Abstract:
A retreaded tire assembly and method for making the same is disclosed. The method and assembly provide for the application of new tread to a buffed tire casing with only a layer of cushion gum disposed therebetween. The cushion gum is applied directly to the buffed circumference of a tire casing without the use of conventional spray cement normally applied to the buffed surface of the entire casing.

Description:
This is a Continuation of application Ser. No. 08/399,070 filed Mar. 8, 1995 abandoned. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to a method for making retreaded tires and particularly to a method for making retreaded tires that eliminates the need for spray cement normally applied to the tire casing. 
     BACKGROUND OF THE INVENTION 
     Retreaded tires have been available for many years and provide an economical way to gain additional use out of a tire casing after the original tread has become worn. According to one conventional method of retreading, sometimes referred to as cold process retreading, the remaining tread on the used tire is removed by a special buffing machine that grinds away the old tread and leaves a buffed surface to which a new layer of tread may be bonded. 
     Removal of the old tread from the tire casing provides a generally smooth treadless surface about the circumference of the tire casing. The tire casing may then be examined for injuries, often called skives, which are filled with a repair gum. After completion of the skiving process, the buffed surface is sprayed with a tire cement that provides a tacky surface for application of bonding material and new tread. Then a layer of cushion gum is applied to the back, i.e., the inside surface, of a new layer of tread. The cushion gum and tread are applied in combination about the circumference of the tire casing to create a retreaded tire assembly ready for curing. The cushion gum forms the bonds between the tread and the tire casing during curing. 
     Following assembly of the tire casing, cement, cushion gum and tread, the overall retreaded tire assembly is placed within a flexible rubber envelope. An airtight seal is created between the envelope and the bead of the tire. The entire enveloped tire assembly is placed within a curing chamber, and subjected to pressure and a raised temperature for a specific period of time. The combination of pressure, temperature and time chemically bonds the layer of cushion gum to both the tire casing and the new tire tread. 
     The above-described method of cold process retreading works well and provides high quality, retreaded tires. However, in certain applications it would be advantageous to eliminate the spray cement. This is particularly true in geographical areas where there is increased regulation of the use of chemicals within spray cement. Generally, available spray cements include either heptane solvent or methyl chloroform. The heptane solvent has been found to contribute to smog formation, and methyl chloroform, although it does not cause smog, has tended to be substantially more expensive then heptane solvent. 
     Use of spray cement can also add to the cost of producing retreaded tires due to the product cost and equipment cost. For example, because cementing of the tire casing should only be dome in a well ventilated spray booth, retreading shops must purchase appropriate ventilation equipment. Elimination of the spray cement thus eliminates the need to purchase ventilated spray booths. 
     A potential solution to smog problems associated with using heptane solvent is the installation of solvent capture equipment at each retreading shop. However, this solution is disadvantageous due to the cost of the equipment and the operational and maintenance costs. The present invention addresses the drawbacks associated with using spray cement during retreading of tires. 
     SUMMARY OF THE INVENTION 
     The present invention includes a method for retreading a tire that comprises the steps of removing the tire tread from a tire casing to present a buffed surface. Then, a layer of cushion gum is applied directly to the buffed surface without spraying cement over the buffed surface. A tread layer is wrapped about the layer of cushion gum, and finally, the tire is treated to form bonds between the casing and the layer of cushion gum and between the tread layer and the layer of cushion gum. 
     Another unique aspect of the invention is a retreaded tire assembly prepared for insertion into a pressurized heating chamber. The tire assembly includes a tire casing having a pair of side walls and a radially outer wall spanning the pair of side walls. The radially outer wall has a buffed surface disposed about the outer circumference of the tire casing. A layer of cushion gum is disposed directly against the buffed surface, and a tread layer is disposed against the cushion gum about the outside circumference of the cushion gum. After appropriate heat and pressure treatment, the tire casing, cushion gum and tread layer became bonded into an integral retreaded tire that may be used on an appropriate over-the-road vehicle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
     FIG. 1 is a cross-sectional view of an exemplary original tire; 
     FIG. 2 is a cross-sectional view of the tire of FIG. 1 after the tread layer has been removed from the tire casing; 
     FIG. 3 is a schematic representation of the layer of cushion gum and the mew tread layer being applied to a tire casing; 
     FIG. 4 is a cross-sectional view of the tire casing illustrated in FIG. 2 with the addition of the layer of cushion gum and the new tread layer; and 
     FIG. 5 is a perspective cross-sectional view of an alternate embodiment of a retreaded tire according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring generally to FIG. 1, an original tire  10  is shown as having a tire casing  12  from which extends a tire tread  14 . The illustrated tire  10  is a radial tire; however, the invention applies equally to other types of tires, such as bias ply tires. 
     More particularly, tire  10  includes a pair of side walls  16  bounded by a generally radially outward wall  18  that spans side walls  16 . Each side wall  16  extends radially inward from outer wall  18  and terminates in a bead area  20  designed for mounting on the tire rim (not shown). Bead area  20  may be designed in a variety of configurations depending on, for example, tire type, tire size or rim configuration. In the illustrated embodiment, each bead area  20  includes a bead heel  22 , a bead toe  24 , and a bead sole  26 . Each bead area  20  may also include a bead bundle  28  and a chafer ply  30 . Both bead bundle  28  and chafer ply  30  may include, for example, metal strands or wires to improve the strength of bead area  20 . 
     Side walls  16  may also include multiple layers, such as a rubber layer  32 , a radial ply  34  and an inner liner  36  which cooperate to provide a strong but flexible side wall. Side walls  16  are joined to radially outward wall  18  and tread  14  through a pair of shoulder areas  38 . Shoulder areas  38  extend towards tire tread  14  which, in turn, is disposed radially outwardly from wall  18  of tire casing  12 . Tire tread  14  may include a plurality of grooves  40  designed to channel water and provide added traction during certain road conditions. Additionally, outer wall  18  may be strengthened by a plurality of belts or cords  42  extending circumferentially about tire  10  within wall  18  (see FIGS.  2  and  5 ). 
     After tire tread  14  wears beyond a certain limit, tire  10  must either be discarded or retreaded before it should be used on the vehicle for which it was designed. In cold process retreading, the remaining tire tread  14  is removed from tire casing  12  by a buffing machine, such as the Model 8110 buffing machine manufactured by Bandag, Incorporated of Muscatine, Iowa. During the buffing operation, the original tire tread  14  is ground away from tire casing  12 , leaving a buffed surface  44  as illustrated in FIG.  2 . Buffed surface  44  extends circumferentially about tire casing  12  and also extends transversely across the outside of outer radial wall  18  until it terminates at buffed shoulder areas  46 . 
     Following removal of the used tread layer, a process called skiving and filling is performed on tire casing  12 . Skiving is the removal of damaged material from a tire prior to making a repair. Often, the tire casing  12  accumulates holes, nicks or tears due to stones or other sharp objects the tire comes in contact with during use. The injured or damaged area is first ground smooth by an appropriate grinding tool and then filled with repair gum, such as Bandag extruder repair rope or repair gum or some other suitable material. It is necessary to fill the injured areas to the level of buffed surface  44  to avoid air pockets between buffed surface  44  and the later applied tread layer. Trapped air can have negative effects on the longevity of a typical retreaded tire. Following the skiving and filling operation, a building step occurs in which a layer of cushion gum and a new tread layer are wrapped about the circumference of tire casing  12  along buffed surface  44 . 
     As illustrated best in FIG. 3, a building machine  48  (shown schematically), such as the Bandag 5110 semiautomatic builder manufactured by Bandag, Incorporated, may be used to apply a layer of cushion gum  50 , such a HD30 cushion gum manufactured by Bandag, Incorporated. Although the layer of cushion gum  50  could be applied to tire casing  12  in a variety of ways, the schematic representation of FIG. 3 shows a roll of the cushion gum  52  rotatably mounted on building machine  48 . The layer of cushion gum  50  moves about a tensioning roller  54  prior to being wrapped circumferentially around buffed surface  44 . 
     Preferably, cushion gum layer  50  is covered by a bottom plastic sheet  56 , e.g. a poly sheet, and a similar top plastic sheet  58 . As illustrated, bottom sheet  56  is peeled away from cushion gum layer  50  shortly before the cushion gum is wrapped about tire casing  12  along buffed surface  44 . Bottom plastic sheet  56  may then be wrapped about tensioning roller  54  as shown in FIG.  3 . 
     Cushion gum layer  50  is preferably applied to buffed surface  44  within eight hours of buffing. Additionally, the application has been found to work best when the layer of cushion gum  50  is applied under tension in the circumferential direction. Depending on the application, it may be desirable to slightly stretch the cushion gum layer  50  to achieve better adherence to buffed surface  44 . Cushion gum layer  50  is cut transversely and the cut edge is spliced with the leading edge so there is no gap between the beginning and the end of cushion gum layer  50 . Any overlap between the leading edge and the trailing cut edge is preferably limited to one-eighth inch or less. 
     After cushion gum layer  50  is applied to tire casing  12 , layer  50  is stitched, or in other words pressed, against buffed surface  44  to drive out any air trapped between the cushion layer and buffed surface  44 . Following stitching, the top layer of plastic  58  is removed from cushion gum layer  50  to permit a new tread layer  60  to be applied over the cushion gum. The stitching step also helps prevent the cushion from lifting away from buffed surface  44  when plastic layer  58  is removed and tread layer  60  is applied. 
     Preferably, tread layer  60  is also applied with the assistance of building machine  48 , although there are a variety of ways to wrap tread layer  60  about the circumference of tire casing  12 . When using building machine  48 , a tread roll  62  is rotatably mounted thereon, and tread layer  60  is guided onto tire casing  12  against cushion gum layer  50  by guide rollers  64 . 
     Tire casing  12  is rotated on building machine  48  until a sufficient length of tread layer  60  is unraveled from tread roll  62  to extend about the circumference of tire casing  12 . Tread layer  60  is then cut generally transversely to the circumferential direction, and the cut end is butted up against the leading edge of tread layer  60  to form a splice. The tread layer splice is often held together by a plurality of staples (not shown). It is also preferred that the spliced area of cushion gum layer  50  and the spliced area of tread layer  60  be disposed at different points along buffed surface  44 . 
     Although the application of cushion gum layer  50  and tread layer  60  to a tire casing  12  by building machine  48  has been generally known in the industry for many years, the unique aspects of this invention method of retreading allows the omission of a previous step, namely the application of spray cement to buffed surface  44 . Previously, spray cement would be initially applied to buffed surface  44 . Then, cushion gum layer  50  would be applied to the inside or lower surface of tread layer  60 . The combination of cushion gum layer  50  and tread layer  60  would be wrapped about cement covered buffed surface  44  and spliced together. 
     The present method permits the elimination of the spray cement which overcomes certain disadvantages described in the background of the invention section above. By first stretching the layer of cushion gum about the circumference of tire casing  12 , stitching the cushion gum and then applying tread layer  60  over the combined tire casing  12  and cushion gum layer  50 , the necessity of using spray cement has been eliminated. It has been found that retreaded tires made according to the new method have very desirable characteristics without requiring an extra cementing step. 
     After application of cushion gum layer  50  and tread layer  60 , a retreaded tire assembly  66  is created and ready for curing under appropriate heat and pressure conditions. A cross section of the retreaded tire assembly  66  is illustrated best in FIG.  4 . After assembly, the overall tire assembly is inserted into a rubberized curing envelop, such as the appropriate Bandag, Incorporated curing envelope designed for the particular tire type and size being retreaded. 
     The retreaded tire assembly  66  is sealed within the curing envelope and placing within a curing chamber, such as the Model 4130 or 4120 curing chamber sold by Bandag, Incorporated. Pressure and heat are applied to the retreaded tire assembly  66  within the curing chamber. The amount of time necessary to cure a given retreaded tire may vary depending on the size of the tire and the materials used. However, the time must be long enough to create sufficient bonding between the tire casing  12  and cushion gum layer  50  and between the tread layer  60  and cushion gum layer  50 . Generally, the bonding results from vulcanization between the tire casing, cushion gum layer and tread layer. The times, pressures and temperatures within the curing chamber would be known by one of ordinary skill in the art. However, exemplary parameters during curing within the curing chamber are temperature: approximately 210° F.; pressure: approximately 85 psi; and time: approximately three and one-half hours. The above listed temperature, pressure and time parameters are only provided as examples, and are not meant to limit the scope of the invention. As stated previously, the time within the curing chamber may vary depending on the tire size and tire materials. Additionally, other combinations of temperature and pressure can potentially provide satisfactory results. After curing, the retreaded tire may undergo certain minor trimming operations, but otherwise is ready for use on a vehicle. 
     Another embodiment of retreaded tire assembly  66  is illustrated in FIG.  5 . The process used for this type of retreaded tire is the same as that described above, except for the addition of a pair of shoulder strips  68  of cushion gum that are added to accommodate arched outer flanges  70  of a slightly different tread layer  72 . In this embodiment, tread layer  72  extends about the circumference of tire casing  12  as described above, but the arched outer flanges  70  curve in the transverse direction generally about shoulder areas  46  of tire casing  12 . Accordingly, additional cushion gum must be added in the form of shoulder strips that run generally along each shoulder area  46  of tire casing  12  and beneath flanges  70 . 
     Thus, after cushion gum layer  50  is applied to buffed surface  44 , and stitched thereto, the top layer of plastic  58  is removed and shoulder strips  68  are applied along shoulder areas  46 . The tread layer  72  including its arched outer flanges  70  is applied over cushion gum layer  50  and shoulder strips  68 , measured, cut, and spliced similarly to that described above. 
     The various parameters involves in cementless retreading of tires may vary depending on the overall design of the tire being retreaded and the composition of the retreading materials. However, in general, it is preferred that the temperature of both tire casing  12  and cushion gum layer  50  be at least 65 degrees Fahrenheit when the cushion gum layer is applied to buffed surface  44 . Additionally, the cushion should be applied to the uncemented casing within eight hours of buffing or, if the buffed casing is covered with poly, the cushion application should be within 72 hours of buffing. Furthermore, to ensure a high quality retreaded tire, it is preferred that the centerline of cushion layer  50  be aligned with the center line of the buffed casing within plus or minus one-eighth inch. When applying the flat style tread illustrated in FIG. 4, there should be at least one-eighth inch of cushion layer  50  extending transversely past the base of the tread on each side of tread layer  60 . Similarly, cushion layer  50  should be applied with enough tension to facilitate conformation to the buffed surface  44 , but the tension should not cause the width of cushion layer  50  to be reduced by more than one-eighth inch. Generally, the length of cushion layer  50  is approximately 2-8 inches shorter than the circumference of buffed surface  44 . 
     It will be understood that the foregoing description is of the preferred exemplary embodiment of this invention and that the invention is not limited to the specific form shown. For example, the invention is directed to a tire assembly and a method for retreading tires that does not require the use of spray cement, and therefore a wide variety of equipment may be used to apply the layers of cushion gum and tread to the tire casing. Additionally, the invention encompasses a broad variety of tires, materials, and tread designs that may be assembled according to the invention. The methods of preparing the tire casing and curing the retreaded tire assembly may vary substantially due to differences in materials, equipment and techniques for creating retreaded tires. These and other modifications may be made in the design and arrangement of the elements without departing from the scope of the invention as expressed in the appended claims.