Process for manufacturing tires

A process of manufacturing a pneumatic tire (300) with oppositely disposed annularly-shaped beads (324) for mounting on flange shoulders (304) of a wheel rim (302) with the opposed beads (324) spaced apart from one another by a distance “i”. The process comprises the steps of: forming a green tire assembly (308) including a tread (312), and a carcass (316) with a ply (320) and opposed sidewalls (318) that each include a radial inner-end bead portion (322) with one of the beads (324) and wherein each bead portion (322) is spaced apart from one another by a distance “f”. The green tire assembly (308) is cured by applying pressure thereto at an elevated temperature in a vulcanization mold (400). The process is characterized by the steps of spacing the opposed beads (324) apart from one another by a distance “g” which is substantially equal to the distance “f” therebetween when the green tire assembly (308) was formed. The tire (300) is removed hot from the vulcanization mold (400) and mounted on a post cure inflation (PCI) stand (460) with the opposed beads (324) being spaced with a distance “h” therebetween which is substantially equal to the distance “i” therebetween when the cured tire (300) is mounted on the wheel rim (302). The hot tire (300) while mounted on the PCI stand (460) is inflated to a pressure of from substantially 25% to 125% of the normal operating pressure of the cured tire (300) and allowed to cool.

RELATED APPLICATIONS

This application relates to an application Ser. No. PCT/US99/24283 entitled IMPROVEMENTS IN BEAD CONSTRUCTION and having a common assignee with the present invention.

TECHNICAL FIELD

This invention generally relates to improvements in a process for manufacturing pneumatic tires and in tires manufactured in accordance therewith. More particularly, this invention is concerned with (a) improvements in a process for manufacturing pneumatic, radial-ply tires, wherein each of the tires includes an improved pair of oppositely disposed beads and a ply extending therebetween and looped about the respective beads; and (b) tires manufactured in accordance with the improved process.

BACKGROUND OF THE INVENTION

The art of manufacturing a pneumatic tire has evolved over the years to include a number of widely used variations of a conventional process which includes the basic steps of: (a) selecting a plurality of raw materials, including chemicals, different kinds of rubber, woven elastomeric fabrics for plies, puncture resistant woven belts and steel wire for tire beads; (b) mixing the selected rubbers with various processing oils, carbon black, pigments, antioxidants, accelerators and other additives, to form different rubber compounds; (c) processing, rolling and cutting the rubber compounds for use in forming the innerliner, sidewalls, tread and other rubber components of the tire; (d) assembling the rubber components, plies, belts and beads together on the drum of a tire building machine, and, under heat and pressure, forming therefrom a “green” tire; (e) inserting the green tire into a vulcanizing mold; and (f) curing the green tire by expanding a bladder therewithin, through the introduction into the bladder of a high pressure medium at a sufficiently elevated temperature to vulcanize the green tire and to conform the tire to its final design shape, including the tire tread pattern and sidewall markings.

Despite numerous attempts to optimize the above described conventional manufacturing process, tires manufactured in accordance prior art processes continue to exhibit non-uniformities in their shape and other deficiencies in their physical characteristics, to which uneven tire wear is generally attributable. For example, it is not unusual to observe that when a prior art tire is mounted on a rim and inflated, the inner, radially-extending, heel seats of the opposed bead portions of the tire are not disposed in abutment with the outer, radially-extending, flange shoulders of the wheel rim, with the result that unbalanced forces are outwardly radially transmitted to the tire tread, causing the tread to become unevenly worn. In addition, due to unrelieved internal stresses developing in prior art tires, in the course of their manufacture, internal flow cracks have been observed to develop in one or the other of the opposed tread shoulders, causing the tires to become unevenly worn.

Of course, processes of manufacturing tires having various structural forms have been the subject of numerous prior art patents. For example: U.S. Pat. No. 3,900,061; U.S. Pat. No. 4,669,519; and U.S. Pat. No. 4,867,218 are directed to subject matter such as improvements in tire cornering performance, the reduction in tire rolling resistance, and the avoidance of the need for larger tire curing presses. In addition, U.S. Pat. No. 4,393,912, issued to Gouttebessis discloses a process of molding a pneumatic tire comprising a crown and opposed sidewalls, wherein each of the sidewalls is terminated by an unreinforced bead, wherein the tire is molded from liquid or paste materials which solidify between an outer mold and an inner core, and wherein the opposed beads are located axially outwardly of their mounted position on a wheel rim. Since the beads are so located, it is necessary to press the opposed bead portions axially toward one another when mounting the tire on the wheel rim.

Despite such steady improvements in tire construction and their manufacturing processes, as described by the prior art, there still exists a need for modifications of the conventional tire manufacturing processes to focus on relieving internal stresses that develop in tires in the course of their manufacture and on avoiding imparting internal stresses to tires in the course of mounting them on wheel rims. In this connection, it has been found that a major factor contributing to the build-up of stresses in prior art tires, is that the ply and rubber around the beads in the opposed bead portions of the tires have a tendency to twist the beads in the course of manufacture of the tires, generally due to the opposed bead portions being required to be moved toward one another in the course of manufacture of the tires. Such internal stresses tend to cause physical deformities and other physical deficiencies to develop in the resulting tires, causing the tire treads to become unevenly worn when in use. Moreover, internal stresses leading to uneven tread wear are developed in tires when the opposed bead portions of the tires are required to be moved toward one another to mount the tires on wheel rims.

SUMMARY OF THE INVENTION

A preferred embodiment of the invention comprises a process of manufacturing a pneumatic tire for mounting on a wheel rim, wherein the tire includes oppositely disposed annularly-shaped beads. The wheel rim includes oppositely disposed flange shoulders for mounting the tire thereon with the opposed beads thereof spaced apart from one another by a distance “i”. The process comprises the steps of: forming a green tire assembly including a central tread with opposite sides, a carcass and a ply. The carcass includes opposed sidewalls respectively extending radially-inwardly from the opposite tread sides and wherein each of the sidewalls includes a radial inner-end bead portion thereof. Each of the bead portions includes one of the beads so that the bead portions of the green tire assembly are spaced apart from one another by a distance “f”, wherein the ply extends between and loops about each of the beads. The green tire assembly is cured by applying pressure thereto at an elevated temperature in a vulcanization mold and is characterized by spacing the opposed beads in the vulcanization mold from one another by a distance “g” which is substantially equal to the distance “f” therebetween when the green tire assembly was formed. The distance “g” is within the range of +2% to −2% of the bead spacing distance “f” when the green tire assembly was initially formed. Then the cured tire is removed from the vulcanization mold while the cured tire is still hot. Next the hot cured tire is mounted on a Post Cure Inflation (PCI) Stand so as to maintain distance “h” between the opposed beads which is substantially equal to the distance “i” therebetween when the cured tire is mounted on the wheel rim. Continuing, the hot cured tire is inflated while mounted on the PCI Stand to a pressure of from substantially 25% to 125% of the expected operating pressure of the cured tire when mounted on the wheel rim. Next the cured tire is allowed to cool.

The process includes mounting the cured tire on the PCI Stand while it is at a temperature within the range of from 250 degrees F. to 350 degrees F. (121 degrees C. to 177 degrees C.). The process includes spacing the beads on the PCI Stand a distance “h” within the range of from substantially zero to 5 centimeters less than the spacing distance “i” between the beads when the tire is mounted on a wheel rim.

The process includes selecting each of the beads to include a bead wire annulus and a rubber filler annulus forming therewith a bead member. Each of the bead members includes a thermoplastic bead cover disposed in surrounding relationship with the bead member. Each of the thermoplastic covers includes an inner layer, an intermediate layer, and an outer layer rotatable relative thereto when the bead is mounted on the PCI Stand.

The process includes the step of curing rubber filler annulus of the bead during the course of vulcanizing the tire assembly. The inner and outer layers of the thermoplastic cover are selected from a class of materials that soften at a lower temperature than the intermediate layer. Moreover, the inner and outer layers of the thermoplastic cover are of a polymer plastic fabric and the intermediate layer is a polyethylene film.

The process also includes selecting the beads to include a bead wire annulus having the thermoplastic cover disposed in surrounding relationship therewith whereby when the cured tire is removed from the vulcanizing mold, the ply looped about the respective beads can rotate when the bead portions are moved toward one another for mounting the cured tire on the PCI Stand.

Another preferred embodiment of the invention is to provide a bead for use in a process for manufacturing a pneumatic tire, wherein the bead has a steel bead wire annulus. The bead includes an annulus made of a rubber filler. The steel bead wire annulus and the rubber filler annulus forming a bead member have a substantially circular transverse cross-section. The bead includes a thermoplastic cover disposed in surrounding relationship with the bead member. The thermoplastic cover includes an inner layer, an intermediate layer and an outer layer. The outer layer is rotatable relative to the inner layer while the cured tire is hot.

DEFINITIONS

“Axial” or “Axially” means the lines or directions extending parallel to the axis of rotation of a tire.

“Bead” generally means of annularly-shaped, member located within either of the inner radial end portions of a tire;

“Bead Portion” generally means either of the opposed radial inner end portions of the carcass of a tire including a bead, the portion of a ply which is looped about the bead, and the rubber material surrounding the bead and ply portion.

“Carcass” generally means the tire structure including the beads and ply, but excluding the belt structure, undertread over the ply and the tread.

“Circumferential” means the lines or directions circularly-extending along the perimeter of the surface of the tire tread and perpendicular to the axial direction; or the lines or directions of a set of adjacent circles whose radii define the curvature of the tire tread as viewed in a transverse cross-section.

“Equatorial Plane” means the imaginary plane extending perpendicular to the axis of rotation of the tire and passing through the center of the tread; or the plane containing the circumferential centerline of the tread.

“Ply” generally means a cord-reinforced layer of rubber-coated, radially deployed material.

“Radial” mean directions extending radially toward or away from the axis of rotation of the tire.

“Sidewall” generally means the radially-extending portion of a tire.

“Toe” generally means the elastomeric, rim-contacting, radial inner end of the bead portion of the tire, extending axially inward of each bead.

“Tread width” means the arc length of the outer circumference of the tread of a tire as viewed in transverse cross-section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows half of a transverse cross-sectional view of a prior art tire100mounted on a wheel rim102having a flange shoulder104. Since the transverse cross-section of the other half of the prior art tire100is the mirror image of the view shown inFIG. 1, and thus includes like or corresponding parts, it will be assumed, for the purposes of this Patent Application that both halves of the prior art tire100are shown in FIG.1.

Accordingly, a typical prior art tire100(FIG. 1) comprises a central tread112having opposed sides, generally indicated by the numeral113. In addition, the tire100includes a pair of belts114, disposed beneath the tread112, and a carcass116. The carcass116includes a pair of oppositely disposed sidewalls118, respectively merging with and radially-extending inwardly from the respective opposed sides113of the tread112and forming therewith a shoulder portion, generally indicated by the numeral119. The carcass116also includes a ply120, having opposed side portions120a, and an innerliner121, and includes a pair of oppositely disposed bead portions122at the radial inner ends of the opposed sidewalls118. Each of bead portions122includes and an annularly-shaped bead124disposed there within. Further, each of the bead portions122includes an annularly-shaped heel126and toe128, and a flat heel seat130extending between the heel126and toe128. The bead124of the prior art tire100is a substantially inextensible annulus of made of steel bead wire144, for retaining the heel seat130in abutment with the flat, annularly-shaped flange shoulder104of a wheel rim102. The ply120, extends between the beads124and has opposite side portions120athereof respectively looped about the respective beads124.

In the typical prior art tire100(FIG.1), each of the beads124includes a plurality of parallel rows145of the steel bead wire144and has a substantially semi-circular transverse cross-section. The parallel rows145(FIG. 2A) of bead wire144preferably describe and an angle “a” of 15 degrees with respect to the axial direction of rotation “x” of the tire100, to match the corresponding 15 degree angle “c” (FIG. 1) that the flange shoulder132of the wheel rim134describes with respect to the axial direction of rotation “x1” of the wheel rim134. However, as hereinbefore discussed, when the prior art tire100is mounted on the wheel rim133, the angle “a” (FIG. 2) has been observed to be substantially less than 15 degrees, for example as little a zero degrees as shown inFIG. 1, due to physical deficiencies of the tire100resulting from internal stresses developed therein in the course of manufacture thereof, as hereinafter described in greater detail.

The prior art tire manufacturing process includes the steps of: (a) building the tire carcass116(FIG. 1) on a first stage tire building drum (not shown); (b) expanding the tire carcass116into a package of belts114and a tread112on a second stage tire building drum (not shown) to form a green tire assembly108(FIG.2A); (c) inserting the tire assembly108into a vulcanizing mold200(FIG.2B); (d) curing the tire assembly108(FIG. 2A) in the mold200through the use of a high-pressure medium at a sufficiently elevated temperature to vulcanize the tire assembly108; and (e) removing the cured tire100(FIG. 2B) from the vulcanizing mold200, and allowing the cured tire100to cool to ambient temperature.

As shown inFIG. 2B, the vulcanizing mold200includes oppositely disposed mold rings250and plate252and a tread ring256, which together define an inner surface257of the mold200. When the green tire assembly108is mounted in the mold200, the mold rings252press against the bead portions122of the green tire assembly (FIG.2A), thereby forcing the opposed bead portions122(FIG. 2B) axially toward one another, symmetrically with respect to the equatorial plane (EP) of the tire assembly108, as indicated by arrows240. Thereafter, a bladder258is inflated within the tire assembly108, through the introduction into the bladder258of a medium, typically steam, at a sufficiently high pressure and elevated temperature to firmly press the tire assembly108against the inner surface257of the mold200and vulcanize the tire assembly, thereby forming a cured tire100FIG. 1having a final design shape, including a tread pattern and sidewall markings.

Within the mold200(FIG.2), the axial distance “d” between the beads124is ideally the same as the spacing therebetween when the cured tire100(FIG. 1) is mounted on the wheel rim102. Moreover the bead spacing distance “d” is ideally the same as the tread width “w” (FIG. 2) of the tire tread112. In the course of manufacture of an exemplary passenger tire100, when the green tire assembly102(FIG. 2B) is removed from the second stage building drum (not shown), the bead spacing “e” is typically about 15 inches (38 cm). When the tire assembly108is mounted within the vulcanization mold200(FIG. 2B) the bead spacing distance “d” is typically 7.5 inches (19 cm). However, when the cured tire100is removed from the vulcanization mold200, although the tread width “w” is typically 7.5 inches (19 cm), the bead spacing distance “d” is typically 7.5 inches (19 cm) to 8 inches (20 cm). And, when the cured tire100is mounted on a wheel rim134(FIG.1), the bead spacing distance “e” is typically about 7.5 inches (19 cm).

In general, as a result of the bead portions122of the green tire assembly108being moved toward one another before vulcanization of the tire assembly108, internal stresses develop at the interfaces between the ply120and the surrounding green rubber material forming the sidewalls118and innerliner121, causing the sidewalls118to become compressed and the innerliner to become stretched. In addition, internal stresses develop between the sidewalls118and the bead portions122causing internal buckling to occur. Moreover internal stresses develop in the bead portions122at the interfaces between looped portions of the ply120and the green rubber material in surrounding relationship therewith, and between the opposed beads124and surrounding rubber material causing the bead portions122to be unstable.

Due to the ply120being looped about the respective beads124, and the rubber material of the tire assembly108being disposed in surrounding relationship with the beads124and ply120, when the opposed bead portions122are axially moved toward one another within the vulcanization mold200, the surrounding rubber material adheres to the beads124and ply120, and exerts oppositely directed rotational forces, shown by the arrows242(FIG.2B), on the opposed beads124, tending to rotate the respective beads124in the opposite directions indicated forces242. On the other hand, such rotational forces242are to some extent offset due to the axially inwardly facing sections125aof the respective beads124, corresponding to the opposed inwardly facing portions of the transverse cross-section of each of the beads124. These inwardly facing sections125aare restrained from such rotation since such sections125ahave a shorter circumferentially-extending arc length125aathan the arc length125bbof the axially outwardly facing portions125bof the transverse cross-section of each of the beads124. Such rotation of the opposed beads124, is not possible, since it tends to force the inwardly and outwardly facing bead sections,124aand124b, to respectively assume longer and shorter circumferentially-extending arc lengths than their original circumferentially-extending arc lengths124aaand124bb. In any event, the resulting rotational and counter-rotational forces cause internal stresses to develop in the opposed bead portions124, causing the opposed beads124to rotate sufficiently to reduce the ideal 15 degree angle “a” (FIG. 2A) of the bead rows145before curing the green tire assembly108, to the less than ideal angle of the bead rows145, such as zero degrees as shown inFIG. 1, after curing the green tire assembly108. Accordingly, the locations of the opposed beads124with respect to one another are unstable, as they are continuously under stress to return to their original orientation in the green tire assembly108(FIG. 2A) before insertion thereof into the vulcanizing mold200, with the result that such tires tend to become non-symmetrical.

As discussed above, various stresses causing the physical deformations and other deficiencies in prior art processes are traceable to deficiencies in the prior art process of manufacturing such tires100(FIG.1). In particular, the prior art process tends to produce tires100which are not symmetrical with respect to the Equatorial Plane (EP) of an ideal tire, causing uneven tread wear and shorter tire life. Moreover, although the green tire material can allow for some movement to compensate for the tendency of prior art tire100develop physical defects, the flow cracks and buckling are widespread in prior art tires100, causing uneven tread wear and shorter tire life. Still further, the problem of uneven wear of the tread112of prior art tires100constructed in accordance with the conventional manufacturing process has, in part, been found to he due to poor seating of the opposed tire bead portions122on the wheel-rim102. When the tire100is poorly seated on the wheel-rim shoulder104, unbalanced forces are radially transmitted to the tread112, causing the tread to become unevenly worn and thereby shortening the life of the tire100.

Preferred Embodiment

FIG. 3shows half of a transverse cross-sectional view of a tire300according to the invention mounted on a wheel rim302having a flange shoulder304. Since the transverse cross-section of the other half of the tire300is the mirror image of the view shown inFIG. 3, and thus includes like or corresponding parts, it can be understood, for the purposes of this Patent Application, that the half of the transverse cross-section of the tire300not shown is substantially identical to the half shown in FIG.3.

Accordingly the tire300comprises a central tread312having opposed sides, generally indicated by the numeral313. In addition the tire300includes at least one belt314, disposed beneath the tread312and a carcass316. The carcass316includes a pair of oppositely disposed sidewalls318, respectively merging with and radially-extending inwardly from opposite sides313of the tread312and forming therewith a shoulder portion, generally indicated by the numeral319. The carcass316also includes at least one ply320, having opposite side portions320a, and includes an innerliner321. Further, the carcass316includes oppositely disposed bead portions322at the radial inner ends of the sidewalls318. Each of the bead portions322includes an annularly-shaped bead324. And, the at least one ply320extends between the opposed beads324. Moreover, the respective side portions320aof the ply320are looped about opposite beads324. Further, each of the bead portions322includes an annularly-shaped heel326and toe328and flat heel seat330extending between the heel326and toe328. As thus constructed and arranged, when the tire300is mounted on the wheel rim302, the bead324retains the heel seat330in abutment with the flat, annularly-shaped, wheel-rim shoulder304.

According to the invention, each of the beads324(FIG. 3A) includes a substantially inextensible annulus344of steel bead wire344A having a substantially semi-circular transverse cross-section. The bead wire344A is preferably arranged in the form of a plurality of parallel rows,345a,345b,345c, and345d, respectively describing an angle “aa” of substantially 15 degrees with respect to an axial direction of rotation “x” of the tire300, to match the substantially 15 degree angle “c” (FIG. 3) that the flange shoulder304describes with respect to the axial direction of rotation “y” of the wheel rim302.

In addition, each of the beads324(FIG. 3A) includes an annulus347made of rubber filler347ahaving a substantially semi-circular transverse cross-section. The rubber filler annulus347, is preferably curable to a hard rubber consistency, such as chafer rubber, and, although preferably cured with the remainder of the tire300, may be cured prior thereto without departing from the spirit and scope of the invention. Accordingly, the rubber filler annulus347may be either cured or green when assembled with the bead wire annulus344. Preferably, the rubber filler annulus347is radially disposed outwardly of, and in abutment with, the bead wire annulus344and forms therewith a bead member348having a substantially circular transverse cross-section. Without departing from the spirit and scope of the invention, the respective transverse cross-sections of the annuli,344and347, may respectively have any transverse cross-section consistent with retaining a combined transverse cross-section which is substantially circular.

As shown inFIG. 3A, each of the beads324preferably additionally includes a thermoplastic cover349disposed in surrounding relationship with the bead member348, as by wrapping the thermoplastic cover349around the annuli344and347. The thermoplastic cover349preferably comprises an inner layer360, made of a polymer plastic fabric which is coated on both sides with an adhesive, such as rubber cement, an intermediate layer362, made of a polyethylene film, and an outer layer364, made of polymer plastic fabric which is coated on both sides with an adhesive, such as rubber cement. More particularly, the inner and outer layers,360and364, are preferably formed from one or more turns of a square-woven nylon fabric coated on both sides with an adhesive such as rubber cement. And the intermediate layer362is preferably formed from one of a class of materials that soften at a lower temperature than the inner and outer thermoplastic layers360and364to permit slippage therebetween when the intermediate layer362is hot, and thus during the processing steps of curing and cooling the tire300. In addition, in the preferred embodiment of the process, when the adhesive coating is applied to the opposite sides, respectively, of the inner and outer thermoplastic layers,360and364, it is preferably tacky. This tackiness ensures, a) that inner layer360adheres on contact to the bead member348and to the intermediate layer362, and b) that the outer layer364adheres on contact to the intermediate layer362and to the rubber material surrounding the bead324. As thus constructed and arranged, the thermoplastic cover349protects the bead member348against deformation in the course of manufacture of the tire300, with the result that there is no need to pre-cure the rubber filler annulus347.

A process of manufacturing a tire (FIG. 3) according to the invention comprises the steps of: (a) building a tire carcass316, generally including the opposed sidewalls318, a ply320, an innerliner321and opposed beads324, on a first stage tire building drum (not shown); (b) expanding the tire carcass316into a tread package, including at least one belt314and a tread312, on a second stage tire building drum (not shown) to form a green tire assembly308(FIG.4A), having a bead spacing distance “f”; (c) inserting the tire assembly308into a vulcanization mold400(FIG.4B); wherein the axial distance “g” between the opposed beads324is substantially equal to the distance “f” therebetween when the green tire assembly308was removed from the second stage building drum; (d) curing the green tire assembly308through the use of a high-pressure medium at a sufficiently elevated temperature to press the tire assembly308against the mold300and to vulcanize the tire assembly308; (e) removing the cured tire300from the vulcanizing mold400while the tire300is still hot; (f) mounting the cured tire300, while hot, on a conventional Post Cure inflation (PCI) Stand460(FIG.4C), wherein the distance “h” between the opposed beads324is substantially equal to the distance “i” (FIG. 3) therebetween when the tire300is subsequently cooled and mounted on a wheel rim302; (g) inflating the hot tire300(FIG.4C), while mounted on the PCI Stand; and (h) allowing the inflated tire300to cool to ambient temperature.

When the green tire assembly308(FIG. 4B) is initially mounted in the vulcanization mold400, the mold rings450are moved upwardly against and in supporting relationship with the opposed bead portions322. Thereafter, a bladder452is inflated within the green tire assembly308, through the introduction there into of a high pressure medium at an elevated temperature, to press the green tire assembly308against the inner surface451of the mold400and to vulcanize the tire assembly308. Preferably, high pressure steam is used as the medium for inflating the tire assembly308And the vulcanization temperature is within the range of from substantially 250 to 350 degrees Fahrenheit (121 to 177 degrees C.), and preferably substantially 300 degrees Fahrenheit (149 degrees C.). While the green tire assembly308is being vulcanized, the bead spacing distance “g” between opposed beads324is substantially equal to the bead spacing distance “f” therebetween when the green tire assembly308was removed from the second stage building drum (not shown). The distance “f” is defined as the spacing between the beads of the green tire immediately after the tire is removed from the second stage tire building machine (not shown). In practice, although the bead spacing distance “g” of the tire assembly308, as mounted in the mold400, may be slightly less than the bead spacing distance “f” of the tire assembly308when removed from the second stage building drum (not shown), the differences between the bead spacing distances “f” and “g” may still be the to be substantially unchanged. The bead spacing distance “g” of the tire assembly308can be defined as 100% to 200% of the distance “h”, corresponding to the distance between the beads when the tire is mounted on a tire rim.

Thus the internal rotational and counter-rotational forces developed in the prior art tire100(FIG.2B), which are attributable to moving the opposed beads124toward one another in the course of manufacture of the tires100have been substantially completely eliminated from tires300(FIG. 3) manufactured in accordance with the present invention. In particular, maintaining the bead spacing distances “f” and “g” substantially unchanged while the tire assembly302is still in the somewhat delicate green state substantially completely eliminates the development of the internal stresses, which give rise to the development of internal buckling and flow cracks.

The resulting toroidally-shaped, cured tire300(FIG.4C), having a conventional tread pattern and sidewall markings, is then mounted on the PCI Stand460while still hot, and thus at the aforementioned temperature within the range of from substantially 250 to 350 degrees F. (121 to 177 degrees C.), and preferably 300 degrees F. (149 degrees C.). The PCI Stand460includes a pair of oppositely disposed rims348which are conventionally movable toward and away from one another. When the cured tire300(FIG. 4C) is initially mounted on the PCI Stand460, the opposed rims348thereof are axially moved toward and into abutment with the opposed bead portions322, and then a sufficient distance thereafter to achieve the bead spacing distance “h” which is substantially equal to the distance “i” (FIG. 3) of the tire300when mounted on a tire rim302. Whereupon the angle “k” that the respective bead wire rows,345a,345b,345cand345d, and heel seat330, describe with respect to an axial direction “x” of the tire300, extend substantially parallel to the angle “c” that the flange shoulder304describes with respect to an axial direction “y” of the wheel rim302. Thereafter, while the cured tire300(FIG. 4C) is still as hot as hereinbefore noted, the tire300is inflated to a pressure of from substantially 25% to 125% of the normal operating pressure thereof to conform the cured tire300to the toroidal shape thereof when mounted on the wheel rim300(FIG.3).

In an exemplary passenger tire300manufactured according to the present invention, having a 7.5 inch (19 cm) tread width “t” (FIG.4C), the opposed beads324may be separated by a distance “f” of 15 inches (38 cm) after removal from the second stage building drum, a distance “g” of 15 inches (38 cm) when in the vulcanizing mold (FIG.4B), a distance “h” of 7.5 inches (19 cm) when mounted on the PCI Stand (FIG.4C), and a distance “i” of 7.5 inches (19 cm) when mounted on the wheel rim302(FIG.3).

Although the bead-spacing distance “g” of the cured tire300when mounted in the vulcanization mold (FIG.4B), was reduced to the bead spacing distance “h” when mounted on the PCI Stand (FIG.4C), due to the respective sidewalls318and bead portions322having been moved toward one another for mounting the cured tire300on the PCI stand460, such movements occurred while the temperature of the cured tire300was at the elevated temperature hereinbefore discussed. As a result, the outer layer364of the thermoplastic cover349was able to rotate relative the inner layer360thereof, because the intermediate layer362thereof having been liquefied and providing a slippage medium between the respective inner and outer thermoplastic layers,362and364. And, due to such slippage, the molecules of the rubber materials surrounding bead324and ply320were able to establish a state of equilibrium relative to one another to relieve the internal stresses that would otherwise have developed in the sidewalls318and bead portions322of the cured tire300.

Accordingly, a tire300having the improved bead324and manufactured in accordance with the aforesaid process is substantially free of the internal rotational and counter-rotational stresses found in prior art tires100. In this connection, it is noted that the improved tire300has not been observed to be physically misshapen or otherwise deformed due to internal stresses developing therein in the course of manufacture thereof. Nor have the improved tires300been observed to have developed internal buckling or flow cracks as commonly found in prior art tires100. Moreover, when the improved tires300are mounted on a wheel rim302, the respective heel seats330have been observed to be properly mounted in abutment with the respective wheel-rim shoulders304, with the result that balanced forces, rather than the unbalanced forces of prior art tires100, are transmitted to the wheel treads312. Thus improved tires300manufactured in accordance with the improved process, are substantially free of internal stresses developed in the course of their manufacture and are substantially free of physical deformities and other physical deficiencies of prior art tires300.

The theoretical tire geometry diagram shown inFIG. 5was considered in the course of determining the bead spacing of the improved tire300when mounted in the vulcanization mold400(FIG.4B). The diagram demonstrates the range of the bead placement to alleviate the disadvantage in the improved process of developing internal stresses in the shoulder portions319of the improved tire300when the beads are moved toward one another for mounting the tire300on the PCI Stand (FIG.4C). As hereinafter discussed, the aforesaid disadvantage may be minimized by slightly reducing the bead spacing distance “g” within the mold400, as compared to the spacing distance “g” hereinbefore discussed in the above embodiment of the invention.

When the green tire assembly308(FIG. 4B) is mounted in the vulcanizing mold400, there are three constraints imposed on the tire assembly308by the mold400: 1) the tire assembly308is maintained symmetrical with respect to the Equatorial Plane (EP); 2) the radial height “rh” (FIG. 3) between the outer diameter of each of the beads324to the center of the innerliner321of the tire300, is set; and 3) the curvedly-extending length (PL) of the ply320, as measured between the respective outer diameters of the opposed beads324, is set. Thus, the three constraints are the symmetry, set radial height “rh” and set ply length (PL).

The three geometric forms500shown inFIG. 5correspond to three different theoretical forms of a pneumatic tire in a theoretical vulcanization mold (not shown). The geometric forms500include a triangle510having a base520, a rectangle514having a base524, and half of an ellipse512having a base522. The triangle510has a pair of opposed sides,510aand510b, the rectangle512has a pair of opposed sides,512aand512b, and the ellipse514has a pair of opposed sides,514aand514b. Each pair of the aforesaid opposed sides is symmetrically located relative to the Equatorial Plane (EP) of the geometric forms. In addition, each of the geometric forms500shares the same height “ht”, as measured along the Equatorial Plane (EP), and has the same Perimeter Length (PL). The shared height “ht” of the respective geometric forms corresponds the set radial height “rh” within the mold, the shared Equatorial Plane (EP) of the geometric forms corresponds to the Equatorial Plane (EP) of the tire assembly308within the mold, and the Perimeter Lengths (PL) of the geometric forms each correspond to the set ply length (PL) between the outer diameters of the opposed beads324.

As shown inFIGS. 4B and 5, given the constraints discussed above, the theoretical maximum distance “g” between the beads324, when a green tire assembly is mounted in a theoretical vulcanizing mold corresponds to the base524of the triangle510, which would call for the ply320to assume a shape of the opposed sidewalls,510aand510b, of the triangle510. If the cured tire assembly308having a ply320shaped like the triangle510was mounted on a conventional PCI Stand460and inflated, severe internal stresses would be developed in the shoulder portions319of the tire300. Moreover, the same may be said for a tire300having a minimum spacing “g” between the beads324, corresponding to the base524of the rectangle512, since that would call for the ply320to assume a shape corresponding to the rectangle512. However, providing a cured tire300with a bead spacing distance “g”, corresponding to the base522of the ellipse514would call for the ply320to assume a shape corresponding to the ellipse514. And, if a tire300having a ply320shaped like an ellipse514was mounted on a conventional PCI Stand460and inflated, minimal, if any, internal stresses would be developed in the shoulder portions319of the tire300, although more stress would be developed in the bead area of a theoretical tire having the shape of half an ellipse. On balance, molding the tire300according to the invention with a bead spacing distance “g” corresponding to the base522of the ellipse514is an acceptable compromise.

Although the inventions described herein have been shown in a few embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing teachings. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims.