Abstract:
A tire building drum and a method of building a tire carcass is disclosed. The tire building drum has a center section comprised of a plurality of segments that are radially and axially movable. The sleeve of the tire building drum over the center section has been eliminated, and instead has two seals located on the outer ends or shoulders of the center section of the tire building drum. The building drum further comprises shoulder sections that are axially movable. The shoulder sections include radially expandable bead locks. The method employs the steps of applying one or more carcass layers, locking the bead locks and moving the center section radially outwardly while moving the bead locks axially inwardly.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a tire building drum, more particularly to a tire building drum with no center sleeve. 
       BACKGROUND OF THE INVENTION 
       [0002]    The manufacture of tires typically involves a tire building drum wherein numerous tire components are applied to the drum in sequence, forming a cylindrical shaped tire carcass. This stage of the tire building process is commonly referred to as the “first stage” of the tire building process. The tire carcass is then typically removed from the tire building drum and sent to a second stage, expandable tire shaping drum where the carcass is expanded into a toroidal shape for receipt of the remaining components of the tire such as the belt package and a rubber tread. The completed toroidally shape unvulcanized tire carcass or green tire is then removed from the second stage drum and subsequently molded and vulcanized into a finished tire. 
         [0003]    The prior art process thus requires two tire building drums and the transfer of the carcass from one drum to the other. Further, a problem often arises in precisely locating and anchoring the tire beads on the unvulcanized tire carcass, especially during the transportation of the tire beads from the first stage drum to the second stage drum. Variations in bead positioning can result in ply distortion in the tire. 
         [0004]    Tire manufacturers have recently begun moving towards the utilization of a single tire building drum, for both the first and second stage tire building. This requires that the tire building drum be capable of axial expansion and contraction as well as radial expansion/contraction. Further, it is important to maintain a positive bead lock during the entire tire building process, including the tire shaping, so that the ply cord length is maintained, resulting in good tire uniformity. 
         [0005]    Tire manufacturers typically use a flexible cylindrical rubberized center sleeve as the outermost element on tire building drums. The center sleeve functions as the surface of application and point of fixation for the innermost component of the tire (innerliner). The section where the centersleeve wraps around the “shoulder” of the radially expansible segments also serves as a pneumatic seal against the bead area of the green tire, enabling inflation (shaping) of the green tire in the full-stage tire building process. The centersleeve also typically has a series of holes for providing a vacuum to secure the innerliner to the drum and the air to shape the green tire. 
         [0006]    There are several disadvantages to the prior art rubber center sleeves. The tire building drums typically have a wide range of width adjustability, while the prior art rubber center sleeves have a very limited range of width operation, typically less than 30 mm. Thus the sleeve limits the action of the tire building drum, resulting in the need to change out the drum with another drum having a different width centersleeve in place. The necessity of changing out of the drum requires the storage of drums for different width sizes, and the loss in productivity during the drum change outs. 
         [0007]    A second disadvantage to the prior art center sleeves is that during the tire building cycle the drum width is progressively reduced as the shaped diameter of the green tire increases. This reduced width action may result in the bunching up or buckling of the sleeve due to compression. As the buckled diameter is larger than the bead diameter of the tire, it is necessary to widen the width of the tire building drum in order to remove the finished tire from the drum. 
         [0008]    A third disadvantage to the prior art center sleeves is that they are the highest maintenance component on the tire building drum, requiring frequent replacement when they become torn or blistered. 
         [0009]    A fourth disadvantage to the prior art center sleeves is that the use of the sleeve results in an increased amount of force required to expand the drum. 
         [0010]    A fifth disadvantage to the prior art center sleeves is that the use of the sleeve can result in uneven air flow distribution during inflation of the carcass, contributing to tire nonuniformity. 
       Definitions 
       [0011]    For ease of understanding this disclosure, the following items are defined: 
         [0012]    “Apex” means an elastomeric filler located radially above the bead and interposed between the plies and the ply turn-up. 
         [0013]    “Axial” and “axially” means the lines or directions that are parallel or aligned with the longitudinal axis of rotation of the tire building drum. 
         [0014]    “Bead” means that part of the tire comprising an annular tensile member commonly referred to as a “bead core” wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers, to fit the design rim. 
         [0015]    “Belt Structure” or “Reinforcing Belts” means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17° to 27° with respect to the equatorial plane of the tire. 
         [0016]    “Carcass” means an unvulcanized 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. 
         [0017]    “Casing” means the tire carcass and associated tire components excluding the tread. 
         [0018]    “Chafers” refers to narrow strips of material placed around the outside of the bead to protect cord plies from the rim, distribute flexing above the rim, and to seal the tire. 
         [0019]    “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction. 
         [0020]    “Cord” means one of the reinforcement strands of which the plies in the tire are comprised. 
         [0021]    “Equatorial Plane (EP)” means the plane perpendicular to the tire&#39;s axis of rotation and passing through the center of its tread. 
         [0022]    “Innerliner” means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire. 
         [0023]    “Insert” means an elastomeric member used as a stiffening member usually located in the sidewall region of the tire. 
         [0024]    “Ply” means a continuous layer of rubber-coated parallel cords. 
         [0025]    “Radial” and “radially” mean directions radially toward or away from the axis of rotation of the tire building drum. 
         [0026]    “Radial Ply Tire” means a belted or circumferentially restricted pneumatic tire in which at least one layer of ply has the ply cords extend from bead to bead at cord angles between 65° and 90° with respect to the equatorial plane of the tire. 
         [0027]    “Shoulder” means the upper portion of sidewall just below the tread edge. 
         [0028]    “Sidewall” means that portion of a tire between the tread and the bead. 
         [0029]    “Tread” means a rubber component which when bonded to a tire carcass includes that portion of the tire that come into contact with the road when the tire is normally inflated and under normal load. 
         [0030]    “Tread Width” means the arc length of the tread surface in the axial direction, that is, in a plane parallel to the axis of rotation of the tire. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The invention will be described by way of example and with reference to the accompanying drawings in which: 
           [0032]      FIG. 1  is a front cross-sectional view of a tire building drum of the present invention shown having two shoulder sleeves mounted on the crown portion of the drum; 
           [0033]      FIG. 2  is a close-up cross-sectional view of the tire building drum of  FIG. 1  showing the drum in the radially expanded position; 
           [0034]      FIG. 3  is a close up cross-sectional view of a tire building drum in the expanded high crown condition shown with a prior art centersleeve; 
           [0035]      FIG. 4  is a close up cross-sectional view of the tire building drum in the expanded high crown condition shown with the shoulder sleeves of the present invention; 
           [0036]      FIG. 5  is a front view of the center section of the tire building drum in the axially contracted position; 
           [0037]      FIG. 6  is a front view of the center section of the tire building drum in the axially expanded position; 
           [0038]      FIG. 7  is a perspective view of the center section of the tire building drum shown in the axially contracted position; 
           [0039]      FIG. 8  is a perspective view of the center section of the tire building drum shown in the axially contracted position and radially expanded position; 
           [0040]      FIG. 9  is a perspective view of the center section in the axially expanded position of the tire building drum with the shoulder seals removed; 
           [0041]      FIG. 10  is a cross sectional view of half of the center section of the tire building drum; 
           [0042]      FIG. 11  is a top view of a single center section segment; 
           [0043]      FIG. 12  is a bottom view of the single center section segment of  FIG. 11 ; 
           [0044]      FIG. 13  is a side view of the single center section segment of  FIG. 11 ; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0045]    With reference to  FIGS. 1 through 2 , an exemplary tire building drum  5  of the present invention is illustrated. As shown more particularly in  FIG. 1 , the tire building drum  5  has a left hand side  7  and a right hand side  9  joined together by a center section  20 . The center section is further divided into a right hand side  22   b  and a left hand side  22   a,  which are both axially and radially movable, as described in more detail, below. Adjacent the center section  20  are first and second bead locking mechanisms  25   a,b,  which are also radially movable as shown in  FIG. 2 . Adjacent the bead locking mechanisms are first and second shoulder sections  29 . Both the bead locking mechanisms and the shoulder sections are axially movable. Thus, both the left hand side and the right hand side of the drum are axially movable. These components are described in more detail, below. 
       Center Section 
       [0046]    The center section  20  of the tire building drum as shown in  FIGS. 2-10  further comprises a plurality of center segments  22   a,b  located about the outer circumference of the drum. Each of the center segments may be further split into a left hand side  22   a  and a right hand side  22   b,  as shown in  FIGS. 4-12  (although not required). As shown in  FIG. 11 , the left hand side center segment  22   a  has one or more finger like projections  24   a,  with recesses  26   a.  The right hand side is the mirror opposite. As shown in  FIG. 10 , left hand center segment  22   a  has three finger-like projections  24   a  which are slidably received in three elongate slots  26   b  in an interdigitated or interlocked manner. Likewise, right hand center segment  22   b  has three finger like projections  24   b  which are slidably received in three opposed elongate slots  26   a.  The center segments  22   a,b  thus cooperate with each other to axially expand or contract as the fingers slide within the recesses. 
         [0047]    The center section  20  may also radially expand as shown in  FIG. 8 . The center section  20  can radially expand in the range of about 20 to about 50 mm. As each center segment  22   a,b  radially expands, the gap between the center segments increases. Provided within each center segment half  22   a,b  is a radially oriented piston chamber  28 . Received in each chamber  28  is an elbow-shaped linkage  30  connected to a common actuator (not shown), such as a piston  33 . A control system (not shown) actuates the pistons  33 , causing linkage  30  to slide from the retracted position (not shown) to the actuated position shown in  FIG. 3 . When the linkages  30  are actuated, the linkages push the center segments radially outward into the high crown position as shown in  FIG. 3 . 
       Shoulder Seals 
       [0048]      FIG. 3  illustrates a typical tire building drum having a center section that is completely covered by a cylindrically shaped center sleeve A. The center sleeve A is typically comprised of thick rubber. The tire building drum of the present invention does not have a center sleeve, nor a sleeve or any type of rubber component that extends from one end of the center section to the other end, nor a sleeve that is located in the center of the center section of the drum. The tire building drum of the present invention has eliminated the center sleeve, and includes a first and second shoulder seal  60   a,b.  The purpose of the shoulder seals is to maintain the pneumatic seal between the bead of the green tire and the tire building drum, enabling inflation and shaping of the green tire in the full stage tire building process. The first and second shoulder seal  60   a,b  are located on the axially outer ends of the segments  22   a,b  forming the center section. Each center seal preferably has an overall annular shape, having a first end  62   a,b  which is secured in seal clamps  70  located adjacent the center section segments. Preferably the first ends  62   a,b  of the seal have an outer bead projection  63  for mating reception with inner protrusion of the seal clamp. The shoulder seals each further comprise a second end  64   a,b  that is a free or unconstrained end. Thus the shoulder seals are not subject to axial tension which substantially reduced the life of the center sleeve. The free end  64   a,b  rests on the outer surface  23   a,b  ( FIG. 11 ) of the center segments  22   a,b,  and will slide relative to the center segments when the drum is radially expanded. The outer surface  23   a,b  has a smaller outer diameter than the center of the center section, forming a radial step so that when the shoulder seals are mounted, the shoulder seals form a flush surface with the center section of the drum. 
         [0049]    Each shoulder seal may be cast in a mold (not shown) in the desired shape or as shown in  FIG. 4 . Preferably each seal is cast or formed in a “L” shape as shown. The seal may be made from rubber, polyurethane, or other flexible material. 
         [0050]    The segments have been redesigned so that the innerliner is applied directly to the outer radial surface of the segments instead of the center sleeve. At least one finger of a segment (see  FIGS. 5-7 ) is equipped with one or more vacuum holes  99  to enable fixing the leading edge of the innerliner to the drum using vacuum. Preferably, a finger of each of a left segment and a right segment is equipped with vacuum holes. 
       Bead Lock Mechanism 
       [0051]    Adjacent the center section  20  are first and second annular bead locking mechanisms  25 . The bead lock mechanism are radially expandable into a bead clamp position in order to secure the bead during the tire building process.  FIG. 2  illustrates the bead locking mechanisms  25  in the retracted position. 
       Shoulder Section and Shoulder Clamp Lock 
       [0052]    The right and left hand shoulder section  29  of the tire building drum  5  is defined as the drum components located axially outward of the centerline of the center section, inclusive of the seal clamps and the bead lock mechanisms. The left and right hand shoulder sections of the tire building drum are axially slidable on bearing sleeves. The shoulder sections  29  are actuated by drive pins  125  mounted on nuts  130 , which ride along drive screw  121 . When the central screw is rotated, the nuts  130  move axially inward/outward, causing the drive pins  125  and each shoulder section to move axially inward/outward in corresponding fashion. In addition, the drive pins are also in mechanical cooperation with the split center segments, causing the split center segments  22   a,b  to axially extend or contract. 
         [0053]    When the center section  20  of the tire building drum  5  moves into the high crown position as shown in  FIG. 2 , the bead lock mechanisms  25  and the seal clamp mechanism  70  are further actuated axially inward so that seal clamp is received in recess  74 . The axial actuation of the bead lock mechanisms and seal clamps preferably occurs simultaneously with the movement of the center segments into the high crown position. 
       Drive Shaft 
       [0054]    A central drive shaft  120  is provided for rotational movement of the tire building drum  5  about its longitudinal axis. The central shaft  120  is connected to a drive means (not shown). Provided within the central drive shaft  120  is a central screw  121 . The central screw  121  is supported at each end by bearings  123 . The threads on one side of the central screw  121  are left handed and on the opposite side are right handed. On the left hand side is an inboard nut  125  connected to the one end of the threaded screw  121  and similarly on the opposite right hand side is an outboard ball nut  125  connected to the central screw  121 . 
       Turn Up Bladders 
       [0055]    An upper bladder  150  extends axially outward from the bead lock mechanism  25  to the respective ends of the tire building drum. The upper bladder  150  extends over a lower bladder  152 , which is mounted in the shoulder area of the drum and extends axially outward to the respective ends of the tire building drum. The upper and lower bladders function as turnup bladders which are used to inflate and, thereby, make the turn-up ends of the ply wrap about the apex and bead cores. 
         [0056]    While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.