CUSTOM PRE-CURED RETREAD

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to retread tires and more specifically, to retread tires having tread bands matched to the prepared base tread. In particular embodiments, the prepared base tread has a thickness that is variable and asymmetric.

2. Description of the Related Art

When tires become worn, they can be restored with new tread. Large truck tires and bus tires, for example, are typically retreaded as part of a routine tire-management program. The carcass of these types of tires is often expected to last several hundred thousand miles and be amenable to having a new tread adhered to it several times. Such tires can be quite expensive and are therefore bought with the expectation that their high initial costs are offset by the long service life of the carcass and the low comparative cost of retreading. Indeed, the economics included in the selection and purchase of such tires often dictate that the original tires be capable of being retreaded as many as three or four times or more.

A variety of procedures and different types of equipment are available for use in recapping or retreading pneumatic tires. One of the first steps in retreading a worn tire is to remove remaining tread material from the tire carcass, for example, by a procedure known as buffing. Next a layer of green (uncured) rubber, known as “cushion gum,” may be applied to the carcass. This layer of uncured rubber may be extruded directly onto or applied as a sheet and rolled (stitched) onto the carcass. Next, a tread band is applied atop the layer of cushion gum.

In the cold recapping or retreading process, the tread band is made of cured rubber, and has a tread pattern already impressed in its outer and/or inner surface. Such precured bands, as the term is used herein, refer to tread bands that have been cured either fully or to some lesser extent but have undergone to some extent a curing process. The tire is then placed in an autoclave, and heated under pressure for an appropriate time to induce curing of the cushion gum layer, and bonding of the gum layer to the tread and the carcass.

In the hot recapping or retreading process, the tread is made of uncured rubber and typically may have no or very little tread pattern when initially placed on the tire carcass. The tire with the uncured tread is placed in a tire mold and heated under pressure for an appropriate time to cure the gum layer and the tread, to mold the tread with the desired tread pattern, and to cause the gum layer to bond with the tread and the carcass. The term “cure” refers to the formation of cross-links between the elastomer molecules in the rubber compound, otherwise known as vulcanization.

Buffing the old tread off of the tire in preparation of the retreading process removes rubber that is discarded as waste or as a low value by-product. Much of this waste rubber that is removed in preparation for retreading is typically replaced during the retreading process as part of the new tread band and cushion gum that is bonded to the carcass during retreading. It would be advantageous if the amount of rubber that is discarded could be reduced.

SUMMARY OF THE INVENTION

Particular embodiments of the present invention include retreaded tires and methods and apparatus for their manufacture. Such embodiments include a retreaded tire, the retreaded tire including a tire carcass having a bonding surface forming an outer surface of the tire carcass extending both circumferentially and laterally about the tire, the bonding surface being arranged along a base layer, the base layer being positioned between the bonding surface and a belt reinforcement package, where the base layer has includes at least one base groove open to the bonding surface, the base layer having a thickness that is variable and asymmetrical about a centerline of a tread width of the tire. The retreaded tire may further include a bonding layer arranged along the bonding surface of the tire carcass, the bonding layer having a thickness that is variable and asymmetrical about a centerline of a tread width of the tire. Embodiments of the retreaded tire may further include a precured tread band bonded to the tire carcass by way of the bonding layer, the precured tread band comprising a back face bonded to the bonding layer, a front face forming a ground-engaging surface and at least one tread groove extending through at least a portion of the tread band thickness and the back face having a discontinuity associated with the at least one tread groove, the tread band being arranged relative the tire carcass such that the at least one tread groove is aligned with one of the at least one base groove.

Other embodiments include methods for retreading a tire. Such methods may include the step of providing a tire for retreading, the tire having a tread area with an associated tread width and a pre-existing tread layer of variable thickness extending at least partially across the tread width, the pre-existing tread layer including a front face forming a ground-engaging surface of the tire. An additional step may include providing a bonding surface along a base layer of the tire by removing a desired amount of tread material from the pre-existing tread layer along at least a portion of the tread width, the bonding surface comprising one or more desired profiles extending laterally along a portion of the tread width, the bonding surface extending both circumferentially around the tire and laterally across a width of the tire, the base layer having a thickness that is variable and asymmetrical and at least one base groove open to the bonding surface. A further step may include providing a bonding layer atop the bonding surface, the bonding layer having a thickness that is variable and asymmetrical. A further step may include providing a precured tread band comprising a back face, a front face forming a ground-engaging surface of the tire, and at least one tread groove extending through at least a portion of the tread band thickness, the back face including a discontinuity associated with the at least one tread groove. Still a further step may include arranging the precured tread band along the bonding layer, where the back face engages a tread band bonding surface of the bonding layer and where the at least one tread groove is laterally aligned with the at least one base groove, the bonding layer being interposed between the precured tread band and the bonding surface of the base layer.

Other embodiments include an extruder die and an extruder having an extruder die. In particular embodiments, the extruder die, which may form a portion of a corresponding extruder, includes a die body having a material outlet formed there through, the material outlet forming an aperture extending through a bottom surface of a die body. Such die may further include one or more longitudinal members spaced across a width of the material outlet, the longitudinal members extending outwardly from the die body and across at least a portion of the material outlet.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more detailed descriptions of particular embodiments of the invention, as illustrated in the accompanying drawings wherein like reference numbers represent like parts of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional partially exploded view of an exemplary retread tire of the prior art.

FIG. 2 is a partial cross-sectional view of an exemplary worn tire before it is retreaded, the tire including a plurality of circumferential grooves spaced apart between a plurality of (four) ribs along a tread of the tire.

FIG. 3 is a partial cross-sectional view of the tire of FIG. 2 showing a pre-existing tread of asymmetrical thickness before (which is identified by dashed lines) and after a full width of the tread has been removed to form a prepared bonding surface for retread operations, where the prepared bonding surface is formed atop a symmetric base layer.

FIG. 4 is a partial cross-sectional partially exploded view of the prepared tire shown in FIG. 3, which shows a bonding layer comprising multiple sections each arranged along a prepared bonding surface of the tire carcass for receiving a precured tread band, where the bonding layer is of constant thickness. In the embodiment shown, each section of the bonding layer is arranged atop a rib of the base layer.

FIG. 5A is a partial cross-sectional view of a tire showing a pre-existing tread of asymmetrical thickness before and after a partial width of the tread has been removed to form a prepared bonding surface for retread operations, where the prepared bonding surface is formed atop an asymmetric, variable thickness base layer and where the bonding surface includes a portion of the pre-existing (e.g., worn) tread surface.

FIG. 5B is a side view of the tire shown in FIG. 5A having prepared bonding surface formed atop an asymmetric, variable thickness base layer and including a portion of the pre-existing tread surface extending annularly about (i.e., about a circumference of) the tire.

FIG. 5C is a partial cross-sectional view of the tire shown in FIG. 5A, which shows a bonding layer comprising multiple (four) independent sections each arranged along a bonding surface of the tire carcass for receiving a tread band, where the bonding layer has a thickness that is asymmetric about a centerline CL of the tread width and the tire width and non-axi-symmetrical about a rotational axis of the tire, the prepared bonding surface including a portion of the pre-existing (e.g., worn) tread surface from which no significant material was removed by any material removal operation but is instead separately prepared for retreading, such as by being roughened or cleaned. In the embodiment shown, each of the bonding layer sections is arranged on one of four ribs of the bonding layer.

FIG. 6 is a partial cross-sectional view of the tire in FIG. 5A showing a variable thickness bonding layer comprised of four independent sections applied to the prepared bonding surface, the bonding layer being asymmetrical about a CL of the tread width and tire width and having a thicker portion associated with an excessively worn portion of the pre-existing tread, the thinner portion of the bonding layer extending along a portion of the bonding surface having a first curvilinear profile (i.e., path) P₁and the thicker portion of the bonding layer extending along a portion of the bonding surface having a second curvilinear profile (i.e., path) P₂, the second profile generally being offset a constant distance P_Δ from the first profile. In the embodiment shown, each of the bonding layer sections is arranged on a rib of the bonding layer and tread.

FIG. 7 is a partial cross-sectional view of the tire shown in FIG. 5A, wherein the excessively worn tread surface is removed to a greater depth by way of a material removal operation to form a bonding surface having two different profiles and to facilitate creation of a bonding layer having an associated thicker portion, the thicker portion having a variable thickness t_44-2associated with bonding surface profile P₂, which intersects the bonding surface profile P₁of the remaining bonding surface. The bonding layer also extends within the base grooves of the base layer.

FIG. 8 is a partial cross-sectional partially exploded view of an exemplary embodiment of a retreaded tire, the base layer and bonding layer forming an alternative to the tire shown in FIG. 7, wherein the base layer bonding surface is formed having two profiles but the bonding layer is formed of multiple sections similar to those of FIG. 6. In the embodiment shown, the precured tread band comprises individual sections forming ribs which are placed atop each of the bonding layer sections, where the tread grooves of the precured tread band extend through a full thickness of the tread band and are aligned with a base groove arranged along the prepared bonding surface in the base layer. Each of the tread grooves opening to the back face of the tread band form a discontinuity along the back face.

FIG. 9 is a partial cross-sectional partially exploded view of an exemplary embodiment of a retreaded tire showing a tread band having secondary tread grooves extending partially through the tread band thickness, as an alternative embodiment to the tire of FIG. 8, wherein each of the secondary grooves are open to the back face of the tread band and aligned with and in fluid communication with a base groove of the base layer. In the embodiment shown, the base layer is prepared such that the bonding surface is formed of multiple profiles as more clearly shown in FIG. 10. The secondary tread grooves of the tread band each form a discontinuity along the back face of the tread band.

FIG. 10 is a partial cross-sectional partially exploded view of an exemplary embodiment of a retreaded tire showing an alternative tread band to the tread bands shown in FIGS. 8 and 9, the tread band shown having a tread groove bottom portion extending from a back face of the tread, each tread groove bottom portion being arranged within a base groove of the base layer. Each of the tread groove bottom portions form a discontinuity along the back face of the tread band as each extend from the back face surface.

FIG. 11 is a cross-sectional view of a tread band having applied to a back face thereof a variable thickness bonding layer for co-application to a bonding surface of a tire.

FIG. 12 is a partial cross-sectional view showing a precured tread band in a desired position relative to a base layer of a tire, wherein the area between the back face of the tread band and the tire bonding surface is to be filled with a bonding layer.

FIG. 13 is a partial cross-sectional view of the tire in FIG. 6 showing a variable thickness bonding layer applied to the prepared bonding surface, the bonding layer being asymmetrical about a tread or tire centerline CL and having a thicker portion associated with an excessively worn portion of the old tread, the thicker portion having had material removed to a greater depth of the old tread. In this embodiment, removal of the old tread is performed in increments of predetermined depth that correspond to the thickness of a constant thickness uncured band (i.e., lamina) used to form the bonding layer, facilitating application of one or more uncured rubber bands to achieve a desired thickness equal to the sum of the one or more bands forming the bonding layer.

FIG. 14 is a side view of an extruder engaging a tire to apply a bonding layer according to an embodiment of the invention.

FIG. 15 is an end view of a die of the extruder shown in FIG. 14, the die having longitudinal members for engaging circumferential grooves in a tire while applying a bonding layer.

FIG. 16 is a partial cross-sectional side view of the extruder die of FIG. 15 showing a longitudinal member arranged within a longitudinal groove of the tire.

FIG. 17 is a cross-sectional top view of the extruder die of FIG. 15 taken along line A-A showing the longitudinal members of the die arranged within circumferential grooves of the tire.

FIG. 18 is a front partial sectional view of the extruder die of FIG. 15, showing the longitudinal members of the die arranged within circumferential grooves of the tire to form a bonding layer across the full tread width of the tire.

FIG. 19 is a front partial sectional view of an extruder die arranged to form a portion of the bonding layer along a portion of the bonding surface of a tire, the portion of the bonding layer being formed between base grooves of the base layer, according to an alternative embodiment. In the particular embodiment shown, the die is arranged to form a bonding layer along a single rib of a tire.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

Particular embodiments of the present invention provide retreaded tires having precured tread bands, and in certain embodiments precured tread bands, bonded to tread band bonding surfaces of the tires, the bonding surfaces located atop a variable thickness and/or asymmetrical bonding layer of the tire, and methods for producing such retreaded tires. A variable thickness and/or asymmetrical bonding layer may arise, for example, to bond tread band to a variable thickness, asymmetrical base layer of a tire, where such base layer may arise when the tread of the pre-existing tire has experienced, for example, uneven wear or manufacturing defects. Particular embodiments utilize variable thickness bonding layers to fill the area between a desired bonded position of the tread band and the bonding surface of the tire, the tread band being located a desired distance from the bonding surface to form a retreaded tire of a particular size or geometry. In particular embodiments, the bonding layer is asymmetrical about a centerline of the tread and/or tire width, and in further embodiments, the bonding layer is non-axi-symmetrical about a rotational axis of the tire. In particular embodiments, the base layer is asymmetrical about a centerline of the tread and/or tire width, and in further embodiments, the base layer is non-axi-symmetrical about a rotational axis of the tire. In other embodiments of the inventive apparatus and methods, the base layer and/or the bonding layer are symmetrical about a centerline of the tread and/or tire width, and in further embodiments, the base layer is axi-symmetrical about a rotational axis of the tire.

Advantageously the new tread bands and/or the bonding layers bonded to the tires during the retreading process and disclosed herein may be thinner and/or less massive for a given useable tread depth, at least for some embodiments, than those used in the prior art and therefore use less material without a resulting loss of expected tread life. The new tread bands and/or bonding layers disclosed herein can be thinner and/or less massive because the retreading process does not remove or replace as much of the pre-existing (i.e., original or old) material from the tire to be retreaded as has typically been removed in the prior art processes. In fact, no material may be removed from the pre-existing tread, or only a portion of the pre-existing tread may be removed across a width of the tread to provide circumferential areas along the tread width that generally maintain the pre-existing tread surface. As used herein, “pre-existing” is used synonymously with “old” and “original” to refer to the tire and/or any material or components thereof, such as the tread, for example, as existing prior to performing retreading operations. In particular embodiments, the pre-existing (i.e., old or original) tread may be asymmetrical about a centerline of the tread and/or tire width and/or non-axi-symmetrical about a rotational axis of the tire. Such asymmetry may arise due to uneven wear or manufacturing defects, for example.

In particular embodiments of the present invention, tread material is removed from the pre-existing tread to one or more desired depth profiles to form a bonding layer having a bonding surface, regardless of whether the resulting base layer has a thickness or bonding surface profile that is symmetrical about a centerline of the tire or axi-symmetrical relative to the rotational axis of the tire. In embodiments providing an asymmetrical or non-axi-symmetrical bonding layer thickness or bonding surface provides an asymmetrical, variable thickness gap extending between a back face of the tread band and the tire bonding surface, which is filled with a complimentary variable thickness bonding layer to position the tread in its desired location relative the bonding surface. Such location may position a back face of the tread band along a generally symmetrical profile relative to the centerline of the tread and/or tire width. Such location may also position a front face of the tread band along a generally symmetrical profile relative to the centerline of the tread and/or tire width, such as when the tread band has a thickness about the tread and/or tire width.

In the prior art, forming a retreaded tire includes removing the old tread entirely from the old tire, and even a portion of the undertread in particular embodiments, to desired radial depth of the tire to form a prepared bonding surface that is symmetrical about the tire centerline or axi-symmetric about the rotational axis of the tire, and which may be uniformly spaced in a radial direction of the tire from the reinforcement package and/or the from the rotational axis of the tire. For example, FIG. 1 is a partial cross-sectional partially exploded view of an exemplary retread tire of the prior art. The retread tire 10 is shown comprising a tire carcass 12 having a crown section 14, a reinforcement package 16 and a sidewall 11. The retread tire further includes a constant thickness cushion gum layer 18 and a precured tread band 20. The cushion gum layer 18 is an example of the material that may be used to bond the tread band 20 to the crown section 14 area of the retread tire 10. The precured tread band 20 includes a front face 22A that contacts the ground and provides traction. Tread grooves 23 have a top open to the front face 22A of the tread band. The tread band 20 further includes the back face 22B that is bonded to the crown section 14 of the tire 10 by the cushion gum layer 18.

FIG. 2 is a partial cross-sectional view of an exemplary tire before it is retreaded. Such tire may be a previously recapped (i.e., retreaded) tire that is ready for recapping again or it may be a tire that has never been recapped before. A tire 30 that is ready for the retreading process has a worn grooved tread area 31 that includes the worn grooves 33. The tire 30 further includes the undertread portion 32 that is positioned radially (e.g., vertically) between the bottoms of the grooves 33 and the top of the belts or reinforcement package 16 of the tire. As used herein, the vertical direction is perpendicular to the ground contacting surface of the tire tread. Tread area 31 includes ribs 34 arranged between grooves 33. The undertread portion 32 provides a cushion and/or protective layer between the ground contacting tread and the belt package 16 in the tire carcass 12, thereby ensuring that the belt package 16 is not exposed through the wearing of the tire tread 31.

During the retreading process typically performed in the prior art, the entire worn grooved tread area 31 and most of the undertread 32 is removed by a buffer or other grinding, cutting, or abrading device or other material removal process as known to one having ordinary skill in the art of tire retreading (generally referred to herein as a “material removal device” or a “material removal process”). With continued reference to FIGS. 1-2, the undertread portion 32 is typically removed to such an extent that only a thin, uniform layer of rubber remains, e.g., between about 1 and about 3 mm, in the area 15 above the reinforcement package 16, as shown in FIG. 1. The material that is removed from the tire 30 to be retreaded creates waste that is discarded and then replaced with new material that is part of the tread band 20 and cushion gum bonded to the tire carcass 12 during the subsequent retread process. Much of this material that is removed and replaced repeatedly at each recap does not contribute to the tire's wear life potential, and simply results in waste.

In many occasions, the pre-existing tire tread is unevenly worn. Uneven wear, extending radially to a particular tread depth, may occur along any portion of the tread in a circumferential direction and/or in an axial (i.e., lateral) direction of the tire. Uneven wear may comprise conical wear, flat spots, rail wear, or diagonal wear, for example. It is not uncommon for one side of the tire tread to wear more than an opposing side of the tread. In the prior art, where the entire tread and most of the undertread is removed in preparation for retreading, such uneven wear has no implication on the retreading process since most of the tread and undertread material is removed to a depth well beyond the irregularities associated with uneven wear. Further, the tire is generally buffed down to provide a thin layer of material above the reinforcement package, where such base layer of material can be generally described as having a profile or thickness that is symmetrical about a centerline of the tread or tire width or axi-symmetrical about the rotational axis of the tire. Such base layer may also have a constant thickness, such as in relation to the reinforcement package and/or the rotational tire axis. Further, the cushion gum layer within the prior art is generally of constant thickness.

Unlike the prior art, the new tread bands and/or bonding layers disclosed herein may be typically thinner and/or less massive for a given useable tread depth because of the need to replace the remaining tread and undertread, which the prior art processes buffed away, is reduced. Particular embodiments of the present invention remove none of, or very little of, the old tread, and may in particular variations remove tread material only along a particular width of the tread. In further embodiments, a portion of the tread width is removed to a desired first depth profile, while a portion of the tread that has been more excessively worn is removed to a desired second depth profile, where the second depth profile extends to a lower depth than the desired first depth profile. Accordingly, the present invention removes less of the old tread and/or undertread during the retreading process thereby allowing the remaining material to be used and not replaced in the newly retreaded tire. Indeed, in some embodiments, as much as possible of the groove of the old tire tread remains, as well as the undertread, when the new precured tread band is bonded to the tire.

When trying to minimize the removal of material from the old unevenly worn tread, removing a minimal amount of tread material from an unevenly worn tire may result in only removing tread material from a portion of the tread, where the high portions of the tread (i.e., the less worn portions) are removed and the lower portions of the tread (i.e., the more highly worn portions) remain to provide an asymmetrical bonding surface, where the bonding surface profile does not generally match the profile of the tread band back surface when the tread band is in its intended or desired bonded position on the retreaded tire. To avoid this consequence, prior art techniques remove the tread to a depth that extends beyond the unevenness in the old tire tread to generally form a symmetric bonding surface. Due to the amount of material removed, this prior art technique promotes waste and does not effectively minimize material removal as desired.

When removing a minimal amount of tread as previously discussed to form a variable thickness base layer in the tire carcass, less of the old tread and undertread is removed and wasted. In such instances, employing the tread band of symmetrical thickness with the constant thickness cushion gum layer of the prior art would result in a tire having an asymmetrical outer tread surface associated with the tread band front face or non-axi-symmetric tread, whereby a ground-engaging front face of the tread is non-axi-asymmetric relative to the rotational axis of the tire. Because less material is removed from the old tread, the cushion gum of the prior art is now arranged at a depth closer to the front face (i.e., the ground-contacting surface) of the tread, which increases the likelihood that the cushion gum layer will be exposed to the ground as the tire wears. Accordingly, particular embodiments of the present invention provide a variable thickness bonding layer formed of tread material, in lieu of cushion gum material, whereby the variable thickness bonding layer compliments the variable thickness base layer such that the top bonding layer surface profile generally matches profile of the tread band back face when the tread band is in a desired arrangement within the retreaded tire. Further embodiments provide asymmetrical base layers and bonding layers.

In one example, FIGS. 3-4 show a tire 10 having pre-existing tread removed to a particular depth profile beyond the worn surface to thereby remove all worn ground-engaging surfaces (i.e., the front face) from the old tread. The tread material may be removed by any known material removal process, such as buffing or grinding, for example. In the present example, old tread material 31 is removed to a desired depth along path (i.e., profile) P-P extending laterally across tread width W_tto form a prepared bonding surface 41 having a profile defined by path P-P (which represents a desired depth profile and a surface contour of the bonding surface), where the final depth is defined by radius r _BUFFextending radially from the tire's rotational axis a variable distance along path P-P. It is noted that radial distance r _BUFFextends from the rotational axis A of the tire (see FIG. 5B), which may change in length as it travels laterally along any desired path P-P, which may form any linear or curvilinear path. A curvilinear path may extend along a constant contour or of multiple and/or variable contours. The distance between the front face surface 31S (i.e., the ground-engaging surface) of the old tread 31 and the prepared bonding surface 41 of the base layer 40 is the thickness t_31Δ, which represents the thickness of old tread material 31 that has been removed. As a result, with continued reference to FIGS. 3-4, the remaining old tread and undertread thicknesses in combination form a base layer 40 of thickness t₄₀located above reinforcement package 16 and having a prepared bonding surface 41 extending across the full tread width W_tabout the full tire circumference.

The base layer 40 of FIG. 4 is formed by removing the old tread material 31 to a depth below the worn tire surface 31 to form a base layer having a symmetrical, constant thickness and a surface 41 profile P-P generally matching the back face surface profile of a corresponding tread band (see FIG. 1, for example). As a result, a constant thickness bonding layer is employed, where the thickness t₄₄is constant minus any local abnormalities that may alter the local thickness. A surface profile of the base layer 40 (which is referred to as a bonding surface 41) generally matching the back face surface profile of a corresponding tread band is a surface that is offset a constant distance from the surface of the back face surface of the tread band when the tread band is in its bonded position within the retreaded tire. The offset distance is the constant thickness t₄₄of bonding layer 44.

However, as discussed previously, to minimize the removal of old tread material, even less tread material may be removed when forming a retreaded tire than was removed in the examples of FIGS. 3-4. For example, with reference to the embodiment of FIG. 5A, the depth selected for tread removal does not remove all of the worn tread surface 31. In such embodiments, after initially removing old tread material 31 to a shallower depth defined by radius r _BUFF, a portion of the old tread surface 31 remains intact below path P-P. Instead of removing additional material below path P-P until all remaining old tread surface 31 is removed, the old tread surface 31 remaining under path P-P may form a separate portion 41A of the bonding surface 41. In particular embodiments, no old tread material, or very little old tread material, is removed from the worn tire surface before receiving a bonding layer, whereby the worn tire surface forms the bonding surface of the base layer. In particular embodiments, when tread grooves from the old tread remain, the old tread material may be removed to provide a tread grooves having a particular groove depth d₃₃. The prepared groove depth d₃₃may be, for example, 1-3 mm, after removing any old tread material.

FIG. 5B shows a side view of the tire in FIG. 5A, whereby the old tread surface portion 41A of bonding surface 41 extends annularly (i.e., 360 degrees about the tire circumference). It is understood, however, that in any particular embodiment the old tread 31 and old tread surface 31S may or may not extend annularly about the tire when forming a portion of the base layer 40 and the bonding surface 41.

In preparing the old worn tire tread for retreading, according to particular embodiments of the present invention, a portion of the worn tread is removed across the tread width to form a bonding surface along a base layer of the tire, where the bonding surface comprises a prepared portion and a worn surface portion around the circumference of the tire. For example, with reference to FIG. 5C, the bonding surface 41 of base layer 40 comprises (1) a prepared portion 41 (where material has been removed by any known material removal method, such as buffing or grinding) to a reference groove depth d₃₃and (2) a worn surface portion 41A, which may be cleaned and/or roughened to improve its ability to bond with a bonding layer applied thereto. Cleaning may be accomplished according to any known method, which includes, for example, scrubbing and rinsing the surface with water and/or applying any known solvent or other cleaner to remove any debris, oil, or other foreign material from the surface. After cleaning, or in lieu thereof, a roughening step may occur that is not considered a material removal process as otherwise discussed herein, even though roughening a surface may include removing a small, insignificant amount of material. Roughening may be performed according to any known method, such as by brushing, blasting, or by used of a solvent, for example.

In other embodiments, the worn tread surface portion 41A of bonding surface 41 may undergo a material removal process to remove worn tread material to a depth below prepared bonding surface 41. Such material removal may occur according to any known material removal process, such as buffing or grinding, for example. With reference to the examples shown in FIGS. 6-7, the tire of FIG. 5A is prepared for retreading by removing a portion of the old tread to form prepared bonding surface 41 having profile or contour P₁, but to then also prepare the remaining more excessively worn tread by removing old tread material there from to form prepared bonding surface portion 41A extending laterally along a second path P₂to a further depth profile extending a distance r _{BUFF 2}from the rotational axis of the tire. Bonding surface 41A may be formed along, or extend along, any lateral or circumferential path along base layer 40. For example, with reference to FIG. 6, the bonding surface 41A extends along a path P₂offset a desired constant distance from the path P₁of bonding surface 41. The difference in bonding layer thickness between P₁(associated with bonding surface 41) and P₂is identified as P_Δ. As an additional example, with reference to FIG. 7, the path P₂defining bonding surface 41A is not offset but instead extends by an angle α relative to the path P₁of bonding surface 41, where such path is chosen to more closely track the old worn tire surface and thereby minimize the removal of excess tread material from the worn tread. In such example, paths P₁and P₂intersect. It is understood that bonding layer surface 41 may be formed of one or more separate surface sections 41A, each extending laterally about an independent surface path or profile. For example, with reference to FIG. 10, an additional section 41B is prepared along a third path P₃. Accordingly, a bonding surface may include one or more, or a plurality of, independent profiles or paths. By only removing tread material in association with the more highly worn portion of the tread, the unnecessary removal of excessive material from other portions of the tread is minimized across the old tread width and circumference.

It is understood that in particular embodiments, the old tread surface 31S may only be cleaned and/or roughened to form a bonding surface 41 without performing any material removal process to remove old tread material to a desired depth. Accordingly, the bonding layer is placed atop the worn tread surface 31S. In further embodiments, the old tire surface 31S may not be cleaned or roughened.

In removing the old material 31 as discussed above, the depth of removal may be preselected. In particular embodiments, an amount of old tread material removed may achieve a desired base layer thickness, a bonding surface location and/or thickness, and/or a desired radial location of the tread band, any of which may be defined or measured relative to a reference location associated with the tire. The reference location may be any location along or within the tire or otherwise associated with the tire. For example, in particular embodiments, the reference location is the base (i.e., bottom) of any groove 33, the top of the reinforcement layer 16, or the rotational axis of the tire. In other words, each base groove 33, the reinforcement layer 16, and the rotational axis A of the tire may be used as a guide or reference for determining the thickness of any base layer, the location of any bonding surface 41 (including 41A, 41B), or the desired thickness of the bonding layer 44 (including 44A, 44B). For example, it may be determined that the final depth or location of the bonding surface 41 is 2 mm above the base of groove 33. In other instances, bonding surface 41 may be 8 mm above the reinforcement layer 16. As discussed further below, the dimensions of the precured tread band may dictate the amount of tread to remove, to provide a prepared tread surface that is a desired distance above the bottom of groove 33.

In particular instances, grooves 33 are arranged along the prepared bonding surface 41. These grooves 33 may remain from the original tread (i.e., each may be an original tread groove), or may be added to the base layer 40 as desired to properly receive a mating feature (such as groove bottom portion 28) arranged along back face 22B of any precured tread band 20. Such grooves 33 may be added by any known material removal method, such as abrading, grinding, or cutting, for example. In further embodiments, the old grooves 33 may be widened or deepened as desired to form an altered groove 33A. With reference to FIGS. 7 and 10, grooves 33 may be altered, for example, to receive a portion of a bonding layer 44.

While all variations in the prepared bonding surface have been shown in association with the tire width in cross-section, variations in the base layer and bonding surface and the worn tread surface may arise and extend about the circumference of the tire. Therefore, variations in the thickness of any base layer, bonding surface, or any corresponding bonding layer may extend about any portion of the tire circumference, where such variations arise in a radial direction of the tire. See FIG. 5B for example, where the bonding surfaces 41, 31S extend 360 degrees about the tire.

As discussed, FIGS. 5A-7, and 10 all exemplify different alternatives for preparing a tire, such as the tire of FIG. 2, for retreading while minimizing the removal of old tread. In each example, it can be said that each includes a base layer having multiple profiled bonding surfaces or multiple bonding surfaces extending along different linear or curvilinear paths across a lateral width of the tire. Further, with respect to FIGS. 5A-5C, the base layer includes a surface formed of the old ground-engaging tire surface, whereby only a portion of the base layer surface is a prepared bonding surface or whereby only a portion of the bonding layer surface has had any material removed according to a material removal process. It can also be said that the base layers and bonding layers resulting in the embodiments of FIGS. 5A-7, and 10 are all of variable thickness, whereby each such layer is asymmetric about a centerline CL of the tire width and/or tread width W_tand/or non-axi-symmetric about a rotational axis A of the tire.

In particular embodiments, retread tire 10 includes a variable thickness bonding layer 44 arranged atop the prepared bonding surface 41. In more specific embodiments, bonding layer 44 has portions of different thickness extending along one or more different paths or profiles of the bonding surface 41. Bonding layer may also be asymmetrical about centerline CL of a tread or tire width, and non-axi-symmetric about a rotational axis A of the tire. With reference generally to FIGS. 5C-13, bonding layer 44 extends circumferentially about the tire and at least partially across a width of the tire to bond the tread band 20 to the tire. Bonding layer 44 includes one or more differently thickened portions 44A, 44B, etc. each associated with corresponding bonding surface portions 41A, 41B, etc., each of which extend laterally along different surface paths (i.e., profiles or contours). For example, FIGS. 9-11 show a bonding layer 44 having multiple thickened portions 44A, 44B. In particular embodiments, such as shown in FIG. 7, for example, bonding layer 44 may comprise a single sheet extending laterally across at least a portion of the tread width, and in particular embodiments, across the full tread width. In other embodiments, such as shown in FIGS. 5C and 6, bonding layer 44 comprises multiple independent sections. For example, as shown, each section may be arranged along bonding surface 41 between base grooves 33 (i.e., along a rib 34). Thickened portions 44A, 44B, etc. may each be of uniform or constant thickness, such as shown in FIG. 6 and FIG. 9 (see 44B) for example, or may be of variable thickness, such as shown in FIGS. 7-9 (see 44A) for example. In particular embodiments, with reference to FIG. 11, the variable thickness bonding layer 44 is arranged along a back surface 22B before placement atop the base layer of the tire.

Generally, each bonding layer 44 includes a portion 44A that is associated with, and in particular embodiments complimentary to, the prepared bonding surface portion 41A to add the additional material lacking in deeper extending bonding surface portion 41A. In particular embodiments, the addition of bonding layer portion 44A to bonding surface portion 41A provides a top tread band bonding layer surface 45 (for receiving a precured tread band) having a surface profile that generally matches the surface profile of the back face of the tread band. In particular embodiments, the top tread band bonding surface 45 extends along a linear or curvilinear lateral profile or path defined by radius r _FINAL, which is a radial dimension extending from the rotational axis of the tire and which varies in length along the laterally extending path. In the embodiment shown in the FIGS. 6 and 13, as well as in other figures, the top tread band bonding layer surface 45 is symmetrical about a centerline CL of the tread width and/or axi-symmetrical about the rotational axis of the tire. Generally, the bonding layer 44 in each figure has a constant thickness t_44-1and at least a second thickness t_44-2, where the second thickness is greater than the first thickness.

As discussed previously, bonding layer 44 may be formed of a tread material, especially when the bonding layer is arranged at a depth of the tire that is reasonably expected to operate as a ground-engaging front face surface of the tread as the tire wears. In other embodiments, the bonding layer 44 may comprise cushion gum material, which is generally less durable than the tread material, that is the tread material is better for wear resistance. The differences between these compounds is readily known to those with ordinary skill in the art of tire design.

The bonding layer may be formed by any method known to one of ordinary skill in the art. For example, the bonding layer may be formed by spraying, painting, spreading and/or extruding bonding layer material onto the tread band back face, the base layer bonding surface, or combinations thereof. Alternatively, either alone or in combination with other bonding materials, a sheet of bonding material may be placed onto the bonding surface. For example, a bonding layer may be formed from a sheet of calendered material, and single sheet may be laid over the bonding surface of the base layer, or independent portions of the bonding layer may be applied to the bonding surface.

With reference to the embodiment of FIG. 13, in particular embodiments, the bonding layer 44 is formed by stacking one or more constant thickness strips or bands 144 (which may also be referred to as a ply or lamina) of bonding layer material atop the bonding surface of the tire. In such embodiments, removal of the old tread can be done in increments of particular depth (i.e., thickness), the depth of each increment corresponding to the thickness t₁₄₄of each strip or band of bonding layer material. Because one or more bands 144 may be applied, the total quantity of material removal increments is equivalent to the total quantity of the bands to be stacked to form a thickness t₄₄of the bonding layer 44. Each band may have any desired width, which, for example, may extend partially, fully, or beyond the tread W_t. The embodiment shown in FIG. 13 exemplifies an alternative to forming the bonding layer of FIG. 6, whereby local tread material is removed to a depth approximately equivalent to the total thickness of a local bonding layer to be formed by assembling layers of bands 144 having a thickness t₁₄₄. As shown in FIG. 13, local portions of the bonding layer 44 are formed of a single band, while the local bonding layer 44A is formed of two (2) bands 144. These embodiments form an assembled multi-layered bonding layer.

In additional embodiments, the bonding layer is formed by extruding bonding layer material along a bonding surface of the tire to a desired depth or thickness. With reference to FIGS. 14-17, particular embodiments provide an extruder 50 having a die 52 for dispensing viscous, uncured bonding layer material onto bonding surface 41. Extruder 50 may comprise any machine known to one of ordinary skill in the art that is capable of dispensing bonding layer material, such as, for example, natural and/or synthetic rubber or any other elastomeric material, in a flowable or viscous form. Such an extruder, for example, may be an extruder employing one or more screws to force material into and from the die 52. Die 52 includes a die body 54 surrounding an outlet 56 that forms an aperture for dispensing bonding material. Die 52 may be formed of any material known to one of ordinary skill in the art, including aluminum or steel, for example, and affixed to any known extruder by any known means. Die 52 may extend any width relative to tire 10. With reference to FIGS. 17 and 18, for example, die 52 is shown to generally extend across and accommodate the full tread width W_t. In other words, die 52 is shown to be capable of forming a bonding layer 44 along bonding surface 41 as desired across the full tread width W_t. With reference to FIG. 19, for example, in other embodiments die 52 may have a width W₅₂less than the full tread width W_tto only form a portion of the bonding layer, such as between a pair of base grooves 33, along a single rib, or along multiple ribs, for example. To control the flow of material, dams 57 forming extensions from die body 54 or bottom face 55 may be arranged along adjacent the tread edge as generally shown in FIG. 18, or along any other edge bonding surface 41 (including 41A). For example, a dam 57 may be used to extend partially within a groove 33 (or 33A) when a longitudinal member 58 is not arranged within such groove 33 (or 33A).

With reference to the embodiments of FIGS. 14-18, longitudinal members 58 are arranged relative to material outlet 56 to control the application of bonding material along bonding surface 41 during bonding layer formation. Longitudinal members 58 may also be used to control or limit any bonding material entering any corresponding circumferential groove 33. In the embodiment shown, longitudinal members 58 extend across length L₅₆of outlet 56 and partially across length L₅₂of die 52. It is understood that longitudinal members 58 may extend any length L₅₈, including partially or fully across length L₅₂of the die 52 or even beyond the length L₅₂.

With reference to FIGS. 15, 17-19, longitudinal members 58 also have a width W₅₈facilitating placement of the member 58 within the full or partial groove depth d₃₃. Because circumferential grooves 33, 33A may be non-linear, such as zig-zagged or curvilinear, for example, the arrangement of longitudinal member 58 along the width W₅₂of the die 52 as well as selection of member width W₅₈may be provided to allow the member 58 to navigate circumferentially about an annular, closed-loop path at a fixed axial location of the tire while arranged within the groove 33 or a modified groove 33A. This is accomplished with there is “see through” within the groove 33, 33A, where “see through” means that there is a portion of the groove that extends annularly along a closed-loop path at a fixed axial location of the tire.

With reference to FIG. 18, longitudinal members 58 have a depth d₅₈that may be selected to control the thickness t₄₄of the bonding layer material being applied. The depth d₅₈of longitudinal member 58 may selected as desired. In particular embodiments, longitudinal member depth d₅₈is selected such that the top tread band bonding surface 45 of bonding layer 44 engages die bottom surface 55, or, in other words, the bonding layer thickness generally fills the variable distance d₅₂between die bottom surface 55 and bonding surfaces 41 (including 41A, 41B). In other arrangements, distance d₅₂may be greater than or less than the desired thickness of the bonding layer, such as to better adapt to the characteristics of the bonding material being applied, for example. The torque, pressure, and feed speed of the bonding material being dispensed from the extruder 50 may also be employed to control and achieve a desired thickness of the bonding layer according to known techniques and methods without reliance on distance d₅₈to control the bonding layer thickness.

Die 52 is shown to be generally flat as it deflects the tire locally to adapt to the generally flat or planar die bottom face 55. In other embodiments, however, die bottom face 55 may be a contoured surface, and may comprise, for example, a surface extending about a radius relative to the rotational axis A of the tire. Die bottom face 55 may be contoured in a circumferential direction and/or a lateral direction of the tire. Longitudinal member bottom surface 59 is also shown to be flat or planar. In other embodiments, the bottom surface 59 of each longitudinal member 58 may also be contoured, and may comprise, for example, a surface extending about a constant radius relative to the rotational axis A of the tire. In particular embodiments, die bottom surface 55 and longitudinal member bottom surface 59 may each be contoured, or one of each may be contoured while the other remains flat or planar.

By employing a variable thickness bonding layer that is complimentary to a variable thickness base layer having a prepared bonding surface that varies radially along the tread width and/or tread circumference, any shaped precured tread may be arranged atop the bonding layer for bonding to the tire. Examples of particular tread bands for retreading tires shown in FIGS. 8-10, each of which have a thickness that is generally symmetric about a centerline CL of the tread band width. Each tread band 20 includes a front face 22A and a back (or bottom) face 22B. Front face 22A is a surface defining an upper bound of the tread band thickness and is arranged to operate as a ground-engaging surface for the tire in operation. Back face 22B is a surface defining a lower bound of the tread band thickness and is arranged to engage and bond to the bonding layer 44. In the non-limiting embodiments shown, the tread bands are generally of constant thickness, that is, the upper bound is defined by front face 22A is uniformly offset from lower face 22B. However, it is understood that the retreaded tires and methods of forming such retreaded tires may utilize tread bands that are of non-constant (i.e., variable) thickness, and which may be symmetrical or asymmetrical about a centerline of the tread band width. Each tread band may include tread grooves 23, which may extend within a thickness of the tread band. Grooves 23 each have a top end 24A and a bottom end 24B.

In the embodiment shown in FIG. 8, precured tread band 20 includes a plurality of segments forming ribs of the tread, the segments being spaced apart laterally along the tread band width. Each segment is independent of the other, but may have been formed together, and even attached to each other by way of a member extending laterally between each adjacent section but later separated before or after application of the tread band to the tire. Tread grooves 23 are formed such that groove top 24A is open to the front face 22A while groove bottoms 24B are open to the back face 22B to form a discontinuity along the back face 22B. The tread band 20 is arranged such that the tread grooves 23 are aligned in a lateral direction with base grooves 33, whereby the groove bottoms 24B open to a corresponding base groove 33.

In the embodiment shown in FIG. 9, a precured tread band 20 includes a plurality of first grooves 23 and a plurality of secondary grooves 25. Such tread band is unitary, but may be formed of independent segments. First grooves 23 each have a top end 24A open to front face 22A and a bottom end 24B terminating within the thickness of the tread band 20. Second grooves 25 each have a top end 26A terminating within the thickness of the tread band and a bottom end 26B open to a back face 22B, the bottom ends 26B each forming a discontinuity along the back face 22B. The tread band 20 is arranged along bonding surface 41 such that second grooves 25 align laterally with the base grooves 33 and whereby the corresponding bottom end 26B of each second groove 25 opens to a corresponding base groove 33.

In the embodiment of FIG. 10, precured tread band 20 includes a groove bottom portion 28 that extends below the back face 22B of the tread band 20 to form a discontinuity along back face 22B. It should be noted that the tread groove bottom portion 28 of the tread groove 23 forms an extension protruding from the back face 22B, where such extension, in the embodiments shown, includes a pair of opposing side walls 29a extending from back face 22B and a floor or base 29b extending between the side walls to form the groove bottom portion 28 extending outwardly from back face 22B. The tread groove 23 may, in those embodiments, extend into the groove bottom portion 28, which is aligned within base groove 33A. Base groove 33A may be widened by any known material removal process to receive the bonding layer 44 and/or the groove bottom portion 28. In embodiments employing a tread band having groove bottom portions 28 extending below the back face 22B, the distance between the terminal end of any groove bottom portion 28 and the back face surface 22B may be used to determine the amount of material to remove from the original tread to form the prepared bonding surface 41 along the base layer of the tire. For example, in determining the amount of material to remove from the old tire tread, the resulting distance between the prepared surface 41 and the bottom of groove 33 may be equal to between the terminal end of any groove bottom portion 28 and the back face surface 22B of the precured tread band.

In particular embodiments, the variable thickness bonding layer 44 (which may include 44A, 44B) may be formed to fill any gap or space between the intended location of the tread band 20 and the base layer bonding surface 41, 41A, 41B. The gap or space may be symmetrical or asymmetrical about a centerline of the tread and/or tire. With reference to FIG. 12, if knowing the intended position of the tread band relative to the base layer 40, the reinforcement package 16, or the rotational axis of the tire A, the relative position can be used to determine the thicknesses and shape of the bonding layer 44, 44A, 44B. For example, a desired thicknesses t_46-1, t_46-2, t_46-3of the variable thickness bonding layers 44, 44A, 44B may be determined by subtracting from a desired distance between a bottom the groove 33, 33A and the back face 22B of the tread band in the retread tire, which is referred to as distance ΔG₁or the desired groove depth, the distance between the bonding surface 41, 41A and bottom of any corresponding groove 33, 33A (i.e., the depth of such groove 33, 33A). In lieu of using the groove bottom as a reference, the reinforcement layer may be used, where the desired distance between a top of reinforcement package 16 and the back face 22B of the tread band in the retread tire is referred to as distance ΔB₁. As suggested above, the rotational axis A of the tire may also be used as the reference to determine a desired thickness of the bonding layer when the desired distance between the rotational axis A and the back face 22B of the tread band is known, which may be calculated by subtracting the thickness of the tread t₂₀from the desired outside radius r_oof the retreaded tire. Measurements of all such distances may be accomplished by any means of measuring known to one of ordinary skill in the art. It is also understood that the thickness and shape of the variable thickness bonding layer 44, 44A, 44B may be determined by measuring the location of the bonding surface 41, 41A, 41B relative to a desired location of the tread band and its back face.

It should be noted that even though the grooves 33 shown in the attached figures are arranged laterally across the ground-contacting face of the tire and may appear to be continuous circumferentially around the tire, the invention is not so limited to such a groove. Indeed such a groove may run laterally across the tire or in any other suitable direction. Such a groove may be an “original” groove, a groove formed in the tire to be retreaded and not removed during the formation of the prepared bonding surface or such a groove may be formed in the surface by any suitable method or operation, including tire wear (which may result in exposure of an underlying groove), as known to one having ordinary skill in the art.

The base groove formed in the base portion of the tire may be formed in any way suitable that allows for the alignment of the base groove with the bottom portion of the precured tread band tread groove so that the tread groove bottom portion is embedded within the base groove. As in the embodiment illustrated in FIGS. 3-6, the base groove may be simply a groove, part of which was the original tread groove of the tire being retreaded. Optionally, the original groove may be further cut using, for example, a grinding tool or other cutting process as known to one having ordinary skill in the art. The grinding tool may be used to deepen and/or widen the original groove and thus provide a deeper and/or wider groove that will provide additional useable tread life for the retreaded tire. Typically this groove forming process may be suitable as long as there still remains sufficient protective undertread (typically, for example, between 1 and 6 mm) between the bottom of the grooves and the reinforcement package.

Alternatively an additional groove may be formed in the base layer adjacent to the original groove of the tire using a grinding tool or other suitable cutting tool. This newly formed groove may then be aligned with the tread groove of the tread band so that a bottom portion of the tread groove can be embedded within the formed base groove. Optionally the original groove and the newly formed groove may each be aligned with the bottom portion of tread grooves of the tread band.

In particular embodiments of the present invention, the base groove may be formed (using, for example, a grinding tool or other cutting tool) in the undertread portion of the tire being retreaded. If the gouges, cracks or and/or cuts are of such depth or if the wear of the tire being retreaded was such that the entire grooved tread portion had to be buffed off, it is still advantageous to leave as much of the undertread as possible during the buffing step so that the undertread can be grooved to provide a base groove and contribute to the useful life of the retreaded tire.

In other embodiments, the base groove may be formed in the base portion of a tire that has already been retreaded. In such embodiments, the base groove may be a groove formed in the tread band that was bonded to the tire in the earlier retread process. Alternatively, the grooved tread area of such a tread band could be buffed away, leaving only the undertread portion of the tread band. In that case, the undertread portion of the tread band could be cut to provide a base groove therein using, for example, a grinding tool or other cutting tool.

Particular embodiments of the present invention further include methods for retreading a tire, such as, for example, the tires shown in FIGS. 3-13.

Such methods include the step of providing a tire for retreading, the tire having a tread area with an associated tread width and a pre-existing tread layer of variable thickness extending at least partially across the tread width, the pre-existing tread layer including a front face forming a ground-engaging surface of the tire. In particular embodiments, the front face includes at least one groove extending into a thickness of the tread layer. In other embodiments, it is understood that the entire tread may have been completely worn, which may eliminate any groove being arranged within the original tread layer. In particular embodiments, the old tread layer is asymmetrical about a centerline of the tire.

Such methods may further include the step of providing a bonding surface along a base layer of the tire by removing a desired amount of tread material from the pre-existing tread layer along at least a portion of the tread width, the bonding surface comprising one or more desired profiles extending laterally along a portion of the tread width, the bonding surface extending both circumferentially around the tire and laterally across a width of the tire, the base layer having a thickness that is variable and asymmetrical and at least one base groove open to the bonding surface. The bonding surface may be an pre-existing grooved tread portion of the tire being retreaded, an original undertread portion of the tire being retreaded, and/or a grooved tread portion or undertread portion of a previously bonded tread band applied during an earlier retread operation on the tire to be retreaded. If the tire was previously retreaded, the undertread portion may include the cushion gum applied during the previous retreading process and bonded to the remaining section of tread band. In particular embodiments, the bonding surface and/or the base layer are asymmetrical about a centerline of the tread width or of the tire width and/or non-axi-symmetrical about a rotational axis of the tire.

In particular embodiments, a portion of the bonding surface extending circumferentially and laterally is a worn tread surface of the pre-existing tire carcass, which may extend annularly about the tire in further embodiments, such as is shown in FIG. 5B for example. Such worn tread surface may be cleaned and/or roughened in particular embodiments of the step of providing a bonding surface. In further embodiments, tread or undertread material is removed from the worn or uneven portion of the pre-existing tread to a desired depth along a desired linear or curvilinear profile in a lateral direction to form portion of the bonding surface. Accordingly, in particular embodiments, the bonding surface formed in the step of providing a bonding surface comprises a plurality of different profiles extending laterally along a portion of the tread width, where each of the plurality of profiles are either linear or curvilinear, such as is shown by example in FIGS. 6-10. In other words, a portion of the bonding surface extends laterally along a path different than a lateral path along which another portion of the bonding surface extends. It follows that in particular embodiments, the base layer includes a first portion having an associated portion of the bonding surface formed to a first profile and a second portion having an associated portion of the bonding surface formed to a second profile, the second portion being thinner than the first portion and being associated with a portion of the pre-existing tread that was thinner or more excessively worn than a pre-existing tread portion associated with the first portion. In summary, as discussed above, the old tire tread may be prepared for retreading without removing any old tread material, or removing a portion of the old tread material to a desired depth. In removing the old tread material, only a portion of the tread is removed along a desired path across a width of a tire. The remaining portion of the tread may be left as a worn tread surface, may be cleaned and/or roughened, or have tread material removed there from to form one or more additional paths across a tire width.

If the original grooved tread portion of the tire being retreaded is used as the prepared bonding surface or if a grooved tread portion of a previously bonded tread band is used as the prepared bonding surface, then the base portion of the tire includes a base tread groove that was not removed during the preparation of the bonding surface. In such embodiments, the base tread groove is a tread groove remaining (not buffed away) from the grooved tread area of the tire to be retreaded.

In such embodiments the step of providing a prepared bonding surface may include removing circumferentially around the tire a determined depth of a grooved tread portion of the base layer of the tire, the grooved tread portion having a base tread groove formed therein, thereby providing the prepared bonding surface. In these embodiments that provide the prepared bonding surface from a grooved tread portion of an original tread or from an old tread band of a previous retreading, the determined depth is less than the depth to the bottom of the base tread groove. Indeed the base tread groove is the base groove into which the tread groove bottom portion is embedded.

If the original undertread portion of the tire being retreaded is used as the prepared bonding surface or if an undertread portion of a previously bonded tread band is used as the prepared bonding surface, then the step of providing a prepared bonding surface includes removing circumferentially around the tire a determined depth of a grooved tread portion of the base portion of the tire, the grooved tread portion having a base tread groove formed therein, wherein the determined depth is less than a depth to a bottom of the base tread groove and wherein the base tread groove is the base groove open to the prepared bonding surface. Such embodiments further include the step of forming the base groove into the prepared bonding surface.

Particular embodiments of providing a bonding surface along a base layer of the tire by removing the tread material in increments of particular thickness or depth. The removal of material from the base layer may continue or be repeated as desired until reaching a sufficient depth. In particular embodiments, the increments of material removed are at a depth or thickness generally equal to a thickness of the bonding layer strip or band that will be applied to the bonding surface, whereby the final thickness of the bonding layer may be achieved by forming a stack of one or more (or a plurality) of bonding layer strips or bands, which can be seen in FIG. 13 for example.

Particular embodiments of such methods may include the step of providing a bonding layer atop the bonding surface, the bonding layer having a thickness that is variable and asymmetrical. In particular embodiments, the bonding layer is asymmetrical about a centerline of the tread width and/or the tire width and/or non-axi-symmetrical about a rotational axis of the tire. In particular embodiments, the step of providing a bonding layer comprises the steps of measuring a distance from a reference location associated with the tire to the top of the bonding surface of the base layer. The reference location may be any location along or within the tire or associated with the tire. For example, in particular embodiments, the reference location is the bottom of the at least one base groove, the top of the belt reinforcement package, or the rotational axis of the tire to the top of the bonding surface of the base layer. Further steps of the step of forming a bonding layer includes determining a thickness of the bonding layer by subtracting the distance measured in the prior step of measuring from a corresponding desired distance between the reference location and the back face of the tread band in the retreaded tire. The previous two steps may be repeated at one or more different locations across a width of the bonding surface. A further step of the step of forming a bonding layer include forming a bonding layer having the thicknesses determined in the previous three steps. In particular embodiments, the desired distance between the reference location and the back face of the tread band in the retreaded tire is determined by subtracting the tread band thickness from a corresponding desired distance between the reference location and the front face of the tread band.

Particular embodiments that include forming the base groove in the undertread may include the step of forming the base groove into the prepared bonding surface. A new groove may be formed into the exposed undertread to provide the base groove in which the tread bottom portion of the tread band will be embedded. Such step may be achieved, for example, through the use of a grinding or cutting operation known to one having ordinary skill in the art.

These methods may also include the step of forming a bonding layer atop the prepared bonding surface, the bonding layer having a variable and asymmetrical and/or non-axi-symmetrical thickness as discussed above. In particular embodiments, the bonding layer is formed of a tread material, while in other embodiments the bonding layer is formed of cushion gum material. In particular embodiments, providing a bonding layer comprises forming a portion of the bonding layer along a portion of the bonding surface and repeating along another one or more portions of the bonding surface until the bonding layer is completed. For example, the step of providing a bonding layer may include arranging one or more plies of bonding layer material along each portion of the bonding surface to form the bonding layer, such as is shown in an exemplary embodiment in FIG. 13. By further example, the bonding layer may be extruded along a portion of the bonding surface, such as is shown by example in FIG. 19, or along the entire bonding surface as exemplarily shown in FIG. 18.

Such methods may also include providing a precured tread band comprising a back face, a front face forming a ground-engaging surface of the tire, and at least one tread groove extending through at least a portion of the tread band thickness, the back face including a discontinuity associated with the at least one tread groove. As discussed above, any precured tread band of desired design may be used. One or more grooves may be arranged to extend inwardly from the front face, while one or more grooves may also be arranged to extend inwardly from the back face. Discontinuities form a break in the back face, such as is shown in exemplary embodiments of FIGS. 8-12. Further steps of such methods may include arranging the precured tread band along the bonding layer, where the back face engages a tread band bonding surface of the bonding layer and where the at least one tread groove is laterally aligned with the at least one base groove, the bonding layer being interposed between the precured tread band and the bonding surface of the base layer. The tread band may be have a thickness that is axi-symmetric about the tire rotational axis, and may also be symmetrical about a radial centerline of the tread band width.

Further, such methods may include bonding the back face of the precured tread band to the bonding layer, and bonding the bonding layer to the base layer of the tire. The bonding layer may comprise tread material, as the bonding layer may be exposed and used as a ground-engaging surface of the tread. Accordingly, using tread material will provide the properties desired for a ground-engaging surface of the tire, such as providing desired wear resistance, durability, traction, and crack resistance, for example. The bonding layer is typically a green (uncured) rubber compound. In other embodiments, bonding may be made by any method known to one having ordinary skill in the art, including the use of a cushion gum layer. Bonding may be finally achieved, for example, by curing the assembled retreaded tire, such as through vulcanization.

These methods may be applied to any type of tire and as such, any type of tire may provide an embodiment of the present invention. However, particular embodiments are especially beneficial for heavy vehicle tires such as for buses and trucks. More specifically embodiments may include truck tires that are steer tires, drive tires or trailer tires. It is contemplated that trailer tires may be particularly suitable for such retread processes.

It should be understood from the foregoing description that various modifications and changes may be made to the embodiments of the present invention without departing from its true spirit. The foregoing description is provided for the purpose of illustration only and should not be construed in a limiting sense. Only the language of the following claims should limit the scope of this invention.

The terms “comprising,” “including,” and “having,” as used in the claims and specification herein, shall be considered as indicating an open group that may include other elements not specified. The terms “a,” “an,” and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The terms “at least one” and “one or more” are used interchangeably. The term “one” or “single” shall be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as “two,” are used when a specific number of things is intended. The term “face” connotes a surface unless otherwise noted herein.

CUSTOM PRE-CURED RETREAD

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