Constrained post cure inflation

Details Constrained post cure inflation Constrained post cure inflation

2000-11-17

2003-12-09

Knable, Goeffrey L. (Department: 1733)

Plastic and nonmetallic article shaping or treating: processes

Direct application of fluid pressure differential to...

Producing toroidal work

C264S236000, C264S237000, C425S058100

Reexamination Certificate

active

06660212

ABSTRACT:

TECHNICAL FIELD
The present invention relates to manufacturing pneumatic tires, and, more specifically, to a method and apparatus to improve or correct tire uniformity.
BACKGROUND
A typical radial tire includes a tread, a belt structure (“belts”) and a carcass. The carcass has an innerliner, a pair of inextensible beads, an apex (rubber filler) over each bead, two sidewalls, and one or more plies (“radial plies”). The plies have parallel reinforcing ply cords of typically nylon or polyester, which extend between, and wrap around, the beads.
Tire Making Process
In the tire making process, a green carcass (“green” meaning as yet uncured and still tacky) is built typically by wrapping a length of green innerliner and at least one radial ply over a “first stage building drum” 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 carcass, one at each side. The portions of the ply that extend beyond the beads are then turned up (wrapped around) the beads, forming “ply turnups”. The resulting assembly, including the innerliner, ply, and beads, is called a green carcass. Then, green (uncured) sidewalls are applied around each side of the plies.
The green carcass is removed from the first stage building drum and mounted on a “second stage machine” where it is inflated to a toroidal shape, and its radially-outer surface is pressed against a green tread and belt package to form a “green tire”. In subsequent steps, the green tire is “stitched” (rolled with a roller) to remove air pockets and adhere internal surfaces together.
The green tire is then mounted in a curing mold, where a bladder is blown up within the tire cavity to press the tire's outer surface tightly against the mold's inner walls 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 inflated on a post-cure inflation stand (“PCI 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.
Uniformity Characteristics
After a tire is cured, it is typically tested for uniformity characteristics, such as radial runout, radial force variation, axial force variation, tangential force variation, and conicity, which are defined in the Definition Section hereinbelow.
Sources Of Nonuniformity
Tire nonuniformity emanates from numerous factors in the tire making process, listed below in their order of occurrence in the tire building sequence:
Deformation Of Raw Components: The raw tire components (tread, sidewall innerliner, plies [ply cords], 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 not remain uniformly thick during storage.
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 in a plane which is perfectly perpendicular to the drum (and tire) axis, or may otherwise not be parallel to each other over the ply on the building drum.
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 the cured tire, will not be uniform. Also, later as the green rubber is blown up, the bead and ply positions can shift nonuniformly.
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.
Nonuniform Mounting In The Mold: If the green tire is not positioned symmetrically within the mold, the finished tire will not be uniform.
Ply Splice: The ply is stiffer and heavier at its splice (where it is doubled due to the overlapping ply ends) compared to other locations.
Ply Stretching and Shrinkage: In the mold, the inflated bladder tensions (stretches) the ply outward, and heat shrinkage of the ply's nylon or polyester fibers tension the ply further. This tension (tensile stress) causes the ply to slip around the bead, but to a different extent at different locations around the bead, with a splice slipping around the bead least.
Nonuniform Curing: The rubber can “lock up” (stiffen under cure) around the ply at different times at different locations, thus locking in nonuniform ply stresses.
TUM Apparatus
After a tire is cured and cooled, it is tested on a force variation machine (also called “tire uniformity machine” abbreviated “TUM”, “tire uniformity inspecting machine”, and “tire uniformity apparatus”). Many patents describe TUM components and TUM designs, almost all of which share the same general principle of operation as follows:
The tire is mounted on a rotatable test rim. To ease mounting, the test rim is a “split rim” having two rim halves with flanges that come together to sealingly engage the tire's bead area. The tire is inflated and pressed against a rotatable load drum (also called “load-wheel”, “load roll” or “test drum”) whose axis is parallel with the tire axis. As the tire rotates against the load drum, force sensors (usually connected to the drum shaft) or displacement sensors measure changes in force (of tire against the drum) or displacement (of the tire surface from the nominal or at rest tire surface location) in various directions (mainly radial and axial).
TUM designs vary as to whether the load drum rotates the tire or vice versa, tire rotational speed, which uniformity characteristics are tested, how to correct for deformities or nonuniformities in the test rim or load drum, how to correct for sensor errors due to TUM vibration, and how to correct for tire imbalance. Designs also vary on rim design and tire conveyance mechanism.
FIGS. 4A and 4B
illustrate simplified results of a TUM test, using radial force variation (RFV) as an example.
FIGS. 4A and 4B
show radial force on the vertical axis
401
versus the tire's rotational angle from 0 to 360 degrees on the horizontal axis
402
.
FIG. 4A
shows a force variation composite curve
405
. The angular location
410
(corresponding to a circumferential location on the tread) of greatest force
411
represents a “hard spot”, where the tire presses hardest against the load drum. The angular location
420
of least force
421
represents a “soft spot”, where the tire presses least against the load drum. The force variation composite curve
405
can be “decomposed” as shown in
FIG. 4B
into a series (“Fourier series”) of constituent harmonic waveforms
431
,
432
,
433
for further mathematical analysis. The first harmonic
431
of radial force variation (abbreviated R
1
h) is also known as “radial runout.” A second harmonic waveform
432
and third harmonic waveform
433
are also illustrated.
With the data thus collected, there are a wide variety of methods for mathematically processing the force variation data to determine the need for uniformity correction and to determine the control parameters for correcting a tire on a uniformity correction machine (which may be the same as the TUM used to make the uniformity measurements).
Prior Art Correction Methods
Grinding
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 (and/or possibly the tread shoulder or tire sidewalls). Numerous patents disclose a wide variety of grinding techniques, differing on how the grinder is interfaced with the TUM, when grinding occurs relative to testing, where laterally on the tread (shoulder, c

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