Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
2000-04-10
2004-05-25
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C264S315000, C264S487000
Reexamination Certificate
active
06740280
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of manufacturing pneumatic tires, and, more specifically, to a method of improving tire uniformity during the tire manufacturing process.
BACKGROUND OF THE INVENTION
A typical pneumatic radial tire includes a tread, a belt structure and a carcass. The carcass has a pair of inextensible beads, one or more plies extending between and wrapping around the beads, two sidewalls, and an apex (rubber filler) over each bead.
In the tire manufacturing process, a green tire carcass (“green” meaning as yet uncured and still tacky) is built by wrapping a length of green innerliner and at least one radial ply over a “first stage building drum” (or “building mandrel”) and splicing the innerliner and ply ends together to form a cylindrical shape around the building drum. Two beads (each comprising a cable of steel filaments encased in green rubber) are then positioned over the ply, one near each side, and the ply is expanded radially outward to tighten against the beads. The portions of the plies that extend outward, beyond the beads are then turned up (wrapped around) the beads, forming “turnups”. Then, green (uncured) sidewalls are applied around each side of the plies.
There are two methods of incorporating the apexes during the tire-making process. In the “pre-apexing” method, an apexing machine adheres (pre-assembles) an annular cross-sectional apex to each annular bead before the bead is positioned over the ply on the building drum. In the “flat application of apex” method, each apex is circumferentially laid down flat, as a triangular strip of green rubber (“gum strip”), onto the ply, next to a bead, so that one of the apex's tacky sides adheres to the tacky green ply.
The resulting assembly, called a green tire “carcass”, typically comprising innerliner, ply, beads, apexes, sidewalls, and other components such as chippers and flippers, is removed from the first stage building drum and mounted on a “second stage machine” where it is inflated (“blown up”) to a toroidal shape, and the radially-outer surface of the carcass is pressed against a green (uncured) tread and a belt package to form a “green tire”. Then, the green tire is stitched (rolled with a roller) to remove air pockets and adhere internal surfaces together.
The resulting green tire is then mounted in a curing (vulcanization) mold, where a bladder is blown up within the tire cavity to press the tire's outer surface tightly against the mold's inner wails while the tire is vulcanized. In the mold, the tire's green rubber initially softens under heat but eventually cures (stiffens through polymerization) enough to be removed from the mold and allowed to cool outside the mold where the curing reaction continues until the tire is cool. In some cases, the tire is kept inflated on a “post-cure inflation stand” while cooling, to keep the tire shape uniform and the ply uniformly stretched, to prevent the ply from shrinking nonuniformly when the tire is still hot from the mold.
After a tire is cured, it is typically tested for uniformity on a force variation machine (also called “tire uniformity machine”, “tire uniformity inspecting machine” and “tire uniformity apparatus”). The patent literature is rich with creative designs for force variation machines and their components. Almost all force variation machines share the same general principle as follows:
The tire is mounted on a rotatable test rim. The tire is inflated and pressed against a drum (called “load-wheel”, “load roll”, “loading drum”, or “test drum”) whose axis is parallel with the tire axis. As the tire rotates against the drum, force sensors connected to the drum's shaft measure changes in force (of the tire against the drum) in various directions (radial, axial and tangential to the tire-drum interface) as the tire rotates.
Graphs of force (from the sensors) vs. tire rotational angle are mathematically processed to yield different uniformity characteristics, each uniformity characteristic defining a different type of tire uniformity. Some uniformity characteristics are radial runout, radial force variation, axial force variation, tangential force variation, wobble, and conicity. These terms are defined in the Definition Section below.
Tire nonuniformity emanates from numerous factors in the tire making process. They are listed below in order of their occurrence in tire building sequence:
a) Deformation While On Rolls: The raw tire components (tread, sidewall innerliner, plies, beads and belts) either are rubber or have a rubber matrix and are stored on long rolls in the deformable green state. So, the tire components may be not remain uniformly thick during storage.
b) Nonuniform Placement On Building Drum: The ply cords may not be laid around the building drum with equal straightness and tension, and the two beads may not be positioned perfectly parallel (relative to each other) over the ply on the building drum.
c) Nonuniform Placement On Second Stage Machine: On the second stage machine, if the belt and tread are not positioned symmetrically over the green carcass, the green tire, and hence cured tire, will not be uniform. Later, as the green rubber is blown up, the bead and ply positions can shift nonuniformly.
d) Components Shift In The Green Tire State: Before curing, the beads and plies are held in place only by their green rubber matrix and the surrounding green rubber. As the green tire is handled, the bead and ply positions can shift nonuniformly.
e) Nonuniform Mounting In The Mold: If the green tire is not positioned symmetrically within the mold, the finished tire will not be uniform.
f) Ply Splice: The ply is stiffer at its splice (where it is doubled over itself) than at other locations causing irregularities in construction.
g) Ply Stretching and Shrinkage: In the mold, the inflated bladder tensions (stretches) the ply outward, and the ply cords, if constructed of nylon or polyester fibers, can shrink when heated, thus tensioning the ply further. Under tension, the ply slips around the bead, possibly to a different extent at different locations around the bead, and a splice slips around the bead least.
h) Nonuniform Curing: The rubber can “lock up” (stiffen under cure) around the ply at different times at different locations, thus causing nonuniform ply stress.
Post-Cure Methods of Correcting Nonuniformity
Grinding Selected Locations
In the patent literature, the most commonly addressed method of correcting a uniformity characteristic is grinding off rubber from selected locations around the tread circumference. Numerous patents disclose a wide variety of methods, differing in how the grinder is interfaced with the force variation machine, how the grinding location (angular position) is determined based on force variation results, and which part of the tread (shoulder, crown, etc.) to grind. Disadvantages of grinding are that it contributes to environmental waste, reduces tread life, and leaves an unattractive surface finish.
Rotating Uninflated
U.S. Pat. No. 5,853,648 discloses rotating a tire in a vertical position, uninflated, while cooling after vulcanization.
Heating Selected Portions
U.S. Pat. Nos. 3,632,701; 3,865,527; 3,872,208 and 3,945,277 disclose various methods of reducing nonuniformities and/or flat spots of a cured uninflated tire based on heating only selected portions of the tire.
Post-inflation
Various patented methods of improving uniformity of a cured tire are based on “post-inflation”, i.e., U.S. Pat. Nos. 2,963,737 and 4,420,453), defined as mounting the hot cured tire on a rim and keeping it inflated as it cools. The patented methods differ as to the inflation pressure and when to start and end the post-inflation.
Rotatingly Pressing Around Tire's Entire Circumference when Hot
U.S. Pat. Nos. 3,529,048; 3,464,264; 3,635,610; and 3,389,193 disclose various methods to improve uniformity characteristics, all based on rotating a cured tire while pressing it against a roller, to “run in”, “knead”, and/or “buckle” the tire's surface around its ent
Brown Robert Walter
Sandstrom Paul Harry
Cohn Howard M.
The Goodyear Tire & Rubber Company
Vargot Mathieu D.
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