evacuation through a space between the surfaces of the mold parts that defines the mold parting line. Both patents provide a single vacuum source and its connection to the mold cavity for forming the tire side wall and tread surfaces. 
   Recently, the inventors of the present invention developed an improved vacuum forming apparatus for forming transport tires that is the subject of a currently pending U.S. patent application Ser. No. 10/936,635, filed Sep. 4, 2004. This patent application sets out an apparatus and method for forming an elastomer tire containing plies, belts and beads, that involves both an evacuation of air from the elastomeric mixture prior to its introduction into the mold cavity, and for pulling the air free mixture through the mold. Which air free flow of elastomeric material fills an area between inner and outer mold walls and travels through the core of plies, belts and beads, to form a finished transport tire that is free of voids or pockets. Unlike this earlier patent application the present invention provides for vacuum forming a homogenous wheel or a wheel core having an outer coating of a urethane material bonded thereto. 
   SUMMARY OF THE INVENTION 
   It is a principal object of the present invention to provide for forming, in a vacuum forming apparatus, a homogenous wheel from, or coating a wheel core with, a urethane material to provide, after curing, an essentially perfectly balanced urethane wheel that has a strength that is the equivalent to, or better than a steel wheel formed for a like application and load bearing. 
   Another object of the present invention is to provide for forming, in a single operation, a wheel from, or coating a wheel core with, a urethane material in a vacuum apparatus where air is removed from the urethane material mixture prior to its passage into an apparatus mold and the urethane material is pulled, under vacuum, through the mold, filling a mold cavity to form a homogenous wheel, or to form a wheel having a core formed from aluminum or a light gauge steel. 
   Another object of the present invention is to provide for forming, in a single operation, a wheel from, or coating a wheel core with, a urethane material, to provide a wheel that, when cured, has a like or better strength than a steel or aluminum wheel formed for a like application and load bearing, in a vacuum casting apparatus that includes a canister that is initially placed under a deep vacuum as it receives a volume of mixed urethane constituents, with the vacuum pulling air from the mixture, and whereafter the canister is opened to atmosphere and the column of the air-free mixture is allowed to pass through a canister exhaust valve and travel into a mold cavity formed between inner and out wheel mold surfaces that is maintained at a low-level vacuum, with the low level vacuum pulling the air-free urethane mixture through the core, filling the mold cavity, and is allowed to cure into a homogeneous finished wheel. 
   Another object of the present invention is to provide a mold with a wheel cavity having opposing top and bottom plate faces that are mirror images of opposing surfaces of a wheel, and where the mold is assembled around a cylindrical inner core and with half ring outer mold segments fitted between the top and bottom plates to form a wheel center between inner and outer wheel flanges, land with the mold arranged as a component of a vacuum forming apparatus. 
   Another object of the present invention is to provide for forming a homogenous wheel or wheel containing a core in a vacuum forming apparatus from a urethane material where, in the formation process, essentially all air is removed from a urethane material mixture before its passage into a mold wherethrough the material is pulled, under a low level vacuum, to completely fill the mold and flow around a wheel core, if one is positioned therein and maintained on spacers, forming, in a single molding operation, a wheel that is ready for removal from the mold after cooling. 
   Still another object of the present invention is to provide a vacuum forming apparatus for manufacturing a homogenous wheel, or wheel with a core, from a urethane material, where the vacuum forming apparatus includes a reservoir canister, that is preferably located within the mold annular area, but may be connected into a mold cavity through a hose, or the like, and which mold cavity mimics the inner and outer surface of a wheel and is under a low-level vacuum, and with the reservoir canister maintained under a deep vacuum whereby such air as is trapped in a urethane mixture of constituents poured into the canister are removed, whereafter, a canister valve is opened and the air-free urethane material mix is pulled into the mold cavity by the low-level vacuum, forming a homogenous wheel, or when a wheel core is positioned in the mold cavity prior to mold closure, forming a wheel with an encapsulated core. 
   Still another object of the present invention is to provide a vacuum forming apparatus for forming a wheel from a urethane material, where the apparatus includes seals for maintaining the integrity of a urethane canister and the mold when they are subjected, respectively, to a deep vacuum and a low level vacuum. 
   Still another object of the present invention is to provide a vacuum forming apparatus for casting a homogenous wheel or wheel containing a core from a urethane material in a single operation, producing a wheel that is essentially perfectly balanced. 
   The present invention is in wheel formed from a mixture of urethane material constituents in a vacuum forming apparatus connected to pass a urethane material flow into a mold. The mold is assembled from components to have a cavity that is the shape of a wheel, and may provide for receiving standoffs or spacers fitted into the mold to support a wheel core. The mold cavity receives a flow of a mixture of urethane material constituents that are selected to provide, when cured, a strength that is like that or better than a steel or aluminum wheel formed to support a design load that is like the load to be supported by the urethane wheel of the invention. The urethane constituents mixture are poured into a canister that is maintained under a deep vacuum to remove the air from the mixture, and whereafter that canister is opened to pass an air free flow into to fill the mold wheel cavity that is under a low level vacuum, flowing throughout the cavity, forming a homogenous wheel. Or, where the mold cavity contains a wheel core, preferably one formed from light gauge steel or suitable aluminum, that is to be coated or encapsulated in the wheel by the flow of urethane material that is pulled through the mold cavity to form the wheel. The mold includes inner and outer mold components that, when assembled form the mold with a cavity that has the shape of a wheel to be cast therein. 
   The mold includes a sleeve as a wheel hub area, arranged between top and bottom plates that have the shape of the opposite sides of the wheel, with a pair of half ring outer mold segments assembled as a ring positioned between the top and bottom plates that form a mirror image of the wheel across the flange area. Which outer mold segments and top and bottom plates include seals for closing off the mold cavity, with the outer mold segments to be easily removed when the mold top plate is lifted off the mold assembly, and the half ring outer mold segments separated, allowing for removal of a cast wheel. 
   For vacuum forming the wheel, the vacuum forming apparatus includes a mold canister that may, but need not, be formed to fit across the mold hub area that is to receive a mix of urethane material constituents and connects to a deep vacuum source for removing air from which mix. After air removal, the urethane mixture is passed through a needle valve into an annular mold cavity area, flowing across the mold cavity to the hub area, and across the outer mold segments, traveling from one wheel flange end to the other, under the urging of a low level vacuum that is pulled through a dome shaped lid that is fitted over the mold top plate. The urethane material mixture is thereby pulled through the mold, filling the cavity from a wheel hub area to the wheel outer flange area. Further, if a wheel core is contained in the mold, it is preferably supported on standoffs or spacers, that allow the flow to encapsulate the core. Additional to the seals between the mold top and bottom plates and the mold outer segments, seals are also provided between the individual outer mold segments, around the mold hub area, and around the canister, if the canister is arranged across the mold hub area. Which seals contain, respectively, the low level and deep vacuums that are preferably generated by separate vacuum sources. 
   Upon receipt of a set volume of the urethane material mixture the canister is sealed and is subjected to a deep vacuum. The vacuum is pulled through a port in the cannister, and is operated until the mix in the urethane mixture in the canister is essentially free of all the air that had been trapped therein during the mixing process. Thereafter, with the mold maintained under a low level vacuum that is pulled through ports at the wheel hub area and the wheel flange ends that open into the cover, the canister, is opened through a needle valve to pass the urethane mixture into the mold cavity, and the canister itself is open to outside air. The air free urethane mixture thereby flows into the mold wheel cavity. The urethane mixture fills the mold wheel cavity, encapsulating a wheel core, if any, mounted therein. With any air in the mold traveling ahead of the mix flow and out the outer mold ports wherethrough the low level vacuum is being pulled. In practice, the needle valve is required to be closed as the canister emptied and comes under ambient air conditions as are present in the canister, with a presence of the urethane mixture at the dome shaped lid ports to indicate that the mold rim cavity has been filled. Then, after cooling, the mold is broken open and a completed wheel is removed that is essentially perfectly balanced. 

   
     DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangement of parts, used to form the apparatus of and practice the steps of the invention that are herein shown as a preferred embodiment and will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof: 
       FIG. 1A  shows an exploded top plan perspective view of a mold dome over a top plate that each have a center opening that is for fitted onto a ring assembled from half ring outer mold segments that are fitted together and that fitted together ring is positioned on an outer portion of a bottom plate, forming the exterior or outer mold, and showing a cylindrical cavity of a vacuum forming apparatus aligned for fitting through the center openings; 
       FIG. 1B  shows the assembled mold of  FIG. 1A  fitted with a dome shaped lid across the top plate and including cylinder canister of a vacuum forming apparatus shown fitted through the dome shaped lid and passed into the top plate center opening; 
       FIG. 2A  shows a side elevation sectional view taken along the line  2 A- 2 A of  FIG. 1B , showing the dome shaped lid lifted off of the mold top plate, arrows A, indicating that the dome shaped lid is for fitting over the top plate and showing top and bottom plates and outer mold segments as including opposing inner mold core sections forming the mold cavity, and showing the cylindrical canister fitted through the dome shaped lid and top and bottom plates that is open to receive a flow of a urethane mixture through a top end, shown as a section of pipe, and is closed by a needle valve across its lower end and showing first and second ports fitted, respectively, into the top of the cylindrical canister and through the dome shaped lid top surface; 
       FIG. 2B  shows the view of  FIG. 2A  with the dome shaped lid lowered onto the mold top plate and showing a urethane mixture being poured into the cylindrical canister and with the canister having a deep vacuum, arow C, pulled therefrom through a deep vacuum port, showing the needle valve as closed and showing a low level vacuum, arrows B, being pulled through a low level vacuum port; 
       FIG. 2C  shows a view like that of  FIG. 2B  only showing the cylindrical canister filled with mixed urethane constituents wherefrom air has been removed and the deep vacuum source has been released with the canister open to atmosphere, arrow D, and showing the needle valve as being opened to pass a urethane mixture therefrom that travels through the mold cavity, as illustrated by arrows E, to exhaust into the space under the dome shaped lid; 
       FIG. 2D  is a view like that of  FIG. 2C  only showing the urethane mixture as having been exhausted from the canister and the needle valve closed, with the urethane mixture filling the mold cavity, and about to pass into the area under the dome, arrows F; 
       FIG. 2E  shows a side elevation sectional view of a homogenous wheel as has been removed from the mold of  FIG. 2D ; 
       FIG. 3  shows a top plan perspective view of the wheel of  FIG. 2E ; 
       FIG. 4A  shows a view like that of  FIG. 2C  with a pour of urethane material passing into a cylindrical canister that is under a deep vacuum, arrow C, pulling air out of the mixture of urethane constituents, showing the canister lower end as including a closed needle valve and showing a cavity mold like that of  FIGS. 2A through 2D  wherein a wheel core has been positioned, with a dome shaped lid shown fitted over the mold top plate that is under a low level vacuum, show as arrows D, that is pulled through a dome port; 
       FIG. 4B  shows a view like that of  FIG. 4A  showing the needle valve as having been opened, opening the mold cavity to a flow of the urethane material passed from the needle valve, arrows E, under the urging of the low level vacuum that is pulled through the dome port, arrows D; 
       FIG. 4C  shows a view like that of  FIG. 4B  showing the urethane mixture as having passed into the mold rim cavity, filling the mold rim cavity and covering the wheel core, and showing the needle valve as having been closed, cutting off the urethane material flow; 
       FIG. 5  shows a side elevation sectional view of a wheel removed from the mold of  FIG. 4C , showing the wheel core cover by a layer of hardened urethane and the low level vacuum as having been released, arrow G; and 
       FIG. 6  shows a top plan perspective view of a wheel where the urethane mixture has been directed around, to encapsulate, the wheel core, that is shown as a removed section. 
   

   DETAILED DESCRIPTION 
   The invention is in a vacuum forming apparatus and process for forming a urethane wheel that may be formed as a homogenous unit from a cured urethane material or may include a wheel core having a cured urethane coating, or includes a wheel core that is entirely encapsulated in the urethane material. For forming a urethane wheel of the invention a mold is provided, as shown in  FIG. 1A , identified as a mold  10  that includes a dome shaped lid  20 . With the mold  10  shown in  FIG. 1B  as having had the dome shaped lid  20  fitted thereover and includes a cylindrical canister  30  fitted through an opening through the center of the dome shaped lid and through the mold center. Which cylindrical canister is to hold and dispense a mixture of urethane constituents poured therein and is for fitting through a center opening  14  formed through a top plate  11  of which mold assembly  10  of  FIG. 1A . 
     FIG. 2A  shows the mold  10  as including the top plate  11  and bottom plate  12 , with outer mold half ring segments  13   a  and  13   b  aligned for assembly into a ring that is an outer mold segment  13 . It should, however, be understood, which outer mold segments may be formed of multiple segments for positioning side by side together to form a ring. The assembled ring is positioned around a bottom plate mold segment  15  that is mounted on top of the bottom plate  12  with end seals  13   c  for fitting into slots in the opposing half ring segments surfaces provided for sealing the half ring segments at their junctions. Shown in  FIG. 2A , number of radial channels  16  are formed in the bottom plate mold segment  15  extending across the bottom plate  12  upper surface  12   b , above the center opening  14   a  to an outer lip  17 . Which outer lip  17  has a ring seal  18  fitted thereto that engages a bottom surfaces of the pair of half ring outer mold segments  13   a  and  13   b  that form the outer mold segment  13 , sealing thereto. With, shown in  FIGS. 1A , and  2 A through  2 C, in mold  10  assembly, after the outer mold segment ring  13  is fitted onto the bottom plate  12  and bottom plate mold segment  15 , the top plate  14 , mounting a ring shaped top plate mold segment  19  is fitted thereover, engaging a ring seal  18   a  fitted into a seal groove formed in undersurface of the top plate  11 , completing the mold assembly. With, in that assembly, a channel  19   b , as shown in  FIG. 2B  is formed between the outer mold segment  13  and outer edges of the bottom plate mold segment  15  and top plate mold segment  19  that will open into a vent passage  19   a , that connects to open into the area beneath the dome shaped lid  20 , as shown in  FIGS. 1A and 2A  through  2 D. Which top and bottom plates  11  and  12 , respectively, as shown in  FIG. 2A  have the mold sections  15  and  19  maintained to the respective bottom and top plates, respectively, forming the wheel inner surfaces, and with the outer mold segments opposing inner surfaces having the wheel opposite faces, and include bead seat and flanges formed therein. So arranged, the spaces  19   b  and  19   a  between the opposing mold sections and cylindrical canister in the assembled mold, becoming a mold channel wherethough the urethane mixture travels in a single molding operation. Which mold  10 , as set out below, includes ring seals  18  and  18   a , fitted, respectively, between the contacting surfaces of the bottom of the formed ring outer mold segment  13  and bottom plate  12  edge, and the top of the outer mold segment  13  and a lip  11   a  of the top plate, as shown in  FIG. 2A . Which seals along with seals  13   c  between the half ring outer mold segments  13   a  and  13   b  provide for isolating the urethane material flow paths to fill the mold cavity, as set out and discussed below. 
     FIG. 2A  shows a center opening  21  of the mold dome shaped lid  20  being fitted over and slid along the cylindrical canister  30  outer surface, as the dome shaped lid  20  is lowered onto the top plate  11 , as illustrated by arrows A, to fit and cover over the top plate  11 . The area under the dome shaped lid  20  is open and is vented from that open area through a vent fitting  22  that is for connection to a low level vacuum source. A ring seal  23  is arranged around the dome shaped lid outer edge for providing dome shaped lid sealing over the top plate  11 , as shown in  FIG. 2B . With the dome shaped lid  20  maintained under the low level vacuum source, a liquid urethane material is passed from the cylindrical canister  30  to be pulled through the mold cavity and just into the open area under the dome shaped lid, forming a wheel  60 , as shown in  FIGS. 2E and 3 , as set out and discussed in detail below. 
   As shown in the sectional view of  FIG. 2A  the cylindrical canister  30  is fitted through the dome shaped lid center hole  21 , sealing against a ring seal  21   a , and travels through the mold center hole  14 , shown in  FIG. 1A , that extends from the mold top plate  11  through the mold bottom plate  12 . The cylindrical canister  30  lower end extends beyond the mold bottom plate  12  under surface  12   a , as shown in  FIGS. 2A through 2D  as an inverted top hat shaped end  30   a  wherein is fitted a needle valve  31  having an actuator rod  32  extending axially out from its lower end. The actuator rod  32  is moved vertically as by operation of a solenoid, not shown, to lift or lower a valve head  33  into and out of engagement with a needle valve  31  seat  34 , opening and closing the cylindrical cavity through the needle valve to pass a flow of urethane material into the mold  10 , as set out below. 
   A feed tube or pipe  35 , shown in  FIG. 2A , is installed through a top end  36  of the cylindrical canister  30  that is for passing mixture of urethane material through a funnel shaped opening  37 , shown in broken lines. Which pour of urethane material is observable through a window  39 . The cylindrical canister  30 , as it receives the mixed urethane material, is maintained under a deep vacuum that is pulled through an end  39  of a vacuum fitting  38  maintained in the cylindrical canister top end  36 , opening into the cavity between the top plate  11  and dome shaped lid  20  undersurface. The feed tube or pipe  35  is shown aligned with the funnel shaped opening  37  to pass a mixture of urethane constituents  40  into the cylindrical canister  30  as shown in  FIG. 2B . 
   In a practice of the process of the invention for forming a wheel  60  like that shown in  FIG. 2E and 3 ,  FIG. 2B  shows that mold  10  is covered by the dome shaped lid  20  fitted thereover, with a pour of a mixture of urethane materials  40  flowing through the tube  35  and passing into the cylindrical container. During which mixture flow, a deep vacuum, shown by arrows C, is pulled through the cylindrical canister  30  and through vacuum fitting  38 . Which flow continues until a proper amount of the urethane mixture has passed into the cylindrical canister, as observed through the window  39  that has been measured to provide enough material to form a single rim  60 . With, in preparation to initiating a flow of which urethane material from the cylindrical canister  30 , a low level vacuum is shown pulling air, arrow B, from under the dome shaped lid  20  with that flow passing through the vent fitting  22 , also illustrated by arrow B. 
     FIG. 2C  shows the mold  11  with the cylindrical canister  30  of  FIG. 2B  fitted therein and with the actuator rod  32  shown as having been moved vertically, as by operation of a solenoid, not shown. The needle valve head  33  is thereby lowered out of engagement with the valve seat  34 , opening the needle valve  31  to pass the urethane mixture. Simultaneous with the needle valve  31  opening, the cylindrical cylinder vacuum fitting  38  is opened, allowing air at atmospheric pressure, shown as arrows D, to enter the cylindrical canister, above the urethane material  40 , that also begins flowing out of the needle valve  31 . The urethane material flow is exhausted through a vent opening  42  in the bottom of the cylindrical canister  30  and travels through a flow path through the mold, identified by arrows E. The urethane material flow, pulled by the low level vacuum, travels first through radial channels  16  that are located at the junction of the bottom plate top surface  12   b  and the bottom plate mold segment  15 . As shown in  FIG. 2A through 2   d , the cylindrical canister vent opening  42  aligns with the radial channels  16  that, in turn, connect to feed the urethane material into that mold wheel cavity  19   b  at a lower flange end  43  of mold rim flange  44 . Thereafter, the urethane material flow  40 , shown as arrows E in  FIG. 2C , under the urging of the low level vacuum, travels up the mold rim flange to branch off at the intersection  45  of the mold rim flange  44 , forming two flows that proceed separately, one across the mold rim flange  44  to the upper flange end  46 , and the other across the rim center section  47  to an upwardly turned mold wheel hub  48 . A flow passage  49  connects to an end  48   a  of which mold wheel hub  48 . Which flow passage  49  extends alongside the cylindrical canister outer surface  30   a  to pass material to the edge of the top plate center opening  14 .  FIG. 2D , as set out above, shows the flow path, arrows E, of the urethane material as it travels through the mold rim cavity, diverging at intersection  45 , with the two flows pulled into the dome shaped lid  20  inner cavity, and pass out of the passages  50  from the mold rim cavity upper flange end  46  and vent along the cylindrical canister  30   a  towards the hole  14  edge. Shown in  FIG. 2D , the urethane material presence within the dome shaped lid  20  inner cavity ends of the passages  50 , arrows F, and at the hole  14  edge indicates that the mold rim cavity is filled with the urethane material and that the urethane material flow should be stopped. Which urethane material flow is stopped by release of the low level vacuum, arrow G, at vent fitting  22 , and shutting off of the needle valve  31 . The needle valve  31  closure occurs after the measured amount of the urethane material has passed out of the cylindrical canister and prior to the end of that flow entering the mold rim cavity at the lower flange end  43 , filling the mold rim cavity, as shown in  FIG. 2D . 
   In which mold rim cavity filling the flow of urethane material flows around rim lug hole plugs  51  that are fitted at spaced radial increments into the bottom plate mold segment  15 , leaving appropriately positioned lug holes  61  in the finished rim  60 , as shown in  FIGS. 2E and 3 . Further, as shown in broken lines in  FIGS. 2C and 2D , a section  47   a  of the rim center section  47  is shown in broken lines to indicate that the bottom plate mold segment  15  also has spaced closed sections wherearound the urethane flow passes, leaving spaced circumferential voids  62 , as shown in the finished rim  60  of  FIGS. 2E and 3 , at the junction of a rim center portion  63  and a rim web area  64  and includes a center hub hole  65 . Which finished rim  60  is formed entirely of urethane. It should, however, be understood that the rim  60  can have circumferential sections or portions thereof that are of different thickness or thicknesses to support an anticipated wheel loading, within the scope of this disclosure.  FIG. 3  shows a top perspective view of the rim  60  of  FIG. 2E . 
     FIGS. 4A ,  4 B and  4 C are views like those of  FIGS. 2B ,  2 C and  2 D only they show a wheel  100  having a wheel core  77  that is encapsulated within a urethane material in a vacuum forming apparatus.  FIG. 4A , like  FIG. 2B , shows a mold  70  that includes top and bottom plates  71  and  72 , respectively, with a top surface  72   a  of the bottom plate  72  shown as mounting a bottom plate mold segment  74  having a lower portion of a wheel core  75  formed therein and includes a ring seal  81   a  for engaging and sealing against an outer mold segment ring  73 . Which outer mold segment ring  73  is formed by a pair of half ring outer mold segments  73   a  and  73   b  that are for fitting together into a ring  73  that is positioned onto an outer edge portion of the bottom plate  72  top surface  72   a , sealing at ring seal  81   a . The half ring outer mold segments  73   a  and  73   b  include a ring seal  73   c  for fitting in a circular slot  73   d  in an edge of the half ring outer mold segment  73   b , opposite to a toe end  73   e  of the half ring mold segment  73   a , sealing the half ring outer mold segments  73   a  and  73   b  against an outward flow of urethane material. The ring seal  81   a  is to preclude a urethane material flow across a toe edge  81  of the top plate  71 . Which top plate undersurface  71   a  mounts a top plate mold segment  76  that has the shape of the upper portion of the wheel core cavity  75 . Accordingly, the inner surfaces of the lower and upper plate mold segments, and the ring shaped mold outer mold segment  74 ,  76  and  73 , respectively, form the wheel core cavity  75  that receives a preformed urethane wheel core  77 , that is cast therein by operation of the vacuum forming apparatus, as set out below. Which wheel core  77  is slightly smaller than the mold wheel core cavity  75 , leaving a urethane material flow path therearound, and is positioned in that wheel core cavity by standoffs  78  that approximately center the wheel core  77  in the wheel core cavity  75 . Which wheel core  77  is shown in  4 A through  4 C and  5  as being a hollow ring shaped tube that is positioned in the mold to be centered on the wheel hub  79  and has a cross section to transmit forces as are applied at the wheel through a saddle  77   a  and flange ends  77   e , through wheel inner and outer sections  77   b  and  77   c , respectively and into the wheel drum section  77   d  and the wheel lug holes. The wheel core  77  is shown as having the saddle  77   a  between the flange ends  77   e  and joins to the inner and outer sections  77   b  and  77   c  that join to the ends of the drum section  77   d  that has the shape of an axle drum. The wheel core  77  is hollow and, accordingly, in the vacuum forming operation, only the outside of the wheel core  77  will be coated. Which finished wheel with wheel core  77  is shown as a urethane wheel  100  in  FIGS. 4C and 5  and discussed hereinbelow. 
   While a hollow ring shaped tube is shown as the wheel core  77  in  FIGS. 4A through 4C  and  5 , it should be understood that another design of core, such as a core formed to fit within and be supported as with standoffs in the cavity of mold  10 , can be provided. Such core is also to receive a flow of the urethane mixture to coat both core sides. In such arrangement the core is fully encapsulated in the urethane mixture. Such core can be formed of a light gauge steel or aluminum to provide a stiffening to the rim.  FIG. 6  shows a top plan perspective view of a wheel  130  that has had a section removed back from a top flange end portion to expose such a core  131  that the wheel is cast around in a practice of the vacuum forming steps and in the apparatus as described above. 
   In a practice of the process of the invention, as shown in  FIG. 4A , the mold  70 , like the mold  10  of  FIG. 2B , has a mold dome shaped lid  80  fitted over the top plate  71 , with a ring seal  81   a  providing sealing of the dome shaped lid  80  outer circumference at foot  81  onto the top of the ring shaped outer mold segment  73  and shows a low level vacuum, arrows D, being pulled through a vent fitting  82 . The cylindrical canister  90  is shown fitted through the center of mold  70  with a stepped lower end  91  thereof shown resting on a lip  72   b  of the lower plate  72 . The cylindrical canister  90 , like the cylindrical canister  30 , is shown as having a cylindrical body  92 , and has its top end covered by a cap  93  that has a funnel shaped opening  94 , shown in broken lines, formed through the center thereof. Which funnel shaped opening  94  receives a feed tube or pipe  95  and includes vacuum fitting  96  formed through the cap  93  that a deep vacuum, arrow C, is being pulled through. 
   In  FIG. 4A , like  FIG. 2B , a urethane material mixture  40  is poured into the cylindrical canister  90  through feed tube or pipe  95  to pass through the funnel shaped opening  94 . Which mixture, during pouring, is subjected to the deep vacuum, removing essentially all air as is present in the urethane material mixture. During which pouring a valve head  98  of a needle valve  97  that is positioned across the cylindrical canister  90  lower end is urged upwardly by an actuator rod  99  into seating engagement within a needle valve seat  97   a , maintaining the needle valve  97  in a closed state. 
     FIG. 4B  shows the cylindrical canister  90  of  FIG. 4A  filled with the urethane mixture wherefrom essentially all entrapped air has been removed. Thereafter, the deep vacuum is removed and the vacuum fitting  96  is opened to atmosphere, releasing the deep vacuum. Simultaneously, the needle valve  97  is opened, allowing the air free urethane mixture to flow out of vent openings  101  that communicate with radial channels  102  that connect to a lower flange end  103  of the mold wheel cavity. The urethane flow, shown as arrows B, branches at a mold cavity junction  104  proceeding both alongside the wheel saddle  77   a  and across the inner section  77   b , respectively, of the wheel core  77 . Which urethane material flows alongside the wheel core inner section  77   b , then flows along the core wheel drum section  77   d  and branches at a junction with a wheel cavity hub portion  105  and the core outer section  77   c  to flow along the wheel core outer section  77   c  and intersect the flow that has crossed the wheel core saddle  77   b , and around lug plugs  108  to the wheel cavity hub portion  105  that becomes the wheel hub portion  105 . Whereafter, the combined flows proceed through the wheel cavity upper flange  106  and vent out of passages  107  into the dome shaped lid  80 . Simultaneously, the urethane material travels into the wheel cavity hub portion  105 , flowing around lug plugs  108 , to a wheel hub  109 , venting, shown as arrows F, up a cylindrical canister out wall passage  110  that bends at a right angle around a collar  111  and also vents at  112  into the dome shaped lid  80 . 
     FIG. 4C  shows the urethane material as having been pulled by the low level vacuum, arrows E, with a first venting of the urethane material out of the passages  107  and  112  indicating that the mold wheel shaped cavity is filled. Whereupon, the low level vacuum that is pulled through the vacuum fitting  82  is released, allowing air at atmospheric pressure, arrow G to enter the dome shaped lid  80 , completing the formation of the urethane wheel with core  100 , as shown in  FIG. 5 . 
   After curing, the mold  70  is broken apart, with the dome shaped lid  80  removed first, followed by the top plate  71  and the top plate mold segment  76  and the half ring outer mold segments  73   a  and  73   b  are separated The wheel urethane wheel with core  120  is then removed off from the bottom plate lower plate mold segment  74  that is pulled over the cylindrical canister  90 . Which urethane wheel with core  100  is shown as a side elevation sectional view in  FIG. 5 . 
   In practice, a deep vacuum that is at least ninety six (96) percent is pulled through cylindrical canister vacuum ports  38  and  96 , pulling air out from the cylindrical canister, as illustrated by arrow C, and a low level vacuum of at least eighty five (85) percent, and not greater than ninety five (95) percent, is pulled through vent fittings  22  and  82  of the dome shaped lids  20  and  80  of the two apparatus embodiments, as set out above. Thereafter, a urethane material  40  that has been recently mixed from constituents, is poured through tubes  35  and  95  through the cylindrical canisters  30  and  90  tops, with the deep vacuum removing air from that urethane material mixture. Whereafter, when a desired volume or weight of urethane material has been poured into the cylindrical canister, the high level vacuum is terminated and the canister is opened to atmosphere through the vacuum ports  38  and  96 . Simultaneously to opening the canister to atmosphere the needle valve  31  and  97  are opened, and the urethane material is passed into the mold, traveling through and filling the mold cavity, with the needle valve then closed prior to a passage of air from the canister that following the urethane material. An operator seeing through the canister windows  39  and  92   a , or by other sensing apparatus, that the urethane material is venting from the mold top plate, closes the needle valve, if it has not already been closed, to prevent air passage into the mold cavity, and ends the low level vacuum draw through the top plate ports. The newly formed wheel is allowed to cool and cure in the mold, with the mold then broken open and the wheel removed. 
   While preferred embodiments of our invention in a vacuum forming apparatus for forming a urethane wheel in a single operation, have been shown and described herein, it should be understood that variations and changes are possible to the apparatus and method for its use in the formation of the described tire, and the materials used, without departing from the subject matter coming within the scope of the following claims, and a reasonable equivalency thereof, which claims we regard as our invention.