Abstract:
Sealing rings for use with an outer curing envelope to retread a tire. Each ring includes an outwardly opening annular channel member having a base portion molded to conform to the contour of the tire bead, and an annular outer flange portion having an enlarged sealing rib for underlapping the outer curing envelope at the outer side of the tire casing near it maximum width. Two rings are required, one on each side of the tire casing, to form with the outer curing envelope a complete seal enclosure around the outside tire.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to tire retreading; and more particularly, it relates to novel and improved curing envelope sealing rings for use with an outer curing envelope to enclose a tire casing and tread strip assembly during retreading. 
     Tire retreading, or recapping, may be applied to any size tire casing, but is more commonly used on large radial truck tires. The casings of these tires usually have a longer useful life than their treads. Therefore, it is often more cost effective to retread a worn casing than to replace it with a new tire. 
     One known process simultaneously bonds and vulcanizes an uncured rubber on a worn tire casing in a tread forming mold. In another known process, a precured rubber strip with a premolded tread is wrapped around the buffed crown surface of the worn tire casing with a bonding agent such as uncured rubber or cushion gum disposed therebetween. The assembly is then sealingly enclosed in an annular elastomeric curing envelope of U-shaped radial cross-section, typically of thin synthetic rubber, or the like, such as manufactured by Presti Rubber Products, Inc. of New Britain, Pa. The annular space between the tread and the envelope is evacuated, thereby stretching the outer envelope into intimate contact with the outer sidewalls of the casing and all surfaces of the tread strip. This insures that uniform pressure is applied over the entire bonding area without tread distortion during the curing process. The outer envelope also prevents either air or steam from being entrapped between the tread strip and the casing and migrating into the bonding agent. The entire assembly is then placed in a curing chamber, or autoclave, at elevated temperatures and pressures to vulcanize the uncured components and to positively bond the casing and tread strip together. The outer envelope is then removed for reuse if desired. 
     Outer curing envelopes as described are not as easy to install as desired, especially when smaller inside diameter envelopes need to be pulled over the outside diameter of large truck tire casings. Therefore various special mountings, rims, and linings have been developed to facilitate sealing of the curing envelope around the tire casing and tread assembly. 
     In one known commercially available arrangement, the side skirts of the outer curing envelope are made longer than the sidewalls of the tire casing with which it is to be used. The excess margin of the outer envelope, i.e. the margins adjacent to the inner peripheries of the skirts, are tucked inside the tire beads and held in place by a radially-expandable ring. In this arrangement, the inside surface of the tire casing is exposed while the entire outside is encased. 
     Another arrangement involves the use with an outer envelope of an inner envelope of non-form fitting, pieced together construction for enclosing the entire inside surface and beads of the casing. This inner envelope includes annular flaps which are overlapped by the skirts of the outer curing envelope on both sides of the tire casing. The entire tire casing is thereby sheathed. 
     An improvement in the inner envelope arrangement described above is disclosed in co-pending U.S. patent application Ser. No. 07/336,758 filed on Apr. 12, 1989, by Frederick J. Presti, now U.S. Pat. No. 5,007,978, owned by the assignee of the present application. In this improvement, the inner envelope is of tripartite construction having a U-shaped portion which engages the inside of the tire casing and a pair of molded form-fit assemblies carried on the skirts of the U-shaped portion. The molded form-fit assemblies are each constructed so that the base and flaps conform to the surface contour of the beads of the casing. The flaps extend radially outward and along the outer sidewalls of the tire casing and terminate in enlarged annular ribs which sealingly underlap the skirts of the outer envelope on both sides of the casing. While very useful for the purposes intended, this improved inner envelope must be provided in numerous sizes and shapes to satisfy the large variety of sizes and shapes of tire casings. For reasons to be stated, there is a need for a retreading system which obtains the advantages associated with the use of an outer envelope but for a wider range of tire sizes. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a novel sealing ring suitable for use with an outer curing envelope in retreading tire casings of various sizes and configurations. 
     Another object is to provide sealing rings which can be readily mounted on, and demounted from, the tire beads while forming a positive seal with the inner sides of an outer curing envelope. 
     A still further object is to provide a unitary rim and sealing ring assembly suitable for use with an outer curing envelope in a tire retreading process. 
     Yet another object is to provide a reusable sealing ring which is particularly useful in tire bead restoration during the retreading process. 
     Briefly, these and other objects and advantages of the invention are accomplished with sealing rings of a molded vulcanized heat-resistant rubber installed between retreading rims and the beads of a tire casing, for cooperating with an outer curing envelope mounted about a tread strip and casing assembly to form an air-tight outer enclosure therefor. Each sealing ring comprises an outwardly opening annular channel, molded to conform to the contour of the bead of a new tire, with a short inner flange and an annular outer flange having an enlarged integral outer peripheral sealing rib for underlapping the outer curing envelope at one outer side of the tire casing near its maximum width. Two rings are required, one on each side, to form a complete sealed enclosure around the outside of the tire casing, the inside of which is exposed. In an alternate embodiment, the sealing rings are bonded to the rims to form a unitary assembly which can be mounted readily. 
     Other objects, features and advantages of the invention will become more apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one embodiment illustrating sealing rings according to the invention installed with an outer curing envelope on a tire casing and tread strip assembly; 
     FIG. 2 is a view in radial cross section taken along the line 2--2 of FIG. 1 of the sealing rings and outer curing envelope showing the tire casing mounted on tire retreading rims and under external pressure; 
     FIG. 3 is a view in radial cross section of the sealing rings and outer curing envelopes of FIG. 1 in an unstressed state; and 
     FIG. 4 is a view in radial cross section of a portion of another embodiment of a curing envelope sealing ring bonded to a tire retreading rim. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings wherein like characters designate like or corresponding parts throughout the several views, FIG. 1 shows a pair of reusable curing envelope sealing rings 10a and 10b, installed with an annular outer curing envelope 12 on a tire casing and tread assembly 13 prepared for retreading. The rings are identical in all respects except for being mounted on opposite sides of the casing. A valve 14 in outer envelope 12 provides a connection for drawing a vacuum in the space between the outer envelope and the tire casing thus forming a seal between the sealing rings 10a and 10b and the outer envelope. 
     FIG. 2 illustrates tire assembly 13 which includes a worn casing 18 with a precured tread strip 20 adhered to the crown of the casing by a layer of a bonding agent 22 such as precured cushion gum or rubber. Sealing rings 10a and 10b and outer envelope 12 are mounted on opposed sealing rims 16a and 16b, evacuated of air, and ready for placing in a curing chamber under controlled temperature and pressure. The rings and outer curing envelope are shown in a stressed state due to their being drawn by vacuum against the surface contours of the treads and sides of the casing. 
     Referring now to FIG. 3, outer curing envelope 12 is preferably of heat-resistant, synthetic rubber, compression-molded construction and is of generally U-shaped radial cross-section having a crown 12a and a pair of radially inwardly extending skirts 12b for contiguously covering tread strip 20 and radially inward portions of the sidewalls of casing 18. Crown 12a is preferably thicker than skirts 12b to allow it to be stretched with ease over the contour of the tire treads while minimizing any distortion of the tread when pressure is applied during vulcanizing. It is to be noted that the skirts 12b extend radially inward beyond the widest dimension of the tire casing, but need not extend as far as the tire casing beads. A preferred outer envelope is manufactured in accordance with the teachings of U.S. Pat. No. 4,036,271 which issued to Frederick J. Presti, the disclosure of which is incorporated by reference herein. 
     Curing envelope sealing rings 10a and 10b are identical to each other but are reversely installed on opposite rim-engaging shoulders, or beads, 18a of the tire casing. Each sealing ring 10a and 10b is also preferably, but not necessarily, of a monolithic compression-molded, heat-resistant rubber, such as disclosed in the above referenced &#39;271 Presti patent. Each ring has a generally U-shaped radial cross-section defined by a base 11 of uniform thickness for engaging the inner periphery of bead 18a, a relatively narrow inner annular flange 11a for engaging an area on the inside of casing 18 adjacent the bead 18a, and a considerably wider outer annular flange 11b engaging an area on the outside of casing 18 and underlapping outer envelope skirt 12b. A complete enclosure around the outer surface of the tire is provided thereby, but the inside of the tire casing is uncovered except for a relatively small region adjacent the beads 18a. 
     The end of each outer flange 11b terminates in an enlarged integral annular sealing rib 11c of outwardly tapering generally wedge-shaped radial cross-section which terminates in an annular sealing shoulder 11d at its widest dimension. The sealing shoulder 11d extends outwardly from the casing sidewall for sealing engagement with the outer curing envelope where it underlaps its skirt 12b, preferably at the widest dimension of the tire casing, or in close proximity thereto. The inner annular flange 11a terminates short of the widest dimension of the tire and defines with the wider flange a U-shaped cross-section having legs of significantly unequal length. In the embodiment illustrated, the inner flange 11a has a length which corresponds substantially to the width of the tire bead 18a. 
     Sealing rings 10a and 10b in the vicinity of tire beads 18a are relatively thick in order to maintain, in molded relief, the original contour of the bead of a new tire when outer curing envelope 12 is drawn under vacuum. Specifically, the base 11 in the region adjacent the bead 18a is thicker than the outer flange 11b in the region radially inward of the sealing rib 11c. Thus, uncured rubber can be built up on the beads to restore it to the original contour during the retreading process. 
     Referring again to FIG. 2, the sealing rings 10a and 10b are installed in underlapping relation with the outer envelope 12 on a reconstructed tire assembly, and retreading rims 16a and 16b are then mounted within the inner periphery of sealing rings 10a and 10b to compress bases 11 against beads 18a and form a seal therewith. A vacuum is then drawn at valve 14 for causing ambient atmospheric pressure to draw the outer envelope into intimate contact with the entire tread surface and with the outer sides of the tire casing 18. In doing so, a positive seal is established along the shoulder 11d where the sealing ribs 11c of the sealing rings 10a and 10b underlap the skirts of outer envelope 12 at the widest dimension of the tire casing. 
     In an alternate embodiment, shown in the fragmentary cross-section of FIG. 4, curing envelope sealing rings 10a and 10b in the vicinity of their bases 11 are bonded to rigid annular rims 16a and 16b as by a vulcanized bonding agent 24, to form a unitary structure for quick mounting. 
     By way of example, and not by way of limitation, a preferred ring 10a for use in retreading an 11R 22.5, U.S. made truck tire, has an outer annular flange 11b length of 6.5 inches, an inner annular flange 11a length of 1.5 inches, and a base 11 length of 1.75 inches. The thickness of the ring in the region of the base is preferably about 0.130 inches. The thickness of the outer flange 11b in its necked-down region radially inward of the terminal end 11c is about 0.090-0.100 inches. The terminal end 11c has a radial extent of 2.0 inches and a shoulder length 11d, or thickness, of 0.5 inches adjacent its outermost end. The ring 10a is preferably fabricated of heat resistant rubber. 
     Some of the many advantages of the invention should now be readily apparent. For example, a reusable curing envelope sealing ring is provided which can be used in pairs for various widths of casings, thereby minimizing the assortment of components required for retreading. The rings can be quickly and easily installed to underlap an outer curing envelope and seal a tread strip and casing assembly for evacuating air or steam therefrom. The ring can also be made into a unitary assembly with a retreading rim. 
     While the present invention may not provide all the advantages associated with the use of the inside envelope which is the subject of co-pending application Ser. No. 07/336,758, supra, such as providing a complete barrier around the entire tire during vulcanization of the tread, its aforementioned advantages are nevertheless commercially significant to the small volume retreader who cannot afford to maintain the large inventory of inner envelopes required to handle a wide range of tire casing sizes. 
     Of course, it is understood that many changes in construction and widely differing embodiments and applications of the invention will be apparent to those skilled in the art to which this invention relates without departing from its spirit and scope as expressed in the appended claims.