Molding a tread belt for a two-piece tire

A tread belt is molded and cured in a mold having a base plate and an inverted cup-shaped top plate. A plurality of inner segments are disposed in the mold. When the mold is closed outer surfaces of the inner segments form a cylindrical surface which is in contact with an inner surface of the tread belt. A first portion of the inner segments are follower segments, a second portion of the inner segments are leader segments, and means are provided for controlling radial movement of the inner segments. A plurality of outer segments are disposed in the mold. When the mold is closed the inner surfaces of the outer segments form a cylindrical surface which is in contact with an outer surface of the tread belt, and means are provided for controlling movement of the outer segments.

TECHNICAL FIELD OF THE INVENTION

The invention relates to the fabrication of tires, particularly pneumatic tires, more particularly large earthmoving tires, more particularly to molding the tread belt component of a two piece tire such as a large earthmoving tire.

BACKGROUND OF THE INVENTION

A pneumatic tire generally comprises a carcass (or “casing”), a tread, sidewalls and bead regions. The tread belt is generally cylindrical, having an inner diameter, an outer diameter, a height, and an overall thickness. A number of belt components, also generally cylindrical, may be incorporated into the tread package. For passenger car and light truck tires, all these components are molded into a single tire. “Green” uncured tire components are laid up on a build drum which is expanded to form the casing, then the casing is put into a mold where the tread is applied and the tread pattern is molded into the external surface of the tread package.

Earthmoving tires are very expensive, and since the tread typically wears out before the casing (or “carcass”) wears out, a separate “tread belt” component is designed to be removable and replaceable. This forms what is known as a “two piece” tire. Often in a two piece tire, the inner surface of the tread belt is molded to have circumferentially-extending grooves which are spaced apart and parallel with one another and which mate with circumferentially-extending ridges on the outer surface of the tire carcass. The grooves and ridges may be appropriately tapered to facilitate the ridges inserting firmly into the grooves. Generally, the expansion of the tire carcass when it is inflated holds the tread belt in place, and the mating grooves and ridges help prevent the tread belt from moving axially with respect to the tire carcass. The large surface area of contact between the tread belt and the coefficient of friction, prevents the tread belt from spinning circumferentially upon the carcass.

Two piece, tread belt pneumatic tires are currently typically very large tires (greater than 119.9 inches outside diameter (OD)) generally designed for use on very large vehicles, generally off-the-road vehicles such as earthmovers and large capacity mining trucks (e.g., 300 short tons or more). The size of these tires is extremely large. For an example, the tire weight can be approximately 8,000 pounds (3,628 kg) to 15,000 pounds (6,803 kg) or more for an unmounted tire. When using a two-piece type tire wherein the tread belt forms the outer structure and the inner structure is formed by a carcass wherein the two parts are separable, the tread belt alone will weigh over 4,000 pounds typically, many times more depending on the size. By way of example, a 57 inch nominal rim diameter two-piece tire having a 45R57 size will have a tread belt assembly having an outside diameter of approximately 12 foot or roughly 144 inches and will weigh approximately a little more than 4,500 pounds. Likewise, a smaller but still very large 51 inch nominal rim diameter tire of a 3300R51 size can yield a 3000 lb. tread belt.

FIG. 1illustrates a generic two piece pneumatic tire100having a carcass comprising two sidewalls and a crown extending between radially outer ends of the sidewalls. Beads are disposed in a bead region at the radially inner ends of the sidewalls. A tread belt is disposed around the crown. The tire has a centerline CL which will be coincident with its axis of rotation. The tire has an equatorial plane EP and is generally symmetrical about the EP. The tire has an inner diameter (d1) which is essentially the diameter of a rim (not shown) to which the tire will be mounted. The tire has an outer diameter (d2) which is the outer diameter of the tread belt when properly mounted on the tire carcass. The tire has a width (W1), from sidewall-to-sidewall (or, across the tread belt). At the left hand side ofFIG. 1, the tread belt is shown spaced apart from the crown (exploded view) for illustrative clarity. Here can be seen the ridges and grooves on the inner surface of the tire belt, and the corresponding (mating) grooves and ridges on the outer surface of the crown portion of the tire. This is all well known.

Presently, tread belts are laid up and cured in individual cure stations. These stations are costly to build, maintain, and operate. These stations can also produce only one specific type of product and generate only a quantity of one product at a time. In the molding concept that will be hereunto declared, the functionality of which, in combination with the conventional means of a pot-heater, replaces that of these costly cure stations. The current process calls for great energy utilization within the cure station to procure the belts in addition to great energy utilization in the pot heater to procure the casings. Utilization of the pot heater allows for greater flexibility of product cure variation and reduces the amount of energy needed to cure both products needed to produce the two-piece tire.

SUMMARY OF THE INVENTION

It is an aspect of the invention to provide an improved technique for forming a removable/replaceable tread belt for two piece (tread belt type) tires, such as large pneumatic earthmoving tires.

According to the invention, a mold apparatus for molding a tread belt component of a two-piece tire, comprises: a generally planar, generally circular base plate having an inner surface and an outer surface; and a cup-shaped top plate having a generally planar base portion and a generally cylindrical sidewall portion extending downward from a periphery of the base portion, the top plate having an inner surface and an outer surface. The mold has a centerline (CL), the base plate is concentric with the centerline, and the top plate is concentric with the centerline. A chamber is formed under the top plate when mold is in a closed position (FIG. 2B). Means are provided for supporting a green tread belt within the mold, concentric with the centerline (CL) of the mold.

A plurality (n1) of inner segments are disposed in the mold, each inner segment comprising a generally elongate element comprising a top surface, a bottom surface, an inner surface and an outer surface, and two opposite side edges.

When the mold is in a closed position (FIG. 2B,FIG. 3D) the outer surfaces of the inner segments form a substantially continuous, cylindrical surface which is in contact with an inner surface of the tread belt.

According to a feature of the invention, the outer surface of the inner segments is patterned with ridges and grooves which will mold corresponding grooves and ridges into an inner surface of the tread belt.

A first portion of the inner segments are follower segments, a second portion of the inner segments are leader segments. Means are provided for controlling radial movement of the inner segments.

In an embodiment of the invention, the means for controlling radial movement of the inner segments comprises a driving shaft having a nominal diameter a strike plate at a top end of the driving shaft; a catch plate disposed below the top end of the driving shaft and having a diameter greater than the nominal diameter of the driving shaft; first resilient means disposed about the driving shaft below the catch plate and having a first spring constant (k1); a collar disposed about the driving shaft, below the first coil spring having a diameter greater than the nominal diameter of the drive shaft and being free to move axially on the driving shaft; second resilient means disposed about the driving shaft below the collar and having a second spring constant (k2) which is greater than the first spring constant (k1); a first set of linkage beams extending from between the strike plate and the catch plate of the driving shaft to the follower segments, and forming an angle theta (θ) with respect to horizontal; and a second set of linkage beams extending from the collar of the driving shaft to the leader segments and forming an angle omega (Ω) with respect to horizontal.

According to a feature of the invention, the opposite side edges of the follower segments are tapered slightly outwardly with respect to a radial direction from the centerline, and the opposite side edges of the leader segments are tapered slightly inwardly with respect to the radial direction from the centerline.

A plurality (n2) of outer segments are disposed in the mold, each outer segment comprising a generally elongate element comprising a top surface, a bottom surface, an inner surface, an outer surface, and two opposite side edges. When the mold is in its closed position (FIG. 2B) the inner surfaces of the outer segments form a substantially continuous, cylindrical surface in intimate contact with an outer surface of the tread belt. Means are provided for controlling movement of the outer segments radially inward and outward, with respect to the centerline (CL). These means comprise a tapered inner surface of the sidewall portion of the top plate; and a tapered outer surface of the outer segments. T-shaped slots are formed in the outer surface of the outer segments, and corresponding features extending from an inner surface of the sidewall portion. A number of lugs may be disposed on the inner surface of selected ones of the outer segments for forming a tread pattern in the tread belt.

According to the invention, a method is provided for molding a tread belt for a two piece tire, comprising the steps of: with a mold in an open position, loading a green tread belt into the mold; then closing the mold; then disposing the closed mold in a pot heater; then curing the green tread belt; and then opening the mold and removing the cured tread belt.

According to a feature of the invention, another mold may be disposed in the pot heater for curing another green tread belt for the tire; and a carcass for the tire may be disposed in the pot heater for curing.

The invention allows for curing of tread belts in a pot-heater environment that currently exists without having to create or develop cure stations. This has potential to be more practical and cost effective than investment into additional cure stations. In fact, the belt (or two belts, in keeping the two belts sold for every casing philosophy. One can stack many molds into a pot-heater.) may very well may be able to be cured at the same time as the tire to which the product will eventually be mated. This provides the ability to cure two belts and one casing in the same time and using the same energy as what it takes to cure just one casing now.

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

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2A and 2Billustrate a mold200for molding a tread belt210(compare110) for a two piece tire, such as a large earthmoving tire. InFIG. 2A, the mold200is shown in an “open” (OPEN) position. InFIG. 2B, the mold200is shown in a “closed” (CLOSED) position. FIGS.3A,B,C,D illustrate in further detail the operation of the mold200.

The mold (molding apparatus)200generally comprises a base, or bottom plate202and a top plate, or actuating ring204.

The base plate202is generally planar, and may be generally circular, having a diameter (D1). The base plate202is preferably disposed horizontally, as illustrated inFIGS. 2A and 2B. The base plate202has an inner surface202aand an outer surface202b.

The top plate204is generally in the form of an inverted cup (cup-shaped) having a generally planar base portion204cdisposed horizontally (i.e., generally parallel to the base plate102) and a generally cylindrical sidewall portion204dextending downward from a periphery (circumference) of the base portion204a. (The sidewall portion204dis tapered, as described hereinbelow.) The top plate204has an inner surface204aand an outer surface204b. The top plate204has a diameter (D2) which is approximately equal to the diameter (D1) of the base plate202. The sidewall portion204dextends vertically downward (vertical in the figures) a distance H (height). The base portion204cof the top plate204may also be generally circular, parallel to the generally circular base plate, both of which are concentric with a centerline (CL) of the mold200.

As best viewed inFIG. 2B, when the mold is in its closed position (CLOSED POSITION),

a chamber216is formed under the top plate204, between the inner surface204aof the top plate204and the inner surface202aof the bottom plate202. In the process of curing the tread belt210(described in greater detail hereinbelow), the entire mold assembly200is disposed in a “pot heater” which provides a high temperature ambient environment with steam, comparable to that of a large-scale “pressure cooker”. Although the mold is not completely airtight in the CLOSED POSITION, a plurality of steam inlets (openings)203are provided through the bottom plate202, and a plurality of steam inlets (openings)205are provided through the top plate204to facilitate steam entering the chamber216of the mold200. An external mechanism is provided for urging the top plate204down onto the bottom plate202, as indicated by the arrow206, thereby “closing” the mold200.

The overall purpose of the mold200is to mold a tread pattern into and cure a tread belt210(compare110) for a pneumatic tire. As will become evident, a plurality of molds are conveniently disposed in a pot heater (not shown) for simultaneously molding and curing a plurality of tread belts.

The tread belt210(or110is more direct to the immediate product & dimensions) is essentially a continuous cylindrical belt having a width dimension W1(vertical inFIGS. 2A,2B) and a thickness dimension T (horizontal inFIGS. 2A,2B). The tread belt210comprises layers of elastomer, as well as belt plies. In its raw (green) state, the tread belt210is essentially a cylinder of green rubber, having a generally planar inner surface and a generally planar outer surface, rectangular in cross section, and is disposed in the mold200concentric with the centerline (CL) of the mold.

A plurality n1of inner segments220are disposed in the mold200. The inner segments220each have a top (towards the top plate204) surface, a bottom (towards the bottom plate202) surface, an inner (towards the centerline CL) surface and an outer (towards the tread belt210) surface. (It is no particular significance that the inner surfaces of the inner segments are illustrated as being tapered.) The inner segments220also have two opposite side edges, better viewed inFIGS. 3A-3D. The inner segments220are generally elongate elements having a height W2which is slightly greater than the width W1of the tread belt. Each of the 12 inner segments extends approximately 30 degrees (360/n1) around the inner circumference of the tread belt. As described in greater detail hereinbelow, the inner segments220move radially outward and inward (with respect to the centerline CL). When all of the inner segments220are moved outward, their outer surfaces form, in aggregate, a substantially continuous, cylindrical surface (mandrel) which is in intimate contact with the inner surface of the tread belt210, for holding and molding the inside surface of the tread belt210. InFIG. 2A, the inner segments220are shown retracted slightly, such as a radial distance R1from the inner surface of the tread belt210.

There are preferably an even number, such as twelve (12) inner segments220. For example, six (6) odd-numbered segments221and six (6) even-numbered segments222. The even-numbered segments222, shown to the right of the drawing, are referred to as “leader” segments, and the odd-numbered segments221, shown to the left of the drawing, are referred to as “follower” segments, for reasons which will become apparent from the description set forth hereinbelow. As best viewed inFIGS. 3A-3D, the odd-numbered follower segments221alternate with the even-numbered leader segments222. InFIGS. 3A-3D, the side edges of the segments220can be seen.

The tread belt210is initially held in place (supported) within the mold200by an annular (segment) lip extending radially outwardly from the outer surface of each of the inner segments220(221,222), forming a “shelf” supporting the tread belt210at its bottom edge. This could also be achieved by a “bolt-in” ring in place of a lip or “shelf” extension from the inner segments.

When the mold is closed (CLOSED POSITION), as illustrated inFIG. 2B, the inner segments220all expand (move radially outward) into intimate contact with the tread belt210. The outer surface of the segments220is patterned with ridges and grooves which will mold corresponding grooves and ridges into the inner surface of the tread belt210. The mechanism for controlling movement of the inner segments220is described hereinbelow. To facilitate the radial movement of the inner segments220, a sliding surface224is disposed on the inner surface202aof the bottom plate202. The sliding surface224may simply comprise aluminum-bronze or some other comparable material. The inner segments220are all disposed (supported) on the sliding surface224. Since the inner segments220all move radially outward (and inward), slots (or the like) can be incorporated in to inner surface202aof the bottom plate202, and corresponding features formed on the bottom surfaces of the inner segments220to limit anything other than radial movement of the inner segments220.

A plurality n2of outer (outside) segments230are disposed in the mold200. The outer segments230each have a top (towards the top plate204) surface, a bottom (towards the bottom plate202) surface, an inner (towards the centerline CL) surface and an outer (away from the centerline CL) surface. The outer segments230also have two opposite side edges. The number n2of outer segments230is independent of the number n1of inner segments220. For purposes of this discussion, there are twelve (12) outer segments230. The outer segments230are generally elongate elements having a height W3which is slightly greater than the width W1of the tread belt210. Each of the twelve outer segments extends approximately 30 degrees around the outer circumference of the tread belt. As described in greater detail hereinbelow, the outer segments230move radially inward and outward (with respect to the centerline CL). When all of the outer segments230are moved inward, their inner surfaces form a substantially continuous, cylindrical surface (mandrel) which is in intimate contact with the outer surface of the tread belt210, for molding the outer surface of the tread belt210. InFIG. 2A, the outer segments230are shown retracted slightly, such as a radial distance R2from the outer surface of the tread belt210.

The inner surface204eof the sidewall portion204dis not vertical, but rather is tapered, as shown, for example at an angle of 15-30 degrees, such as 20-25 degrees from vertical, so that the inside diameter of the sidewall portion204dis smaller where the sidewall portion204djoins the base portion204cand greatest where the sidewall portion204dis distal from the base portion204c. The outer surface of the outer segments230is similarly tapered, as shown. These two tapered surfaces cooperate with one an other. The purpose of the tapered surfaces is to impart inward radial movement of the outer segments230, when the actuating ring (top plate) is urged downwards, as described hereinbelow, and to control the radial positioning of the outer segments230. (The tapered surfaces constitute a means for controlling movement of the outer segments230.)

The outer segments230are suitably held in place on the inner surface204eof the sidewall portion204dof the top plate204by T-shaped slots232formed in the outer surface of the outer segments230, and corresponding featured such as T-shaped lugs (or a rail, not shown) extending from (or on) the inner surface204eof the sidewall portion204d. In this manner the outer segments230are free to slide up and down. InFIG. 2A, the mold is in the OPEN POSITION and the outer segments are shown “hanging” from the bottom end of the sidewall of the top plate. (The T-slot232does not extend completely to the top of the outer segment230.) InFIG. 2B, the mold is in the CLOSED POSITION, and the outer segments are shown disposed higher up within the sidewall portion. In the CLOSED POSITION, the outer segments230will rest upon the aforementioned sliding surface224(along with the inner segments220).

As shown inFIGS. 2A and 2B, a number n3of lugs234are disposed on the inner surface of each outer segment230. In the cross-sectional view, only two lugs are visible, but there may for example be as many as six lugs—3 rows of 2 lugs. This is a design choice, depending on the desired tread pattern and the number of outer segments available.

Typically, in the CLOSED POSITION, the inner surfaces of the outer segments230for a continuous cylindrical surface. When the outer segments230are moved radially inward they impress the tread pattern upon the outer surface of the tread belt210.

A Mechanism for Controlling Movement of the Inner Segments220

A mechanism240is provided for causing and controlling the aforementioned radial outward (and subsequent radial inward) movement of the inner segments220(221,222). The mechanism240generally comprises the following components:a driving shaft242;a catch plate243disposed below the top of the driving shaft242;a first coil spring244disposed about the driving shaft242below the catch plate243;a collar246disposed about the driving shaft242, below the first coil spring244;a second coil spring248disposed about the driving shaft242below the collar246;a first set of linkage beams251extending from the driving shaft242to the odd-numbered follower segments221; anda second set of linkage beams252extending from the driving shaft242to the even-numbered leader segments222.

The driving shaft242is an elongate member having a length L, a top end242aand a bottom end242b, and is disposed centrally in the mold200. The driving shaft242has a nominal diameter. A strike plate241is disposed at the top end242aof the driving shaft242, and has a greater diameter than the driving shaft242. The strike plate241can be a separate piece fixed to the top of the driving shaft, or it may simply be a region of increased diameter (like the head of a nail). The top end242aof the driving shaft242is disposed at a height V0above the inner surface202aof the bottom plate202with the mold200in its OPEN position (FIG. 2A).

The catch plate243is disposed below the top242aof the driving shaft242and has a diameter greater than that of the driving shaft242. The catch plate243can be a separate piece fixed to the driving shaft, or simply a region of increased diameter (e.g., a flange).

The first coil spring244is disposed about the driving shaft242below the catch plate243and, as will be seen, is acted upon by the catch plate243when the driving shaft242is moved downwards. (There is a small gap between the top of the spring244and the bottom of the catch plate243.) The first coil spring244has a spring constant (k1) which is generally lower than a spring constant (k2) of the second coil spring248.

The collar246is ring disposed about the driving shaft242below the first coil spring244and, as will be seen, is acted upon by the first coil spring244when the driving shaft242is moved downwards. The collar246has a greater diameter than the diameter of the driving shaft242and is not fixed to the driving shaft but rather is free to “float” (move axially) on the driving shaft.

The second coil spring248is disposed about the driving shaft242below the collar246and, as will be seen, is acted upon by the collar246when the driving shaft242is moved downwards. The second coil spring248has a spring constant (k2) which is generally higher than the spring constant (k1) of the first coil spring244. The second coil spring248rests upon the inner surface202aof the bottom plate202. It is within the scope of the invention that one or both of the coil springs244,248can be replaced by other resilient means, such as but not limited to hydraulic pistons.

The driving shaft242extends through the first coil spring244, through the floating collar246and through the second coil spring248. It may also extend through a hole in the bottom plate202to keep the driving shaft centered within the mold. Or, a spindle (not shown) may extend upwardly from the bottom plate into a central hole in the driving shaft to keep the driving shaft centered within the mold.

A first set of linkage beams251extend from lugs (linkage nodes)253disposed on the driving shaft242to lugs255on the inner surface of the odd-numbered, inner “follower” segments221. The lugs253are between the strike plate241and the catch plate243. The linkage beam251is elongate, having a first inner end pivotally connected to the lug253and a second, opposite, outer end pivotally connected to the lug255. (The numbers253and255may also be used to refer to the corresponding ends of the linkage beam attached to the lugs.) The inner end253is disposed higher in the mold than the outer end255. InFIG. 2A, in the OPEN position, the linkage beam251forms an angle θ0with respect to horizontal. InFIG. 2B, in the CLOSED position, the linkage beam251forms an angle θ1with respect to horizontal (and the inner end253is still higher than the outer end255). The angle θ0is approximately but not limited to 25-35 degrees. Any angle combination can exist. When the driving shaft242is moved downwards, the angle theta θ decreases and the outer end255of the linkage beam251moves radially outward, thereby urging the odd-numbered, inner “follower” segments221radially outwards.

A second set of linkage beams252extend from lugs254disposed on the floating collar246to lugs256on the inner surface of the even-numbered, inner “leader” segments222. The linkage beam252is elongate, having a first inner end pivotally connected to the lug254and a second, opposite, outer end pivotally connected to the lug256. (The numbers254and256may also be used to refer to the corresponding ends of the linkage beam attached to the lugs.) The inner end254is disposed higher in the mold than the outer end256. InFIG. 2A, in the OPEN position, the linkage beam252forms an angle Ω0with respect to horizontal. InFIG. 2B, in the CLOSED position, the linkage beam252forms an angle Ω1with respect to horizontal (and the inner end254is still higher than the outer end256). The angle Ω0is approximately but not limited to 5-20 degrees. When the driving shaft242is moved downwards, the angle omega Ω decreases and the outer end256of the linkage beam252moves radially outward, thereby urging the even-numbered, inner “leader” segments222radially outwards.

Opening and Closing the Mold200

The mold200and its constituent elements have been described. With the mold200in an open position (labeled OPEN POSITION inFIG. 2A), the “green” tread belt210is loaded into the mold, resting on the lips extending radially outwardly from the outer surface of the inner segments220, as described hereinabove. The top half of the mold is then lowered onto the bottom plate and working mechanism of the mold. This mold is then lifted as one piece, possibly along with a stack of other molds, and hoisted into the pot heater. Then the mold is pinched tight typically by raising the bottom plate202upwards by means of an internal pot-heater hydraulic ram pressure (rather than pushing the top plate204downwards), thereby bringing the top and bottom plates together until the sidewall204dof the top plate204contacts the bottom plate202. (In theory, the top plate104can be moved downward onto a stationary bottom plate202, and the description is geared to this possibility since it may be easier to envision.) This is shown inFIG. 2B, labeled CLOSED POSITION. As the mold is closing, a number of things are happening, as follows.

When the mold is closed, the outer segments230move downwards and inwards, as indicated by the intersecting down and inward arrows appearing on the outer segments230inFIG. 2B. As mentioned above, the inner surface204eof the sidewall portion204dis tapered and the outer surfaces of the outer segments230are similarly tapered to that these two tapered surfaces cooperate with one an other to impart inward radial (as well as axial) movement of the outer segments230, when the actuating ring (top plate) is urged downwards, as well as to control the radial positioning of the outer segments230. (The tapered surfaces together constitute a “Mechanism For Controlling Movement Of The Outer Segments230”.) In the CLOSED POSITION, the outer segments230are radially inward and engage the outer surface of the tread belt210so that the tread lugs234form a tread pattern in the outer surface of the tread belt210.

When the mold is being closed, a sequence of events happens with respect to the inner segments220.First, the inner surface204aof the top plate204contacts the strike plate241which is disposed at the top end242aof the driving shaft242and the driving shaft242begins to move downward. This moves the inner ends253of the linkage beams251downward (see arrow adjacent lug253), which will “flatten out” (reduce) the angle theta θ of the linkage beams251, and will urge the inner, odd-numbered follower segments221radially outward (see arrow adjacent bottom of inner segment221). (The height of the outer ends255of the linkage beams251does not vary. It is the height of the lug255to which is it attached. The lug255is fixed to the inner surface of the inner segment221which moves only radially.)Next, the driving shaft242continues to move downward until the catch plate243contacts the first spring244. (There is a small gap between the top of the spring244and the bottom of the catch plate243.) As this is happening, the linkage beams251continue to flatten out and the inner, odd-numbered follower segments221continue to be moved radially outward.Next, the first spring244which is weaker (lower spring constant) than the second spring248compresses, until it bottoms out. As this is happening, the linkage beams251continue to flatten out and the inner, odd-numbered follower segments221continue to be moved radially outward.As this is happening (i.e., the first spring244collapsing), the floating collar246begins to move downward, resisted only by the larger spring248, which begins to compress. When the floating collar246moves downward, this moves the inner ends254of the linkage beams252downward (see arrow adjacent lug254), which will “flatten out” (reduce) the angle omega Ω of the linkage beams252, and will urge the inner, even-numbered leader segments222radially outward (see arrow adjacent bottom of inner segment222). (The height of the outer ends256of the linkage beams252does not vary. It is the height of the lug256to which is it attached. The lug256is fixed to the inner surface of the inner segment222which moves only radially.)As the bottom spring248compresses, this allows the floating collar246to continue to move downward, the result of which is that (i) the linkage beams251continue to flatten out and the inner, odd-numbered follower segments221continue to be moved radially outward, and (ii) the linkage beams252continue to flatten out and the inner, even-numbered leader segments222continue to be moved radially outward. (Since the angle theta θ and angle omega Ω are different than one another, as the driving shaft242and the floating collar246move downward, different amounts of radial motion will be imparted to the follower segments221than to the leader segments222. This is all straightforward, and one having ordinary skill in the art to which the invention most nearly pertains will readily understand what angles will work with each other, and how, based on his given application and the description set forth herein.)Eventually, all of the inner segments220will be fully expanded so that in the CLOSED POSITION, the inner segments220engage the inner surface of the tread belt210so that (i) the tread belt is secured against the force coming in on it from the outer segments and (ii) a desired pattern (e.g., grooves and ridges) is formed on the inner surface of the tread belt210. In other words, the tread belt210is compressed between the inner segments220and the outer segments230.This all continues until either (i) the engagement of the inner and outer segments upon the tread belt disposed therebetween prevents further movement of the inner and outer segments, or (ii) the sidewall204dof the top plate comes to rest against the inner surface202aof the bottom plate202. (Preferably, dimensions and clearances are designed so that (ii) happens before (i).) During all this movement described hereinabove, the tread belt210does not move per se, it just gets radially squeezed (or compressed).With the mold in its CLOSED POSITION, the linkage beam251forms an angle θ1with respect to horizontal. The inner end253is still disposed higher in the mold than the outer end255. The angle θ1is substantially non-zero, such as but not limited to 15 degrees. The linkage beam252forms an angle Ω1with respect to horizontal. The inner end254is still disposed higher in the mold than the outer end256. The angle Ω1is nearly zero, such as but not limited to 5-10 degrees.With the mold in its CLOSED POSITION, the top end242aof the driving shaft242is disposed at a height V1above the inner surface202aof the bottom plate202. The difference between V0and V1(i.e., V0−V1=S) equals the extent S of the vertical movement of the driving shaft242.With the mold in its CLOSED POSITION (FIG. 2G), annular raised feature204g(best viewed inFIG. 2A) which extends downward from the inner surface204aof the top plate204urges downward on top surfaces of the tread belt110. Notice also that the top ends of the inner segments220and the outer segments230extend axially higher than the tread belt210. In these top end regions, the inner and outer segments are formed to have a gap between them when the mold is in its CLOSED POSITION (FIG. 2G) and the annular raised feature204gbecomes disposed in this gap, preventing further closure of the outer segments230onto the inner segments220(i.e., limits how much the tread belt210becomes radially compressed).With the mold in its CLOSED POSITION, the entire mold (200) is disposed in a pot heater to cure the green tread belt210, as discussed in further detail hereinbelow. A corresponding tire carcass (not shown) can also be disposed in the same pot heater for curing, along with one or more additional tread belts for the given carcass.After curing the tread belt, the mold is removed from the pot heater and the sequence is reversed (the top and bottom plates are moved apart), the segments220and230retract, and the cured tread belt210can be removed.

From the above, it can be observed that the follower segments221begin moving before the leader segments222. This is described in greater detail below, with respect toFIGS. 3A-3D.

Operation of the Mold200and the Mechanism240

FIGS. 3A-3Dillustrate the operation of the mold200, from which it can more readily be seen that the mechanism240operates as a kinematic timing device for controlling the timed, sequential movement of the inner segments220(221and222) in response to downward movement of the top plate204upon initial mold closure outside of the pot heater (as mentioned before, typically it is the bottom plate202that moves up during final pinch-off, rather than it being the top plate104which moves down) and consequent downward movement of the driving shaft242. The sequence starts off (FIG. 3A) with the mold200in its OPEN POSITION (FIG. 2A). The sequence finishes (FIG. 3D) with the mold200in its CLOSED POSITION (FIG. 2B). The sequence can then be reversed, starting withFIG. 3Dand finishing withFIG. 3Aat the end of the process, to remove the tread belt210(not shown).

In these figures, the outermost circle (solid line) represents the substantially cylindrical surface formed by the outer surfaces of the inner segments230when they are fully expanded, in the CLOSED POSITION (FIG. 2B). (Or, the outermost circle represents the inner surface of the tread belt210.) The other, concentric dashed circles are included as an aid to the reader, to judge distances. Various angles around the circle are also set forth, as an aid to the reader.

Each figure shows six follower segments221alternating with six leader segments222. Each segment221and222spans approximately 30 circumferential degrees. For example, the follower segment221at the top of the figures spans 30 degrees between 345° and 15°. The leader segments222to the left and right of that follower segment span 30 degrees between 315° and 345° and 15° and 45°, respectively.

It can be seen that the follower segments221have a slightly different profile than the leader segments222. The opposite side edges of the follower segments221are tapered slightly outwardly (with respect to radial), and the side edges of the leader segments222are tapered slightly inwardly, so that they can “merge” (move radially outwardly) to their most radial outward position without crashing into each other.

Each figure shows six linkage beams251connecting to the six follower segments221, and six linkage beams252connecting to the six leader segments222. In some of the figures, one or both of the linkage beams251,252are shaded. The shading indicates vertical movement of the linkage.

InFIG. 3A, the inner segments220are shown in their open position. The follower segments221are more inward than the leader segments220. Neither of the linkage beams251,252are shaded in this figure.

InFIG. 3B, it can be seen that the follower segment221begins to move first when the top plate204engages the driving shaft242, as described above. The leader segments222have not yet moved. Note in this figure that only the linkage beams251to the follower segments221are shaded.

FIG. 3Cillustrates that the leader segments222begin to move as the top plate204pushes the driving shaft242further down and the floating collar246engages the lower spring248. After the floating collar246engages the lower spring248, both sets of inner segments221and222are moving (note that all of the linkage beams252,252are shaded in this figure). It should be noted that although the leader segments222are the second to start moving, they will be the first to arrive at their final (radial outward) position.

InFIG. 3D, the segments320(321,322) are shown in the CLOSED POSITION (FIG. 2B). In the CLOSED POSITION, the outer surfaces of the inner segments320cooperate to form a substantially continuous, substantially cylindrical surface (outer, solid line circle,FIG. 3A) for molding the inner surface of the tread belt (210). Although not shown, with the mold in its CLOSED POSITION, the inner surfaces of the outer segments (230) cooperate to form a substantially continuous substantially cylindrical surface for molding the outer surface of the tread belt (210).

With the tread belt210loaded, the inner segments220radially expanded (pressing radially outwardly on the inner surface of the tread belt210), the outer segments230radially contracted (pressing radially inwardly on the outer surface of the tread belt210), the mold200is put into a pot heater (not shown) and essentially cooked—i.e., exposed to steam heat and pressure for a period of time and the tread belt210becomes cured.

Then, the mold200can be removed from the pot heater, and opened. When opening the mold, the inner segments will retract, so that the cured tread belt can be removed. It should be noted that, when retracting (whole sequence in reverse), the follower segments221will be the first to retract (i.e., before the leader segments222). When opening the mold200, the outer segments230will also retract.

Exemplary Dimensions and Parameters

By way of example, the mold200is suitable for molding a tread belt for an exemplary two-piece 37R51 tire having the following dimensions and parameters for the mold components (and tire components) are exemplary and approximate, and are intended to convey a sense of proportion (relative scale):the outer diameter d2of the tire100: 100″ Dia. (302.51 cm)the inner diameter d1of the tire100: 57 inches (140 cm)the width W1of the tread belt210: 35″ (89 cm)the thickness T of the tread belt210: 5.6″ (14.2 cm)the diameter D1of the bottom plate202: 145-165″ (368-419 cm)the diameter D2of the top plate204: 140-145″ (356-368 cm)the height H of the top plate sidewall204d: 50-65″ (127-165 cm)the number n1of inner segments220: 8-14, such as 12the height W2of the inner segments220: 40-50″ (102-172 cm)the number n2of outer segments230: 8-14, such as 12the height W3of the outer segments230: 40-50″ (102-172 cm)the number n3of lugs per outer segment230: 6the length L of the driving shaft242: 50-65″ (127-165 cm)the radial distance R1between the inner segments220and the inner surface of tread belt210when the segments are retracted (FIG. 2A): Leader=1.5″-2.0″ (4-5 cm); Follower=5″-8″ (13-20 cm)the radial distance R2between the outer segments230and the outer surface of tread belt210when the segments are retracted (FIG. 2A): 12-18″ (31-48 cm)the angle θ025-35 degreesthe angle θ110-20 degreesthe angle Ω05-20 degreesthe angle Ω12-15 degreesthe extent S (S=V0−V1) of the vertical movement of the driving shaft242: 9-12″ (23-30 cm)

The invention has been illustrated and described in a manner that should be considered as exemplary rather than 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 techniques 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.