Abstract:
A method and apparatus for curing large radial pneumatic tires using a plurality of like molds each having top and bottom mold sections provided with radially movable groove-defining tread segments which are automatically extended into a tire to be cured when the molds are positioned within an autoclave and which are automatically retracted when the molds are withdrawn from the autoclave to free the cured tire from its respective mold.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to molds required to cure large radial pneumatic tires.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is well known that conventional radial tires run cooler and therefore provide longer service hours than conventional bias-ply tires. The superiority of a conventional radial tire, as compared to a bias-ply tire, results from the provision in a radial tire of substantially inextensible cables arranged in generally radial planes of the tire from one bead to the other bead, with a circumferential belt package of low angle cords (e.g., 5-7 degrees relative to a radial plane of the tire) being secured radially outwardly of such cables. The provision of the cables and the belt package restrains circumferential expansion of a radial tire, and accordingly, the belt package cords do not scissor relative to one another. The radial tire therefore operates at a lower temperature. The conventional bias-ply tire does not utilize a circumferential belt package and instead employs a plurality of cris-crossed plies which extend at relatively large angles relative to a radial plane of the tire. This construction subjects the tire to a heat build-up generated by the tendency of the plies to undergo scissoring relative to one another, and it is well known that excess heat tends to cause delamination and rapid tread wear resulting in a reduced service life.  
           [0003]    Tire molds for curing complete tires are generally of two types: full circle molds and segmental molds. In the case of segmented molds, heated exterior components of the mold are moved into contact position with the tread and sidewall portions of the uncured tire and cure the tire from the outside, while a bladder is inflated to contact the inner surface of the tire to help shape the tire, and heating fluids are injected into the inside of the bladder to cure the tire from the inside. An example of a full circle clamshell mold is shown in U.S. Pat. No. 4,957,676 to Greenwood. Full circle clamshell molds are proven, reliable, and lower in cost than segmental molds to manufacture. Another benefit of conventional clamshell molds is that a significant portion of the mold, typically the bottom half, may remain stationary as only the top half needs to be raised and lowered with respect thereto by a molding press, along an axis of rotation of the tire, to open and close the mold. However, clamshell molds are not appropriate for molding radial tires because a radial tire will not expand or contract in diameter and the inner molding surface of the clamshell mold cannot move radially outwardly to receive an uncured tire and radially inwardly to close around a tire casing.  
           [0004]    Another type of mold for curing tires is the segmental mold, examples of which are shown in U.S. Pat. No. 5,676,980, to Gulka et al. U.S. Pat. No. 3,787,155 to Zangl, and U.S. Pat. No. 3,806,288 to Materick. Unlike clamshell molds, which are split about the centerline of the tread pattern, segmental molds are radially segmented into a plurality of arcuate tread segments about the circumference of the mold. Each of the segments is attached to a top section of a mold container so that when the top section is lowered and raised by a press in which the container is installed, the mold section correspondingly moves up and down along the axis of tire rotation. In this direction, movement of the top mold section corresponds generally to that of the top portion of a clamshell mold. The fact that a radial tire is not radially expandable or contractible creates serious manufacturing problems when attempting to mold an uncured radial tire in a conventional segmental mold. Segmented molds such as shown in Gulka 5,676,980, are indicated as being openable to the full outside diameter of a radial tire, but present a serious problem to curing a satisfactory large diameter radial tire (e.g., about 50 inches in diameter), particularly a heavy tire for use on large off-the road vehicles, i.e., unless the mold is used in conjunction with a molding press that maintains the uncured tire in a centered position as the mold closes, when the mold is opened to receive a heavy uncured tire there exists a vertical and horizontal gap between the radially outer edge of the lower mold sections&#39; sidewall plate and the radially inner edge of the lower tread segments. Accordingly, as the uncured tire is lowered into the cavity of the lower mold section, the heavy weight of the tire causes the cords of the belt package tire to flex which in turn causes the tire&#39;s belt package to be deformed relative to the uncured rubber in which the cords are encased as they encounter the aforementioned gap. Because of such deformation, discontinuities between the belt package cords and the uncured rubber are created, precluding the formation of an integral bond between the cords and the rubber when the tire is cured. As a result, there is a likelihood that delamination of the belt package cords relative to the tire body will occur seriously reducing the service life of the tire. The deformation can be even severe enough to render the cured tire unusable.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides an improved method and apparatus for curing a radial tire within a segmental mold in a conventional autoclave without deforming the cords of the belt package relative to the uncured ruber of the tire. The segmental mold of the present invention includes a top mold section and a bottom mold section. The top mold section is movable with respect to the bottom mold section between a raised open position and a lower closed position. The top and bottom mold sections each contain a plurality of like tread segments arranged in a circular pattern. Each segment is slidably coupled to its mold section by a slanted alignment pin, and two compression springs are positioned on either side of the alignment pin to bias the treads segments outwardly with respect to their respective mold sections. Each of the tread sections is formed with radially inwardly extending tread groove-defining lugs. The bottom mold section is so configured that when the top mold section is in its open raised position, the tread segments of the bottom mold section are arranged radially outwardly of the outer diameter of the uncured tire to be molded. When the top mold section is moved to its closed lower position, the tread segments of both the top and bottom mold sections are automatically moved radially inwardly so that the tread-defining lugs of the segments engage the uncured crown of the tire during curing of the tire. When the tire has been cured, the top mold section is raised and the upper and lower tread segments automatically move outwardly away from the cured tire so such tire can be freely withdrawn from the bottom mold section without the tread segments tearing the tire.  
           [0006]    It is a particular feature of the present invention that an uncured tire can be cured in a mold without any deformation taking place between the cords of the bead package and the uncured rubber of the tire thereby precluding the formation of discontinuities between the cords and the uncured rubber surrounding such cords. This feature is accomplished by extending the lower sidewall of the bottom mold section substantially the entire distance from the tire bead area to the tread portion of the uncured tire. With this arrangement, the complete sidewall of the uncured tire is supported by the lower sidewall of the bottom mold section and the latter provides a firm platform for the uncured tire without causing a deformation of the belt package of such tire. Additionally, the radially outer portion of the lower sidewall of the bottom mold section is formed with auxiliary lugs that define the lower outer sidewall portion of the treads of a cured tire. The lugs of the tread segments and the lower mold sidewall auxiliary lugs cooperate to form a complete lower tread pattern of a cured tire. The lugs of the upper mold section tread segments and the upper mold sidewall cooperate to form the upper tread pattern of a cured tire.  
           [0007]    It is another feature of the present invention that a plurality of the aforementioned molds each containing an uncured tire may be arranged in a conventional autoclave for concurrent curing of the tires. After the tires have been cured the molds are removed from the autoclave and the cured tires withdrawn from their respective molds.  
           [0008]    Yet another feature of the present invention is that a single size mold may be utilized to cure tires of varying width.  
           [0009]    Further advantages afforded by the method and apparatus of the present invention will become apparent from the following detailed description, when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a perspective view of a tire mold embodying the present invention showing the top mold section thereof in a raised open position with respect to the bottom mold section of such apparatus;  
         [0011]    [0011]FIG. 1 a  is a broken side elevation view showing tread segments supported by the top and bottom mold sections.  
         [0012]    [0012]FIG. 2 is a vertical sectional view taken in enlarged scale along line  2 - 2  of FIG. 1 when a tire to be cured is being lowered into the confines of the bottom mold section;  
         [0013]    [0013]FIG. 3 is a view similar to FIG. 2, showing the uncured tire disposed in the bottom mold section;  
         [0014]    [0014]FIG. 4 is a view similar to FIGS. 2 and 3 showing the top mold section being lowered towards its closed position above the bottom mold section;  
         [0015]    [0015]FIG. 5 shows the top mold section in a further lowered position with respect to FIG. 4;  
         [0016]    [0016]FIG. 6 shows the top mold section in a still further lowered position with respect to the bottom mold section with the mold sections ready to be positioned within an autoclave to cure the tire;  
         [0017]    [0017]FIG. 7 is a side elevational view showing an autoclave utilized to cure a tire disposed within the mold of FIGS.  1 - 6 , with one of such molds being lowered into the autoclave.  
         [0018]    [0018]FIG. 8 is a view similar to FIG. 7 showing a plurality of the aforedescribed molds as the tires contained within such molds are being cured.  
         [0019]    [0019]FIG. 9 is a vertical sectional view of two of the molds as a tire is being cured in the autoclave;  
         [0020]    [0020]FIG. 10 shows a top mold section being removed from a bottom mold section after the mold has been removed from the autoclave and the tire has been cured;  
         [0021]    [0021]FIGS. 11 and 12 show the top mold section removed and the cured tire being lifted out of the lower mold section while the tread segments are opened radially;  
         [0022]    [0022]FIG. 13 is a perspective view showing a cured tire made in accordance with the present invention;  
         [0023]    [0023]FIG. 14 is a sectional view taken in enlarged scale along line  14 - 14  of FIG. 13;  
         [0024]    [0024]FIG. 15 is a vertical sectional view of a second embodiment of a mold embodying the present invention which may be utilized to cure tires of differing widths; and  
         [0025]    [0025]FIG. 16 is an enlarged view of the encircled area designated  16  in FIG. 15.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]    Referring to FIG. 1, there is shown a perspective view of a preferred form of tire mold M embodying the present invention for use in curing a radial tire R shown in FIGS. 13 and 14. The entire molding apparatus is generally toroidal in shape, corresponding to the shape of the tire R to be cured therein, and includes a bottom mold section B and a top mold section T. As shown in FIGS. 2 and 3, the bottom mold section B includes a horizontally extending base plate  20  integrally formed with an outwardly and upwardly extending peripheral bowl  22 . The bowl  22  encompasses a plurality of bottom tread segments BS of like configuration. Each bottom tread segment is supported by an upwardly and outwardly extending guide rod  24  which is anchored to the base plate  20 , as indicated at  26 . Guide rods  24  are slidably received in complementary passages  27  in their respective tread segment. A pair of coil compression springs  30  and  31  are disposed on either side of each guide rod, with the upper portion of such coil spring being supported within a cylindrical cavity  33  that is coaxial with its respective spring by a support pin  35 . The lower end of each rod is anchored to the mold base plate  20 . The radially inner surface of each bottom tread segment is formed with a radially inwardly extending male lug  36  which is adapted to mold the generally horizontally extending portion of the groove  38  defining the left side of the tread pattern of a cured tire R shown in FIGS. 13 and 14.  
         [0027]    Referring now to FIG. 4, the top mold section T includes a top plate  39  formed with an integral downwardly and outwardly extending peripheral bowl  40 . Bowl  40  supports a plurality of upper tread segments US similar to but mirror images of the bottom tread segments BS. Each upper tread segment is supported for vertical and horizontal movement by a downwardly and outwardly extending guide pin  41 , having its upper end anchored to the top plate  39 , as indicated at  42 . A pair of coil compression springs  43  and  44  are disposed on either side of guide pins  41 , with the lower portion of each of such springs being supported within a cylindrical cavity  45 , by a rod  50 . The lower end of each is secured to the top plate  39 . The radially inner facing surface of each upper tread segment US is formed with a radially inwardly extending male lug  51  which is adapted to mold the horizontally extending portion of the groove  53  defining the right side of the tread pattern of cured tire R. The upper and lower mold sections are guided for vertical reciprocal movement by means of a plurality of vertically extending guide bars  54 . The upper end of each guide bar is rigidly secured to the bowl  40  of the top plate  39 , with the lower end of each guide bar being slidably disposed within a vertically extending bore  55  formed in a peripheral flange  56   a  of the bottom mold section bowl  22 . The top and bottom tread segments US and BS are arcuate and collectively form a circular pattern corresponding to the shape of the tire to be cured when positioned abutting one another. The upwardly-facing side wall surfaces  56  of plate  20  and the downwardly-facing side wall surfaces  62  of top plate  39  form the upper and lower side walls  63  and  64  of the tire to be cured when the top mold is closed on the bottom mold section. Preferably, the mold top and bottom sections are constructed of steel and the top and bottom tread segments are constructed of aluminum.  
         [0028]    Referring to FIGS.  1 - 6 , it is important to note that base plate  20  is formed at its outer portion with a plurality of auxiliary lugs  66  that define a downward extension of lugs  36  of each bottom tread segment BS. Similarly, the top plate  39  is formed at its outer portion with a plurality of auxiliary lugs  68  that define an upward extension of lugs  51  of the upper tread segments US. The purpose of such auxiliary lugs is set forth hereinafter.  
         [0029]    As indicated in FIG. 2, a tire UR to be cured is supported during the curing process by an annular tire carrier C having complimentary upper and lower bead rings  66  and  67  formed with opposed mirror-image surfaces  70  and  71  that conform to the shape of the bead and inner sidewall portions of a tire to be cured. A conventional inflatable curing bladder BL is sealingly clamped between the bead rings and a vertically extending sleeve  74  that connects the bead rings  66  and  67 . Sleeve  74  is provided with a fluid inlet and outlet fitting  68  in a conventional manner.  
         [0030]    In the operation of the aforedescribed apparatus, referring first to FIG. 2, with the top mold section T removed, a conventional hoist (not shown) lowers the uncured tire body UR into the bottom mold section B by a disengageable connector  76 . The uncured tire body is maintained partially inflated at a pressure of about 3 to 6 pounds during the loading process in a conventional manner as by water or air forced into bladder B through fitting  68 . At this time, the bottom tread segments BS will be maintained in their uppermost position by springs  31 . In this position of the bottom tread segments, the lugs  36  thereof are spaced radially outwardly of the extreme periphery of the uncured tire. Referring now to FIG. 3, the uncured tire body UR is shown resting upon sidewall surfaces  56  of the base plate  20 , with the tire lifter  76  removed. In FIG. 4, the top mold section T is shown spaced above the bottom mold section BL, and being lowered towards such bottom section as by a three-leg lifting arm  77  supported by a hoist hook  78 . The ends of the bar  77  are each connected to a cable  81 , the lower ends of which are releasably attachable to lifting lugs  82  (FIG. 1) formed on the top mold section. Referring to FIG. 5, as the top mold section continues its downward movement the flat lower end  83  of each of the upper tread segments US will engage the flat upper end  84  of each of the bottom tread segments BS. Such engagement causes the top and bottom tread segments to be cammed radially inwardly by the slanted camming surfaces  85  and  86  formed on the bowls  22  and  40  of the top and bottom mold sections. Such radially inward movement of the tread segments forces the lugs  36  and  51  partially into the uncured rubber of the tread portion  58  of the uncured tire. It should be understood that the pliable uncured rubber permits the lugs  36  and  51  to move the uncured casing inwardly while partially forming grooves in the uncured rubber. In FIG. 6, the top mold section T has been further lowered into the confines of the bottom mold section B. It will be noted that the tread segment lugs  36  and  51  have been urged deeper into the uncured rubber of the tread pattern. At this time the complete mold M comprising the top and bottom mold sections will be transferred to the autoclave A shown in FIGS. 7 and 8.  
         [0031]    Referring now to FIG. 7, there is shown a conventional autoclave A having a heater shell  90  provided with a removable dome  92 . Steam for curing tires in the heater shell is provided by piping  94 . A vertically movable fluid-actuated ram  95  arranged within the heater shell is provided at its upper end with a mold support platform  96 . A pressurized liquid such as water for operating the ram is provided by piping  97 . In FIG. 7, the ram  95  is disposed in its uppermost position to receive one of the aforedescribed complete molds, designated M- 1 . Mold M- 1  is placed upon mold support platform  96  by a three-leg lifting bar  77  such as described hereinbefore, with the three cables  81  having their lower ends releasably attached to lifting lugs  98  formed on bottom mold section B (FIG. 1). Lifting bar  77  is connected to a crane hook  99 .  
         [0032]    Referring now to FIG. 8, a plurality, such as two additional molds M- 2  and M- 3 , have been positioned upon mold M- 1  after ram  95  has been lowered within heater shell  90 . Piping  100  from a hot water source has been connected to the interior of the bladder B of each mold. Dome  92  is then closed and steam at about 125 psi is admitted to the heater shell to heat the molds which effect curing of the uncured tires. Concurrently, hot water at about 350 psi is forced into the bladders to urge the uncured tires firmly against the confines of the mold sections&#39; cavities and also to cure the tires from inside out. Nitrogen can be utilized to increase the pressure within the bladders to about 450 psi. After the tires have been cured (usually about 11 hours), the steam pressure in the heater shell and the water pressure in the bladders is reduced to zero. Cool water can then be sprayed inside the heater shell by piping  101  to reduce the temperature within the molds. Dome  92  is then opened and the ram  95  actuated to lift the molds out of the heater shell.  
         [0033]    Referring now to FIG. 9, it should be noted that the top mold section T of the lowermost mold M- 1  will be urged downwardly towards its closed position of this figure by the weight of the second mold M- 2  as the latter is positioned upon mold M- 1  within the autoclave A. In a similar fashion the weight of the third mold M- 3  will partially or completely close the top mold section of the second mold section when mold M- 2  is lowered onto mold M- 1  within autoclave A.  
         [0034]    Final closing of the molds M- 1 , M- 2 , and M- 3  is effected, however, when the mold sections have been moved upwardly by ram  95  until the top of the uppermost mold M- 3  is moved into engagement with the bolster plate  106  formed on the bottom of dome  22 . The ram will then squeeze each of the mold sections tightly together under great pressure. This squeezing causes the top mold sections to cam the upper and lower tread segments to US and BS to their radially innermost positions whereby lugs  36  and  51  will be forced into the uncured tread portion  58  of each tire, as shown in FIG. 9, with respect to mold M- 1 . At the same time the auxiliary lugs  66  and  68  will be forced into the side portions of the tread grooves. Simultaneously, the highly pressurized bladders BL will urge the inside of the uncured tire tightly against the cavities of the top and bottom mold sections while curing the tire from the inside out. In this manner the tread grooves will be formed as the tire cures.  
         [0035]    Referring now to FIG. 10, after each mold M has been lifted out of the heater shell  90 , its top mold section T will be lifted clear of its bottom mold section B. At this time the weight of the cured tire R and tire carrier C will cause the bottom tread segments BS to remain in their radially innermost position, while the upper tread segments US will retract radially under the influence of springs  43  to the extent that the radially inner surfaces of the lugs  51  will be clear of the outer periphery of the tire tread portion  5   8 . Referring now to FIGS. 11 and 12, connector  76  now raises the cured tire R out of the bottom mold section B. As the tire is moved upwardly, the bottom tread segments BS will be urged radially outwardly and upwardly by springs  31  until the radially inner surfaces of the lugs  32  completely clear the outer periphery of the tire tread portion. Lugs  32  will have formed the horizontal portions  38  of one side of the grooves of the tires tread pattern, while the auxiliary lugs  66  have formed the lower portions of such grooves. It is an important advantage that the upper and lower lugs  36  and  51  will be moved radially out of the tire grooves preventing stripping which could cause the tire rubber to pull loose from the tires&#39; belt package. The cured tire R is then removed from the bladder BL and tire carrier C in a conventional manner and the water allowed to drain from the bladder.  
         [0036]    Referring now to FIG. 15, there is shown a second embodiment of a mold M′ embodying the present invention. Like parts in FIG. 15 to those of the aforedescribed embodiment of FIGS.  1 - 12  bear primed reference numerals. The difference between mold M′ and mold M is that a plurality of like spacer plates SP are interposed between the top and bottom mold sections T′ and B′. Each spacer plate is releasably secured to bottom mold section B′ by a cap screw  110 . When spacer plates SP are interposed between the top and bottom mold sections the mold M′ can be utilized to cure a tire having a greater width than mold sections T and B of FIGS.  1 - 12 . For example, by interposing the spacer plates between mold sections T′ and B′, the same mold sections can be converted to cure a wider low profile tire, as compared to a more conventional radial tire. It should be noted that opening  112  permits access to cap screw  114  and its stop-washer for easy removal and cleaning of tread segments BS′.  
         [0037]    It should be noted that conventional clamshell molds can be converted to molds embodying the present invention, thereby effecting important cost savings for owners of clamshell molds.  
         [0038]    Various modifications and changes may be made with respect to the foregoing description without departing from the scope of the present invention.