Background Art Elastomeric components for tires such as treads, sidewalls, and apexes are usually cut to length during the tire assembly process or prior to tire assembly. Some components are cut at a splice angle 8 relative to a plane perpendicular to the component. For many components a splice angle 0 is equal to 0°. This variety of splice is often called a"butt splice."Most components are cut to length at a splice angle 0 between 30° and 60°. These splices are often called"lap splices." For example, United States Patent No. 5,638,732 discloses an apparatus that is capable of cutting tire components at an angle WA that can vary between 10° and 80°.

However there is no teaching or suggestion in that patent that tire components are actually cut at angles nearing either 10° or 80°, rather, the machine is simply capable of cutting at those angles. In fact, the reference discloses a preferred cutting angle for treads of 22.5°.

One advantage of cutting elastomeric components at splice angles 8 greater than 80° is the resulting increase in the surface area of the splice. The greater surface area of the splice results in increased strength both in the unvulcanized state and the vulcanized state. This greater strength is essentially due to the greater adhesion between the respective halves of the splice, as adhesion strength is related to surface area. Generally the splice angle 9 is directly proportional to the strength of the splice.

A second advantage of cutting elastomeric components at splice angles 6 greater than 75° is to reduce the sensitivity of the component splice to non- uniformities such as balance and force variation. Generally the splice angle 0 is directly proportional to tire uniformity, with a greater splice surface area resulting in a more uniform tire.

Elastomeric components are cut to length at splice angles A using various

processing methods. Tread components are usually cut with an apparatus commonly known in the tire industry as a"skiver."Skivers typically cut at a splice angle 9 equal to or less than 70°. A skiver is a rotating circular knife blade usually lubricated with water or steam.

Some components such as sidewalls are typically cut with a traversing hot knife, again at a splice angle A equal to or less than 70°.

Some components such as treads or sidewalls are typically cut with an apparatus known as a"guillotine knife"or a"rolling circular knife,"again typically at splice angles A less than or equal to 45°.

If any type of cutting system is used which heats the elastomeric to the point of surface vulcanization, the splice strength could be weakened. In the worst case, the splice could come apart prior to vulcanization. For these reasons it is most desirable not to heat the ends of the component to the point of vulcanization during the cutting process.

Brief Descriptions of the Drawings FIGURE 1 is a perspective view of a tire component, specifically a tread.

FIGURE 2 is a side view of a tire tread showing the splice angle.

FIGURE 3 is a schematic side view of a tread illustrating the splice angle of this invention.

FIGURE 4 is a side view of a tread splice.

FIGURE 5 is a side view of a tread splice illustrating how manufacturing tolerance can stack up, making the splice area thicker than the rest of the tread.

Disclosure of the Invention This invention pertains to a method of cutting an elastomeric component for a pneumatic tire. The disclosure can be best understood with reference to the following definitions that may be used to describe the invention.

"Axial"and"axially"means lines or directions that are parallel to the axis of rotation of the tire.

"Carcass"means an unvulcanized laminate of tire ply material and other tire components cut to length suitable for splicing, or already spliced, into a cylindrical or toroidal shape. Additional components may be added to the carcass prior to its being vulcanized to create the molded tire.

"Casing"means the tire carcass and associated tire components excluding the tread.

"Circumferential"means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.

"Equatorial Plane (EP)"means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread.

"Lateral"means an axial direction.

"Radially"and"radially"means directions radially toward or away from the axis of rotation of the tire.

"Radial Ply Tire"means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65° and 90° with respect to the equatorial plane of the tire.

"Sidewall"means that portion of a tire between the tread and the bead.

"Tread"means a rubber or elastomeric component which when bonded to a tire carcass includes that portion of the tire that comes into contact with the road when the tire is normally inflated and under normal load.

The invention involves a method of cutting the tire component across its width and the thickness to a specified length at an angle 9 greater than or equal to 75° relative to a plane perpendicular to a plane passing through the center of the component. The cutting is accomplished by passing the cutting element from one side of the component to the other side of the component.

The principle of permitting the cutting element to cut through the elastomeric component at angles 0 in excess or equal to 75° is called"oscillation."The cutting element oscillates at a wide range of frequencies from 250 hertz to 5,000 hertz.

Generally frequencies above 20,000 hertz are considered ultrasonic. Various designs of ultrasonic cutting elements are included within the scope of this invention.

Frequencies below the ultrasonic range are also utilized with a mechanical oscillating mechanism such as an eccentric or a cam.

The amplitude of the oscillating cutting element may also be varied to optimize cutting of different elastomers. The maximum useful amplitude of the oscillating cutting element is believed to be 25 mm (0.63 inches).

The invention will now be applied to a particular tire component, in this case

tire treads. With reference to Figures 1-4, a typical tread 10 is illustrated. The tread 10 has a first end 12 that is cut at a splice angle 0. When the tire (not shown) is assembled, the first end 12 will be matched with a second end 14 of the tread 10 to assemble the tread 10 in a hoop configuration. The surface created by the cutting of the tread 10 is called the splice surface 20 of the first end 12. The splice surface 20 has a certain area associated with it. The tread 10 has a tread thickness TT. The angle at which the tread 10 was cut is called the splice angle 0.

With continuing reference to Figures 1-3, the geometric relationship between splice angle 0, the tread thickness TT and the splice length SL is illustrated. The splice length SL is related to the area of the splice surface 20. Through trigonometry one can determine that the splice length SL is equal to the thickness TT divided by the cosine of the splice angle 8. Expressed algebraically, SL = (TT)/ (cousine0) The application of the invention is especially helpful in tires having thinner treads. One common application of such treads is in high performance tires. The uncured treads of high performance tires often have tread thicknesses TT of less than 1.7 cm (0.5 inch). Some high performance and racing tires have treads with tread thicknesses TT less than 1 cm (0.25 inches).

In a tread 10 having a tread thickness TT equal to 0.25 inches, the splice length SL when the splice angle 0 is 45° is only 0.35 inches. Because of the small tread thickness TT, a very small splice length SL is generated, leading to a small splice area. For some applications, this small splice area may be insufficient to deliver the kind of performance desired. However, in tires featuring thicker treads, the same splice angle 0 equal to 45° could deliver sufficient splice area.

Returning to the example of a tread thickness equal to 0.25 inches, even a splice angle 9 of 60° yields only a splice length of 0.50 inches. This may, too, be inadequate in some applications. However, when the splice angle 0 is 80°, the effective splice length SL is 1.44 inches. In some high performance applications, this splice length SL is desirable, but even greater effective splice lengths SL are sometimes preferred. For example, in an application where splice angle 9 is equal to

85° and the tread thickness TT is equal to 0.25 inches, the effective splice length is 2.87 inches. This is a better solution in some applications. At the present time the preferred embodiment of the invention is a tread with a splice angle 0 equal to 82°.

With reference to Figures 4 and 5, some of the advantages of the longer effective splice length SL will be explained. Ideally, the splice length SL of the first end 12 will be exactly the same length as the splice length SL of the second end 14.

However, due to"real-world"manufacturing tolerances, variances in splice length SL occur. One advantage of the present invention is that any additional thickness of the tread at the splice due to the splice length SL of the first end 12 being longer than the splice length SL of the second end 14 at the splice 28 will be very small. This leads to the great advantage that the variation in tread thickness TT across the splice 12 is very low.

With reference to Figure 5, this advantage will be further illustrated.

In Figure 5 the situation is illustrated where the first end 12 of the tread 10 doesn't match well with the second end 14 of the tread 10. For this example we will define a term"effective splice length ESL"which shall denote the portions of the splice surfaces 20 that actually mate.

With continuing reference to Figure 5, the amount of overlap is a function of the splice length SL. In some applications the relationship between effective splice <BR> <BR> <BR> length ESL and the splice length SL is that the effective splice length ESL is equal to 60% of the splice length SL. Thus a 1.0 inch splice length SL can have an effective splice length ESL of 0.6 inch. Such a splice length SL will create an overlap of 0.4 inches, centered so that each side of the splice has an overlap OL1, OL2 of 0.2 inch.

With continuing reference to Figure 5, as splices are made, the respective halves of the splice are"stacked up"and are additive. In such splices, the tread thickness at the point of the splice TTS is greater than the tread thickness TT at other points of the tread 10. The variation in the thickness of the tread 10 can be about 5 % of the tread thickness TT. In high performance tires, where a tread is about 0.64 cm (0.25 inch) thick, this variance in tread thickness TT is about 0.04cm (0.015 inches).

Because high performance tires operate and are tested at high speeds, some above 149 miles per hour, even small variations can be important. The small splice joint created by the inventive method and article of this invention is imperceptible to radial force

machines. In contrast, in splices made at splice angles of 0 in the range of 45° to 80° the splice overlap is noticeably present on radial force machines. At very high speeds at which high performance and racing tires operate, these force variations create a radial first harmonic input causing noticeable vibration testing on tires having no grooves, i. e. "slicks,"demonstrating that the variations in splice thickness contribute to tire nonuniformity.

A second advantage of the very low angle splice is the surface bonding adhesion area is increased several times. This yields a much more secure bond.

The above-described inventive splice design can be cut by using a wire or fine ultrasonic cutter, and can be accomplished cold, meaning no surface curing is seen at the splice as is common with hot knives.

Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification.