Radially expandable bead molding ring for a tire mold

Apparatus and method for molding a tire (110) with a radially expandable bead molding ring (252). When expanded, the bead molding ring has a circumferentially continuous radially outward-facing surface (259) for molding the bead. The bead molding ring comprises a plurality of segments (254, 256), half of the segments being first segments (254) that are complementary to, and circumferentially alternated with second segments (256). The first segments are wedge shaped, having circumferentially lateral faces (255) that converge towards the radially outward-facing bead molding surface of the bead molding ring, the first segment lateral faces being planar and oriented in the axial direction; and the second segments have lateral faces (257) that are complementary to the first segment lateral faces, such that radially outward movement of the first segments (254) causes radially outward movement of the second segments (256). Guide rods (260) restrict first and second segments to radial movement (310) only. The elements of the bead molding ring are preferably combined in a single assembly (280) with the sidewall mold to form a unit that is easily maintained and changed to adapt to different profiles to be molded on beads of different tire constructions. Expansion of the bead molding ring can be driven by a simple wedging action caused by a single frustraconical cam 266.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the molding of tires. In particular, it pertains to methods and apparatus for molding a tire bead using a radially expandable bead molding ring.

BACKGROUND OF THE INVENTION

Reference is made herein to an “undercut” bead, referring to the shape of the bead base (the radially inner surface of a tire bead that seats in the bead seat portion of a wheel rim). Tire bead bases are most commonly substantially flat and are angled from zero to several degrees relative to the axial direction with the bead base angle opening axially outward. An undercut bead base may be similarly shaped except that the bead base angle opens axially inward. Examples of tires with undercut bead bases, and examples of wheel rims using such tires, are seen in U.S. Pat. No. 6,092,575. In particular, it should be noted that a common variant of a tire with the undercut bead base design comprises beads of two different diameters on the same tire.

In order to mold certain tire constructions, such as those having undercut beads, it becomes necessary to introduce a portion of the tire mold known as the bead molding ring or counter-molding ring into the interior of the tire in order to engage a molding surface against the bead base. In the prior art, means are known for accomplishing the molding of an undercut portion of a tire bead. For example, U.S. Pat. No. 5,129,802 proposes using two counter-molding rings (bead molding rings) for the axially and radially inner portion of the bead, said rings being continuous. In order to introduce the counter-molding rings into the interior of the tire, it is necessary to deform the raw blank of the tire by ovalizing at least one of the beads, so that the bead can be made to pass beyond the counter-molding ring or rings.

Rings for molding the radially and axially inner portion of a bead have also been described in connection with so-called membrane-less vulcanizing presses. See, for example, U.S. Pat. No. 4,236,883 (referred to hereinafter as the '883 patent), which discloses such rings, in this instance made in several segments circumferentially adjacent in molding position. These rings are radially retractable so that they can be introduced into the tire interior without requiring deformation of the tire beads. The '883 patent describes a mechanism occupying integrally the inner volume of the press, so that the necessary movements can be imparted to the several ring segments in order for said segments to accommodate a closing or opening movement in sequence. By a “movement in sequence” is meant that, from a configuration in which the mold is open, the segments do not all go to their molding position at the same time. A first group is brought to its final molding position, then the segments of a second group are inserted between segments of the first group to make a continuous ring. As seen in the '883 patent'sFIGS. 1-2, the first and second segments join along axially aligned planar surfaces, and all segments rotate into position by means of bellcranks (66) rotating on pivots (70) in depending clevis' (74). The bellcranks have cam followers that coact with a multi-faceted linear cam assembly (102) for controlled actuation of the segments mounted on the bellcranks.

U.S. Pat. No. 6,238,193 (referred to hereinafter as the '193 patent) discloses a mold for a tire and a vulcanizing press fitted to receive said mold: a mold for molding a tire having beads of different diameters, Φ0being the minimum diameter of the tire area at the bead of smaller diameter, Φ2being the minimum diameter of the tire area at the bead of greater diameter. The mold has two sidewall plates for molding, respectively, the outer surface of the sidewalls and the outer portion of each bead up to a radially inner limit where the diameter of the tire area is Φ0and Φ2, respectively, a continuous counter-molding ring to mold the bead of smaller diameter from the said radially inner limit where the diameter of the tire area is Φ0to an axially inner limit of diameter Φ1, where Φ1is smaller than Φ2, and a split counter-molding ring to mold the bead of greater diameter from the said radially inner limit where the diameter of the tire area is Φ2to an axially inner limit of diameter Φ3. As seen in the '193 patent'sFIG. 1, the tire bead bases are undercut, i.e., Φ1is greater than Φ0, and Φ3is greater than Φ2. The split ring includes a plurality of retractable segments adjacent in molding position. A flexible membrane molds the inner surface of the tire in the portion of the inner cavity of the tire between the limit of diameter Φ1and the limit of diameter Φ3.

As viewed in itsFIGS. 2-11, the '193 patent discloses a complex mechanism for engaging the split counter-molding ring to mold the lower bead (the bead with the greater diameter). The split counter-molding ring is annular and comprises large segments (141) with beveled edges and smaller key segments (142) having corresponding beveled edges. The edges are beveled at an angle to the axial direction (see FIG.4), so that the key segments can be fitted into the annular ring by moving axially down in between the large segments. After the segments have been fitted together (FIGS.8-10), the ring is pressed down axially against the lower mold sidewall plate12to form the bead area (FIG.11). A problem with the split counter-molding ring design is a complex set of linkages and mechanisms attached to the mold press that is difficult and expensive to manufacture, and that also makes maintaining and changing the vulcanizing mold in the press a time-consuming and difficult process. As viewed in the '193 patent'sFIG. 2, the split counter-molding ring (14) comprises first segments (141) each mounted on a rocking arm (52), itself mounted rotatably on the slide (17) that is mounted on the lower frame22of the press. A roller (521) mounted on each of the rocking arms acts against a first cam42that is integral with the lower membrane plate (32). The second (key) segments (142) are mounted on a guide plate (321) in grooves (53) formed between said guide plate (321) and the first cam (42). A roller (531) is rotatably mounted on each of the second segments and rides against a second cam (43) fixed on the lower frame (22) of the press. The profile of the radially outer surface of said second cam (43) serves to impart a controlled motion for the advance of each of the second segments (142).

It is an object of the present invention to overcome the problems and limitations of the prior art tire molds, particularly molds using radially expandable bead molding rings, such as for molding undercut beads. Problems to be solved include reduction of mechanical complexity to simplify manufacturing of the molds, and to ease mold/press maintenance and changeover.

BRIEF SUMMARY OF THE INVENTION

According to the invention, a bead molding ring is disclosed for a tire mold in a mold press that is configured to mold a green tire comprising a tread, two beads, and two sidewalls extending between the beads and the tread. The bead molding ring characterized in that the bead molding ring comprises a plurality of segments, half of the segments being first segments that are complementary to, and circumferentially alternated with second segments. The first segments are wedge shaped, having circumferentially lateral faces that converge towards a radially outward-facing bead molding surface of the bead molding ring. The first segment lateral faces are planar and oriented in an axial direction. The second segments have lateral faces that are complementary to the first segment lateral faces. Structural means are provided for radially expanding the bead molding ring from a first outside diameter (Dr) to a second outside diameter (De), thereby forming a circumferentially continuous radially outward-facing surface for molding one of the beads.

Further according to the invention, the first outside diameter (Dr) is less than or equal to the inside diameter (D4′) of an unmolded bead that is to be molded by the bead molding ring.

According to the invention, the bead molding ring is further characterized by radially aligned guiding means movably connecting the mold with each of the first and second segments to restrict first and second segments to radial movement only. The molding ring also has spring means pressing radially inward on the first and second segments.

According to the invention, the bead molding ring is further characterized by a cam surface on the radially inner portion of the first and second segments of the bead molding ring. The cam surface slopes radially inward and axially outward at a cam angle to form an annular surface complementary to a frustraconical section. A cam is attached to an axially-moving part of the mold press such that the cam interacts with the cam surfaces of at least the first segments to wedge the first segments radially outward as the cam moves in an axial direction. Preferably the cam is a ring with a frustraconical radially outer cam surface that has a cam angle that matches the cam angle of the cam surfaces of the bead molding ring.

According to the invention, a mold is disclosed for a green tire comprising a tread, two beads each having a radially inward-facing bead base extending from an axially outer heel to an axially inner toe, and two sidewalls extending between the beads and the tread. The mold comprises first and second sidewall plates for molding, respectively, an outer surface of each of the sidewalls plus an axially outer portion of each of the beads approximately in to the heel. The mold also has first and second bead molding rings for molding at least the bead bases of the two beads and an inflatable vulcanizing membrane for molding the inside surfaces of the tire. At least a first bead molding ring comprises a plurality of segments, half of the segments being first segments that are complementary to, and circumferentially alternated with second segments. The first segments are wedge shaped, having circumferentially lateral faces that converge towards a radially outward-facing bead molding surface of the first bead molding ring. The first segment lateral faces are planar and oriented in the axial direction and the second segments have lateral faces that are complementary to the first segment lateral faces. Structural means radially expand the first bead molding ring from a first outside diameter (Dr) to a second outside diameter (De) thereby forming a circumferentially continuous radially outward-facing surface for molding one of the beads in cooperation with an adjacent first sidewall plate and the vulcanizing membrane.

According to the invention, the mold is further characterized by guide rods to restrict first and second segments to radial movement only. Each guide rod is mounted in a radially aligned mounting hole bored in a one of the first and second segments, and each mounting hole is aligned with a guide hole bored in the adjacent first sidewall plate such that the guide rod slides within the radially-aligned guide hole. Springs are preloaded to force radially-inward movement of the first and second segments. Each spring resides in a radially aligned spring holding hole bored in the adjacent first sidewall plate and is aligned with a spring pocket cut in an adjacent one of the first and second segments, so that a spring can be positioned with one end in the spring holding hole and the other end in an adjacent spring pocket. Preferably the mold is further characterized by an assembly comprising the first sidewall plate, all of the plurality of first segments and second segments, all of the guide rods, and all of the springs. The assembly is held together by stop bolts extending from a side of at least one of the guide rods, each stop bolt protruding into a cavity adjoining a portion of the corresponding guide hole.

According to the invention, the mold is further characterized by a cam surface on the radially inner portion of the first and second segments of the bead molding ring. The cam surface slopes radially inward and axially outward at a cam angle to form an annular surface complementary to a frustraconical section. A cam is attached to an axially-moving part of the mold press such that the cam interacts with the cam surfaces of at least the first segments to wedge the first segments radially outward as the cam moves in an axial direction. Preferably the cam is a ring with a frustraconical radially outer cam surface that has a cam angle that matches the cam angle of the cam surfaces of the bead molding ring. Furthermore, the cam can be attached to a clamp ring for clamping one end of the vulcanizing membrane.

According to the invention, the mold is further characterized in that the second bead molding ring is functionally the same as the first bead molding ring.

According to the invention, alternatively the second bead molding ring is a non-segmented, non-expandable, continuous ring. The tire may have asymmetric bead diameters such that a first bead has a first diameter (D4) and a second bead has a second diameter (D2) such that the second diameter is less than or equal to the first diameter in a way that allows the first bead to pass over the continuous second bead molding ring before passing over the first bead molding ring while the first bead molding ring is retracted to its first outside diameter (Dr).

According to the invention, the mold is further characterized in that the two beads have an undercut bead base.

According to the invention, a method is disclosed for molding a green tire comprising a tread, two beads, and two sidewalls extending between the beads and the tread. The method comprises the steps of: loading the tire into a mold comprising at least one retractable bead molding ring; passing an unmolded bead of the tire over the retractable bead molding ring while the ring is retracted to an outside diameter (Dr) that is less than or equal to the inside diameter (D4′) of the unmolded bead; and expanding the retractable bead molding ring to engage the unmolded bead by moving only in a radially outward direction.

According to the invention, the method further comprises the step of, after engaging a first one of the beads with the retractable bead molding ring, expanding a vulcanizing membrane inside the tire to draw a second one of the beads into engagement with a bead molding ring.

According to the invention, the method further comprises the step of using an axial movement of a portion of the press to drive the radially outward movement of the retractable bead molding ring.

According to the invention, the method further comprises the step of composing the retractable bead molding ring of circumferentially alternated first segments and second segments such that radial expansion of the first segments causes radial expansion of the second segments.

According to the invention, the method further comprises the step of: assembling the retractable bead molding ring together with a sidewall molding plate.

Other objects, features and advantages of the invention will become apparent in light of the following description thereof.

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1a tire10of the prior art (see U.S. Pat. No. 6,092,575) is shown in meridional cross-section. The tire10comprises a tread16, first and second beads12aand12b, respectively, and two sidewalls14aand14bextending between the tread16and the beads12aand12b, respectively. The beads12a,12bare undercut and the tire is asymmetric, having different bead diameters. Each bead12a,12bhas a heel20a,20b, respectively, a toe22a,22b, respectively, and a bead base24a,24b, respectively, extending between the heel20a,20band toe22a,22b. Typically a tire's bead base is planar from heel to toe, but it can have multiple surfaces as illustrated in FIG.1. The undercut nature of the beads12a,12bis characterized by one or more acute bead base angles α, β that open axially inward. As a consequence, the bead diameter at the heel (the axially outermost extent of the bead base) is less than the bead diameter at the toe (the axially innermost extent of the bead base), i.e., bead heel diameter D1is less than bead toe diameter D2for the first bead12a, and bead heel diameter D4is less than bead toe diameter D3for the second bead12b. The asymmetric nature of the tire10is characterized in that the nominal diameters of the two beads12a,12bare different. More particularly, for the tire10as illustrated, the bead toe diameter D2of the first bead12ais less than the bead heel diameter D4of the second bead12b. The radially inner limits of the beads12aand12bare labeled L1and L2, respectively. These limits correspond to the point where the tire diameter is least. Thus, for the bead12a, the diameter at the limit L1is D1. For the bead12b, the diameter at the limit L2is D4. This tire construction allows mounting on special wheel rims, and also provides advantages in tire molding, as will be described hereinbelow.

The present invention will be described in a preferred embodiment that advantageously molds green (unvulcanized) tires that have undercut beads and asymmetric bead diameters such as for the prior art tire10of FIG.1. It should be understood that the present invention is not limited to the molding of such tires. Rather, the present invention can provide improvements and benefits compared to the prior art when used in any tire mold, particularly molds wherein the use of a radially expandable bead molding ring is desired. For example, two radially expandable bead molding rings according to the present invention could be used in a mold for tires with normal, symmetric bead diameters and any bead base profile, but especially for undercut bead bases that cannot be molded without positioning at least a portion of the bead molding rings axially inward of the beads. Or, for example, two radially expandable bead molding rings according to the present invention could be used to grip inside portions of the beads in order to allow tire molding in “membrane-less vulcanizing presses” such as those described in U.S. Pat. No. 4,236,883.

The detailed description will include certain directional terms, including “radial”, “axial”, “meridional”, “inward”, and “outward”. These terms are well known for tires, and when used herein with respect to tire molds and mold presses the terms should be understood in an analogous way wherein a center post of the mold press is located at the axis of rotation of the mold as well as that of a tire placed in the mold. Thus “axial” directions are directions parallel to the center post and parallel to the axis of rotation of a tire placed in the mold. Likewise, a radial direction is in the direction of a radius line originating at the axis of rotation of the mold that is also the axis of a tire placed in the mold. Similarly, “inward”, “outward” and related terms are relative to the interior cavity of the mold and/or the tire.

FIGS. 2-5illustrate key steps of the preferred embodiment of the inventive molding process carried out on a tire110, as shown in meridional cross-section for one half of the tire110and mold200in a mold press220. Referring first toFIG. 5, showing the tire110being molded, it can be seen that the tire110is similar to the tire10, having undercut beads112a,112b(collectively referred to as112) and asymmetric bead diameters such that the diameter D4at the heel120bof the bottom bead112bis greater than or equal to the diameter D2at the toe122aof the top bead112a. This particular bead diameter asymmetry enables the use of a solid (continuous ring, not segmented) top bead molding ring230such as the continuous counter molding ring (13) of the prior art '193 patent. An inventive radially expandable bead molding ring assembly250is utilized for molding the bottom bead112b.

For the sake of simplicity and clarity inFIGS. 2-5, cross-section shading of parts is omitted, as are the internal elements of the tire110. The tire110has beads112, a tread116, and sidewalls114a,114b(collectively referred to as114) extending between the tread116and each bead112.

The axially outer surface of the sidewalls of a tire, including the beads, is generally molded by a part called a sidewall plate, illustrated as a top sidewall plate202aand a bottom sidewall plate202b, referred to collectively as sidewall plates202. A sidewall plate202starts from the position of least diameter, conventionally the radially innermost tip of the bead112, and extends about to the shoulders of the tire. In fact, sometimes elements independent of the sidewall plates202are used to mold the axially outer face of a bead112, but in the context of the present invention, it is immaterial whether the part molding the outer surface of the bead112is integrated with the sidewall plate202or separate from it.

The loading, molding, and release of a tire110involve relative motions in an axial direction between the tire110and each of the sidewall plates202molding it. InFIGS. 2-5, it is readily seen that the shape to be imparted to the outer surface of the beads112and sidewalls114is compatible with relative motion in an axial direction between each of the sidewall plates202and the tire110. The undercut bead design creates axially-inward facing portions of the beads112that must be molded to a shape that cannot be imposed with the desired accuracy by means of a vulcanizing membrane210. Hence, the use of additional rigid molding parts, the bead molding rings, is required. In the preferred embodiment shown in the drawings, the top bead molding ring230is a continuous ring, and the bottom bead molding ring252is a segmented ring. The fact that the ring for molding the bead of greater diameter is a segmented ring makes it possible to mold undercut beads, such as the illustrated beads112. The bead molding rings230,252are thus intended to mold the portion of each of the beads112from the point where the sidewall plates202end their molding effect, inward to the point where the vulcanizing membrane210can begin effective molding.

In the mold200proposed for the preferred embodiment of the present invention, the value of the diameter D2for the bead112aof lesser diameter is less than or equal to the diameter D4for the bead112bof greater diameter. Hence, it is possible to pass the continuous bead molding ring230inside the opposite bead112b. This continuous bead molding ring230is made in one piece. On the other side, the segmented bead molding ring252is made in several segments: a group of first segments254and a group of second segments256. This enables the segmented bead molding ring252to be retracted so that the tire110can be placed in the mold200and be extracted after vulcanizing.

More specifically,FIGS. 6A and 6Bshow that the bead molding ring252comprises a number N of first segments254(here N=3), and a like number N of second segments256complementary to, and circumferentially alternated with, the first segments254. The first segments254(also known as wedge segments) are wedge shaped, having circumferentially lateral faces255that converge towards a radially outward-facing bead molding surface (259as seen in the cross-sectional view ofFIG. 9) of the bead molding ring252, the first segment lateral faces255being planar and oriented in the axial direction. The second segments256have lateral faces257that are complementary to the lateral faces255of the first segments254. To avoid clutter in the drawings, the lateral faces255and257are only labeled with numbers around the first segment254at the top ofFIGS. 6A and 6B, but it should be understood that similar labeling applies to all of the segments254and256.FIG. 6Ashows the segmented bead molding ring252in a radially expanded state, andFIG. 6Bshows the segmented bead molding ring252in a radially retracted state. It can be seen that pushing radially outward (direction310) on the first segments254causes the first segments254to wedge between the second segments256and to push them radially outward also. The segmented bead molding ring252is radially expandable from a retracted outside diameter Dr(outlined inFIG. 6Bwith a dotted circle) to an expanded outside diameter De. The retracted outside diameter Dris less than or equal to the inside diameter D4′ (seeFIG. 2) of an unmolded bead112b′ that is to be molded by the segmented bead molding ring252. When expanded to the expanded outside diameter De, the segmented bead molding ring has a circumferentially continuous radially outward-facing surface259for molding the bead112b′, typically to form the bead base124b.

Finally, for molding the rest of the inner cavity of the tire110, a vulcanizing membrane210is used, membrane vulcanizing being a long used and proven technique. Also, the mold200utilizes multiple sectors201(e.g., sixteen sectors), movable relative to the sidewall plates202, to mold the outer surface of a tread116.

The mold200is used in conjunction with a press220comprising a base206on which is fixed the bottom sidewall plate202b, and a center post204. The press220also comprises a movable frame (not shown), also called the top frame, to which is fixed the top sidewall plate202a. Here, certain parts of the press220, mold200, and tire110are referred to by the adjectives “bottom” and “top” to correspond to the usual terminology, because the presses are generally built to receive a mold positioned with its axis vertical. Of course, the “bottom” or “top” description of parts of the press220, mold200, and tire110is not limiting, and these is terms are employed only to use conventional terminology.

The mold200uses a symmetrical vulcanizing membrane210, but the symmetry of the membrane is not restrictive. The top end of the vulcanizing membrane210is clamped between the top bead molding ring230and a top clamp ring208athat is movably attached to the center post204. At its bottom end, the vulcanizing membrane210is clamped between a bottom lock ring266, and a bottom clamp ring208bthat is movably attached to the center post204by a hub209that slides up and down (axially). The bottom lock ring266has a special shape (frustraconical) and function according to the invention, as will be described hereinbelow.

The press220generally includes other standard elements, not illustrated but well known, that supply vulcanizing heat and pressure, as well as providing required motions to the parts of the mold200and press220. In particular, the hub209is generally caused to slide up and down on the center post204at various times during the molding process. The present invention utilizes this standard movement capability to drive the expansion and retraction of the inventive segmented bead molding ring252.

The inventive molding process will now be described with reference toFIGS. 2-5, which illustrate key steps of the process.

First, as illustrated inFIG. 2, an unmolded, unvulcanized tire110′ is loaded down into the mold200, which is in an opened, loading state. The vulcanizing membrane210is deflated and folded inward out of the way, and the tread sectors201(not shown) and upper sidewall plate202a(not shown) are also moved to a non-obstructing position, according to standard practice. The unmolded lower bead112b′ has an inner diameter D4′ that is large enough to pass over the continuous top bead molding ring230that has a maximum outside diameter D2, which is less than or equal to the diameter D4′. This allows the non-segmented, non-expandable top bead molding ring230to be axially inside the unmolded top bead112a′. The unmolded bottom bead112b′ comes to rest in a bead molding portion of the bottom sidewall plate202b, after passing over the bottom, segmented bead molding ring252so that the segmented bead molding ring252is axially inside the unmolded bottom bead112b′. The segmented bead molding ring252is retracted (as shown in FIG.6B), as allowed by a vertical upward movement of the bottom lock ring266that is pulled upward by the bottom clamp ring208band hub209to which the bottom lock ring266is attached. The retraction of the segmented bead molding ring252is driven by springs as detailed hereinbelow.

Next, as illustrated inFIG. 3, the segmented bead molding ring252is radially expanded (as shown inFIG. 6a), wedged radially outward in reaction to a vertical downward movement of the bottom lock ring266that is pushed downward by the bottom clamp ring208band hub209to which the bottom lock ring266is attached. In the expanded state, the segmented bead molding ring252places its circumferentially continuous bead molding surface259in a position to work with the adjacent bottom sidewall plate202bto form a bottom bead molding pocket240bthat will mold all surfaces of the bottom bead112b′ except the interior surfaces that are moldable by the vulcanizing membrane210. The segments254,256of the segmented bead molding ring252are restricted to move only in a radial direction by guide rods260as detailed hereinbelow.

The radial-only expansion of the segmented bead molding ring252is a feature of the present invention. As illustrated inFIG. 2, the unmolded bead112b′ has a poorly defined shape that may extend to an inner diameter D4′ that is somewhat less than the final, molded inner diameter D4. As a result, a portion of the unmolded bead112b′ may extend radially inward over a surface203of the bottom sidewall plate202b. With expandable bead molding rings that pivot down into place, a portion of the bead112b′ could become pinched between the ring and the bottom sidewall plate surface203. As seen in the transition fromFIG. 2toFIG. 3, the radially expandable bead molding ring252of the present invention slides radially outward across the surface203, thereby pushing the unmolded bead112b′ into the bottom bead molding pocket240bwithout pinching any of it.

Next, as illustrated inFIG. 4, the vulcanizing membrane210is inflated within the unmolded tire110′. The bottom bead112bis held in the bottom bead molding pocket240bby the segmented bead molding ring252. Finally, as illustrated inFIG. 5, the molding of the tire110is completed in a conventional manner, closing the mold200around the tire110by moving the tread-molding sectors201and the top sidewall plate202ainto place. Pressure and heat are applied in conventional manner, utilizing the mold press220and the vulcanizing membrane210. When the top sidewall plate202ais in place, it works with the adjacent continuous bead molding ring230to form a top bead molding pocket240athat will mold all surfaces of the top bead112aexcept the interior surfaces that are moldable by the vulcanizing membrane210.

With reference toFIGS. 6A,6B,7A,7B,8, and9, details of the inventive radially expandable bead molding ring assembly250will be presented. In general, the key elements of the bead molding ring assembly250are the segmented bead molding ring252comprising first segments254and second segments256(seeFIGS. 6A,6B); guide rods260(FIGS. 7A,8); springs268(FIG.7B); and the bottom lock ring266(FIGS. 7A,7B,8). The elements of the bead molding ring assembly250are readily removable, so that some or all of the elements may be easily changed according to the desired dimensions and profile to be molded on the corresponding bead of the tire. The segmented bead molding ring252is assembled with the bottom sidewall plate202bby means of the guide rods260, so that mold changeover is greatly simplified: the bottom sidewall plate202band the segmented bead molding ring252are simultaneously changed out since they are attached together. The bottom lock ring266is usable with a variety of segmented bead molding rings252that have different bead molding surfaces259and different expanded outside diameters Debut, if desired, the bottom lock ring266can also be easily removed by un-bolting it from the bottom clamp ring208b.

FIG. 6A, also discussed hereinabove, shows a top view of the segmented bead molding ring252in its expanded state. A cross-section taken along the9—9line is shown inFIG. 9, which illustrates a cross-sectional profile common to both the first segments254and the second segments256. In the preferred embodiment, the first segments254and the second segments256differ only in their circumferential extent and in the orientation of their circumferentially lateral faces255and257, respectively, as discussed hereinabove. The solid lines inFIGS. 6A and 6Brepresent profile edges or corners that are visible in top view, and the dashed lines represent edges or corners that are hidden. In the cross-sectional view ofFIG. 9, it can be seen that the radially inner surface of the segmented bead molding ring252is a cam surface258that slopes radially inward and axially outward (downward as illustrated), at an angle θ to form an annular surface complementary to a frustraconical section. The radially outermost surface of the segmented bead molding ring252is the bead molding surface259, typically shaped to mold the bead base124b. The bead molding surface259may be any desired shape, possibly including a tip270to provide multiple angles to the bead base124b, for example the bead base angles α and β illustrated inFIG. 1for the prior art tire10.

Also visible inFIGS. 6A and 6Bare holes272for mounting the guide rods260(one in each of the segments254and256); and spring pockets274for seating the springs268(two in each of the segments254and256). Reference numbers272and274are shown for one each of the segments254and256inFIG. 6A, but should be understood to apply similarly to all of the segments254and256inFIGS. 6A and 6B. The utility of the holes272and spring pockets274will become evident in the discussion hereinbelow ofFIGS. 7A,7B, and8.

FIGS. 7A,7B and8are detailed “close-up” cross-sectional views of the radially expandable bead molding ring assembly250of the mold200.FIGS. 7A and 7Bshow the assembly250with the segmented bead molding ring252in the retracted state as inFIGS. 6B and 2, andFIG. 8shows the assembly250with the segmented bead molding ring252in the expanded state as inFIGS. 6A and 3,4and5.FIG. 7Ais a cross-section taken radially through the center of the hole272in a typical segment (e.g., first segment254) of the segmented bead molding ring252.FIG. 7Bis a cross-section taken radially through the center of the spring pocket274in a typical segment (e.g., first segment254) of the segmented bead molding ring252. Although the first segment254is shown in the illustrations and discussion ofFIGS. 7A,7B and8, it should be understood that the same elements are present in a similar fashion in the second segments256.

FIG. 7Bshows the spring268residing in a radially aligned spring holding hole275bored in the bottom sidewall plate202b. The spring holding hole275is aligned with one of the spring pockets274of the segment254, so that the spring268can be positioned with one end in the spring holding hole275and the other end in the spring pocket274. The spring268is one of two such springs268for the segment254, one on either side of the guide rod260, and the pair of springs268are compression springs designed to apply (as a pair) sufficient force in a radial direction to push the segmented bead molding ring252radially inward to a retracted position as shown inFIGS. 2,6B,7A and7B. InFIG. 7B, it can be seen that the frustraconically-shaped bottom lock ring266is in a raised position that allows the segmented bead molding ring252to retract, i.e., move radially inward toward the center post204.

FIG. 7Ashows the guide rod260mounted in a radially aligned mounting hole272bored in the segment254. The guide rod260is held in place by a drive pin264. The mounting hole272is aligned with a guide hole273bored in the bottom sidewall plate202b. The radially-aligned guide rod260slides within the radially-aligned guide hole273, thereby confining the segments254,256of the segmented bead molding ring252to movement only in radial inward and outward directions. Adjoining below a suitable portion of the guide hole273, a cavity276is cut into the bottom of the bottom sidewall plate202b. A stop bolt262is screwed into the underside of the guide rod260in order to provide a limit to the radially inward movement of the segment254when the stop bolt262stops against a stop surface277on the radially inward side of the cavity276. This limiting effect provides a way to keep the bottom sidewall plate202b, the segments254,256, the guide rods260(with pins264and stop bolts262), and the springs268all together as a mold assembly280that can be easily changed out as a whole during mold changeover. Disassembly requires only the removal of the stop bolts262. The limiting effect of the stop bolts262also keeps the segmented bead molding ring252from falling apart (retracting too far under spring action) whenever the bottom lock ring266is raised too much, for example, when the bottom lock ring266and bottom clamp ring208bare removed in order to maintain the vulcanizing membrane210. Furthermore, the stop bolts262can be used to define a stopping point for the retracted state of the segmented bead molding ring252, i.e., to stop the segments254,256in the positions shown inFIG. 6B, with a maximum outside retracted diameter Drthat is less than or equal to the minimum inside diameter D4′ of the tire bead to be molded. It should be noted that it is within the scope of the invention to have stop bolts262on the guide rods260of: all of the segments254,256of the segmented bead molding ring252; on none of the segments254,256; or on some of them (preferably only on the first segments254, since they, in turn, control radial movement of the second segments256).

FIG. 8shows the segmented bead molding ring252in the expanded state, i.e., as shown inFIGS. 3-5and6A. The downward movement (axially outward, in the direction indicated by arrow320) that the mold press220imparts to the hub209and the bottom clamp ring208bis utilized to also move the bottom lock ring266downward (direction320). The bottom lock ring266wedges the first segment254radially outward in the direction indicated by arrow310, the only direction of movement allowed by the radially aligned guide rods260. As noted hereinabove with reference toFIGS. 6A and 6B, the second segments256are in turn wedged radially outward by the first segments254. It can be seen fromFIGS. 6A and 6Bthat the bottom lock ring266will not contact the cam surface258of the second segments256until the segmented bead molding ring252is fully expanded as in FIG.6A. The bottom lock ring266is preferably a ring with a frustraconical radially outer cam surface267(best seen inFIG. 7A) that has a cam angle θ that matches the cam angle θ of the complementary cam surface258(seeFIG. 9) of the segments254,256of the segmented bead molding ring252. It is within the scope of the present invention to construct alternate embodiments wherein the frustraconical cam surface267of the bottom lock ring266is replaced by other devices that interact with the cam surfaces258of at least the first segments254to wedge the first segments outward (direction310) as the hub209is moved downward (direction320). For example, cam rollers (not shown) could be attached to the hub209so that they roll against the cam surfaces258of at least the first segments254.

InFIG. 8it can be seen that as a result of wedging the segmented bead molding ring252radially outward to a fully expanded state, the segment254(and256), in combination with the bottom sidewall plate202b, and the vulcanizing membrane210(not shown) forms a bottom bead molding pocket240bthat will completely surround a tire bead112b′ (not shown) to mold it on all sides to the desired profile. By comparison withFIG. 7A, it can be seen that the bead molding surface259of the segment254has moved radially over the surface203of the bottom sidewall plate202b, thereby forming an unmolded bead112b′ without pinching it. The guide rod260has moved into the guide hole273, thereby moving the stop bolt262into the cavity276away from the stop surface277. Outward movement of the segments254,256of the segmented bead molding ring252is stopped when the ring252reaches the fully extended state, preferably by causing the segments254,256to stop against the bottom sidewall plate202b. For example, as best seen inFIG. 7A, an outer stop surface278(also shown inFIG. 9) of the segments254,256can stop against an inner surface242of the bottom sidewall plate202b.

Thus has been described an inventive tire mold with an inventive radially expandable bead molding ring and an inventive method for molding tires using the inventive mold. The expandable bead molding ring252has been simplified over prior art expandable rings, its expansion being only in the radial direction, driven by a simple wedging action caused by a single ring-shaped cam266. The elements of the expandable bead molding ring252are combined with the sidewall molding plate202bto form a mold assembly280that is easily maintained and easily switched in a mold press220to adapt to different profiles to be molded on beads of different tire constructions.

Although the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character—it being understood that only preferred embodiments have been shown and described, and that all changes and modifications that come within the spirit of the invention are desired to be protected. Undoubtedly, many other “variations” on the “themes” set forth hereinabove will occur to one having ordinary skill in the art to which the present invention most nearly pertains, and such variations are intended to be within the scope of the invention, as disclosed herein.