Abstract:
An apparatus for shaping a green tire carcass is provided having a bladder mounted to a first and second support, a retractable support shaft mounted inside the bladder, and upper and lower bead ring for mounting the beads of the tire carcass thereon, wherein one of said bead rings has a channel in fluid communication with a pressurized source of fluid, wherein said channel has an outlet located between said bladder and said carcass for injecting pressurized fluid between the carcass and the bladder.

Description:
FIELD OF THE INVENTION 
       [0001]    This application relates to the bladder shaping of green tire carcasses prior to vulcanization, and more particularly to large tire shaping of carcasses. 
       BACKGROUND OF THE INVENTION 
       [0002]    Tire uniformity is important for all tires, especially large off the road tires. One type of tire nonuniformity can occur in the tire carcass. For the green tire carcass, it is important that the carcass ply wire spacing be evenly distributed. It is further important that the liner gage be evenly distributed as well. Failure to meet specific uniformity criteria often results in the scrapping of tire carcasses, which can be expensive and wasteful. One cause of carcass nonuniformity may be attributable to the bladder shaping process. For very large radial tires, there tends to be a shape mismatch between the collapsed bladder and the green tire carcass. For example, prior to inflating the bladder, the collapsed outer diameter or circumference of the bladder used in the tire shaping process may exceed the inner diameter or circumference of the green tire. In addition, as the bladder is inflated, the bladder has an outer diameter much larger than the carcass inner diameter. 
         [0003]      FIG. 1  illustrates a simplified schematic of a green carcass  30  with a folded bladder  40  inside. Certain edges  42  of the folded bladder are in contact with the inner surface  32  of the green tire carcass. The bladder edges have a tendency to grip the tire carcass, so that as the bladder is inflated, it results in the over stretching of the casing between the contact points and a localized thinning of the liner gauge. Once the overstretching occurs, the tire carcass must be scrapped. Thus an improved method and apparatus for shaping a large green tire carcass is desired, without any of the afore-mentioned disadvantages. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention provides in a first aspect a method of shaping a green tire carcass comprising the steps of: positioning a green tire carcass about an internal bladder, mounting a first bead of the green tire onto a first ring, and a second bead onto an air shaping ring, injecting pressurized fluid through said air shaping ring, into the cavity formed between the carcass and the bladder to inflate the carcass, and then inflating the bladder to further shape the carcass. Preferably the fluid between the carcass and the bladder is removed prior to inflating the bladder. 
         [0005]    The invention provides in a second aspect an apparatus for shaping a green tire carcass comprising: a bladder mounted to a first and second support, a retractable support shaft mounted inside the bladder, and upper and lower bead ring for mounting the beads of the tire carcass thereon, wherein one of said bead rings has a channel in fluid communication with a pressurized source of fluid, wherein said channel has an outlet located between said bladder and said carcass for injecting pressurized fluid between the carcass and the bladder. 
       DEFINITIONS 
       [0006]    “Aspect Ratio” means the ratio of a tire&#39;s section height to its section width. 
         [0007]    “Axial” and “axially” mean the lines or directions that are parallel to the axis of rotation of the tire. 
         [0008]    Bead” or “Bead Core” means generally that part of the tire comprising an annular tensile member, the radially inner beads are associated with holding the tire to the rim being wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes or fillers, toe guards and chafers. 
         [0009]    “Bias Ply Tire” means that the reinforcing cords in the carcass ply extend diagonally across the tire from bead-to-bead at about 25-65° angle with respect to the equatorial plane of the tire, the ply cords running at opposite angles in alternate layers 
         [0010]    “Carcass” means a laminate of tire ply material and other tire components cut to length suitable for splicing, or already spliced, into a cylindrical or toroidal shape. Additional components may be added to the carcass prior to its being vulcanized to create the molded tire. 
         [0011]    “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction; it can also refer to the direction of the sets of adjacent circular curves whose radii define the axial curvature of the tread as viewed in cross section. 
         [0012]    “Cord” means one of the reinforcement strands, including fibers, which are used to reinforce the plies. 
         [0013]    “Ply” means a cord-reinforced layer of elastomer-coated, radially deployed or otherwise parallel cords. 
         [0014]    “Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire. 
         [0015]    “Radial Ply Structure” means the one or more carcass plies of which at least one ply has reinforcing cords oriented at an angle of between 65° and 90° with respect to the equatorial plane of the tire. 
         [0016]    “Radial Ply Tire” means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65° and 90° with respect to the equatorial plane of the tire. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0018]      FIG. 1  illustrates a simplified schematic of a cross sectional view of the uninflated green carcass with a folded bladder inside. 
           [0019]      FIG. 2  is a simplified schematic of cross-sectional view of a deflated bladder shown inside a green tire carcass of a tire shaping device; 
           [0020]      FIG. 3  is a perspective view of a large tire shaping bladder shown under internal vacuum in solid lines, and in the relaxed state in phantom; 
           [0021]      FIG. 4  is a perspective view of an air shaping ring; 
           [0022]      FIG. 5  is a cross-sectional view of the air shaping ring in the direction  5 - 5  of  FIG. 4 ; 
           [0023]      FIGS. 6-10  illustrate the various stages of the carcass shaping process;  FIG. 9  is a top view of the air shaping ring; 
           [0024]      FIGS. 10A ,  10 B,  10 C are cross sectional views taken in the directions indicated on  FIG. 9 ; 
           [0025]      FIGS. 11A ,  11 B,  11 C are cross sectional views taken in the directions indicated on  FIGS. 10A ,  10 B and  10 C, respectively. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 2  illustrates a cross-sectional view of a green tire shaping mechanism, shown generally at  10 . The tire shaping mechanism  10  is mounted upon a support frame  12 . Connected to the support frame  12  is a lower end of a bottom annular mold ring  14 . The mold ring  14  is removably mounted to the support frame  12 . The mold ring  14  has an interior hole  15  for receiving an inner support shaft  16 . The support shaft  16  has a first end  17  received in the upper part of the tire shaping mechanism  18 . The support shaft has a second end  20  received in a cylindrically shaped chamber  22  of the support frame  12 , to allow the support shaft to retract into the chamber  22  during tire shaping. 
         [0027]    The bottom mold ring  14  is connected to a lower annular bead ring  26  for receiving and securing a first bead ring  32  of a green tire carcass  30 . A bladder retention ring  34  is secured to the lower annular bead ring  26 . The bladder retention ring  34  has an annular groove  36  for securing the bottom end  42  of a bladder  40  to the retention ring. The bladder  40 , as shown in this embodiment, is a very large, cylindrically shaped bladder in the at rest position, typically with multiple folds as shown in  FIG. 3 . The bladder folds may be numerous, with the bladder outside circumference greater than the tire inside circumference (position shown in phantom). The bladder has a second end  44  which is received in a groove of an upper bladder retention ring  50 . Connected to the upper bladder retention ring is an annular fluid shaping mold ring  60 . The shaping ring  60  has an inner bore  62  for receiving the shaft  16 . A pressure retaining cap  18  is received onto shaft end  17 . 
         [0028]    As shown in  FIG. 5 , the fluid shaping ring  60  has an internal annular manifold  64  for channeling pressurized supply fluid, typically air, from a pressurized fluid supply  68  to the inner portion of the shaping ring  60 . Supply fluid is channeled through the shaping ring manifold  64  to one or more interior channels  66 , typically 5 or more, which extend from the manifold on the upper surface of the ring to the lower radial surface or toe end  70  of the ring  60 . Pressurized fluid is directed from manifold through the channel  66  and out the orifices  71  located on the lower toe end  70  of the ring  60  and then through annular channel  73 . The pressurized fluid is then directed from the annular channel into the space between the bladder  40  (shown in phantom in  FIG. 5 ) and the tire carcass  30  (shown in phantom) to help shape the tire carcass, as described in more detail, below. 
         [0029]    The fluid shaping ring  60  may additionally comprise optional vent holes  75  spaced along the outer circumference of the shaping ring  60  located on lower radial toe end surface  70 . The fluid shaping ring may further comprise one or more optional jumper channels  77  typically about 0.5-1.0 inch wide, located on the lower toe end  70 . The jumper channels  77  interconnect annular channel  73  located on the inner surface of the toe end of the shaping ring. The optional jumper channel and vents function to provide additional pathways for the pressurized fluid to follow should one of the orifices  71  be blocked by the bladder during filling. 
         [0030]    The fluid shaping ring may further comprise optional labyrinth grooves  90  located on the radially inner surface of the fluid shaping ring  60  which mates with the upper bladder retention ring  50 . The labyrinth grooves provide a controlled venting of the pressurized medium during bladder shaping without the need for valves or other mechanical means. 
         [0031]    The steps for shaping the carcass can now be described. First the green tire carcass to be shaped is mounted upon the tire shaping device  10 . Then, an internal vacuum is drawn on the bladder to reduce the bladder outer diameter, as shown in  FIG. 3  (in solid lines). Next, the green tire carcass is positioned over the bladder so that a first end of the bead is mounted on the lower bead ring  26 . The air shaping ring  60  is positioned over the tire shaping device so that the outer circumferential edge of the shaping ring is in contact with the tire bead. The pressure retaining cap is next installed over the support shaft. The tire carcass is now ready for shaping. 
         [0032]    As shown in  FIGS. 2 and 6 , the shaping bladder is inflated and pressurized to an internal pressure of about 0.5 to 1 psig. Just holding the tire carcass in place, the bladder is still with many longitudinal folds, as the circumference of the curing bladder at rest has a larger diameter than the inside of the green tire carcass. Shaping fluid as indicated by the flow arrows in  FIG. 2 , is introduced between the bladder and the tire carcass. Pressurized fluid, typically air at about 4 to about 5 psig at about 100-300 scfm, typically about 200 scfm, is fed to inflate the tire casing in the range of about 4 to about 5 psig. See  FIG. 7 . During this step, the bladder initially collapses due to the higher external pressure (Pressure*volume=constant), and then the pressure balances resulting in the bladder expanding slightly. 
         [0033]    As shown in  FIG. 7 , the tire shaping device draws the green casing down in height when the support shaft  16  is retracted within the chamber  22 . The bladder and supply fluid pressure is maintained constant, at about 4-5 psig. As the casing is drawn down in height, the carcass inner circumference increases to a value greater than the interference diameter of the bladder. The casing is now free from the bladder so when the bladder is inflated, the tire carcass will not adhere or pull on the inner liner and body ply causing cord spacing anomalies and thin liner gauge. 
         [0034]    Next the shaping fluid may be turned off. The shaping fluid vents out the labyrinth grooves  90 , which act like air brakes to slowly vent the supply fluid from the chamber. As the pressure medium is pumped out, the bladder slowly increases in volume. 
         [0035]    The bladder is then inflated to suitable pressure, typically about 6 psig. The bladder inflates and assumes the shape it would have at 1.5-2 psig. The shaping air has been completely evacuated, and the curing bladder expands due to the pressure differential. The casing is then further shaped by the bladder as shown in  FIG. 8 . 
         [0036]    The benefit to this process is that the tire cords and liner gauge are more uniform. Further, there is an increase in bladder life as there is less wear and tear on the bladder due to the bladder sticking and slipping issues described above. 
         [0037]    Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.