EXPANDABLE TREAD MOLD AND METHOD FOR RETREADING TIRES

Abstract: Tire recapping or retreading apparatus and method of use including the use of an expandable tread mold with a plurality of mold segments. A tread mold loading machine (20) is used to position a prepared tire carcass (182) or built tire relative to the mold segments (202) and to install the mold segments on the exterior of the built tire. The mold segments are retained in place on the exterior of the tire carcass by a tension band. Resilient elastic tension bands or metal tension springs (204) hold the mold segments on the tire carcass after the mold segments have been released from the tread mold loading machine. The use of the tread mold segments eliminates distortion of the tire carcass during installation of the tread mold on the exterior of the built tire.

Description: EXPANDABLE TREAD MOLD AND METHOD FOR RETREADING TIRES TECHNICAL FIELD OF THE INVENTION This invention relates generally to methods and apparatus for retreading a tire casing. More particularly, but not by way of limitation, this invention relates to an expandable tread mold having a plurality of mold segments and a method of retreading a tire casing. ■ • BACKGROUND OF THE INVENTION A wide variety of procedures and different types of equipment are available for use in recapping or retreading tires. One of the first steps in retreading a worn tire is to remove existing tread material from the tire carcass by buffing. Various procedures are available to apply one or more layers of uncured rubber or retreading material with appropriate bonding agents to the buffed tire carcass. The uncured rubber may also be stitched to the buffed carcass as required. For purposes of this patent application, the term "built tire" is used to refer to a buffed tire carcass or casing which has been built up with one or more layers of uncured rubber and other material as required by the retreading equipment and procedures being used to retread the worn tire. In the past, heavy duty mechanical and/or hydraulic closing devices have often been used to install molds which form a new tread in retreading material on a prepared tire carcass or built tire. Tire distortion sometimes occurs as the tread molds are closed on the built tire. This problem is particularly common if the built tire is slightly larger in diameter than desired. In such cases, the prepared tire carcass will often buckle and can thus no longer be used. Damage to a built tire during mold installation represents a substantial loss of time and material spent preparing the built tire for mold installation. One method of recapping or retreading tires is illustrated in United States Patent 4,767,480 entitled Cold Recapping Method for Tires Utilizing Uncured Rubber and Sectioned Mold, issued August 30, 1988 to Leon C. Goldstein. This patent describes apparatus and methods for retreading which uses a cold process. In this process, a flexible tread mold is stretched over the prepared tire. Subsequently, an envelope is placed over the mold and built tire and the entire unit or assembly is placed in a chamber for curing of the rubber. United States Patent 4,588,460 entitled Method and Apparatus for Recapping a Tire wi th a Flexible Segmented Mold, issued May 13, 1986 to Arthur W. McGee, et al. illustrates another method and apparatus for retreading a tire that includes a relatively flexible mold which is formed by a plurality of mold segments. United States Patents 5,306,130, entitled Apparatus for Recapping a Tire and an Improved Curing Envelope for Use Therein, and 5,342,462, entitled Apparatus and Method for Retreading a Tire, show other types of tire retreading equipment and methods. Pneumatic tires may also be recapped or retreaded by installing a continuous replacement tread on a prepared tire carcass. Both uncured and cured or vulcanized rubber compounds have previously been used to provide the continuous replacement tread. Examples of equipment and procedures used to install continuous replacement treads on a tire casing are shown in United States Patents 3,976,532 entitled Tread Applying Machine, dated August 24, 1976 and issued to C.K. Barefoot; 4,088,521 entitled Method of Retreading a Tire wi th an Endless Premolded Tread, dated May 9, 1978 and issued to P.H. Neal; 4,036,677 entitled Machine for Treating Worn Out Pneumatic Tires and for Applying a Pre-Molded Tread Ring, dated July 19, 1977 and issued to Carlo Marangoni; and 4,957,574 entitled Tread Centering Method and Apparatus, dated September 18, 1990 and issued to A.R. Clayton, et al . Most retreading procedures also require the use of a flexible envelope to seal around the tire casing, retread material and tread mold (if used) . The complete assembly, including the tire casing, retread material, tread mold (if used) and envelope, are placed in a high pressure, high temperature chamber in preparation for curing the components which comprise the completed tire assembly. The high pressure, high temperature chamber is frequently referred to as an autoclave. Examples of a tire retreading envelope and high pressure, high temperature curing chamber are shown in United States Patent 4,309,234 entitled Tire Retreading Envelope Seal , dated January 5, 1982 and issued to P.L. Witherspoon.. As noted above, United States Patent 4,767,480 also contains information on the use of envelopes to assist with curing retreaded tires. The above listed patents are incorporated by reference for all purposes within this application. SUMMARY OF THE INVENTION In accordance with the present invention, the disadvantages and problems associated with previous methods and apparatus for retreading tires including installing rigid tread mold segments on the exterior of a built tire have been substantially reduced or eliminated. One object of this invention is to provide methods and apparatus for retreading pneumatic tires which eliminate the need for high pressure mold closing equipment. The present invention includes an expandable tread mold and a method of installing the expandable tread mold on a wide range of tire sizes with significant variations in critical tire dimensions without causing damage to the associated tire casing. The resulting retread tire assembly can be cured in existing hot air chambers using conventional chamber cure retreading techniques. Another object of the present invention is to provide a method and apparatus for retreading tires that avoids deforming the tire carcass when tread mold segments are placed thereon and thus reduces tire loss during the retreading operation. The present invention includes the use of an expandable tread mold having a plurality of mold segments which will accommodate variations in casing dimensions. Mold segments with a wide variety of different tread patterns may be used with the present invention. Examples of these tread patterns include tread designs for drive tires, intermodal tires, trailer tires, and most commercial radial tires. An expandable tread mold can be provided in accordance with the teachings of the .present invention with tread patterns having the necessary width and depth to meet a wide variety of applications. The present invention provides, in one aspect, apparatus for retreading a prepared tire carcass or casing having a layer of retreading material disposed on the exterior thereof. Various techniques may be used to prepare or build the tire carcass without requiring a splice in the retread material. The expandable tread mold includes resilient retainers which encircle the tread mold urging the mold segments toward the casing.and maintain the desired relationship between the mold segments while preparing the retread tire assembly for curing. An expandable tread mold incorporating teachings of the present invention securely contacts the retreading material on the exterior of a built tire but does not place any unusual stress on the associated tire casing. Technical advantages of the present invention include providing an expandable tread mold which sinks into the retreading material and is drawn tighter against the casing while filling any small voids in the buffed surface of the prepared tire carcass. Retreading tires in accordance with the present invention provides greater adhesion between the retreading material and the prepared tire carcass which results in higher dependability for the resulting retread tire. Further technical advantages of the present invention include the ability to use a wide variety of spliceless retreading material such as die size rubber or extruded rubber in preparing the built tire prior to placing the expandable tread mold on the retreading material. The method of retreading tires in accordance with the teachings of the present invention results in a retread tire with no splices in the retread material, a more attractive cosmetic appearance, enhanced reliability and better balance. Additional technical advantages of the present invention include combining the best techniques associated with precure tire retreading and mold cure tire retreading in a chamber cure retreading process to provide excellent tread-to-casing bonding, increased mileage, better tire balance and greater reliability at a lower cost per mile of tire use as compared to other retreading systems and methods. Another aspect of the present invention includes placing an appropriate expandable tread mold on a tread mold loading machine and expanding the tread mold to receive a built tire. After centering the built tire within the expanded tread mold, the tread mold loading machine closes the tread mold onto a layer of retreading material. The built tire and tread mold assembly may then be removed from the tread mold loading machine and placed in an elastomeric curing envelope. Seal rings are preferably added to form a seal between the curing envelope and the rim of the built tire. This package may then be 'placed in a curing chamber. The appropriate amount of heat and pressure are applied to the package which results in the individual mold segments closing with respect to each other and forming the desired tread pattern in the retreading material as the built tire is cured. BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which: FIGURE 1 is a schematic drawing in elevation with portions broken away showing a tread mold loading machine incorporating one embodiment of the present invention; FIGURE 2 is a schematic drawing in section and elevation with portions broken away, taken along line 2-2 of FIGURE 1, showing a built tire mounted on the tread mold loading machine of FIGURE 1; FIGURE 3 is an enlarged schematic drawing showing the front of the control panel for the tread mold loading machine of FIGURE 1; FIGURE 3A is a schematic drawing showing a safety latch satisfactory for use with one embodiment of the present invention; FIGURE 4 is a schematic drawing showing an isometric view of an expandable tread mold incorporating one embodiment of the present invention which may be used with the tread mold loading machine of FIGURE 1; FIGURE 5 is an isometric drawing of a mold segment associated with the expandable tread mold of FIGURE 4; FIGURE 6 is a schematic drawing with portion broken away showing the mold segment of FIGURE 5 engaged with a tread mold supporting arm; FIGURE 7 is a schematic drawing showing an isometric view of the expandable tread mold of FIGURE 4 loaded on a built tire in accordance with one aspect of the present invention; FIGURE 8 is a schematic drawing in section with portions broken away showing a mold segment mounted on a built tire and disposed within a curing envelope in accordance with one aspect of the present invention; and FIGURE 9 is a schematic drawing in section showing the mold segment of FIGURE 8 embedded in cured retreading material after removing the built tire from a curing chamber and taking off the curing envelope. DETAILED DESCRIPTION OF THE INVENTION The preferred embodiments of the present invention and its advantages are best understood by referring to FIGURES 1 through 9 of the drawings, like numerals being used for like and corresponding parts of the various drawings. Tread mold loading machine 20, as best shown in FIGURES 1 and 2, is provided to install expandable tread mold 200 on the exterior of prepared tire carcass or built tire 180. Tread mold loading machine 20 may also be used to remove expandable tread mold 200 from built tire 180 after retreading material 184 has been properly cured. Expandable tread mold 200 is formed from a plurality of rigid mold segments 202. Ten segments are illustrated in FIGURE 1, but any number of mold segments 202 can be used as required for the specific tread mold loading machine and specific tread mold design. For purposes of this patent application, built tire 180 refers to pneumatic tire carcass or casing 182, which has been buffed to remove any old tread material (not shown) , and a layer of adhesive or similar bonding agent (not shown) along with retreading material 184 applied to the exterior of carcass 182. Built tire 180 may be prepared for retreading using conventional procedures and equipment prior to mounting built tire 180 on tread mold loading machine 20. Tread mold loading machine 20 may also be referred to as a "tread mold expander." Expandable tread mold 200 is sometimes referred to as an adjustable tread mold because it will accommodate built tires with significant variations in critical tire dimensions. The components which comprise expandable tread mold 200 will be described later in more detail. These components include a plurality of mold segments 202 and one or more annular tension springs 204. Mold segments 202 are preferably spaced radially from main axle 22 prior to mounting built tire 180 on main axle 22. As shown in FIGURE 1, mold segments 202 are positioned by tread mold loading machine 20 to define expanded opening 206 to receive built tire 180 therein. As will be explained later in more detail, an important feature of tread mold loading machine 20 is .the ability to move mold segments 202 radially with respect to main axle 22 and built tire 180 when mounted thereon. Equally important features of tread mold loading machine 20 include the ability to move built tire 180 longitudinally relative to expandable tread mold 200 while mounted on main axle 22 and the ability to rotate built tire 180 while mounted on main axle 22. Brake system 250 is also provided to prevent undesired rotational and/or longitudinal movement of main axle 22 while installing expandable tread mold 200 on retreading material 184. The various components and subassemblies which comprise tread mold loading machine 20 are secured to, supported by or contained within housing 24, which in turn is attached to and rests upon base 26. Components contained within housing 24 include prime mover or electrical motor 28 and electrical power supply box 30. Control panel 32 is attached to the side of housing 24 and extends outwardly therefrom. Control panel 32 is secured to one end of cable channel and supporting frame 34. The other end of cable channel and supporting frame 34 is secured to housing 24 at opening 35. Electrical cables and other conduits (not shown) may be disposed within cable channel and supporting frame 34 to extend from control panel 32 through opening 35 to the appropriate component contained within housing 24 or secured to housing 24. Cable channel and supporting frame 34 extends from housing 24 to preferably position control panel 32 exterior from and adjacent to expandable tread mold 200 when built tire 180 is mounted on main axle 22. The embodiment of tread mold loading machine 20 shown in FIGURES 1 and 2 is operated by a combination of electrical and pneumatic power. The various components and functions of tread mold loading machine 20 are controlled by a combination of electrical and/or pneumatic signals as appropriate. If desired, the electrical power functions and electrical control functions could be replaced by pneumatic and/or hydraulic power and control systems. In the same manner many of the components which are operated and controlled by pneumatic systems could be replaced by a hydraulic or electrical system with the exception of inflating built tire 180. Since built tire 180 is preferably inflated with air pressure while installing or loading expandable tread mold 200 thereon, there are several practical benefits from using the available air supply for other functions and purposes within tread mold loading machine 20. However, for specific applications and designs, these pneumatically operated components could be replaced by hydraulic and/or electrically operated components as desired. Several of the components and subassemblies which comprise tread mold loading machine 20 are secured to or supported by main axle 22. These components include expandable hub 40, a pair of rotary bearings 60, a pair of linear bearings 70, hollow drive shaft 80 and brake system 250. Rotary bearings 60 and linear bearings 70 are preferably disposed between the exterior of main axle 22 and the interior of hollow drive shaft 80. Head assembly 90 is secured to the front portion of housing 24 by annular plate 92 which is bolted to the front of housing 24. Annular plate 92 and the attached head assembly 90 are concentrically disposed around the exterior of main axle 22. Main axle 22 is supported within housing 24 by annular plate 92 and associated components. As best shown in FIGURES 1 and 2, ten sets of radial arms 94 and there associated guide rails 96 and 98 extend outwardly from head assembly 90. Head assembly 90 includes appropriate openings which extending radially therethrough to secure one end of each set of guide rails respectively 96 and 98 thereto. Additional openings are provided through head assembly 90 to allow the installation of each radial arm 94 between its associated guide rails 96 and 98. Radial arms 94 are disposed within head assembly 90 in a manner which allows rotation of radial arms 94 in unison with each other. A plurality of tread mold supporting arms 120 are secured to their associated radial arm 94 and guide rails 96 and 98. Each radial arm 94 is used to position its associated tread mold supporting arm 120 with respect to built tire 180 after built tire 180 has been mounted on main axle 22. Since radial arms 94 are rotated in unison with respect to each other, tread mold supporting arms 120 also move in unison with respect to each other. Expandable hub 40 is secured to the end of main axle 22 which extends through head assembly 90 and the front of housing 24. Expandable hub 40 and tire rim 178 provides a portion of the means for releasably mounting built tire 180 onto main axle 22. Preferably, tire rim 178 will be formed from multiple segments with elastomeric band 185 surrounding the segments. By using segmented tire rim 178 and enclosing the exterior of tire rim 178 with elastomeric band 185, different sizes of tire casings may be satisfactorily mounted on main axle 22 using the same expandable hub 40 and segmented tire rim 178. For purposes of illustration, segmented tire rim 178 is shown in FIGURE 2 but not in FIGURE 1. Main axle 22 preferably has one or more longitudinal bores extending therethrough and communicating with expandable hub 40. Air coupling 38 is provided on the end of main axle 22 contained within housing 24 and opposite from expandable hub 40. Expandable hub 40 includes housing 44 with a tapered cone (not shown) slidably disposed therein. Housing 44 and the tapered cone are concentrically disposed with respect to each other. Built tire 180 is placed on tire rim 178 when expandable hub 40 is in its first position. By directing pneumatic (air) pressure through coupling 38, air will flow through the longitudinal bore and move the tapered cone towards the end of housing 44 and expand nylon inserts (not shown) through radial slots 56. As the inserts expand radially from housing 44, they will force the segments which comprise tire rim 178 and the associated elastomeric band 185 outwardly to form a fluid tight seal with tire beads 186 provided on the inside diameter of built tire 180. Expandable hub 40 preferably includes one or more hose connections (not shown) . The air pressure flowing through the longitudinal bore of main axle 22 is typically 120 to 150 psig. A regulator (not shown) and sliding valve (not shown) are preferably provided_to reduce the air pressure and to control the flow of air pressure from main axle 22. Tire rim 178 will preferably have at least one valve stem (not shown) to allow inflating built tire 180 when mounted on expandable hub 40. Another feature of the present invention, as shown in FIGURE 2, is the cooperation between rotary bearings 60, linear bearings 70 and main axle 22 which allows longitudinal movement of expandable hub 40 relative to housing 24 and the other components which comprise tread mold loading machine 20. Rotary bearings 60 and linear bearings 70 allow expandable hub 40 to be moved longitudinally away from head assembly 90 and its associated tread mold supporting arms 120. The first position for expandable hub 40 and main axle 22, shown in FIGURE 2 by dotted lines, facilitates mounting built tire 180 onto tire rim 178 and expandable hub 40. Tire rim 178 preferably remains on expandable hub 40 and may be used on a repeating basis with a large number of built tires to load expandable tread mold 200 on respective built tires 180. A pair of rotary bearings 60 and a pair of linear bearings 70 are disposed between the exterior of main axle 22 and the interior of hollow drive shaft 80. Linear bearings satisfactory for use with the present invention may be obtained from Boston Gear, a Division of Rockwell International. Rotary bearings satisfactory for use with the present invention may be obtained from INA/Torrington. Dust cover 72 is installed on the front of head assembly 90 to protect the bearings and gears associated with main axle 22 and hollow drive shaft 80 from contamination and debris. Pinion gears 100 are secured to the end of each radial arm 94 which extends into head assembly 90. By disposing each pinion gear 100 contact with an annular gear coupled to drive shafter 80, rotation of hollow drive shaft 80 will be translated into rotation of each radial arm 94. Thus, rotation of hollow drive shaft 80 in a clockwise direction is translated into clockwise rotation of radial arms 94. In a similar manner, rotation of hollow drive shaft 80 in a counterclockwise direction will result in counterclockwise rotation of radial arms 94. An important feature of the present invention is that rotation of hollow drive shaft 80 results in rotation of each radial arm 94 in unison with the other radial arms 94. Sprocket gear 74 is mounted on the exterior of hollow drive shaft 80. Drive chain 76 connects sprocket gear 74 with electrical motor 28. Appropriate control signals are transmitted from control panel 32 to electrical motor 28 to cause either clockwise or counterclockwise rotation of hollow drive shaft 80 via drive chain 76 and sprocket gear 74. If desired for specific applications, electrical motor 28 could be replaced with other types of prime movers such as a hydraulic motor or a pneumatic motor. Air pressure can be supplied to expand inserts radiating outwardly to releasably lock tire rim 178 to expandable hub 40. When built tire 180 has been inflated and releasably mounted on expandable hub 40, built tire 180, expandable hub 40 and main axle 22 may be moved to their second position in which built tire 180 is radially adjacent to tread mold supporting arms 120 and centered within expanded opening 206 of expandable tread mold 200. Additional details concerning the design and operation of radial arms 94, tread mold supporting arms 120, expandable hub 40, rotary bearings 60 and linear bearings 70 may be found in U.S. Patent 5,354,406 entitled Apparatus for Retreading a Tire. Expandable tread mold 200 is installed or loaded onto retreading material 184 when built tire 180 is in its second position. As will be explained later in more detail, after tread mold segments 202 have been released from their respective mold supporting arms 120, expandable hub 40 along with rim 178 and built tire 180 may be returned to their first position. In this first position, built tire 180 may be deflated and then removed from tire rim 178 by releasing the pneumatic pressure which holds segmented tire rim 178 radially expanded. With built tire 180 and expandable hub 40 depressurized, built tire 180 with expandable tread mold 200 loaded thereon may be removed from tread loading machine 20. Another expandable tread mold 200 may be loaded onto tread mold supporting arms 120 and another built tire . 180 placed on tire rim 178 to repeat the process of installing another expandable tread mold 200 onto another built tire 180. The front of control panel 32 is shown in FIGURE 3. First switch 271 is provided with open and close buttons 271a and 271b respectively. First switch 271 is used to move tread mold supporting arms 120 radially with respect to main axle 22 and expandable hub 40 and to open or close expandable tread mold 200 as desired. Second switch 272 is provided to open and close clamps 140 associated with each tread mold supporting arm 120. For some applications, safety latch 282 may be provided to prevent accidental movement of second switch 272 from the close position to the open position. This feature of control panel 32 is shown in more detail in FIGURE 3A. Third switch 273 is provided on control panel 32 for use in centering built tire 180 within expanded opening 206 formed by expandable tread mold 200. Fourth switch 274 is preferably provided to inflate and deflate built tire 180 as desired. Fifth switch 275 is provided on control panel 32 to inflate and deflate expandable hub 40 and segmented tire rim 178 for use in mounting and removing built tire 180 therefrom. Sixth switch 276 is provided to activate brake system 250 and prevent undesired longitudinal movement of main axle 22 and expandable hub 40. Seventh switch 277 is provided to control brake system 250 to prevent undesired rotation of main axle 22 and expandable hub 40 while loading expandable tread mold 200 on retreading material 184. For some applications, eighth switch 278 may be provided to increase the inflation rate of built tire 180. As shown in FIGURE 2, tread mold loading machine 20 preferably includes brake system 250 disposed within housing 24 and coupled with main axle 22. Brake system 250 preferably includes a pair of rails 252 and 254 and an angle iron (not shown) which are aligned parallel with and offset from main axle 22. Rails 252 and 254 and the angle iron are secured to housing 24 so that brake system 250 may be used to prevent longitudinal and/or rotational movement of main axle 22 as desired. Brake rotor 256 is mounted on the exterior of main axle 22 adjacent to the end of main axle 22 having air coupling 38. A portion of brake rotor 256 extends into a pair of C-calipers and caliper housing 262 such that main axle 22 and the caliper housing will only move in unison with each other. A pair of C-calipers are provided in caliper housing 262. Caliper housing 262 is slidably disposed on rails 252 and 254. The C-calipers are substantially similar to each other in design and are preferably operated by pneumatic air pressure. However, electrical brake calipers may be satisfactorily used with tread mold loading machine 20. One of the C-calipers along with housing 262, brake rotor 256 and the angle iron cooperate with each other to provide a first brake assembly to prevent undesired longitudinal movement of main axle 22. Linear brake switch 276 on control panel 32 is used to control the flow of pneumatic air pressure which activates the first brake assembly preventing longitudinal movement of caliper housing 262 and main axle 22. A second C-calliper along with brake rotor 256, housing 262 and rails 252 and 254 cooperate with each other to provide a second brake assembly which prevents undesired rotational movement of main axle 22. Rotary brake switch 277 on control panel 32 is used to provide pneumatic pressure to activate the second brake assembly and tightly grip brake rotor 256 which prevents rotation of main axle 22. The pair of C-calipers can be activated independently from each other. Thus, brake system 250 may be used to prevent longitudinal movement of axle 2.2 while allowing rotational movement of axle 22 or prevent rotational movement of axle 22 while allowing longitudinal movement of axle 22 or prevent both rotational and longitudinal movement of axle 22. Each mold supporting arm 120 includes housing 122 with clamp assembly 140 partially contained therein. The principal elements of clamp assembly 140 includes a pair of fingers 142 and 144 which extend from housing 122-. For the embodiment of the present invention, rotation of a pinion gear (not shown) contained with housing 122 in one direction will cause movement of associated fingers 142 and 144 longitudinally towards each other. In the same respect, rotation of the pinion gear in the other direction causes movement of fingers 142 and 144 longitudinally away from each other. Such movements are u-sed to engage and disengage each clamp assembly 140 from its associated mold segment 202. For some applications it may be desirable to collar code one or more tread mold supporting arms 120 and the associated mold segments 202. By providing appropriate collar coding on at least one mold segment 202 a unique identifier is provided to allow placing expandable tread mold 200 in a selected position within tread mold loading machine 20. For other applications a ridge 244 may be formed on exterior surface 210 of at least one tread mold segment 202 to allow positioning expandable tread mold 200 at a desired location within tread mold loading machine 20. Heads 143 and 145 are provided respectfully on the end of each finger 142 and 144 extending from housing 122. Heads 143 and 145 may be inserted into appropriately sized slots 208 in each side of the respective mold segment 202. Another important feature of the present invention is that various types of mold segments may be used with tread mold loading machine 20 by either simply replacing the head on fingers 142 and 144 to match slots in each side the new mold segments or providing slot 208 in each side of the new mold segments matching the existing heads 143 and 145. As best shown in FIGURES 1 and 6, actuators 158 are positioned on the exterior of each housing 122. Actuator 158 is preferably air operated. As previously noted, various components of tread mold loading machine 20 may be either air operated, electrically operated or hydraulically operated. Actuator 158 is an example of an air operated component which could be replaced by an electric motor or a hydraulic motor. As shown in FIGURES 2 and 6, tread mold supporting arms 120 preferably include air cylinder 118 with piston 116 disposed therein. When mold clamp switch 272 on control panel 32 is moved to the close position, pneumatic air pressure is supplied to actuator 158 to move the respective clamp 140 associated with each tread mold supporting arm 120 to the closed position as shown in FIGURES 2 and 6. After heads 143 and 145 have been engaged with slots 208 in the respective mold segment 202, pneumatic air pressure is supplied to cylinder 118 to extend piston 116 and contact exterior surface 210 of the associated mold segment 202. Thus, air cylinder 118 and piston 116 cooperate with fingers 142 and 144 to ensure that each mold segment 202 is securely engaged with its respective clamp 140 by applying force to the exterior of each mold segment 202. Air cylinder 118 is preferably deactivated after each mold segment 202 has been securely engaged with its respective clamp 140. At least one mold supporting arm 120 will preferably include a first sensor assembly (not shown) to indicate when the associated mold segment 202 has contacted retreading material 184. When the selected mold segment 202 associated with the first sensor assembly contacts retreading material 184, the selected mold segment 202 will move upwardly and activate a limit switch (not shown) and prevent prime mover or electrical motor 28 from further rotation of radial arms 94 to move tread mold supporting arms 120 inwardly towards built tire 180. The first sensor assembly thus prevents placing undesired forces on built tire 180 if radially inward movement of mold supporting arms 120 continued after mold segments 202 contacted retreading material 184. A second limit switch (not shown) may also be secured to one or more tread molds supporting arms 120. When the associated mold segment 202 initially contacts retreading material 184, the second limit switch will be activated and to shift prime mover 28 from its first speed to its second speed. Thus, the speed of prime mover 28 is reduced when tread molds supporting arms 120 are a selected distance from retreading material 184. The first limit switch may be used to then stop movement of tread mold supporting arms 120 after expandable tread mold 200 has been properly engaged with retreading material 18 . As shown in FIGURES 2 and 5, expandable tread mold 200 includes a pair of tension springs 204 disposed in grooves 205 on the exterior of each mold segment 202. For some applications, each tension spring 204 may be disposed within hollow elastomeric tube 203 to minimize corrosion of the respective spring 204. If desired, an elastomeric band could also be provided on the exterior of mold segment 202 between tension springs 204 A segmented tread mold with tension springs and an elastomeric band are shown in more detail in United States Patent 5,342,462. As shown in FIGURE 4, each mold segment 202 is expandably engaged with an adjacent mold segments 202 for placement on retreading material 184. Tension springs 204 provide resilient means encircling mold segments 202 and urging mold segments 202 toward retreading material 184. Each mold segment 202 has a generally rectangular configuration with exterior surface 210 and interior surface 212 having a radius of curvature corresponding approximately to the radius of curvature of retreading material 184 on the exterior of built tire 180. The desired tread pattern 214 is formed on interior surface 212 of each mold segment 202. Engagement slots 208 are formed on opposite sides of each mold segment 202. Each engagement slot 208 preferably includes tapered surfaces 216 and 218 having dimensions which correspond approximately with the dimensions of chamfered surfaces 147 formed on heads 143 and 145 of the respective clamp 140. Each mold segment 202 preferably includes a pair of frames 220 and 222 extending along and attached to opposite sides of each mold segment 202. Frames 220 and 224 are essentially identical with each other. Frames 220 and 222 have a radius of curvature corresponding approximately with the radius of curvature of exterior surface 210 and interior surface 212. Frames 220 and 222 are longer than the associated mold segment 202. End 224 of each frame 220 and 222 extends from one end of the respective mold segment 202. In the same manner, end 226 of each frame 220 and 222 extends from the opposite end of the respective mold segment 202. Frames 220 and 222 form channels 225 and 227 which are sized to respectively receive ends 224 and 226 of frames 220 and 222 of adjacent mold segments 202. Thus, ends 224 and channels 225 along with ends 226 and channels 227 cooperate with each other to maintain the desired alignment of mold segments 202 with respect to each other while at the same time allowing expansion and contraction of expandable tread mold 200. Metal plate 228 is preferably attached to exterior surface 210 of each mold segment 220 between frames 220 and 222. For some applications metal plate 228 is formed from aluminum. Metal plate 228 extends from one end of the respective mold segment 202 and covers the end of an adjacent mold segment 202. The length of plate 228 is selected to cover a portion of exterior surface 210 of an adjacent mold segment 202 and the gap formed between adjacent mold segments 202 when mold segments 202 are expanded relative to each other. When expandable tread mold 200 is in its fully expanded position as shown in FIGURE 1, a gap of approximately one and one-half inches may be formed between the ends of adjacent mold segments 202. When expandable tread mold 200 has been installed or loaded on built tire 180 as shown in FIGURE 7, the gap between adjacent mold segments 202 for a typical truck tire will be approximately five eighths of an inch. The size of the gap between adjacent mold segments will depend upon the dimensions associated with built tire 180 and the amount of retreading material 184 disposed on the exterior of built tire 180. During the curing process, the gap between adjacent mold segments 202 will be reduced even further until the ends of adjacent mold segments 202 are almost in contact with each other. The present invention results in only a very small amount of rubber flashing (if any) being extruded between the ends of adjacent mold segments 202 during the curing process which produces a retread tire having a desirable visual appearance. One of the advantages of the present invention includes the ability to modify the dimensions of expandable tread mold 200 and mold segments 202 for use with a wide variety of tread patterns and tire sizes. The dimensions of interior surface 212 may vary from approximately six and one-half inches to twelve and one-half inches in width. The dimensions of exterior surface 210 may vary from seven inches to thirteen and one-half inches in width. The length of mold segments 202 may vary from approximately twelve inches.to twenty-four inches. As shown in FIGURES 7 and 8, a layer of wicking material 230 is preferably disposed on the exterior of at least mold segment 202. In a process using the apparatus of the present invention, tire casing 182 is prepared to receive retreading material 184. One of the steps in preparing tire casing 182 includes buffing to completely remove the old tread pattern (not shown) and to provide the desired diameter, tread width and tire radius for built tire 180. Proper buffing will ensure maximum adhesion between retreading material 184 and tire casing 182. Uncured tread rubber along with one or more adhesive layers are then applied to tire casing 182 to form a layer of retreading material 184. Since the present invention includes expandable tread mold 200 which can accommodate variations in the dimensions of built tire 180, retreading material 184 with ample thickness may be used to provide a reservoir of uncured tread rubber to flow into any peaks or valleys associated with the buffed surface of tire casing 182. The bond strength between retreading material 184 and tire casing 182 is increased by providing ample thickness for retreading material 184 which results in increased dependability of the resulting retread tire. The present invention allows the use of various types of mold cure tread compounds to form retreading material 184. Examples of these mold cure tread compounds include "UltraPneu, " "Pneuflex" and "PneuModal" which are available from Oliver Rubber Company located in Athens, Georgia. Tread mold loading machine 20 and expandable tread mold 200 allow selecting the appropriate mold cure tread compound having desired characteristics to optimize the performance of the resulting retread tire. Expandable tread mold 200 is initially placed on tread mold loading machine 20 and expanded to its fully open position 206 as shown in FIGURES 1 and 2. Expandable hub and tire rim 178 are moved to their first position as shown by dotted lines in FIGURE 2 and built tire 180 mounted on tire rim 178. Built tire 180 is then inflated and expandable hub 40 moved to its second position as shown in FIGURE 2. Mold segments 202 of expandable tread mold 200 are next placed on retreading material 184 with tread pattern 214 engaging the outer surface of retreading material 184. After expandable tread mold 200 has been loaded on retreading material 184, built tire 180 and the associated tread mold 200 are removed from tread mold loading machine 20. A pressure envelope or elastomeric curing envelope 232 is then stretched over the assembled tread mold 200 and built tire 180. Pressure envelope 232 includes hollow valve stem 242 which is preferably installed over wicking material 230 as shown in FIGURE 8. Wicking material 230 provides the desired air flow path in cooperation with hollow valve stem 242 to allow removing air to create a vacuum within pressure envelope 232. Seal rings 234 are used to form a seal between tire beads 186 and the curing envelope 232. Seal rings satisfactory for use with the present invention are available from Oliver Rubber Company located in Athens, Georgia. U.S. Patent 5,306,130 entitled Apparatus for Recapping a Tire and an Improved Curing Envelope for Use Therein and U.S. Patent 5,342,462 entitled Method and Apparatus for Retreading a Tire provide additional information concerning the use of elastomeric curing envelopes. A hose assembly (not shown) may be attached to hollow valve stem 242 to connect the sealed assembly with a vacuum pump (not shown) . A vacuum is then drawn within curing envelope 232 to remove any air and to assist in creating a pressure differential across expandable tread mold 200 and retreading material 184 during the curing process. The sealed assembly while connected to the vacuum source is then placed in a curing chamber (not shown) at the appropriate pressure and temperature and for the length of time required to cure retreading material 184 with tread pattern 214 provided by mold segments 202. After proper curing of retreading material 184, the sealed assembly may be removed from the curing chamber. Built tire 180 and expandable mold 200 are then removed from curing envelope 232 and mounted on tire rim 178 and expandable hub 40. FIGURE 9 shows mold segment 202 with tread mold pattern 214 embedded in cured retreading material 184a. Built tire 180 and expandable tread mold 200 are centered within tread mold support arms 120 and each clamp 140 engaged with its respective mold segment 202. The tread mold supporting arms 120 are moved to their fully expanded position which releases expandable tread mold 200 from built tire 180 with cured retreading material 184 having the desired tread pattern. From the foregoing description, it will be appreciated that the apparatus and methods of the present invention, permit retreading of tires without the necessity of distorting the tire casing or requiring the use of expensive mold stretchers. The operation of loading or installing a tread mold on a prepared tire casing can be performed simply and quickly to efficiently retread tires. Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.

Claims: WHAT IS CLAIMED IS: 1. An expandable tread mold for mounting on a built tire which includes a prepared tire carcass with retreading material on the exterior thereof, comprising: a plurality of mold segments expandably engaged with each other for placement on the retreading material; resilient means encircling the mold segments to urge the mold segments toward the retreading material; each mold segment having a generally rectangular configuration with an exterior surface and an interior surface; the interior surface having a radius of curvature corresponding approximately to the radius of curvature of the built tire; a tread pattern formed on the interior surface of each mold segment; an engagement slot formed in opposite sides of each mold segment; a frame attached to and extending along opposite sides of each mold segment; each frame having a first end which extends from one end of the associated mold segment and a second end which extends from the other end of the associated mold segment; and each mold segment having a pair of channels formed on opposite sides thereof to slidably receive respective ends of each frame from an adjacent mold segment. 2. The tread mold of Claim 1 wherein the resilient means comprises at least one annular tension spring encircling the mold segments. 3. The tread mold of Claim 1 wherein each mold segment further comprises: at least one groove formed in the exterior surface thereof; and an annular tension spring located in each groove. 4. The tread mold of Claim 1 wherein the resilient means further comprises: a pair of grooves formed in the exterior surface of each mold segment and aligned with corresponding grooves formed in the exterior of adjacent mold segments; and an annular tension spring disposed in each annular groove. 5. The tread mold of Claim 1 wherein the resilient means comprises: at least one annular tension spring encircling the mold segments; and each annular tension spring disposed with a hollow elastomeric tube to minimize corrosion of the respective tension spring. 6. The tread mold of Claim 1 further comprising: a plate attached to the exterior of each mold segment and extending from one end thereof; and the length of the plate selected to cover a portion of the exterior of an adjacent mold segment and the gap formed between adjacent mold segments when the mold segments are expanded relative to each other. 7. The tread mold of Claim 1 further comprising at least one of the mold segments having a unique identifier to allow placing the tread mold in a selected position within a tread mold expander. 8. The tread mold of Claim 1 further comprising a ridge formed on the exterior of the tread mold to allow positioning the tread mold at a desired location within a tread mold expander. 9. The tread mold of Claim 1 further comprising a layer of wicking material attached to the exterior surface of at least one mold segment. 10. The tread mold of Claim 1 further comprising ten mold segments. 11. The tread mold of Claim 1 further comprising: each mold segment having a width of approximately six inches to twelve inches; and each mold segment having a length of approximately twelve inches to twenty-four inches. 12. A method for installing an expandable tread mold on a built tire which includes a prepared tire carcass having a strip of retread material disposed on the exterior thereof, comprising the steps of: placing a resilient means on the exterior of a plurality of mold segments to urge the mold segments toward each other; releasably securing the plurality of mold segments to a plurality of respective mold supporting arms provided by a tread mold loading machine; applying force to the exterior of each mold segment while releasably securing the respective mold segments and mold supporting arms with each other; positioning the plurality of mold segments with the tread mold loading machine to define in part an expanded opening to receive the built tire therein; mounting the built tire on the tread mold loading machine; positioning the built tire within the expanded opening of the tread mold defined in part by the mold segments; moving the mold segments to contact the retreading material on the exterior of the built tire; and releasing the mold segments from the mold supporting arms after engagement with the retreading material. 13. The method of Claim 12 wherein the step of releasably securing the mold segments further comprises the step of engaging a clamp carried by each mold supporting arm with one of the mold segments. 14. The method of Claim 13 wherein the step of releasing the mold segments further comprises the step of activating each mold supporting arm to disengage its respective clamp from the associated mold segment. 15. The method of Claim 12 wherein the step of . mounting the built tire on the tread mold loading machine further comprises the step of: providing an expandable hub engaged with a main axle which extends longitudinally through the tread mold loading machine; positioning the expandable hub outside the expanded opening defined in part by the mold segments; mounting the built tire on a tire rim associated with the expandable hub; and positioning the built tire, the tire rim and the expandable hub within the expanded opening defined in part by the mold segments. 16. The method of Claim 15 wherein the step of mounting the built tire on the tread mold loading machine f rther comprises the steps of: installing a segmented tire rim on the expandable wheel hub; placing an elastomeric band on the exterior of the tire rim; and mounting the built tire on the tire rim whereby the built tire will contact the elastomeric band to form a pressure seal therewith. 17. The method of Claim 12 wherein the step of moving the mold segments to contact the retreading material further comprises the steps of: ' moving the mold segments radially inward until the mold segments contact the retreading material; providing a sensor on at least one of the mold supporting arms to indicate that the associated mold segment has contacted the retreading material; and stopping movement of the mold segments in response to a signal from the sensor. 18. The method of Claim 15 further comprising the steps of removing the built tire with the mold segments loaded thereon from the tread mold loading machine and curing the retreading material with the mold segments disposed thereon. 19. The method of Claim 15 further comprising the steps of: removing the built tire with the mold segments loaded thereon from the tread mold loading machine; placing the built tire and mold segments within a curing envelope; and placing the built tire, mold segments and curing envelope in a curing chamber to cure the retreading material. 20. The method of Claim 19 further comprising the steps of: removing the curing envelope from the built tire; mounting built tire on the expandable hub of the tread mold loading machine; engaging each mold segment with one of the tread, mold supporting arms; and moving the tread mold supporting arms radially outward from the built tire to release the mold segments from the cured retreading material. 21. An expandable tread mold for mounting on a built tire which includes a prepared tire carcass having a strip of retreading material disposed on the exterior thereof, comprising: a plurality of rigid mold segments which are engaged with each other to allow radial expansion relative to each other for loading on the retreading material; means for releasably engaging each mold segment with a tread mold loading machine; resilient means encircling the mold segments to urge the mold segments toward the retreading material; each mold segment having a generally rectangular configuration with an exterior surface and an interior' surface; the interior surface having a radius of curvature corresponding approximately to the radius of curvature of the retreading material on the exterior of the built tire; a tread pattern formed on the interior surface of each mold segment; means for aligning each end of each mold segment with one end of an adjacent mold segment to define a generally circular opening; and a layer of wicking material disposed on the exterior of at least one mold segment.

Inventors: CLAYTON ANDREW R, FLYNN ROBERT A, KING MICHAEL J, CLAYTON, ANDREW, R., FLYNN, ROBERT, A., KING, MICHAEL, J.
Applicants: OLIVER RUBBER CO, OLIVER RUBBER COMPANY
Application year: 1996
Main classification: B29C35
IPC codes: B29D30