Abstract:
A segmented annular mold for forming a tread belt having a reinforcing belt structure, the belt structure having a radial thickness (t) is disclosed. The mold has a plurality of radially movable and outwardly expandable inner segments for forming the inner surface of the tread belt and a plurality of radially movable and contracting outer segments for forming the outer tread belt surface. The radially inner and radially outer segments form a mold parting line at a location radially outward of a midpoint of the belt reinforcing structure of the tread belt at a location greater than 50% (t) as measured from the radially innermost surface of the belt reinforcing structure. The radially inner segments have upper and lower lateral edge forming portions extending outwardly to the parting line. Similarly, the radially outer mold segments have upper and lower lateral edge forming portions extending inwardly to the parting line. The parting line is located at least radially outwardly of a radially inner second belt layer of the belt reinforcing structure.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a mold for curing annular or ring treads, more preferably an annular tread belt assembly and further includes a unique method for molding said annular assemblies.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the making and curing of tire treads or tire tread and belt assemblies, it has been a common practice to wrap one or more layers of an uncured elastomer such as rubber, with or without reinforcements, such as metal cord reinforced plies or fabric and the like about a cylindrical core. The cylindrical core was selected to have a diameter equal to the desired inside diameter, the cylindrical core, with the elastomeric layers attached is generally placed in the center of a cylindrical core of a larger segmented cylinder, which larger segmented cylinder can include mold faces with desired tread patterns on the interior surface thereof, the diameter of the larger segmented cylinder is reduced until it properly contacts the material wrapped about the inner core apparatus and the entire apparatus is heated. The outer mold face segmented cylinder can, of course, be constantly heated but it is more difficult to heat the inner core about which the rubber is wrapped. As a result, premature curing might then take place. In U.S. Pat. No. 4,207,052 it was disclosed that this type of uneven curing of the elastomer deforms the cured tire tread or track belt assembly, in particular the metal cords within the tread belt can be displaced in such prior art molds due to the large temperature gradient between the inner core and the tread forming outer core. Accordingly, U.S. Pat. No. 4,207,052 showed a plurality of inner segments which fit together to form a generally cylindrical mold face surface to form the inner surface of the tread belt along with a means for retracting said plurality of inner segments toward the axis of said inner cylinder and a means for heating said segments. Additionally, the apparatus included a plurality of outer segments which fit together to form an inner generally cylindrical mold face surface of an outer cylinder, said outer cylinder being coaxial with said inner cylinder and of equal lengths therewith along with the means for retracting the plurality of outer segments away from the common axis of said cylinders and a means for heating said plurality of outer segments. The apparatus further included a pair of rings for sealing said inner cylinder to said outer cylinder at the ends thereof, at least one of said sealing rings being removable so that an uncured tire tread or track belt could be positionable between said plurality of inner segments and said plurality of outer segments wherein said plurality of inner segments was retracted toward said common axis and said plurality of outer segments is retracted away from said common axis.  
         [0003]     The advantage of the above-referenced prior art mold for producing a tire tread or track belt assembly was that a uniformity of heat and pressure could be achieved upon the molded assembly.  
         [0004]     In the prior art it was common for the radially retractable segments to have curved or arcuate shapes with vertically extending edges or sides. The outer segments could move inwardly and create an annular ring for forming the outer tread surface including the tread lugs. The inner segments would move sequentially radially outwardly in an alternating pattern wherein every other inner tread segment would be extended and then every other retracted inner tread segment could be then extended outwardly thereby forming a ring in the fully extended position thereby providing a mold that would cure the tread belt assembly over a period of time. This time was considered the mold cure cycle. Each radially outer segment and each radially inner segment had edges that were generally vertically extending and parallel to the common axis of both the inner and outer segments. Upon curing the tread the inner segments would then be retracted such that the inner surface of the molded tread could be separated from the first radially inward moving segments while the adjacent inner segments held in the closed position would retrain the tread belt assembly within the tread forming outer segments. Once the first radially inner segments had been moved inwardly, the second set of radially inner segments could be moved inwardly thereby releasing the entire inner surface of the tread. Thereafter the outer tread forming segments could be moved radially outwardly thereby releasing the tread belt assembly from the mold in its entirety. As the tread is removed from the outer segments a device would be used to lift the cured tread belt assembly from the mold.  
         [0005]     In this type of prior art tread belt assembly molding the radially inner tread forming surface had equal sized tread segments generally with vertical extending edges that extended generally parallel to the axis of the mold rings when in the closed position. Similarly, the outer segments also had vertically extending or generally parallel side faces such that when the mold closed these faces would abut forming a tight joint between the segments. In principle the above-referenced prior art mold as described in U.S. Pat. No. 4,207,052 works generally well for fairly large tread belt assemblies. However, the application of the forces when one closes the inner segments and outer segments of such a mold is such that all movement works in a radial direction increasing the amount of pressure on the radially inward segments substantially.  
         [0006]     It has been an objective of the present invention to provide a tread belt mold that would provide improved stability of both the inner and outer segments as the tread belt assemblies being cured such that a uniformity of curing pressure can be insured around the entire 360° circumference.  
         [0007]     A second objective of the present invention is to provide a way in which the radially outer mold segments can be provided with improved structural integrity wherein the parting line between the radially inner and radially outer adjacent segments located to minimize rubber flow in an area near the belt reinforcing structure.  
       SUMMARY OF THE INVENTION  
       [0008]     A segmented annular mold for forming a tread belt having a reinforcing belt structure, the belt structure having a radial thickness (t) is disclosed. The mold has a plurality of radially movable and outwardly expandable inner segments for forming the inner surface of the tread belt and a plurality of radially movable and contracting outer segments for forming the outer tread belt surface. The radially inner and radially outer segments form a mold parting line at a location radially outward of a midpoint of the belt reinforcing structure of the tread belt at a location greater than 50% (t) as measured from the radially innermost surface of the belt reinforcing structure.  
         [0009]     The radially inner segments have upper and lower lateral edge forming portions extending outwardly to the parting line. Similarly, the radially outer mold segments have upper and lower lateral edge forming portions extending inwardly to the parting line. The parting line is located at least radially outwardly of a radially inner second belt layer of the belt reinforcing structure.  
         [0010]     In a preferred embodiment, the tread belt has a radially inner 0° wire reinforced layer, two or more cross angled wire reinforced belt layers interposed between a 90° wire reinforced belt layer and the 0° wire layer; and the mold parting line is located radially between or above the radially outermost cross ply layer and the 90° wire reinforced layer.  
         [0011]     The segmented annular mold for forming a tread belt has a plurality of outer tread belt forming segments; a plurality of radially movable and outwardly expandable inner segments for forming the inner surface of the tread belt; and a slidable hub assembly, the slidable hub assembly having a central shaft. The hub assembly has an upper hub portion and a lower hub portion each slidably mounted onto the central shaft. Each upper and lower hub portions have a plurality of linkage arms pivotably connected to the respective hub and the radially inner segments. Each circumferentially adjacent segment is connected to either an upper or lower hub in an alternating pattern. The movement of one hub relative to the other is independently actuated by one or more means for moving the hub portions. The movement of the lower hub and upper hub into interlocking alignment moves the inner segments to form an annular ring.  
         [0012]     The segmented annular mold for forming a tread belt has a plurality of split “J” frames, one split “J” frame for supporting each outer tread belt forming segment. A base plate support is attached to each split J frame. A pair of linear bearing rails is attached to the base plates and a plurality of and bearing blocks are mounted onto the linear bearing guide rails. The bearing blocks are attached to the inner and outer segments and the pair of linear bearing rails provides linear guides for the segments.  
         [0013]     A cooling plate is attached to the respective segment and interposed between each segment and the linear bearing blocks. The cooling plate has a plurality of passages for passing a coolant medium.  
       DEFINITIONS  
       [0014]     “Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.  
         [0015]     “Cord” means one of the reinforcement strands of which the plies in the track are comprised.  
         [0016]     “Equatorial plane (EP)” means the plane perpendicular to the track&#39;s axis of rotation and passing through the center of its tread.  
         [0017]     “Footprint” means the contact patch or area of contact of the tread with a flat surface under load and pressure.  
         [0018]     “Lateral” and “laterally” means lines or directions that are parallel to the axis of rotation of the tire (also “axial”).  
         [0019]     “Ply,” means a continuous layer of rubber-coated parallel cords.  
         [0020]     “Radial” and “radially” means directions extending radially toward or away from the axis of rotation of the track.  
         [0021]     “Zero-degree wires” means at least one layer of parallel cords &amp;usually metal wire), underlying the tread, unanchored to the bead, spiraling circumferentially around the tread, and having cord angles in the range from 0 degrees to 5 degrees with respect to the equatorial plane of the tire. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The invention will be better understood by reference to the drawings when like numbers denote like parts throughout and wherein:  
         [0023]      FIG. 1  illustrates a plan view of a mold according to the present invention and tread belt assembly shown in a cross-sectional view and shows the tread belt being supported on a transfer means while the mold is in a full open position;  
         [0024]      FIG. 2  is a cross-sectional view of the mold according to the present invention and the tread belt assembly being cured in a fully closed position;  
         [0025]      FIG. 3  is a top view of the mold according to the present invention showing the tread belt being supported by the transfer means and with the plurality of the radially inner segments in a retracted and open position;  
         [0026]      FIG. 4  is a second top view showing the tread belt while still being supported by the transfer means and a plurality of the inner segments and a partially closed plurality of outer segments;  
         [0027]      FIG. 5  is a perspective view of the inner actuating sliding hub assembly showing the upper hub portion and lower hub portion in a separated fully open position;  
         [0028]      FIG. 6  is a perspective view of the inner actuating sliding hub assembly showing the upper and lower hub portion interlocked in the fully closed position wherein the inner segments would be radially moved outwardly by the action of the hub portions to form an annular ring.  
         [0029]      FIG. 7  is a partial end view of the mold taken from  FIG. 2  showing the linear bearing mechanism.  
         [0030]      FIG. 8  is an enlarged view of the lower portion of a mold segment taken form  FIG. 2 .  
         [0031]      FIG. 9  is an enlarged view of the mold segments taken from  FIG. 2 .  
         [0032]      FIG. 10  is a perspective view of a split J frame of the mold frame.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     With reference to  FIG. 1 , a plan view of a mold  2 , according to the present invention, and a tread belt assembly  4  is shown in a cross-sectional view. The right half shows the tread belt  4  being supported on a transfer means  50  while the mold  2  is in a full open position. The left half of the mold  2  shows the tread belt  4  held by the transfer means  50  and the radially retracted open position that is less open than the right half. As illustrated, the transfer means  50  has a plurality of legs  52  with tread supporting feet  54  that support the entire weight of the tread belt  4  during a transfer of the tread belt  4  to the mold  2 . These tread belts  4  can weigh in excess of 4,000 pounds, some many more times that. The transfer means  50  supports the weight such that the tread belt  4  can be positioned into an annular space between a plurality of inner mold segments  12  consisting of alternating segments  12 A,  12 B and a plurality of outer mold segments  14  consisting of alternating segments  14 A,  14 B. As better shown in  FIG. 9 , the inner mold segments  12  form the inner surface  3  of the tread belt assembly  4 . Each inner segment  12  has radially extending outer portions  16 , 18  at both the top and the bottom, respectively, and the tread belt  4  can be positioned such that it is supported by these radially outward extending portions  16 , 18 .  
         [0034]     As shown in  FIG. 3 a  top view of the mold  2  is shown and the plurality of legs  52  supporting the tread belt  4  are illustrated wherein alternating inner segments  12 A of the mold  2  are retracted but in close proximity to the tread belt assembly  4 . When these inner segments  12 A are moved in contact with the tread belt assembly  4 , the legs  52  are shown interposed between two of such contacting inner segments  12 A. Accordingly, where the inner segments  12 B are still shown in a retracted position not contacting the tread belt, the legs  52  are positioned fully supporting the tread belt assembly  4 .  
         [0035]     With reference to  FIG. 4 , the plurality of radially outer segments  14 A is moved into a contacting position with the tread belt assembly  4 . These outer segments  14 A are aligned with a contacting inner segment  12 A. This provides a means for supporting the tread belt  4  at which point the transfer means  50  can be moved away from the tread belt  4  and the tread belt  4  can be supported by these alternating patterns of contacting inner and outer segments  12 A,  14 A. To remove the transfer means  50  (portions of which have been removed for clarity), the legs  52  are radially expanded outwardly and can be lifted vertically between the space between the tread belt  4  and the outer segments  14 B. Once this is accomplished, the inner segments  12 B that were in the retracted position can also be moved radially outward into a full contacting position with the tread belt  4 . Once that is accomplished, the remaining outer segments  14 B can be moved into a partial contact position aligned with the outer segments  14 A at which point the outer segments  14 A and  14 B can be moved inwardly into a fully closed position and the tread belt  4  can be cured in the mold  2 . This is as illustrated in  FIG. 2 .  
         [0036]     An important aspect of the present invention is that after the outer segments  14 A partially close against the tread belt assembly  4  in an alternating fashion the remaining outer segments  14 B also come to a partially closed position once the legs  52  are removed. Once the outer segments  14 A and  14 BB are in this partially closed position while the inner segments  12 A,  12 B are in full contact position then it is possible to do a final close of the mold  2  at which point all the mold outer segments  14 A and  14 B come into a closed position as illustrated in  FIG. 2 . Once this is accomplished, the tread belt  4  is completely encapsulated within the mold  2 . The movement of the mold mechanisms is controlled by several devices which will be discussed in greater detail later. What is of interest is that this tread belt  4  is extremely large and has a very sophisticated tread belt reinforcing structure. It is important that the tread belt assembly  4  be positioned within a mold and cured without distorting the tread belt&#39;s reinforcing structure  5 . A further important aspect and concern of the present invention is that because the inner segments  12  and the outer segments  14  are rigid the volume that is available to form the tread belt assembly  4  between each segment  12 , 14  is generally fixed. However, due to the fact that rubber grows at approximately 2% while the component is being cured one of the sets of segments  12  or  14  has to be able to expand radially outwardly or inwardly to permit the tread belt  4  to grow as it is being cured. The alternative to growing the tread belt as the mold moves is to provide a tread belt  4  as slightly undersized within the mold cavity  13  and allow the tread belt  4  to expand to fill the cavity  13 . This, unfortunately, has the drawback of creating opportunities for the rubber to flow in a rather uncontrolled manner causing defect features such as are commonly referred to as “lights”. Far superior to providing undersized tread belts  4  it is more preferable to provide the tread belt at a proper size that will fit the cavity  13  between the inner and outer segments  12 , 14  and allow either the inner or outer segments  12 , 14  to be pushed by the tread belt assembly. Preferably not both of the segment sets  12 , 14  should be pushed or moved in the process. In the present invention it was determined that due to the critical nature of the tread belt reinforcing structure  5  it is preferable that movement of the outer segments  14  be allowed while the inner segments  12  be maintained at a relatively constant dimension. This is true because movement in the tread area  9  only affects the tread rubber compound but not the metal cords and wires of the belt structure  4  which need to be in a non-disturbed orientation during curing. This is best achieved by allowing the outer segment  14  to expand slightly due to thermal growth of the rubber.  
         [0037]     To achieve the optimal size of the tread belt  4  it is important that the tread belt assembly  4  as it is being formed is provided to a size or volume that is controlled by either weight or specific gravity, preferably the specific gravity of the rubber as it is being applied to the tread belt  4  is known and the precise amount of rubber is then applied. Accordingly, the volume of the tread belt  4  at any location is generally known and matches the cavity  13  of the mold  2  sufficiently that movement of rubber is minimized.  
         [0038]     As noted, the outer segments  14  are all partially in contact with the tread rubber just prior to closing and then are driven into a full contact closed position in the mold  2  curing cycle such that the movement of the tread forming ribs on the outer segments  14  is occurred rather uniformly such that the rubber as it is being pushed is pushed uniformly around the 360° circumference of the tread belt  4 .  
         [0039]     As shown in  FIGS. 1 and 2 , the movement of the outer segments is controlled by a large cylinder connected by pins  17  to the outer segments  14  and attached to what is called a split J frame. The split J frame  10  as shown in  FIG. 10  provides support for the outer segment  14  and also for an attachment to a frame structure  20  that supports the inner segments  12 . The split J frame  10  is a casting that provides a flat base and curves upwardly to a pair of slots  11 . These slots  11  provide an axle support  7  for the cylinder  6  as shown in  FIG. 1 . Between the split J a reinforcement brace  15  is positioned to provide added structural integrity. In the illustrated embodiment as shown in  FIG. 4  there are approximately twelve inner and outer segments  12 , 14 . Each outer segment  14  rests on a split J frame  10  supporting the outer segment. Each split J frame is  10  is securely attached to the floor and is exposed to approximately 1.8 million pounds force during curing. As shown, the J frames are also cantilevered off the frame  20  and under load can deflect about 0.12 inches (3 mm) or less which is easily accommodated by the pivoting axle support  7  and pin  17  connecting the cylinders  6  to the J frame and the outer segments  14 . The entire mold sees approximately 22 million pounds force around the entire periphery. The outward cylinders  6  are quite massive and are approximately 16 inches in diameter and have a stroke of approximately 20 inches.  
         [0040]     Due to the fact that the during curing outer segments  14  are allowed to move to accommodate the thermal expansion of the rubber and the tremendous forces that are exerted, it was desirable that the inner segments  12  be provided so that a tremendous mechanical advantage can be achieved to prevent the inner segments  12  from moving radially inwardly. This has the advantage of ensuring that the diameter of the molded tread belt  4  will be precise in every manufacture and that the tolerance changes will only result in very minor or subtle variations. With reference to  FIGS. 1 and 2  the inner segments  12  are supported on a frame  20  and the driving mechanism includes an actuating slidable hub assembly  30  that provides radial movement for the inner segments  12  and is co-axially mounted slidably onto a central post or shaft  60 . This slidable hub assembly mounted onto the central post or shaft  60  is best illustrated in  FIGS. 5 and 6 . The slidable hub assembly  30  has an upper portion  32 B and a lower portion  32 A as illustrated. Each upper portion  32 B and each lower portion  32 A has casting locations  33  with a hole  34  for attaching a mechanical link  8 . These mechanical links  8  are shown in  FIGS. 1 and 2  and one link  8  is connected by pins  17  to each radially inner segment  12 A,  12 B. The upper hub portion  32 B has attached to it through the pivotable links  8  all the inner segments  12 B in alternating sequence and interspaced between each inner segment  12 B and an upper hub portion  32 B of the hub assembly  30  are the links  8 . This enables the upper hub portion  32 B and lower hub portion  32 A of the hub assembly  30  to move independently and to drive the inner segments  12 A,  12 B in an alternating pattern around the circumference independent of either the connected upper portion segments or the connected lower portion segments. This means  36  for providing radial movement of the inner segments  12 A,  12 B includes not only the hub assembly  30  but also cylinders  31 , 35  as clearly illustrated in  FIG. 2 . One cylinder  31  moves the lower hub  32 A into a lower position such that the linkage mechanism or links  8  are shown almost horizontal. The upper portion of the hub  32 B is driven by the second cylinder  35  which also moves the hub  32 B downward until the linkage mechanism or links  8  connected to that segment  12 B are also shown in an almost horizontal position. Once this is achieved the upper and lower portions  32 A,  32 B of the hub assembly  30  are intertwined as shown in  FIG. 6 . This creates an interlocking of the central hub assembly  30  providing superior strength and also providing a way of achieving an almost horizontal mechanical locking of the inner segments  12 A,  12 B. Once this is achieved, a tremendous mechanical advantage has occurred such that the forces trying to push the inner segment  12 A,  12 B inwardly are resisted by a complete mechanically stiffened structure. The linkages  8  between each segment  12 A,  12 B as illustrated are approximately six inches in diameter to handle the massive loads and to prevent buckling of the components.  
         [0041]     As shown in  FIG. 2  the hub assembly  30  when moved to the mold close position has the holes  34  virtually aligned in both the upper hub portion  32 B and the lower hub portion  32 A with the centerline of the tread belt  4  as defined as the distance halfway between the lateral edge of the tread belt between the mold portions  16 ,  18 . As further noted the linkages  8  are pinned at locations  34  of the hub assembly  30  and at the inner segments  12 A and  12 B at the vertical centerline of the formed tread belt. This ensures that the linkages all line in the same horizontal plane minimizing any off-center loading due to the curing pressure.  
         [0042]     Assuming one designs a hub assembly  30  using vertical pairs of linkages  8  in place of a single linkage  8 , then it would be desirable that the midpoint of the pairs be on the vertical centerline and that the upper and lower attachment locations of one hub portion could be aligned with the corresponding attachment locations of the other hub portions although this would not be critical as long as the midpoints of the pairs of linkages align with the vertical centerline of the tread.  
         [0043]     The inner and outer segments  12 ,  14  are mounted onto a support plate  22  and the support plate  22  has a pair of linear bearings  40  as illustrated in  FIG. 7  that extend inwardly towards the central shaft  60 . These linear bearings  40  provide movement about the inner and outer segments  12 , 14 . The pair of linear bearing rails  41  as shown in  FIG. 7  have linear bearing blocks  42  attached to the inner and outer segments  12 .  14 , respectively. Each inner segment  12  and each outer segment  14  has four bearing blocks  42  as illustrated, two bearing blocks  42  being slidably attached to each linear bearing rail  41 .  
         [0044]     With reference to  FIG. 8 , a cooling line  70  is shown. The cooling line  70  passes of fluid medium  72  into channeled cooling plate  19 , to which inner and outer segments  12 ,  14  are attached. This cooling medium  72  keeps the cooling plate  19  at approximately ambient or room temperature such that the linear bearing blocks attached to the cooling plate  19  remain at a low temperature while the inner and outer segments  12 ,  14  are heated to provide the curing temperature. It was found that on such a large mold  2  having a diameter of approximately ten feet or greater, that the movement of the linear bearings  40  and the thermal contraction and expansion of the frame  20  had to be controlled such that the frame  20  is generally always at room temperature and not growing substantially with a thermal gradient which would provide an uncontrolled internal diameter based on the growth of the mold  2  and its associated frame  20  over a period of time as the temperature gradient increased. By maintaining the frame  20  at approximately room temperature the dimensional control of the finished product is greatly improved. In addition, the cooling of the plate  19  between the inner segments  12  and the bearing blocks  42  and the outer segments  14  and the bearing blocks  42  greatly enhances the life of the linear bearings  40 .  
         [0045]     With reference to  FIG. 9  an enlarged view of the tread belt  4  in the closed position is illustrated. As shown, the inner segment  12  has fluid medium passages  74  to provide heated fluid  76 , either water or steam or any other suitable heating medium, to provide a curing temperature. Similarly, the outside segments  14  also have a fluid medium  76  and passages  74  providing heat to the outer segment  14 . An important feature illustrated is that the parting line  80  for the two mold segments  12 , 14 , that is, the place where the two mold segments  12 , 14  meet, is approximately at the radially outer location of the belt layers  5 A,  5 B,  5 C,  5 D, preferably between the two radially outermost belt layers  5 C,  5 D. As illustrated, the parting line  80  is shown in a closed position. The closure of the parting lines  80  very precisely was achieved in the present invention by providing shims  8 A as shown in  FIG. 1  in the mechanical links  8 . The shims  8 A were machined precisely to the closed position at temperature for mold curing. This ensures that the parting line  80  starts in a fully closed abutting position or approximately fully closed depending on the size of the tread belt assembly. As the tread belt  4  is being cured and the rubber expands, the parting line  80  is allowed to gap or open. It was determined that providing a parting line  80  towards the radially outer portion of the tread belt  4  enables the tread belt  4  to be performed very uniformly. Furthermore, by providing the parting line  80  very close to the tread area  9  permits the tread area to flow in and fill the parting line  80  gap as the tread rubber and belt rubber expand. This is quite beneficial and it ensures that very little movement of the rubber near the tread belt  5  area can occur. The tread belt  5  has belt layers such that the radially inner belt layer  5 A is approximately very close to the lateral edge of the tread belt assembly  4 . This being so, if the inner segments  12  have the parting line  80  as shown near the radially inner belt it is possible for the rubber to flow at that area. When that occurs, the tread belt structure  5  distorts the lateral ends creating a weakened position. If the parting line  80  is moved outwardly as illustrated, the tread belt assembly has very little rubber flow movement in the area near the belt structure  5 . As illustrated, the parting line  80  is actually achieved by an upper and lower plate  81 ,  82  that has been bolted with fasteners  90  to the inner segment  12 . This effectively moves the parting line  80  outwardly towards the outer segment  14  and closer to the tread rubber  9 .  
         [0046]     As further illustrated, the tread belt assembly  4  has a radially outer tread area  9  and a radially inner surface  3  having a plurality of ribs  3 A and grooves  38 . The radially inner surface  3  provides an interface between a carcass or casing assembly to which the tread belt  4  is to be later mounted for use. Above the inner surface  3  is the entire tread belt reinforcing structure  5 . As illustrated, the tread belt reinforcing structure includes a first belt layer  5 A including zero degree wires circumferentially wound about the tread belt assembly  4  and interposed between the circumferential wire layers  5 A and a radially outermost belt layer  90  are two cross plies  5 B,  5 C, each cross ply  5 B,  5 C having lateral edges being moved axially inwardly from the circumferential belt wire  5 A lateral edges such that each radially outer belt layer  5 B,  5 C,  5 D, respectively, is slightly narrower than the radially inner adjacent layer. Outward of the two cross ply layers  5 B,  5 C as illustrated is a 90° wire layer  50  which provides tremendous axial strength. The parting line  80  is positioned very close to this 90° wire layer  50 . As can be appreciated as the parting line  80  is in alignment with a 90° layer  50  growth in the lateral extent is resisted by the 90° wires. This provides substantial strength and helps prevent buckling or other non-uniformities to occur in the lower layers  5 A,  5 B and  5 C. A further benefit is that as the parting line  80  is closer to the narrowest belt  50 , far less movement of the rubber compound around the belt structure  5  can occur and the primary movement will be from the tread rubber  9  which is of no consequence. While these features may seem subtle, they are extremely important in manufacturing a quality tread belt structure  4 . For example, a typical large off-road pneumatic radial tire has the largest or widest belt layer 3.65 inches from the tread&#39;s lateral edge. A similarly sized two-piece tread belt has the widest belt layer 1.25 inches or approximately 300% closer to the lateral edge of the mold. Accordingly, the sensitivity to belt distortion at the lateral edges of the tread belt  4  is significantly increased. Avoidance of undesirable flows of rubber are mandated because the resultant distortion of the belt layers  5 A through  5 D can adversely affect the durability of the tread belt  4 .